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

ABSTRACT 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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    • "On the third question, it will be extremely interesting to develop techniques to fabricate graphene structures with deliberately designed defect patterns. Currently, chemical vapor deposition (CVD) [13] [14], a popular method to grow large scale graphene, can only produce samples with randomly distributed defects. A recent study has explored using irradiation to control the types and positions of defects in graphene [15], which provides a promising way to make tailored graphene structures. "
    Journal of Applied Mechanics 05/2015; 82(5). DOI:10.1115/1.4030052 · 1.37 Impact Factor
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    • "In 2011, the first experimental study was conducted on polycrystalline graphene and the failure strength was found to be $35 GPa [12], about a quarter of that of single crystalline graphene. Huang et al. [13] examined the failure strength of polycrystalline graphene by AFM and showed that grain boundaries (GBs) can severely weaken the mechanical strength. Unfortunately, current techniques of producing large areas of graphene sheets via chemical vapor deposition (CVD) growth on metal foils [14] [15] [16] [17] result in the inevitable formation of GBs. "
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    ABSTRACT: We investigate the mechanical properties of polycrystalline graphene deforming under uniaxial tension by using molecular dynamics simulations, focusing on the effects of grain size, temperature and strain rate. It is found that polycrystalline graphene with smaller grain size shows a larger drop of Young’s modulus and fracture strength. For the polycrystalline graphene with grain size of 7.5 nm, the Young’s modulus and fracture strength is about 80% and 40% that of single-crystalline graphene, respectively. Our simulation results also reveal that the Young’s modulus and fracture strength of polycrystalline graphene are more sensitive to the changes of temperature and strain rate than that of single-crystalline graphene. When temperature increases from 100 to 1200 K, the fracture strength of polycrystalline graphene reduces by around 45%. At room temperature (300 K), the fracture strength of polycrystalline graphene increases by 10% as the strain rate increases from 5 × 10−5 to 5 × 10−3 ps−1. Furthermore, the strain rate has a stronger influence on the fracture strength of polycrystalline graphene at a higher temperature than at a lower temperature; while the temperature has a stronger influence at a lower strain rate than at a higher strain rate. Our study thus provides a comprehensive understanding of the mechanical properties of polycrystalline graphene.
    Carbon 04/2015; 85. DOI:10.1016/j.carbon.2014.12.092 · 6.20 Impact Factor
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    • "The CVD methods have also provided new possibilities for controlling the properties of graphene due to its polycrystalline nature. It has been found that graphene grown using CVD methods (CVD graphene) is highly likely to form multiple grains accompanied by the formation of various types of grain boundaries (GBs) [16] [18] [19]. The properties of graphene can significantly change depending on the types of GBs present in the CVD graphene sample [20] [21] [22] [23]. "
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    ABSTRACT: Grain boundaries (GBs) in graphene can migrate when irradiated by electron beams from a transmission electron microscope (TEM). Here, we present an ab initio study on the atomic scale-mechanism for motion of GB with misorientation angle of ∼30° in graphene. From total energy calculations and energy barrier calculations, we find that a Stone-Wales (SW)-type transformation can occur more easily near GBs than in pristine graphene due to a reduced energy barrier of 7.23 eV; thus, this transformation is responsible for the motion of GBs. More interestingly, we find that a mismatch in the crystalline orientation at GBs can drive the evaporation of a carbon dimer by greatly reducing the corresponding overall energy barrier to 11.38 eV. After evaporation of the carbon dimer, the GBs can be stabilized through a series of SW-type transformations that result in GB motion. The GB motion induced by evaporation of the dimer is in excellent agreement with recent TEM experiments. Our findings elucidate the mechanism for the dynamics of GBs during TEM experiments and enhance the controllability of GBs in graphene.
    Carbon 04/2015; 84(1):146-150. DOI:10.1016/j.carbon.2014.12.009 · 6.20 Impact Factor
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