Degradation processes in surface layers of indium oxide

The degradation of In ₂O ₃ (110) surface as a working surface in the In ₂O ₃ -based sensor is studied. Theoretical and experimental investigations of electronic and atomic processes on this surface caused by the adsorption of H ₂ molecules are performed. In the framework of the density functional theory, we determined the energetically preferable position of the adsorbed H ₂ molecule over In ₂O ₃ surface. It was found that the adsorbed H ₂ molecule is mainly bonded with In atom. The redistribution of the electron density around In atom leads to a weakening of chemical bonds in the vicinity of In atom, and this circumstance is a reason of its destabilization. The temperature dependence of the resistance of In ₂O ₃ films in a wide interval of temperatures was measured. This dependence is characterized by a specific maximum. The obtained experimental results are interpreted using theoretical results concerning a destabilization of surface In atoms induced by the adsorbed H ₂ molecules and, on the basis of our recent results in an earlier paper, concerning a high-temperature degradation of the In ₂O ₃ (110) surface layers as a working surface in sensor devices. We suggested a two-stage model of the degradation process: In the first stage, the disordering of surface caused by H ₂ -adsorption- stimulated displacement of In atoms leads to the increase of surface resistance, and in the second stage, displaced In atoms form precipitates and this process causes a metallization of In ₂O ₃ surface and a decrease of the resistance.