Theory-assisted detection of nano-rippling and impurities in STEM images of angle-mismatched bilayer graphene

ORAL

Abstract

Two-dimensional (2D) materials commonly contain ripples and impurity atoms that limit carrier mobilities, create pseudo-magnetic fields, and affect other electronic and magnetic properties. While scanning transmission electron microscopy (STEM) provides high-accuracy determination of the atomic positions and columns in the image plane, it is difficult to obtain precise atomic positions in the perpendicular direction. Detection of impurities with similar atomic numbers can also be difficult in Z-contrast imaging. In the case of multilayer 2D materials such as bilayer graphene, misalignment of the layers results in a moiré pattern that further compounds the problem of atomic identification. In this work, we introduce a combined approach utilizing STEM imaging and density-functional-theory calculations to recover this information from the experimentally accessible xy-coordinates in twisted bilayer graphene. We find that the strain-induced rippling obeys the continuum model of elasticity and that the moiré-pattern-induced undulations are approximately an order of magnitude smaller. Additionally, using the presented methodology, we are able to establish the presence of a substitutional nitrogen impurity.

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Presenters

  • Andrew O'Hara

    Physics, Vanderbilt University, Department of Physics and Astronomy, Vanderbilt University

Authors

  • Andrew O'Hara

    Physics, Vanderbilt University, Department of Physics and Astronomy, Vanderbilt University

  • Oleg S Ovchinnikov

    Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Department of Physics and Astronomy, Vanderbilt University

  • Jordan A. Hachtel

    Department of Physics and Astronomy, Vanderbilt University, Oak Ridge National Laboratory

  • Stephen Jesse

    Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge National Laboratory

  • Sergei Kalinin

    Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge National Laboratory

  • Albina Y Borisevich

    Center for Nanophase Materials Sciences, Oak Ridge National Lab, Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge National Laboratory

  • Sokrates T Pantelides

    Department of Physics and Astronomy, Vanderbilt University, Vanderbilt University, physics, Vanderbilt University, Physics, Vanderbilt University, Department of Physics and Astronomy and Department of Electrical Engineering and Computer Science, Vanderbilt University, Dept. of Physics and Astronomy, Vanderbilt University, USA