The Effect of Crystal Structure on Sputtering: Molecular Dynamics Calculations

Abstract

AbstractMolecular dynamics calculations have been used to study the ion-etching process by a focused-ion beam. Ion-induced atomic displacement in a Ag surface initiates collision cascades which lead to particle sputtering from the surface. Tracing collision cascades reveals that the sputtering is mainly caused by a surface atom being sideswiped by its neighboring atom traveling in a surface channel oriented a certain angle away from the direction of ejection. Depending on the angle of detection and on the kinetic energy of sputtering, the ejecting particles may proceed along crystallographic directions parallel to either the close-packed or the non-close-packed rows of atoms in the surface. The preferred direction of ejection is sensitive to variations in the polar angle of detection and in the ejection energy. For those residual atoms initially located within four lattice spacings from the target atom, the most probable distance of displacement is less than one eighth of the equilibrium bond length in the crystal bombarded by Ar† ions of I keV energy. The structural perturbation increases as the ion energy is increased from 0.2 keV to I keV, but decreases as the energy is increased further.