Degradation Processes in Surface Layers of Indium Oxide

The degradation of
$\hbox{In}_{2}\hbox{O}_{3}$
(110) surface as a working surface in the
$\hbox{In}_{2}\hbox{O}_{3}$
-based sensor is studied. Theoretical and experimental investigations of electronic and atomic processes on this surface caused by the adsorption of
$\hbox{H}_{2}$
molecules are performed. In the framework of the density functional theory, we determined the energetically preferable position of the adsorbed
$\hbox{H}_{2}$
molecule over
$\hbox{In}_{2}\hbox{O}_{3}$
surface. It was found that the adsorbed
$\hbox{H}_{2}$
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
$\hbox{In}_{2}\hbox{O}_{3}$
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
$\hbox{H}_{2}$
molecules and, on the basis of our recent results in an earlier paper, concerning a high-temperature degradation of the
$\hbox{In}_{2}\hbox{O}_{3}$
(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
$\hbox{H}_{2}$
-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
$\hbox{In}_{2}\hbox{O}_{3}$
surface and a decrease of the resistance.