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.
Large-scale atomically thin metals can be stabilized through confinement epitaxy at graphene/SiC interface, which exhibit a gradient bonding type and are air stable, providing a compelling platform ...for quantum and optoelectronic technologies.
Graphene nanoribbons will be essential components in future graphene nanoelectronics. However, in typical nanoribbons produced from lithographically patterned exfoliated graphene, the charge carriers ...travel only about ten nanometres between scattering events, resulting in minimum sheet resistances of about one kilohm per square. Here we show that 40-nanometre-wide graphene nanoribbons epitaxially grown on silicon carbide are single-channel room-temperature ballistic conductors on a length scale greater than ten micrometres, which is similar to the performance of metallic carbon nanotubes. This is equivalent to sheet resistances below 1 ohm per square, surpassing theoretical predictions for perfect graphene by at least an order of magnitude. In neutral graphene ribbons, we show that transport is dominated by two modes. One is ballistic and temperature independent; the other is thermally activated. Transport is protected from back-scattering, possibly reflecting ground-state properties of neutral graphene. At room temperature, the resistance of both modes is found to increase abruptly at a particular length--the ballistic mode at 16 micrometres and the other at 160 nanometres. Our epitaxial graphene nanoribbons will be important not only in fundamental science, but also--because they can be readily produced in thousands--in advanced nanoelectronics, which can make use of their room-temperature ballistic transport properties.
Carbon Nanotubes: The Route toward Applications Baughman, Ray H.; Zakhidov, Anvar A.; de Heer, Walt A.
Science (American Association for the Advancement of Science),
08/2002, Letnik:
297, Številka:
5582
Journal Article
Recenzirano
Many potential applications have been proposed for carbon nanotubes, including conductive and high-strength composites; energy storage and energy conversion devices, sensors; field emission displays ...and radiation sources; hydrogen storage media; and nanometer-sized semiconductor devices, probes, and interconnects. Some of these applications are now realized in products. Others are demonstrated in early to advanced devices, and one, hydrogen storage, is clouded by controversy. Nanotube cost, polydispersity in nanotube type, and limitations in processing and assembly methods are important barriers for some applications of single-walled nanotubes.
The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental carrier-carrier interactions and carrier-phonon relaxation processes in two-dimensional materials, and ...understanding of the physics underlying novel high-speed electronic and optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy and related techniques have interpreted the variety of observed signals within phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder. Here, we present an integrated experimental and theoretical programme, using ultrafast time-resolved terahertz spectroscopy combined with microscopic modelling, to systematically investigate the hot-carrier dynamics in a wide array of graphene samples having varying amounts of disorder and with either high or low doping levels. The theory reproduces the observed dynamics quantitatively without the need to invoke any fitting parameters, phenomenological models or extrinsic effects such as disorder. We demonstrate that the dynamics are dominated by the combined effect of efficient carrier-carrier scattering, which maintains a thermalized carrier distribution, and carrier-optical-phonon scattering, which removes energy from the carrier liquid.
Carbon Nanotube Quantum Resistors Frank, Stefan; Poncharal, Philippe; Wang, Z. L. ...
Science (American Association for the Advancement of Science),
06/1998, Letnik:
280, Številka:
5370
Journal Article
Recenzirano
Odprti dostop
The conductance of multiwalled carbon nanotubes (MWNTs) was found to be quantized. The experimental method involved measuring the conductance of nanotubes by replacing the tip of a scanning probe ...microscope with a nanotube fiber, which could be lowered into a liquid metal to establish a gentle electrical contact with a nanotube at the tip of the fiber. The conductance of arc-produced MWNTs is one unit of the conductance quantum G$_0$ = 2e$^2$/h = (12.9 kilohms)$^{-1}$. The nanotubes conduct current ballistically and do not dissipate heat. The nanotubes, which are typically 15 nanometers wide and 4 micrometers long, are several orders of magnitude greater in size and stability than other typical room-temperature quantum conductors. Extremely high stable current densities, J > 10$^7$ amperes per square centimeter, have been attained.
The addition of nitrophenyl groups to the surface of few-layer epitaxial graphene (EG) by the formation of covalent carbon−carbon bonds changed the electronic structure and transport properties of ...the EG from near-metallic to semiconducting.
This paper describes the behavior of top-gated transistors fabricated using carbon, specifically epitaxial graphene on SiC, as the active material. Although graphene devices have been built before, ...in this paper, we provide the first demonstration and systematic evaluation of arrays of a large number of transistors produced using standard microelectronics methods. The graphene devices presented feature high-k dielectric, mobilities up to 5000 cm 2 /Vldr s, and I on /I off ratios of up to seven, and are methodically analyzed to provide insight into the substrate properties. Typical of graphene, these micrometer-scale devices have negligible band gaps and, therefore, large leakage currents.
The recent observation of non-classical electron transport regimes in two-dimensional materials has called for new high-resolution non-invasive techniques to locally probe electronic properties. We ...introduce a novel hybrid scanning probe technique to map the local resistance and electrochemical potential with nm- and μV resolution, and we apply it to study epigraphene nanoribbons grown on the sidewalls of SiC substrate steps. Remarkably, the potential drop is non-uniform along the ribbons, and μm-long segments show no potential variation with distance. The potential maps are in excellent agreement with measurements of the local resistance. This reveals ballistic transport, compatible with μm-long room-temperature electronic mean-free paths.
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<B<5 T. An extremely sharp weak-localization resistance peak at B=0 is also observed. These features quantitatively agree with graphene weak-(anti)localization theory implying the chiral electronic character of the samples. Scattering contributions from the trapped charges in the substrate and from trigonal warping due to the graphite layer on top are tentatively identified. The Shubnikov-de Haas oscillations are remarkably small and show an anomalous Berry's phase.
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