Raman spectroscopy

NITISH KUMARMPHARM (ANALYSIS)

2015-2016

GT Road (NH-95) Ghal Kalan Moga(142001) Punjab India

2

INTRODUCTIONbull Raman spectroscopy is the measurement of the

wavelength and intensity of inelastically scattered light from molecules The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations

bull Raman spectroscopy is used to determine the molecular motions especially the vibrational one

3

Time lap

bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in

scattering from quartz

bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents

bull 1930 ndash CV Raman wins Nobel Prize in Physics

bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible

4

OVERVIEW

bull A vibrational spectroscopy

- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species

- Based on inelastic scattering of a monochromatic excitation source

- Routine energy range 200 - 4000 cmndash1

bull Complementary selection rules to IR spectroscopy

- Selection rules dictate which molecular vibrations are probed

- Some vibrational modes are both IR and Raman active

bull Great for many real-world samples

- Minimal sample preparation (gas liquid solid)

- Compatible with wet samples and normal ambient

- Achilles Heal is sample fluorescence

5

Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of

definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency

Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering

The line with lower frequency are called Stokersquos lines

Also the line with higher frequency are called Antistokersquos lines

The line with the same frequency as that of the incident light is called Rayleigh line

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

2

INTRODUCTIONbull Raman spectroscopy is the measurement of the

wavelength and intensity of inelastically scattered light from molecules The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations

bull Raman spectroscopy is used to determine the molecular motions especially the vibrational one

3

Time lap

bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in

scattering from quartz

bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents

bull 1930 ndash CV Raman wins Nobel Prize in Physics

bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible

4

OVERVIEW

bull A vibrational spectroscopy

- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species

- Based on inelastic scattering of a monochromatic excitation source

- Routine energy range 200 - 4000 cmndash1

bull Complementary selection rules to IR spectroscopy

- Selection rules dictate which molecular vibrations are probed

- Some vibrational modes are both IR and Raman active

bull Great for many real-world samples

- Minimal sample preparation (gas liquid solid)

- Compatible with wet samples and normal ambient

- Achilles Heal is sample fluorescence

5

Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of

definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency

Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering

The line with lower frequency are called Stokersquos lines

Also the line with higher frequency are called Antistokersquos lines

The line with the same frequency as that of the incident light is called Rayleigh line

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

3

Time lap

bull 1923 ndash Inelastic light scattering is predicted by A Smekelbull 1928 ndash Landsberg and Mandelstam see unexpected frequency shifts in

scattering from quartz

bull 1928 ndash CV Raman and KS Krishnan see ldquofeeble fluorescencerdquo from neat solvents

bull 1930 ndash CV Raman wins Nobel Prize in Physics

bull 1961 ndash Invention of laser makes Raman experiments reasonablebull 1977 ndash Surface-enhanced Raman scattering (SERS) is discoveredbull 1997 ndash Single molecule SERS is possible

4

OVERVIEW

bull A vibrational spectroscopy

- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species

- Based on inelastic scattering of a monochromatic excitation source

- Routine energy range 200 - 4000 cmndash1

bull Complementary selection rules to IR spectroscopy

- Selection rules dictate which molecular vibrations are probed

- Some vibrational modes are both IR and Raman active

bull Great for many real-world samples

- Minimal sample preparation (gas liquid solid)

- Compatible with wet samples and normal ambient

- Achilles Heal is sample fluorescence

5

Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of

definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency

Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering

The line with lower frequency are called Stokersquos lines

Also the line with higher frequency are called Antistokersquos lines

The line with the same frequency as that of the incident light is called Rayleigh line

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

4

OVERVIEW

bull A vibrational spectroscopy

- IR and Raman are the most common vibrational spectroscopes for assessing molecular motion and fingerprinting species

- Based on inelastic scattering of a monochromatic excitation source

- Routine energy range 200 - 4000 cmndash1

bull Complementary selection rules to IR spectroscopy

- Selection rules dictate which molecular vibrations are probed

- Some vibrational modes are both IR and Raman active

bull Great for many real-world samples

- Minimal sample preparation (gas liquid solid)

- Compatible with wet samples and normal ambient

- Achilles Heal is sample fluorescence

5

Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of

definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency

Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering

The line with lower frequency are called Stokersquos lines

Also the line with higher frequency are called Antistokersquos lines

The line with the same frequency as that of the incident light is called Rayleigh line

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

5

Raman spectrometerrsquos mechanismWhen a substances (in any state) is irradiated with a monochromatic light of

definite frequency(v)the light scattered at right angle to the incident light contains lines of 1 Incident frequency and 2Also of lower frequency

Sometimes lines of higher frequency are also obtained that of the incident beam will be scattered It is called Raman scattering

The line with lower frequency are called Stokersquos lines

Also the line with higher frequency are called Antistokersquos lines

The line with the same frequency as that of the incident light is called Rayleigh line

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

6

Frequency -

This difference is called Raman frequency or Raman shift

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

8

bull It may be noted that raman frequencies for a particular substances are characteristic of that substances

bull The various observation made by raman are called raman effect

bull Also the spectrum obtained is called raman spectrum

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

9

Classical theory of raman effect

bull According to the classical theory of electromagnetic radiation electric and magnetic fields oscillating at a given frequency are able to give out electromagnetic radiation of the same frequency One could use electromagnetic radiation theory to explain light scattering phenomena

bull For a majority of systems only an induced electric dipole moment μ is taken into consideration This dipole moment which is induced by the electric field E could be expressed by the power series

μ=μ(1)+μ(2)+μ(3)+⋯whereμ(1)=α Esdotμ(2)=12β EEsdotμ(3)=16γ EEEsdot

α is termed the polarizability tensor It is a second-rank tensor with all the components in the unit of CV-1m2 Typically orders of magnitude

for components in α β and γ are as follows α 10-40 CV-1m2

β 10-50 CV-2m3 and γ 10-61 CV-3m4

According to the values the contributions of μ(2)and μ(3) are quite small unless electric field is very high Since Rayleigh and Raman scattering are observed quite readily with very much lower electric field intensities one may expect to explain Rayleigh and Raman scattering in terms of μ(1) only

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

10

Classical theory of raman effecty of Raman Effect

Colthup et al Introduction to Infrared and Raman Spectroscopy 3rd ed Academic Press Boston 1990

mind = aE

polarizability

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

11

ElectronicGround State

1st ElectronicExcited State

Exci

tatio

n En

ergy

s (c

mndash1

)

Vibstates

4000

25000

0

fluor

esce

nce

IRs

s semit

2nd ElectronicExcited State

Raman∆s=semit-s

s ∆sflu

ores

cenc

eIm

purit

y

Fluorescence = Trouble

Raman Spectroscopy Absorption Scattering and Fluorescence

Stokes Anti-Stokes

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

12

Raman Spectroscopy Classical Treatment

bull Number of peaks related to degrees of freedom

DoF = 3N - 6 (bent) or 3N - 5 (linear) for N atomsbull Energy related to harmonic oscillator

bull Selection rules related to symmetry Rule of thumb symmetric=Raman active asymmetric=IR active

Raman 1335 cmndash1

IR 2349 cmndash1

IR 667 cmndash1

CO2

s or s c

2k(m1m2)

m1m2

Raman + IR 3657 cmndash1

Raman + IR 3756 cmndash1

Raman + IR 1594 cmndash1

H2O

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

13

Theory of raman spectraTwo cases may arise depending upon whether a collision between a photon and molecules In itrsquos ground state is elastic or inelastic in natureCase 1- if the collision is elastic ndash this lead to the appearance of unmodified lines (or unmodified frequency of light) in the scattered beam and this explain rayleigh scatteringCase 2 - if the collision is inelastic ndash there will be exchange or transfer of energy between the scattering molecules and the incident photonThe frequency of scattered light and the incident photon which is either higher or lower than that of the incident photon is called raman frequency

Total energy before collision = total energy after collision

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

14

Presentation of Raman Spectra

lex = 1064 nm = 9399 cm-1

Breathing mode9399 ndash 992 = 8407 cm-1

Stretching mode9399 ndash 3063 = 6336 cm-1

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

15

Rayleigh Scattering- Occurs when incident EM radiation induces an oscillating dipole in a molecules which is re-radiated at the same frequency

Eugene Hecht Optics Addison-Wesley Reading MA 1998

bullElastic (l does not change)

bullRandom direction of emission

bullLittle energy lossbullof emission

bullLittle energy loss

4 2 20

4 2

8 ( ) (1 cos )( )sc

EE

d a

l

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

16

Raman ScatteringOccurs when monochromatic light is scattered light has been weakly modulated

by the characteristic frequencies of the molecules Raman spectroscopy measures the differences between the wavelengths of the

incident radiation and the scatted radiation

max 0

max max 0

max max 0

( ) cos 21 cos 2 ( )21 cos 2 ( )2

equilz zz

zzvib

zzvib

t E td r E tdr

d r E tdr

m a a

a

Selection rule v = plusmn1Overtones v = plusmn2 plusmn3 hellip

Must also have a change in polarizability

Classical Description does not suggest any difference between Stokes and Anti-Stokes intensities

1

0

vibhkTN e

N

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

17

The Raman polarization

The Raman Polarization is a property of waves that can oscillate with more than one orientation EMR or waves such as light and gravitational wave exhibit polarization

Polarization state - the shape traced out in a fixed plane by the electric vector as such a plane wave passes over it is a description of the polarization

Eg linear polarization circular polarization

elliptical polarization orthogonally polarization

Polarization changes are necessary to form the virtual state and hence the Raman effect

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

18

Condition for raman spectroscopyVibrational modes that are more polarizable are more Raman-active Examples ndash N2 (dinitrogen) symmetric stretch cause no change in dipole (IR-inactive) cause a change in the polarizability of the bond ndash as the bond gets longer it is more easily deformed (Raman -active)

ndash CO2 asymmetric stretch cause a change in dipole (IR-active) Polarizability change of one C=O bond lengthening is cancelled by the shortening of the other ndash no net polarizability (Raman-inactive) Some modes may be both IR and Raman-active others may be one or the other

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

19

Condition for raman spectroscopy

Raman spectra occurs as a result of oscillation of a dipole moment induced in a molecules by the oscillating electric field of an incident wave

As the induced dipole moment is directly proportional to the polarisability of the molecules the molecules must possess anisotropic polarisability which should change during molecular rotation or vibration for vibrational or rotational-vibrational raman spectra

Anisotropic polarisability depends upon the orientation of the molecules

In the presence of an electric field the electron cloud of an atom or molecules is distorted or polarised

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

20

Mutual Exclusion Principle

For molecules with a center of symmetry no IR active transitions are Raman active and vice versa

THORNSymmetric molecules IR-active vibrations are not Raman-active Raman-active vibrations are not IR-active

O = C = O O = C = O

Raman active Raman inactive IR inactive IR active

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

21

Raman Instrumentation

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

22

There are following component involves

1 Laser or source of light 2 Filter3 Sample holder 4 detector

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

23

The block design dispersive Raman scattering system

Radiation sources

Sample Wavelength

selector

Detector InGaAs or

Ge

RecorderDetector InGaAs or

Ge

RecorderDetector

InGaAs or Ge

Recorder

Block diagram

90

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

24

Flow diagram dispersive Raman scattering system

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

25

Schematic diagram dispersive raman scattering system

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

26

1 Laser or source of light

bull Lasers are generally the only source strong enough to scatter lots of light and lead to detectable raman scattering

bull Lasers operate using the principle of stimulated emission

bull Electronic population inversion is required to achieve gain via stimulated emission (before the fluorescence lifetime is reached)

bull Population inversion is achieved by ldquopumpingrdquo using lots of photons in a variety of laser gain media

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

27

List of Various laser source

SNo Laser wavelength01 NdYAG 1064nm

02 HeNe 633nm

03 Argon ion 488nm

04 GaAlAs diode 785nm

05 Co2 10600nm

06 Ti-Sapphire 800nm

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

28

A - HeNe laserbull Filled with 71 He amp Ne gas optimum output of 6328 Aring

bull High voltage excitation is preferred

B - NdYAG Systembull A typical laser system ndashthe neodymium-doped yttrium aluminum garnet or Nd+3

bull YAG is a cubic crystalline material

bull Crystal field splitting causes electronic energy level splitting

bull NdYAG laser are optically pumped using a flash tube or laser diodes

bull These are the one of the most common type of laser

bull It emits 1064 nm wavelength

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

29

2Filter bull It is therefore essential to have monochromatic radiations

bull For getting monochromatic radiations filters are used

bull They may be made of nickel oxide glass or quartz glass

bull Sometimes a suitable colored solution such as an aqueous solution of ferricyanide or iodine in CCl2 may be used as a monochromator

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

30

3Sample holder bull For the study of raman effect the type of sample holder to be used

depends upon the intensity of sources the nature and availability of the sample

bull The study of raman spectra of gases requires samples holders which are generally bigger in size than those for liquids

bull Solids are dissolved before subjecting to raman spectrographbull Any solvents which is suitable for the ultraviolet spectra can be

used for the study of raman spectra

bull Water is regarded as good solvents for the study of inorganic compounds in raman spectroscopy

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

31

4detectorbull Researchers traditionally used single points detectors such as

photocounting photomultiplier(PMT) not because of the weakness of a typical raman signal longer exposure times were often required to obtains raman spectrum of a decent quality

bull Now days multichannel detectors like photodiode arrays(PDA) charged couple devices(CCD)

bull Sensitivity amp performance of modern CCD detectors are high

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

32

APPLICATIONPharmaceuticals and Cosmetics-bull Compound distribution in tabletsbull Blend uniformitybull High throughput screeningbull API concentrationbull Powder content and puritybull Raw material verificationbull Polymorphic formsbull Crystallinitybull Contaminant identificationbull Combinatorial chemistrybull In vivo analysis and skin depth profiling

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

33

bull Geology and Mineralogybull Raman spectra of (top to bottom) olivine apatite garnet and

gypsum illustrating how Raman can be used for fast mineral ID

bull Gemstone and mineral identification

bull Fluid inclusions

bull Mineral and phase distribution in rock sections

bull Phase transitions

bull Mineral behavior under extreme conditions

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

34

Carbon Materialssbull Peak fitting of the D and G bands in a DLC spectrumbull Single walled carbon nanotubes (SWCNTs)bull Purity of carbon nanotubes (CNTs)bull Electrical properties of carbon nanotubes (CNTs)bull sp2 and sp3 structure in carbon materialsbull Hard disk drivesbull Diamond like carbon (DLC) coating propertiesbull Defectdisorder analysis in carbon materialsbull Diamond quality and provenance

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

35

Semiconductors

bull Photoluminescence image of a 3rdquo MQW semiconductor wafer showing variation of emission peak width

bull Characterisation of intrinsic stressstrainbull Puritybull Alloy compositionbull Contamination identificationbull Superlattice structurebull Defect analysisbull Hetero-structuresbull Doping effectsbull Photoluminescence micro-analysis

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

36

Life Sciences

bull Multivariate clustering of spectra acquired from three bacterial species illustrating how Raman can be used to characterise and distinguish bacteria at the single cell level

bull Bio-compatibilitybull DNARNA analysisbull Drugcell interactionsbull Photodynamic therapy (PDT)bull Metabolic accretionsbull Disease diagnosisbull Single cell analysisbull Cell sortingbull Characterisation of bio-moleculesbull Bone structure

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

37

Differences between IR and Raman methodsSNo Raman IR

01 It is due to the scattering of light by the vibrating molecules

It is the result of absorption of light by vibrating molecules

02 The vibration is Raman active if it causes a change in polarisability

Vibration is IR active if there is change in dipole moment

03 The molecule need not possess a permanent dipole moment

The vibration concerned should have a change in dipole moment due to that vibration

04 Water can be used as a solvent Water cannot be used due to its intense absorption of IR

05 Sample preparation is not very elaborate it can be in any state

Sample preparation is elaborateGaseous samples can rarely be used

06 Gives an indication of covalent character in the molecule

Gives an indication of ionic character in the molecule

07 Cost of instrumentation is very high

Comparatively inexpensive

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

38

Advantages of Raman over IR

bull Water can be used as solvent bull Very suitable for biological samples in native state (because water

can be used as solvent)bull Although Raman spectra result from molecular vibrations at IR bull frequencies spectrum is obtained using visible light or NIR bull radiationbull =gtGlass and quartz lenses cells and optical fibers can be used bull Standard detectors can be usedbull Few intense overtones and combination bands =gt few spectral

overlaps bull Totally symmetric vibrations are observablebull Raman intensities a to concentration and laser power

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

39

Advantages of IR over Ramanbull Simpler and cheaper instrumentation

bull Less instrument dependent than Raman spectra because IR spectra are based on measurement of intensity ratio

bull Lower detection limit than (normal) Raman

bull Background fluorescence can overwhelm Raman

bull More suitable for vibrations of bonds with very low polarizability (eg CndashF)

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

40

Several variations of Raman spectroscopy

1 Surface-enhanced Raman spectroscopy (SERS) ndash Normally done in a silver or gold colloid or a substrate containing silver or gold Surface plasmons of silver and gold are excited by the laser resulting in an increase in the electric fields surrounding the metal

bull Given that Raman intensities are proportional to the electric field there is large increase in the measured signal (by up to 1011)

bull This effect was originally observed by Martin Fleischmann but the prevailing explanation was proposed by Van Duyne in 1977

bull A comprehensive theory of the effect was given by Lombardi and Birke

41

2 Resonance Raman spectroscopy The excitation wavelength is matched to an

electronic transition of the molecule or crystal so that vibrational modes associated with the excited electronic state are greatly enhanced This is useful for studying large molecules such as polypeptides which might show hundreds of bands in conventional Raman spectra It is also useful for associating normal modes with their observed frequency shifts

42

3 Surface-enhanced resonance Raman spectroscopy (SERRS) ndash A combination of SERS and resonance Raman spectroscopy that uses proximity to a surface to increase Raman intensity and excitation wavelength matched to the maximum absorbance of the molecule being analysed

4 Coherent anti-Stokes Raman spectroscopy (CARS) ndash

Two laser beams are used to generate a coherent anti-Stokes frequency beam which can be enhanced by resonance

43

5 Raman optical activity (ROA) ndash Measures vibrational optical activity by means of a small difference in the intensity of Raman scattering from chiral molecules in right- and left-circularly polarized incident light or equivalently a small circularly polarized component in the scattered light

6 Spatially offset Raman spectroscopy (SORS)

7 Spontaneous Raman spectroscopy (SRS) 8 Optical tweezers Raman spectroscopy (OTRS)

44

9 Angle-resolved Raman spectroscopy10 Inverse Raman spectroscopy11 Tip-enhanced Raman spectroscopy

(TERS) 12 Surface plasmon polariton enhanced

Raman scattering (SPPERS)13 Stand-off Remote Raman ndash 14 Fourier-transform Rama spectroscopyapplied

to photobiological systems

45

• Raman spectroscopy
• INTRODUCTION
• Time lap
• OVERVIEW
• Raman spectrometerrsquos mechanism
• Slide 6
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Theory of raman spectra
• Presentation of Raman Spectra
• Slide 15
• Slide 16
• The Raman polarization
• Condition for raman spectroscopy
• Condition for raman spectroscopy (2)
• Slide 20
• Raman Instrumentation
• There are following component involves
• The block design dispersive Raman scattering system
• Slide 24
• Schematic diagram dispersive raman scattering system
• Slide 26
• List of Various laser source
• A - HeNe laser
• 2Filter
• 3Sample holder
• 4detector
• APPLICATION
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Differences between IR and Raman methods
• Slide 38
• Slide 39
• Several variations of Raman spectroscopy
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45