ELECTRONIC-STRUCTURE OF A CU75PT25 DISORDERED ALLOY

We present angle-resolved photoemission spectra from the (100) surface of a Cu75Pt25 substitutionally disordered alloy single crystal for He I, Ne I, He II, and Ne II radiation and compare the results with the corresponding spectra from Cu(100). The results are interpreted in terms of fully relativistic Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) calculations of the electronic densities of states, Bloch spectral densities, and complex energy bands in the alloy. Our theoretical results provide a reasonable overall understanding of the experimental results. In particular, we find that in Cu-rich CuPt alloys, a nearly dispersionless Pt-induced band centered at 1.4 eV binding energy appears above the Cu d-band edge, with an additional weak Pt-induced emission around 5 eV binding energy near the bottom of the Cu d-band complex. The Cu d bands remain quite distinct in the alloy, but move to a lower binding energy of 0.6 eV compared to Cu. We compare and contrast the electronic spectra of Cu-rich CuPt and CuPd alloys, and find that Pt induces a substantially larger density of states at the Fermi energy in Cu compared to Pd, suggesting that an electronic factor may possibly be involved in explaining the better catalytic properties of CuPt over CuPd alloys.