Atom vacancy lines and surface patterning: The role of stress for Br-Si(100)-(2×1)at 700 K

Abstract

Using variable-temperature scanning tunneling microscopy, we studied Br-induced roughening of Si͑100͒-͑2 ϫ1͒ 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 ͑3ϫ2͒ 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 ͑3ϫ2͒ structure. Though favored, the conversion is slow at high coverage. Continuous scanning over ϳ72 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 ͑3ϫ2͒ symmetry. These areas become unstable when the Br concentration drops below a critical value and conversion to ͑2ϫ1͒ terraces and extended islands occurs.

Step free energies, surface stress, and adsorbate interactions for Cl-Si(100) at 700 K

“…The adsorbate concentration was determined directly from the STM images since Si dimers with Cl can be distinguished from bare dimers. 11,19 The samples were then heated to 700 K for extended imaging.…”

“…Hence, the processes and consequences of the production of pits and regrowth islands on Si(100)-(2ϫ1) have attracted extensive attention. [6][7][8][9][10][11][12][13] To date, however, there have been no studies of the step free energies on Si͑100͒ with halogen adatoms, though such investigations would provide insights into the effects of a large class of adsorbates.…”

Si epitaxial growth on Br-Si(100): How steric repulsive interactions influence overlayer development

“…Direct counting reveals that about 1 / 3 of the sites on the addimer chains are bare, while the Br atoms are almost conserved on the terrace. (The determination of halogen coverages has been discussed by Xu et al 6 ) For example, the four Si atoms in the lower right circle are all terminated with Br, while the six in the dashed ellipse are Br free. The structure near the center is made up of four dimers, and the contrast indicates that all of the Si adatoms are terminated with Br, except the two marked with arrows.…”

“…The adlayers that grew from the ejected Si also have ͑3 ϫ 2͒ patches. Xu et al 6 followed this roughening in real time with variable temperature STM at 700 K, and they showed that ͑3 ϫ 2͒ first formed at high Br coverage but then reverted to ͑2 ϫ 1͒ as the concentration diminished; ͑3 ϫ 2͒ structures also form as a Si overlayer assembles in the presence of Br. In both cases, there is a reduction in total energy for ͑3 ϫ 2͒ rather than ͑2 ϫ 1͒ domains.…”

“…The latter was a surprise because the Si surface was thought to be stable against such roughening. [1][2][3][4][5][6][7] In this paper, we use atomic resolution scanning tunneling microscopy (STM) results to compare Si surfaces that are roughened by Br to those that evolve when Si adatoms are deposited onto a Br-saturated Si͑100͒-͑2 ϫ 1͒ surface. Our focus is on the adsorption and diffusion of Si adatoms and the nucleation and growth of the adlayer in the presence of Br.…”