Transferred charge of brush discharges in explosive gas atmospheres – A verification of the ignition threshold limits

A wide series of experiments has been performed to check the incentivity of hydrogen/air, ethene/air and propane/air mixtures due to brush discharges. Thereby, the transferred charge as a criterion to judge the ignition potential is determined to verify the thresholds of transferred charge given in the standards IEC 60079-0 and in EN 13463-1. These thresholds have never been examined directly in an experiment before. It is stated that the thresholds for explosion group IIA, IIB and IIC represent different levels of safety. Using adequate thresholds the criterion of transferred charge is suitable for a judgement of potential electrostatic ignition sources.     

“Magnetodipole” self-organization of charge carriers in high-T c superconductors and the kinetics of phase transition

A phenomenological model describing “magnetodipole” self-organization of charge carriers (the formation of so-called stripe-structures and the energy gap in the spectrum of states) was suggested to interpret the data of nonstationary nonlinear spectroscopy of high-T _c superconductors. It was shown that, after rapidly heating a superconducting sample, the kinetics of the succeeding phase transition depended on initial temperature T. At small “overheatings” T*<T<T _m x≈(1.4?1.5)T* (T _c and T*≈T _c are the temperatures of the transition to the superconducting state and the formation of stripe-structures) and the optimal level of doping, the decay of stripe-structures (and of the gap in the spectrum of states) occurred at a low rate (in times above to 10^?9 s) in spite of the virtually instantaneous disappearance of superconductivity.     

Estimating the sound speed of the surface layer of the seabed using ocean ambient noise in shallow water

To improve the inversion efficiency, a method for quickly and directly estimating the sound speed of the surface layer of the seabed is proposed. According to the energy flux theory, the ocean ambient noise data received by the vertical line array can be used to extract the bottom loss(BL) passively. The BL curve has an effect on the critical angle, which is used to estimate the sound speed of the surface layer of the seabed. Based on the ray model,the difference between the BL calculated from t...     

Mechanism of collection of non-equilibrium charge carriers in the presence of ionization losses in π-ν-n-structures based on GaAs

The distribution of an electric field and the amplitude spectra obtained experimentally in the presence of ionization losses of charge particles in a detector of π-ν-n-structures are presented in this paper. It is shown that trapping of nonequilibrium holes by negatively charged deep centers keeps the electric field in the tract high enough for electron drift with maximum velocity. Due to this, the charge collection efficiency (CCE) reaches 50–60%. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 32–37, March 1999.     

Nature of charge carriers in disordered molecular solids: are polarons compatible with observations?

Polaronic theories for charge transport in disordered organic solids, particularly molecularly doped polymers, have been plagued by issues of internal consistency related to the magnitude of physical parameters. We present a natural resolution of the problem by showing that, in the presence of correlated disorder, polaronic carriers with binding energies Delta approximately 50-500 meV and transfer integrals J approximately 1-20 meV are completely consistent with the magnitudes of field and temperature dependent mobilities observed.     

Dynamics of the phase transitions in the system of nonequilibrium charge carriers in quantum-dimensional Si1 − x Ge x /Si structures

The dynamics of the phase transition from an electron-hole plasma to an exciton gas is studied during pulsed excitation of heterostructures with Si_{1 ? x} Ge _x /Si quantum wells. The scenario of the phase transition is shown to depend radically on the germanium content in the Si_{1 ? x} Ge _x layer. The electron-hole system decomposes into a rarefied exciton and a dense plasma phases for quantum wells with a germanium content x = 3.5% in the time range 100–500 ns after an excitation pulse. In this case, the electron-hole plasma existing in quantum wells has all signs of an electron-hole liquid. A qualitatively different picture of the phase transition is observed for quantum wells with x = 9.5%, where no separation into phases with different electronic spectra is detected. The carrier recombination in the electron-hole plasma leads a gradual weakening of screening and the appearance of exciton states. For a germanium content of 5–7%, the scenario of the phase transition is complex: 20–250 ns after an excitation pulse, the properties of the electron-hole system are described in terms of a homogeneous electron-hole plasma, whereas its separation into an electron-hole liquid and an exciton gas is detected after 350 ns. It is shown that, for the electron-hole liquid to exist in quantum wells with x = 5–7% Ge, the exciton gas should have a substantially higher density than in quantum wells with x = 3.5% Ge. This finding agrees with a decrease in the depth of the local minimum of the electron-hole plasma energy with increasing germanium concentration in the SiGe layer. An increase in the density of the exciton gas coexisting with the electron-hole liquid is shown to enhance the role of multiparticle states, which are likely to be represented by trions T ⁺ and biexcitons, in the exciton gas.     

Recent trends in the tuning of polymersomes’ membrane properties

“Polymersomes” are vesicular structures made from the self-assembly of block copolymers. Such structures present outstanding interest for different applications such as micro- or nano-reactor, drug release or can simply be used as tool for understanding basic biological mechanisms. The use of polymersomes in such applications is strongly related to the way their membrane properties are controlled and tuned either by a precise molecular design of the constituting block or by addition of specific components inside the membrane (formulation approaches). Typical membrane properties of polymersomes obtained from the self-assembly of “coil coil” block copolymer since the end of the nineties will be first briefly reviewed and compared to those of their lipidic analogues, named liposomes. Therefore the different approaches able to modulate their permeability, mechanical properties or ability to release loaded drugs, using macromolecular engineering or formulations, are detailed. To conclude, the most recent advances to modulate the polymersomes’ properties and systems that appear very promising especially for biomedical application or for the development of complex and bio-mimetic structures are presented.     

Numerical investigations on the current conduction in bilayer organic light-emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trapped charge limited conduction. The dependences of the current density on the operation voltage, the thickness and trap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure anode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trap depth, total trap density, and cv~rrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL to the sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentially with the mean reduced trap depth.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Numerical investigations on the current conduction in bilayer organic light—emitting devices with ohmic injection of charge carriers

A numerical model for bilayer organic light-emitting diodes (OLEDs) has been developed on the basis of trappedcharge limited conduction. The dependences of the current density on the operation voltage, the thickness andtrap properties of the hole transport layer (HTL) and emission layer (EML) in bilayer OLEDs of the structure an-ode/HTL/EML/cathode have been numerically investigated. It has been found that, for given values of reduced trapdepth, total trap density, and carrier mobility of HTL and EML, there exists an optimum thickness ratio of HTL tothe sum of HTL and EML, by which a maximal current density, and hence maximal quantum efficiency and luminance,can be achieved. The current density decreases quickly with the mean trap density, and decreases nearly exponentiallywith the mean reduced trap depth.     

Theoretical study of the optical and charge transport properties in non-peripherally octasubstituted phthalocyanine–tetrabenzoporphyrin hybrids

The charge transfer rate of seven non-peripherally phthalocyanine–tetrabenzoporphyrin hybrids was investigated theoretically at the level of B3LYP/6-31+G(d,p) using density functional theory. The results showed that the hybrids are semiconductor molecules, which have a certain absorption in the visible region. The hole or electron transport capability of a non-peripherally substituted octamethyl phthalocyanine molecule is obviously better than that of phthalocyanine or non-peripherally substituted octafluorine, octamethoxy phthalocyanine molecules at 300 K, whereas the holes or electron transport capabilities of four non-peripherally substituted octamethoxy phthalocyanine–tetrabenzoporphyrin hybrids are basically the same. Overall, the hole transport capability of hybrids is superior to their electron transport capability. The charge transfer rate constant and the carrier mobility rate of three representative molecules using three methods, that is the long range-corrected functionals CHB-B3LYP and WB97XD, the metahybrid GGA M06-2X functional, are consistent with the use of the density functional B3LYP method.     

Investigation of crystal/electronic structure effects on the photoluminescence properties in the BaO–SiO2:Eu2+ systems

BaO–SiO₂:Eu²⁺ phosphors with different Ba/Si mole ratio were prepared using a solid-state reaction method, and their crystal structure dependent-photoluminescence properties were investigated. The prepared phosphor powders were characterized using X-ray diffraction (XRD), field-emission electron microscopy (FE-SEM) and fluorescence spectroscopy. The emission band of the Eu²⁺ activator varied from orange to blue with varying crystal structure of the host materials, which was related to the crystal field splitting of the Eu 5d orbitals. These emission color changes were examined by calculating the electronic band structure properties such as the density of the state. Moreover, the host material with Ba/Si=1 (BaSiO₃) for Eu²⁺, which exhibited a yellow emission when excited with near UV light, was further characterized for enhancing its emission intensity.     

Quantum transport of spin-polarized carriers in quasi paramagnetic quantum wires: Green’s function formalism

In this paper, the Schrödinger equation is solved for approximation of the ground state energies and associated wave functions of carriers confined in a rectangular semiconductor (SC) quantum wire embedded in a SiO₂ matrix. The problem was treated with the effective one band Hamiltonian. The finite difference scheme was used for the discretization of 2D Schrödinger equation and LAPACK package to resolve the band matrix. The energy levels were determined and the coupling between quantum wires was investigated. The effect on energies and relative wave functions of quantum wires number, size and separation was studied. The results obtained show that the energy levels can be importantly modified and controlled by these parameters. The interaction is manifested by a reduction in energies and an increase in the peak value of the wave function of the higher energy wire. This study offers a fast and inexpensive way to check device designs and processes and can be used in diverse device applications.     

Investigation of the crystallinity,structural, and optical properties in hydrotreating of Li–W co-doped ZnO thin films

The hydrotreated Li–W co-doped ZnO (LWZO:H) thin films was prepared on quartz glass substrates by RF magnetron sputtering at substrate temperature 100 °C with varied hydrogen flow ratios. The X-ray diffraction spectra indicated that the hydrotreating Li–W co-doped ZnO films showed a preferred orientation toward the c-axis. The chemical compositions of all samples were confirmed by X-ray photoelectron spectroscopy, which clearly showed the existence of W as a doping element into ZnO crystal lattice. The surface morphology of LWZO:H thin films changed with the increasing R value can clearly be seen. The average transmittance of the films was found to be almost 85 % for the wavelength range of 400–1,200 nm. Meanwhile, the optical band gap increase of the films may be attributed to the band Burstein–Moss effect.     

Influence of charge carriers on magnetic order in lightly doped manganites, detected by μSR: Evidence for a superparamagnetic transition to the antiferromagnetic state

We detected two spontaneous precession frequencies in antiferromagnetic pure LaMnO₃, the end member of different families of charge-doped manganites. The muon site and local field orientation are identified for one frequency, which provides a measure of the staggered magnetization. We present additional zero and longitudinal field muon relaxation data on an LaMnO_3.045 sample in which a new regime appears above an intermediate temperatureT*, where regions of magnetic order coexist with domains of fluctuating moments. These results are discussed in terms of nucleation of the ordered phase in a superparamagnetic matrix.     

Electrostatic force between rings and discs of charge inside a grounded metallic pipe using the Green’s function technique

We derive analytic formulae for the electrostatic force between ring and disc charge distributions inside a grounded metallic pipe using the Green’s function technique. These distribution models are useful in the modeling of electron beams commonly employed in microwave tubes. We analyze the electric force between two discs, between two rings, and between a disc and a ring and we compare the results for the electric potential, field, and force to numerical ones obtained from a 3D electrostatic solver. Present expressions were developed to avoid an oscillatory noise when the field diverges by axial proximity between source and observer.     

The dependence of interfacial properties on the layer number in 1T′/2H-MoS2 van der Waals heterostructures

Metallic 1T′-MoS₂ monolayers are predicted to be efficient hole injection contacts for nanoelectronic devices composed of 2H-MoS₂ monolayers. The layer number can affect the physical properties of two-dimensional materials. In this paper, the dependence of the interfacial properties of 1T′/2H-MoS₂ van der Waals (vdW) heterojunctions on the layer number was studied using density functional theory. The calculation results show that 1T′-MoS₂ forms p-type contacts with 2H-MoS₂, and the p-type Schottky barrier height (SBH) is between -75 and 30 meV and depends on the number of 1T′-/2H-MoS₂ layers. Thus, the efficiency of 1T′-MoS₂ as a hole injection contact for 2H-MoS₂ can be tuned by the layer number. This work provides a method for tuning the contact-resistance in nanodevices composed of 2H-MoS₂.