Vacancy dynamics and reorganization on bromine-etched Si(100)-(2 x 1) surfaces

Subsurface diffusion in crystals and effect of surface permeability on the atomic step motion

A new theoretical approach to characterize the diffusion of both surface and bulk point defects in crystals is presented. In our model, atomic steps are considered as sources and sinks not only for adatoms and advacancies but also for self-interstitials and bulk vacancies, providing a new mechanism for bulk point defect generation and annihilation. It is shown that the creation and annihilation of self-interstitials and vacancies occur at atomic steps and can be described by introducing a diffusive layer of the bulk point defects adsorbed just below the surface. The atomic step rate of advance is studied taking into account finite permeability of the surface for bulk and surface point defects. The surface permeability results in the appearance of the dependence of the total step rate of advance not only on the supersaturation in vapor phase but also on the supersaturation of point defects in the bulk.

Tunneling electron induced bromine hopping on Si(100)-(2 x 1)

Tunneling electrons from the tip of a scanning tunneling microscope can be used to induce adatom hopping on Br-terminated Si(100)-(2x1) at low current and without voltage pulses. Hopping does not occur when electrons tunnel from a sample to a tip. The threshold energy is +0.8 V, and tunneling spectroscopy shows antibonding Si-Br states 0.8 eV above the Fermi level. Electron capture in these states is a necessary condition for hopping, but repulsive adsorbate interactions that lower the activation barrier are also required. Such interactions are strong near saturation for Br but are insufficient when the coverage is low or when Br is replaced by Cl.

Spontaneous roughening: fundamental limits in Si(100) halogen etch processing

A dynamical scanning tunneling microscopy and density functional theory study of the thermodynamic stability of halogen-terminated Si(100) surfaces is presented. Significant steric repulsion is shown to exist on all halogen-terminated Si(100) surfaces. This repulsion is the driving force for a roughening phenomenon, which is favored for all halogens except fluorine. Since roughening is an intrinsic property of these surfaces, it sets a lower bound on the atomic scale perfection that can be achieved using halogen etch processing.