Atomic recoil events on free surfaces orthogonal to 2 different antiphase boundaries and 2 grain boundaries in Ni3Al were simulated using molecular dynamics methods. The threshold energy for sputtering, Esp, and adatom creation, Ead, were determined as a function of recoil direction. The study was relevant to scanning transmission electron microscope (fitted with a field emission gun) experiments on preferential Al sputtering and/or enhancement of the Ni-Al ratio near boundaries. Surfaces intersected by {110} and {111} antiphase boundaries had a minimum Esp of 6.5eV for an Al atom on the Ni-Al mixed (M) surface, which was close to the value of 6.0eV for a perfect M surface. High values of Esp of an Al atom generally occur at a large angle to the surface normal and depended strongly on the detailed atomic configuration of the surface. The mean Esp, averaged over all recoil directions, revealed that antiphase boundaries had a small effect upon the threshold sputtering. However, the results for Ead implied that an electron beam could create more Al adatoms on surfaces intersected by antiphase boundaries than on those without. The equilibrium minimum energy structures for a (001) surface intersected by either Σ5[001](210) or Σ25[001](340) symmetrical tilt grain boundaries were computed. Esp for surface Al atoms near to these grain boundaries increased monotonically with increasing recoil angle to the surface normal, with a minimum value which was only about 1eV different from that obtained for a perfect surface. Temperatures of up to 300K had no effect upon this result. It was concluded that the experimental observations of preferential sputtering were due to effects beyond those for Esp studied here.

Low-Energy Sputtering Events at Free Surfaces near Antiphase and Grain Boundaries in Ni3Al. Gao, F., Bacon, D.J., Lai, W.S., Kurtz, R.J.: Philosophical Magazine, 2006, 86[27], 4243-58