Charge-Transfer Effect on Surface-Enhanced Raman Scattering (SERS) in an Ordered Ag NPs/4-Mercaptobenzoic Acid/TiO₂ System

Abstract

With the explosive development of analysis and detection techniques based on surface-enhanced Raman scattering (SERS), the further understanding and exploitation of the chemical mechanism becomes particularly important. We investigated the charge transfer (CT) effect on SERS in a semiconductor–molecule–metal system constructed with Ag NPs, 4-mercaptobenzoic acid (MBA) molecule, and atomic level TiO2. To ensure more ordering, the system is constructed by a layer-by-layer self-assembly method. After introducing TiO2, we found that the relative band intensity of some peaks displayed a distinct difference, which is attributed to the Herzberg–Teller contribution that occurs via CT. We also proposed a possible mechanism responsible for the selective enhancement observed in the SERS spectra of the Ag NPs/MBA/TiO2 system. This work will not only provide much deeper insight into the CT mechanism in SERS but also help in the development of a method to construct metal–semiconductor-based SERS substrates.