  Atomically resolved imaging and spectroscopic characteristics of graphene
grown by chemical vapor deposition (CVD) on copper are investigated by means of
scanning tunneling microscopy and spectroscopy (STM/STS). For CVD-grown
graphene remaining on the copper substrate, the monolayer carbon structures
exhibit ripples and appear strongly strained, with different regions exhibiting
different lattice structures and electronic density of states (DOS). In
particular, ridges appear along the boundaries of different lattice structures,
which exhibit excess charging effects. Additionally, the large and non-uniform
strain induces pseudo-magnetic field up to ~ 50 Tesla, as manifested by the
integer and fractional pseudo-magnetic field quantum Hall effect (IQHE and
FQHE) in the DOS of graphene. In contrast, for graphene transferred from copper
to SiO2 substrates after the CVD growth, the average strain on the whole is
reduced, so are the corresponding charging effects and pseudo-magnetic fields
except for sample areas near topographical ridges. These findings suggest
feasible "strain engineering" of the electronic states of graphene by proper
design of the substrates and growth conditions.
