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Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol

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Stacking-dependent optical properties in bilayer WSe₂.

Kathleen M McCreary¹, Madeleine Phillips¹, Hsun-Jen Chuang²

¹Naval Research Laboratory, Washington, DC 20375, USA. kathleen.mccreary@nrl.navy.mil.

|December 14, 2021

Summary

This summary is machine-generated.

The twist angle in WSe2 bilayers significantly alters optical properties. Researchers found distinct spectral shifts and Raman responses between 2H and 3R stacking, explained by DFT calculations.

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Area of Science:

Materials Science
Condensed Matter Physics
Nanotechnology

Background:

Van der Waals heterostructures offer tunable material properties via twist angle.
Tuning the interlayer twist angle in WSe2 bilayers impacts their electronic and optical characteristics.

Purpose of the Study:

To investigate the stacking-dependent optical properties of WSe2 homobilayers.
To compare 2H and 3R stacking configurations using various spectroscopic techniques.
To elucidate the underlying physics of stacking-dependent optical variations using DFT.

Main Methods:

Photoluminescence spectroscopy
Raman spectroscopy
Reflectance contrast measurements
Density Functional Theory (DFT) calculations

Main Results:

Stacking-dependent differences in optical properties were observed at both ambient and cryogenic temperatures.
A blue shift in spectral features was noted for 2H compared to 3R stacking in photoluminescence and reflectance contrast.
DFT calculations confirmed larger exciton energies for 2H stacking.
Raman mode intensity showed resonant enhancement dependent on laser excitation wavelength, stacking, and temperature.

Conclusions:

The twist angle in WSe2 bilayers is a critical factor influencing optical properties.
2H and 3R stacking exhibit distinct excitonic features and optical responses.
Resonant enhancement effects play a key role in the observed Raman intensity variations.