By using variable-temperature scanning tunneling microscopy, a study was made of the Br-induced roughening of Si(100)-(2×1) at 700K. The roughening pathway required Br-free dimmers, so that a saturated surface was inactive. The initial roughening involved the formation of atom vacancy lines and re-growth chains of Si dimers on the terraces. The atom vacancy lines grew longer via a stress-induced process that created dimer vacancies. The Br adatom repulsion then split these dimer vacancies into pairs of single-atom vacancies. A (3×2) reconstruction derived from dimer rows and atom vacancy lines was energetically favored at high concentrations, due to Br-Br repulsive interactions and a Br bond-angle relaxation that was facilitated by the (3×2) structure. Although favored, the conversion was slow at high coverages. Continuous scanning over ~72h revealed a correlation between Br concentration and surface morphology. A highly dynamic configuration was finally reached in which large re-growth islands and large terrace areas had (3×2) symmetry. These areas became unstable when the Br concentration fell below a critical value, and conversion to (2×1) terraces and extended islands occurred.

Atom Vacancy Lines and Surface Patterning - the Role of Stress for Br-Si(100)-(2×1) at 700K. G.J.Xu, E.Graugnard, B.R.Trenhaile, K.S.Nakayama, J.H.Weaver: Physical Review B, 2003, 68[7], 075301 (13pp)