Researchers from the international LIMMS laboratory and the University of Tokyo have identified the conditions under which heat can flow through graphite like a liquid. These results, which make it possible to present highly efficient heat dissipation devices, are published in the journal Nature Communications. a) Hydrodynamic phonon flux in purified graphite, the heat flux shows a characteristic parabolic profile (red arrows).
b) Scanning electron micrographs of graphite ribbons of different widths.
c) Plot of the non-contact measurement of thermal conductivity by a time-domain thermal reflection (TDTR) technique using an excitation laser beam (pump) and a measurement beam (probe).
©LIMS.
Under certain conditions, heat can propagate through a material by behaving like a liquid: phonons—the particles associated with propagating vibrations in the crystal lattice—flow like a liquid through a pipe. However, this hydrodynamic phonon flux was still poorly understood theoretically and difficult to confirm experimentally. A theoretical and experimental study published in Nature Communications and conducted by the Laboratory for Integrated Micro Mechatronics Systems (LIMMS, CNRS/University of Tokyo) and the Institute of Industrial Sciences at the University of Tokyo provides a better understanding and explanation of this phenomenon under the conditions where it occurs.
Researchers studied the propagation of heat in graphite, a material previously found to be able to induce hydrodynamic flux of phonons. Specifically, they used purified graphite, which contains only 0.02% of the carbon-13 isotope, compared to 1.1% in natural graphite. In fact, the theoretical model predicts that the hydrodynamic flow of phonons is disrupted by their interaction with the C13 isotope. The geometry of the material also plays a key role in the origin of the phenomenon.
To experimentally confirm the predictions of the theoretical model, graphite microribbons with a length of 30 microns and a maximum width of 5.5 microns were fabricated. The samples were made from natural graphite and purified graphite. Through measurements over a wide temperature range from 10 K (-263 °C) to 300 K (27 °C), the researchers showed that the thermal conductivity of purified graphite can reach a value twice that of natural graphite. The hydrodynamic flow regime is observed in bands up to 90K.
These results could eventually lead to very efficient heat dissipation devices, for example to cool the “hot spots” of increasingly dense micro- or nanoelectronic circuits. Materials are found where the hydrodynamic heat flow occurs at temperatures compatible with the intended applications. For their part, the researchers continue the study with purified graphite to deepen various aspects of the analogy with the flow of a liquid and are interested in other types of specific phonon propagation regimes. in materials.
references
Observation of the Poiseuille phonon flux in isotopically purified graphite ribbons
Xin Huang, Yangyu Guo, Yunhui Wu, Satoru Masubuchi, Kenji Watanabe, Takashi Taniguchi, Zhongwei Zhang1, Sebastian Volz, Tomoki Machida and Masahiro Nomura.
Nature Communications, April 19, 2023.
https://doi.org/10.1038/s41467-023-37380-5
Searchable article in the open archive database Arxiv