Lowering of surface melting temperature in atomic clusters with a nearly closed shell structure

TL;DR

This study explores how nearly closed shell atomic clusters with extra atoms exhibit reduced surface melting temperatures due to structural stress, potentially explaining experimental observations of suppressed surface melting.

Contribution

It introduces a mechanism linking structural stress in nearly closed shell clusters to lowered surface melting temperatures, supported by Monte Carlo simulations.

Findings

Strained clusters have lower energy barriers for surface diffusion.

Surface melting temperature T_S can fall below bulk values.

The mechanism explains experimental suppression of surface melting.

Abstract

We investigate the interplay of particle number, N, and structural properties of selected clusters with N=12 up to N=562 by employing Gupta potentials parameterized for Aluminum and extensive Monte-Carlo simulations. Our analysis focuses on closed shell structures with extra atoms. The latter can put the cluster under a significant stress and we argue that typically such a strained system exhibits a reduced energy barrier for (surface) diffusion of cluster atoms. Consequently, also its surface melting temperature, T_S, is reduced, so that T_S separates from and actually falls well below the bulk value. The proposed mechanism may be responsible for the suppression of the surface melting temperature observed in a recent experiments.