723 research outputs found
Synthesis and Post-growth Doping of Silicon Nanowires
High quality silicon nanowires (SiNWs) were synthesized via a thermal evaporation method without the use of catalysts. Scanning electron microscopy and transmission electron microscopy showed that SiNWs were long and straight crystalline silicon with an oxide sheath. Field effect transistors (FETs) were fabricated to investigate the electrical transport properties. Devices on as-grown material were p-channel with channel mobilities 1 - 10 cm2 V-1 s-1. Post-growth vapor doping with bismuth converted these to n-channel behavior
Systematic study of contact annealing: Ambipolar silicon nanowire transistor with improved performance
High performance ambipolar silicon nanowire (SiNW) transistors were fabricated. SiNWs with uniform oxide sheath thicknesses of 6â7 nm were synthesized via a gas-flow-controlled thermal evaporation method. Field effect transistors (FETs) were fabricated using as-grown SiNWs. A two step annealing process was used to control contacts between SiNW and metal source and drain in order to enhance device performance. Initially Ï-channel devices exhibited ambipolar behavior after contact annealing at 400 ÂșC. Significant increases in on/off ratio and channel mobility were also achieved by annealing
Silicon Nanowires: Doping Dependent N- And P- Channel FET Behavior
The electrical transport properties of field effect transistor (FET) devices made of silicon nanowires (SiNWs) synthesized by pulsed laser vaporization (PLV) were studied. From as-grown PLV-SiNW FET, we found p-channel FET behavior with low conductance. To improve conductance, spin on glass (SOG) and vapor doping were used to dope phosphorus and indium into SiNW, respectively. From doping after synthesis, we could successfully make both n- and p-channel FET devices
Applications of electron microscopy to the characterization of semiconductor nanowires
We review our current progress on semiconductor nanowires of ÎČ-Ga2O3, Si and GaN. These nanowires were grown using both vaporâsolid (VS) and vaporâliquidâsolid (VLS) mechanisms. Using transmission electron microscopy (TEM) we studied their morphological, compositional and structural characteristics. Here we survey the general morphologies, growth directions and a variety of defect structures found in our samples. We also outline a method to determine the nanowire growth direction using TEM, and present an overview of device fabrication and assembly methods developed using these nanowires
Towards reliability centred maintenance of wind turbines
Reliability centred maintenance applied to a fleet of wind turbines is presented in this paper. The key components and failure modes are identified via analysis of maintenance records. Corrective actions which an operator can take to mitigate such failures are discussed, together with implementation issues. By developing a robust set of RCM tools, wind farm operators can better quantify and minimise operational expenditure of wind farm fleets
Projecting the Most Likely Annual Urban Heat Extremes in the Central United States
Climate studies based on global climate models (GCMs) project a steady increase in annual average temperature and severe heat extremes in central North America during the mid-century and beyond. However, the agreement of observed trends with climate model trends varies substantially across the region. The present study focuses on two different locations: Des Moines, IA and Austin, TX. In Des Moines, annual extreme temperatures have not increased over the past three decades unlike the trend of regionally-downscaled GCM data for the Midwest, likely due to a âwarming holeâ over the area linked to agricultural factors. This warming hole effect is not evident for Austin over the same time period, where extreme temperatures have been higher than projected by regionally-downscaled climate (RDC) forecasts. In consideration of the deviation of such RDC extreme temperature forecasts from observations, this study statistically analyzes RDC data in conjunction with observational data to define for these two cities a 95% prediction interval of heat extreme values by 2040. The statistical model is constructed using a linear combination of RDC ensemble-member annual extreme temperature forecasts with regression coefficients for individual forecasts estimated by optimizing model results against observations over a 52-year training period
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
Search for Chargino-Neutralino Associated Production at the Fermilab Tevatron Collider
We have searched in collisions at = 1.8 TeV for events
with three charged leptons and missing transverse energy. In the Minimal
Supersymmetric Standard Model, we expect trilepton events from
chargino-neutralino (\chione \chitwo) pair production, with subsequent decay
into leptons. We observe no candidate , ,
or events in 106 pb integrated
luminosity. We present limits on the sum of the branching ratios times cross
section for the four channels: \sigma_{\chione\chitwo}\cdot
BR(\chione\chitwo\to 3\ell+X) 81.5 \mgev\sp and
M_\chitwo > 82.2 \mgev\sp for , ~\mgev\sp and
M_\squark= M_\gluino.Comment: 9 pages and 3 figure
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