4,679 research outputs found
Creation and suppression of point defects through a kick-out substitution process of Fe in InP
Indium antisite defect In P-related photoluminescence has been observed in Fe-diffused semi-insulating (SI) InP. Compared to annealed undoped or Fe-predoped SI InP, there are fewer defects in SI InP obtained by long-duration, high-temperature Fe diffusion. The suppression of the formation of point defects in Fe-diffused SI InP can be explained in terms of the complete occupation by Fe at indium vacancy. The In P defect is enhanced by the indium interstitial that is caused by the kick out of In and the substitution at the indium site of Fe in the diffusion process. Through these Fe-diffusion results, the nature of the defects in annealed undoped SI InP is better understood. © 2002 American Institute of Physics.published_or_final_versio
Optical characteristics of GAN/SI micro-pixel light-emitting diode arrays
Two-dimensional arrays of emissive micro-light-emitting diodes (μ-LEDS) have been developed for a variety of applications such as high resolution micro-displays, maskless photo-lithography and multichannel visible-light optical communications amongst others. μ-LEDs have traditionally been
fabricated on InGaN LED wafers grown on transparent sapphire substrates, and have suffered from optical crosstalk issues. When a single pixel is addressed, adjacent pixels and regions appear
illuminated simultaneously. Such problems could result in functional failure in high-density μ-LED
applications, including reduced resolution of micro-display and decreased signal-to-noise ratio in ...postprin
Local tunneling characteristics near a grain boundary of a d-wave superconductor as probed by a normal-metal or a low-T-c-superconductor STM tip
Journals published by the American Physical Society can be found at http://journals.aps.org/We study the local single-particle tunneling characteristics [as observed with scanning tunnel microscopy (STM)] for N-D and S-D tunneling, where D is a d-wave superconductor with a {100}{110} grain boundary. The tunneling Hamiltonian method is used. The self-consistent order parameter is first determined using the quasiclassical Green's-function method, and then the tunneling characteristics at various distances from the interface, reflectivity of the interface, and temperature, are studied. For N-D tunneling, a zero-bias conductance peak (ZBCP) occurs near the interface, with diminishing magnitude away from it. For S-D tunneling, the ZBCP splits to exhibit the gap of the s-wave low-T-c superconducting tunneling tip, and there is a range of negative conductance just outside the peaks, when the tunneling point is near the grain boundary. The results are compared with those obtained by using a constant order parameter in each grain
A Double-Voltage-Controlled Effective Thermal Conductivity Model of Graphene for Thermoelectric Cooling
© 1963-2012 IEEE. Graphene provides a new opportunity for thermoelectric study based on its unique heat transfer behavior controllable by a gate voltage. In this paper, an effective thermal conductivity model of graphene for thermoelectric cooling is proposed. The model is based on a double-voltage-control mechanism. According to the law of Fourier heat conduction, an effective thermal conductivity model of the proposed thermoelectric cooling device is derived taking a tunable external voltage into account. Then, a gate voltage is used which can change graphene's thermoelectric characteristics. To verify the correctness and effectiveness of the proposed model, a circuit simulation model using HSPICE is built based on the thermoelectric duality. The simulation results from HSPICE and the calculated results from the mathematic model show good agreements with each other. This paper provides a novel precisely controlling method for thermoelectric cooling
High-energy scale revival and giant kink in the dispersion of a cuprate superconductor
In the present photoemission study of a cuprate superconductor
Bi1.74Pb0.38Sr1.88CuO6+delta, we discovered a large scale dispersion of the
lowest band, which unexpectedly follows the band structure calculation very
well. The incoherent nature of the spectra suggests that the hopping-dominated
dispersion occurs possibly with the assistance of local spin correlations. A
giant kink in the dispersion is observed, and the complete self-energy
containing all interaction information is extracted for a doped cuprate in the
low energy region. These results recovered significant missing pieces in our
current understanding of the electronic structure of cuprates.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett. on May 21, 200
On the Inability of Markov Models to Capture Criticality in Human Mobility
We examine the non-Markovian nature of human mobility by exposing the
inability of Markov models to capture criticality in human mobility. In
particular, the assumed Markovian nature of mobility was used to establish a
theoretical upper bound on the predictability of human mobility (expressed as a
minimum error probability limit), based on temporally correlated entropy. Since
its inception, this bound has been widely used and empirically validated using
Markov chains. We show that recurrent-neural architectures can achieve
significantly higher predictability, surpassing this widely used upper bound.
In order to explain this anomaly, we shed light on several underlying
assumptions in previous research works that has resulted in this bias. By
evaluating the mobility predictability on real-world datasets, we show that
human mobility exhibits scale-invariant long-range correlations, bearing
similarity to a power-law decay. This is in contrast to the initial assumption
that human mobility follows an exponential decay. This assumption of
exponential decay coupled with Lempel-Ziv compression in computing Fano's
inequality has led to an inaccurate estimation of the predictability upper
bound. We show that this approach inflates the entropy, consequently lowering
the upper bound on human mobility predictability. We finally highlight that
this approach tends to overlook long-range correlations in human mobility. This
explains why recurrent-neural architectures that are designed to handle
long-range structural correlations surpass the previously computed upper bound
on mobility predictability
A 5d/3d duality from relativistic integrable system
We propose and prove a new exact duality between the F-terms of
supersymmetric gauge theories in five and three dimensions with adjoint matter
fields. The theories are compactified on a circle and are subject to the Omega
deformation. In the limit proposed by Nekrasov and Shatashvili, the
supersymmetric vacua become isolated and are identified with the eigenstates of
a quantum integrable system. The effective twisted superpotentials are the
Yang-Yang functional of the relativistic elliptic Calogero-Moser model. We show
that they match on-shell by deriving the Bethe ansatz equation from the saddle
point of the five-dimensional partition function. We also show that the
Chern-Simons terms match and extend our proposal to the elliptic quiver
generalizations.Comment: 30 pages, 4 figures. v2: typo corrected, references adde
A compact model for magnetic tunnel junction (MTJ) switched by thermally assisted Spin transfer torque (TAS + STT)
Thermally assisted spin transfer torque [TAS + STT] is a new switching approach for magnetic tunnel junction [MTJ] nanopillars that represents the best trade-off between data reliability, power efficiency and density. In this paper, we present a compact model for MTJ switched by this approach, which integrates a number of physical models such as temperature evaluation and STT dynamic switching models. Many experimental parameters are included directly to improve the simulation accuracy. It is programmed in the Verilog-A language and compatible with the standard IC CAD tools, providing an easy parameter configuration interface and allowing high-speed co-simulation of hybrid MTJ/CMOS circuits
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Superconducting ECR ion source: From 24-28 GHz SECRAL to 45 GHz fourth generation ECR.
The development of superconducting ECR source with higher magnetic fields and higher microwave frequency is the most straight forward path to achieve higher beam intensity and higher charge state performance. SECRAL, a superconducting third generation ECR ion source, is designed for 24-28 GHz microwave frequency operation with an innovative magnet configuration of sextupole coils located outside the three solenoids. SECRAL at 24 GHz has already produced a number of record beam intensities, such as 40Ar12+ 1.4 emA, 129Xe26+ 1.1 emA, 129Xe30+ 0.36 emA, and 209Bi31+ 0.68 emA. SECRAL-II, an upgraded version of SECRAL, was built successfully in less than 3 years and has recently been commissioned at full power of a 28 GHz gyrotron and three-frequency heating (28 + 45 + 18 GHz). New record beam intensities for highly charged ion production have been achieved, such as 620 eμA 40Ar16+, 15 eμA 40Ar18+, 146 eμA 86Kr28+, 0.5 eμA 86Kr33+, 53 eμA 129Xe38+, and 17 eμA 129Xe42+. Recent beam test results at SECRAL and SECRAL II have demonstrated that the production of more intense highly charged heavy ion beams needs higher microwave power and higher frequency, as the scaling law predicted. A 45 GHz superconducting ECR ion source FECR (a first fourth generation ECR ion source) is being built at IMP. FECR will be the world's first Nb3Sn superconducting-magnet-based ECR ion source with 6.5 T axial mirror field, 3.5 T sextupole field on the plasma chamber inner wall, and 20 kW at a 45 GHz microwave coupling system. This paper will focus on SECRAL performance studies at 24-28 GHz and technical design of 45 GHz FECR, which demonstrates a technical path for highly charged ion beam production from 24 to 28 GHz SECRAL to 45 GHz FECR
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