Step structures on Br-chemisorbed vicinal Si(111)

Abstract

To investigate the effects of chemisorption on step energetics, Si surfaces miscut by 1.2° to 12° from the (111), as well as Si(335) and Si(112), have been exposed to bromine, and studied using scanning tunneling microscopy. As the atomic structure on (111) terraces changes from the (7 × 7) or (5 × 5) reconstruction to a (1 × 1) after Br exposure and annealing at 800-900 K, the density of triple-layer steps on samples miscut towards [211] decreases dramatically. The structures of the steps themselves have been measured 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 surface. Br-chemisorption extends the miscut angle range over which the sample can be described as a vicinal Si(111) surface from ≤14° for clean Si to ∼19°. Analysis of kink densities shows that step diffusivity on Br-covered surfaces is governed by the intrinsic step misorientation as on the clean surfaces, however the kink size is registered to the 1 × 1 lattice on the Br-covered surface. The measured terrace width distributions are the same on the clean and Br-covered surfaces, indicating the same ratio of step diffusivity to direct step-interaction energy. The coexistence of single and triple steps on both the clean and Br-chemisorbed surfaces can be described semi-quantitatively with a model based on elasticity theory. 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-chemisorption. On the equilibrium step-bunched structures that form on surfaces miscut towards [211], removal of the 7 × 7 reconstruction during halogen exposure and annealing below 900 K does not break the step-bunching.