The electronic properties of the Cs/GaAs(100) interface and the formation of metastable Cs clusters

The method of threshold photoemission spectroscopy is used to investigate t he electronic properties of the ultrafine gallium-enriched Cs/GaAs(100) int erface. The rearrangement of the spectrum of surface photoemission as a fun ction of Cs coating, as well as the temperature dependence of the spectrum, enable one to identify two phases of adsorption with strong (Cs-Ga) and we ak (Cs-Cs) bonds. In the first phase of adsorption with the coating of appr oximately 0.3 monolayers, two surface bands are detected which are due to t he local interaction of cesium adatoms with gallium dimers. It is found tha t the transition from the first to the second phase of adsorption occurs wi th the Cs coating of approximately 0.7 monolayers, which corresponds to the saturation of all dangling bonds of gallium on the gallium-enriched GaAs(1 00) surface. In the second phase of adsorption with the coating of more tha n 0.7 monolayers, a number of additional photoemission singularities are ob served in the spectra, whose emergence is associated with the formation of metastable Cs formations. Photoemission peaks at 1.9 and 2.17 eV may be ass ociated with the excitation of quasi-two- and/or quasi-three-dimensional Cs clusters, and the peaks at 2.05, 2.4, and 2.78 eV may be associated with t he excitation of an interface plasmon and of surface and bulk Cs plasmons, respectively. (C) 2001 MAIK "Nauka/Interperiodica".