Observation of quasimelting at the atomic level in Au nanoclusters

Experimental evidence is presented for the atomic origin of quasimelting of small Au clusters. Real-time high-resolution transmission electron microscopy, an in situ evaporation facility, and the choice of a controlled substrate clearly shows atomic motion adjacent to and on nanoclusters in the <20 size range. We have been able to observe partial melting, atom sharing, absorption of small clusters, and shape adjustment. These phenomena are consistent with low-energy surface sputtering, energy minimization, and diffusive surface migration. Related to the transformation from icosahedral multiply twinned to single crystal observed under low voltage conditions, we propose a geometric model of the transformation which produces a continuum of low-energetic intermediate structures.