Tunable thermal emission and waveguiding by SiC nanowires via collective localized surface phonons

Abstract

This work investigates the thermal emission from SiC nanowires mediated by collective localized surface phonons (cLSPhs). Specifically, the spectral, directional emissivity of solitary and chains of SiC nanowires is calculated using a fluctuational electrodynamics-based Poynting vector formulation of the generalized many-body approach. The SiC nanowires are modeled as ellipsoidal dipoles characterized by a semimajor axis length of 375 nm and semiminor axis lengths of 10 nm. It is shown that solitary SiC nanowires exhibit quasi-monochromatic and directional thermal emission due to localized surface phonon (LSPh) resonances. The low-frequency LSPh resonance along the ellipsoid semimajor axis exhibits strong emission near polar angles of ±90°, whereas the high-frequency LSPh resonances along the ellipsoid semiminor axes result in much weaker, quasi-isotropic emission. SiC nanowire chains support traveling cLSPhs generated by the coupling of LSPhs. Thermal emission from SiC nanowire chains is highly sensitive to the nanowire edge-to-edge gap spacing. As the spacing decreases from 90 to 30 nm, the frequency and directions of maximum emissivity shift significantly: strong normal emission originates from longitudinal cLSPhs, while maximum emission near ±90° is mediated by transverse cLSPhs. For smaller edge-to-edge spacings of 20 and 10 nm, emissivity is suppressed to near zero at all frequencies and directions, as all cLSPhs become dark modes. Dispersion relations for chains with 10 nm spacing confirm that these dark cLSPh modes maintain long propagation lengths exceeding 1 μm, indicating their potential for thermally driven waveguiding with low emission losses. These findings have implications in thermal management, nanophotonic circuitry, and infrared detection.