Interaction of ultrathin nickel oxide films with single‐crystal zirconia and alumina surfaces

The behaviour upon thermal annealing of ultrathin nickel oxide films formed on yttria‐stabilized ZrO 2 (100) (YSZ) and α‐Al 2 O 3 (0001) (sapphire) by in situ oxidizing vapour‐deposited Ni films of 0.2–5 ML thickness, was investigated by XPS/x‐ray‐induced Auger electron spectroscopy (XAES). The sapphire substrate was also used following room‐temperature argon ion sputtering to create a defective surface. Heating the nickel oxide films in ultrahigh vacuum (UHV) leads to decomposition in a temperature range strongly dependent on the substrate. On YSZ, the oxide decomposes towards metallic Ni at ∼200 K lower temperature compared with sapphire, where the decomposition temperature is close to the estimated thermodynamic stability limit for nickel oxide in the UHV chamber (∼900 K). This result supports the previously conjectured substrate‐mediated nickel oxide decomposition on YSZ. Furthermore, upon oxide decomposition on sapphire, a chemical interaction with the substrate is evidenced, especially by XAES. This interaction, which appears to exist already at 580 K on the sputtered sapphire substrate, is attributed to the formation of an NiAl 2 O 4 spinel‐like interfacial compound. Copyright © 2002 John Wiley & Sons, Ltd.