How high is a MoSe₂monolayer?

Area of Science:

• Materials Science
• Nanotechnology
• Condensed Matter Physics

Background:

• Transition metal dichalcogenides (TMDCs) are vital for optoelectronics, photovoltaics, and photoelectrochemistry.
• The performance of TMDCs depends heavily on their layer number.
• Layer counting is typically performed post-fabrication using optical and atomic force microscopy (AFM) methods.

Purpose of the Study:

• To investigate discrepancies in height measurements of exfoliated Molybdenum Diselenide (MoSe2) flakes.
• To evaluate the reliability of different AFM methods for layer counting.
• To highlight the influence of electrostatic forces on AFM height measurements.

Main Methods:

• Photoluminescence spectroscopy
• Raman spectroscopy
• Three distinct Atomic Force Microscopy (AFM) techniques

Main Results:

• Significant variations in MoSe2 flake height measurements were observed across different AFM methods.
• Electrostatic forces were identified as a potentially misleading factor in AFM height measurements.
• Discrepancies challenge the routine use of AFM for precise layer counting.

Conclusions:

• Standard AFM height measurements may not accurately determine the layer number of MoSe2 flakes.
• Careful consideration of measurement techniques and environmental factors is necessary for reliable TMDC characterization.
• Further development of accurate and consistent layer-counting methodologies is required for TMDC applications.