Faceting of copper surfaces at 1000°C

Abstract

Polished copper surfaces were observed to facet on annealing at 1000°C in wet hydrogen atmospheres. It was found that the quantity hi p H 2O p H 2 must be greater than zero for extensive faceting to occur, though some faceting, particularly at the sample edges, can occur for In p H 2O p H 2 as small as −3.5. The criteria for faceting to occur by the reduction of surface free energy are discussed and it is shown that facets near the (111) orientation are thermodynamically stable. The effect of anisotropy of surface free energy on facet nucleation is discussed. The outlines of lens-shaped facets were measured. The shapes and sizes of the lens-shaped facets are consistent with a volume diffusion mechanism of facet formation. The observed profiles of the curved surfaces near separated linear facets are compared to theoretically calculated profiles. The calculations by Mullins of facet profiles are extended slightly to facilitate the comparison. The observed profiles are in reasonable agreement with the calculated profiles for facet formation by surface diffusion with the surface diffusion coefficient the same on both the low index and the complex surfaces.