Collective Phonon–Polaritonic Modes in Silicon Carbide Subarrays

Abstract

Localized surface phonon polaritons (LSPhPs) can be implemented to engineer light−matter interactions through nanoscale patterning for a range of midinfrared application spaces. However, the polar material systems studied to date have mainly focused on simple designs featuring a single element in the periodic unit cell. Increasing the complexity of the unit cell can serve to modify the resonant near-fields and intra-and inter-unit-cell coupling as well as to dictate spectral tuning in the far-field. In this work, we exploit more complicated unit-cell structures to realize LSPhP modes with additional degrees of design freedom, which are largely unexplored. Collectively excited LSPhP modes with distinctly symmetric and antisymmetric near-fields are supported in these subarray designs, which are based on nanopillars that are scaled by the number of subarray elements to ensure a constant unit-cell size. Moreover, we observe an anomalous mode-matching of the collective symmetric mode in our fabricated subarrays that is robust to changing numbers of pillars within the subarrays as well as to defects intentionally introduced in the form of missing pillars. This work therefore illustrates the hierarchical design of tailored LSPhP resonances and modal near-field profiles simultaneously for a variety of IR applications such as surface-enhanced spectroscopies and biochemical sensing.

Near-Unity Light–Matter Interaction in Mid-Infrared van der Waals Metasurfaces

“…The observed dynamics can be understood via an effective medium picture: as the disk size is reduced, the effective permittivity of the overall hBN film is also reduced, resulting in the decrease of the resonance frequency; at some point, as the film thickness is fixed, a cutoff condition is met (see also discussion pertaining to Figure c). Numerical simulations also predict multiple resonance branches inside the RB, which are familiar phonon-polariton modes seen in a number of experiments. ,, The excitation of these modes is not clearly observed in our experiments. Taller hBN pillars are needed in order to observe phonon polariton modes, , as we show below for our 500 nm flake in Figure .…”

“…Midinfrared (mid-IR) radiation plays an important role in a wide range of applications covering thermal imaging, − mimicry, , molecular and biosensing, , waste heat management, − and radiative cooling, − among others. Many diverse pathways have been proposed and examined recently to control mid-IR radiation, including such systems as plasmon-polaritons in graphene and doped semiconductors, − all-dielectric metasurfaces, , and polar dielectrics. − Of great interest are polar dielectrics, such as silicon carbide − and hexagonal boron nitride (hBN), − which, owing to their intrinsically strong phonon resonances, , offer unique avenues for light–matter interactions in the midwave and long-wave infrared bands (see also Supporting Information, section I). In addition, phonons can couple with optical modes forming hybridized phonon-polariton states. ,− …”

“…Phonon-polaritons ,, have received significant attention due to their ability to squeeze light well below the diffraction limit. , As a result, deep subwavelength (<1 μm) phonon-polariton devices , can be designed to control mid-IR radiation (λ > 5 μm). A range of phonon-polariton systems, including waveguides, metasurfaces, ,, and nanoscale resonators, have been proposed and studied for mid-IR radiation guidance, emission, and absorption.…”

“…In addition, phonons can couple with optical modes forming hybridized phonon-polariton states. 33,37−40 Phonon-polaritons 30,32,38 have received significant attention due to their ability to squeeze light well below the diffraction limit. 28,32 As a result, deep subwavelength (<1 μm) phononpolariton devices 28,39 can be designed to control mid-IR radiation (λ > 5 μm).…”

Probing Near-Field Thermal Emission of Localized Surface Phonons from Silicon Carbide Nanopillars

“…The Reststrahlen band of polaritonic materials is located in the infrared part of the electromagnetic spectrum, where thermal emission is commonly spectrally located. It is theoretically shown that metamaterials made of nanoparticles of polaritonic materials can emit localized surface phonons (LSPhs) in their Reststrahlen band, causing narrow-band peaks in the near-field spectra. ,, It is proposed that the spectral location of the thermally emitted LSPhs can be modulated by varying the size and shape of the nanoparticles. ,, Tuning the spectrum of far-field thermal radiation by engineering the geometry of the polaritonic metamaterials has been demonstrated experimentally. ,− However, near-field thermal emission of LSPhs from polaritonic metamaterials has not been experimentally demonstrated yet. Indeed, while there have been several experimental studies on total (spectrally-integrated) near-field radiative heat transfer, ,,,− measurements of the spectrum of near-field thermal radiation have been scarce. ,− A limited number of studies have experimentally explored the near-field response of polaritonic metamaterials to an external illumination using scattering-scanning near-field optical microscopy (sSNOM). ,, Using sSNOM, an external infrared electromagnetic field is shined to an AFM tip which is located at a subwavelength distance from the metamaterials.…”