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

Abstract

The behaviour upon thermal annealing of ultrathin nickel oxide films formed on yttria-stabilized ZrO2(100) (YSZ) and α-Al2O3(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 NiAl2O4 spinel-like interfacial compound. Copyright © 2002 John Wiley & Sons, Ltd.