Ballistic to diffusive crossover of heat flow in graphene ribbons

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Abstract

Heat flow in nanomaterials is an important area of study, with both fundamental and technological implications. However, little is known about heat flow in two-dimensional (2D) devices or interconnects with dimensions comparable to the phonon mean free path (mfp). Here, we find that short, quarter-micron graphene samples reach ~35% of the ballistic heat conductance limit up to room temperature, enabled by the relatively large phonon mfp (~100 nm) in substrate-supported graphene. In contrast, patterning similar samples into nanoribbons (GNRs) leads to a diffusive heat flow regime that is controlled by ribbon width and edge disorder. In the edge-controlled regime, the GNR thermal conductivity scales with width approximately as ~W^{1.8+/-0.3}, being about 100 W/m/K in 65-nm-wide GNRs, at room temperature. Manipulation of device dimensions on the scale of the phonon mfp can be used to achieve full control of their heat-carrying properties, approaching fundamentally limited upper or lower bounds.

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A. C. Ferrari, J. Robertson (2000)

Physical Review B, 61(20), 14095-14107

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Two-dimensional phonon transport in supported graphene.

Jae Hun Seol, Insun Jo, Arden L Moore … (2010)

The reported thermal conductivity (kappa) of suspended graphene, 3000 to 5000 watts per meter per kelvin, exceeds that of diamond and graphite. Thus, graphene can be useful in solving heat dissipation problems such as those in nanoelectronics. However, contact with a substrate could affect the thermal transport properties of graphene. Here, we show experimentally that kappa of monolayer graphene exfoliated on a silicon dioxide support is still as high as about 600 watts per meter per kelvin near room temperature, exceeding those of metals such as copper. It is lower than that of suspended graphene because of phonons leaking across the graphene-support interface and strong interface-scattering of flexural modes, which make a large contribution to kappa in suspended graphene according to a theoretical calculation.

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Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Alexander Balandin (2011)

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range - of over five orders of magnitude - from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.