利用拉曼和表面光电压谱对一维TiO_2@CdS核壳结构界面电荷行为研究

Study on Charge Carriers Behavior at CdS/TiO_2 Interface of One Dimensional TiO_2@CdS Core-shell Structure by Raman Scattering and Surface Photovoltage Spectroscopy

利用化学气相沉积法制备了直径约90 nm,长数十微米的高质量TiO2纳米线.通过化学浴沉积法(CBD)在纳米线表面生长CdS包覆层,形成了一维TiO2@CdS核壳结构.不同包覆层厚度的一维TiO2@CdS核壳结构拉曼光谱研究发现TiO2/CdS界面的光生电荷转移对CdS和TiO2拉曼响应均有增强效应.结合表面光电压谱研究发现表面包覆层的厚度对TiO2/CdS界面光生电荷转移有显著的影响.表面CdS包覆层厚度对拉曼和表面光伏响应影响的研究表明电子在CdS包覆层中的电子扩散距离在30～60 nm.

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.