24 research outputs found
Half integer quantum Hall effect in high mobility single layer epitaxial graphene
The quantum Hall effect, with a Berry's phase of is demonstrated here
on a single graphene layer grown on the C-face of 4H silicon carbide. The
mobility is 20,000 cm/Vs at 4 K and ~15,000 cm/Vs
at 300 K despite contamination and substrate steps. This is comparable to the
best exfoliated graphene flakes on SiO and an order of magnitude larger
than Si-face epitaxial graphene monolayers. These and other properties indicate
that C-face epitaxial graphene is a viable platform for graphene-based
electronics.Comment: Some modifications in the text and figures, 7 pages, 2 figure
Approaching the Dirac point in high mobility multi-layer epitaxial graphene
Multi-layer epitaxial graphene (MEG) is investigated using far infrared (FIR)
transmission experiments in the different limits of low magnetic fields and
high temperatures. The cyclotron-resonance like absorption is observed at low
temperature in magnetic fields below 50 mT, allowing thus to probe the nearest
vicinity of the Dirac point and to estimate the conductivity in nearly undoped
graphene. The carrier mobility is found to exceed 250,000 cm/(V.s). In the
limit of high temperatures, the well-defined Landau level (LL) quantization is
observed up to room temperature at magnetic fields below 1 T, a phenomenon
unique in solid state systems. A negligible increase in the width of the
cyclotron resonance lines with increasing temperature indicates that no
important scattering mechanism is thermally activated, supporting recent
expectations of high room-temperature mobilities in graphene.Comment: 5 pages, 3 figure
First direct observation of a nearly ideal graphene band structure
Angle-resolved photoemission and X-ray diffraction experiments show that
multilayer epitaxial graphene grown on the SiC(000-1) surface is a new form of
carbon that is composed of effectively isolated graphene sheets. The unique
rotational stacking of these films cause adjacent graphene layers to
electronically decouple leading to a set of nearly independent linearly
dispersing bands (Dirac cones) at the graphene K-point. Each cone corresponds
to an individual macro-scale graphene sheet in a multilayer stack where
AB-stacked sheets can be considered as low density faults.Comment: 5 pages, 4 figure
Large area and structured epitaxial graphene produced by confinement controlled sublimation of silicon carbide
After the pioneering investigations into graphene-based electronics at
Georgia Tech (GT), great strides have been made developing epitaxial graphene
on silicon carbide (EG) as a new electronic material. EG has not only
demonstrated its potential for large scale applications, it also has become an
invaluable material for fundamental two-dimensional electron gas physics
showing that only EG is on route to define future graphene science. It was long
known that graphene mono and multilayers grow on SiC crystals at high
temperatures in ultra-high vacuum. At these temperatures, silicon sublimes from
the surface and the carbon rich surface layer transforms to graphene. However
the quality of the graphene produced in ultrahigh vacuum is poor due to the
high sublimation rates at relatively low temperatures. The GT team developed
growth methods involving encapsulating the SiC crystals in graphite enclosures,
thereby sequestering the evaporated silicon and bringing growth process closer
to equilibrium. In this confinement controlled sublimation (CCS) process, very
high quality graphene is grown on both polar faces of the SiC crystals. Since
2003, over 50 publications used CCS grown graphene, where it is known as the
"furnace grown" graphene. Graphene multilayers grown on the carbon-terminated
face of SiC, using the CCS method, were shown to consist of decoupled high
mobility graphene layers. The CCS method is now applied on structured silicon
carbide surfaces to produce high mobility nano-patterned graphene structures
thereby demonstrating that EG is a viable contender for next-generation
electronics. Here we present the CCS method and demonstrate several of
epitaxial graphene's outstanding properties and applications
Spectroscopy of Covalently Functionalized Graphene
International audienceThe atomically flat surface of graphene provides an opportunity to apply carbon-carbon bond-forming chemical reactions to engineer the electronic properties of graphene circuitry. In particular, covalent functionalization of the surface or the edge of graphene ribbons provides a novel way to introduce patterning that can modulate the energy band gap, affect electron scattering, and direct current flow by producing dielectric regions in a graphene wafer. We discuss the use of Raman spectroscopy and scanning tunneling microscopy to characterize the surface functionalization periodicities and densities that have been produced by the chemical derivatization of epitaxial graphene together with the concomitant changes in the electronic and magnetic properties of the graphene surface laye
The first Ordovician cyclocystoid (Echinodermata) from Gondwana and its morphology, paleoecology, taphonomy, and paleogeography
International audienceMoroccodiscus smithi represents a new cyclocystoid genus and species based on moldic specimens from the Middle Ordovician Taddrist Formation (Darriwilian) of SE Morocco. This represents the earliest articulated member of the Cyclocystoidea and is the first complete cyclocystoid described from the Ordovician of Gondwana, as well as the first cyclocystoid ever recorded from Africa. The anatomy and morphology of this new species were studied using a combination of conventional paleontological methods and nondestructive X-ray computed tomography. Because Moroccodiscus differs from other cyclocystoids, in particular by lacking cupules attached to the marginal ossicles, it is assigned to the new family Moroccodiscidae. This new taxon illustrates the relatively poorly known early diversification of these enigmatic extinct echinoderms and sheds light on the mode of life of cyclocystoids, including injuries to plate circlets during early ontogeny and folding of these disk-like specimens at the time of death. The overall thecal shape was very similar in cyclocystoids and many domal edrioasteroids, probably because they were both sessile or attached, benthic, suspension feeders. However, many oral surface, ambulacral, and marginal ring features had become very different, indicating that these two groups had either converged because of similar life modes or were only distantly related sister groups
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A New Approach to Riparian Area Education in Arizona
From the Proceedings of the 2006 Meetings of the Hydrology Section - Arizona-Nevada Academy of Science - April 8, 2006, University of Arizona, TucsonThis article is part of the Hydrology and Water Resources in Arizona and the Southwest collections. Digital access to this material is made possible by the Arizona-Nevada Academy of Science and the University of Arizona Libraries. For more information about items in this collection, contact [email protected]