Raman Scattering of 4-Aminobenzenethiol Sandwiched between Au Nanoparticles and a Macroscopically Smooth Au Substrate: Effect of Size of Au Nanoparticles

Abstract

In order to obtain information on the nature of the “hot” sites in surface-enhanced Raman scattering, we have fabricated a model nanostructure composed of 4-aminobenzenethiol (4-ABT) that has further been sandwiched between Au nanoparticles and a macroscopically smooth Au substrate. In the absence of Au nanoparticles, that is, when 4-ABT is adsorbed solely onto a planar Au substrate, no Raman peak is identified at all using 632.8 nm radiation as the excitation source. When Au nanoparticles are attached onto the amine groups of 4-ABT on a planar Au substrate, Raman peaks are readily observed, however. What is intriguing is that a more intense Raman signal is obtained with increasing size of the Au nanoparticles at least with dimensions of under ∼100 nm. Much the same trend is confirmed from the finite-difference time-domain calculation. This is thought to suggest that the electromagnetic coupling of the localized surface plasmon of Au nanoparticles with the surface plasmon polariton of the underneath smoot...