CHARACTERIZATION STUDY OF OXIDIZED POLYCRYSTALLINE TIN OXIDE SURFACES BEFORE AND AFTER REDUCTION IN H-2

An oxidized polycrystalline tin oxide film has been examined using electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy (AES), ion-scattering spectroscopy (ISS), and electron energy loss spectroscopy (ELS) before and after reduction in 40 Torr of H-2 for 1 h at 200-degrees-C. The data indicate that the oxidized tin oxide surface is fairly inert to this strongly reductive treatment. The ISS spectra show that the oxygen concentration in the outermost atomic layer does not change significantly during the reduction but that the reduced surface is more electrically conductive. This is due to the loss of oxygen in the subsurface region which is detected by ESCA. The ELS data were taken using primary beam energies of 200, 400, and 600 eV in order to vary depth sensitivity. Over the depths examined, the ELS data indicate that the predominant component of the reduced, oxidized, and reoxidized surfaces is a transitional oxide phase which has a composition between that of SnO and SnO2. Both the ESCA and ELS data indicate that a small portion of this transitional oxide phase is reduced to SnO during the reduction. The reduced surface was then reoxidized in 40 Torr of O2 for 1 h at 200-degrees-C. The ISS spectrum obtained from this surface indicates a large increase in the amount of oxygen contained in the outermost atomic layer, and the ESCA and ELS data indicate that most of the SnO produced during the reduction is reoxidized to SnO2.