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

1. 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

2. outline • Introduction to SPR sensor based on diffraction gratings • Characterization of gratings • Application of multilayer gratings as optochemical sensors • Sensitivity of SPR sensors using prism couplers • Sensitivity of SPR sensors using diffraction gratings • Discussion • Reference

3. Three major approaches to optical excitation of SPW prism coupling waveguide coupling grating coupling

4. 18nm 652nm Au 45nm A SPR sensor based on diffraction grating

5. AFM image of diffraction grating Cross section of multilayer structures with diffraction grating Upper layer Au or Ag film 形成Schottky Junction Intermediate layer substrate

6. Δ 65 70 Ψ 75 ε1 ε2 The quality of SPR is increased When the void contents decrease.

7. Schematic diagram of opto-chemical sensor • 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

8. 3nm 650nm • Incident angle vs. reflectance • SiOx thickness • 0 nm • 3 nm • 6 nm • 9 nm • 12 nm • 15nm • Wavelength at 632.8nm • The SPR photoresponse/angle dependencies for Ag/GaAs photodetector at different wavelengths • 650 nm • 625 nm • 600 nm • 550 nm • 500 nm • Metal thickness is 60nm • The dependencies of the refractive index on the thickness of SiOx film • Multi-Angle-of-Incidence ellipsometry • SPR technique

9. The SPR photoresponse curves for an Au-Cr-GaAs sensor as function of incidence angle obtained with various concentration • Water in alcohol (vol.%) • 0 • 11.2 • 20.2 • 27.5 • 33.6 • 38.8 • 43.7 • Alcohol in water (vol.%) • 0 • 7.3 • 13.6 • 19.2 • 24.0 • 28.3 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.

10. Sensitivity of SPR sensors using prism couplers 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) http://home.hccnet.nl/ja.marquart/BasicSPR/BasicSpr01.htm

11. 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)

12. A. Angular interrogation from 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)

13. B. Wavelength interrogation 在短波長時, 很小 所以可以把分母第二項省略 得到 Prism - metal - analyte (50nm) (na=1.32)

14. Sensitivity of SPR sensors using diffraction gratings m the order of diffracted waves θ the angle of incidence of the optical wave Λ the pitch of the grating G grating vector

15. 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↓ Grating depth 70 nm Grating pitch 800nm

16. A. Angular interrogation from Grating depth 70 nm Grating pitch 800nm

17. B. Wavelength interrogation Grating depth 70 nm Grating pitch 800nm 分子及分母的第二項皆遠小於第一項, 所以可以簡化為

18. 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

19. Discussion II • 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 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。

20. 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

21. Thank You!!