Photoelectron Spectroscopy Study of the Oxidation of ZrC(100)

Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) are used to study the oxidation of a ZrC(100) surface. When the surface is exposed to O 2 at room temperature, carbon atoms in the surface region are found to be depleted and the substrate zirconium atoms are oxidized. The Zr oxide is proposed to be a ZrO-like state at low coverage (<3 L) and to become a ZrO x (1< x <2) state with further O 2 exposure. When the 100-L-O 2 -exposed surface is heated at elevated temperatures, the work function is substantially decreased. By heating at 1000°C, the work function reaches a minimum value which is lower than that of the clean surface by 0.6 eV. The oxidation state which gives the minimum work function is deduced to be an ordered ZrO-like state whose periodicity is similar to that of ZrC(100) based on XPS and low-energy electron diffraction (LEED) measurements.