Boundary-Induced Auxiliary Features in Scattering-Type Near-Field Fourier Transform Infrared Spectroscopy

ACS Nano 2020, 14, 1, 1123–1132

DOI: 10.1021/acsnano.9b08895

In this paper, the authors combined s-SNOM single wavenumber imaging and broadband scattering IR nanospectroscopy to provide new insights into phonon-polaritons (PhPs) in layered crystals of hexagonal boron nitride (hBN) on SiO₂/Si wafers. Specifically, using the high-power broadband IR laser source on their nanoIR-3s instrument, the authors were able to quantitatively resolve multiple groups of auxiliary peaks in the near-field amplitude spectra that have not been observed previously. 

By systematically studying over a variety of different boundary conditions, differences between the near-field auxiliary signatures when the hBN layers were supported or suspended were observed and identified. The observed differences are attributed to the interference between the microwell edge and the hBN edge, depending on the distances from the edges. Having such information about these localized boundaries can be useful for engineering and creating nanophotonic heterostructures for advanced sensing applications.
 

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_SUBJECT(S):

• Exploring s-SNOM-based FTIR spectra features originating from the impact of boundaries in phonon-polaritons (PhPs) in layered crystals

_{FEATURED BRUKER TECHNOLOGY:}

_{KEY FINDINGS:}

• Found that, as the IR illumination moves away from the hBN edge, the major PhP propagation interference peak moves toward the major in-plane phonon peak
• Demonstrated specific differences between the near-field amplitude spectra from supported and suspended hBN sheets related to different boundary conditions, especially edges and substrate interfaces

_{KEY TERMS:}

Nano-FTIR, Phonon-polaritons (PhPs), Scattering-type near-field FTIR spectroscopy, s-SNOM imaging