Preparation and characterisation of ultrathin films of In2O3 on NiIn(0001)

In an attempt to grow epitaxial In2O3 following the alloy-oxidation route, we have studied the oxidation of NiIn(0001) using Auger electron spectroscopy, low-energy electron diffraction, X-ray photoemission spectroscopy and sputter depth-profiling. Oxidation at room temperature produces an amorphous oxide, with saturation occurring at exposures of 10 000 L. The film growth can be divided into two regions of differing kinetics, with oxygen uptake initially following a power law and exponential uptake being found at exposures >200 L. No long-range order is seen, with oxygen desorption occurring at temperatures >625 K, significantly below the temperature required to obtain ordered oxide films in other oxide/alloy systems. Annealing of the saturated amorphous film to 550 K, however, produces an ultrathin film (∼10 Å thick) of stoichiometric In2O3, with identical results obtained through a saturated dose at 550 K. This relatively flat, clean surface can be obtained reproducibly in ultrahigh vacuum, and it is suggested that it makes a suitable model for (technologically important) indium–tin oxide (ITO) in interface studies.