Light enhancement in surface-enhanced Raman scattering at oblique incidence

Abstract

Surface enhanced Raman scattering (SERS) measurements have been carried out at different focusing conditions using objective lenses of different numerical apertures. The experimentally observed dependence of SERS intensity of thiophenol-coated Ag nano-islands shows a close-to-linear scaling with the collection aperture. The linear relationship breaks down for large numerical apertures, which suggests that the scattering is anisotropic. Numerical simulations of realistically shaped Ag nano-islands were carried out, and the spatial distribution of hot-spots has been revealed at different heights near the nano-islands. Local field enhancements of up to 100 times were estimated. The simulation also suggests an explanation for the anisotropy in the scattering observed for larger numerical aperture objectives. This appears to be due to a reduction in the local field enhancement as the electric field vector component in the plane of the shallow metal islands reduces at larger angles of incidence.

Keywords

Surface-enhanced Raman scattering, metal island films, finite difference time domain

References

[1] Smith W.. Practical understanding and use of surface enhanced Raman scattering/surface enhanced resonance Raman scattering in chemical and biological analysis. Chemical Society Reviews, 2008, 37(5): 955-964.

[2] Hering K., Cialla D., Ackermann K., Dorfer T., Moller R., Schneidewind H., . SERS: a versatile tool in chemical and biochemical diagnostics. Analytical and Bioanalytical Chemitry, 2008, 390(1): 113-124.

[3] Nishijima Y., Rosa L., Juodkazis S.. Surface plasmon resonances in periodic and random patterns of gold nano-disks for broadband light harvesting. Optics Express, 2012, 20(10): 11466-11477.

[4] Yokota Y., Ueno K., Juodkazis S., Mizeikis V., Murazawa N., Misawa H., . Nano-textured metallic surfaces for optical sensing and detection applications. Journal of Photochemistry. Photobiology A: Chemistry, 2009, 207(1): 126-134.

[5] Brown R., Milton M.. Nanostructures and nanostructured substrates for surface-enhanced Raman scattering (SERS). Journal of Raman Spectroscopy, 2008, 39(10): 1313-1326.

[6] Banholzer M. J., Millstone J. E., Qin L., Mirkin C. A.. Rationally designed nanostructures for surface-enhanced Raman spectroscopy. Chemical Society Reviews, 2008, 37(5): 885-897.

[7] Jayawardhana S., Kostovski G., Mazzolini A. P., Stoddart P. R.. Optical fiber sensor based on oblique angle deposition. Applied Optics, 2011, 50(2): 155-162.

[8] Driskell J. D., Shanmukh S., Liu Y., Chaney S. B., Tang X. J., Zhao Y. P., . The use of aligned silver nanorod arrays prepared by oblique angle deposition as surface enhanced Raman scattering substrates. Journal Physical Chemistry C, 2008, 112(4): 895-901.

[9] Bryant M. A., Pemberton J. E.. Surface Raman-scattering of self-assembled monolayers formed from 1-alkanethiols at Ag. Journal American Chemical Society, 1991, 113(10): 3629-3637.

[10] Pettinger B., Wenning U., Wetzel H.. Angular resolved Raman-spectra from pyridine adsorbed on silver electrodes. Chemical Physics Letters, 1979, 67(1): 192-196.

[11] Liu Y. J., Fan J. G., Zhao Y. P., Shanmukh S., Dluhy R. A.. Angle dependent surface enhanced Raman scattering obtained from a Ag nanorod array substrate. Applied Physics Letters, 2006, 89(17): 173134.