Three-body recombination of electrons and ions in the presence of two-level atoms

The distribution function of bound electrons and the recombination rate of electrons and ions in the presence of two-level atoms is considered within a diffusion model. Two cases are considered: (a) it is assumed in accordance with traditional theories that relaxation occurs as a result of binary collisions; (b) it is assumed that the anomalous drift previously discovered on the basis of a first-principles simulation takes place. It is shown that the distribution of bound electrons obtained on the basis of the theory of binary Coulomb collisions is not consistent with the results of a numerical many-particle dynamics simulation, while a kinetic model which utilizes the theory of anomalous drift is consistent with the simulation results. Zh. Tekh. Fiz. 68, 15–19 (January 1998)     

On the ultracold plasma evolution

The time evolution of the Coulomb system whose initial total energy is zero is considered. The solution for a system of 2000 particles in the range of 8000 inverse plasma frequencies was obtained by themolecular dynamicsmethod. It is shown that under conditions typical of experiments with ultracold plasma the nonideality parameter of the plasma cannot reach large values due to recombination heating, and the relaxation process itself is not described within the conventional model of three-body recombination.     

Recombination in Dense Ion Plasmas

A theory is developed to treat ion recombination in dense ion plasmas. Numerical results are obtained with the method of molecular dynamics. Exponential suppression of recombination is found for the discharge afterglow plasma in sulfur hexafluoride at strong Coulomb nonideality Γ. The reason for suppression is an increase of the recombination activation energy ΔE with increase of Γ. The range ΔE corresponds to the multiparticle fluctuations. Ion solvation is another suppression factor. Its importance is demonstrated for the discharge afterglow plasma in fluorine at weak Coulomb nonideality. The theory developed agrees with the experimental data available. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Certain properties of an electrically insulated Coulomb plasma. Numerical simulation of microfields and thermodynamic properties. the problem of ball lightning

Many-body dynamics is used to study the (quasi-)steady state of a classical Coulomb plasma. The shortest relaxation time in such a plasma, for both the Debye screening and the thermodynamic properties, is the electron transit time over the average distance between ions. The steady-state energy of the Coulomb interaction of the particles and the steady-state potential near a fixed charge can be described well by the Debye-Hückel theory, even if there is less than a single particle in a Debye sphere, on the average. Distributions of instantaneous values of the microfields in the plasma are derived. The results calculated for the electron turning distance are compared with the results of the quasibinary theory. An attempt is made to link the anomalously long lifetime of the plasma of ball lightning to a retardation of the recombination of a classical Coulomb plasma in the absence of a stochastic external agent.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 10–23, February, 1992.     

First-principles theory of intermediate-valence f-electron systems

We propose a first-principles based method for calculating the electronic structure and total energy of solids in an intermediate-valence configuration. The method takes into account correlation effects (d-f Coulomb interaction) and many-body renormalization of the effective hybridization parameter of the f system. As an example, the formation of a pressure-induced intermediate-valence state in Yb is considered and its electronic structure and equation of state are calculated and compared to experimental data. The agreement is found to be excellent for both properties, and we argue that the developed method, which applies to any element or compound, provides for the first time a quantitative theoretical treatment of intermediate-valence materials.     

Electrical Conductivities of Nonideal Iron and Nickel Plasmas

Electrical conductivities of iron and nickel plasmas are calculated using a nonideal plasma ionization balance model that takes into account the excess free energy due to strong Coulomb couplings between charged particles in the pressure‐ionization regime. The electrical conductivities calculated for partially ionized plasmas are in fair agreement with data measured in exploding wire discharge experiments and effectively demonstrate the insulator‐metal transition near solid densities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semiclassical theory of the radiative-collisional cascade in a Rydberg atom

We have developed a two-dimensional semiclassical model of the radiative-collisional cascade for hydrogen-like systems. We describe the collisions with electrons and ions by classical diffusion in the space of principal and orbital quantum numbers and use an iterative procedure that consistently takes into account the quantum nature of the radiative cascade for radiative transitions. The model establishes the correspondence between the quantum and classical approaches and indicates that the latter cannot be directly used to calculate the population kinetics of highly excited atomic states. Our calculations of the two-dimensional populations of highly excited atomic hydrogen states for selective, three-body, and photorecombination sources of population allow the data of one-dimensional kinetic models to be refined. The calculated intensities of recombination lines demonstrate the degree of nonequilibrium of the Rydberg state populations under typical astrophysical plasma conditions.     

Kinetics of laser-induced oxidation of silicon near room temperature

The growth of ultra-thin (<6 nm) silicon-dioxide films on Si(100):H, Si(111):H, and a-Si:H surfaces in a dry oxygen atmosphere (0.1–10 Pa) at low temperatures (35–200 °C) was investigated. Oxidation was induced by pulsed F₂-laserradiation at 157 nm. The thickness and composition of the growing films were monitored in real time by spectroscopic ellipsometry in the photon energy range of 1.15–4.75 eV. The kinetics of low-temperature oxidation was similar for the Si surfaces investigated and differs from that of high-temperature thermal oxidation (900–1200 °C) that can be described by the Deal–Grove model. To explain the faster growth at the initial stage, it is proposed that oxidation occurs by diffusion of oxygen atoms O and/or ions O^-rather than oxygen molecules. The recombination of diffusive species to oxygen molecules limits their penetration into the bulk. A diffusion model is developed for low-temperature oxidation which takes into account the recombination process of the diffusive species. Good agreement between theory and experiment is found. The activation energy of diffusion of the active species was found to be 0.15 eV, in agreement with previous results and recent calculations for O^- ions. PACS 82.65.+r; 07.60.Fs; 81.65.Mq; 82.50.Hp     

Coulomb collisions and the bound-electron recombination distribution function

A detailed analysis is made of how the distribution function of bound electrons is formed in the presence of three-bodyi—e—e recombination. The kinetic K matrix is obtained, characterizing the number of transitions from one energy range to another due to Coulomb collisions. It is found to have a pole of the third order in the magnitude of the transferred energy. This makes it possible to transform from the balance equation described by the K matrix to the Fokker — Planck equation describing diffusion and drift along the energy axis. Numerical solution of the time-dependent Fokker — Planck equation demonstrates that the characteristic relaxation time of the bound-electron distribution function is the time interval between Coulomb collisions. A comparison with previous computer modeling of the distribution function from first principles demonstrates that these results cannot be in agreement without rejecting the principle of detailed balance in its present formulation for a Coulomb plasma. This agrees with the conclusions previously reached in a computer modeling of the properties of a classical Coulomb plasma.General Physics Institute, Russian Academy of Sciences, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 3–19, September, 1994.     

A Monte-Carlo method for coulomb collisions in hybrid plasma models

A procedure for implementing Coulomb collisions into hybrid (particle-fluid) plasma models is outlined which is rapid in execution due to the use of approximate expressions for the collision integrals and conserves energy and momentum exactly. Particles undergo dynamic friction and diffusion in velocity-space at rates consistent with the velocity-dependent Fokker–Planck diffusion coefficients and there are no assumptions made about the shape or size of the particle distribution function. The method is tested against the analytical theory of test particle slowing in a background plasma and the thermal equilibration of a Maxwellian distribution.     

Grain Growth Kinetics of BaTiO3 Nanocrystals During Calcining Process

以醋酸钡和钛酸四丁酯为原料,采用溶胶-凝胶法合成了纳米BaTiO3粉体;运用差示/热重、X射线衍射及透射电镜对前驱体凝胶和产物进行了表征,并根据XRD结果,研究了纳米BaTiO3的晶格常数、晶格畸变度和晶粒尺寸随焙烧温度及时间的变化。结果表明,焙烧温度与时间对纳米BaTiO3晶格常数的影响不明显;随焙烧温度或时间的延长,纳米BaTiO3的晶格畸变度减小,晶粒尺寸增大,但晶格畸变度和晶粒尺寸更敏感于焙烧温度. 基于扩散控制机理的传统模型探讨了焙烧过程纳米BaTiO3晶粒生长动力学,得出其晶粒生长指数为7,晶粒生长活化能为75.49 kJ/mol. 将基于扩散与反应共同控制机理的新型等温模型应用于本研究中,结果表明,新型等温模型更能真实地反映纳米BaTiO3焙烧过程中的晶粒生长行为,说明纳米BaTiO3晶粒生长过程同时受溶质扩散和表面反应控制,其藕合晶粒生长活化能为27.23 kJ/mol.     

Influence of electron-phonon coupling on the energy of an exciton bound to a donor-acceptor pair

The influence of electron-phonon coupling on the binding energy of excitons bound to donor-acceptor pairs is investigated. It is shown that the experimental data in ZnSe agree very well with a theory which takes into account Coulomb overlap and the configuration interaction. The contribution of electron-phonon coupling is small, but not negligible.     

Mass transport and energy equilibration in heavy ion collisions

The lack of mass drift observed in Kr-induced collisions is explained assuming energy and particle transfer from the light to the heavy fragment during the equilibration stage in asymmetric heavy-ion reactions. Transferred energy and particle number can be estimated from the interfragment thermal equilibrium distribution provided the initial partition is known which we calculate within a semiclassical theory based on TDHF. The experimental findings are consistent with the theoretical predictions. In particular, the experimental mass drift as function of total kinetic energy loss is quantitatively described within a modified diffusion model which takes into account the mass exchange prior to the transport stage.     

Possibility of solar energetic particles enrichment with trans-iron ions via the effect of coulomb losses in the acceleration region

We discuss the possibility of the enrichment of solar energetic particles (SEP) with trans-iron ions in impulsive events. Aiming to estimate the acceleration of ions in the weight range of 84–210 atomic units, we calculated the energy dependences of the ionization and recombination rates of energetic ions of Kr, Te, and Pb. On the basis of the charge-consistent model of the stochastic acceleration of ions in Alfven turbulence (including the spatial diffusion of ions and Coulomb losses of energy), we calculated energy spectra of O, Fe, Kr, Re, and Pb at various values of the spectral index of turbulence for a wide range of parameters of plasma in the acceleration region. It was demonstrated that the Coulomb losses could be one reason for the observed significant SEP enrichment with trans-iron ions in impulsive events.     

Tight-binding investigation of electron tunneling through ultrathin SiO2gate oxides

We investigate electron tunneling through ultrathin gate oxides using scattering theory within a tight-binding framework. We employ Si[100]/SiO₂/Si[100] model junctions with oxide thicknesses between 7 and 18 Å. This approach accounts for the three-dimensional microscopic structure of the model junctions and for the three-dimensional nature of the corresponding complex energy bands. The equilibrium positions of the atoms in the heterostructure are derived from first-principles density-functional calculations. We show that the present method yields qualitative and quantitative differences from conventional effective-mass theory.     

LiFePO4中对位缺陷的第一性原理研究

基于考虑了Fe-3d电子间的库仑作用U和交换作用J的GGA+U方案,应用第一性原理计算方法系统研究了LiFePO₄的对位缺陷,以及对位缺陷的形成对材料的电导率和离子扩散速率的影响.结果表明,Li/Fe交换缺陷是最容易形成的,形成缺陷后的Fe—O键变长,扩宽了Li离子传输通道,有利于Li离子在通道中的扩散,对材料电化学性能的改善起到了一定的作用.     

Spectroscopy of few-electron collective excitations in charge-tunable artificial atoms

We report the investigation of electronic excitations in InGaAs self-assembled quantum dots using resonant inelastic light scattering. The dots can be charged via a gate by N=1, em leader,6 electrons. We observe excitations, which are identified as transitions of electrons, predominantly from the s to the p shell (s-p transitions) of the quasiatoms. We find that the s-p transition energy decreases and the observed band broadens, when the p shell is filled with 1 to 4 electrons. By a theoretical model, which takes into account the full Coulomb interaction in the few-electron artificial atom, we can confirm the experimental results to be an effect of the Coulomb interaction in the quantum dot.     

Ionization of atoms in strong low-frequency electromagnetic field

The ionization of atoms in a low-frequency linearly polarized electromagnetic field (the photon energy is much lower than the ionization potential of an atom) is considered under new conditions, in which the Coulomb interaction of an electron with the atomic core in the final state of the continuum cannot be considered in perturbation theory in the interaction of the electron with the electromagnetic field. The field is assumed to be much weaker that the atomic field. In these conditions, the classical motion of the electron in the final state of the continuum becomes chaotic (so-called dynamic chaos). Using the well-known Chirikov method of averaging over chaotic variations of the phase of motion, the problem can be reduced to non-linear diffusion on the energy scale. We calculate the classical electron energy in the final state, which is averaged over fast chaotic oscillations and takes into account both the Coulomb field and the electromagnetic field. This energy is used to calculate the probability of ionization from the ground state of the atom to a lower-lying state in the continuum using the Landau-Dykhne approximation (to exponential accuracy). This ionization probability noticeably depends on the field frequency. Upon a decrease in frequency, a transition to the well-known tunnel ionization limit with a probability independent of the field frequency is considered.     

Thermalization of atomic particles in gases

A model of the atomic particle thermalization process due to scattering in various gases with application of the Born-Mayer potential is presented. The thermalization process of atomic particles using the statistical modeling method is considered. Our thermalization model is adapted to a wide class of atomic collision partners, takes into account the real energy and angular distributions of atomic particle sources, and makes it possible to calculate the parameters of the spatial zone of their thermalization and transfer into the diffusion motion mode. The energy range of applicability for the atomic particle thermalization model is interesting for many applied problems in plasma physics, gas discharge, and ion plating processes.