On the theory of convection of electrons in metals

With the kinetic equation, the phenomenon of convection of electron gas in metals is described and the drag force, undergone by the convective flow of electrons, is calculated. As a result of the theory, the coefficient of volume expansion of the gas of free electrons, β _e , is numerically estimated.     

The kinetic model of Al oxidation in heterogeneous aluminum-water plasma. Negative ions

We investigate the mechanisms of formation and death of negative ions in aluminum-water plasma, their role in kinetics of its ionization and recombination, and influence on plasma parameters. Negative ions, in contrast to the positive, do not in fact participate in the heterogeneous processes and require, to enhance their influence on the plasma parameters, first, high electron temperatures (~1.5 eV and higher) and, second, low n _e and [Al] concentrations: in this way, they make a great contribution to the H₂O dissociation at the expense of the electron energy (2–8 electrons per a molecule). We show that, even in the most favorable conditions at low H and O concentrations within the experimental temperature range, T _e = 0.6–1 eV, the negative ions do not, in fact, influence the Al concentration and, in the operation reactor zone, the other parameters, except for the microparticle concentration. We reveal the source, important for the spectral diagnostics of the atomic emission, of recombination populating of the excited Al levels. The main negative ion (OH^–) is established. We have concluded the impossibility of its use in order to optimize the operation of the aluminum-water plasma-chemical reactor.     

Semiempirical Model of Equation of State for Condensed Media

An approximation of equation of state for matter is treated, which involves the consistent use of interpolation approach with respect to both density and temperature in the entire nonrelativistic region. The cold component is defined under normal conditions by four experimentally obtained parameters, namely, specific volume, bond energy, bulk modulus, and parameter κ = ?(?lnB _S /?lnV) _S . The thermal ion component describes the transition from lattice vibrations with free Debye energy as a function of characteristic temperature being introduced, which makes possible the extension of the range of its application from zero temperature to ideal gas. The thermal electron component describes the transition of free electrons from ideal degenerate gas to nondegenerate state. A formula is suggested which enables one to calculate the degree of ionization at arbitrary densities and temperatures. Continuous functions are described which approximate ionization potentials and energies. The phase diagram, shock adiabats for continuous and porous matter, and isentropes are calculated. An analytical approximation of the Debye function is suggested. The results are illustrated by dependences on compression ratio in the range ρ/ρ ₀ = 1 to 10⁶. Comparison is made with experimental data.     

Formation and energy relaxation of a fast electron beam in cathode regions of a glow discharge in helium

Results of a three-dimensional direct statistical simulation of formation and energy relaxation of a group of high-energy electrons in cathode regions of the low pressure (p < 1 Torr) glow discharge in helium are given. It is demonstrated that the electron distribution function at the exit from the cathode sheath contains a group (beam) of high-energy electrons which did not suffer inelastic collisions and had energy close to the cathode fall potential. The beam is shown to be a main source of charged particle production in the negative glow region. The calculated electron energy distribution function is compared with experimental data.     

The interaction of ultrasound with electrons in hybridized states of iron impurity in a mercury selenide crystal

We have studied the propagation of transverse ultrasonic waves with a frequency of 52 MHz in an iron-doped mercury selenide (HgSe:Fe) crystal with an impurity concentration of 10¹⁹ cm^?3, for which the effects of resonant electron scattering on the impurity are most pronounced in the conduction behavior. The temperature dependences of the absorption coefficient α and the phase velocity v of the transverse acoustic waves, which have been studied in the temperature interval T = 1.48-80 K, exhibit anomalies at a temperature of about 5 K: a peak in the α(T) curve for a slow transverse wave and a minimum in the v(T) curve. These anomalies are explained using the theory of interaction between ultrasound and electrons in hybridized states on iron impurity atoms.     

Rankinite synthesis and pyrolysis inversion

The thermal transformation of the pyrolysis–condensation–rankinite synthesis process at a normal pressure is considered in detail. Rankinite pyrolysis is performed with a step-by-step increase in enthalpy (TERRA software system). Rankinite pyrolysis components condense on a surface with temperature Т = 298.15 K. Condensate components are equivalent to pyrolysis components. Wollastonite and limestone can precipitate upon condensation to form a mineral deposit. Synthesis is performed by mixing the condensate components. The components and heat of chemical reactions, the enthalpy, the temperature, and the heat content are determined. It is shown that the decomposition of rankinite (Т _dec = 2598.36 K), wollastonite (Т _dec = 3662.7 K), and limestone (Т _dec = 3680–3810 K) occurs in the process of synthesis and pyrolysis at a constant temperature. The complete pyrolysis–condensation–synthesis process picture typical for various compounds is given.     

Monte Carlo study of the ion-induced electron current tunneling through a metal-insulator-metal junction

A Monte Carlo program is developed to investigate the kinetically excited electrons passing through a realistic Ag-Al₂O₃-Al junction when Ar⁺ ions impact on the top Ag layer. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons) and subsequent transport of these excited electrons from Ag to bottom Al layer of the metal-insulator-metal (MIM) junction. The calculated tunneling electron yield is consistent with the recently reported experimental results. The simulation, however, enables the calculation of partial tunneling electron yields of the electrons excited by the projectile ions, recoil atoms and cascade electrons, the depth distribution of the electron excitation points in the MIM junction and energy distribution of the tunneling electrons. Our calculation showed that the electrons excited by fast cascade electrons are the major contributor to the tunneling electron yield while the direct contribution of projectile ions to tunneling electron yield is evident only at the projectile energies greater than 10 keV. The tunneling electrons have their origin close to the bottom end of the Ag layer and bulk of the tunneling electrons have energies around 2 eV.     

Structure and Magnetic Properties of Ce-Substituted Yttrium Iron Garnet Prepared by Conventional Sintering Techniques

Y_3?xCe _x Fe₅ O ₁₂ (CeYIG) ceramics, with x = 0, 0.15, 0.25, 0.35, 0.45, and 0.5, were fabricated by a conventional ceramic sintering technique. We studied the structures and magnetic fields of a series of CeYIG ceramics using X-ray powder diffraction, a scanning electron microscope, and a superconducting quantum interference device magnetometer. Findings showed that the substitution limit of the concentration of Ce³⁺ ions in the yttrium iron garnet structure was approximately x = 0.25. An extra CeO₂ phase was detected in the ceramic when the addition of CeO₂ content overtook the limit. The lattice constants and relative densities increased by increasing the Ce³⁺ contents in the ceramics. First, the saturation magnetization increased gradually with increases in the substitute concentration of Ce³⁺ ions and then decreased gradually when x = 0.35, 0.45, and 0.5. Overall, this study showed that the Y_3?xCe _x Fe₅ O ₁₂ material with x ≤ 0.15 exhibited excellent magnetic properties. Hence, the material show promise for magneto-optical and microwave communication applications.     

Inhomogeneous State of the Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Doped with Manganese

Basing on electron spin resonance (ESR) data for Bi₂Te₃ doped by Mn ions we argue that this compound can be inhomogeneous and consists of two components with the different structures. Its main phase Bi _2?x Mn _x Te ₃ is intertwined with the microscopical inclusions of MnBi phase. The integral volume of these intermetal clusters is less than 1 % but nevertheless they exert the serious impact on the dynamic magnetic properties of the entire system. These inclusions are ferromagnetic with the Curie temperature of 630 K, while the main bulk phase Bi _2?x Mn _x Te ₃ has x= 0.05 orders at T _c= 10 K (qualitatively this twophase picture is valid not only for this given x). Below this temperature two ferromagnetic phases coexist. Since the integral spontaneous polarization in MnBi phase is averaged out due to its random orientations in different clusters the time-reversal symmetry of Bi ₂Te ₃ doped by Mn ions is violated only at the low-temperature ferromagnetic transition.     

Seebeck coefficient of Ca<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3–δ</Subscript> paramagnetic manganites

The Seebeck coefficient (S) of Ca_1–x Pr _x MnO_3–δ (х = 0, 0.05, 0.10, 0.15) manganites with a perovskite-like structure has been measured in air at temperatures (T) from 300 to 1200 K. The negative sign of their S indicates that all of the samples have n-type conductivity. The observed increase in the magnitude of the Seebeck coefficient with increasing T is interpreted in terms of small-polaron transport with allowance for the decrease in Mn³⁺ concentration as a result of the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺. Based on a theoretical analysis of experimental S(T) data, we calculated equilibrium constants for the disproportionation reaction, carrier concentration, and the concentration of sites available for carrier migration as functions of temperature. It has been shown that, for an adequate analysis of electron hopping and calculation of the Seebeck coefficient of the electron-doped manganites, the spin state of the Mn⁴⁺ ions should be taken into account.     

Evolution of nonequilibrium aerosol parameters in crown-streamer discharge plasma

Nonstationary parameters of an aerosol formed from unsaturated vapors of styrene and n-hexane in a pulsed crown-streamer discharge in air or argon at atmospheric pressure have been studied. In the initial stage of aerosol formation, the concentration of aerosol particles was on the order of 10⁷ cm⁻³. The characteristic time of nonequilibrium hexane aerosol degradation in the experimental chamber amounted to several hours. The aerosol particle size distribution function has a bimodal shape. Within the first seconds upon aerosol formation, the maximum particle size does not exceed 0.6 μm, whereas in several hours, the boundary of the particle size spectrum reaches the micron range.     

Effect of the water vapor density on the field dependence of the ion mobility increment for nitro compounds in air

The dependence of the ion mobility increment coefficient α on the electric field strength in the presence of a variable water vapor density C = (0.3?15) × 10¹⁶ cm^?3 in air has been studied for the ions of explosive nitro compounds including DNT (2,4-dinitrotoluene), TNT (2,4,6-trinitrotoluene), and their degradation products DNB (1,3-dinitrobenzene) and TNB (1,3,5-trinitrobenzene). The influence of the water vapor density C on the α value decreases in the following sequence: DNB > TNB > DNT > TNT. The obtained dependences can be used for the creation and exploitation of experimental and commercial analytical ionization devices used for the detection of explosive vapors.     

Thermodynamic and transport properties of cesium vapors on binodal and in its vicinity

To check the earlier proposed hypothesis on the considerable cluster effect and the ion-atom nonideality in saturated cesium vapors, a chemical model is proposed that accounts for the presence of neutral, positively, and negatively charged small-sized cluster ions and the main types of interatomic interactions. The partition sums of atoms, ions, and clusters are calculated as are the composition and pressure of cesium vapors on the binodal. It is shown that, on the saturation line, cesium vapor in the near-critical region consists mainly of atoms and a small admixture of molecules, whereas the charged component consists predominantly of Cs^?, Cs ₃ ⁺ , and Cs ₂ ⁺ ions whose amount is considerably lower than the amount of atoms. Interactions between charged particles and between the charged and neutral ones significantly influence the charge composition of vapors and weakly affect the equation of state and the composition of neutral component of vapors. The calculated compressibility and conductivity of the cesium vapor plasma are in good agreement with the experimental data for the near-critical isobars.     

The effect of different platinum concentrations as nucleation agent in the BaO/SrO/ZnO/SiO<Subscript>2</Subscript> glass system

The recently reported solid solution of Ba_1?xSr _x Zn₂Si₂O₇ has a similar structure to the high-temperature phase of BaZn₂Si₂O₇ and possesses a coefficient of thermal expansion close to zero or even negative. Without nucleating agents, glasses in this system show solely surface crystallization. In order to stimulate volume crystallization, different quantities of platinum were added to the glass. The characteristic temperatures of the glasses were obtained by differential scanning calorimetry. In order to achieve volume crystallization, a two-step thermal treatment (nucleation and crystal growth) above the glass transition temperature was carried out. The phase identification was performed by X-ray diffraction, and the microstructure was studied by scanning electron microscopy including energy-dispersive X-ray spectroscopy and electron backscatter diffraction.     

A model of hydrogen absorption by metals

The influence of the electron spectrum of transition metals on the hydrogen absorption process is considered. An absorption model is proposed where electrons, followed by protons, from adsorbed molecules or atoms of hydrogen transit into the metal. In terms of this model, the driving force of the absorption process ΔX is equal to the difference of the total electron energies in a hydrogen atom and in a metal at the Fermi level: ΔX = E _H ? (E _F + A _work). The equilibrium state in the absorption process corresponds to the equation 13.53 = E _F + A _work, which makes it possible to find the Fermi energy of transition metals and the valence of hydrogen absorbing metals, to define the molecular formula of hydrides, and to calculate the maximum hydrogen content in hydride phases. The hydrogen content in the composition of hydrides is shown to decrease in approaching the middle of the transition-metal rows. In groups, on the contrary, the hydrogen content grows as the atomic weight of metals increases. A good agreement of calculated and experimental compositions of hydride phases is found for the transition metals whose d band is less than half-filled with electrons.     

Secondary electron emission in scanning Ga ion, He ion and electron microscopes

The secondary electron (SE) emission for Ga ion, He ion and electron impact have been calculated using Monte-Carlo simulations, in which the trajectories of all the collision partners (i.e., primary ions, recoiled target atoms, and excited electrons (electron cascade) along which SEs are excited) have been simulated. The SE yields for Ga ion impact show a gradual decrease with increasing Z₂ which is opposite to that found for electron impact. The main reasons for the decrease in SE yield for Ga are the decrease in number and energy of electrons excited by the primary ions and the decrease in contribution of the recoiled atoms to the SE yield with increasing Z₂. For electron impact, both primary electrons and backscattered electrons (BSEs) excite the SEs. The additional SE excitation created by the electron cascade by BSEs is enhanced for high-Z₂ metals especially at E > a few keV. For He ion impact, the Z₂-dependence is between that for the Ga ions and the electrons and is weak because the He ion is light but still much heavier than an electron. As to the lateral resolution, the electron excitations by trapped He ions dominate the SE yield, so that the SE excitation volume is narrower than for electron and Ga impacts. This small contribution of BS He ions to the SE yield does not increase the information depth determined by the trapped He ions, in contrast with the large contribution of BSEs to the SE yields for SEM imaging. The simulated incident-angle dependence in SE yields shows that the topography contrast for He-SIM imaging is clearer than that obtained by SEM and Ga-SIM imaging.     

The conditions for realization of the Boltzmann distribution of negative ions in a plasma

The self-consistent electric field acting in a plasma retards the most mobile charged particles, which usually leads to a Boltzmann distribution of electrons. If negative ions cross the discharge volume several times during their lifetime in the volume processes, these particles also obey the Boltzmann distribution. It is demonstrated that this condition is usually satisfied when the characteristic time of electron attachment is small as compared to the time of ambipolar diffusion of the negative ions (ion diffusion at an electron temperature). In the opposite case, the profiles of electrons and negative ions are similar.     

Effect of methyltrimethoxysilane hydrolysis and condensation conditions on the properties of thin polymethylsilsesquioxane films

We have studied the influence of methyltrimethoxysilane hydrolysis and condensation conditions in aprotic solvents on the formation, composition, and properties of thin polymethylsilsesquioxane films. The condensation of silanol groups and the structuring of the silicon–oxygen skeleton at different heat-treatment temperatures have been investigated by IR spectroscopy. The dielectric permittivity k and refractive index n of the films have been determined as functions of annealing temperature t_a: at t_a = 430°C, k = 2.75 and n = 1.38.     

Effect of Al Substitution in Structural and Magnetic Properties of MnCr<Subscript>2</Subscript>O<Subscript>4</Subscript>

Single-phase samples of Mn(Cr_1?x Al _x )₂O₄ (x = 0 – 0.30) with cubic spinel structure were prepared and the lattice constant is found to decrease from a = 8.4396 Å for x = 0 to a = 8.3801 Å for x = 0.30. The substitution of Al at Cr site is confirmed from the blue shift of Raman modes. Magnetization measurements and analysis show all the prepared samples exhibit ferrimagnetic transition with transition temperature in the range of 46 K for x = 0 to 33 K for x = 0.30. The saturation magnetization (M _s ) and the estimated anisotropy constant (K) show an anomalous behavior up to x = 0.10 and beyond that they decrease monotonously. They are explained by considering different site preferences of Al ³⁺ ions as the doping concentration is increased. The theoretical and experimental effective magnetic moment of the samples is found to be comparable and it decreases with increase in Al concentration.     

The carbon phases formed during pyrolysis of gaseous hydrocarbons in reaction volume of a fluidized bed apparatus

In view of the kinetic laws of hydrocarbon pyrolysis, three mechanisms of the carbon phase formation are considered: the mechanism of individual atoms, the two-stage model of growth, and the mechanism of agglomerate. The macrostructure is investigated by means of optical and scanning electron microscopy, and the microstructure of carbon deposits is investigated with the help of transmission electron microscopy. The parameters of crystal structure are determined as well: the parameter of lattice (a), the interlayer distance (d ₀₀₂), and the coherent dispersion areas L _a and L _c . The radiation stability of pyrocarbon is investigated under irradiation with a stream of high-energy electrons. The fact of a noncatalytic growth of the carbon fibers on the outfit walls of a fluidized bed apparatus (above the level of the particles) forming owing to interfacing globular deposits in the pores is established.