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Phonon hydrodynamics and ultrahigh–room-temperature thermal conductivity in thin graphite

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Science  17 Jan 2020:
Vol. 367, Issue 6475, pp. 309-312
DOI: 10.1126/science.aaz8043

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Thin graphite gets cool fast

In nonmetallic solids, heat is transported primarily through crystal vibrations called phonons. These phonons can have wavelike properties under certain conditions, which increases the thermal conductivity of the material. Machida et al. found that making graphite samples thin expands the hydrodynamic regime from cryogenic to room temperatures. The researchers measured an extremely high thermal conductivity in the very thin graphite samples, which may be important for a variety of electronics applications.

Science, this issue p. 309

Abstract

Allotropes of carbon, such as diamond and graphene, are among the best conductors of heat. We monitored the evolution of thermal conductivity in thin graphite as a function of temperature and thickness and found an intimate link between high conductivity, thickness, and phonon hydrodynamics. The room-temperature in-plane thermal conductivity of 8.5-micrometer-thick graphite was 4300 watts per meter-kelvin—a value well above that for diamond and slightly larger than in isotopically purified graphene. Warming enhances thermal diffusivity across a wide temperature range, supporting partially hydrodynamic phonon flow. The enhancement of thermal conductivity that we observed with decreasing thickness points to a correlation between the out-of-plane momentum of phonons and the fraction of momentum-relaxing collisions. We argue that this is due to the extreme phonon dispersion anisotropy in graphite.

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