Tunable Super-Planckian Near-field Radiative Heat Transfer with Thermochromic Metamaterials

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Materials at finite temperature above zero Kelvin can emit propagating electromagnetic waves over long distances related to conventional thermal radiation with heat flux limited by blackbodies, as well as decaying waves in close proximity where radiative heat flux could exceed the blackbody limit by orders of magnitude when the distance is much smaller than the characteristic thermal wavelength. This project studies tunable near-field radiative thermal transport with thermochromic materials whose color changes with temperature. The project could impact many potential energy applications including thermal management of microelectronics and energy conversion in solid-state thermopower generation. It will also pave the way to radiation-based near-field devices for active heat control, thermal circuits and thermal computers. The research outcomes will be disseminated through journal publications, conference presentations and course teaching. The PI will train researchers and leaders for the next generation of work force, emphasizing on broader participation of underrepresented groups. Graduate students will learn the fundamentals and skills of multiple disciplines. The Arizona State Fulton Undergraduate Research Initiative program offers a great opportunity for undergraduate students to participate in the research activities in the PI’s lab. The PI will engage local K-12 students and reach out to local public and society through various programs at ASU.This research project aims to advance the fundamental understanding in tunable near-field radiative thermal transport with thermochromic metamaterials across nanometric vacuum gaps based on different physical mechanisms with super-Planckian heat flux exceeding the blackbody limit. Vanadium dioxide as one unique thermochromic material could experience insulator-to-metal phase transition when its temperature increases beyond 68°C. Theoretical calculations based on fluctuational electrodynamics incorporated with thin-film uniaxial wave optics as well as numerical modeling based on rigorous coupled-wave analysis will be implemented to predict the spectral and total radiative heat flux with different thermochromic nanostructures. Advanced nanofabrication methods including thin-film deposition, deep-UV lithography and electron-beam lithography will be used to fabricate the designed thermochromic nanostructures, while unique techniques such as temperature-dependent infrared spectroscopy will be employed to characterize the radiative thermal properties of fabricated samples. Novel near-field thermal metrology that could achieve down to 100-nm vacuum gaps will be utilized for the experimental study of near-field radiative heat transfer to understand how different physical mechanisms enable the tunable heat flux upon phase transition of different thermochromic nanostructures. Potential applications such as near-field radiative thermal rectification and switching will be experimentally demonstrated.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.