AVS 61st International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP18
Conductivity of Graphene as a Function of its Lattice Orientation Relative to Substrate Layers

Tuesday, November 11, 2014, 6:30 pm, Room Hall D

Session: Surface Science Poster Session
Presenter: Hyunsoo Lee, KAIST, Republic of Korea
Authors: H. Lee, KAIST, Republic of Korea
Y. Qi, Okinawa Institute of Science and Technology Graduate University, Japan
S. Kwon, KAIST, Republic of Korea
M.B. Salmeron, Lawrence Berkeley National Laboratory
J.Y. Park, KAIST, Republic of Korea
Correspondent: Click to Email
We report strongly varying electrical transport properties of graphene layers on graphite that depend on the relative lattice orientation of the surface and subsurface layers. Employing the pressure dependence of conductance on the surface of highly ordered pyrolytic graphene (HOPG) using the conductive tip of an atomic force microscope as an electrode, we found that the electrical conductivity of graphite terraces separated by steps can vary by large factors of up to 100. This effect can be attributed to interlayer interactions when stacked commensurately in a Bernal sequence (ABAB…), which opens a band gap, while rotational misaligned layers behave as graphene. Small angular misorientations of a few degrees were found to give rise to large increases in the conductivity of the top layer, with the maximum occurring at around 30°. In addition, two types of steps were encountered on HOPG surface: external steps where the edge C atoms have dangling or broken bonds, and internal steps where the bonds are only broken in the second layer or deeper. Accordingly, graphite layers covering several underlying terraces and steps retain the same conductivity across the terraces. Top layer terraces have higher friction on the edges, making it easy to distinguish them from subsurface steps where no friction changes occur. These results suggest new applications for graphene multilayers using stacked layers at various angles to control the resistance of connected graphene ribbons in devices.