Melting of Simple Monatomic Amorphous Nanoparticles

Abstract

Melting of the simple monatomic amorphous spherical nanoparticles has been studied via molecular dynamics (MD) simulation. Initial amorphous nanoparticles have been heated toward a normal liquid state to study a melting process with Lennard-Jones–Gauss interatomic potential [Engel, M.; Trebin, H.-R. Phys. Rev. Lett. 2007, 98, 225505]. Temperature dependence of various thermodynamic quantities of the system is found and discussed. Atomic mechanism of melting is monitored via analysis of the appearance/growth of the liquid-like atoms upon heating. Liquid-like atoms are determined by using the Lindemann melting criterion. In the premelting stage (i.e., below a glass transition temperature, Tg), liquid-like atoms occur first in the surface shell to form a quasi-liquid surface layer. Further heating leads to the formation of a purely liquid skin at the surface of nanoparticles together with a simultaneous occurrence/growth of liquid-like atoms in the remaining glassy matrix. Melting process proceeds further via propagation/growth of liquid-like configuration into the solid core. Liquid-like configuration includes a purely liquid skin, and liquid-like atoms occurred in the liquid–solid interfacial shell of nanoparticles. Total melting occurs at temperature much higher than Tg. Heat capacity of the system exhibits a single peak at around a total melting point. We find a strong thermal hysteresis between amorphous nanoparticles obtained by heating/cooling.