  Thermal emission of localized surface phonons (LSPhs) from nanostructures of
polaritonic materials is a promising mechanism for tuning the spectrum of
near-field thermal radiation. Previous studies have theoretically shown that
thermal emission of LSPhs results in narrow-band peaks in the near-field
spectra, whose spectral locations can be modulated by changing the dimensions
of the nanostructure. However, near-field thermal emission of LSPhs has not
been experimentally explored yet. In this study, we measure the spectrum of
near-field thermal radiation from arrays of 6H-silicon carbide (6H-SiC)
nanopillars using an internal-reflection-element based spectroscopy technique.
We present an experimental demonstration of thermal emission of the transverse
dipole, quadrupole, and octupole, as well as longitudinal monopole from 6H-SiC
nanopillars at a near-field distance from the array. We show that the spectral
location of the longitudinal monopole and transverse dipole are significantly
affected by the near-field coupling between neighboring nanopillars as well as
the intercoupling of the nanopillars and the substrate. We also experimentally
demonstrate that the spectrum of near-field thermal radiation from 6H-SiC
nanopillar arrays can be tuned by varying the dimensions of the nanopillars,
providing an opportunity for designing emitters with tailored near-field
thermal radiation.
