Enhanced Raman scattering when scatterer molecules located in TiO2/Ag nanojunctions

Abstract

The TiO₂/4-mercaptopyridine (4-Mpy)/Ag sandwich structure has been fabricated by a self-assembly method and the enhanced Raman scattering of the molecule embedded in the nanojunction, known as surface-enhanced Raman spectroscopy (SERS), was studied. X-ray photoelectron spectroscopy (XPS) has been employed to investigate the formation process of the TiO₂/4-Mpy/Ag sandwich structure. Raman spectra of the TiO₂/4-Mpy/Ag sandwich structure were significantly enhanced relative to those observed on 4-Mpy adsorbed on Ag particles or TiO₂/4-Mpy. A possible distribution of 4-Mpy molecules in the fabrication of TiO₂/4-Mpy/Ag assemblies has been proposed. It shows that 4-Mpy molecules adsorb on the surface of the TiO₂ NPs, and the 4-Mpy molecules connect with Ag NPs via the S atom. The analysis of XPS confirms the result obtained from Raman spectra of TiO₂/4-Mpy/Ag assemblies. The SERS enhancement mechanism is discussed briefly in the article, and we ascribed it to the charge-transfer mechanism.