Atom Vacancy Lines and Surface Patterning: The Role of Stress for Br-Si(100)-(2×1) at 700 K

Using variable-temperature scanning tunneling microscopy, we studied Br-induced roughening of Si(100)-(2×1) at 700 K. The roughening pathway requires Br-free dimers so that a saturated surface is inactive. Initial roughening involves the formation of atom vacancy lines and regrowth chains of Si dimers on the terraces. The atom vacancy lines grow longer through a stress-induced process that creates dimer vacancies. Br adatom repulsion then splits these dimer vacancies into pairs of single-atom vacancies. A (3×2) reconstruction derived from dimer rows and atom vacancy lines is energetically favored at high concentration due to Br-Br repulsive interactions and Br bond angle relaxation that is facilitated by the (3×2) structure. Though favored, the conversion is slow at high coverage. Continuous scanning over ∼72 h shows the correlation between Br concentration and surface morphology. Ultimately, a highly dynamic configuration is reached in which large regrowth islands and large terrace areas have (3×2) symmetry. These areas become unstable when the Br concentration drops below a critical value and conversion to (2×1) terraces and extended islands occurs.