Atom Ejection in Low Energy Sputtering of Single Crystals of bcc Metals

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Abstract
The spatial distribution of atoms ejected from low index planes of the bcc metals V, Fe, Nb, Mo, Ta, and W have been studied in detail for bombardment by Hg+‐, Xe+‐, Ar+‐, and Ne+‐ions of energies up to 800 eV. The principal atom ejection directions are the 〈111〉 and 〈100〉, which are the directions of focuson propagation in bcc crystals. Other atom ejection directions were observed in which momentum focusing is not possible. These are interpreted to be the result of 〈111〉 focusons (directed outwardly with sufficient energy) intercepting surface atoms which are not in normal atom sites. For bombardment of (100) surfaces the center spot ([100] ejection) appears above a certain minimum energy which increases in the order Ne, Ar, Xe, Hg. This is true for widely different masses of the target atoms, and seems to be related to the spatial distribution of momenta in the crystal. For heavier bombarding ions the momenta tend to be directed more in the forward direction and the center spot becomes less pronounced than for lighter bombarding ions.