| 研究実績の概要 |
Firstly, we investigated the strength of phonon hydrodynamic flow in finite-sized isotopically purified graphite structures based on a direct solution of the phonon Boltzmann equation with ab initio scattering rates. We found that with the widening of the structure from 2 to 10μm, the hydrodynamic strength enhances owing to larger space for dominant normal processes over the diffuse boundary scattering. Our mapping of the hydrodynamic strength provides straightforward and crucial information in future attempts to observe prominent hydrodynamic heat flow.
Furthermore, based on the suspended microstructure system and the μ-TDTR method, we selected high-quality graphite samples and measured thermal conductivity in a wider temperature range of 10-300K. At 90K, isotope enrichment plays an important role in phonon transport, resulting in an enormous enhancement of thermal conductivity of purified graphite ribbon compared to that of the natural one by 105%. Following our newly advocated more explicit criteria, we observed an enhancement of thermal conductivity over the ballistic thermal conductance by 51% from 40 to 90K. In our updated results, we demonstrated unambiguous experimental evidence of phonon Poiseuille flow in an 5.5μm-wide isotopically purified graphite ribbon up to 90K, which is much elevated compared to the temperature range of previous observations in other solid-state materials. This research provides a deeper understanding of phonon transport in the hydrodynamic regime and opens innovative possibilities for thermal management in modern electronic devices.
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