ON THE INTERACTION OF HALOGEN ATOMS WITH (111) AND (100) SURFACES OF SILICON

The chemisorption of F, Cl, Br, and I atoms on the (111) and (100) surfaces of silicon has been studied by the MNDO method and using clusters of Si atoms to simulate the substrate. In the case of the adducts F-Si//4H//9 and Cl-Si//4H//9 the MNDO results are in close agreement with previous ab-initio ones concerning both the equilibrium distance and the chemisorption energies. For all the cases considered, the binding energy decreases in the order F greater than Cl greater than Br greater than I. The most stable adduct is always obtained upon chemisorption at the bridge position on the (100) surface. Chemisorption at on-top positions leads to slightly less stable adducts and is nearly isoenergetic on (100) and (111) surfaces. All the results are essentially insensitive to the dimensions of the clusters used to simulate the substrate.