Graphene grain boundary resistivity revealed by scanning tunneling potentiometry

All large-scale graphene films contain extended topological defects dividing graphene into domains or grains. Here, we study grain boundary (GB) resistivity in CVD graphene on Cu subsequently transferred to a SiO2 substrate. By using a scanning tunneling potentiometry (STP) setup with a cryogenic four-probe STM, the spatial variation of the local electrochemical potential is resolved across individual GBs on a graphene surface in the presence of a current [1]. The 2D distributions of electric field and conductivity were then numerically extracted by solving conduction equations. The derived conductivity of individual grains was compared to that measured with microscopic four-probe STM method to provide a model-independent determination of conductivity map for specific type of defect in graphene. The resistance of a GB is found to change with the width of the disordered transition region between adjacent grains. A quantitative modeling of boundary resistance reveals the increased electron Fermi wave vector within the boundary region, possibly due to boundary induced charge density variation. [1] K. W. Clark et al. ACS Nano 2013, 7, 7956