Transfer of monolayer TMD WS₂ and Raman study of substrate effects

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenides (TMDs) like tungsten disulfide (WS2) are crucial for next-generation electronics.
• Controlling the properties of WS2 flakes after transfer is essential for device fabrication.
• Understanding substrate interactions is key to optimizing TMD-based devices.

Purpose of the Study:

• To report a facile transfer process for WS2 flakes.
• To investigate the influence of different substrates on the properties of transferred WS2 flakes.
• To differentiate between transfer effects and substrate interaction effects on WS2.

Main Methods:

• WS2 flakes were transferred using a polymethyl methacrylate (PMMA) assisted wet etch process.
• Flakes were transferred onto various substrates including HfO2, parylene-C, and graphene.
• Raman spectroscopy was employed to analyze material quality and substrate-induced property changes.

Main Results:

• A reliable method for transferring WS2 flakes onto diverse substrates was established.
• Raman spectroscopy confirmed the quality of transferred WS2 flakes.
• Significant changes in WS2 Raman spectra were observed due to substrate interactions, affecting both in-plane and out-of-plane phonon modes.
• Strongest substrate effects were noted on graphene and HfO2.

Conclusions:

• The transfer process is effective for preparing WS2 flakes on various substrates.
• Substrate interactions significantly modify the intrinsic properties of WS2 flakes.
• Understanding and controlling these substrate effects is critical for the successful development of WS2-based electronic and optoelectronic devices.