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      Transport in Nanoribbon Interconnects Obtained from Graphene Grown by Chemical Vapor Deposition

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          Abstract

          We study graphene nanoribbon (GNR) interconnects obtained from graphene grown by chemical vapor deposition (CVD). We report low- and high-field electrical measurements over a wide temperature range, from 1.7 to 900 K. Room temperature mobilities range from 100 to 500 cm2/V/s, comparable to GNRs from exfoliated graphene, suggesting that bulk defects or grain boundaries play little role in devices smaller than the CVD graphene crystallite size. At high-field, peak current densities are limited by Joule heating, but a small amount of thermal engineering allows us to reach ~2 x 10^9 A/cm2, the highest reported for nanoscale CVD graphene interconnects. At temperatures below ~5 K, short GNRs act as quantum dots with dimensions comparable to their lengths, highlighting the role of metal contacts in limiting transport. Our study illustrates opportunities for CVD-grown GNRs, while revealing variability and contacts as remaining future challenges.

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          Most cited references 20

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          Atomically precise bottom-up fabrication of graphene nanoribbons.

          Graphene nanoribbons-narrow and straight-edged stripes of graphene, or single-layer graphite-are predicted to exhibit electronic properties that make them attractive for the fabrication of nanoscale electronic devices. In particular, although the two-dimensional parent material graphene exhibits semimetallic behaviour, quantum confinement and edge effects should render all graphene nanoribbons with widths smaller than 10 nm semiconducting. But exploring the potential of graphene nanoribbons is hampered by their limited availability: although they have been made using chemical, sonochemical and lithographic methods as well as through the unzipping of carbon nanotubes, the reliable production of graphene nanoribbons smaller than 10 nm with chemical precision remains a significant challenge. Here we report a simple method for the production of atomically precise graphene nanoribbons of different topologies and widths, which uses surface-assisted coupling of molecular precursors into linear polyphenylenes and their subsequent cyclodehydrogenation. The topology, width and edge periphery of the graphene nanoribbon products are defined by the structure of the precursor monomers, which can be designed to give access to a wide range of different graphene nanoribbons. We expect that our bottom-up approach to the atomically precise fabrication of graphene nanoribbons will finally enable detailed experimental investigations of the properties of this exciting class of materials. It should even provide a route to graphene nanoribbon structures with engineered chemical and electronic properties, including the theoretically predicted intraribbon quantum dots, superlattice structures and magnetic devices based on specific graphene nanoribbon edge states.
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            Imaging Grains and Grain Boundaries in Single-Layer Graphene: An Atomic Patchwork Quilt

            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 2D materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, a hexagonal two-dimensional crystal of carbon atoms; Single-atom-thick graphene sheets can now be produced by chemical vapor deposition on up to meter scales, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical, and mechanical properties which 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 microscope 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 via pentagon-heptagon pairs. We then 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 scanned probe measurements, we show that these grain boundaries dramatically weaken the mechanical strength of graphene membranes, but do not measurably 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 2D materials.
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              Raman scattering from high frequency phonons in supported n-graphene layer films

              Results of room temperature Raman scattering studies of ultrathin graphitic films supported on Si (111)/SiO2 substrates are reported. The results are significantly different from those known for graphite. Spectra were collected using 514 nm radiation on films containing from n=1 to 20 graphene layers, as determined by atomic force microscopy. Both the 1st and 2nd order Raman spectra show unique signatures of the number of layers in the film. The nGL film analog of the Raman G-band in graphite exhibits a Lorentzian lineshape whose center frequency shifts linearly relative to graphite as ~1/n (for n=1 G-band frequency ~1588 cm-1). Three weak bands, identified with disorder-induced 1st order scattering, are observed at ~ 1350, 1450 and 1500 cm-1. The 1500 cm-1 band is weak but relatively sharp and exhibits an interesting n-dependence. In general, the intensity of these D-bands decreases dramatically with increasing n. Three 2nd order bands are also observed (~2450, ~2700 and 3248 cm-1). They are analogs to those observed in graphite. However, the ~2700 cm-1 band exhibits an interesting and dramatic change of shape with n. Interestingly, for n<5 this 2nd order band is more intense than the G-band.
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                Author and article information

                Journal
                2012-09-02
                Article
                10.1021/nl300584r
                1209.0148

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                Custom metadata
                Nano Letters vol. 12, pp. 4424-4430 (2012)
                Nano Letters (2012); supplement available online
                cond-mat.mes-hall cond-mat.mtrl-sci

                Condensed matter, Nanophysics

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