466 research outputs found
Near-thermal limit gating in heavily-doped III-V semiconductor nanowires using polymer electrolytes
Doping is a common route to reducing nanowire transistor on-resistance but
has limits. High doping level gives significant loss in gate performance and
ultimately complete gate failure. We show that electrolyte gating remains
effective even when the Be doping in our GaAs nanowires is so high that
traditional metal-oxide gates fail. In this regime we obtain a combination of
sub-threshold swing and contact resistance that surpasses the best existing
p-type nanowire MOSFETs. Our sub-threshold swing of 75 mV/dec is within 25% of
the room-temperature thermal limit and comparable with n-InP and n-GaAs
nanowire MOSFETs. Our results open a new path to extending the performance and
application of nanowire transistors, and motivate further work on improved
solid electrolytes for nanoscale device applications.Comment: 6 pages, 2 figures, supplementary available at journa
Towards low-dimensional hole systems in Be-doped GaAs nanowires
GaAs was central to the development of quantum devices but is rarely used for
nanowire-based quantum devices with InAs, InSb and SiGe instead taking the
leading role. p-type GaAs nanowires offer a path to studying strongly-confined
0D and 1D hole systems with strong spin-orbit effects, motivating our
development of nanowire transistors featuring Be-doped p-type GaAs nanowires,
AuBe alloy contacts and patterned local gate electrodes towards making
nanowire-based quantum hole devices. We report on nanowire transistors with
traditional substrate back-gates and EBL-defined metal/oxide top-gates produced
using GaAs nanowires with three different Be-doping densities and various AuBe
contact processing recipes. We show that contact annealing only brings small
improvements for the moderately-doped devices under conditions of lower anneal
temperature and short anneal time. We only obtain good transistor performance
for moderate doping, with conduction freezing out at low temperature for
lowly-doped nanowires and inability to reach a clear off-state under gating for
the highly-doped nanowires. Our best devices give on-state conductivity 95 nS,
off-state conductivity 2 pS, on-off ratio ~, and sub-threshold slope 50
mV/dec at T = 4 K. Lastly, we made a device featuring a moderately-doped
nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a
plateau in the sub-threshold region that is reproducible in separate cool-downs
and indicative of possible conductance quantization highlighting the potential
for future quantum device studies in this material system
Nonlocality of Majorana modes in hybrid nanowires
Spatial separation of Majorana zero modes distinguishes trivial from topological midgap states and is key to topological protection in quantum computing applications. Although signatures of Majorana zero modes in tunneling spectroscopy have been reported in numerous studies, a quantitative measure of the degree of separation, or nonlocality, of the emergent zero modes has not been reported. Here, we present results of an experimental study of nonlocality of emergent zero modes in superconductor-semiconductor hybrid nanowire devices. The approach takes advantage of recent theory showing that nonlocality can be measured from splitting due to hybridization of the zero mode in resonance with a quantum dot state at one end of the nanowire. From these splittings as well as anticrossing of the dot states, measured for even and odd occupied quantum dot states, we extract both the degree of nonlocality of the emergent zero mode, as well as the spin canting angles of the nonlocal zero mode. Depending on the device measured, we obtain either a moderate degree of nonlocality, suggesting a partially separated Andreev subgap state, or a highly nonlocal state consistent with a well-developed Majorana modeThis research was supported by Microsoft, the Danish National Research Foundation, the European Commission, and the Spanish Ministry of Economy and Competitiveness through Grants No. FIS2015-65706-P, No. FIS2015-64654-P, and No. FIS2016-80434-P (AEI/FEDER, EU), the Ramón y Cajal programme Grant No. RYC-2011-09345, and the María de Maeztu Programme for Units of Excellence in R&D (Grant No. MDM-2014-0377). C.M.M. acknowledges support from the Villum Foundation. M.-T.D. acknowledges support from State Key Laboratory of High Performance Computing, Chin
Transport via coupled states in a C60 peapod quantum dot
We have measured systematic repetitions of avoided crossings in low
temperature three-terminal transport through a carbon nanotube with
encapsulated C60 molecules. We show that this is a general effect of the
hybridization of a host quantum dot with an impurity. The well-defined nanotube
allows identification of the properties of the impurity, which we suggest to be
a chain of C60 molecules inside the nanotube. This electronic coupling between
the two subsystems opens the interesting and potentially useful possibility of
contacting the encapsulated molecules via the tube.Comment: 6 pages, 3 figure
Torsional response and stiffening of individual multi-walled carbon nanotubes
We report on the characterization of torsional oscillators which use
multi-walled carbon nanotubes as the spring elements. Through
atomic-force-microscope force-distance measurements we are able to apply
torsional strains to the nanotubes and measure their torsional spring constants
and effective shear moduli. We find that the effective shear moduli cover a
broad range, with the largest values near the theoretically predicted value.
The data also suggest that the nanotubes are stiffened by repeated flexing.Comment: 4 page
The Influence of Electro-Mechanical Effects on Resonant Electron Tunneling Through Small Carbon Nano-Peapods
The influence of a fullerene molecule trapped inside a single-wall carbon
nanotube on resonant electron transport at low temperatures and strong
polaronic coupling is theoretically discussed. Strong peak to peak fluctuations
and anomalous temperature behavior of conductance amplitudes are predicted and
investigated. The influence of the chiral properties of carbon nanotubes on
transport is also studied.Comment: 17 pages, 3 figures. Replaced with published version. Important
changes. Open access: http://stacks.iop.org/1367-2630/10/04304
The impact of radiosounding observations on numerical weather prediction analyses in the Arctic
The radiosounding network in the Arctic, despite being sparse, is a crucial part of the atmospheric observing system for weather prediction and reanalysis. The spatial coverage of the network was evaluated using a numerical weather prediction model, comparing radiosonde observations from Arctic land stations and expeditions in the central Arctic Ocean with operational analyses and background fields (12h forecasts) from ECMWF for January 2016 – September 2018. The results show that the impact of radiosonde observations on analyses has large geographical variation. In data‐sparse areas, such as the central Arctic Ocean, high‐quality radiosonde observations substantially improve the analyses, while satellite observations are not able to compensate for the large spatial gap in the radiosounding network. In areas where the network is reasonably dense, the quality of background field is more related to how radiosonde observations are utilized in the assimilation and to the quality of those observations
Associations between disease severity, coping and dimensions of health-related quality of life in patients admitted for elective coronary angiography – a cross sectional study
<p>Abstract</p> <p>Background</p> <p>In patients with suspected coronary artery disease (CAD), the overall aim was to analyse the relationships between disease severity and both mental and physical dimensions of health related quality of life (HRQOL) using a modified version of the Wilson and Cleary model.</p> <p>Methods</p> <p>Using a cross-sectional design, 753 patients (74% men), mean age 62 years, referred for elective cardiac catheterisation were included. The measures included 1) physiological factors 2) symptoms (disease severity, self-reported symptoms, anxiety and depression 3) self-reported functional status, 4) coping, 5) perceived disease burden, 6) general health perception and 7) overall quality of life. To analyse relationships, we performed linear and ordinal logistic regressions.</p> <p>Results</p> <p>CAD and left ventricular ejection fraction (LVEF) were significantly associated with symptoms of angina pectoris and dyspnea. CAD was not related to symptoms of anxiety and depression, but less depression was found in patients with low LVEF. Angina pectoris and dyspnea were both associated with impaired physical function, and dyspnea was also negatively related to social function. Overall, less perceived burden and better overall QOL were observed in patients using more confronting coping strategy.</p> <p>Conclusion</p> <p>The present study demonstrated that data from cardiac patients to a large extent support the suggested model by Wilson and Cleary.</p
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