Phonon thermal conduction in graphene: Role of Umklapp and edge roughness scattering

Abstract

Phonon thermal conduction in graphene: Role of Umklapp and edge roughness scattering, Phys. Rev. B (2009) -Editors' Suggestion . 1 arXiv:0812.0518 [cond-mat.mtrl-sci] Phonon thermal conduction in graphene: Role of Umklapp and edge roughness scattering, Phys. Rev. B (2009) -Editors' Suggestion .2 AbstractWe investigated theoretically the phonon thermal conductivity of single layer graphene. The phonon dispersion for all polarizations and crystallographic directions in graphene lattice was obtained using the valence-force field method. The three-phonon Umklapp processes were treated exactly using an accurate phonon dispersion and Brillouin zone, and accouting for all phonon relaxation channels allowed by the momentum and energy conservation laws. The uniqueness of graphene was reflected in the two-dimensional phonon density of states and restrictions on the phonon Umklapp scattering phase-space. The phonon scattering on defects and graphene edges has been also included in the model. The calculations were performed for the Gruneisen parameter, which was determined from the ab initio theory as a function of the phonon wave vector and polarization branch, and for a range of values from experiments. It was found that the near room-temperature thermal conductivity of single layer graphene, calculated with a realistic Gruneisen parameter, is in the range ~ 2000 -5000 W/mK depending on the defect concentration and roughness of the edges. Owing to the long phonon mean free path the graphene edges produce strong effect on thermal conductivity even at room temperature. The obtained results are in good agreement with the recent measurements of the thermal conductivity of suspended graphene.

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

“…For instance, theoretical calculations have revealed a superior lifetime of the bending modes in twodimensional graphene. 52,53,56 Our auto-correlation function calculations are consistent with these results. The TW and LA modes have much shorter lifetime than the bending modes at 300 K. From the comparison between these curves for 300K and 1200 K, we find that the lifetime for the two bending modes and the LA mode decrease considerably with increasing temperature.…”

“…This is similar as what have been observed in both graphene and carbon nanotubes, where the TA modes dominate the thermal conductivity. 52,61 From this qualitative analysis, the contribution from the TW and LA modes should be at least one order of magnitude smaller than the TA modes, and forms the justification for neglecting the contribution from the TW and LA modes in the present analysis. Overall, the error due to the neglect of the LA and TW modes should be less than 10% in this analysis.…”

“…The surface or boundary scattering is a common mechanism in low-dimensional NW structures, which is closely related to weaker phonon-phonon scattering. 51,52,53,54 The experimental value for the exponent is above 1.0, which is attributed to other phonon scattering mechanisms be- sides the phonon-phonon scattering, 28 for example intrinsic vacancy point defects or isotropic disorder. In our simulations, all ZnO NWs are pristine without defects, so the temperature exponents from our calculations are smaller than the experimental values.…”

“…This preserving mechanism for the bending mode is crucial for the much higher thermal conductivity of the free ZnO NW because it is well-known that thermal energy is mainly transported by the bending modes in both two-dimensional and one-dimensional nanosystems. 52,53,56 Hence, the preservation of the bending mode directly leads to much higher thermal conductivity in the free ZnO NW.…”

Anomalous Size Dependence of the Thermal Conductivity of Graphene Ribbons

“…Although the strong size dependence was reported in many studies of heat conduction in graphene or CNTs [13,[16][17][19][20][21][25][26][27][28][29][30][31][32][33], it is usually difficult to distinguish among the various possible mechanisms. Among them are the K(L) dependence in the ballistic thermal transport regime where L<< the K dependence on the nanoribbon width due to the acoustic phonon -rough edge scattering, or the fundamental K size dependence in 1D or 2D lattices where anharmonic interactions are not sufficient for establishing finite K over the given length scale L. These important questions call for a rigorous study of the lateral size effects on the thermal conductivity of graphene ribbons and graphite slabs.…”