Paper SS2-FrM3
Synthesis and Characterization of Surface Oxide Films on CoGa(100)

Friday, November 4, 2011, 9:00 am, Room 109

Methanol is currently garnering a lot of attention as both a chemical feedstock for synthesis of organic substances and as a possible source of energy. It is currently produced industrially from a mix of syngas and hydrogen over a copper-zinc oxide catalyst. However, it has been shown that palladium-gallium oxide is a more active catalyst for methanol production, and uses a carbon dioxide-hydrogen feed, which is desirable for efforts toward CO₂ mitigation^{1, 2}. Surface Science characterization of this catalyst poses a problem as a gallium oxide substrate is not conductive enough for use with X-ray photoelectron spectroscopy (XPS) or low energy electron diffraction (LEED). The most straightforward way to circumvent this limitation is to grow Ga₂O₃ on a conductive substrate. It has been shown that a Ga₂O₃ film forms on the surface of CoGa alloy crystals when exposed to oxygen^{3, 4}. In this work we report the results of the characterization of Ga₂O₃ films on the CoGa(100) surface using XPS, LEED, and ion scattering spectroscopy (ISS). The films were synthesized using either O₂ or NO₂ as the oxidant at 300 K or in excess of 700K. ISS scans showed that cobalt was always present in the top surface layer regardless of oxidation conditions. XPS illustrated that depending on the oxidant and the temperature, the composition of the oxide films vary with some being nearly all Ga₂O₃ and ordered and others Co-Ga mixed oxides that gave no diffraction pattern.

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