Fourier analysis of the IR response of van der Waals materials

TL;DR

This paper introduces a Fourier-based analytical method for optical analysis of van der Waals materials, enabling extraction of thickness variations and removal of Fabry-Perot fringes to improve spectral interpretation.

Contribution

It presents a novel Fourier transform technique for optical spectra that reveals sample thickness variations and simplifies spectral analysis of layered van der Waals materials.

Findings

Detected large step edges and thickness inhomogeneity in layered materials.

Identified potential voids in the bulk of cleaved samples.

Enhanced spectral analysis by removing Fabry-Perot fringes.

Abstract

In this letter, we report on an analytical technique for optical investigations of semitransparent samples. By Fourier transforming optical spectra with Fabry-Perot resonances we extract information about sample thickness and its discrete variations. Moreover, this information is used to recover optical spectra devoid of Fabry-Perot fringes, which simplifies optical modelling, and can reveal previously concealed spectral features. To illustrate its use, we apply our technique to a Si wafer as well as six different cleavable layered materials, including topological insulators, thermoelectrics, and magnetic insulators. In the layered materials, we find strong evidence of large step edges and thickness inhomogeneity, and cannot conclusively exclude the presence of voids in the bulk of cleaved samples. This could strongly affect the interpretation of transport and optical data of crystals with topologically protected surfaces states.