Probing the Limits to Near-Field Heat Transfer Enhancements in Phonon-Polaritonic Materials.
basic_science · Level V
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- Record sourced from PubMed, PMID 36888651.
- Also identified by DOI 10.1021/acs.nanolett.2c04735.
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Abstract
Near-field radiative heat transfer (NFRHT) arises between objects separated by nanoscale gaps and leads to dramatic enhancements in heat transfer rates compared to the far-field. Recent experiments have provided first insights into these enhancements, especially using silicon dioxide (SiO<sub>2</sub>) surfaces, which support surface phonon polaritons (SPhP). Yet, theoretical analysis suggests that SPhPs in SiO<sub>2</sub> occur at frequencies far higher than optimal. Here, we first show theoretically that SPhP-mediated NFRHT, at room temperature, can be 5-fold larger than that of SiO<sub>2</sub>, for materials that support SPhPs closer to an optimal frequency of 67 meV. Next, we experimentally demonstrate that MgF<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> closely approach this limit. Specifically, we demonstrate that near-field thermal conductance between MgF<sub>2</sub> plates separated by 50 nm approaches within nearly 50% of the global SPhP bound. These findings lay the foundation for exploring the limits to radiative heat transfer rates at the nanoscale.