Defect activated optical Raman modes in single layer MoSe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenides (TMDs) are crucial for optoelectronics, but defect quantification remains a challenge.
• Understanding and controlling defects are key to optimizing TMD performance in devices.
• Raman spectroscopy has proven effective for defect analysis in 2D materials like graphene.

Purpose of the Study:

• To develop a method for quantifying defects in monolayer Molybdenum Diselenide (MoSe2).
• To investigate the origin of defect-activated Raman bands in MoSe2.
• To establish a defect quantification model applicable to TMDs for technological applications.

Main Methods:

• Monolayer MoSe2 was bombarded with Helium ions to introduce defects.
• Raman spectroscopy was used to identify defect-activated Raman bands.
• Density functional theory (DFT) calculations were performed to analyze electronic and phonon properties.

Main Results:

• Three defect-activated Raman bands were observed in MoSe2 between 250-300 cm-1.
• DFT calculations suggest these bands originate from inter-valley Raman double resonance processes.
• A defect quantification model, similar to that used for graphene, was found to be applicable to TMDs.

Conclusions:

• This research establishes a pathway for macroscopic defect quantification in TMDs.
• The findings are essential for advancing the use of TMDs in optoelectronic devices.
• The study demonstrates the potential of Raman spectroscopy for defect analysis in 2D materials.