The equilibrium crystal shape of nickel

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(O 2)) and iron content using scanning and transmission electron microscopy. The chemical composition of the surface was characterized by atom-probe tomography. Unlike other face-centered cubic (fcc) equilibrium crystal shapes, the Ni crystals containing little or no impurities exhibited a faceted shape, indicating large surface anisotropy. In addition to the {1 1 1}, {1 0 0} and {1 1 0} facets, which are usually present in the equilibrium crystal shape of fcc metals, high-index facets were identified such as {1 3 5} and {1 3 8} at low P(O 2), and {0 1 2} and {0 1 3} at higher P(O 2). 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.