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Graphene-layered steps and their fields visualized by 4D electron microscopy

Park, Sang Tae, Yurtsever, Aycan, Baskin, John Spencer, Zewail, Ahmed H.
Proceedings of the National Academy of Sciences of the United States of America 2013 v.110 no.23 pp. 9277-9282
electric field, electrons, graphene, image analysis, mathematical models, nanomaterials, transmission electron microscopy
Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses.