Effect of silver nanoplates on Raman spectra of p-aminothiophenol assembled on smooth macroscopic gold and silver surface

Recently, metal-molecule-metal junctions have been actively researched due to their potential applications in molecular electronics, and probing the structure of the molecules in the junctions is crucial for understanding electron-transfer properties. In this paper, self-assembled monolayers (SAMs) of p-aminothiophenol (p-ATP) are formed on a smooth macroscopic gold and silver surface, and colloidal silver nanoplates (similar to 100 mn edge length and 12 nm thickness) are assembled onto the SAM surface to form the silver nanoplates-moleculegold (silver) junctions for the first time. The resulting silver nanoplates-molecules-gold (silver) structures are studied with surface enhanced Raman scattering (SERS) at 514.5, 794.4, and 1064 nm excitations, respectively. Initially, there is very weak Raman signal of p-ATP on the smooth macroscopic gold and silver substrates, respectively, but Raman spectra are considerably enhanced by the presence of the silver nanoplates, which is due to the strong electromagnetic coupling between the localized surface plasmon (LSP) of silver nanoplates and the surface plasmon polariton (SPP) of the smooth gold and silver, respectively, so-called LSP-SPP coupling. The Raman spectra obtained are compared with that obtained on silver nanoplates deposited on glass at the specific excitation wavelengths. It was found that the enhancement factor (EF) of the junctions to the probe molecule is 3-9 times larger than that at silver nanoplates deposited on glass, indicating great potential in the research of molecular electronic device and biology by SERS.