A. Yu. Poroykov

Kinetics of in oxygen RF discharges

Studies of the kinetics in the afterglow of three RF discharges having different configurations are presented. Experiments with a slow flow velocity transverse capacitive RF discharge were performed and detailed measurements of the spatial evolution of , O2(a1?g), O(3P) and flow temperature were taken. Simulations of three different experimental configurations were in good agreement with the data for the spatial decay of . The simulations also provided reasonable agreement with experimental data for atomic oxygen, O2(a1?g) and temperature, where the data were available. Updated electron impact cross-sections for oxygen dissociation were included in the simulations; this proved critical for proper modelling of the production of atomic oxygen and the subsequent decay of . At low oxygen atom densities the decay of was principally from heterogeneous quenching. For the slow flow velocity experiment, O atom recombination and deactivation by the walls play an important role; in the far downstream afterglow region a quasi-stationary concentration was found owing to a near-equilibrium between the pooling reaction and losses to the walls for this slow velocity case.

Nonstationary effects in ozone generation by barrier discharges in N2/O2 mixtures

The yield of ozone in barrier discharges in oxygen–nitrogen mixtures containing 0.001 to 40% of nitrogen is investigated experimentally. Phenomena of the nonstationarity of processes of ozone generation that differ from the known ozone-zero phenomenon (OZP) apparent in the reduced efficiency of ozone generation in very high purity oxygen at long periods (from hours to tens of hours) of ozonator operation are found. It is established that the characteristic times (from minutes to tens of minutes) of ozone attaining stationary values after changes in the discharge parameters indicate slow adjustment of the surface condition of insulators and thus the heterogeneous decay of ozone to more rapidly changing flows of neutral and charged particles from gas discharge plasma on the surfaces of dielectrics. The possibility of such a scenario is confirmed using a new analytical approach and numerical calculations of the plasma–chemical kinetics of N2/O2 mixtures presented in the accompanying theoretical study.

Simulation of optical properties of silicon solar cells textured with penetrating V-shaped grooves

The coefficients of reflection (R), transmission (T), and absorption (A) of light for two wavelengths λ = 1000 and 1100 nm for silicon wafers that have thicknesses t = 50, 100, and 200 μm and are textured with penetrating V-shaped grooves with various geometries have been calculated; the half-width of groove’s base w (10, 20, and 30 μm) and the depth of the groove d (0 ≤ d ≤ t) have been varied. In the case of an increase in the aspect ratio d/w (in the case of λ = 1100 nm), the absorption curve A(d/w) monotonically ascends from 6.6 to 67.6%, whereas, for λ = 1000 nm, a nontrivial dependence A(d/w) is observed: the absorption coefficient first increases to 54%, attains then a maximum of 97% at d/w = 3, and then decreases at d > t/2 for all values of w. This effect of a decrease in absorption with an increase in d/w distinguishes texturing with penetrating grooves from conventional surface texturing. Distributions of angles of deviations of photons in the plane of bottoms of grooves are obtained; these distributions are represented by a set of δ-type functions.

Ozone production and losses in N2/O2 mixtures in an ozone generator

Nonunique ozone concentrations at the output of an ozone generator under identical external conditions of barrier discharge activation of N2/O2 mixtures but with different prehistories of operating practice and employed gas mixtures are investigated theoretically. An analytical approach is developed to determine the ozone yield with regard for its heterogeneous loss. Plasma-chemical and electron kinetics in the N2/O2-mixtures are calculated numerically. The results of numerical calculations are compared to experimental data obtained by the authors. It is noted that the heterogeneous loss of ozone is the probable reason for the observed variety of behavior of О3 concentrations, depending on prehistory of ozone generator operation, along with the N2 and O2 gas flow rates and the specific active power.

Plasmachemical and heterogeneous processes in ozonizers with oxygen activation by a dielectric barrier discharge

Plasmachemical and heterogeneous processes of generation and loss of ozone in the atmosphericpressure dielectric barrier discharge in oxygen are studied theoretically. Plasmachemical and electronic kinetics in the stage of development and decay of a single plasma filament (microdischarge) are calculated numerically with and without allowance for the effects of ozone vibrational excitation and high initial ozone concentration. The developed analytical approach is applied to determine the output ozone concentration taking into account ozone heterogeneous losses on the Al2O3 dielectric surface. Using the results of quantummechanical calculations by the method of density functional theory, a multistage catalytic mechanism of heterogeneous ozone loss based on the initial passivation of a pure Al2O3 surface by ozone and the subsequent interaction of O3 molecules with the passivated surface is proposed. It is shown that the conversion reaction 2O3 → 3O2 of a gas-phase ozone molecule with a physically adsorbed ozone molecule can result in the saturation of the maximum achievable ozone concentration at high specific energy depositions, the nonstationarity of the output ozone concentration, and its dependence on the prehistory of ozonizer operation.

Laminated grid solar cells (LGCells) on multicrystalline silicon. Application of atomic hydrogen treatment

For the first time, solar cells of laminated grid cell (LGCell) design are fabricated on multicrystalline nontextured silicon (mc-Si). An efficiency of 15.9% is achieved. The effect of (n+pp+)-mc-Si structure treatment by atomic hydrogen generated by a hot filament and microwave plasma is studied. Hydrogenation improves the parameters describing the dependence of the open-circuit voltage on the radiation intensity and the long-wavelength (λ = 1000 nm) sensitivity of the solar cell by 10–20%, which indicates that defects in mc-Si are passivated. Hydrogenation of the emitter side results in an increase in the series resistance of the solar cell, a decrease in the short-wavelength (λ = 400 nm) sensitivity by 30–35%, and the appearance of an oxygen peak in the energy-dispersive spectra (EDS). These effects are eliminated by fine etching of the emitter.

Multi beam X-ray tube with the field emitter on the base of nanocrystalline graphite for computer tomography

A multiple-beam X-ray tube on the basis of field emitters has been designed and developed. The X-ray tube is powered by 140 kV anode supply. Each beam is driven by 1 kV cathode to grid supply. Electron trajectories calculation and experimental measurement of I–V characteristics are presented.

Formation of low-reflection multicrystalline silicon surface by laser- induced structuring for application on silicon solar cells

The formation of laser-induced structures on the multicrystalline silicon surface has been investigated. Optimum performances of the surface structurization have been explored. A cardinal decrease in reflectance from modified surface has been discovered in a wide spectral range in comparison with the samples of chemically texturized monocrystalline silicon. The influence of subsequent chemical etching on the reflection spectra of the texturized samples surface has been analyzed.

Triode generators on the basis of FE emitters

Electron phase trajectories for high frequency Ku-band in a diode with a nanocrystalline graphite (NCG) field emitter are compared with one with a thermo-cathode. It is shown that the field electron (FE) cathode differs from the thermo-cathode and forms short electron bunches, which can be efficiently decelerated in an output cavity. The scheme and advantages of a triode generator with a FE cathode are described. 1-D analytical evaluation of output power for the triode generator is carried out. The conclusion is drawn that maximum output power strongly depends on current density, and rises up to 80 W for 15 A/cm2.