Silicon-carbon bond inversions driven by 60 keV electrons in graphene

Silicon-carbon bond inversions driven by 60 keV electrons in graphene
Toma Susi, Jani Kotakoski, Demie Kepatsoglou, Clemens Mangler, Tracy C. Lovejoy, Ondrej L. Krivanek, Recep Zan, Ursel Bangert, Paola Ayala, Jannik C. Meyer, Quentin Ramasse
Faculty of Physics, University of Vienna, Vienna, Austria SuperSTEM Laboratory, STFC Daresbury Campus, Daresbury, United Kingdom Faculty of Physics, University of Vienna, Vienna, Austria Nion Co., Kirkland, Washington, United States School of Materials, University of Manchester, Manchester, United Kingdom Faculty of Physics, University of Vienna, Vienna, Austria SuperSTEM Laboratory, STFC Daresbury Campus, Daresbury, United Kingdom
toma.susi@univie.ac.at
Single-layer graphene is arguably an ideal material for atomic resolution electron microscopy. But even in the so-called 'gentle' conditions used for atom-by-atom investigations, beam damage effects cannot be neglected. Imperfections such as doping also change the effect an electron beam has on the atomic structure of graphene, as we have recently shown for nitrogen substitutions [1]. We now demonstrate that 60 keV electron irradiation drives the diffusion of threefold coordinated Si dopants in graphene by one lattice site at a time [2]. First principles molecular dynamics simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely than the direct bond inversion. Our results thus provide a model of non-destructive and atomically precise structural modification and detection for two-dimensional materials. [1] T. Susi, J. Kotakoski, R. Arenal, S. Kurasch, H. Jiang, V. Skakalova, O. Stephan, A. V. Krasheninnikov, E. I. Kauppinen, U. Kaiser, and J. C. Meyer, ACS Nano 6, 8837 (2012). [2] T. Susi et al., submitted (2014)