Charge Transfer Tuned by the Surrounding Dielectrics in TiO(2)-Ag Composite Arrays

TiO(2)/Ag bilayer films sputtered onto a 2D polystyrene (PS) bead array in a magnetron sputtering system were found to form a nanocap-shaped nanostructure composed of a TiO(2)-Ag composite on each PS bead, in which the Ag nanoparticles were trapped partially or fully in the TiO(2) matrix, depending on the TiO(2) thickness. X-ray Photoelectron Spectroscopy (XPS) results showed the opposite shifts of binding energy for Ti 2p and Ag 3d, indicating the transfer of electrons from metallic Ag to TiO(2) owing to the Ag-O-TiO(2) composite formation. UV-Vis absorption spectra showed the blue shifts of the surface plasma resonance peaks, and the maximum absorption peak intensity was obtained for TiO(2) at 30 nm. The surface-enhanced Raman scattering (SERS) peak intensity first increased and then decreased when the TiO(2) thickness changed. The observations of SERS, XPS, and UV-Vis absorption spectra were explained by the dependency of the charge-transfer process on TiO(2) thickness, which was ascribed to the changing dielectric properties in the metal/semiconductor system.