Energetics and Interactions of Mixed Halogen Adsorbates on the Si(100) Surface

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The energetics of various ordered structures of the Si(100) surface with a 1:1 mixture of two adsorbates (hydrogen–halogen) or (two halogens) are investigated using ab initio density functional theory (DFT) calculations. Through an analysis of the calculated energies of various ordered adsorbate structures, the nearest-neighbor and next-nearest-neighbor interactions between halogen adsorbates are unveiled and observed to fit well with a proposed electron-cloud overlap model. Systematic trends are revealed: The mixing energy of two adsorbates favors desegregated structures. A (2 × 2) structure has the lowest energy on the rectangular Si(100) dimerized surface for all mixed adsorbate systems resulting from the stoichiometric adsorption of diatomic interhalogen molecules and hydrogen halides. These results are in good agreement with the scanning-tunneling microcopy (STM) observations on Si(100) after the adsorption of chlorine-contained molecules HCl and ICl but not for HBr and IBr.