Inverse-photoemission study of ordered Cu, Ag, and Au overlayers on Si(111)

Si(111)-(7 × 7) surfaces with deposits of noble metals form ordered overlayers after annealing. Coverages in the monolayer range of Ag and Au result in ( 3 × 3)-R30° overlayer structures and for Cu a pseudo "(5 × 5)" structure is produced, while at higher coverage of Au a (6 × 6) overlayer structure is formed. We have studied all four overlayer structures with k-resolved inverse-photoemission spectroscopy and observed strong surface-state emission at ∼ 2.0 eV above the Fermi level for all these surfaces. This emission can hardly be quenched by exposure to oxygen or hydrogen. Hence we attribute it to the local bonding between the metal atoms and the Si(111) surface. In addition we observe an increased spectral intensity near the Fermi level for the two larger unit-cell surfaces, corresponding to the long-range order and a possible onset of metallization. © 1986.