SICOI wafer+Near-Field Retrieval of the Surface Phonon Polariton Dispersion in Free-Standing Silicon Carbide Thin Films

This work investigates the dispersion of surface phonon polaritons (SPhPs) in free-standing silicon carbide (SiC) thin films, which are polar dielectric membranes with thicknesses of 100 nm and 200 nm. SPhPs, hybrid modes arising from the coupling of photons with lattice vibrations, are central to applications in subwavelength optics, enhanced near-field thermal transfer, and nanoscale heat management. While theoretical models predict mode splitting in thin films due to the hybridization of top and bottom interfaces, direct experimental measurements of this dispersion have been lacking.

The authors employ scattering-type scanning near-field optical microscopy (sSNOM) combined with nano-FTIR spectroscopy to directly probe SPhP modes at subwavelength resolution. The free-standing membranes allow for reduced damping compared to substrate-supported films, and the AFM tip provides the missing momentum for polariton excitation. Measurements capture complex interference patterns resulting from tip-launched, edge-launched, and multiple reflection pathways of SPhPs. By applying fast Fourier transforms and isolating edge-launched contributions, the in-plane momentum–frequency dispersion is reconstructed. The experimental dispersion matches theoretical predictions, including even (symmetric) and odd (antisymmetric) modes, demonstrating wavelength shrinking and mode splitting as the film thickness decreases.

From the measured propagation lengths and group velocities, SPhP lifetimes were determined to be ~8 ps for the 200 nm membrane and ~9.5 ps for the 100 nm membrane, consistent with previously reported values for other polar dielectrics. The study shows that commercially available free-standing SiC membranes can serve as a versatile platform for phonon polaritonics, enabling tunable subwavelength light confinement, enhanced near-field thermal transport, and nanoscale energy management.