Improved gas sensing performance of p-copper oxide thin film/n-TiO2 nanotubes heterostructure

CuO thin film/TiO2 nanotubes heterostructures were fabricated to investigate the effect of p-n heterojunction on sensing properties. TiO2 nanotubes were synthesized via anodization of Ti foil. Then, CuO thin film was covered on the nanotubes by oxidation of thermally evaporated Cu layer. For comparison, sensor devices those are composed of only CuO thin film and composed of TiO2 nanotubes have been also fabricated. The heterostructure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to H2, ethanol, acetone, chloroform and NO2 gases at different operation temperatures. Experimental results showed that the heterostructure sensor has better performance toward H2 in sensing with low operation temperature, low detection limit and high sensor response compared to TiO2 nanotubes and CuO thin film. Moreover, the formation of heterostructure not only increased response toward H2 but also dramatically decreased response toward VOCs and NO2. These improved sensing properties are attributed to the heterojunction between CuO thin film and TiO2 nanotubes.