Chirality and thickness-dependent thermal conductivity of few-layer graphene: A molecular dynamics study

Abstract

The thermal conductivity of graphene nanoribbons (layer from 1 to 8 atomic planes) is investigated by using the nonequilibrium molecular dynamics method. We present that the room-temperature thermal conductivity decays monotonically with the number of the layers in few-layer graphene. The superiority of zigzag graphene in thermal conductivity is only available in high temperature region and disappears in multi-layer case. It is explained that the phonon spectral shrink in high frequency induces the change of thermal conductivity. It is also reported that single-layer graphene has better ballistic transport property than the multi-layer graphene.In the past decade, more and more attentions have been given to the question of what happens with thermal conductivity when goes to low-dimensional materials [1]. A two-dimensional materials-graphene [2], in addition to its exceptional electric [3] and optical properties [4] , [5], reveals unique high thermal conductivity. Thermal conductivity of single-layer graphene as well as of carbon nanotubes is dependent on the chirality [6]. Recent theoretical studies suggest that the thermal conductivity of single-layer zigzag graphene is 20-50% larger than that of the singlelayer armchair graphene [7]. However, whether the superior thermal conductivity of zigzag graphene remains available for multi-layer graphene has not got enough attention and concern.Additionally, experimental demonstrations have shown that the thermal conductivity gets a decrease at the twoto three-dimensional (2D to 3D) crossover of few-layer graphene [8]. The fact that the thermal conductivity of large enough graphene sheets should be higher than that of basal planes of bulk graphite was predicted theoretically by Klemens [9]. Generally, thermal transport in conventional thin films still retains 'bulk' features because the crosssections of these structures are measured in many atomic layers. Heat conduction in such nanostructures is dominated by extrinsic effects, for example, phonon-boundary or phonon-defect scattering [10]. A recent experimental observation of high-quality few-layer graphene materials shows that the room-temperature thermal conductivity changes from˜2,800 to˜1,300 Wm −1 K −1 when the number of atomic planes in few-layer graphene increases from 2 to 4. It is explained that the observed evolution from two dimensions to bulk attributed to the cross-plane coupling of the low-energy phonons and changes in the phonon Umklapp scattering [8].Recently, the method of molecular dynamics simulation has been successful in discovering thermal conductivity and thermal rectification of the nanostructures [7] , [11]. This method, which builds the system from the bottom up, is useful to understand the intrinsic behavior, i.e., the phonon spectral behavior behind the significant change of a material's ability to conduct heat [12]. In this paper, we will study the thermal conductivity of graphene ribbons (layer from 1 to 8 atomic planes) by using the nonequilibrium molecular dynamics method. By inve...

Substrate coupling suppresses size dependence of thermal conductivity in supported graphene

“…The maximum thickness considered in our study is 12 layers, which has a total number of 91,496 atoms including the substrate atoms. With the increase of graphene layers, it exhibits a very rapid enhancement in thermal conductivity of supported FLG at the beginning, followed by a much slower increase after six layers, showing an obvious two-stage increase characteristic which has also been observed in a recent experimental study on the thickness dependent thermal conductivity of encased graphene [29].On the other hand, it has been reported that thermal conductivity of suspended FLG decreases with the thickness due to the inter-layer interactions [30,31]. It is known that both inter-layer interaction and graphene-substrate interaction can lead to the reduction of thermal conductivity in graphene due to damping of the ZA phonons.…”

“…On the other hand, it has been reported that thermal conductivity of suspended FLG decreases with the thickness due to the inter-layer interactions [30,31]. It is known that both inter-layer interaction and graphene-substrate interaction can lead to the reduction of thermal conductivity in graphene due to damping of the ZA phonons.…”

Thermal transport in nanostructures

“…7(d)) of single-layer and multi-layer GNRs are also investigated by using MD simulations. 111 Zhai and Jin investigated the strain effect on ballistic thermal transport in GNR by combination of NEGF and the elastic theory. 106 At temperature below 50 K, the thermal conductance increases observably for GNR with stretching strain of 10% and 19%, due to a lot of dispersive phonon modes are converged to the low frequency region.…”

“…There are rich physical phenomena about thermal property of GNRs. The effects of size, [95][96][97][98] defects, 99, 100 doping, 101,102 shape, 103,104 stress/strain,, [105][106][107][108] substrates, 109 inter-layer interactions, [110][111][112] nanoscale junctions, 113 chirality, 114 topological structure, 115 edge effect, [116][117][118][119] foldings (gradfolds), 23,120 etc. on thermal conductivity of nanoribbons [121][122][123][124][125][126][127][128] have been widely studied.…”

Thermal rectification in thickness-asymmetric graphene nanoribbons

“…The Nosé-Hoover thermostats are applied to the left and right end of GNRs [6,7,20]. We integrate the equations of motion for atoms by the Verlet method [21].…”