Spectroscopic analysis of tungsten oxide thin films for sensor applications.

摘要

The objective of this study is targeted toward improving the quality of pure tungsten oxide (WO3) for application to the detection of poisoning gases, especially of H2S. While pure WO 3 is a recognized candidate for gas sensing, its characteristics are strongly dependent on the conditions and methods used in its deposition.Samples of WO3 thin films analyzed in this work were grown on silicon and sapphire substrates using RF magnetron sputtering at a number of different substrate temperatures and Ar:O2 pressure ratios. The properties of the samples were investigated spectroscopically with the goal of determining how variations in the above preparation parameters effect structural changes in the sensor materials. Such structural changes are of crucial importance to the question of improving the sensitivity, specificity, and durability of WO3 based gas sensors. Experimental characterization was performed using the techniques of infrared (IR) absorption, confocal Raman, and X-ray photoelectron spectroscopy (XPS). The results from both IR and Raman demonstrate that the WO3 sample grown at room temperature has an amorphous nature, and that an initial crystallization into a monoclinic WO 3 structure occurs for samples grown at temperatures between 100 and 300 °C. For 400 and 500 °C, the existence of a strained WO3 structure together with the monoclinic one is observed in the Raman spectra. XPS indicates that the film surface maintains the stoichiometry WOx, with a value of x slightly greater than 3 at room temperature due to oxygen contamination x decreases with increasing temperature.