  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 using the discrete system
Green's function (DSGF) approach, which is a volume integral numerical method
based on fluctuational electrodynamics. This method is applicable to finite,
three-dimensional objects, and all system interactions are defined independent
of thermal excitation by a generalized system Green's function. 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 vacuum separation distances smaller than the particle size, a regime
in which NFRHT is a surface phenomenon. At vacuum separation distances larger
than the particle size, NFRHT becomes a volumetric process, and 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.

Applied Physics