Paper SS1-ThM1
Step Etching and Restructuring on Cl₂-exposed, Cl-saturated Si(001)-(2x1)

Thursday, October 23, 2008, 8:00 am, Room 207

We use scanning tunneling microscopy and density functional theory to investigate the etching of rebonded step atoms and the concomitant restructuring of the B-type step for Cl₂-exposed, Cl-saturated Si(001)-(2x1) at 675 K ≤ T_S ≤ 725 K. Previous studies have shown that these exposure conditions allow uptake beyond "saturation," providing inserted Cl moieties, Cl_i, that lead to novel etching patterns without regrowth structures. Using surfaces with narrow terraces, we show that Cl_i diffuses to the rebonded S_B step and our calculations identify a stable adsorption configuration that bridges the rebonded and non-rebonded step atoms. Step etching removes the rebonded step atoms and results in the formation of an atom-wide vacancy line (AVL) along the step. Step restructuring begins with AVL diffusion into the terrace and ends with step retreat by one dimer unit to reestablish the rebonded S_B step structure. We use theory and experiment to show that restructuring is driven by the reduction of step energies and adsorbate-adsorbate repulsion. These results identify the rebonded step structure as the most energetically favored step structure on Cl-terminated Si(001)-(2x1).