In situ atomic-scale observation of melting point suppression in nanometer-sized gold particles.

Phase stabilities of nanometer-sized materials are quite different from those of the corresponding bulk materials. Among the phase stabilities, melting point suppression is one of the most fundamentally important issues. In this work, real-time, atomic-scale direct observation of melting point suppression in nanometer-sized Au particles, along with simple size reduction, was carried out by means of in situ high resolution electron microscopy. Namely, it was confirmed in real space on an atomic scale that a solid-to-liquid transition occurred when the size of a particle, placed on a graphite substrate maintained at 1100 K, decreased to 5 nm during diminution. Furthermore, a monolayer-thick hole was formed on the substrate at the position of the liquid Au particle, probably due to carbon dissolution into the liquid Au particle.