High-resolution electron energy loss spectra of reconstructed Si(100) surfaces : first-principles study

We present ab initio calculations of electron energy loss spectra in the reflection geometry (REELS) for the Si(100) surface, for which several experimental data are available. The standard surface models [p(2x1), c(4x2), and p(2x2)] are structurally very similar in nature, and precise calculations are necessary to differentiate between them. Starting from optimized geometries we compute REELS spectra within the framework of the three-layer model. We adopt several methodologies to ensure a realistic model of the experiment, including a precise partitioning of the surface and bulk dielectric functions and a numerical integration over the detector aperture. We obtain good agreement with the various available experimental energy loss and reflectance anisotropy spectra. The calculations allow us to definitively rule out the presence of the p(2x1) reconstruction. For the first time, we interpret the S0 peak observed by Farrell et al. [Phys. Rev. B. 30, 721 (1984)] in high resolution REELS. Furthermore, we explain the observed dependence of the spectra on temperature by inferring the presence of dimer flipping at room temperature.