title: A Two-Dimensional Liquid Structure Explains the Elevated Melting Temperatures of Gallium Nanoclusters.
abstract: Melting in finite-sized materials differs in two ways from the solid-liquid phase transition in bulk systems. First, there is an inherent scaling of the melting temperature below that of the bulk, known as melting point depression. Second, at small sizes changes in melting temperature become nonmonotonic and show a size-dependence that is sensitive to the structure of the particle. Melting temperatures that exceed those of the bulk material have been shown to occur for a very limited range of nanoclusters, including gallium, but have still never been ascribed a convincing physical explanation. Here, we analyze the structure of the liquid phase in gallium clusters based on molecular dynamics simulations that reproduce the greater-than-bulk melting behavior observed in experiments. We observe persistent nonspherical shape distortion indicating a stabilization of the surface, which invalidates the paradigm of melting point depression. This shape distortion suggests that the surface acts as a constraint on the liquid state that lowers its entropy relative to that of the bulk liquid and thus raises the melting temperature.
authors.affiliation: Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University , Auckland Campus, Private Bag 102904, North Shore City, 0745 Auckland New Zealand.|Department of Chemistry, University of Kansas , Lawrence, Kansas 66045, United States.
authors.forename: Krista G
authors.initials: KG
authors.lastname: Steenbergen
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington , P.O. Box 600, 6140 Wellington, New Zealand.
authors.forename: Nicola
authors.initials: N
authors.lastname: Gaston
mesh_terms: D003460:Crystallization; D019277:Entropy; D005615:Freezing; D005708:Gallium / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D053761:Nanocomposites / Q000737:chemistry*; D044367:Phase Transition; D013696:Temperature
chemical_list: D005708:Gallium
keywords: Ga nanoclusters; Two-dimensional materials; finite-size effects; solid−liquid phase transition; surface stability