Imaging spectroscopic ellipsometry of MoS2.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Molybdenum disulfide (MoS2) is a promising 2D material with unique electronic and optical properties.
• Understanding the optical constants of MoS2 is crucial for its application in optoelectronic devices.

Purpose of the Study:

• To investigate the optical properties of micromechanically exfoliated MoS2 monolayers and multilayers.
• To determine the complex dielectric functions and absorbance of MoS2 flakes on various substrates.
• To assess the lateral homogeneity of optical properties and identify factors influencing them.

Main Methods:

• Spectroscopic imaging ellipsometry combined with knife edge illumination for flake detection and classification.
• Analysis of ellipsometric angles using multilayer models with anisotropic and isotropic fit approaches.
• Complementary micro-Raman spectroscopy for assessing material quality.

Main Results:

• Complex dielectric functions for monolayer and trilayer MoS2 were extracted.
• Optical constants' critical point energies were model-independent, but magnitudes varied.
• Anisotropic model indicated ~14% absorbance for monolayer and ~10% for trilayer MoS2 on sapphire.
• Minor lateral fluctuations in dielectric functions were observed, attributed to van der Waals interactions from preparation.

Conclusions:

• Spectroscopic ellipsometry is effective for characterizing MoS2 flakes on diverse substrates with high lateral resolution.
• The optical properties of MoS2 are sensitive to preparation-induced variations in interlayer interactions.
• Micromechanically exfoliated MoS2 monolayers exhibit high quality in wrinkle-free regions, as confirmed by Raman spectroscopy.