Synergistic contribution to the enhanced charge transfer of the silver/4-mercaptobenzoic acid/polyaniline (Ag/MBA/PAN) system: thickness-dependent of PAN

The purpose of this paper is to study the charge transfer (CT) process of a Ag/MBA/PAN system with different thicknesses of PAN and explore its SERS enhancement mechanism. It is found that as the PAN thickness is increased, the frequency and intensity of the characteristic MBA band gradually increases. The intensity of the b2 mode increases significantly, which is attributed to the CT mechanism. As the PAN thickness is increased, the degree of CT (ρCT) gradually increases, which is due to the excited SPR from Ag. The electromagnetic enhancement mechanism, which occurs at the interface between PAN and Ag, generates hot electrons and rearranges the interface between PAN and Ag, thereby promoting electron transfer for the whole CT in Ag/MBA/PAN. These results show that CT occurs from the Fermi level of Ag to the LUMO level of MBA and then to the LUMO level of PAN. Additionally, the direction of CT is verified by 2D-COS. Therefore, this study not only reveals the ultrahigh SERS activity of the substrate but also explains the detailed process of regulating the substrate through the PAN thickness, which affects the SERS mechanism. This conductive polymer will open up a new horizon of SERS research and applications.