Effect of spin–orbit coupling on spectral and transport properties of tubular electron gas in InAs nanowires

We constructed the Hamiltonian of spin–orbit splitting for carriers of a tubular electron gas in InAs nanowires. The spectral problem is solved using an exact numerical diagonalization. It is shown that the contribution of k-linear Dresselhaus-like spin–orbit (SO) coupling leads to renormalization of the so-called SO-gaps and appearance of anticrossings in subband spectrum. These features can be detected in ballistic transport.     

Analytic study of electron transmission through serial mesoscopic metallic rings

We investigate the electron transmission through a structure of serial mesoscopic metallic rings coupled to two external leads. A set of analytical expressions based on the quantum waveguide transport and the transfer matrix method are derived and used to discuss the effects of geometric configurations on transmission probabilities. It is found that in the contact ring case the existence of an applied magnetic flux is necessary to create transmission gaps, while in the non-contact ring case transmission gaps always appear irrespective of whether there is an applied magnetic flux or not. The transmissions for periodic rings with a defect ring and periodic rings built by two sorts of rings are also briefly studied. It is also found that the transmission periodicity with wave vector must be ensured by the commensurability of two characteristic lengths, i.e., of the half perimeter of a ring and the connecting wire between two adjacent rings. The special points of wave vector and magnetic flux which give rise to the transmission resonance and antiresonance are analyzed in detail.     

Size effect modulation light sources — Possibility of LED mode operation at room temperature

A new method is proposed to realize a constant charge operation in a size effect modulation LED (SEM/LED) with a high speed switching capability. The theoretical estimation shows a possibility of promising LED mode operation of the SEM/LED at 300K with the aid of the proposed circuit scheme.     

Photoelectric emission from the negative electron affinity (100) diamond surface — exciton effects

Investigation of the photoelectric yield characteristics of the negative electron affinity NEA (100) diamond surface (produced by hydrogen plasma exposure) finds a striking similarity to the emission from NEA (111) diamond surfaces. Work on NEA diamond (111) surfaces has revealed the important role (sometimes dominant) of photoexcited excitons in the photoelectric yield. Comparison of the electron emission properties among surfaces with different crystallographic orientations can give further insight into electron emission mechanisms. We find that the kinetic energy distribution, the photon energy dependence of photoelectric yield, and the photon energy dependence of constant final state measurements of NEA (100) diamond are characteristically similar to the emission from NEA (111) diamond surfaces. Observed differences appear related to the change in band bending at the surface.     

流注放电低温等离子体中电子输运系数计算的蒙特卡罗模型

流体或者粒子-流体混合数值仿真是研究流注放电基本物理机制的常用手段,而精确的电子输运系数是保证其仿真正确性的必要前提.鉴于现有电子输运系数求解工具存在一定缺陷,本文开发了采用蒙特卡罗方法求解低温等离子体中电子输运系数的仿真工具,测试表明其准确性和精确度均较高.研究了氮氧气体混合比及大气压下三体碰撞吸附对电子输运系数的影响.氮气中流注放电仿真表明,流体仿真中采用本模型改进后的电子输运系数可显著改善流注通道内部的等离子体参数分布.     

Study of two‐electron jumps in relaxation of Coulomb glasses

A long‐standing debate in the theory of hopping insulators concerns the role of multi‐electron transitions in the dynamics of the system. The natural assumption is that as temperature is lowered, two‐electron transitions will play an increasingly important role since they provide a way of tunneling through additional energy barriers which would be energetically unfavorable as successive one‐electron transitions. This was disputed in [1], but later it was seen in [2]. The reason for this discrepancy is not clear and deserves further attention. One point where the two approaches diverged was in the selection and weighting of the two‐electron transitions relative to one‐electron transitions. We present calculations of the transition rates to second order in the tunneling matrix element, which will be used in improved numerical studies. We compare results for only one‐electron jumps with results including also two‐electron jumps.     

Effects of temperature and impurities on electron radiation damage in the high voltage microscope

This paper describes the results of irradiation of specimens of copper and copper containing up to 2 at % beryllium in the high-voltage electron microscope. The results of irradiation at temperatures ranging from 20–500 K are described and discussed in the light of recently proposed theories of defect nucleation. Although the results are difficult to interpret because of the many diverse factors which influence the nucleation and growth of the damage it was found that the values for the volume density of defects were in general agreement with the predictions, if the effects of the foil surfaces were taken into account.

The corrected densities were used to derive values for the activation energy for motion of an interstitial in copper, E_m , and the binding energy between an interstitial and a beryllium atom, E_b . The results obtained were 0.12±0.03 eV for E_m and 0.29±0.07 eV for E_b .     

Room temperature CW lasing operation of monolithically grown 1.55 μm vertical external cavity surface emitting laser

We report room temperature (20 °C) continuous-wave operation of 1.55 μm vertical-external-cavity surface-emitting lasers. The optically pumped monolithic InP-based structure, grown by metal–organic chemical vapor deposition, includes a InP/InGaAsP Bragg reflector, and an active region with strain compensated quantum wells. Output power up to 4 mW is obtained at 0 °C. The thermal impedance of the structure is deduced from the experimental data.     

Monte Carlo simulations of the two-dimensional quantal and classical spin systems — A new type of phase transition with vortices

A new type of phase transition has been found in the two-dimensional XY-model using Monte Carlo simulations, which show a divergence of susceptibility, but no divergence of specific heat. Vortices appear below T_c as was predicted by Kosterlitz and Thouless.     

Room temperature polarized photoreflectance and photoluminescence characterization of AlGaAs/InGaAs/GaAs high electron mobility transistor structures

We have characterized the properties of three AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor structures with two different well widths fabricated by molecular beam epitaxy on (0 0 1) GaAs substrates with different threading dislocation densities using room temperature photoreflectance (PR) and photoluminescence (PL). The samples were denoted as A, B and C with well widths of 140, 160 and 160 Å, respectively. Samples A and B were grown on substrates with lower threading dislocation densities. For samples B and C, the well width exceeds the pseudomorphic limit so that there is some strain relaxation and related misfit dislocations, as determined from X-ray measurements. In order to detect the anisotropic strain of the misfit dislocations related to strain relaxation, the PR measurements were performed for incident light polarized along [1 1 0] and directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polarized PR features and reduction of the intensity of PL signals in the InGaAs channel layer. The lowest lying intersubband transition has been confirmed by a comparison of the PR and PL spectra. Signals have been observed from every region of the sample making it possible to evaluate the In and Al compositions, channel width and two-dimensional electron gas density as well as the properties of the GaAs/AlGaAs multiple quantum well buffer layer.     

Volatile metal β-diketonates — new precursors for the sonochemical synthesis of nanosized materials — sonolysis of thorium(IV) β-diketonates

Ultrasonic irradiation (22 kHz, Ar atmosphere) of Th(IV) β-diketonates Th(HFAA)₄ and Th(DBM)₄, where HFAA and DBM are hexafluoroacetylacetone and dibenzoylmethane respectively, causes them to decompose in hexadecane solutions, forming solid thorium compounds. The first-order rate constants for Th(IV) β-diketonate degradation were found to be (9.3±0.8)×10⁻³ for Th(HFAA)₄ and (3.8±0.4)×10⁻³ min⁻¹ for Th(DBM)₄, (T=92°C, I=3 W cm⁻²). The rate of the sonochemical reaction increased with the rising β-diketonate volatility and decreased with the rising hydrocarbon solvent vapor pressure. Solid sonication products consisted of a mixture of thorium carbide ThC₂ and Th(IV) β-diketonate partial degradation products. The average ThC₂ particle size was estimated to be about 2 nm. ThC₂ formation was attributed to the high-temperature reaction occurring within the cavitating bubble. The thorium β-diketonate partial degradation products formed in the liquid reaction zones surrounding the cavitating bubbles.     

Localization of π‐electron density in twisted bilayer graphene

In bilayer graphene, mutual rotation of layers has strong effect on the electronic structure. We theoretically study the distribution of electron density in twisted bilayer graphene with the rotation angle of 21.8° and find that regions with AA‐like and AB‐like stacking patterns separately contribute to the interlayer low‐energy van Hove singularities. In order to investigate the peculiarities of interlayer coupling, the charge density map between the layers is examined. The presented results reveal localization of π‐electrons between carbon atoms belonging to different graphene layers when they have AA‐like stacking environment, while the interlayer coupling is stronger within AB‐stacked regions.

Charge density map for bilayer graphene with a layer twist of 21.8° (interlayer region).     

Effect of temperature,electric and magnetic field on spin relaxation in single layer graphene: A Monte Carlo simulation study

In this article, we employ the semiclassical Monte Carlo approach to study the spin polarized electron transport in single layer graphene channel. The Monte Carlo method can treat non-equilibrium carrier transport and effects of external electric and magnetic fields on carrier transport can be incorporated in the formalism. Graphene is the ideal material for spintronics application due to very low Spin Orbit Interaction. Spin relaxation in graphene is caused by D'yakonov-Perel (DP) relaxation and Elliott-Yafet (EY) relaxation. We study effect of electron electron scattering, temperature, magnetic field and driving electric field on spin relaxation length in single layer graphene. We have considered injection polarization along z-direction which is perpendicular to the plane of graphene and the magnitude of ensemble averaged spin variation is studied along the x-direction which is the transport direction. This theoretical investigation is particularly important in order to identify the factors responsible for experimentally observed spin relaxation length in graphene.     

Characterization of the Metrology beamline at the SOLEIL synchrotron and application to the determination of mass attenuation coefficients of Ag and Sn in the range 3.5 ≤ E ≤ 28 keV

This work presents the new Metrology beamline at the SOLEIL synchrotron facility and a first attempt to quantitative measurements of mass attenuation coefficients for Ag and Sn performed on the hard X‐ray branch. We first describe the beamline itself and the characterization performed of the unfocused monochromatic beam running mode. We performed a first experimental measurement of mass attenuation coefficients in the range 3.5 ≤ E ≤ 28 keV and we also derived the K‐absorption and L‐absorption jump ratios. The results are compared with theoretical values as well as with other experimental data and agree well with previous published values. Copyright © 2011 John Wiley & Sons, Ltd.     

What mesoscopic structures really “remember”: insufficiency of the open boundary approximation

We analyze the influence of contact electrons on quantum transport in a resonant-tunneling diode (RTD), using a many-body density matrix formalism for open systems. We explicitly relate the net current in the RTD to the memory-containing effective interaction between the RTD active region and the contacts. This effect can only be captured if the RTD active region is treated fully as a dynamically open system.     

Quantum Transport in Presence of Bound States – Noise Power

The impact of bound states in Landauer‐Büttiker scattering approach to non‐equilibrium quantum transport is investigated. We show that the noise power at frequency ν is sensitive to all bound states with energies ω_b satisfying . We derive the exact expression of the bound state contribution and compare it to the one produced by the scattering states alone. The theoretical and experimental consequences of this result are discussed.     

Investigation of light scattering from rough periodic surfaces — numerical solutions

The Beckmann scalar scattering model based on the Kirchhoff approximation was used to investigate the scattering of light from periodic surfaces whose roughness amplitude is comparable to, and greater than, the illumination wavelength. Solutions by numerical integration were obtained for surfaces of different profiles and of different roughnesses. It was found that the scattering patterns from these surfaces were very different at large roughness amplitudes. As the incident angle was varied on a given surface, it was also observed that the intensity of any individual diffraction order oscillated and the degree of oscillation was directly related to roughness. By utilizing this property, a new procedure could be developed for surface roughness assessment.     

Light scattering properties of a rough-ended optical fibre — theoretical evaluation

Almost uniform wide-angle laser irradiation, for use in medical applications, is achieved by roughening chemically the output end of an optical fibre. The angular distribution of the scattered light is studied theoretically using perturbation theory. The theoretical results evaluated from a simple method of calculation are in sufficiently good agreement with experiment.