Visibility of dichalcogenide nanolayers

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Dichalcogenides (MX2) are layered materials with tunable electrical properties.
• Ultrathin two-dimensional (2D) materials offer unique electronic and optical characteristics.
• Optical detection methods are crucial for characterizing nanoscale materials.

Purpose of the Study:

• To establish optimal imaging conditions for the optical detection of ultrathin dichalcogenide nanocrystals.
• To develop an optical model for predicting contrast of nanolayers on SiO2 substrates.
• To differentiate between single, double, and triple layers of MoS2, WSe2, and NbSe2.

Main Methods:

• Development of a simple optical model to calculate contrast for nanolayers on SiO2 wafers.
• Extension of the optical model for imaging using the green channel of a video camera.
• Utilizing Atomic Force Microscopy (AFM) and optical imaging for confirmation.

Main Results:

• Confirmed optical detection of single layers of MoS2 and WSe2 on 90 nm and 270 nm SiO2.
• Demonstrated the ability to distinguish between single, double, and triple layers of MoS2 and WSe2 via contrast measurements.
• Observed and discussed discrepancies in the optical detection of NbSe2.

Conclusions:

• Optimal optical imaging conditions were identified for detecting and characterizing ultrathin dichalcogenide layers.
• The developed optical model provides a reliable method for predicting contrast and layer number.
• Further investigation is needed to understand the behavior of NbSe2 using this optical technique.