Transformation of surface structures on vicinal Si(111) during heating

We investigated transformation processes of holes and hillocks on vicinal Si(111) surfaces during annealing at around 1200°C using ultra-high-vacuum scanning electron microscopy. A hole and a hillock decay symmetrically with one another: their shapes are complementary, and the decay rate is almost the same except during the final stage, where hillocks decay faster than holes. Flat surfaces appear both at the bottom of the hole and at the top of the hillock due to layer-by-layer decay. As a result of transformation, regularly arranged atomic-step bunches are formed in both cases. The electric current used for sample heating greatly affects the final shape of step bunches. The current direction that induces step bunching on a flat surface creates straighter step bunches than the opposite direction. For holes larger than the adatom diffusion length, step-flow sublimation becomes the dominant process instead of layer-by-layer filling-in of the bottom terrace, which is the dominant process for holes smaller than the adatom diffusion length.