A theoretical description and experimental demonstration of diffraction in electron-stimulated desorption.

The role of diffraction in electron-stimulated desorption (DESD) is demonstrated experimentally and described theoretically. Specifically, initial state effects in DESD of Cl (+) from Si(111)-(1 × 1):Cl and Si(111)-(7 × 7):Cl are examined and a theoretical treatment that includes spherical-wave effects and multiple scattering of low-energy incident electrons is presented. Although contributions from complicated defect configurations such as SiCl2 and SiCl3 cannot be ruled out, comparison of the experimental data with theory indicates that Cl (+) desorption from Si(111)-(1 × 1):Cl and Si(111)-(7 × 7):Cl surfaces may be dominated by monochloride terminal sites. The initial states probably contain significant Si 3s and/or Si-Cl σ-bonding character. In the Si(111)-(7 × 7):Cl case, these excitations favor a propensity for Cl (+) desorption from the unfaulted, rather than faulted, zones of the 7 × 7 reconstructed rest atom area. This propensity may be related to increased screening and hole localization in the Si-Si backbonds within the faulted region. Finally, introducing Debye-Waller factors into each scattering path accounts for much of the experimentally observed DESD width broadening at room temperature.