Adsorbate-to-Si(100) bonding coordination numbers and structural determinations from synchrotron photoemission studies

The initial stages of interface formation between In, Sb, Sn, and Ag adsorbates and the Si(100)-(2 × 1) surface have been examined with high resolution core-level photoemission spectroscopy. In each case, the Si 2p surface-shifted core-level component is seen to be converted into a component which is indistinguishable from the bulk component through adsorption. The average number of Si surface dimer atoms modified in the presence of an adatom, which is referred to as the adsorbate-to-Si bonding coordination number (BCN), is obtained for various coverages. The relative homogeneity of the adsorbate site bonding is evaluated by examining the line shapes of the adsorbate core-level spectra. The In-to-Si BCN is 3 for very low coverages and decreases to 2 for 1/2-monolayer coverage. The results are consistent with an In/Si(100)-(2 × 2) structural model which involves sp² hybrid bonding of In dimers. The Sn 4d core levels reveal the existence of two different Sn bonding sites which form sp³ and s²p² hybrid bonding configurations; a structural model for the Sn/Si(100)-c(4 × 4) is presented. The Ag-to-Si BCN measurement indicates that adsorbed Ag forms linear sp hybrid bonds between two neighboring Si dimers along the direction of dimerization at low coverages. Sb chemisorption is found to yield a BCN behavior similar to that of In.