Molecular dynamics simulations of 30 and 2 keV Ga in Si

Focused Ga+ ion beams are routinely used at high incident angles for specimen preparation. Molecular dynamics simulations of 2 and 30 keV Ga bombardment of Si(011) at a grazing angle of 88° were conducted to assess sputtering characteristics and damage depth. The bombardment of atomically flat surfaces and surfaces with vacancies shows little energy transfer yielding ion reflection. The bombardment of surfaces with adatoms allows for the coupling of the energy of motion parallel to the surface into the substrate resulting in sputtering. The adatom and one other Si atom eject, and motion in the substrate occurs down to a depth of 13 Å. Experimental evidence shows that sputtering is a reality, suggesting that an atomically flat surface is never achieved.