INTERACTION OF OXYGEN AND CO WITH NI-3 TI ALLOY SURFACES

Clean surfaces of polycrystalline Ni3Ti have been prepared and their interaction with oxygen expanding into the oxidation regime has been studied with ultraviolet photoelectron spectroscopy (UPS) and Auger electron spectroscopy (AES) methods at 7> 150 K. The elemental surface concentrations of properly prepared alloy surfaces are found close to the bulk values. Low-temperature oxygen adsorption leads to oxygen bonding to Ni and Ti and in the oxidation regime Ni and Ti oxides are formed simultaneously. Metallic sites which are capable to serve for molecular CO adsorption, presumably Ni sites, are still available at the surface of this mixed oxide. Upon heating to high temperatures, T> 700K Ni oxide gets reduced to metallic Ni. The resulting surface is covered by TiO which acts as a passivating coating. Interaction of oxygen with clean Ni3Ti surfaces at higher temperatures, T>300 K initially leads to enhanced Ti-oxygen interaction leaving the Ni constituent unaffected. After annealing to high temperatures a thin TiO layer covers the surface. Adsorption of CO at clean Ni3Ti surfaces is molecular at 150 K and predominantly molecular at 300 K. © 1990, American Vacuum Society. All rights reserved.