Thickness mapping and layer number identification of exfoliated van der Waals materials by Fourier imaging micro-ellipsometry

TL;DR

This paper introduces a Fourier imaging micro-ellipsometry technique capable of accurately mapping the thickness of exfoliated van der Waals materials at the micro-scale, overcoming limitations of traditional methods.

Contribution

The authors develop a high-resolution, fast data acquisition Fourier imaging micro-ellipsometer for precise, non-invasive thickness and layer number identification of 2D materials.

Findings

Achieves angstrom-level thickness accuracy for various 2D materials.

Maps minute thickness variations over micro-scale flakes.

Effectively distinguishes monolayer hBN from multilayer samples.

Abstract

As properties of mono- to few layers of exfoliated van der Waals heterostructures are heavily dependent on their thicknesses, accurate thickness measurement becomes imperative in their study. Commonly used atomic force microscopy and Raman spectroscopy techniques may be invasive and produce inconclusive results. Alternatively, spectroscopic ellipsometry is limited by tens-of-microns lateral resolution and/or low data acquisition rates, inhibiting its utilization for micro-scale exfoliated flakes. In this work, we demonstrate a Fourier imaging spectroscopic micro-ellipsometer with sub-5 microns lateral resolution along with fast data acquisition rate and present angstrom-level accurate and consistent thickness mapping on mono-, bi- and trilayers of graphene, hexagonal boron nitride and transition metal dichalcogenide (MoS2, WS2, MoSe2, WSe2) flakes. We show that the optical microscope integrated ellipsometer can also map minute thickness variations over a micro-scale flake. In addition, our system addresses the pertinent issue of identifying monolayer thick hBN.