Grains and grain boundaries in single-layer graphene atomic patchwork quilts. Nature 469:389

School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
Nature (Impact Factor: 41.46). 01/2011; 469(7330):389-92. DOI: 10.1038/nature09718
Source: PubMed


The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition on scales of up to metres, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical and mechanical properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here we use a combination of old and new transmission electron microscopy techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly through pentagon-heptagon pairs. Rather than individually imaging the several billion atoms in each grain, we use diffraction-filtered imaging to rapidly map the location, orientation and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanning probe and transport measurements, we show that these grain boundaries severely weaken the mechanical strength of graphene membranes but do not as drastically alter their electrical properties. These techniques open a new window for studies on the structure, properties and control of grains and grain boundaries in graphene and other two-dimensional materials.

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    • "Graphite, a precursor to produce graphene by exfoliation, has GBs with pentagoneheptagon line defects, so that they can change the geometrical chirality to form zigzag-and armchair-edge coexisting structures, which was proposed first by Terrones et al. [17] and observed experimentally later by scanning tunneling microscopy(STM ) in highly ordered pyrolytic graphite (HOPG) [18] [19]. So far, universal existence of GBs in graphene have also been confirmed in the transmission electron microscopy (TEM) and optical microscopy measurements [20] [21]. Recently, Lahiri, et al. [22] reported that structurally well-defined one-dimensional topological defect could be controllably introduced in epitaxial graphene, and found that such defects would yield a pronounced perturbation into the electronic structure. "

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    • "Transmission electron microscopy (TEM) analysis can provide significant information of the nitrogen dopant and other structures of graphene lattice [16]. Dark-field TEM (DF-TEM) and aberration-corrected annular dark-field scanning TEM (ADF- STEM) has been used to identify grain size and grain boundaries of CVD synthesized graphene in atomic scale [35]. These techniques provide insight of CVD synthesized graphene at atomic level to determine the induced defect structures. "
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    ABSTRACT: Doping of a foreign element in sp2 hybridized graphene lattice is of significant importance to tune the electrical and chemical properties. Here, we report on the grain structures of substitutional nitrogen-doped graphene synthesized by an atmospheric pressure (AP) solid source-based chemical vapor deposition (CVD) technique. Nitrogen-doped graphene was synthesized by mixing solid camphor and melamine as carbon and nitrogen source, respectively. The precursor materials quantity significantly affects the graphene growth on Cu foil and thereby the nitrogen doping and content. Transmission electron microscopy (TEM) analysis was performed to determine the nitrogen substitutional sites in the graphene. Dark-field (DF) TEM analysis was carried out to evaluate the graphene grain structure grown with introduction of nitrogen dopant. We obtained different grain orientations, where an individual grain size is more than 5 μm. Our findings show that graphitic nitrogen defects can be introduced in the large individual graphene grain by the developed solid source-based CVD technique.
    Carbon 09/2015; DOI:10.1016/j.carbon.2015.09.086 · 6.20 Impact Factor
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    • "In this work, combined AFM and Raman analysis was used to assess the crystallinity of the pads. Since AFM phase-imaging is sensitive to a number of chemical, structural and tribological properties and it is instrumental in revealing grain boundaries in monolayer graphene [18], circular pads were analysed by using this technique. Fig. 2 "
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    ABSTRACT: Recently, hexagonal boron nitride (h-BN) has been shown to act as an ideal substrate to graphene by greatly improving the material transport properties thanks to its atomically flat surface, low interlayer electronic coupling and almost perfect reticular matching [1]. Chemical vapour deposition (CVD) is presently considered the most scalable approach to grow graphene directly on h-BN. However, for the catalyst-free approach, poor control over the shape and crystallinity of the graphene grains and low growth rates are typically reported [2–5]. In this work we investigate the crystallinity of differently shaped grains and identify a path towards a real van der Waals epitaxy of graphene on h-BN by adopting a catalyst-free CVD process. We demonstrate the polycrystalline nature of circular-shaped pads and attribute the stemming of different oriented grains to airborne contamination of the h-BN flakes. We show that single-crystal grains with six-fold symmetry can be obtained by adopting high hydrogen partial pressures during growth. Notably, growth rates as high as 100 nm/min are obtained by optimizing growth temperature and pressure. The possibility of synthesizing single-crystal graphene on h-BN with appreciable growth rates by adopting a simple CVD approach is a step towards an increased accessibility of this promising van der Waals heterostructure.
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