TiO₂ nanowires with the diameter of about 90 nm and length of dozens of micron meter were synthesized by thermal annealing of Ti foil under the catalysis of Pd nanoparticles which were deposited on Ti foil with the ultraviolet light photoreduction. CdS shell grew on the surface of TiO₂ nanowires by chemical bath deposition (CBD) to form the 1D TiO₂@CdS core/shell nanostructures. The thickness of CdS shell was controlled by varying the concentration of the citric acid. The scanning electron microscope (SEM) and transmission electron microscope (TEM) characterization implied that CdS shell thickness on TiO₂ nanowire were about 20, 30 and 60 nm, synthesized in the solutions with citric acid concentration of 0.095, 0.19 and 0.38 mmol/L, respectively. The Raman scattering of pure TiO₂ nanowire and TiO₂@CdS core/shell structures excited by 488 nm Argon ion laser indicates that the modification of CdS on TiO₂ nanowire with proper thickness (20 to 30 nm) can increase both the Raman scattering resulted from CdS and TiO₂. It is attributed to the photo-induced electron transfering from CdS shell and TiO₂ core, which results in the quenching of fluorescence of CdS, and the increase of electron distribution density for TiO₂ excited state. The surface photovoltage (SPV) spectrum characterization, based on the separation of photo-generated electron-hole in space, agrees well with the Raman scattering results. That is, TiO₂@CdS core/shell structures with 30 nm CdS have highest SPV response intensity and broadest spectrum range, due to the effective charge transfer between CdS and TiO₂. The systematic study about the dependence of the Raman scattering and SPV on the CdS shell thickness demonstrated that the diffusion length of electron in CdS shell is between 30 and 60 nm, and it is optimal for one-dimension TiO₂@CdS nanostructures in optoelectric devices application with the CdS shell thickness thinner than light penetration depth and electron diffusion length in CdS.

Key words: TiO₂ nanowire, TiO₂@CdS, Raman scattering, surface photovoltage spectroscopy (SPS)