Graphene-layered steps and their fields visualized by 4D 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.
Additional Information© 2013 National Academy of Sciences. Freely available online through the PNAS open access option. Contributed by Ahmed H. Zewail, April 9, 2013 (sent for review March 14, 2013). This work was supported by National Science Foundation Grant DMR-0964886 and Air Force Office of Scientific Research Grant FA9550-11-1-0055 for research conducted in The Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. Author contributions: A.Y. and A.H.Z. designed research; S.T.P., A.Y., and J.S.B. performed research; S.T.P., A.Y., and J.S.B. analyzed data; and S.T.P., A.Y., J.S.B., and A.H.Z. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1306661110//DCSupplemental.
Published - PNAS-2013-Park-9277-82.pdf
Supplemental Material - sapp.pdf