Palladium clusters on graphite: evidence of resonant hybrid states in the valence and conduction bands

M. Cini, M. De Crescenzi, F. Patella, N. Motta, M. Sastry, F. Rochet, R. Pasquali, A. Balzarotti, C. Verdozzi

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The electronic structure of Pd clusters deposited on polycrystalline graphite has been investigated by x-ray photoemission, Auger spectroscopy, and bremsstrahlung isochromat spectroscopy. Initial- and final-state shifts of energy levels as a function of the average cluster size R are small, but important modifications of the density of filled and empty states at the Fermi level are observed. With decreasing particle size, the d portion of the conduction band broadens and shifts to higher energy while its valence counterpart shows the opposite shift. A simple analytical model is developed which accounts in some detail for the measured shifts and linewidths and also explains earlier x-ray-absorption data. The size dependences are explained in terms of mixing of Pd 4d and graphite * continua with a squared coupling constant V2 proportional to R-1. As a consequence a gap opens up across the Fermi level in the cluster density of states and unoccupied hybrid resonances arise as observed experimentally. Initial-state energy shifts and cluster charging are estimated and found to play a minor role for the present system.

Original languageEnglish
Pages (from-to)5685-5695
Number of pages11
JournalPhysical Review B
Issue number9
Publication statusPublished - 1990
Externally publishedYes

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