Nanoscale Spectroscopy of Dielectric Properties of Mica

Abstract

Infrared dielectric properties of muscovite mica, one of the first van der Waals crystals, exfoliated on silicon and SiO2 substrates is studied using near-field nano-FTIR spectroscopy. The spectra of mica show strong thickness and wavelength dependence down to the monolayer-scale, with a prominent broad peak centered around ∼1080 cm-1 assigned to stretching vibrations of Si-O. We reveal that the infrared dielectric permittivity of mica is anisotropic, that is, has opposite signs along the in-plane and out-of-plane axes, implying a Type I hyperbolic behavior in the range 920-1010 cm-1 and a Type II hyperbolic behavior in the range 1050-1130 cm-1. Experimentally measured nano-FTIR spectra agree well with analytical model calculations based on an extended finite dipole model for layered systems of the tip-sample interaction when the out-of-plane dielectric values (instead of the in-plane dielectric values) were used in the calculations.