SPR sensors based on multilayer diffraction gratings and comparison with prism couplers

指導教授 : 林啟萬研究生 : 蘇明啟日期 : 2004/3/24

outline• Introduction to SPR sensor based on diffraction g

ratings• Characterization of gratings• Application of multilayer gratings as optochemica

l sensors• Sensitivity of SPR sensors using prism couplers• Sensitivity of SPR sensors using diffraction grati

ngs• Discussion• Reference

Three major approaches to optical excitation of SPW

prism coupling waveguide coupling

grating coupling

A SPR sensor based on diffraction grating

2

2

)sin(amr

amra n

nmn

Au 45nm652nm

18nm

AFM image of diffraction grating

Cross section of multilayer structures with diffraction grating

形成 Schottky Junction

Au or Ag film

Upper layer

Intermediate layer

substrate

6570

75Ψ

Δ

ε1

ε2

The quality of SPR is increased

When the void contents decrease.

(1) He-Ne laser

(2) Polarizer

(3) Quartz cuvette with tested solution

(4)(5) light beam direction through the cuvette without solution

(6) The same as (5), but for cuvette with tested solution

(7) Cr film-10nm / Au film-45nm

(8) GaAs substrate with diffraction grating

Schematic diagram of opto-chemical sensor

Incident angle vs. reflectance

SiOx thickness

1. 0 nm

2. 3 nm

3. 6 nm

4. 9 nm

5. 12 nm

6. 15nm

Wavelength at 632.8nm

650nm

3nm

The dependencies of the refractive index on the thickness of SiOx film

1. Multi-Angle-of-Incidence ellipsometry

2. SPR technique

The SPR photoresponse/angle dependencies for Ag/GaAs photodetector at different wavelengths

1. 650 nm

2. 625 nm

3. 600 nm

4. 550 nm

5. 500 nm

Metal thickness is 60nm

The SPR photoresponse curves for an Au-Cr-GaAs sensor as function of incidence angle obtained with various concentration

Alcohol in water (vol.%)

1. 0

2. 7.3

3. 13.6

4. 19.2

5. 24.0

6. 28.3

Water in alcohol (vol.%)

1. 0

2. 11.2

3. 20.2

4. 27.5

5. 33.6

6. 38.8

7. 43.7

Note:

Just measure the angle relative to one for a standard sample, instead of measuring absolute angle, because the accuracy of the absolute angular measurement is lower than that of the relative angular measurement.

http://home.hccnet.nl/ja.marquart/BasicSPR/BasicSpr01.htm

ko free space wavenumber

na refractive index of the dielectric (analyte)

np refractive index of the prism coupler

θ the angle of incidence (in the prism)

metal) theofconstant c(dielectri mimrm i

Sensitivity of SPR sensors using prism couplers

spwamr

amrpx k

n

nknkk

2

2

00 )sin(

0k

kn spwef

The effective index of SPW as a function of the wavelength for SPW propagating along the metal-analyte interface for two different values of the refractive index of analyte.

在相同的 na 下 ,Au 的 nef 都比 Ag高

因為 εmr(Au) < εmr(Ag)

nnndn

dS

amramr

mrmr

aP

22

A. Angular interrogation

from spwamr

amrpx k

n

nknkk

2

2

00 )sin(

22

1

aP

PPnn

SS

短波長時 , 有較高的 sensitivity

長波長時 ,sensitivity 較不隨波長變化而改變

故可簡化為

Prism - metal - analyte

(50nm) (na=1.32)

B. Wavelength interrogation

P

aPmramr

mra

mr

aP

nn

ddn

nddndn

dS

23

2

2

dd

nSS

mra

mrPP

3

22

在短波長時 , 很小

所以可以把分母第二項省略

得到

ddnP

Prism - metal - analyte

(50nm) (na=1.32)

Sensitivity of SPR sensors using diffraction gratings

2

2

)sin(

'

amr

amra

xmx

n

nmn

kmGk

m the order of diffracted waves

θ the angle of incidence of the optical wave

Λ the pitch of the grating

G grating vector

Grating depth 70 nm

Grating pitch 800nm

Resonant angle of incidence as a function of the wavelength for gold coated grating (Λ=800nm) and two different refractive indices of analyte

m=1 na ↑ θ↑

m=-2 na↑ θ↓

A. Angular interrogation

)sin()cos(

1

coupler grating th thecontact wiin not is analyte theif

)sin()cos(

1

coupler grating th thecontact wiin is analyte theif

2

2

3

2

amr

mr

aaG

amr

mr

aaG

nndn

dS

nndn

dS

from

2

2

)sin(amr

amra n

nmn

Grating depth 70 nm

Grating pitch 800nm

B. Wavelength interrogation

aG

mr

amrmr

a

amr

a

amr

mr

a

aG

nS

dd

n

nm

n

nnn

m

dn

dS

2 2

32

3

2

2

2

分子及分母的第二項皆遠小於第一項 , 所以可以簡化為

Grating depth 70 nm

Grating pitch 800nm

Discussion I• 利用角度調變時 在短波長時 , 靈敏度較高 但 grating-based 較為複雜 SPθdepends on na/np

SGθdepends on m

m=1 λ=800nm SGθ 只有 0.5 倍的 SPθ

m=2 λ=630nm SGθ 約等於 SPθ

λ=830nm SGθ 約比 SPθ 高出 10%

在長波長時 ,accuracy χ=s/w 較高 λ=630nm χP=15RIU-1

χG=11RIU-1

λ=830nm χP=83RIU-1

χG=48RIU-1

在長波段時 , 金屬材料的選擇 (Au 或 Ag) 則較不重要 See P11

w denote the full-width-half-

maximum of SPR dip

s denote the sensitivity

• 利用波長調變時 在長波段有較高的靈敏度 但 grating-based 的方式遠小於 prism-coupler

λ=630nm χP=108RIU-1

χG=48RIU-1

和角度調變比較 , 利用波長調變的方式 , 可得到較佳的 accuracy, 因此 resolution 也較高

但和角度調變相同的是 χP > χG

Discussion II

Discussion III• grating-based sensor 雖然靈敏度不如 prism-coupled sensor, 但擁有

體積微小化的優點 , 更適合於可攜式系統或植入式系統的應用。

Reference• N.L. Dmitruk, O.I. Mayeva, S.V. Mamykin, O.B. Yastrubchak, M. Klopfleisch,

Characterization and application of multilayer diffraction gratings as optochemical sensors, Institute for Physics of Semiconductors, National Academy of Sciences, Ukraine; Technical University, Germany, Sensors and Actuators A. Physical, September 2000

• Jiri Homola, Ivo Koudela, Sinclair S. Yee, Surface plasmon resonance sensors based on diffraction gratings and prism couplers: sensitivity comparison, Electrical Engineering Department, UW,USA; Institute of Radio Engineering and Electronics, Czech Republic, Sensors and Actuators B. Chemical, 1999

• N.L. Dmitruk, O.I. Mayeva, O.B. Yastrubchak, S.V. Mamykin, Multilayer Gratings: Characterization and Application, Institute of semiconductor physics of NAS of Ukraine, IEEE 1999

• Jiri Homola, On the sensitivity of surface plasmon resonance sensors with spectral interrogation, Institute of Radio Engineering and Electronics AS CR, Czech Republic, Sensors and Actuators B. Chemical, 1997

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