What can technology do for you?

What can you do with the aid of technology?

Why look at surfaces at high magnification?

Description and identification of constituent phases by morphology, emission and absorption properties, or other physical responses.

Observation of features which give you insight into processes and the relevant mechanisms.

What is chemical microanalysis all about and why do it?

Phase identification by element ID and stoichiometry.

Identify and quantify chemical processes.

Establish qualitatively and quantitatively the distribution of elements in a sample at the micro-scale, and quantify kinetic processes.

Provide quantitative data for thermodynamically constrained processes (establish the temperature, pressure, solution activities, etc. of chemical reactions in nature.)

Use technology to gain insights into the processes of nature…

How? Examine controlled physical interactions between matter and energymicroscopy spectroscopy

Resources and engineering

Planetary processes

The array of microanalysis tools…sorting through the acronyms

EPMA

SEM-EDS

STEM

TEM

SHRIMP

EELS

AESEBSD

FTIR

UV-VIS

μ-XRF

XPS

SIMS

LA-ICP-MS

μ-XRD

AFM

STM

TAP

nanoSIMS

XANES

SPM

LE

XE

SESCA

MFM

IRA

S

FIM

CFM

ARPES

HAS

LEIS

LEED

PE

EM

PIXE

XAFS

SCEMH

IM

LRS

The array of microanalysis tools…

Photon ablationLA-ICP-MS – Laser ablation inductively coupled plasma mass spectrometry

Ion ablation and activation(focused ion beam techniques) SIMS-Ion Microprobe – Secondary ion mass spectrometry SHRIMP – sensitive high resolution ion microprobenanoSIMSHe-ion microscopy

OtherSPM – Scanning probe microscopies

STM – Scanning tunneling microscopyAFM – Atomic force microscopyMFM – Magnetic force microscopy

Atom probe (TAP) tomographic atom probe or atom probe microscopy (APM)

LA-WATAP (laser assisted wide angle)PIXE – proton induced x-ray emission

Electron excitation and absorption techniquesSEM – Scanning electron microscopyEPMA – Electron probe microanalysisLEXES – low energy electron induced x-ray emission spectroscopyTEM-STEM – Transmission electron microscopy (and scanning transmission electron microscopy or “analytical electron microscopy” = AEM)EELS – electron energy loss spectroscopyEBSD – electron backscatter diffraction in SEMAES – Auger electron spectroscopy

Photon excitation and absorption techniquesOptical MicroscopyXPS – X-ray photoelectron microscopy (or ESCA = electron spectroscopy for chemical analysis)FTIR – fourier transform infrared analysisUV-VISLaser Raman Spectroscopyμ-XRF – micro-X-ray fluorescenceX-ray microdiffractionSynchrotron techniques

XANESXAFS

The array of microanalysis tools…

Electron excitation and absorption techniquesSEM – Scanning electron microscopyEPMA – Electron probe microanalysisLEXES – low energy electron induced x-ray emission spectroscopyTEM-STEM – Transmission electron microscopy (and scanning transmission electron microscopy or “analytical electron microscopy” = AEM)EELS – electron energy loss spectroscopyEBSD – electron backscatter diffraction in SEMAES – Auger electron spectroscopy

Photon excitation and absorption techniquesOptical MicroscopyXPS – X-ray photoelectron microscopy (or ESCA = electron spectroscopy for chemical analysis)FTIR – fourier transform infrared analysisUV-VISLaser Raman Spectroscopyμ-XRF – micro-X-ray fluorescenceX-ray microdiffractionSynchrotron techniques

XANESXAFS

Surface imaging down to a few Å (or less) – primarily morphologyQuantitative microanalysis and compositional imagingUltra low kV X-ray microanalysis (10’s of μm) at low voltage

Imaging by electron transmission for extreme magnification of internal structure.

Compositional analysis, bonding and valence (low Z)Microstructural analysisUltra low energy surface analysis for elemental composition Similar to XPS, but higher spatial resolution (10-100nm)

Microstructural observation, including polarization propertiesSurface (upper few nm) chemical analysis (parts per thousand) Spatial resolution 100’s of μmMolecular fingerprintingAnalysis of transition metal ions, organic compoundsVibrational modes – molecular identification via bond info.Quantitative analysis of major and minor elements, 100s of μmMicrostructural analysis

Valence and coordination, material band structureScattering of photoelectrons from surrounding atoms = local structure.

The array of microanalysis tools…

Photon ablationLA-ICP-MS – Laser ablation inductively coupled plasma mass spectrometry

Ion ablation and activation(focused ion beam techniques) SIMS-Ion Microprobe – Secondary ion mass spectrometry SHRIMP – sensitive high resolution ion microprobenanoSIMSHe-ion microscopy (HIM)

OtherSPM – Scanning probe microscopies

STM – Scanning tunneling microscopyAFM – Atomic force microscopyMFM – Magnetic force microscopy

Atom probe (TAP) tomographic atom probe or atom probe microscopy (APM)

LA-WATAP (laser assisted wide angle)PIXE – proton induced x-ray emission

Trace elements and isotopic compositions, 10’s to 100’s of microns (ppt in some cases), destructive.

Ion mass/charge ratios, 10-30 microns, ppm-ppb sensitivity, isotope ratios and geochronology (destructive)Isotope ratios (limited range, 10’s of nanometers)Ultra high resolution surface imaging – RBS possible

Surface atomic imaging (conductors) – nm or less, indirectSurface atomic imaging – 0.1nm – directSurface magnetic structureAtom scale 3D composition (destructive)

TAP on insulatorsCompositional analysis down to μm scale (accelerator)

Chemical analysis of microvolumesElemental concentrationsSEM - EDSEPMA (WDS)LA-ICP-MSμ-XRFSIMSPIXEFTIR (bonding, functional groups)

Chemical analysis of microvolumesIsotopic concentrationsLA-ICP-MSSIMS

Surface imagingSEMSTM - atomicAFM - atomicEBSD - SEMAESXPSSIMS

Surface chemistrySIMSAESXPSTAP-APMEPMA – LEXES (WDS)

Analysis of microstructureTEM-STEMEBSD - SEMX-ray microdiffractionSTMAFMTAP-APM

Micro-scaleSEM - EDSEPMASIMS (ablation)AES (surface)XPS (surface)

Nano-scaleHR-SEM-EDSHe-ion microscopeEPMA (special)TEM-STEM-EDSSTM (atomic scale)AFM (atomic scale)NanoSIMS (ablation)TAP-APM (atomic scale)

Electron…Elementary particle (no internal structure)Fermion (Half integer spin, constrained by Pauli Exclusion principle)Lepton (do not interact through the color force = no strong interaction) of charge -1, mass = 0.511 MeV/c2

Electron properties and interaction with matterWavelength (0.01-0.04nm) much shorter than visible light (400-650nm)Charged, so will interact with EM fields – can be focusedInteract with matter

Elastically -BackscatterInelastically – to produce

Secondary electronslightX-raysheat (phonon excitation/lattice oscillation)

Observations…Size, shape, relationships of objects(What does what you “see” actually represent?)

Paleotemperature, pressure, solution activities, age, etc.Calculated results with assumptions…

Elemental concentration…do we actually measure this?

Measured…Intensities of X-rays at specified wavelengthsMass ratios

Data?

Scanning Electron Microscopy and Electron Microprobe Analysis

• High magnification surface imaging• Chemical analysis of materials on a

scale of microns (or less)

Focused electron beam generates detectable signals from specimen

• Secondary electrons• Backscattered electrons• X-rays

• Non-destructive• In-situ analysis

Scanning Electron Microscope

Focused electron beam is scanned over surface - excites atoms of target – signals emitted and detected

High magnification surface imaging with resolution of few nm to sub-nm for secondary electrons

Scanning Electron Microscope

Artificial artery

foraminifera

V-oxide

Zeolite surface

Electron Microprobe (Electron Probe Microanalysis - EPMA) quantitative chemical microanalysis and compositional imaging

Primarily designed for precise characteristic X-ray detectionX-ray wavelengths relate to electronic structure – can identify specific elements.

Intensity variation in specimen relates to spatial distribution of these elementsX-ray counts from specimen compared to standards of known composition →

computed elemental concentrations

PURPOSE

Analysis of individual mineral grains or amorphous solid phases

In-situ (preserve textural relationships!)

Compositional imaging and spatial distribution of elements in the scanned area.

Quantitative chemical variation within mineral grains or discrete phases - zoning and growth histories

Mg Kα

Ag distribution in solder

Y distribution in natural monazite

Solder bumps on IC

50 μm

GENERAL “LIMITATIONS”

Spatial resolution – it dependsElectron beam focused to 0.01 to 0.2 μm diameterScattering → electron interaction volume and signal emission volume.Imaging (SEM) – from few nm to hundreds of nmChemical analysis (EPMA) - Silicates 1 to 3 μm diameter volume

Compositional sensitivity (detection limits) – it depends 50-200 ppm (a few ppm in some special cases)

For EPMA, mostly major and minor elementsElement rangeRoutinely Na and heavier – but it depends…Also B, C, N, O (special circumstances)

ELECTRONS

λ shorter than visible light → higher image resolution(light 400-650nm, electrons ~ 0.04 -.01nm,1-10kV)

Charged particles - can be electromagnetically focused

Interact with specimen to produce detectable signalsBSESEX-Rays

ELECTRON OPTICS

Electron source (gun)Cathode + AnodeControls beam voltage

Condenser lensesControls beam current

Objective lensControls beam size, shape, depth of field at specimen

Result = electron beam of specified voltage, current and diameter.

Wavelength dispersive, X-ray spectrometer

Vacuum System - mean path length of electrons must be greater than column length10-3 to 10-5 pa (~10-5 to 10-7 torr)

specimen

Raimond Castaing

What happens when beam reaches specimen?

Beam/Specimen interactions

1) Some beam electrons scattered back out-More effectively by heavier target atoms-Results in BSE signal

2) Some beam electrons interact inelastically with atoms in the targetEnergy is transferred

A) Can result in ejection of some weakly bound outer shell electrons → secondary electron signal (low energy)

B) Some cause inner shell ionizations leading to characteristic X-ray emission

15 kV

10 kV

1 mm

Electron trajectory modeling - Casino

Labradorite (Z = 11)

INNER SHELL IONIZATION

1) If energy equal or greater than critical excitation potential…

Can eject inner shell electron

2) Atom wants to return to ground stateouter shell electron fills vacancy – relaxation

Outer shell electron in higher energy state relative to inner shell electron

some energy surplus in the transition → photon emission (X-ray)

X-ray is characteristic of the target element

Example: E SiKα = 1.740 KeV (7.125Å)

E FeKα =6.404 KeV (1.936Å)

Kα

ψp

ψ1sψp2

ψp1

Kβ

ψp

ψ1sψp2

ψp1

Also produce background spectrum

Originates from deceleration reactions of insufficient energy to ionize the target atom

Produce overall X-ray spectrumCharacteristic peaks superimposed on a background

How are X-rays detected?

Discriminated by energy (EDS) Or wavelength (WDS)

EDS DetectorsSolid state semiconductor detectorsSee entire spectrum at onceFastRelatively low resolution

WDS Select analytical lines by diffraction

nλ = 2d sin θ

Relatively high resolution

WDS used for most quantitative analysisEDS for qualitative evaluation

crystal

detector (counter)

sample

Wavelength Dispersive Spectrometry (WDS)

Bragg Law:

θ

nλ = 2d sinθ

d

At certain θ, rays will be in phase,

otherwise out of phase = destructive interference

DetectorsUsually gas filled counter tubes

1) ionize counter gas (Xe, Ar)2) eject photoelectron3) photoelectron ionizes other gas atoms4) electrons collected by wire5) output pulse = x-ray count

pulse height proportional to x-ray energy

Measure counts per second of a particular X-raycompare to standard of known composition to get concentration

Must correct for matrix effectsZ atomic #A absorptionF secondary fluorescence

I

I % S i

S iK (un k )

S iK (std )std un co rr. w t%

Ci / C(i) = [ZAF] [Ii / I(i)]

IMAGING

Secondary electron detectorelectron strikes scintillator and converted to light pulse - Amplified and displayed

Raster the beam over sample and display at the same time and get image (basically an intensity map)

Scan smaller and smaller areas to increase magnification

Object: Convert radiation into an electrical signal which is then amplified

SelectSecondary electronsBackscattered electronsX-raysAuger electronsPhotons from CathodoluminescenceAbsorbed electron current

Incident beamLight

(cathodoluminescence)

BremsstrahlungSecondary electrons

Backscattered electrons

heat

Elastically scattered electrons

Transmitted electrons

Specimen current

Auger electrons

Characteristic X-rays

Sample

Any of the collected signals can be displayed as an image if you either scan the beam or the specimen stage

5 mm

Electron Backscatter

Backscattering more efficient with heavier elements

Can get qualitative estimate of average atomic number of target

Image will reveal different phases

Brighter = higher average Z

Garnet, Grand Canyon MgKα

X-ray mapping display spatial distribution of characteristic X-ray intensity to get qualitative compositional information

Garnet - Moretown Formation, MA CaKα

Garnet - Italy MgKα Garnet – Grand Canyon MnKα

Corona texture - CaKα Saskatchewan

Originalopx

Cpx + qtz

opx

plag

opx+plag+ mt

garnet

matrixplag

Lobster cuticle – composite element map

calcite

100 μm

Monazite – thorium map

Monazite Geochronology

Quantitative Analysis – Geosciences applications

Mineral chemistry – in-situ, single phase characterizationmicroscale compositional changes within phases - zoning

Crystallization paths and evolution of magmatic systems

Geothermometry

Geobarometry

Geochronology

Low-temperature geochemistryclay mineralogymass transfer / weathering reactionspaleoclimate applications – speleothem microchemistry

Fundamental geochemical processesPhase equilibria

Kineticsdistribution coefficients

Two generations of garnet growthBlack Hills, SD

grossular

spessartine

0 10 20 30 40 50 60 70 80 90 100 110 120

20

25

30

35

40

45

Mg

/Ca

*(1

03 )

Age KY B.P.

0.2

0.4

0.6

0.8

1.0

1.2

Sr/C

a*(1

03)

980

960

940

920

900

880

860

840

820

Fe

b. in

sola

tion

(30

0S)

-6

-4

-2

0

(d)

(c)

(b)

(a)

18

O

Paleoclimate

20 30 40 50 60 70 80 90 1000

2

4

6

8

10

12

14

16

GeO2

Tm2O3

microns

wt.

%

Element concentrations in optical fiber

CoreCladding Cladding

Geochronology – traditionally using isotopic/mass-spectrometric techniques• IDTIMS• Ion Probe

Electron Microprobe (EPMA)• High spatial resolution

access to ultra-thin rims,micro-domains, and inclusions

• In-situ: relate composition (and age) tomicro/macro-structure and mineral paragenesis

• Non-destructive• Integrated spatial / compositional / age relationships

Monazite: LREE-phosphate with Th and U (→ radiogenic Pb)Common accessory phase in many rocksFabric formerDissolution/re-precipitation reactions result in polygenetic

nature, and ties into overall reaction history

ThMα

Dating events{

Map, map, map…

Map compositional domains, then quantitatively measure Th, U, and Pb concentrations. Compute age via:

The Ultrachron Project

Electron optics• Optimize analytical resolution

(Smaller phase analysis) for a range of kV and current

• High, stable current for trace element analysis

• Minimize excitation volume in high Z material

Detection

BSE and X-Ray optics• Improve precision (Optimize

counting - PbMα)• Integrate spectrometers• Improve accuracy – background

estimation

Techniques• Minimize beam damage• Background• Analytical protocols

Improve dynamic range of BSE amplifier

BSE shielding for high current applications

New high intensity crystals (VLPET) + VL detectors

Counters optimized (gas mixture, pressure, HV)

Completely dry vacuum system

Anticontamination

CeB6 /LaB6

New HV power supply

Decouple operation of condensers to optimize brightness down column

Current regulation up to 1 microamp

ψp

ψ1sψp

ψp