  Tailoring the interlayer twist angle of bilayer graphene (BLG) has a
significant influence on its electronic properties, including
superconductivity, topological transitions, ferromagnetic states and correlated
insulating states. These exotic electronic properties are sensitively dependent
on the work functions of bilayer graphene samples. Here, the twisted
angle-dependent work functions of CVD-grown twisted bilayer graphene (tBLG) are
detailed investigated by Kelvin Probe Force Microscopy (KPFM) in combination
with Raman spectra. The thickness-dependent surface potentials of
Bernal-stacked multilayer graphene were measured. The AB-BLG and tBLG are
directly determined by KPFM due to their twist angle-specific surface
potentials. The detailed relationship of twist angles and surface potentials
are further obtained by the in-situ combination investigation of KPFM and Raman
spectra measurements. The thermal stability of tBLG was further explored
through controlled annealing process. Our work provides the twisted
angle-dependent surface potentials of tBLG and lays the foundation for further
exploring their twist-angle-dependent novel electronic properties.
