Electronic structure of the Zr suboxide layer formed on a ZrC(1 0 0) surface

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the electronic structure of the ZrC(1 0 0) surface covered by a ZrO-like layer. When the ZrC(1 0 0) surface exposed to 50 L O2 is heated at 950 °C, a ZrO-like layer is formed on the surface and the surface is activated towards gas adsorption. Angle-resolved photoemission measurements show that the O 2p-derived bands show clear dispersion along both the 〈1 0 0〉 (ΓM) and 〈0 1 1〉 (ΓX) symmetry directions of ZrC(1 0 0). Since the surface gives a sharp (1×1) LEED pattern, it is concluded that a well ordered ZrO layer having a (1×1) periodicity is formed on the ZrC(1 0 0) surface. The O 2p-derived bands show no dispersion along the axis normal to the surface, thus the bands can be viewed as two-dimensional electronic states. In addition to the O 2p-derived bands, partially filled states are found around the Fermi level in the ZrO-like layer. The states are removed by water or oxygen adsorption. The origin of the states is discussed and the states are ascribed to partially filled Zr 4d states.