Paper SS1-ThM2
Cu_xNi_1-xO and Zn_xNi_1-xO Rocksalt Oxide Surfaces: Novel Environment for Cu²⁺, Zn²⁺ and Its Effect on the NiO Electronic Structure

Thursday, October 18, 2007, 8:20 am, Room 608

The effect on surface composition, electronic structure and bonding has been investigated for rocksalt Cu_xNi_1-xO and Zn_xNi_1-xO solid solutions, which form at the nickel-rich end of the phase diagram up to approximately x = 0.3. Octahedral coordination presents an unusual environment in solid state oxides for the "guest" Cu²⁺ and Zn²⁺ cations, and their bonding properties can be shown to be significantly different in the rocksalt environment. For example, ab initio calculations of the Zn_xNi_1-xO valence band structure indicate that zinc interacts with the lattice oxygen primarily through the Zn 4s orbitals and is less covalent than in wurtzite ZnO. Photoemission results also provide insight into the bonding, and the Ni 2p photoemission changes substantially with increased guest ion concentration due to attenuation in non-local screening effects. The charge-transfer nature of the NiO electronic structure, however, remains largely intact. Auger parameter analysis confirms that the guest ions are octahedrally coordinated, and Auger and x-ray photoelectron spectroscopies show comparable surface and bulk concentrations until phase separation occurs.