Role of oxide ionicity in electronic screening at oxide/metal interfaces -art. no. 075410

Metal and oxygen core-level Auger and photoemission spectra have been measu red for ultrathin epitaxial films of alpha -Cr2O3 and alpha -Fe2O3 on Pt(11 1). The binding-energy shifts of monolayer films relative to thicker films suggest a much smaller extent of screening by the metal substrate than that reported earlier for MgO/ Ag(001) [S. Altieri, L. H. Tjeng, F. C. Voogt, T . Hibma, and G. A. Sawatsky, Phys. Rev. B 59, R2517 (1999)]. This finding s uggests that the higher degree of bond covalency in alpha -Cr2O3 and alpha -Fe2O3 relative to MgO results in more effective intrinsic screening of cha rge-transfer processes, rendering the metal much less effective for extrins ic screening. As a result, the metal is expected to have a negligible effec t on the optical, electronic, and magnetic properties of the oxide.