Twisted MoSe₂ Bilayers with Variable Local Stacking and Interlayer Coupling Revealed by Low-Frequency Raman...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Transition metal dichalcogenide (TMD) bilayers, such as MoSe2, are crucial for novel electronic and optoelectronic applications.
• Controlling interlayer coupling and stacking configurations in TMD bilayers is essential for tuning their properties.

Purpose of the Study:

• To investigate the stacking configurations and interlayer couplings in MoSe2 bilayers within a specific range of twist angles.
• To understand the relationship between twist angle, stacking orientation, and the resulting material properties.

Main Methods:

• Low-frequency Raman spectroscopy was employed to experimentally probe the vibrational modes.
• Ab initio theoretical modeling was used to predict and interpret the spectral features based on stacking configurations.

Main Results:

• Unique twisted MoSe2 bilayers with multiple stacking configurations (AA', AB', A'B) were identified in the twist angle range of 60 ± 3°.
• The presence of different stacking configurations was experimentally confirmed by observing two distinct breathing modes in Raman spectra.
• Theoretical calculations accurately predicted changes in low-frequency mode frequencies and intensities with varying twist angles and stacking.

Conclusions:

• Deviations from the ideal 60° twist angle in MoSe2 bilayers lead to a coexistence of multiple high-symmetry stacking domains.
• The observed variable interlayer coupling and spacing offer a promising platform for developing next-generation optoelectronic devices based on TMDs.