  Stacking order has strong influence on the coupling between the two layers of
twisted bilayer graphene (BLG), which in turn determines its physical
properties. Here, we report the investigation of the interlayer coupling of the
epitaxially grown single-crystal 30{\deg} twisted BLG on Cu(111) at the atomic
scale. The stacking order and morphology of BLG is controlled by a rationally
designed two-step growth process, that is, the thermodynamically controlled
nucleation and kinetically controlled growth. The crystal structure of the
30{\deg}-twisted bilayer graphene (30{\deg}-tBLG) is determined to have the
quasicrystal like symmetry. The electronic properties and interlayer coupling
of the 30{\deg}-tBLG is investigated using scanning tunneling microscopy (STM)
and spectroscopy (STS). The energy-dependent local density of states (DOS) with
in-situ electrostatic doping shows that the electronic states in two graphene
layers are decoupled near the Dirac point. A linear dispersion originated from
the constituent graphene monolayers is discovered with doubled degeneracy. This
study contributes to controlled growth of twist-angle-defined BLG, and provides
insights of the electronic properties and interlayer coupling in this
intriguing system.
