Grain Boundary Mapping in Polycrystalline Graphene
Using advanced electron microscopes at the National Center for Electron Microscopy, researchers have reported direct mapping of grains and grain boundaries in large-area monolayer polycrystalline graphene sheets, at length scales from micrometers to single atoms. Global mapping is performed using electron diffraction in scanning transmission electron microscopy or using dark-field imaging. Additionally, the TEAM microscope is used to extract direct images of the local atomic arrangements of graphene grain boundaries. The images reveal a characteristic alternating pentagon-heptagon structure along high-angle boundaries. The methods can readily be used to assess the quality of polycrystalline graphene samples and aid in engineering grain boundaries to exploit their peculiar electronic properties. These findings will likely benefit future theoretical and experimental studies on thin membrane grains and grain boundaries, including boundary diffusion, electronic structure modification, and possible enhanced chemical reactivity at the boundary.
This research was supported in part by the Director, Office of Energy Research, Materials Sciences and Engineering Division, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 which provided for preliminary TEM and Raman characterization; by the National Science Foundation within the Center of Integrated Nanomechanical Systems, under Grant EEC-0832819, which provided for CVD graphene synthesis; and by the National Science Foundation under Grant No. 0906539 which provided for design of the experiment, suspended sample preparation, and analysis of the results. Portions of the present study were performed at the National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, which is supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. K.K. acknowledges further support from a Samsung Scholarship, and W.R. acknowledges support through a National Science Foundation Graduate Research Fellowship.