On the origin of pyramids and cones on ion-bombarded copper surfaces

Abstract

It is shown that ion-bombardment-induced pyramids or cones on pure Cu surfaces originate mainly, at least in the absence of major surface impurities, from pre-existing asperities. Such features can in principle be formed due to mechanical treatment, to chemical treatment, to inclusions, to surface impurities, or to other causes, the precise details being unimportant. Once asperities are present, regions which have a convex-up curvature should, as argued by Carter, Colligon, and Nobes, evolve into facets having an angle near θ̂ between the beam and the target normal, θ̂ being the angle at which the sputtering coefficient, S(θ), maximizes. By considering the velocity of motion of the facets it follows that, after a critical bombardment dose given approximately by Nh1/[S(θ̂)−S(0)], the asperities will be pyramidal. (N = number density, h1 = height of asperity.) It is also shown that the following play little or no direct role with Cu in causing pyramids or cones: grain boundaries, chemical etch pits, a Ti impurity on a smooth surface, minor surface impurities due to oxide or hydrocarbon films, annealing an otherwise stable surface. Major hydrocarbon contamination appeared to play a role but it was unclear whether it was a direct or indirect one, that is, whether or not pre-existing roughness was involved. © 1980, All rights reserved.