Humidity sensors based on ZnO/TiO(2) core/shell nanorod arrays with enhanced sensitivity

Abstract

Highly aligned arrays of ZnO/TiO(2) core/shell nanorods were fabricated on glass substrates by hydrothermal 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 spectroscopy, 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(6) pF 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. (C) 2011 Elsevier B.V. All rights reserved.