Stable icosahedral nanostructure in gold copper alloy clusters

Different formation rates of stable icosahedral nanostructures were observed for the clusters of four different Au- 13, 25, 39 and 57 at.% Cu alloys. The rate was found to be maximum, 80%,for Au-25 at.% Cu alloy clusters and decrease with increasing and decreasing the Cu content from 25 at.%. The icosahedral structures along 5-, 3- and 2-fold axes were identified clearly by high resolution transmission electron microscope. The critical size for the ic formation was found to be 6 nm in diameter for all the alloys. Cu content in the alloys plays an important role to form the stable Ic and controls the formation rate. (C) 1998 Acta Metallurgica Inc.