Nanostructured WO3 deposited by modified thermal evaporation for gas-sensing applications

In this work, we present a simple method, based on a modified thermal evaporation technique, to obtain films of nanostructured WO3 with high surface roughness. This method consists on sublimation from a metallic tungsten wire followed by oxidation in low vacuum conditions and reactive atmosphere (pO2=0.22 mbar), with substrates heated at high temperature (600 -C). Electron microscopy (SEM, TEM) and atomic force microscopy (AFM) analysis revealed that the deposited films are composed of agglomerates with nanometric size and present high surface roughness and large effective area suitable for gas-sensing applications. Sensing measurements highlighted promising performances, particularly at the working temperature of 100 -C: high responses towards sub-ppm concentrations of NO2 have been observed compared to the lower ones observed for NH3 and CO. NO2 tests performed with sensors based on sputtered thin films highlighted that sensors obtained by this thermal evaporation like method exhibit improved performances.