Low-Frequency Interlayer Raman Modes to Probe Interface of Twisted Bilayer MoS2

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Van der Waals (vdW) homo- and heterostructures, assembled by stacking monolayers, offer tunable optoelectronic properties for advanced applications.
• Interlayer stacking and coupling critically influence the properties of these 2D materials, necessitating detailed investigation.

Purpose of the Study:

• To investigate the low-frequency interlayer shear and breathing Raman modes in twisted bilayer molybdenum disulfide (MoS2).
• To understand how twisting influences interlayer stacking and coupling, and consequently, the material's properties.

Main Methods:

• Utilized Raman spectroscopy to analyze low-frequency interlayer shear and breathing modes (<50 cm(-1)) in twisted bilayer MoS2.
• Employed first-principles modeling to complement experimental observations and elucidate stacking-dependent phenomena.

Main Results:

• Twisting significantly alters interlayer stacking and coupling, causing notable changes in the frequency (up to 8 cm(-1)) and intensity (up to ~5x) of low-frequency Raman modes, especially near 0° and 60° twist angles.
• Interlayer coupling remains nearly constant for twist angles between 20° and 40° due to mismatched lattices, resulting in a uniform Raman signature.
• Multiple breathing mode peaks observed in some samples indicate nonuniform interfacial coupling.

Conclusions:

• Low-frequency Raman modes are highly effective for probing interfacial coupling and the local environment in twisted bilayer MoS2.
• This approach holds promise for characterizing other 2D materials and heterostructures with tunable interlayer interactions.