Surface photoemission from Si(100) and inelastic electron mean-free-path in silicon

Core-level photoemission spectra of the buckled Si(100)2x1 surface taken at various energies and emission angles are used to determine the inelastic mean-free-path (IMFP) in silicon. The resultant values fall somewhat below an extrapolation to smaller energy of the empirical formulation of Tanuma, Penn and Powell. The IMFP was estimated from a fit with a model function in which an effective attenuation length (EAL) was used to constrain the intensities of the contributions to the 2p signal of the first three surface layers and the bulk. This ansatz successfully represents data from the clean Si(100) surface at all emission angles and photon energies. For surfaces covered with an overlayer that provides strong elastic scattering, like Cs, an angular averaging would be required. At normal emission, where the scattering is less important, data from surface with saturation K coverage shows that the buckling has been removed and that the charge transfer to the substrate is small, implying a largely covalent interaction. (C) 2000 Elsevier Science B.V. All rights reserved.