STEP STRUCTURES ON BR-CHEMISORBED VICINAL SI(111)

To investigate the effects of chemisorption on step energetics, Si sur faces miscut by 1.2 degrees to 12 degrees from the (111), as well as S i(335) and Si(112), have been exposed to bromine. and studied using sc anning tunneling microscopy. As the atomic structure on (111) terraces changes from the (7 x 7) or (5 x 5) reconstruction to a (1 x 1) after Br exposure and annealing at 800-900 K, the density of triple-layer s teps on samples miscut towards [2 (1) over bar (1) over bar] decreases dramatically. The structures of the steps themselves have been measur ed with high resolution. The edges of a triple step on the Br-covered surfaces resembles a (112) facet, while it is (113)-like on a clean su rface. Br-chemisorption extends the miscut angle range over which the sample can be described as a vicinal Si(111) surface From less than or equal to 14 degrees for clean Si to similar to 19 degrees. Analysis o f kink densities shows that step diffusivity on Br-covered surfaces is governed by the intrinsic step misorientation as on the clean surface s. however the kink size is registered to the 1 x 1 lattice on the Br- cocered surface. The measured terrace width distributions are the same on the clean and Br-covered surfaces. indicating the same ratio of st ep diffusivity to direct step-interaction energy. The coexistence of s ingle and triple steps on both the clean and Br-chemisorbed surfaces c an be described semi-quantitatively with a model based on elasticity t heory. The analysis shows that the reduced triple-step density is due to both the seven-fold decrease in step-step repulsion energy and the seven-fold increase in triple-step formation energy after Br-chemisorp tion. On the equilibrium step-bunched structures that form on surfaces miscut towards [(2) over bar 11], removal of the 7 x 7 reconstruction during halogen exposure and annealing below 900 K does not break the step-bunching. (C) 1998 Elsevier Science B.V.