▎ 摘　　要

Grain boundaries, the characteristic topological defects of chemical vapor deposition grown graphene samples, are expected to substantially alter the electronic properties of the unperturbed graphene lattice. However, there is very little experimental insight into the underlying mechanisms. Here, we systematically map the electronic properties of individual graphene grain boundaries by scanning tunneling microscopy and spatially resolved tunneling spectroscopy measurements. The tunneling spectroscopy data reveal that the conductivity inside the boundaries is markedly suppressed for both electron and hole-type charge carriers. Furthermore, graphene grain boundaries can give rise to n-type inversion channels within the p-doped graphene sheets, forming p-n junctions with sharp interfaces on the nanometer scale. These properties persist for grain boundaries of various configurations and are robust against structural disorder. (C) 2012 American Institute of Physics. [doi:10.1063/1.3681375]