STM MEASUREMENTS OF STEP-FLOW KINETICS DURING ATOM REMOVAL BY LOW-ENERGY-ION BOMBARDMENT OF SI(001)

We create mobile surface vacancies on vicinal Si(001) by bombarding th e surface with 300 eV Xe ions at a substrate temperature of 465 degree s C. The vacancies preferentially annihilate at the rough steps retrac ting them with respect to their smooth neighbors. This process leads t o a bimodal terrace width distribution. The retraction of the rough st eps due to the vacancy annihilation is in competition with the healing process by which the surface tries to maintain its equilibrium config uration of equally spaced steps. As the two competing processes balanc e, the surface reaches steady state and subsequent removal of surface atoms is manifest as simple step now.