OBSERVATION OF QUASI-MELTING AT THE ATOMIC-LEVEL IN AU NANOCLUSTERS

Experimental evidence is presented for the atomic origin of quasimelti ng of small Au clusters. Real-time high-resolution transmission electr on microscopy, an in situ evaporation facility, and the choice of a co ntrolled substrate clearly shows atomic motion adjacent to and on nano clusters in the < 20 angstrom size range. We have been able to observe partial melting, atom sharing, absorption of small clusters, and shap e adjustment. These phenomena are consistent with low-energy surface s puttering, energy minimization, and diffusive surface migration. Relat ed to the transformation from icosahedral multiply twinned to single c rystal observed under low voltage conditions, we propose a geometric m odel of the transformation which produces a continuum of low-energetic intermediate structures.