| Graphene is composed of single-layed carbon atoms, with high thermal conductivity and carrier mobility, and with stable chemical properties. As the graphene’s allotrope, the corresponding graphyne also has a single atomic layer topology. But the grapheme has two-dimensional structure with sp2hybrid orbitals, while graphyne is based on the hybrid acetylene sp and sp2carbon bonds. Both graphnene and graphyne has some similar excellent properties, such as good thermal and chemical stability and high carrier mobility, and can be used as storage of lithium and hydrogen storage materials. Due to these excellent physical and chemical properties, graphyne has wide applications in energy storage and nano-optoelectronic device. So far, studies of the graphyne are mainly focused on optical, mechanical and electrical aspects, research on its thermal aspects of nature is still relatively less. In this paper, thermal transport properties of graphyne are investigated, using nonequilibrium molecular dynamics simulation.Firstly, graphyne systems (graphyne, graphdiyne and squarographenes) are constructed. Based on the rebo empirical potential, we use Muller-Plathe method to study the relationship between thermal conductivity and system size, and to explore the influence of boundary conditions on the thermal conductivity. Our results demonstrate that the thermal conductivity increases with the growth of the simulation length. The relationship between thermal conductivity and the simulation size behaves power-law. The relation of the thermal conductivities is κsquarographene>κgraphyne>κgraphdiyne. There is a long phonon mean free path in the graphyne and graphdiyne nanobelts. Their thermal conductivity is not converged with the length. It is found that thermal conductivity also increases with the growth width. It is consistent with the classical theory of phonon scattering boundary. But the increasing trend is gradually weakened. We also find that thermal conductivity with periodic boundary condition is greater than that with free boundaries.Secondly, the same method is used to study the thermal transport properties of graphene and supergraphene using nonequilibrium molecular dynamics simulations. Supergraphene has the similar hexagonal honeycomb structure like that of graphene with a extra-added acetylene bond on the phenyl ring topology. It both has sp and sp2bonds and is a gapless semiconductor. Our investigations show that the thermal conductivity of supergraphene nanoribbons is obviously lower than that of graphene nanoribbons. The calculated value of graphene is690W·(m·K)-1while that of the supergraphene is22.8W·(m·K)-1. It is also found that the thermal conductivity of supergraphene nanoribbons increase with the increasing of length. With the growth of nanoribbon width, it is found that the length dependence of thermal conductivity obviously cross from one-dimensional κ∝Lβ to two-dimensional κ∝ln L. Compared with the free boundary condition, the value of periodic boundary is significantly larger.Finally, using the MP non-equilibrium molecular dynamics, we have calculated thermal conductivity among different stacking graphyne layers. We find that thermal conductivity is gradually increased with the size in the case of double-stacked layer and is close to the values in the β1,β2stacked graphyne-layers. In contrast, thermal conductivity in the β3stacked samples is the lowest.In conclusion, we have found a significant impact on the topology of the thermal conductivity. Thermal conductivity in the graphyne structures is closely related to the acetylene links. For the fixed width, the system with more acetylene chains has smaller thermal conductivity. This conclusion is also valid for the super-graphene structures. We also have calculated the phonon density of states and the dispersion relation. It is found that both the number of phonon modes and the group velocity of phonons play an import role in the thermal conductivity. |
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