Photoelectron spectroscopy study of the oxidation of ZrC(100)

Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectr oscopy (XPS) are used to study the oxidation of a ZrC(100) surface. When th e surface is exposed to O-2 at room temperature, carbon atoms in the surfac e region are found to be depleted and the substrate zirconium atoms are oxi dized. The Zr oxide is proposed to be a ZrO-like state at low coverage (<3 L) and to become a ZrOx (1 < x < 2) state with further O-2 exposure. When t he 100-L-O-2-exposed surface is heated at elevated temperatures, the work f unction is substantially decreased. By heating at 1000 degrees C, the work function reaches a minimum value which is lower than that of the clean surf ace 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 th at of ZrC(100) based on XPS and low-energy electron diffraction (LEED) meas urements.