Fast Twist Angle Mapping of Bilayer Graphene Using Spectroscopic Ellipsometric Contrast Microscopy

Area of Science:

• Condensed matter physics
• Materials science
• Optoelectronics

Background:

• Twisted bilayer graphene is a key material for exploring correlated electronic properties and optoelectronic applications.
• Accurate and rapid characterization of the twist angle in twisted bilayer graphene is crucial but remains a significant challenge.
• Existing methods for twist angle determination can be time-consuming or destructive.

Purpose of the Study:

• To introduce and validate spectroscopic ellipsometric contrast microscopy (SECM) as a novel tool for mapping twist angle disorder.
• To optimize SECM parameters for enhanced contrast in imaging twisted bilayer graphene.
• To demonstrate the capability of SECM for large-area, nondestructive characterization.

Main Methods:

• Development and application of spectroscopic ellipsometric contrast microscopy (SECM).
• Optimization of ellipsometric angles based on reflection coefficients for improved image contrast.
• Correlation of SECM results with established techniques like Raman spectroscopy and angle-resolved photoelectron emission spectroscopy (ARPES).

Main Results:

• SECM successfully maps twist angle disorder in twisted bilayer graphene with high contrast.
• Optical resonances observed via SECM align with van Hove singularities, confirming accuracy.
• SECM measurements show strong correlation with Raman and ARPES data, validating the technique's precision.

Conclusions:

• SECM is a fast, nondestructive, and accurate method for characterizing twist angle in twisted bilayer graphene over large areas.
• The technique facilitates efficient screening of materials and devices.
• SECM opens new avenues for cross-correlative measurements in bilayer and multilayer systems.