Melting of graphene clusters

TL;DR

This study uses computational simulations to analyze how small graphene clusters melt, revealing size-dependent melting points and the effects of hydrogen passivation on stability.

Contribution

It introduces a detailed computational analysis of melting behavior in graphene nano-clusters, including the influence of size, structure, and passivation.

Findings

Larger rings have higher melting points.

Hydrogen passivation increases melting temperature.

Edges exhibit multiple metastable states before melting.

Abstract

Density-functional tight-binding and classical molecular dynamics simulations are used to investigate the structural deformations and melting of planar carbon nano-clusters $C_{N}$ with N=2-55. The minimum energy configurations for different clusters are used as starting configuration for the study of the temperature effects on the bond breaking/rotation in carbon lines (N$<$6), carbon rings (5$<$N$<$19) and graphene nano-flakes. The larger the rings (graphene nano-flake) the higher the transition temperature (melting point) with ring-to-line (perfect-to-defective) transition structures. The melting point was obtained by using the bond energy, the Lindemann criteria, and the specific heat. We found that hydrogen-passivated graphene nano-flakes (C$_{N}$H$_M$) have a larger melting temperature with a much smaller dependence on its size. The edges in the graphene nano-flakes exhibit several different meta-stable configurations (isomers) during heating before melting occurs.