Franck Condon shift assessment in 2D MoS₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Optical spectroscopy (OS) and density functional theory (DFT) are crucial for studying defects in 2D materials.
• Previous studies often assume negligible vibrational effects (Franck-Condon shift) in these calculations.
• Large FC shifts can misattribute observed spectral peaks to specific defect transitions.

Purpose of the Study:

• To investigate the magnitude of the Franck-Condon (FC) shift for sulfur vacancies in 2D molybdenum disulfide (MoS2).
• To validate the assumption of negligible FC shift in correlating OS and DFT results for defect characterization.
• To establish a reliable connection between experimental OS data and theoretical DFT predictions for defect-related emissions.

Main Methods:

• Utilized first-principles constrained DFT calculations.
• Employed the hybrid HSE06 functional for enhanced accuracy.
• Analyzed the electronic and structural properties related to sulfur vacancies in 2D MoS2.

Main Results:

• Demonstrated that the FC shift associated with electronic transitions from a sulfur vacancy in 2D MoS2 is small (~28 meV).
• Confirmed the validity of combining OS and DFT for defect analysis in this material.
• Showed that the 0.75 eV cathodoluminescence peak attribution is consistent with DFT predictions.

Conclusions:

• The assumption of a small FC shift is valid for sulfur vacancies in 2D MoS2.
• Direct correlation between DFT calculations and OS techniques is reliable for this material.
• A one-to-one relationship can be established between defect-related emission bands and electronic transitions from defect levels.