Anisotropic emission in single crystal sputtering measurements on HCP single crystals

The ejection characteristics of single crystals of zinc, magnesium (hcp) and aluminum (fcc) were determined by bombarding various crystal surfaces with a beam of inert gas ions. The energy of the bombarding ions varied between 10 and 40 keV. The sputtered particles were collected on cooled, hemicylindrical metal collectors; with the help of an electron probe the thickness of the deposit was measured. Pronounced anisotropic emission was observed in all cases, although random emission comprises the major part of the total ejection. By comparing the 〈2023〉 ejection, which is produced by pure surface collisions, and the 〈1120〉 ejection, where focusing collisions are involved, we deduce that surface collisions are mainly responsible for the anisotropic emission. The width of both emission distributions increases linearly to the same extent in the temperature regime between 100 and 370 K. The agreement of the Mg 〈1120〉 ejection with the 〈110〉 ejection from an aluminum (111) single crystal is good and thus allows a comparison with the gold 〈110〉 ejection reported in the literature.

The assisted focusing ejection in 〈0001〉, which is very pronounced in zinc single crystals and strongly influences the 〈2023〉 ejection from the basal plane, does not show up in magnesium. No 〈111〉 ejection occurred in aluminum either. In both cases the weak repulsive potential of the low-Z atoms accounts for the lack of this preferential emission.