MODELING OF LAYER-BY-LAYER SPUTTERING OF SI(111) SURFACES UNDER IRRADIATION WITH LOW-ENERGY IONS

Molecular dynamics (MD) simulations of ion-solid interactions and nume rical solutions of coupled reaction-diffusion equations for surface va cancies and adatoms are used to investigate layer-by-layer sputtering of Si(111) surfaces by 225 eV xenon ions. The model of Bedrossian and co-workers that low-energy sputtering is dominated by the creation of isolated surface vacancies and nucleation of vacancy islands is not su pported by our model. Our MD calculations show that, besides a few spu ttered surface atoms, additional surface vacancies are caused by the e xcitation of surface atoms in adatom positions. These additional surfa ce vacancies and adatoms have a great influence on the sputtering kine tics. In each collision, surface vacancies are produced not in isolati on but in clusters. The MD results are taken as input for the solution of the reaction-diffusion equations.