Applications brief: Mid-infrared nanospectroscopy of Berreman mode and epsilon-near zero local field confinement in thin films

Key results


  • Thin films with vanishing real part of the dielectric function (Re[ε ] = 0) in the midinfrared region are promising photonic materials for manipulating and enhancing IR light–matter interactions at the nanoscale
  • Two fundamental polaritonic phenomena near Re[ε ] = 0 were characterized by AFM-IR
  • Far-field applicability of polaritonic AFM-IR studies was demonstrated through the characterization of a nanoscale plasmonic ENZ grating on Si with 2 nm native SiO2 using polarization-dependent IR microscopy

Key words

AFM-IR | thin films | silica | near-field microscopy | polaritons | spectroscopy | infrared | spectroscopy | photothermal | optical properties

Authors

T. Shaykhutdinov A. Furchner, J. Rappich, K. Hinrichs

Abstract

Thin films with vanishing real part of the dielectric function (Re[ε ] = 0) in the midinfrared (MIR) region are promising photonic materials for manipulating and enhancing IR light–matter interactions at the nanoscale. We present a nanospectroscopic characterization of two fundamental polaritonic phenomena near Re[ε ] = 0 by atomic force microscope infrared spectroscopy (AFM-IR): the Berreman mode (BE) in 100 nm SiO2 and Si3 N4 films on Si, and epsilon-near-zero (ENZ) local field confinement in a 2 nm native SiO2 layer on Si. AFM-IR is an emerging photothermal technique that provides direct information on nanoscale IR absorption, allowing unambiguous identification of BE and ENZ effects supported by simulations. We demonstrate far-field applicability of polaritonic AFM-IR studies by characterizing a nanoscale plasmonic ENZ grating on Si with 2 nm native SiO2 using polarization-dependent IR microscopy.


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Normalized AFM-IR spectra of thermally grown 100 nm SiO2 (a) and Si3N4 (b) films on Si indicating strong tip induced absorption at ν(SiO2) and ν(Si3N4), and the non-invasively probed BE absorption. The insets show zoomed-in BE regions. The noise is due to MIR transparency of Si.

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