Optical contrast analysis of {\alpha}-RuCl$_3$ nanoflakes on oxidized silicon wafers

TL;DR

This study demonstrates that optical contrast imaging, combined with spectroscopic measurements and simulations, provides a fast, non-invasive, and accurate method to determine the thickness of { extalpha}-RuCl$_3$ nanoflakes on silicon wafers.

Contribution

The paper introduces a systematic approach to quantify { extalpha}-RuCl$_3$ nanoflake thickness using optical contrast and spectroscopic ellipsometry, validated by simulations and experimental data.

Findings

Optical contrast correlates well with nanoflake thickness below 100 nm.

Spectroscopic ellipsometry accurately characterizes the refractive index of { extalpha}-RuCl$_3$.

Thickness estimation via optical contrast has a mean deviation of -0.2 nm with a 1 nm standard deviation.

Abstract

{\alpha}-RuCl$_3$, a narrow-band Mott insulator with large work function, offers intriguing potential as a quantum material or as a charge acceptor for electrical contacts in van der Waals devices. In this work, we perform a systematic study of the optical reflection contrast of {\alpha}-RuCl$_3$ nanoflakes on oxidized silicon wafers and estimate the accuracy of this imaging technique to assess the crystal thickness. Via spectroscopic micro-ellipsometry measurements, we characterize the wavelength-dependent complex refractive index of {\alpha}-RuCl$_3$ nanoflakes of varying thickness in the visible and near-infrared. Building on these results, we simulate the optical contrast of {\alpha}-RuCl$_3$ nanoflakes with thicknesses below 100 nm on SiO$_2$/Si substrates under different illumination conditions. We compare the simulated optical contrast with experimental values extracted from optical microscopy images and obtain good agreement. Finally, we show that optical contrast imaging allows us to retrieve the thickness of the RuCl$_3$ nanoflakes exfoliated on an oxidized silicon substrate with a mean deviation of -0.2 nm for thicknesses below 100 nm with a standard deviation of only 1 nm. Our results demonstrate that optical contrast can be used as a non-invasive, fast, and reliable technique to estimate the {\alpha}-RuCl$_3$ thickness.