Enhancement of NO2 sensing properties of In2O3-based thin films using an Au or Ti surface modification

Abstract Metal oxide gas sensors using In 2 O 3 are able to detect low concentrations of NO 2 . The gas sensitive properties of In 2 O 3 can be improved by adding catalysts or promoters. In the present work, the surface modification of reactively RF-sputtered In 2 O 3 films (cubic phase) using Ti or Au is presented. The surface modified In 2 O 3 films are investigated with respect to physical and gas sensitive properties. Fine distributed Au particles can be formed on top of the In 2 O 3 surface. This enhances the NO 2 sensitivity significantly by a factor of 9 at 350°C and by a factor of 3.6 at 400°C. A low cross-sensitivity toward several gases, such as SO 2 , NH 3 , CO and H 2 , is found. The response time τ 50 at 400°C is decreased from 4.0 to 2.2 min. On the other hand, particles of amorphous TiO 2 can be produced on top of the In 2 O 3 surface. The Ti additive improves the signal shape of the response toward traces of NO 2 . The response time τ 50 at 400°C is decreased from 4.0 to 1.8 min. For the Au surface modification a possible sensing mechanism is discussed.

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