Characteristics of transverse volume discharge in Cf2Cl2 and in Ar/Cf2Cl2 mixture

The conditions of ignition and the characteristics are given for a nanosecond transverse volume discharge in Freon-12 (CF₂C1₂) and in an Ar/CF₂C1₂ mixture. It is shown that, in the ultraviolet and visible ultraviolet spectral region, a plasma based on CF₂C1₂ molecules is a source of radiation of excited carbon atoms and Cl₂ molecules. The volumetric stage of the discharge exists atU _charge ≤ 12 kV and [CF₂C1₂] = 0.1–3 kPa, and the current and voltage oscillograms are similar to the respective characteristics of a transverse discharge with prior-to-prebreakdown electron multiplication in He(Ne)/SF6(F2) mixtures. A plasma of an Ar/CF2C12 mixture is a source of radiation of the λ = 258 nm bands for Cl ₂ ^* , 193 nm for ArF, and 175 nm for ArCl. Such sources may be used in short-wave pulse photometry, microelectronics, and photo- and biochemistry.     

Thermal conductivity of gaseous CFCl3 (Freon 11) and CF2Cl2 (Freon 12) and their mixtures with N2 at 292K

Thermal conductivity of the gases CFCl₃ (Freon 11), CF₂Cl₂ (Freon 12), and their binary mixtures with nitrogen have been measured at 292 K. The results for the mixtures are compared with various theoretical models, which give the thermal conductivity as a function of concentration using properties of the pure components. From the experimental results, the mutual diffusion coefficients for the two systems are calculated.     

Characteristics of a submicrosecond transverse discharge in mixtures of helium with N2 and CO molecules and xenon atoms

An investigation is made of the electrical and optical characteristics of a moderate-pressure transverse discharge in typical active media of infrared CO lasers. The discharge was ignited in a system of unprofiled “ grid-plane” electrodes with automatic ultraviolet preionization by a corona discharge and had a 2×3 cm aperture. The pulse repetition frequency was 1–10 Hz, the current pulse length was ≤0.5 μs, and the pressure of the working mixtures was 10–100 kPa. Studies were made of the transverse discharge current voltage pulses, and also the spectral and temporal characteristics of the plasma radiation in N₂:CO, He:N₂:CO, and He: N₂:CO:Xe mixtures in the ultraviolet and visible ranges. Pis’ma Zh. Tekh. Fiz. 23, 71–76 (October 12, 1997)     

Use of a transverse nanosecond discharge at the prebreakdown electron ionization multiplication stage for selective excitation of neon atoms

An investigation is made of the characteristics of a transverse nanosecond discharge in Ne/SF₆ and He/Ne/SF₆ mixtures at the prebreakdown electron ionization multiplication stage. The conditions needed to obtain a stable transverse discharge with ultraviolet spark preionization are studied as well as the spectral and temporal characteristics of the plasma radiation. It is shown that this transverse discharge burning regime may be promising for the selective excitation of neon atoms which may be used to develop an electric-discharge, λ=585.3 nm, Ne(3s–3p) plasma laser. Pis’ma Zh. Tekh. Fiz. 24, 85–90 (January 12, 1998)     

Formation of ArCl(B) molecules in a transverse volume discharge

Results of optimizing a λ=175 nm ArCl(B-X) emitter pumped by a transverse volume discharge are presented. The formation of ArCl(B) molecules was investigated in a plasma formed by mixtures of rare gases with HCl and Cl₂ molecules. It is shown that the Cl₂ molecule is the most efficient chlorine carrier and that neon at pressures ≥ 50 kPa is the most efficient buffer gas. Pis’ma Zh. Tekh. Fiz. 25, 29–33 (June 12, 1999)     

Investigation of the degradation of silane molecules in a pulsed volume discharge

Results are presented of an investigation of the electrical and optical characteristics of a pulsed transverse discharge ignited in a 54×2.0×0.7 cm volume of an Ar+4%SiH₄ mixture. Studies were made of general spectra of the plasma radiation and the temporal and service-life characteristics of the radiation from the degradation products of the silane molecules. This type of discharge is of interest for obtaining porous silicon coatings over large areas. Pis’ma Zh. Tekh. Fiz. 24, 35–39 (November 12, 1998)     

Characteristics and plasma parameters of a short-wavelength low-pressure discharge lamp

We have studied the working optical characteristics and electron kinetic coefficients of a short-wavelength, electric discharge exciplex-halogen UV-VUV lamp employing a mixture of argon and chlorine with a total pressure of P = 0.5–10 kPa. The lamp operates on a system of broadened electron-vibrational bands of ArCl (175 nm) and chlorine (200, 258 nm) molecules, which overlap to form a continuum in the spectral range of 160–260 nm. It is established that the optimum mixtures are those with p(Ar) − p(Cl₂) = (2–4)−(0.15–0.30) kPa. The average output power of the short-wavelength radiation is 1–2 W at an efficiency of ∼5%. The electron energy distribution functions (EDFs) and the discharge plasma parameters have been calculated by solving the Boltzmann equation for a gas mixture with the experimentally determined optimum composition in the range of E/P values from 1 to 200 V/(cm Torr), where E is the electric field strength and P is the total gas pressure. Using the obtained EDFs, the electron transport characteristics, specific discharge power losses for the main elementary processes, and rate constants of electron processes are determined.     

Structure of the short-lived absorption and luminescence spectra of barium and calcium fluorides accompanying pulsed electron irradiation

It is established that the optical absorption in the hole and electron components of autolocalized excitons in BaF₂ excited by a pulsed electron beam consists of a collection of overlapping bands with a half-width no greater than 0.1 eV. Simultaneous subexcitation with the stimulated emission of II–VI semiconductors made it possible to isolate three groups of bands, caused, by analogy with CaF₂ [Phys. Solid State 39, 1060 (1997)], by different configurations of autolocalized excitons in the fluorite lattice. The process of radiative decay of autolocalized excitons in CaF₂ and BaF₂ when they are optically excited in the region of the electron component of the absorption has been detected. The spectral rate parameters of the radiation that appears during simultaneous subexcitation coincide with the characteristics of the radiation ascribed earlier to core-valence transitions. The photostimulated variation of the absorption spectra of autolocalized excitons is accompanied by selective variation of the luminescence spectra of autolocalized excitons, which also is evidence of their complex spectral content. Pis’ma Zh. Tekh. Fiz. 23, 45–50 (November 12, 1997)     

Low-pressure inductive rf discharge in a rare gas-halogen mixture for economical mercury-free luminescence light sources

It is demonstrated that an inductive rf discharge in an Xe+Cl₂ mixture may be used as the active medium of an efficient, mercury-free luminescence light source. Pis’ma Zh. Tekh. Fiz. 24, 63–67 (March 26, 1998)     

Analysis of the possibilities of using ballistic systems for investigating the stratosphere

An analysis is made of the possibility of conducting practical experiments in which ozone-active components of emissions (such as NO₂, Cl₂, and so on) are supplied to the stratosphere using a 203mm self-propelled howitzer. Pis’ma Zh. Tekh. Fiz. 25, 1–6 (June 12, 1999)     

Continuous optical discharge in a thermionic converter for conversion of laser radiation energy into electrical energy

A model is developed and calculations are made of the characteristics of a continuous optical discharge in the interelectrode gap of a thermionic converter for conversion of laser radiation energy into electrical energy. Pis’ma Zh. Tekh. Fiz. 25, 90–95 (April 12, 1999)     

A planar excimer-halogen radiation source pumped by transverse RF discharge

We present the characteristics of a planar source of wideband shortwave radiation pumped by transverse RF (f=1.76 MHz) discharge in a Kr/Xe/Cl₂ mixture (P≤500 Pa). The spectral characteristics of the plasma emission were studied in the wavelength interval of 130–600 nm. The oscillograms of the voltage, current, and output radiation intensity and the diagrams of the output power depending on the gas pressure, partial composition of the working gas mixture, and discharge power are presented. It is established that the source produces emission predominantly in the spectral interval of 170–330 nm, representing a system of the molecular emission bands XeCl(D, B-X), KrCl(B-X), Cl₂(D′-A′), and Cl₂**. For a maximum output power in the UV-VUV range, the optimum working gas mixture is Kr/Xe/Cl₂ with the partial pressures P(Kr)/P(Xe)/P(Cl₂)=150–200/150–200/20–40 Pa. The maximum power irradiated within a solid angle of 4π via two output holes with a total area of S≤ 100 cm² reaches 30–40 W. In the region of a threshold with respect to the transverse discharge initiation, there are narrow peaks of plasma emission that are probably related to the jumps in the density of electrons and the positive and negative ions at the boundary between the plasma and the RF discharge layer.     

Determination of the electron density in a discharge with nonmetallic liquid electrodes in atmospheric-pressure air from the absorption of microwave probe radiation

Measurements were made of the absorption of microwave power in a discharge plasma generated using tapwater electrodes in atmospheric-pressure air in order to determine the electron density. The high-voltage discharge burned in a bulk (diffuse) form with a lower current density than an arc discharge. This type of discharge with nonmetallic liquid electrodes is extremely promising for various technical applications. Regimes with I=50–60 mA and voltages U=2.9–3.1 kV were studied. The measurements were made at probe radiation frequencies F=29.6 and 35.2 GHz. A two-conductor transmission line was used to localize the microwave power in the plasma. An estimate was obtained for the average electron density in the central part of the discharge (4×10¹¹)<n _e <,(7×10¹¹)cm⁻³. This result shows good agreement with the results of earlier probe measurements. Pis’ma Zh. Tekh. Fiz. 24, 52–57 (December 12, 1998)     

Selective infrared multiphoton dissociation of CF3I molecules in a pulsed gasdynamic stream: Dependence of the 13C enrichment factor in the C2F6 product on the molecular concentration in the beam

An investigation was made of isotopically selective infrared multiphoton dissociation of CF₃I molecules in a pulsed gasdynamic stream. It was observed that the ¹³C enrichment factor in the C₂F₆ product depends strongly on the molecular concentration in the stream. Reasons for this result are discussed. Pis’ma Zh. Tekh. Fiz. 24, 35–40 (December 12, 1998)     

Suppression of plasma fluctuations in the transition to the improved-confinement regime when the current is raised rapidly in the FT-2 tokamak

Collective scattering of CO₂-laser radiation is used to study the microturbulence of the plasma in the FT-2 tokamak when the current is rapidly raised, while the magnetic-field shear is varied appreciably. The experiment exhibited suppression of the plasma fluctuations, the appearance time of which was correlated with the transition of the discharge to the improvedconfinement regime. The resulting data are evidence that the suppression of the oscillations occurred predominantly in the central zone of the tokamak, and a suppression-extending phenomenon or hysteresis is detected. The evolution of the spectral characteristics of the fluctuations during the suppression is analyzed, using model calculations of the magnetic-field shear. Pis’ma Zh. Tekh. Fiz. 23, 51–57 (November 12, 1997)     

Photoluminescence properties of AlxGa1−x As epitaxial layers grown under conditions of ultrafast flux cooling

Results are presented of studies of the photoluminescence properties of epitaxial layers of Al_xGa_1−x As solid solutions grown by liquid-phase epitaxy with nonequilibrium crystallization achieved by ultrafast rates of cooling of the flux (V∼10²–10³ °C/s). The photoluminescence characteristics obtained indicate that the epitaxial layers are of high quality. It is also observed that when samples with x _buff=0.5–0.55 are exposed to laser radiation of power density ∼1 kW/cm² at a temperature of 77 K, the spectral composition of the radiation undergoes irreversible changes caused by the formation of an arsenic vacancy (V _As)-donor impurity complex. Pis’ma Zh. Tekh. Fiz. 23, 8–13 (March 12, 1997)     

On the conditions for contraction of a multielectrode corona discharge in He/Ar, Kr, Xe mixtures

The results of an investigation of the contraction of a corona discharge in “needle-grid” and “needle-plane” electrode systems maintained by a constant negative voltage are presented. The discharge was ignited in working media of infrared lasers on p-d transitions of atoms of heavy inert gases (He/Ar, Kr, Xe mixtures). Investigation of the current-voltage characteristics showed that in the mixtures He/Ar/Kr there is no hysteresis on the rising section of the current-voltage characteristic, while hysteresis does appear for a corona discharge in the mixture He/Xe. For voltages ≥5.5 kV on the needles and ballast resistance R_b≥0.5 MΩ dynamical contraction of a corona discharge together with current pulses with f=3–5 kHz and hysteresis loops were found on the descending section of the curve I=f(U), where I and U are the average current and voltage on the discharge gap. The maximum content of atoms of heavy inert gases for [He]=200–300 kPa is [Ar]≤12, [Kr]≤8, and [Xe]≤4 kPa. Pis’ma Zh. Tekh. Fiz. 25, 90–94 (September 12, 1999)     

Thermodynamic Assessment of EuCl<Subscript>3</Subscript>–MgCl<Subscript>2</Subscript> and EuCl<Subscript>3</Subscript>–BaCl<Subscript>2</Subscript> Systems

Using the CALPHAD technique, an assessment of the binary EuCl₃–MgCl₂ and EuCl₃–BaCl₂ systems has been carried out in this study. The modified quasi-chemical model was defined to describe the Gibbs energies of the liquid phases, and the model parameters were optimized from the experimental phase diagram data. The phase diagrams and enthalpies of mixing of the EuCl₃–MgCl₂ and EuCl₃–BaCl₂ systems were calculated. The calculated results by the present method agree well with the experimental data. The Gibbs energies of formation of Mg₃Eu₂Cl₁₂, Ba₃Eu₂Cl₁₂, and Ba₂Eu₃Cl₁₃ from the pure components were predicted.     

GaAsN/GaAs and InGaAsN/GaAs heterostructures grown by molecular beam epitaxy

Molecular beam epitaxy was used to fabricate GaAsN/GaAs and InGaAsN/GaAs heterostructures, and the influence of the growth regimes on their characteristics was studied. It is shown that implantation of nitrogen causes a substantial long-wavelength shift of the radiation. The possibility of obtaining 1.4 μm radiation at room temperature was demonstrated using In_0.28Ga_0.72As_0.97N_0.03/GaAs quantum wells. Pis’ma Zh. Tekh. Fiz. 24, 81–87 (December 12, 1998)     

Generation of vibrationally excited H2 molecules in a hydrogen stream flowing through a cesium-hydrogen discharge

A theoretical analysis is made of the electronic-vibrational kinetics in a stream of molecular hydrogen flowing through a cesium-hydrogen discharge. An analysis is made of the vibrational pumping of hydrogen molecules in the discharge and vibrational relaxation is studied in the cold flow zone beyond the discharge. It is shown that a very substantial increase in the concentration of vibrationally excited H₂ molecules may be achieved in the old zone. Pis’ma Zh. Tekh. Fiz. 23, 26–32 (January 12, 1997)