In_2O_3 thin films on sapphire substrates, have been prepared from commercially pure In_2O_3 powders by high vacuum thermal evaporation (HVTE) and from indium isopropoxide solutions by Sol-gel techniques (SG). The as deposited HVTE and SG films have been annealed at 500 °C for 12h and 1 h respectively. XPS characterisation has revealed chemical compositions close to that of In_2O_3 for the HVTE annealed. SEM characterisation has highlighted the formation of a well developed nano-particles structure for the HVTE film as respect to SG. All the films have shown high sensitivity to NO_2 gas (0.7-7 ppm) at 250 °C temperature. The SG films have resulted to be more sensitive to NO2, but to be affected by the same cross sensitivity drawbacks as the HVTE films, if exposed to H_2O, C_2H_5OH and SO_2.
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