Direct structural study of Cl on Si {111} and Ge {111} surfaces: New conclusions

Surface extended x-ray-absorption fine-structure measurements show that the lowest-energy adsorption site for Cl on annealed Si {111}-(7×{}7), annealed Ge {111}-(2×{}8), and quenched Si111-(√19×√19) surfaces is the onefold-atop site. This is in contrast to earlier photoemission studies which suggested different sites for Cl on Si {111} vs Ge {111}. The observed electronic differences between these two systems are shown to be due to matrix element effects. The measured geometries for both are in excellent agreement with recent parameter-free total-energy calculations.