A microscopic study of preferred orientation and adhesion of solid copper particles on (0001) sapphire substrates

The microscopic phenomena of solid copper particles equilibrating on (0001) sapphire surfaces have been investigated by scanning electron microscopy. Very sharp and clear silhouettes of the particles are developed. At temperatures between 900 and 1080° C, with the oxygen partial pressure lower than 10^–17 atm, the copper particles tend toward their equilibrium shape as the {111} and {110} preferred faces develop eventually into truncated octahedra or tetrakaidecahedra. Recrystallization of the particles originating at the particle-substrate interface by a heteroepitaxial mechanism is discussed. The {111} plane of the copper particles does not grow parallel to the (0001) sapphire surface as previously reported, but rather with about 20° of tilt, suggesting epitaxial growth of the Cu {112} plane on the (0001) sapphire surface. The surface energy of solid copper decreases with the increase of temperature and/or oxygen partial pressure while the work of adhesion between solid copper and (0001) sapphire can be enhanced by increasing the temperature and/or decreasing the oxygen partial pressure.