Melting and Freezing of Metal Clusters

Abstract

Recent developments allow heat capacities to be measured for size-selected clusters isolated in the gas phase. For clusters with tens to hundreds of atoms, the heat capacities determined as a function of temperature usually have a single peak attributed to a melting transition. The melting temperatures and latent heats show large size-dependent fluctuations. In some cases, the melting temperatures change by hundreds of degrees with the addition of a single atom. Theory has played a critical role in understanding the origin of the size-dependent fluctuations, and in understanding the properties of the liquid-like and solid-like states. In some cases, the heat capacities have extra features (an additional peak or a dip) that reveal a more complex behavior than simple melting. In this article we provide a description of the methods used to measure the heat capacities and provide an overview of the experimental and theoretical results obtained for sodium and aluminum clusters.

Continuous melting and thermal-history-dependent freezing in the confined Na-K eutectic alloy

“…However, even when the emergence of a liquid skin on the particle surface led to some broadening of the melting transition, the well defined solid and liquid states coexisted within a temperature range and the melting transition in the solid cores remained sharp. Ultra-small supported and unsupported metallic clusters were studied predominantly by various calorimetric methods (see [1,7,8,[17][18][19][20] and references therein). Smooth caloric curves were observed upon melting in some experiments, for instance for sodium clusters comprising of 139 atoms [8], which agree with computer models, while sharp changes were found for larger sodium clusters.…”

Size-dependent freezing temperature of metallic and semi-metallic nanoparticles

“…2 the excellent agreement between predicted values in terms of Eqs. (9) and (11b) and experimental results for T m (r) and T f (r) of Bi semi-metallic nanoparticles. The predicted critical radius r = 1.86 nm = 2r 0 is consistent with Kellermann's result with r = 1.9 nm [2].…”

“…The hysteresis decreases with the size decrease and it will disappear at the critical size [2,[4][5][6][7][8]. Aguado et al [9] indicated that what size the liquid and solid phases of a nanoparticle start to coexist in contact is an interesting and important questions that remain to be addressed. In order to clarify the hysteresis of nanomaterials, the size effect on T m (r) and T f (r) should be carefully analyzed.…”

Growth modes of thin films of ligand-free metal clusters

“…26,27 Especially, the low coordinated surface atoms are more or less liquid at room temperature and two clusters touching each other merge into a larger particle similar to two drops of water. This holds for clusters of materials with relatively low melting points such as Ag, Au, Bi, and Sb.…”