Charge transfer process at the Ag/MPH/TiO 2 interface by SERS: alignment of the Fermi level.

A nanoscale metal-molecule-semiconductor assembly (Ag/4-mercaptophenol/TiO2 ) has been fabricated over Au nanoparticle (NP) films as a model to study the interfacial charge transfer (CT) effects involved in Ag/MPH/TiO2 . Due to the interaction between Au NPs and Ag NPs, some distinct differences occur in the SERS spectra. We also measured the SERS of Ag/MPH (4-mercaptophenol), Ag/MPH/TiO2 , and Au/Ag/MPH/TiO2 assemblies at excitation wavelengths of 477, 514, 532, 633, and 785 nm. We found that the changes in the CT process, caused by the introduction of TiO2 and Au, can be reflected in SERS. Then in combination with other detection methods, we proposed a possible CT process involved in the Ag/MPH, Ag/MPH/TiO2 , and Au/Ag/MPH/TiO2 assemblies. A Pt/Ag/MPH/TiO2 assembly was also constructed to verify our proposed CT mechanism. This work not only provides more details about CT between metal-molecule-semiconductor interfaces but also aids in constructing nanoscale models to study interfacial problems with the SERS technique.