Humidity sensors based on ZnO/TiO2 core/shell nanorod arrays with enhanced sensitivity

摘要

Highly aligned arrays of ZnO/TiO_2 core/shell nanorods were fabricated on glass substrates by hydrother-mal growth of ZnO nanorods cores followed by the deposition of anatase TiO_2 shells in a sol-gel process. The characterization of these composite materials with scanning electron microscopy (SEM), Raman spec-troscopy, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and transmission emission microscopy (TEM) points to the formation of crystalline ZnO nanorod cores that are coated with anatase TiO_2 shells. Humidity sensors based on these core/shell nanorod arrays exhibit outstanding sensitivities with capacitances varying from 10~1 to 10~6pF over a relative humidity (RH) range of 11%-95% at room temperature, which is 1.5 and 3 orders of magnitude higher than that of pristine TiO_2 films and ZnO nanorods, respectively. Complex impedance analysis indicated that the enhanced humidity sensitivity is probably due to the high surface/volume ratio of this core/shell material in combination with the remarkable hydrophilicity of the TiO_2 shell.