Stages of melting of graphene model in two-dimensional space

VV Hoang and LTC Tuyen and TQ Dong, PHILOSOPHICAL MAGAZINE, 96, 1993-2008 (2016).

DOI: 10.1080/14786435.2016.1185183

Spontaneous melting of a perfect crystalline graphene model in 2D space is studied via molecular dynamics simulation. Model containing 10(4) atoms interacted via long-range bond-order potential (LCBOP) is heated up from 50 to 8,450K in order to see evolution of various thermodynamic quantities, structural characteristics and occurrence of various structural defects. We find that spontaneous melting of our graphene model in 2D space exhibits a first-order behaviour of the transition from solid 2D graphene sheet into a ring-like structure 2D liquid. Occurrence and clustering of Stone-Wales defects are the first step of melting process followed by breaking of C-C bonds, occurrence/growth of various types of vacancies and multi-membered rings. Unlike that found for melting of a 2D crystal with an isotropic bonding, these defects do not occur homogeneously throughout the system, they have a tendency to aggregate into a region and liquid phase initiates/grows from this region via tearing-like or crack-propagation-like mechanism. Spontaneous melting point of our graphene model occurs at T-m=7,750K. The validity of classical nucleation theory and Berezinsky-Kosterlitz-Thouless- Nelson-Halperin-Young (BKTNHY) one for the spontaneous melting of our graphene model in strictly 2D space is discussed.

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