J.M. Nicholls

Electronic structure of Si(111) surfaces with group III ad-atoms

Abstract Angle-resolved photoelectron spectroscopy has been used to study the electronic structure of Si(111)√3×√3 surfaces with Al and In ad-atoms. The metal atom coverage for these stable surfaces is 1 3 monolayer. Both surfaces exhibit two occupied bands of surface states. For the Si(111)√3×√3:Al surface a single surface state peak is observed in the spectra with a dispersion, E( k | ) , that must be interpreted as due to two bands in the √3×√3 surface Brillouin zone. For the surface with In ad-atoms there are spectra in which emission from two bands can be seen simultaneously. The surface states are derived from dangling bond electrons on silicon surface atoms that are modified by the presence of the group III atoms. There is good agreement between experiment and theoretical calculations concerning the surface state band dispersions and the k | dependence of the visibility. Two low-energy configurations for the group III ad-atoms give similar theoretical surface band structures, both consistent with the experimental results.

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.

Direct and inverse surface photoemission: Sources of ambiguities near the fermi level

We show that the measured peak positions of direct- and inverse-photoemission features near the Fermi level are off from their true values by the order of the energy resolution. Sources of ambiguities are the energy and k resolution, asymmetric line shapes, and high backgrounds. Surface-state bands and/or surface emission which cross the Fermi level are particularly affected. As examples we discuss surface states on Ag(111) and Ge(111)−(2×1) as well as band-gap surface emission on Ni(110).