Electron-stimulated ion desorption from bromine-chemisorbed Si(111) surfaces

Electron-stimulated ion desorption from bromine-chemisorbed Si(111) surfaces was studied, using electrons in the energy range of 0.1-2 keV. Ion desorption behavior is classified into three regimes in terms of the initial bromine coverage. Only small yields of Br⁺ ions are observed at low coverages, of the order of 0.01 monolayer (ML). In addition to an increased yield of Br⁺ ions, SiBr⁺ and SiBr⁺₂ also appear at medium coverages of the order of 0.1 ML. The yield of all ion species is dramatically decreased at high coverages, of over 1 ML. The yield of the three kinds of desorption ions reaches its maximum at electron energies of around 0.2-0.3 keV, which suggests the effectiveness of exciting the Br M or Si L shells in the desorption process. The distribution of the kinetic energies of the Br⁺ ions about 3 eV is interpreted as indicating a screened Auger-stimulated desorption model. In contrast, the desorption of the SiBr⁺₂ cannot easily be explained by the model. The structural strain introduced by interatomic repulsion between neighboring bromine atoms may affect the localization of the holes in the back bonds and thus facilitate the desorption of the ions.