Near-Field Radiative Heat Transfer Between Irregularly Shaped Dielectric Particles Modeled with the Discrete System Green's Function Method: arXiv:2105.05927 [cond-mat.mtrl-sci]

Near-field radiative heat transfer (NFRHT) between irregularly shaped dielectric particles made of SiO2 and morphology characterized by Gaussian random spheres is studied. Particles are modeled with a new numerical method based on fluctuational electrodynamics, called the discrete system Green's function (DSGF) approach, that defines system interactions deterministically via a self-consistent Green's function equation and is applicable to finite, three-dimensional objects. The DSGF method is deemed suitable to model NFRHT between irregularly shaped particles after verification against the analytical solution for chains of two and three SiO2 spheres. The NFRHT results reveal that geometric irregularity in particles leads to a reduction of the total conductance from that of comparable perfect spheres at small separation distances where NFRHT is a surface phenomenon. At larger separation distances where NFRHT becomes a volumetric process, the total conductance between irregularly shaped particles converges to that of comparable perfect spheres. Spectral analysis reveals, however, that particle irregularity leads to damping and broadening of resonances at all separation distances, thereby highlighting the importance of the DSGF method for spectral engineering in the near field. The reduced spectral coherence when particle size is larger than the vacuum separation distance is attributed to coupling of surface phonon-polaritons within the randomly generated, distorted particle features. For particle size smaller than the vacuum separation distance, resonance broadening and damping is linked with the multiple localized surface phonon modes supported by the composite spherical harmonic morphologies of the Gaussian random spheres.