  Recent advances in large-scale synthesis of graphene and other 2D materials
have underscored the importance of local defects such as dislocations and grain
boundaries (GBs), and especially their tendency to alter the electronic
properties of the material. Understanding how the polycrystalline morphology
affects the electronic properties is crucial for the development of
applications such as flexible electronics, energy harvesting devices or
sensors. We here report on atomic scale characterization of several GBs and on
the structural-dependence of the localized electronic states in their vicinity.
Using low temperature scanning tunneling microscopy (STM) and spectroscopy
(STS), together with tight binding and ab initio numerical simulations we
explore GBs on the surface of graphite and elucidate the interconnection
between the local density of states (LDOS) and their atomic structure. We show
that the electronic fingerprints of these GBs consist of pronounced resonances
which, depending on the relative orientation of the adjacent crystallites,
appear either on the electron side of the spectrum or as an electron-hole
symmetric doublet close to the charge neutrality point. These two types of
spectral features will impact very differently the transport properties
allowing, in the asymmetric case to introduce transport anisotropy which could
be utilized to design novel growth and fabrication strategies to control device
performance.
