Measurement of the surface susceptibility and the surface conductivity of atomically thin $\rm MoS_2$ by spectroscopic ellipsometry

TL;DR

This paper presents a method to accurately extract surface susceptibility and conductivity of monolayer MoS2 from spectroscopic ellipsometry data, highlighting errors in common modeling approaches.

Contribution

It introduces a surface current model for monolayer MoS2 and demonstrates the inaccuracies of the slab approximation in optical property measurements.

Findings

The slab model causes at least 10% error in susceptibility estimation.

The surface current model provides more accurate optical parameters.

Significant discrepancies arise from traditional modeling methods.

Abstract

We show how to correctly extract from the ellipsometric data the surface susceptibility and the surface conductivity that describe the optical properties of monolayer $\rm MoS_2$. Theoretically, these parameters stem from modelling a single-layer two-dimensional crystal as a surface current, a truly two-dimensional model. Currently experimental practice is to consider this model equivalent to a homogeneous slab with an effective thickness given by the interlayer spacing of the exfoliating bulk material. We prove that the error in the evaluation of the surface susceptibility of monolayer $\rm MoS_2$, owing to the use of the slab model, is at least 10% or greater, a significant discrepancy in the determination of the optical properties of this material.