Article

# Tailoring Electrical Transport Across Grain Boundaries in Polycrystalline Graphene

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Department of Applied Physics, Cornell University, Ithaca, NY 14853, USA.
(Impact Factor: 33.61). 06/2012; 336(6085):1143-6. DOI: 10.1126/science.1218948
Source: PubMed

ABSTRACT

Graphene produced by chemical vapor deposition (CVD) is polycrystalline, and scattering of charge carriers at grain boundaries (GBs) could degrade its performance relative to exfoliated, single-crystal graphene. However, the electrical properties of GBs have so far been addressed indirectly without simultaneous knowledge of their locations and structures. We present electrical measurements on individual GBs in CVD graphene first imaged by transmission electron microscopy. Unexpectedly, the electrical conductance improves by one order of magnitude for GBs with better interdomain connectivity. Our study suggests that polycrystalline graphene with good stitching may allow for uniformly high electrical performance rivaling that of exfoliated samples, which we demonstrate using optimized growth conditions and device geometry.

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Available from: Fereshte Ghahari, Aug 21, 2015
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• "Graphene has been prepared using various methods since it was first isolated via mechanical exfoliation [10]: these include chemical vapor deposition (CVD) using metal (nickel [11], and copper [12]), SiC [13], and chemical exfoliation [14] [15] [16] [17]. Among those methods the CVD process provides opportunity for large-area graphene as well as layer control [8] [12], which result in excellent electrical [18] and mechanical [19] properties comparable to those of pristine exfoliated graphene. Graphene transfer on a desired silicon substrate utilizes protective polymer layer such as poly (methyl methacrylate) (PMMA) for various applications [8] [11] [20] [21]. "
##### Article: Role of Residual Polymer on Chemical Vapor Grown Graphene by Raman Spectroscopy
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ABSTRACT: Although various applications extensively utilize polymer-assisted graphene transfer step, the role of residual polymer on graphene was not well-understood. Here, we report the effect of poly (methyl methacrylate) (PMMA) on chemical vapor deposition-grown hexagonal graphene via Raman spectroscopy. Analysis of bare-, PMMA-covered supported, and PMMA-covered suspended graphene exhibits that their G and 2D band positions are progressively downshifted in that order. Mapping of spatial G and 2D band shifts into doping and strain contributions shows that PMMA residue exerts moderate 0.15% tensile strain on graphene/substrate, as compared to that of bare graphene. During this tensile strain, residual PMMA-covered graphene maintains its doping level as much as bare graphene does.
Full-text · Article · May 2015 · Carbon
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• "The formation of bump in GB has been reported by ab initio calculation [21]. Note that the formation of this bump is due to the presence of intrinsic strain originating from the lattice mismatch between the tilted grains. "
##### Article: Atomic-scale mechanism of grain boundary motion in graphene
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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.
Full-text · Article · Apr 2015 · Carbon
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• "For a long time presence of grain boundaries in graphene was treated as setback, but lately as GB's effect was understood to be very complex [13] [14] researchers turned to seek possible advantages of having localized lines of defects in graphene. It was shown that specific structure of GB should be taken into account as effect would vary with change of defects arrangement [15] [16] and selective use of GB may be used for specific purposes [17] [18] [19] [20]. "
##### Article: Kinetically determined shapes of grain boundaries in CVD graphene
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ABSTRACT: Predicting the shape of grain boundaries is essential to control results of the growth of large graphene crystals. A global energy minimum search predicting the most stable final structure contradicts experimental observations. Here we present Monte Carlo simulation of kinetic formation of grain boundaries (GB) in graphene during collision of two growing graphene flakes. Analysis of the resulting GBs for the full range of misorientation angles $\alpha$ allowed us to identify a hidden (from post facto analysis such as microscopy) degree of freedom - the edge misorientation angle $\beta$. Edge misorientation characterizes initial structure rather than final structure and therefore provides more information about growth conditions. Use of $\beta$ enabled us to explain disagreements between the experimental observations and theoretical work. Finally, we report an analysis of an interesting special case of zero-tilt GBs for which structure is determined by two variables describing the relative shift of initial islands. We thereby present analysis of the full range of tilt GB ( $\beta\neq$ 0) and translational GB ( $\beta$ = 0). Based on our findings we propose strategies of controlling the GB morphology in experiments, which paves the way to a better control over graphene structure and properties for advanced applications.
Full-text · Article · Dec 2014