Substrate coupling suppresses size dependence of thermal conductivity in supported graphene

Abstract

Thermal conductivity κ of both suspended and supported graphene has been studied by using molecular dynamics simulations. Obvious length dependence is observed in κ of suspended single-layer graphene (SLG), while κ of supported SLG is insensitive to the length. The simulation result of room temperature κ of supported SLG is in good agreement with experimental value. In contrast to the decrease in κ induced by inter-layer interaction in suspended few-layer graphene (FLG), κ of supported FLG is found to increase rapidly with the layer thickness, reaching about 90% of that of bulk graphite at six layers, and eventually saturates at the thickness of 13.4 nm. More interestingly, unlike the remarkable substrate dependent κ in SLG, the effect of substrate on thermal transport is much weaker in FLG. The underlying physics is investigated and presented. Size dependence of thermal conductivity has been reported in various low dimensional nanomaterials [1][2][3][4][5][6][7] as well as in many low dimensional lattice models [8,9]. The most striking and controversial finding is that thermal conductivity in one dimensional systems (like nanotube and nanowire) diverges with length as power law, whereas it diverges logarithmically in two dimensional systems.As a novel two dimensional material, graphene has been the focus of intense studies in recent years [10][11][12]. It is found that thermal conductivity of suspended graphene [5, 6] and graphene nanoribbons (GNRs) [7] is also size dependent.However, in many device applications, graphene sheets are usually supported by and integrated with substrates. It is therefore of primary interest to understand the size dependence of thermal conductivity in supported graphene.In this paper, we systematically investigate the impacts of sample size, the thickness of graphene layers, and the substrate coupling strength on thermal conductivity of supported graphene on amorphous silicon dioxide (SiO 2 ) substrate.We employ molecular dynamics (MD) simulations in combination with phonon spectral analysis to elucidate the underlying physical mechanisms responsible for the heat conduction in supported graphene. Our study provides useful insights to better understand the thermal transport in supported graphene, which will be helpful in the design of graphene based devices.In our study, all MD simulations are performed by using LAMMPS package [13].Tersoff potential with optimized parameters for graphene [14] is adopted to model the intra-layer C-C interactions within the same graphene sheet. Tersoff parameter set for , where r ij is the interatomic distance, ε ij and σ ij are the bond-order force field parameters, and χ is a dimensionless scaling factor (χ=1 by default). The LJ potential parameters for C-C bond are taken from Ref. [16], and the LJ parameters for C-Si and C-O bonds are taken from Ref. [17]. The cut-off distance in LJ potential is set as 2.5σ ij for all kinds of bonds. Moreover, the neighbor list is dynamically updated every ten time steps, and each time step is set as 0.5 ...

Generalized Two-Temperature Model for Coupled Phonons in Nanosized Graphene

“…In our simulations, the width of simulation cell is set as 5. is consistent with previous studies 35,36 .…”

Significant reduction of graphene thermal conductivity by phononic crystal structure

“…Page 7 Along the heat transfer direction (longitudinal), the thermal conductivity depends on the length of material in nanoscale. Previous works 14,21,46 on graphene found that the thermal conductivity increases as the length of graphene increases and the thermal conductivity does not converge even at several micrometers. We study the κ GPnC dependence on the length of GPnCs at room temperature, which is shown in Fig.…”

Phonon thermal conduction in novel 2D materials

“…On the amorphous silicon dioxide substrate, both the theoretical [124] and experimental [122] studies show that thermal conductivity of supported multi-layer graphene saturates to that of bulk graphite at the thickness of about 40 layers. Similar thickness-dependence behavior also was observed by several independent groups on black phosphorous [73,111,112], and MoS 2 [108].…”