Pressure-induced SERS enhancement in MoS2/Au/R6G system by a two-step charge transfer process
Abstract Pressure-induced surface-enhanced Raman spectroscopy (PI-SERS) represents a new frontier in the research field of SERS. However, relatively few works have been focusing on the PI-SERS due to many difficulties, such as easy aggregating of nanoparticles and understanding the interaction mechanisms between probe molecules and the SERS substrate at high pressure. Here we developed an efficient semiconductor-metal SERS substrate (MoS2/Au) to study the PI-SERS. Different from the previously reported monotonous decrease in Raman intensities upon compression, an anomalous Raman enhancement of R6G molecules adsorbed on MoS2/Au substrate was observed up to 2.39 GPa, at which the degree of charge transfer (ρCT) between R6G molecule and MoS2/Au substrate reaches a maximum. By comparison, it is proposed that the decoration of Au in the SERS system could bring about a two-step charge transfer (CT) process, introduce the localized surface plasmon resonance (LSPR), and thus favor the PI-SERS enhancement. Moreover, such a charge transfer also causes obvious change in the optical behaviors of R6G molecule upon compression. This brings new insights into the SERS study and also offers new ideas for the development of SERS application in high pressure study.