2,548 research outputs found
Approaching the Intrinsic Bandgap in Suspended High-Mobility Graphene Nanoribbons
We report electrical transport measurements on a suspended ultra-low-disorder
graphene nanoribbon(GNR) with nearly atomically smooth edges that reveal a high
mobility exceeding 3000 cm2 V-1 s-1 and an intrinsic band gap. The
experimentally derived bandgap is in quantitative agreement with the results of
our electronic-structure calculations on chiral GNRs with comparable width
taking into account the electron-electron interactions, indicating that the
origin of the bandgap in non-armchair GNRs is partially due to the magnetic
zigzag edges.Comment: 22 pages, 6 figure
Mobility enhancement and highly efficient gating of monolayer MoS2 transistors with Polymer Electrolyte
We report electrical characterization of monolayer molybdenum disulfide
(MoS2) devices using a thin layer of polymer electrolyte consisting of
poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO4) as both a
contact-barrier reducer and channel mobility booster. We find that bare MoS2
devices (without polymer electrolyte) fabricated on Si/SiO2 have low channel
mobility and large contact resistance, both of which severely limit the
field-effect mobility of the devices. A thin layer of PEO/ LiClO4 deposited on
top of the devices not only substantially reduces the contact resistance but
also boost the channel mobility, leading up to three-orders-of-magnitude
enhancement of the field-effect mobility of the device. When the polymer
electrolyte is used as a gate medium, the MoS2 field-effect transistors exhibit
excellent device characteristics such as a near ideal subthreshold swing and an
on/off ratio of 106 as a result of the strong gate-channel coupling.Comment: 17 pages, 4 figures, accepted by J. Phys.
High Fidelity State Transfer Over an Unmodulated Linear XY Spin Chain
We provide a class of initial encodings that can be sent with a high fidelity
over an unmodulated, linear, XY spin chain. As an example, an average fidelity
of ninety-six percent can be obtained using an eleven-spin encoding to transmit
a state over a chain containing ten-thousand spins. An analysis of the magnetic
field dependence is given, and conditions for field optimization are provided.Comment: Replaced with published version. 8 pages, 5 figure
Room-Temperature High On/Off Ratio in Suspended Graphene Nanoribbon Field Effect Transistors
We have fabricated suspended few layer (1-3 layers) graphene nanoribbon field
effect transistors from unzipped multiwall carbon nanotubes. Electrical
transport measurements show that current-annealing effectively removes the
impurities on the suspended graphene nanoribbons, uncovering the intrinsic
ambipolar transfer characteristic of graphene. Further increasing the annealing
current creates a narrow constriction in the ribbon, leading to the formation
of a large band-gap and subsequent high on/off ratio (which can exceed 104).
Such fabricated devices are thermally and mechanically stable: repeated thermal
cycling has little effect on their electrical properties. This work shows for
the first time that ambipolar field effect characteristics and high on/off
ratios at room temperature can be achieved in relatively wide graphene
nanoribbon (15 nm ~50 nm) by controlled current annealing.Comment: 19 pages, 6 figures, accepted for publication in Nanotechnology
(2011
Electrical Transport Properties of Graphene Nanoribbons Produced from Sonicating Graphite in Solution
A simple one-stage solution-based method was developed to produce graphene
nanoribbons by sonicating graphite powder in organic solutions with polymer
surfactant. The graphene nanoribbons were deposited on silicon substrate, and
characterized by Raman spectroscopy and atomic force microscopy. Single-layer
and few-layer graphene nanoribbons with a width ranging from sub-10 nm to tens
of nm and length ranging from hundreds of nm to 1 {\mu}m were routinely
observed. Electrical transport properties of individual graphene nanoribbons
were measured in both the back-gate and polymer-electrolyte top-gate
configurations. The mobility of the graphene nanoribbons was found to be over
an order of magnitude higher when measured in the latter than in the former
configuration (without the polymer electrolyte), which can be attributed to the
screening of the charged impurities by the counter-ions in the polymer
electrolyte. This finding suggests that the charge transport in these
solution-produced graphene nanoribbons is largely limited by charged impurity
scattering.Comment: 19 pages, 5 figures, accepted for publication in Nanotechnology 201
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Regulation of axon repulsion by MAX-1 SUMOylation and AP-3.
During neural development, growing axons express specific surface receptors in response to various environmental guidance cues. These axon guidance receptors are regulated through intracellular trafficking and degradation to enable navigating axons to reach their targets. In Caenorhabditis elegans, the UNC-5 receptor is necessary for dorsal migration of developing motor axons. We previously found that MAX-1 is required for UNC-5-mediated axon repulsion, but its mechanism of action remained unclear. Here, we demonstrate that UNC-5-mediated axon repulsion in C. elegans motor axons requires both max-1 SUMOylation and the AP-3 complex β subunit gene, apb-3 Genetic interaction studies show that max-1 is SUMOylated by gei-17/PIAS1 and acts upstream of apb-3 Biochemical analysis suggests that constitutive interaction of MAX-1 and UNC-5 receptor is weakened by MAX-1 SUMOylation and by the presence of APB-3, a competitive interactor with UNC-5. Overexpression of APB-3 reroutes the trafficking of UNC-5 receptor into the lysosome for protein degradation. In vivo fluorescence recovery after photobleaching experiments shows that MAX-1 SUMOylation and APB-3 are required for proper trafficking of UNC-5 receptor in the axon. Our results demonstrate that SUMOylation of MAX-1 plays an important role in regulating AP-3-mediated trafficking and degradation of UNC-5 receptors during axon guidance
The Implementation of NEMS GFS Aerosol Component (NGAC) Version 1.0 for Global Dust Forecasting at NOAA NCEP
The NOAA National Centers for Environmental Prediction (NCEP) implemented the NOAA Environmental Modeling System (NEMS) Global Forecast System (GFS) Aerosol Component (NGAC) for global dust forecasting in collaboration with NASA Goddard Space Flight Center (GSFC). NGAC Version 1.0 has been providing 5-day dust forecasts at 1deg x 1deg resolution on a global scale, once per day at 00:00 Coordinated Universal Time (UTC), since September 2012. This is the first global system capable of interactive atmosphere aerosol forecasting at NCEP. The implementation of NGAC V1.0 reflects an effective and efficient transitioning of NASA research advances to NCEP operations, paving the way for NCEP to provide global aerosol products serving a wide range of stakeholders, as well as to allow the effects of aerosols on weather forecasts and climate prediction to be considered
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Possible detection of hydrazine on Saturn’s moon Rhea
We present the first analysis of far-ultraviolet reflectance spectra of regions on Rhea’s leading and trailing hemispheres collected by the Cassini Ultraviolet Imaging Spectrograph during targeted flybys. In particular, we aim to explain the unidentified broad absorption feature centred near 184 nm. We have used laboratory measurements of the UV spectroscopy of a set of candidate molecules and found a good fit to Rhea’s spectra with both hydrazine monohydrate and several chlorine-containing molecules. Given the radiation-dominated chemistry on the surface of icy satellites embedded within their planets’ magnetospheres, hydrazine monohydrate is argued to be the most plausible candidate for explaining the absorption feature at 184 nm. Hydrazine was also used as a propellant in Cassini’s thrusters, but the thrusters were not used during icy satellite flybys and thus the signal is believed to not arise from spacecraft fuel. We discuss how hydrazine monohydrate may be chemically produced on icy surfaces
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