88 research outputs found
Direct Imaging of Graphene Edges: Atomic Structure and Electronic Scattering
We report an atomically-resolved scanning tunneling microscopy (STM)
investigation of the edges of graphene grains synthesized on Cu foils by
chemical vapor deposition (CVD). Most of the edges are macroscopically parallel
to the zigzag directions of graphene lattice. These edges have microscopic
roughness that is found to also follow zigzag directions at atomic scale,
displaying many ~120 degree turns. A prominent standing wave pattern with
periodicity ~3a/4 (a being the graphene lattice constant) is observed near a
rare-occurring armchair-oriented edge. Observed features of this wave pattern
are consistent with the electronic intervalley backscattering predicted to
occur at armchair edges but not at zigzag edges
Facile Synthesis of High Quality Graphene Nanoribbons
Graphene nanoribbons have attracted attention for their novel electronic and
spin transport properties1-6, and because nanoribbons less than 10 nm wide have
a band gap that can be used to make field effect transistors. However,
producing nanoribbons of very high quality, or in high volumes, remains a
challenge. Here, we show that pristine few-layer nanoribbons can be produced by
unzipping mildly gas-phase oxidized multiwalled carbon nanotube using
mechanical sonication in an organic solvent. The nanoribbons exhibit very high
quality, with smooth edges (as seen by high-resolution transmission electron
microscopy), low ratios of disorder to graphitic Raman bands, and the highest
electrical conductance and mobility reported to date (up to 5e2/h and 1500
cm2/Vs for ribbons 10-20 nm in width). Further, at low temperature, the
nanoribbons exhibit phase coherent transport and Fabry-Perot interference,
suggesting minimal defects and edge roughness. The yield of nanoribbons was ~2%
of the starting raw nanotube soot material, which was significantly higher than
previous methods capable of producing high quality narrow nanoribbons1. The
relatively high yield synthesis of pristine graphene nanoribbons will make
these materials easily accessible for a wide range of fundamental and practical
applications.Comment: Nature Nanotechnology in pres
Snap-through instability of graphene on substrates
We determine the graphene morphology regulated by substrates with herringbone
and checkerboard surface corrugations. As the graphene/substrate interfacial
bonding energy and the substrate surface roughness vary, the graphene
morphology snaps between two distinct states: 1) closely conforming to the
substrate and 2) remaining nearly flat on the substrate. Such a snapthrough
instability of graphene can potentially lead to desirable electronic properties
to enable graphene-based devices.Comment: 13 pages, 4 figures; Nanoscale Research Letters, in press, 200
In-situ electronic characterization of graphene nanoconstrictions fabricated in a transmission electron microscope
We report electronic measurements on high-quality graphene nanoconstrictions
(GNCs) fabricated in a transmission electron microscope (TEM), and the first
measurements on GNC conductance with an accurate measurement of constriction
width down to 1 nm. To create the GNCs, freely-suspended graphene ribbons were
fabricated using few-layer graphene grown by chemical vapor deposition. The
ribbons were loaded into the TEM, and a current-annealing procedure was used to
clean the material and improve its electronic characteristics. The TEM beam was
then used to sculpt GNCs to a series of desired widths in the range 1 - 700 nm;
after each sculpting step, the sample was imaged by TEM and its electronic
properties measured in-situ. GNC conductance was found to be remarkably high,
comparable to that of exfoliated graphene samples of similar size. The GNC
conductance varied with width approximately as, where w is the constriction
width in nanometers. GNCs support current densities greater than 120 \muA/nm2,
two orders of magnitude higher than has been previously reported for graphene
nanoribbons and 2000 times higher than copper.Comment: 17 pages, 4 figures. Accepted by Nano Letter
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