Atom Ejection in Low Energy Sputtering of Single Crystals of fcc Metals and of Ge and Si

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Abstract
The spatial distribution of atoms ejected from low index planes of Cu, Ni, Au, Al, Ge, and Si have been studied for bombardment by Hg+, Ne+, and Ar+ ions of energies up to 800 ev. In addition, the atom ejection for Hg+‐ion bombardment of various Ge planes (12° apart) belonging to the [110] zone has been investigated in detail. For the fcc crystals, ejection was observed in 〈110〉 directions at all energies, in〈100〉 directions at higher energies, and in 〈411〉 directions under certain conditions. The ejection in the 〈110〉 and 〈100〉 directions are interpreted to be the result of focusons intercepting the surface with sufficient energy to cause a surface atom to be ejected. It is shown that a reasonable interpretation of the atom ejection in 〈411〉 directions is that a 〈110〉 focuson may intercept and eject a surface atom which is in a twin position rather than a normal position. For ion bombardment of Ge and Si atom ejection is observed in 〈111〉 and 〈100〉 directions. A possible interpretation is that many of the natural interstitial positions are filled near the surface as a result of the bombardment and that the structure resembles more that of a bcc structure. The systematic deviation in ejection directions from the associated crystallographic direction observed for the Hg+‐ion bombardment of various Ge surfaces suggests that the atomic collisions resulting in atom ejection for Ge and Si occur in the outer few surface layers.