Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10 12 cm −2 per graphene sheet. The most highlyordered sample exhibits Shubnikov -de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

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We investigate the ultrafast relaxation dynamics of hot Dirac fermionic quasiparticles in multilayer epitaxial graphene using ultrafast optical differential transmission spectroscopy. We observe differential transmission spectra which are well described by interband transitions with no electron-hole interaction. Following the initial thermalization and emission of high-energy phonons, the electron cooling is determined by electron-acoustic phonon scattering, found to occur on the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers. The spectra also provide strong evidence for the multilayer structure and doping profile of thermally grown epitaxial graphene on SiC.

After the pioneering investigations into graphene-based electronics at Georgia Tech, 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 important material for fundamental two-dimensional electron gas physics. It was long known that graphene mono and multilayers grow on SiC crystals at high temperatures in ultrahigh 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 Georgia Tech 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 for the first time the CCS method that outperforms other epitaxial graphene production methods.

Transport in ultrathin graphite grown on silicon carbide is dominated by the electron-doped epitaxial layer at the interface. Weak antilocalization in 2D samples manifests itself as a broad cusplike depression in the longitudinal resistance for magnetic fields 10 mT

Graphene oxide (GO) flakes have been deposited to bridge the gap between two epitaxial graphene electrodes to produce all-graphene devices. Electrical measurements indicate the presence of Schottky barriers (SB) at the graphene/graphene oxide junctions, as a consequence of the band-gap in GO. The barrier height is found to be about 0.7 eV, and is reduced after annealing at 180• C, implying that the gap can be tuned by changing the degree of oxidation. A lower limit of the GO mobility was found to be 850 cm 2 /Vs, rivaling silicon. In situ local oxidation of patterned epitaxial graphene has been achieved. PACS numbers: 73.61.Ph, 73.40.Sx Inspired by the exceptional properties of carbon nanotubes, epitaxial graphene based electronics was conceived as a possible new platform for post-CMOS electronics. In contrast to carbon nanotubes, graphene layers can be patterned to produce interconnected all-carbon structures, thereby overcoming a wide variety of problems facing nanotube-based electronics. Our earlier work focused primarily on producing and characterizing device quality epitaxial graphene (EG) on silicon carbide [1,2,3,4,5]. Here we demonstrate the production and properties of the epitaxial-graphene/graphene-oxide Schottky barrier. We also successfully chemically patterned epitaxial graphene to produce seamless graphene oxide to graphene junctions, thereby dramatically enhancing epitaxial graphene electronics.We recently showed that EG can be reliably patterned over large areas to produce hundreds of functioning high mobility field effect transistors (FET) over the entire surface of a 3×4 mm chip using high k dielectrics [6]. Next steps involve patterning and tailoring the properties of EG. Conventional semiconductor devices rely on a significant band gap; graphene, by contrast, is a semimetal, which severely limits the switching potential of graphene FETs (currently the maximum off-to-on resistance ratio for EG is about 35). The high mobility of EG (up to 25,000 cm 2 /Vs) offsets this deficiency for certain specialized applications. Clearly, the versatility of graphene electronics is greatly increased by converting graphene into a semiconductor. One way to achieve this is by nanopatterning. It was predicted that the electronic structure of a nanoscopic graphene ribbon should mimic that of a carbon nanotube [7,8] and semiconducting nanopatterned graphene ribbons on exfoliated graphene flakes have been demonstrated [9,10].A far more convenient scheme is to chemically convert graphene to a semiconductor. In this Letter we demonstrate the properties of (semiconducting) graphene oxide (GO), integrated into patterned EG structures. GO, first described in 1859 [11], consists of graphene layers whose surfaces are oxidized without disrupting the hexagonal graphene topology. Impressive demonstrations of deposited single layer GO [12] spurred research into alternative methods to produce a single graphene layer, by reducing deposited GO back to graphene [13,14]. In contrast, here we are interested in the semiconductin...

Both systemic and local infections are associated with increased risk of access vein occlusion. We found no support for the hypothesis that venous occlusion increases with the number of leads present. Lead extraction was more difficult in patients with venous occlusion, requiring advanced tools and more time.