Imaging grain boundary scattering of graphene in real space

Graphene grain boundaries are unavoidable defects in most growth methods, in particular chemical vapor deposition and thermal decomposition on the SiC(000\underline {1}) surface. How electrons are scattered by those grain boundaries has not been experimentally demonstrated at the nanoscale. Here we report atomic-scale images of grain boundary scattering measured by scanning tunneling potentiometry (STP). Monolayer graphene sheets were synthesized on the SiC(000\underline {1}) surface by thermal decomposition in a background of disilane, using low energy electron microscopy to monitor the graphene thickness during its formation. High resolution scanning tunneling microscopy (STM) reveals graphene grain boundaries and various grain orientations, and STP shows variations in voltage across grains and terraces as current flows across the graphene layer. We have identified two types of grain boundary. One shows a trench structure in STM images; potential mapping shows prominent potential drops. These boundaries between grains appear to be weak links and the dominant scattering locations. The other type of boundary shows a continuous lattice between the grains, with periodic dislocations accommodating the grain misorientation. Potential mapping indicates much weaker scattering despite the grain misorientation. We will discuss transport in polycrystalline graphene based on these measurements.