Abstract
Abstract Bilayer graphene (BLG) grown via chemical vapor deposition (CVD) tends to exhibit twisted stacking. The twist angle θ t in twisted BLG (tBLG) provides a new degree of freedom for engineering its electronic and optical properties. In this paper, we investigate the θ t-dependent optical absorption in tBLG and deeply understand the electronic structure-optical properties correlations. New absorption peaks, whose wavelengths are modified by θ t, are observed on the feature of optical contrast (OC) in tBLG. Under the corresponding energy excitation, the Raman G mode in tBLG exhibits a significant enhancement. Furthermore, the results of θ t obtained by OC absorption peak are verified to be consistent with those by the Raman R mode. All these properties are proved to be related to the energy difference between low-energy Van Hove singularities (E VHS) in the density of states of tBLGs. This work builds a relation between optical absorption and twist angle, providing a viable method to identifying twist angles in tBLGs.
Highlights
The large-area and high-quality graphene films grown via chemical vapor deposition (CVD) have been of particular interest in the technological and practical applications due to its simplicity and cost effectiveness
Due to the novel electronic states caused by twist angle of twisted BLG (tBLG), absorption peak appears in optical contrast (OC) of tBLG whose energy is closely related to energy Van Hove singularities (EVHS) in joint density of states (JDOS)
The Raman G mode and R mode are significantly enhanced at EVHS
Summary
The large-area and high-quality graphene films grown via chemical vapor deposition (CVD) have been of particular interest in the technological and practical applications due to its simplicity and cost effectiveness. Novel physical properties emerge in tBLGs, such as Dirac-like linear dispersion with lower Fermi velocity than that in SLG [4], new Van Hove singularities (VHSs) [5] in the low-energy electronic density of states, and correlated insulator and superconductivity behaviors in magic-angle tBLG [6, 7] These properties provide the possibility of potential optoelectronic devices with multiple degrees of freedom, and it is essential to understand θt-property correlations in tBLGs. Raman spectroscopy of tBLG has provided evidence of intriguing θt-dependent optical properties [8, 9], these studies are not comprehensive enough to generalize tBLG with diverse θt because it is time-consuming and difficult to determine θt for a rapid measurement over a large area of samples. These provided an ideal platform by optical methods to study θt in tBLGs
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