Characteristics of electron drift in the low-pressure gas discharge

The features of the energy distribution function of electrons during their drift in neon are analyzed for typical conditions of experiments with dust structures in plasma. The energy balance of electrons and drift characteristics in an electric field at strengths 13 < E/N < 42 Td were calculated taking into account inelastic collisions and the effect of electron loss on gas-discharge tube walls.     

Characteristics of the backscattering of moderate-energy electrons by solids having different atomic numbers

The coefficient of backscattering of primary electrons is discussed as a function of their energy and atomic number Z. The amplitude of the wave function obtained in the first Born approximation and the Thomas-Fermi atom model are used to calculate the constant for screening of the electric field of the nucleus by atomic electrons. The theoretically calculated integral backscattering coefficients of primary electrons are compared with the experimental values in the range 12<Z<92 for primary electron energies of 10 and 40 keV. Possible applications of these results are indicated. Zh. Tekh. Fiz. 69, 40–45 (June 1999)     

Scanning of a laser beam and purification of materials through the use of light-induced particle drift in semiconductors

The light-induced drift of electrons, light-absorbing impurities, and defects in II-VI semiconductors is investigated experimentally, along with some potential practical applications of the phenomenon. It is shown that the light-induced drift of electrons induces a very pronounced change in the refractive index, |Δn|∼0.01, and can be used to implement effective scanning of nanosecond and picosecond laser pulses through frustration of total internal reflection. The light-induced drift of absorbing particles increases their density in the surface layer of the crystals, and this effect can be exploited in semiconductor technology. Zh. Tekh. Fiz. 68, 121–124 (April 1998)     

The high-acceptance dielectron spectrometer HADES

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion-induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from 18^° to 85^° , a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range ( 0.1 < p < 1.0 GeV/c . This paper describes the main features and the performance of the detector system.     

(2γ,2e) total and differential cross-section calculations for helium with ?ω = 40–50 eV

We consider two-photon double ionization of helium and analyse the electron dynamics in the region where the process is direct (39.49 eV < ħω < 54.42 eV). The fundamental process of two-photon double ionization (TPDI) is far from being well understood. In order to gain physical insight into the dynamics involved in TPDI, we investigate the electron energy distributions for ħω = 46 eV and ħω = 50 eV, angular distributions are also analysed. The theoretical approach is based on the resolution of the time-dependent Schr?dinger equation (TDSE), using a spectral approach. At the end of the pulse the TPDI probability is extracted from the total wavefunction using two different approaches. The first one neglects the electron interaction in the double continuum while the second one includes electron correlation effects. At ħω ≈ 45 eV the electrons are preferably emitted back-to-back with equal energy. At ħω = 50 eV the excess energy is likely to be transfered to one of the electron, while the electrons are emitted in opposite or same directions.     

Effect of small admixtures of N<Subscript>2</Subscript>, H<Subscript>2</Subscript> or O<Subscript>2</Subscript> on the electron drift velocity in argon: experimental measurements and calculations

The electron drift velocity in argon with admixtures of up to 2% of nitrogen, hydrogen or oxygen is measured in a pulsed Townsend system for reduced electric fields ranging from 0.1 Td to 2.5 Td. The results are compared with those obtained by Monte Carlo simulations and from the solution of the electron Boltzmann equation using two different solution techniques: a multiterm method based on Legendre polynomial expansion of the angular dependence of the velocity distribution function and the S _n method applied to a density gradient expansion representation of the distribution function. An almost perfect agreement between the results of the three numerical methods and, in general, very good agreement between the experimental and the calculated results is obtained. Measurements in Ar-O₂ mixtures were limited by electron attachment to oxygen molecules, which contributes to the measured drift velocity. As a result of this attachment contribution, the bulk drift velocity becomes larger than the flux drift velocity if attachment is more probable for electrons with energy below the mean value and smaller in the opposite case. Attachment also contributes to the negative differential conductivity observed in Ar-O₂ mixtures.     

Electrical conductivity of germanium with dislocation grids

Samples of n-type germanium with a donor concentration N _d=2.4×10¹⁶ cm⁻³ are plastically deformed to a degree of strain equal to 18–40% to detect static conduction by electrons trapped on dislocations in a system of dislocation grids. In samples with 20%<δ<31%, which retain an electronic type of conductivity, the conductivity for T<8 K, which is weakly temperature-dependent, is associated with conduction by electrons trapped on dislocations. The nonmonotonic dependence of the conductivity at 4.2 K on the degree of strain as the latter increases from 18% to 40% attests to the existence of an energy gap between the donor and acceptor dislocation states in strongly plastically deformed germanium. Zh. éksp. Teor. Fiz. 115, 115–125 (January 1999)     

On the role of correlation energy produced by the spin-spin interaction in the formation of binding energy for two-electron atomic systems

An algorithm is proposed for computing the correlation energy produced by the spin-spin interaction V _SS of electrons in He-like atomic systems. The algorithm takes into account the singular nature of V _SS and the formation of a compact finite motion of electrons in the range of distances Ze ²/mc ² < r ₁₂ < ħ/mc between the electrons under the action of the magnetic fields of spins for a singlet ground state. Good agreement with experimental values of the ionization potential is attained for a wide set of two-electron atomic systems without resorting to variational procedures, but only using hydrogen-like wavefunctions and correctly taking into account the singular nature of the spin-spin interaction of electrons.     

Spatial evolution of the generation and relaxation of excited carriers near the breakdown of the quantum Hall effect

We have measured the generation and relaxation of excited carriers along their drift direction near the breakdown of the quantum Hall effect (QHE). The dissipative resistivity ρ_xx(x) at current densities close to the critical value for the QHE breakdown was measured as a function of the distance x from the electron injection at x=0. By injecting “cold” electrons into constrictions at supercritical current levels, the evolution of the breakdown along the drift direction was monitored. After a smooth increase of the resistivity with the drifting distance, an avalanche-like rise towards a saturation value occurs. Drastic changes of the resistivity profiles with the applied current were found in a narrow range around the critical current. The observed behavior is attributed to impurity-assisted tunneling between Landau levels. By injecting hot electrons (excited in a periodic set of constrictions) into a region with subcritical current density, the relaxation process was analyzed. Inelastic relaxation lengths with typical values in the range from 0.3 to 4 μm were found, which agree within 10% with the elastic mean free path determined from the Hall mobility at zero magnetic field. We conclude that the energy relaxation process is triggered by scattering at impurity potentials.     

Absolute Electron Impact Cross Sections for Single Ionization of Metastable Atoms of H,He, Ne,Ar, Kr,Xe and Rn

Cross sections for single ionization of metastable atoms of H, He, Ne, Ar, Kr, Xe and Rn by electrons with impact energy E (threshold < E < 200 eV) are determined using a recently developed semiclassical formula. The formula consists of an energy dependent term (classical binary encounter approximation) and a term containing the weighted sum of the squared radii of maximum charge density of the outer electron subshells (Born Bethe approximation). Although this formula was originally devised and applied for ground state atoms, a comparison of the present calculations with previous calculations and measurements indicates that this formula can also be used successfully in case of metastable atoms.     

Ferromagnetic phases in spin-Fermion systems

Spin-Fermion systems which obtain their magnetic properties from a system of localized magnetic moments being coupled to conducting electrons are considered. The dynamical degrees of freedom are spin-s operators of localized spins and spin-1/2 Fermi operators of itinerant electrons. Renormalized spin-wave theory, which accounts for the magnon-magnon interaction, and its extension are developed to describe the two ferromagnetic phases in the system: low temperature phase 0 < T < T*, where all electrons contribute the ordered ferromagnetic moment, and high temperature phase T* < T < T _C , where only localized spins form magnetic moment. The magnetization as a function of temperature is calculated. The theoretical predictions are utilize to interpret the experimentally measured magnetization-temperature curves of UGe₂.     

The anomalous PAMELA effect and its explanation

The anomalous effect discovered in the PAMELA experiment includes the unusual behavior of the ratio r of fluxes of Galactic positrons to the total flux of Galactic positrons and electrons. According to theory, the value of r should decrease with increasing energy E of these particles. The experiment has shown, however, that in the energy range of 0.1 GeV < E < 5 GeV, the value of r declines; then, beginning with E > 5 GeV and up to E ≈ 150 GeV (measurements have been conducted only up to this energy level), we observe its growth. An explanation for this phenomenon is given.     

Modeling of the energy spectrum of the CdTe/Hg1-xCdxTe/CdTe quantum well by varying the band offset, well width, and composition x

Currently, CdTe/Cd _x Hg_1-x Te/CdTe heterostructures attract particular interest and are very promising for developing the next-generation terahertz radiation detectors. However, properties of such structures have not yet been studied in sufficient detail. The energy spectrum and wave functions of the CdTe/Cd _x Hg_1-x Te/CdTe heterostructure were theoretically modeled for various well widths, the valence band offset, and composition x in the range 0<x<0.16. Characteristic features of the behavior of energy levels of two-dimensional electrons in such structures were studied with respect to x variation. A criterion for determining the number of electronic levels below the conduction band bottom, applicable to compositions 0<x<0.16 was obtained. The time of two-dimensional electron relaxation by longitudinal optical phonons was calculated.     

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa-Maxwellian auroral plasmas

The presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa-Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.     

A method for studying catalytic reactions based on chemiemission of electrons

It was found that, if the energy released in the formation of product molecules in a heterogeneous reaction was smaller than the work function of the surface, the current density of the chemiemission of electrons from the surface of any semiconductor satisfied the condition j ≈ Bexp(βE), where B and β are coefficients and E is the electric field in the semiconductor surface plane. A mathematical model describing the transfer of hot metal electrons excited in a catalytic reaction through the metal-gas interphase boundary was studied. The parameters of the system at which a study of the distribution of catalytic centers over the surface of a metal or semiconductor by the scanning tip method on the basis of the chemiemission of electrons stimulated by an electric field was possible (resolution δr ∼ 10⁻⁸–10⁻⁷ m) were determined. Theoretical results corresponded to the experimental data obtained using weak electric fields (0 < E < 5 × 10⁶ V/m) for the heterogeneous recombination of hydrogen atoms on the surface of calcium, titanium, and n-type silicon.     

Energy and angular distributions of backscattered electrons from collisions of 5 keV electrons with thick Al,Ti, Ag,W and Pt targets

The energy and angular distributions of backscattered electrons produced under the impact of 5 keV electrons with thick Al, Ti, Ag, W and Pt targets are measured. The energy range of backscattered electrons is considered between E _B = 50 eV and 5000 eV. The angle of incidence α and take-off angle θ are chosen to have values α = 0 and 10 and θ = 100, 110 and 120 respectively. The measured energy spectra are compared with the available theoretical models for α = 0 and 10. The elastic peak intensity of backscattered electrons is found to be a function of angle of incidence, take-off angle and atomic number of the target material. The considered theories are reasonably in good agreement with experiment for the energy spectra of the backscattered electrons having their reduced energies ∈ (= E _B/E ₀) in the range of 0.20 to 1.00.      

Dynamic drift of the magnetic domains in ferrite-garnet crystals

The drift of stripe-domain walls in a (111) ferrite-garnet plate with orthorhombic anisotropy and quality factor Q < 1 in an alternating magnetic field of 30–1000 Hz was investigated. The obtained experimental dependences of the domain wall drift velocity on the magnetic field frequency and amplitude are compared to the corresponding theoretical dependences.     

Determination of the drift velocity of electrons in hydrogen from the low-pressure rf-discharge breakdown curves

A method is proposed for determining the drift velocity of electrons from the position of the reversal point of the breakdown curve of an rf capacitative gas discharge. This method is used to obtain values of the electron drift velocity in hydrogen in the rangeE/p ≈ 50–2000 V·cm ⁻¹ ·Torr ⁻¹ which are in good agreement with experimental and theoretical data of other authors. State University, Kharkov. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 108–112, April, 1998.     

霍尔漂移对阳极层霍尔等离子体加速器电离效率的影响

以洛伦兹变换方法为基础,分析了阳极层霍尔等离子体加速器中电子的霍尔漂移,结果表明在交叉场中,霍尔漂移并不总是存在的,E/B的比值大于光速时,霍尔漂移将不存在.进一步的分析表明,霍尔漂移也并不总是回旋形式的,不同的电磁场配置以及不同的电子初始能量将带来不同形式的漂移,包括回旋形式,波浪线形式,甚至直线形式.电磁场的配置也决定着霍尔漂移的速度,在很大程度上影响着电子的能量,这就决定了放电时的电离效率.对不同电磁场配置进行数值模拟发现,合理的电磁场比值能够得到更好的电离效率(对于氩,这个数值大约为4×10⁶).不同的气体,根据其电离碰撞截面与电子能量的关系,都有不同的合理比值.     

Crystal-field effects in the intermediate-valence compound YbCu2Si2

Inelastic thermal-neutron scattering is used to study the intermediate-valence system YbCu₂Si₂. The magnetic scattering in two nonoverlapping ranges of transfer energies, 2<ε<5 meV and 5<ε<100 meV, is analyzed under the assumption that the regions influence each other only weakly. As a result, two sets of phenomenological crystal-field parameters are established, and their difference constitutes the experimental error in determining these parameters. A comparison of the fourth-order crystal field with other compounds belonging to the RCu₂Si₂ series (R stands for a rare-earth element) suggests that in YbCu₂Si₂ hybridization occurs between f electrons and copper electrons, in contrast to the heavy-fermion system CeCu₂Si₂, for which it was established earlier that hybridization occurs between f electrons and Si p electrons. Zh. éksp. Teor. Fiz. 114, 291–314 (July 1998)