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

Thin films with vanishing real part of the dielectric function (Re[epsilon] = 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[epsilon] = 0 by atomic force microscope infrared spectroscopy (AFM-IR): the Berreman mode (BE) in 100 nm SiO2 and Si3N4 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. (C) 2017 Optical Society of America