Ballistic Thermal Conductance of Graphene Ribbons

Muñoz, Enrique; Lü, Jianxin; Yakobson, Boris I.

doi:10.1021/nl904206d

Cited by 196 publications

(149 citation statements)

References 26 publications

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“…For the ultra-narrow W=1nm channel (solid-blue line), very large MFPs of the order of several 100s of nanometers are observed for the low frequency phonons close to the zone center originating from the LA modes. This is consistent with the MFP in other carbon nanostructures such as carbon nanotubes and graphene sheets, which is reported to be ~500nm [29,93,94,95], even in the presence of defects [33]. For slightly larger energies, i.e.…”

Section: Thermal Conductancesupporting

confidence: 89%

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

et al. 2015

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We investigate the influence of low-dimensionality and disorder in phonon transport in ultra-narrow armchair graphene nanoribbons (GNRs) using non-equilibrium Green's function (NEGF) simulation techniques. We specifically focus on how different parts of the phonon spectrum are influenced by geometrical confinement and line edge roughness. Under ballistic conditions, phonons throughout the entire phonon energy spectrum contribute to thermal transport. With the introduction of line edge roughness, the phonon transmission is reduced, but in a manner which is significantly non-uniform throughout the spectrum. We identify four distinct behaviors within the phonon spectrum in the presence of disorder: i) the low-energy, low-wavevector acoustic branches have very long mean-free-paths and are affected the least by edge disorder, even in the case of ultra-narrow W=1nm wide GNRs; ii) energy regions that consist of a dense population of relatively 'flat' phonon modes (including the optical branches) are also not significantly affected, except in the case of the ultra-narrow W=1nm GNRs, in which case the transmission is reduced because of band mismatch along the phonon transport path; iii) 'quasi-acoustic' bands that lie within the intermediate region of the spectrum are strongly affected by disorder as this part of the spectrum is depleted of propagating phonon modes upon both confinement and disorder (resulting in sparse E(q) phononic bandstructure), especially as the channel length increases; iv) the strongest reduction in phonon transmission is observed in energy regions that are composed of a small density of phonon modes, in which case roughness can introduce transport gaps that greatly increase with channel length. We show that in GNRs of widths as small as W=3nm, under moderate roughness, both the low-energy acoustic modes and dense regions of optical modes can retain semi-ballistic transport properties, even for channel lengths up to 2 L=1μm. These modes tend to completely dominate thermal transport. Modes in the sparse regions of the spectrum, however, tend to fall into the localization regime, even for channel lengths as short as 10s of nanometers, despite their relatively high phonon group velocities.

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Section: Thermal Conductancesupporting

confidence: 89%

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

et al. 2015

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“…155 This temperature behavior of thermal conductance, ∝ T 1.5 , also agrees with the prediction that the out-of-plane acoustic phonon has dominant contribution to thermal conduction in suspended graphene. 155,156 The thermal conductivity measured in the same work 154 is around 190 W/m-K at room temperature, which is one order of magnitude smaller than that from the Raman based measurements. This may be reasonable due to the differences in the sample length, as thermal conductivity in 2D lattice models has been predicted to be size dependent even before the discovery of graphene.…”

Section: B 2d Nanostructuresmentioning

confidence: 66%

Thermal transport in nanostructures

et al. 2012

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This review summarizes recent studies of thermal transport in nanoscaled semiconductors. Different from bulk materials, new physics and novel thermal properties arise in low dimensional nanostructures, such as the abnormal heat conduction, the size dependence of thermal conductivity, phonon boundary/edge scatterings. It is also demonstrated that phonons transport super-diffusively in low dimensional structures, in other words, Fourier's law is not applicable. Based on manipulating phonons, we also discuss envisioned applications of nanostructures in a broad area, ranging from thermoelectrics, heat dissipation to phononic devices.

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“…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.…”

Section: Context Imagementioning

confidence: 99%

“…We specifically focus on ribbons with the micrometer width d and length L in order to deal with the actual phonon dispersion in graphene and to ensure the diffusive transport regime. In the nanometerthick graphene ribbons the phonon dispersion is different owing to the phonon mode quantization and the lateral size dependence is dictated by the ballistic conduction [32].…”

Section: Context Imagementioning

confidence: 99%

Anomalous Size Dependence of the Thermal Conductivity of Graphene Ribbons

2012

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We investigated the thermal conductivity K of graphene ribbons and graphite slabs as the function of their lateral dimensions. Our theoretical model considered the anharmonic three-phonon processes to the second-order and included the angle-dependent phonon scattering from the ribbon edges. It was found that the long mean free path of the longwavelength acoustic phonons in graphene can lead to an unusual non-monotonic dependence of the thermal conductivity on the length L of a ribbon. The effect is pronounced for the ribbons with the smooth edges (specularity parameter p>0.5). Our results also suggest that -contrary to what was previously thought -the bulk-like 3D phonons in graphite can make a rather substantial contribution to its in-plane thermal conductivity. The Umklapp-limited thermal conductivity of graphite slabs scales, for L below ~ 10 m, as log(L) while for larger L, the thermal conductivity approaches a finite value following the dependence K 0 -A×L -1/2 , where K 0 and A are parameters independent of the length. Our theoretical results clarify the scaling of the phonon thermal conductivity with the lateral sizes in graphene and graphite. The revealed anomalous dependence K(L) for the micrometer-size graphene ribbons can account for some of the discrepancy in reported experimental data for graphene.

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Ballistic Thermal Conductance of Graphene Ribbons

Cited by 196 publications

References 26 publications

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

Low-dimensional phonon transport effects in ultranarrow disordered graphene nanoribbons

Thermal transport in nanostructures

Anomalous Size Dependence of the Thermal Conductivity of Graphene Ribbons

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