Multiphonon Resonant Raman Scattering and Photoinduced Charge-Transfer Effects at ZnO–Molecule Interfaces

Abstract

Detailed understanding of the underlying mechanisms of surface-enhanced Raman scattering (SERS) remains challenging for different experimental conditions. In this study, a novel laser-driven photoinduced interfacial charge transfer (CT) was observed based on UV–visible–infrared excitation wavelengths (325, 488, 514, 633, and 785 nm) through surface modification of ZnO nanorods by 4-aminothiophenol (PATP). SERS spectra combined with well-characterized surface morphology and optical spectroscopy indicate that the chemical enhancement occurs at visible-infrared excitation but at ultraviolet excitation (325 nm) multiphonon resonant Raman Scattering (MRRS) results in additional strong enhancements of particular Raman transitions through Cu–ZnO–PATP model. The relationships between the excitation photon energies (3.82, 2.54, 2.41, 1.96, and 1.58 eV), and its Raman shift were discussed. We found the strong dependence of the Raman shifts with the exchanges of excitation photon energies. These results highlight the role of excitation energy in determining the interface enhanced Raman scattering for semiconductor-molecule models. This implies that copper sheet under the ZnO improve the interfacial CT in ZnO-molecule and act as an effective donor for inhibiting reversible CT, and there was a strong interaction, which might be regarded as CT resonance process, between PATP molecules and the ZnO surface. This work not only shows a possibility for further understanding the origin of the SERS mechanism from semiconductor substrates but also for exhibits a situ characterization technique for probing the photoinduced interfacial charge-transfer processes.