Interfacial effects in ultra-thin nickel deposits on yttria-stabilized zirconia

Ultra-thin films with 0.2 ML of Ni vapor-deposited in UHV near RT on yttria-stabilized-zirconia YSZ(1 0 0), were studied by X-ray photoelectron spectroscopy (XPS). Upon extensive annealing of the deposits in UHV between 480 and 850 K, it was found that there exists a critical temperature, below which the deposits tend to be fully oxidized via the substrate and above which they are stable in the metallic state. Nickel oxide formed on YSZ by either substrate or RT gas-phase oxidation is stable in UHV at least up to the critical temperature. This critical temperature appears to be sensitive to the history of the clean substrate treatments, as expressed by the O1s/Zr3d XPS intensity ratio, being higher than 850 K for the fully oxidized state of the clean YSZ surface and falling even below 635 K after repeated Ar+ sputtering cycles and extensive heating of the clean substrate in UHV at 870 K leading to an oxygen-deficient surface.