There is increasing interest in the chemistries of amorphous alloy thin films for a wide range of applications. An advantage of amorphous alloy thin films, compared to polycrystalline alloy films, is that they can have atomically smooth surfaces with a wide distribution of distinct surface sites. Extreme ranges of composition can also be obtained for amorphous alloy thin films, even for immiscible substances. These properties potentially allow the control of surface chemistry by modifying the density of states and the atomic structure at amorphous alloy surfaces. In this study, we are investigating two alloy thin film catalysts, Ni-Ga and Co-Ge. The Ni-Ga system is of interest for CO2 hydrogenation to methanol, while the Co-Ge system is of interest for methane reforming reactions. For both material systems we are depositing films using RF magnetron sputtering from alloy targets. We have characterized as deposited film thermal stabilities using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD measurements indicate that Ni-Ga is primarily nanocrystalline as deposited, while Co-Ge crystallizes after annealing in vacuum. For Ni-Ga, XPS indicates that Ga is preferentially oxidized, and that Ga2O3 desorbs from the surface for temperatures above 600 °C. For Co-Ge, XPS indicates that Ge is preferentially oxidized, and that GeO desorbs from the surface at ~400 and 800 °C. We will compare the adsorption of H2O and O2 on amorphous (obtained by surface sputtering) and nanocrystalline Ni-Ga and Co-Ge films to compare oxidation rates depending on composition and structure.

Preparation and characterization of amorphous/nanocrystalline thin film catalysts

253rd National Meeting (2017)

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