Chemisorption of fluorine and chlorine on a Si(111) surface

The total energy profiles along the onefold on-top site axis and the threefold hollow site axis of chemisorption of fluorine and chlorine on a Si(111) surface have been determined by using the CNDO method. Clusters of 19 and 23 silicon atoms, respectively, are used to simulate onefold-site and threefold-site chemisorbed systems. The distance between the on-top site and the nearest silicon atoms is found to be 2.18 AA, which compares favourably with the experimental value of 2.03 AA. The authors also find that the fluorine atom can penetrate into the silicon substrate while the chlorine atom cannot. The on-top site is the most stable site for both chemisorbed systems.