A Systematic Scanning Electron Microscopy Study on MoS2 Layers Using In-lens Detector and Everhart-Thornley Detector

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Molybdenum disulfide (MoS2) is a key transition metal dichalcogenide with diverse electronic properties.
• Characterizing MoS2 layers, especially monolayer films, using Scanning Electron Microscopy (SEM) is crucial for understanding their behavior.
• Optimizing SEM imaging parameters is essential for accurate material analysis.

Purpose of the Study:

• To systematically investigate the SEM imaging contrast of monolayer MoS2 on different substrates.
• To compare the effectiveness of in-lens and Everhart-Thornley detectors for MoS2 imaging.
• To elucidate the mechanisms behind contrast variations with changing SEM parameters.

Main Methods:

• Systematic SEM imaging of CVD-grown and exfoliated MoS2 on SiO2/Si and Si substrates.
• Utilized both in-lens and Everhart-Thornley detectors.
• Varied acceleration voltage and working distance during imaging.

Main Results:

• The in-lens detector provides superior MoS2 contrast, appearing darker than the substrate (mass-thickness contrast), even at 10 kV and 20 mm working distance.
• The Everhart-Thornley detector exhibits contrast reversal: MoS2 appears brighter (atomic number contrast) at ≤10 mm and darker at ≥15 mm working distance.
• The study analyzed secondary electron (SE) responses to explain contrast mechanisms.

Conclusions:

• The in-lens detector is highly effective for MoS2 SEM characterization, offering consistent and superior contrast.
• Understanding contrast mechanisms with different detectors and parameters is vital for accurate MoS2 analysis.
• These findings facilitate improved SEM characterization of MoS2 and other transition metal dichalcogenides.