NO2 response of In2O3 thin film gas sensors prepared by sol-gel and vacuum thermal evaporation techniques

In2O3 thin films have been prepared by high vacuum thermal evaporation (HVTE) and by sol-gel (SG) techniques. The deposited HVTE and SG films have been annealed at 500 degrees C for 24 and 1 h, respectively. After annealing at 500 degrees C, the films are highly crystalline cubic In2O3. XPS characterization has revealed the formation of stoichiometric In2O3 (HVTE) and nearly stoichiometric In2O3-x (SG). SEM characterization has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO2 gas (0.7-7 ppm concentration range), at 250 degrees C working temperature. Negligible H2O cross has resulted in the 40-80% relative humidity range. Only 1000 ppm C2H5OH has resulted in a significant cross to the NO2 response. (C) 2000 Elsevier Science S.A. All rights reserved.