Collapsing Carbon Nanotube Enhances Its Phonon Transport

Carbon nanotubes (CNTs) radially deform when they interact with the surrounding matrix in heterostructures or metal electrodes in electronic devices, affecting their electrical properties. As thermal management becomes increasingly important for high-performance CNT-based nanoelectronics, understanding how such deformations affect the thermal conductivity (κ) of CNT-based devices has emerging significance. The investigation shows that the CNT's radially malleable nature enables the CNT to collapse, allowing atoms across the circumference to couple directly and enhance its thermal transport. Through solving the phonon Boltzmann transport equation at 300 K, the κ of a long (6,6) CNT increases up to six times upon radial compression to 18 GPa. The carbon-carbon bonds become stretched but the acoustic and optical phonons of non-longitudinal polarizations are surprisingly stiffened. This stiffening weakens the anharmonicity, leading to an increase in the phonon relaxation time and κ. However, for CNTs shorter than 10³ nm, a peak in κ occurs with increasing stress. This peak is produced as the increased phonon-boundary scatterings in shorter CNTs offset the increased phonon relaxation time at high stress. Hence, an optimal stress level can increase the κ of CNTs, optimizing the performances of radially-deformed CNT heterostructures.