WO3 gas sensors prepared by thermal oxidization of tungsten

Tungsten trioxide (WO3) was grown by direct thermal evaporation of metal tungsten foils in an oxygen atmosphere. The samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-rays (EDX) analysis and Raman spectroscopy. The synthesized products consisted of crystalline aggregates having a mean size of about 0.8 mu m. Raman spectroscopy evidenced typical vibrational peaks of the monoclinic WO3 phase. The samples were investigated as resistive gas sensors towards NO2, NO and NH3 gases. The influence of the working temperature on the sensor response was also studied. The sensors were sensitive enough to detect NO2 and less sensitive to NO and NH3. The relative variation of resistance as a function of gas concentration was found to be reversible and to follow a power-law relationship. The response and recovery times were determined according to a simple adsorption kinetic model. (c) 2008 Elsevier B.V. All rights reserved.