Competition between Random and Preferential Ejection in High-Yield Mercury-Ion Sputtering

Abstract

A radioactive tracer technique was employed to determine the yield (atoms/ion) and angular distribution (atoms/ion·sr) of atoms sputtered from Cu (100) and Mo (100) surfaces by a 1 to 10 keV Hg⁺‐ion beam. Values of the yield for Ni (100) surfaces were also determined. Analytical models for normal and oblique ion incidence cases were fitted to the angular distribution data. The functions describing the preferential emission in the closest‐packed direction and the [100] direction were Gaussians, whereas the background distribution was represented by a cosine, which was tilted away from the surface normal for oblique incidence. Integration of the total distribution gave the relative contributions to the sputtering yield of the directed emissions and background. In all cases, the cosine contribution, which is interpreted in terms of emission from a random lattice, accounted for more than ⅔ of the atoms sputtered. However, intense Wehner spots were present even when the cosine distribution accounted for ⅘ of the ejections. These spots, which are commonly attributed to preferential ejections, are more accurately interpreted as a combination of random emission and collimated preferential emission.