Complex diffusion mechanisms of a silicon adatom on hydrogenated Si(100) surfaces: on terraces and near steps

We present first-principles total-energy calculations which reveal microscopic mechanisms of silicon adatom diffusion on the flat terraces and near the single-layer steps of hydrogenated Si(100) surfaces. The diffusion of the silicon adatom is not a simple motion on a single potential-energy surface but a complex atomic reaction in which hydrogen-atom release and capture as well as adatom exchange are involved. The calculated diffusion barrier is sensitive to hydrogen coverage. Near the step edges, the hydrogen-atom capture and release are also crucial processes as on the terrace, and an additional activation barrier near the step edges (the Schwoebel effect) is absent. The S_B step is found to be a deep sink for the adatom.