Scaling quantum-dot light-emitting diodes to submicrometer sizes

We introduce a device structure and a fabrication technique that allow the realization of efficient light-emitting diodes (LEDs) with dimensions of the active area in the 100 nm range. Using optical lithography, selective oxidation, and an active region consisting of InAs quantum dots (QDs), we fabricated LEDs with light–current–voltage characteristics which scale well with nominal device area down to 600 nm diam at room temperature. The scaling behavior provides evidence for strong carrier confinement in the QDs and shows the potential for the realization of high-efficiency single-photon LEDs operating at room temperature. ©2002 American Institute of Physics

Magnetic properties of epitaxial single crystal ultrathin Fe\u3csub\u3e3\u3c/sub\u3eSi films on GaAs (001)

Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 Å thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML

Remarks on D_p and D_{p-2} with each carrying a flux

We explore various properties of interaction between D$_p$ and D$_{p'}$ with each carrying a worldvolume flux and with the $p'$-branes placed along $p'$ spatial worldvolume directions of the p-branes at a separation when $p - p' = 2$. Carefully analyzing the annulus amplitudes calculated via the boundary state approach, we find that many features of amplitudes remain similar to those studied when $p = p'$ such as the nature of force on the brane separation, the onset of various instabilities when the brane-separation is on the order of string scale and the occurrence of pair production of open strings when there is a relevant electric flux present. In addition, we have also found many new features of interaction which don't appear in the absence of fluxes or when $p = p'$ in the presence of fluxes, for examples, the nature of interaction can be repulsive and there is no onset of tachyonic instability under certain conditions. Even in the absence of a magnetic flux, we can have an exponential enhancement of the rate of pair production of open strings in certain cases, which may be significant enough to give observational consequences.Comment: 15 pages, 3 tables, revised version to appear in PL

Three-Particle Correlations from Parton Cascades in Au+Au Collisions

We present a study of three-particle correlations among a trigger particle and two associated particles in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using a multi-phase transport model (AMPT) with both partonic and hadronic interactions. We found that three-particle correlation densities in different angular directions with respect to the triggered particle (`center', `cone', `deflected', `near' and `near-away') increase with the number of participants. The ratio of `deflected' to `cone' density approaches to 1.0 with the increasing of number of participants, which indicates that partonic Mach-like shock waves can be produced by strong parton cascades in central Au+Au collisions.Comment: 9 pages, 6 figures; Final version to appear in Physics Letters

Process Analysis and Trial Tests for Hot-Rolled Stainless Steel/Carbon Steel Clad Plates

The trials of 304 stainless steel-clad plate made of plain Q345B carbon steel were performed on hot-rolling line of the Hesteel Group. After the two runs of pilot production, the key process parameters for the stainless steel/carbon steel clad plate were found to meet the GB/T 8165-2008 requirements. The interface shear strength of the clad plate was higher than 360 MPa, the yield strength of the final product was over 257 MPa, the clad plate tensile strength and elongation exceeded 351 MPa and 39.8%, respectively. The interpenetration of stainless steel and plain carbon steel layers was established to be complete, with the adequate composite interface. The tensile and shear properties of stainless steel-clad plates produced by the rolling process were at the same level as those obtained via the explosive method as an alternative, while their production cost were somewhat reduced.Проведено промышленное испытание листа, плакированного нержавеющей сталью 304 с обычной углеродистой сталью Q345B, с использованием линии горячей прокатки группы Hesteel. После двух этапов опытного производства было установлено, что основные техниРефераты ческие показатели производства листа удовлетворяют требованиям GB/T 8165 2008. Прочностьпри сдвиге на поверхности раздела плакированного листа превышала 360 МПа, предел текучести конечного продукта превышал 257 МПа, прочность при растяжении испытуемого материала превышала 351 МПа, а удлинение плакированного листа превышало 39,8%. Показано, что степень амальгамации слоя нержавеющей стали и нелегированной углеродистой стали была высокой, а поверхность раздела композита ровной и совершенной. Свойства при растяжении и сдвиге плакированных нержавеющей сталью листов, изготовленных с помощью процесса взрывной прокатки, соответствовали таковым, изготовленным путем взрывного процесса. Однако эффективность процесса взрывной прокатки существенно выше, чем взрывного процесса, при этом производственные затраты были гораздо меньше.Проведено промислове випробування листа, плакованого нержавіючої сталлю 304 зі звичайною вуглецевою сталлю Q345B, з використанням лінії гарячої прокатки групи Hesteel. Після двох етапів дослідного виробництва було встановлено, що основні технічні показники виробництва листа задовольняють вимогам GB/T 8165-2008. Міцність при зсуві на поверхні розділу плакованого листа перевищувала 360 МПа, межа плинності кінцевого продукту перевищував 257 МПа, міцність при розтягузі випробуваного матеріалу перевищувала 351 МПа, а подовження плакованого листа перевищувало 39,8%. Показано, що ступінь амальгамування шару нержавіючої сталі і нелегованої вуглецевої сталі була високою, а поверхня розділу композиту рівною і досконалою. Властивості при розтязі і зсуві плакованих нержавіючої сталлю листів, виготовлених за допомогою процесу вибуховий прокатки, відповідали таким, виготовленим шляхом вибухового процесу. Однак ефективність процесу вибуховий прокатки істотно вище, ніж вибухового процесу, при цьому виробничі витрати були набагато менше

Vortex structure in d-density wave scenario of pseudogap

We investigate the vortex structure assuming the d-density wave scenario of the pseudogap. We discuss the profiles of the order parameters in the vicinity of the vortex, effective vortex charge and the local density of states. We find a pronounced modification of these quantities when compared to a purely superconducting case. Results have been obtained for a clean system as well as in the presence of a nonmagnetic impurity. We show that the competition between superconductivity and the density wave may explain some experimental data recently obtained for high-temperature superconductors. In particular, we show that the d-density wave scenario explains the asymmetry of the gap observed in the vicinity of the vortex core.Comment: 8 pages, 10 figure

Di-hadron azimuthal correlation and Mach-like cone structure in parton/hadron transport model

In the framework of a multi-phase transport model (AMPT) with both partonic and hadronic interactions, azimuthal correlations between trigger particles and associated scattering particles have been studied by the mixing-event technique. The momentum ranges of these particles are $3< p^{trig}_T< 6$ GeV/$c$ and $0.15< p_{T}^{assoc} < 3$ GeV/$c$ (soft), or $2.5<p^{trig}_T<$ 4 GeV/$c$ and $1< p_{T}^{assoc} < 2.5$ GeV/$c$ (hard) in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. A Mach-like structure has been observed in correlation functions for central collisions. By comparing scenarios with and without parton cascade and hadronic rescattering, we show that both partonic and hadronic dynamical mechanisms contribute to the Mach-like structure of the associated particle azimuthal correlations. The contribution of hadronic dynamical process can not be ignored in the emergence of Mach-like correlations of the soft scattered associated hadrons. However, hadronic rescattering alone cannot reproduce experimental amplitude of Mach-like cone on away-side, and the parton cascade process is essential to describe experimental amplitude of Mach-like cone on away-side. In addition, both the associated multiplicity and the sum of $p_{T}$ decrease, whileas the $$ increases, with the impact parameter in the AMPT model including partonic dynamics from string melting scenario.Comment: 9 pages, 5 figures; Physics Letters B 641, 362-367 (2006

Phonon effects in molecular transistors: Quantum and classical treatment

We present a comprehensive theoretical treatment of the effect of electron-phonon interactions in molecular transistors, including both quantal and classical limits and we study both equilibrated and out of equilibrium phonons. We present detailed results for conductance, noise and phonon distribution in two regimes. One involves temperatures large as compared to the rate of electronic transitions on and off the dot; in this limit our approach yields classical rate equations, which are solved numerically for a wide range of parameters. The other regime is that of low temperatures and weak electron-phonon coupling where a perturbative approximation in the Keldysh formulation can be applied. The interplay between the phonon-induced renormalization of the density of states on the quantum dot and the phonon-induced renormalization of the dot-lead coupling is found to be important. Whether or not the phonons are able to equilibrate in a time rapid compared to the transit time of an electron through the dot is found to affect the conductance. Observable signatures of phonon equilibration are presented. We also discuss the nature of the low-T to high-T crossover.Comment: 20 pages, 19 figures. Minor changes, version accepted for publication in Phys. Rev.