Twisted bilayer graphene provides an ideal solid-state
model to
explore correlated material properties and opportunities for a variety
of optoelectronic applications, but reliable, fast characterization
of the twist angle remains a challenge. Here we introduce spectroscopic
ellipsometric contrast microscopy (SECM) as a tool for mapping twist
angle disorder in optically resonant twisted bilayer graphene. We
optimize the ellipsometric angles to enhance the image contrast based
on measured and calculated reflection coefficients of incident light.
The optical resonances associated with van Hove singularities correlate
well to Raman and angle-resolved photoelectron emission spectroscopy,
confirming the accuracy of SECM. The results highlight the advantages
of SECM, which proves to be a fast, nondestructive method for characterization
of twisted bilayer graphene over large areas, unlocking process, material,
and device screening and cross-correlative measurement potential for
bilayer and multilayer materials.