Sol-gel-derived WO3 thin films with structure-dependent NO2 sensing properties.

The structure of metal oxide thin films can greatly affect their gas sensing properties. However, the structure-property relationship has not been fully established for the NO 2 sensing properties of WO 3 thin films. In this study, WO 3 thin films with two distinct structures have been prepared by the sol-gel technique via employing two different precursor sols. Dense and porous WO 3 thin films were successfully prepared as tungsten and WCl 6 was used as the precursor source, respectively. Both WO 3 thin films are exclusively sensitive to NO 2 as low as 80 ppb. Porous WO 3 thin films exhibit higher response toward NO 2 but slower response/recovery kinetics as compared to the dense ones. Hall measurement and electrochromic coloration confirm the higher carrier mobility in the porous WO 3 thin films. The response/recovery kinetics is found to be determined by the gas-solid reaction (receptor function), which is combinedly influenced by the porosity and grain size of the WO 3 thin films. [ABSTRACT FROM AUTHOR]