Protrusion formation and surface porosity development on thermally annealed helium implanted copper

Abstract

Surface effects on (1 1 1) copper single crystal surfaces after 30 keV helium implantation up to 2.4 × 1016 ions cm−2 and subsequent annealing at 973 K have been studied using scanning electron and confocal microscopy. Since one aim of the work was to develop a method of studying the adhesion of surface coatings, the implantations were performed both directly and through periodical microsieves with pore sizes of 1.5 and 4.5 μm. Different behaviour was observed depending on the sample area studied. Of particular interest was the appearance of surface protrusions in directly implanted areas for all implantation doses, with faceted spheroids above 1.8 × 1016 ion cm−2. These spheroids increase in number with dose and have sizes of 1–2 μm with distinguishable {1 1 1} and {1 0 0} facets, in agreement with the Wulff diagram. The implantation through the periodical microsieve with 4.5 μm pore size resulted in clear periodical patches reflecting the escape of helium from these areas. However, decreasing the pore size to 1.5 μm broke the periodical pattern. The results have been interpreted in terms of bubble migration, coalescence and swelling.