Phonon thermal transport in graphene has attracted significant interest in recent years. Phonon thermal properties of graphene are investigated by molecular dynamics simulations using the Tersoff, Tersoff-2010, REBO, and AIREBO potentials. By calculating the phonon properties and thermal conductivity of graphene, the performance of the potentials is evaluated based on comparisons with experimental data. It shows that the Tersoff-2010 and REBO display better dispersion curves for graphene than the original Tersoff and AIREBO. The Tersoff-2010 correctly provides the Γ point phonon velocities of the LA and TA branches as well as the G peak frequency with a value of 46 THz. In addition, the acoustic phonon relaxation time derived from the Tersoff-2010 satisfies the ideal relation "τ ∝ ν." It is also found that the Tersoff-2010 provides the highest graphene thermal conductivity among the used potentials, and estimates about 30.0% contribution for flexural phonons to the total thermal conductivity. By comparison, the Tersoff-2010 potential is demonstrated to be the most suitable one to describe the phonon thermal properties of graphene.

Graphene has attracted enormous attention due to its extraordinary physical properties, which have potential for increasing the thermal conductivity of nanocomposites or nanofluids, and the thermal resistance between graphene and the surrounding matrices arises as an important issue. In this paper, the thermal transport at the graphene-water interface is investigated by molecular dynamics simulations. The interfacial thermal resistance decreases with the graphene layer number. Interlayer functionalization by oxygen atoms is applied to tune the interfacial thermal resistance. A peak thermal resistance reduction of nearly 50% is generated with the oxygen ratio of only 0.5% for two-layer graphene. Based on the analyses of vibrational density of states, it is found that lower thermal resistance is consistent with more vibrational density of states overlaps at the interface. Our results are instructive for improving the interfacial thermal transport in graphene-based nanocomposites and nanofluids.

Phonon thermal properties of graphene on hexagonal boron nitride are investigated by the molecular dynamics simulations combined with lattice dynamics theory. It is found that the dispersion curves have minor changes for supported graphene because the interlayer coupling is too weak to shift the harmonic phonon properties. The ZA and ZO phonon lifetimes are significantly reduced in supported graphene due to the breakdown of the symmetry-based selection rule. The dominant mean free path (MFP) of graphene is reduced from 90-800 nm to 60-500 nm at 300 K. The mode thermal conductivities of free and supported graphene are 3517 W/ (mÁK) and 2200 W/ (mÁK) at 300 K, respectively. The thermal conductivity of supported graphene decreases by about 37.4% due to the large reduction of flexural phonon lifetimes, and the relative contribution of flexural modes decreases from 35.0% to 16.7%.

Graphene is promising for thermal management applications due to its superior thermal conductivity, but the inherent thermal transport mechanism is not fully understood. In this work, we directly extract the mode contributions to the thermal conductivity of free-standing and supported graphene nanoribbons using nonequilibrium molecular dynamics simulations. With the aid of the mode analyses, it is uncovered that the acoustic contribution increases with respect to the characteristic length in suspended graphene, and such a size-dependency is compromised in supported graphene. In addition, the contribution of optical modes could be more than 25% for heat conduction in narrow graphene nanoribbons because of strong boundary scatterings. Furthermore, the LA and TA modes rather than the ZA modes are dominant heat carriers in suspended and supported graphene owing to their large group velocities and long mean free path. Our results are instructive for understanding the mode thermal transport in free and supported graphene.

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