Low-energy oxygen bombardment of silicon by MD simulations making use of a reactive force field

Abstract

In the field of Secondary Ion Mass Spectrometry (SIMS), ion–matter interactions have been largely investigated by numerical simulations. For MD simulations related to inorganic samples, mostly classical force fields assuming stable bonding structure have been used. In materials science, level-three force fields capable of simulating the breaking and formation of chemical bonds have recently been conceived. One such force field has been developed by John Kieffer [1] , [2] . This potential includes directional covalent bonds, Coulomb and dipolar interaction terms, dispersion terms, etc. Important features of this force field for simulating systems that undergo significant structural reorganization are (i) the ability to account for the redistribution of electron density upon ionization, formation, or breaking of bonds, through a charge transfer term, and (ii) the fact that the angular constraints dynamically adjust when a change in the coordination number of an atom occurs. In this paper, the modification of the force field to allow for an exact description of the sputtering process, the influence of this modification on previous results obtained for phase transitions in glasses as well as properties of particles sputtered at 250–1000 eV from a mono-crystalline silicon sample will be presented. The simulation results agree qualitatively with predictions from experiments or models. Most atoms are sputtered from the first monolayer: for an impact energy of 250 eV up to 86% of the atoms are sputtered from the first monolayer and for 750 eV, this percentage drops to 61%, with 89% of the atoms being sputtered from the first two monolayers. For sputtering yields, 250 and 500 eV results agree with experimental data, but for 750 eV sub-channelling in the pristine sample becomes more important than in experiments where samples turn amorphous under ion bombardment.