Surface Effects on Phonon Polariton-Mediated Thermal Conductivity

Heat conduction in nanostructures can be significantly suppressed due to enhanced phonon scattering at surfaces, leading to critical issues such as overheating and reduced reliability in microelectronics and nonlinear nanophotonics applications. Recently, surface phonon polaritons (SPhPs) have been shown to serve as effective energy carriers for heat conduction along polar nanostructures [1–3], offering a potential solution to enhance heat dissipation in miniaturized structures. SPhPs arise from the coupling between infrared photons and optically active phonons, exhibiting high group velocities and long propagation lengths conducive to effective heat conduction. However, despite these advantages, the contribution of SPhPs to heat conduction has been largely neglected in the past due to their low number density. Notably, the thermal conductivity mediated by SPhPs with equilibrium number densities is only experimentally discernable for large sample lengths, with a contribution of less than 0.5 W/m×K [2,3].
Recently, we have experimentally demonstrated a significantly higher SPhP-mediated thermal conductivity of ~6 W/m×K at room temperature in an 11.8 μm long 3C-SiC nanowire sample [1]. This increase was achieved by coating the end(s) of the SiC nanowire with a short segment of Au, which efficiently launches SPhPs with number densities well beyond the equilibrium values propagating along the uncoated wire segment. To further confirm that this enhanced thermal conductivity is indeed due to surface waves, we modify the surface of the SiC nanowires by applying a thin polymer coating, either polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS), to the conduction channel (the wire segment between the heat source and sink). Thermal measurements indicate that while the PMMA coating only minimally reduces thermal conductivity, the PDMS coating significantly drops the heat conduction. These experimental results are further supported by numerical modeling, showing a much stronger optical attenuation effect of PDMS over the PMMA layer on the propagation of SPhPs. These results not only confirm the crucial role of SPhPs in heat conduction along SiC nanowires but also offer valuable insights into how the surrounding media could modulate the SPhP-mediated thermal conductivity, providing important guidance for designing efficient heat dissipation strategies based on SPhPs.
1. Z. Pan, G. Lu, X. Li, J. R. McBride, R. Juneja, M. Long, L. Lindsay, J. D. Caldwell, and D. Li, "Remarkable heat conduction mediated by non-equilibrium phonon polaritons," Nature 623, 307–312 (2023).
2. Y. Pei, L. Chen, W. Jeon, Z. Liu, and R. Chen, "Low-dimensional heat conduction in surface phonon polariton waveguide," Nat. Commun. 14, 8242 (2023).
3. S. Li, J. Wang, Y. Wen, and S. Shin, "Long Propagating Polaritonic Heat Transfer: Shaping Radiation to Conduction," ACS Nano 18, 14779–14789 (2024).