Analysis of Low-Energy Sputtering

Abstract

It is postulated that for low-energy sputtering the interatomic energy and distance relation can be represented by a Morse curve, and that the energy transfer in the lattice proceeds essentially by two-particle (i.e., binary) collisions.Based on these assumptions, a two-collision sputtering mechanism near the threshold is described. Under optimum energy transfer conditions, the analysis of this process gives the ion energy for a sputtering threshold of a surface particle tied by $N$ bonds.It is shown further that under a prolonged ion bombardment a surface contains particles with a number of bonds $N$, ranging from a maximum determined by a complete surface to a minimum determined by inaccessible bonds to underlying surface layers.Based on this information, the form of the sputtering yield-energy function is derived, consisting of a parabolic and a linear part. Predicted and experimental Pt-${\mathrm{Hg}}^{+}$ curves are compared, and the agreement is excellent.Two thresholds are defined: the lower threshold is the actual intercept of the yield curve, whereas the upper threshold corresponds to the intercept of the linear part of the yield curve. The two thresholds are computed for 20 metals bombarded by the ${\mathrm{Hg}}^{+}$ ion. The agreement with experimental values and the empirical threshold formula of Wehner is satisfactory.