The oxidation and surface speciation of indium and indium oxides exposed to atmospheric oxidants

Metallic indium and its oxides are useful in electronics applications, in transparent conducting electrodes, as well as in electrocatalytic applications. In order to understand more fully the speciation of the indium and oxygen composition of the indium surface exposed to atmospheric oxidants, XPS, HREELS, and TPD were used to study the indium surface exposed to water, oxygen, and carbon dioxide. Clean In and authentic samples of In₂O₃ and In(OH)₃ were examined with XPS to provide standard spectra. Indium was exposed to O₂ and H₂O, and the ratio of O^{2 -} to OH^- in the O1s XPS region was used to monitor oxidation and speciation of the surface. HREELS and TPD indicate that water dissociates on the indium surface even at low temperature, and that In₂O₃ forms at higher temperatures. Initially, OH^- is the major species at the surface. Pure In₂O₃ is also OH^- terminated following water exposure. Ambient pressure XPS studies of water exposure to these surfaces suggest that high water pressures tend to passivate the surface, inhibiting extensive oxide formation.