Correlation between the optical absorption and twisted angle of bilayer graphene observed by high-resolution reflectance confocal laser microscopy

Abstract

We report a systematic study of the optical absorption of twisted bilayer graphene (tBLG) across a large range of twist angles from 0° to 30° using a high-resolution reflectance confocal laser microscopy (RCLM) system. The high-quality single crystalline tBLG was synthesized via the efficient plasma enhanced chemical vapor deposition techniques without the need of active heating. The sensitivity of acquired images from the RCLM were better than conventional optical microscopes. Although the highest spatial resolution of RCLM is still lower than scanning electron microscopes, it possesses the advantages of beam-damage and vacuum free. Moreover, the high intensity-resolution (sensitivity) images firstly allowed us to distinguish the slight absorption differences and analyze the correlation between the optical absorption and twisted angle of tBLG after data processing procedures. A maximum absorption (minimum transmission) was observed at the stacking angle of tBLG from 10° to 20°, indicating the interplay between the laser and the electron/hole van-Hove singularities when tBLG oriented around the critical angle (θ c ∼13°). The twisted angle correlated optical absorption paves an alternative way not only to visibly identify the interlayer orientation of tBLG but also to reflect the characterization of the interlayer coupling via its band structure.

Twisted Bilayer Graphene: A Journey Through Recent Advances and Future Perspectives

“…The developed photodetector consisted of metal-graphene-metal lay-ers and the results show that the photovoltage intensities depend on the number of graphene layers present and the twist angle. [160] Another study reported on the observation of photogalvanic effects in TBG and showed that the excitation of TBG causes a photocurrent depending on the orientation of the radiation electric field and photo helicity. The observed results may further assist in a deep understanding of the rich spectra of phenomena observed in TBG.…”

Angle-Resolved Optical Imaging of Interlayer Rotations in Twisted Bilayer Graphene

“…However, the current CVD process frequently produces TBG in irregular or joint grains with arbitrary rotation angles, which poses challenges in recognizing the twist angles of the TBG. To address these challenges, a variety of techniques have been employed to characterize the rotation angles of TBG, including transmission electron microscopy (TEM), , scanning probe microscopies (SPMs), − low-energy electron microscopy/diffraction (LEEM/LEED), , and Raman spectroscopy. ,− Among them, high-resolution microscopy techniques, such as TEM and SPM, provide highly precise angle determinations with an accuracy below ∼1°. However, these characterization techniques require samples with extremely clean surfaces and are typically time-consuming and labor-intensive.…”