Direct growth of twisted bilayer graphene with controllable twist angle by plasma-enhanced chemical vapor deposition*

We report a direct plasma-enhanced chemical vapor deposition (PECVD) method to grow single crystalline bilayer graphene (BLG) flakes and mm-size BLG films with the interlayer twist angle controlled by the growth parameters.¹ The average twist angle can be controlled from 0° to approximately 20° by tuning the CH₄-to-H₂ pressure ratio (P_CH4/P_H2). Raman spectroscopic studies on our PECVD-grown BLG together with x-ray and ultraviolet-light photoelectron spectroscopy indicate high-quality samples and reveal twist-angle dependent spectral characteristics. Atomically resolved scanning tunneling microscope (STM) is employed to identify the Moiré pattern and the value of the corresponding twist angle between two layers. Our PECVD-grown BLG provides a perfect platform to study the twist-angle dependence of its electronic properties. We performed transport measurements on our BLG samples with twist angles varying between 0° and 20°. The electronic properties of BLG of different twist angles are systematically investigated as a function of temperature and gate voltage, which provides useful information for the origin of various correlated phenomena.