Equilibrium Crystal Shape of Nickel

Abstract

The crystal shape of Ni particles, dewetted in the solid state on sapphire substrates, was examined as a function of the partial pressure of oxygen (P(O2)) and iron content using scanning and transmission electron microscopy. The chemical composition of the surface was characterized by atom-probe tomography. Unlike other FCC equilibrium crystal shapes, the Ni crystals containing little or no impurities exhibited a facetted shape, indicating large surface anisotropy. In addition to the {111}, {100} and {110} facets, which are usually present in the equilibrium crystal shape of FCC metals, high index facets were identified such as {135} and {138} at low P(O2), and {012} and {013} at higher P(O2). The presence of iron altered the crystal shape into a truncated sphere with only facets parallel to denser planes. The issue of particle equilibration is discussed specifically for the case of solid-state dewetting.