NSF Award
2406022
Efficient heat dissipation from electronic and optoelectronic devices is critical to prevent them from being overheated. One key challenge is the lower heat conduction capability of various nanostructures in these devices. Heat conduction in solids is mainly through transport of electrons and atomic vibrations (phonons). As the characteristic size of structures reduces to the nanoscale, scattering of electrons and phonons at thermal boundaries can significantly suppress the thermal conductivity. One promising strategy to address this issue is to construct new heat dissipation channels from the coupling between infrared light and optically active phonons, which has recently been shown to serve as effective energy carriers to enhance the thermal conductivity of polar nanostructures. This novel observation motivates this project to pursue the maximum possible heat conduction capability via these novel energy carriers in solids, which will be realized through systematic measurements to understand and tune the factors that control their excitation and propagation along polar nanowires, nanoribbons, and thin films, which are widely used in various engineering devices. As such, the obtained knowledge will contribute to novel solutions of electronic device cooling. The project will train graduate and undergraduate students from diverse backgrounds, stimulate scientific curiosities from K-12 students, and contribute towards cultivating the future workforce for the U.S. high-tech industry.<br/> <br/>The primary technical objective of this project is to understand the excitation and propagation mechanisms of coupled infrared light and optically active phonons, which are called surface phonon polaritons (SPhPs), and to maximize the SPhP-mediated heat conduction. Systematic experiments will be conducted to answer key scientific questions including: (1) What is the upper limit for SPhP-mediated thermal conductivity? (2) How can SPhPs be optimized to maximize their thermal transport capabilities? and (3) What are the roles of various confinement effects on SPhP-mediated thermal transport? Through carefully designed experiments targeted for addressing these questions, the project will generate new fundamental knowledge about SPhP-mediated heat conduction. Importantly, the new understanding will enable rational engineering design to achieve a SPhP-mediated thermal conductivity of potentially >100 W/mK, which could effectively offset the classical size effect that significantly suppresses the thermal conductivity of nanostructures. Importantly, substantial SPhP contribution to conduction occurs under a non-equilibrium condition with SPhP number densities well beyond the corresponding equilibrium values, which is in a regime remarkably different from the classical near-equilibrium approximation. As such, this project could both shift the conventional paradigm of near-equilibrium heat conduction and produce transformative engineering impacts through providing an effective SPhP-based heat dissipation channel.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
