  Graphite crystals used to prepare graphene-based heterostructures are
generally assumed to be defect free. We report here scanning tunneling
microscopy results that show that graphite commonly used to prepare graphene
devices can contain a significant amount of native defects. Extensive scanning
of the surface allows us to determine the concentration of native defects to be
6.6$\times$10$^8$ cm$^{-2}$. We further study the effects of these native
defects on the electronic properties of Bernal-stacked bilayer graphene. We
observe gate-dependent intravalley scattering and successfully compare our
experimental results to T-matrix-based calculations, revealing important
carrier density dependence in the distribution of the scattering vectors. We
also present a technique for evaluating the spatial dependence of short-scale
scattering (intervalley scattering in our case), revealing a
spatially-dependent coupling between inter- and intra-valley scattering. Our
findings suggest that the impact of native defects on the electronic properties
of graphene devices could be more important than previously thought.
