Sensitive surface-enhanced Raman scattering of TiO2/Ag nanowires induced by photogenerated charge transfer

Abstract

In this work, the semiconductor TiO2 nanowires were successfully coupled with plasmonic metal Ag nanoparticles to fabricate hybrid nanostructures with enhanced sensitive Raman substrate. The SERS activities of fabricated hybrid nanostructures were evaluated by detecting the Raman signals of R6G molecules. The fabricated TiO2/Ag nanowire/nanoparticle hybrid nanostructures show sensitive detection ability for R6G molecules. Based on the band structures of Ag nanoparticle, TiO2 nanowire and R6G molecule, the enhanced sensitive SERS activities of hybrid nanostructures is ascribed to an efficient charge transfer process, in which the photogenerated electrons transfer to the conduction band of TiO2 nanowires from metal Ag nanoparticles, and then to LUMO level of R6G molecules, leading to enhanced SERS activities. This efficient charge transfer process is achieved by the synergistic effects of plasmonic metal Ag nanoparticle, semiconductor TiO2 nanowire and R6G molecule. Furthermore, the transfer process of photoexcited electrons from metal Ag nanoparticle to conduction band of TiO2 nanowire is evidently confirmed by the photoresponse properties of hybrid nanostructures under illumination only with visible light (λ>420nm). The findings achieved in this work demonstrate that efficient turning the charge transfer in plasmonic metal nanoparticle/semiconductor/molecule hybrid nanostructure can significantly enhance its SERS activity.