A probe investigation of the structure of electrode microwave discharge in nitrogen

A probe investigation is performed of the structure of electrode microwave discharge in nitrogen at a pressure from 0.5 to 2.5 torr, incident power of up to 500 W, a power of 10 to 50 W absorbed in the system, and a gas flow rate from zero to 1000 cm³/min under normal conditions. It is demonstrated that, if the discharge diameter exceeds considerably that of antenna, the discharge is a close-to-spherical formation with a clearly defined boundary. The antenna is surrounded by a bright luminous film of plasma. A considerable nonuniformity of the parameters of the electron component of plasma and of constant potentials in plasma is demonstrated. It is possible that the discharge structure is related to the existence of a region of self-maintained discharge (luminous film surrounding the electrode) and a region of semi-self-maintained discharge (spherical region). The existence of considerable constant fields in the plasma of an electrode microwave discharge is found, whose emergence may be due to a nonlinear transformation of the microwave power maintaining the discharge. The discharge is surrounded by an isotropic region with decreasing electron temperature and concentration.     

Non-self-maintained discharge supported by a proton beam for studying stretched dust structures

The main parameters of non-self-maintained discharge supported by a proton beam in inert gas are obtained. The discharge is used to study dust structures in nuclear excited plasma. Its main features include low gas pressure (～133 Pa) and low proton beam current density (～10^?6 A/cm²). It is shown that a trap for negatively charged dust particles is formed in the discharge near-collector area at a sufficiently large negative voltage on the collector (?100 V), which is caused by a large negative potential jump in the Langmuir electrode layer whose width increases with distance from the center of the discharge. The possibility of generating stretched dust structures in non-self-maintained discharge is considered.     

Plasma density in discharge sustained in inhomogeneous gas flow by high-power radiation in the terahertz frequency range

We have measured the density of plasma (electron concentration) in discharge maintained in inhomogeneous argon flow under the action of high-power pulsed radiation of gyrotron (frequency, 0.67 THz; power 40 kW; pulse duration, 20–30 μs) in a range of background gas pressures in the discharge chamber from 10^–3 to 300 Torr. The electron concentration at low pressures (10^–3 to 7 Torr) was determined using Starkeffect induced broadening of the H_α atomic emission line (656.3 nm) of hydrogen present in discharge as a small impurity in residual gases. The maximum observed Stark broadening of the H_α line corresponded to a plasma density on the order of 2 × 1016 cm^–3, which exceeded the critical value for the given frequency of radiation sustaining the discharge. At background pressures above 7 Torr, the plasma density was estimated from analysis of the spatiotemporal patterns and waveforms of discharge glow in the visible spectral range. These estimations gave electron concentrations on the level of (1–2) × 10¹⁵ cm^–3.     

Generating H<Superscript>−</Superscript> ions in a low-voltage xenon-hydrogen discharge

Low-voltage discharge in a xenon-hydrogen (Xe-H₂) mixture has been theoretically studied. It is established that, at the optimum concentrations of hydrogen and xenon (on the order of 10¹⁵ cm^?3), the optimum total pressure of the plasma (about 1 Torr), a sufficiently high concentration of negative hydrogen ions (on the order of 10¹² cm^?3) in discharge plasma can be reached. The necessary emission current density at the cathode is on the order of 10 A/cm².     

The parameters of nonequilibrium microwave discharge in nitrogen in a tube in a rectangular waveguide

Computer codes are developed for the processing of emission spectra of nonequilibrium plasma in nitrogen for the purpose of obtaining information about the translational T _g and rotational T _rot temperatures, the populations of vibrational levels in the ground electron and electron-excited states, the electron energy distribution function, the electron concentration N _e , and the electric field intensity E. The computer codes are used to determine the parameters of microwave-discharge plasma in nitrogen in discharge systems of two types, namely, in a discharge tube (with a radius of 1 cm), which crosses a rectangular waveguide (plasmatron on the H ₁₀ wavelength, at a pressure of 1.7 torr and absorbed power density of 1.5 W/cm³), and in a discharge section of similar structure on the basis of prismatic resonator (at a pressure of 1.0 torr and absorbed power density of 0.4 W/cm³). The mechanisms of population of the N₂(C ³Π_u) state are treated.     

Films of nanocrystalline graphite synthesized in dc discharge plasma as a material for electrochemical capacitors

Films of nanocrystalline graphite were synthesized in dc discharge plasma in an atmosphere of methane and hydrogen. Studies of the structural properties show that the films consist of a dense set of nanowalls with a thickness of 10?C15 nm oriented perpendicularly to the support surface. The synthesized films were used as an active electrode material in supercapacitors. It is shown that the specific electrochemical capacitance of the synthesized material reaches about 38 mF/cm².     

Some peculiarities of electric discharge between a solid electrode and technical water

We present the results of experimental study of the electric discharge between metal electrodes of various geometry and technical water within the pressure range of 8 × 10³–10⁵ Pa at the saw-tooth voltage generator frequency, f = 40 MHz, and the interelectrode distance, l = 3–30 mm. We consider transfer of the streamer discharge into spark one depending on the geometry of the metal electrode and its material. We investigate the electrical characteristics of the discharge between the plate electrode and the technical water within a wide pressure range. The essential influence of the streamer discharge type on the ozone release within the investigated parameters range is discovered.     

Nitriding of technical-purity titanium in hollow-cathode glow discharge

The process of nitriding at low pressures and temperatures (≤550°C) in hollow-cathode glow discharge plasma was studied for technical-purity titanium of the VT1-0 commercial grade. The diffusion saturation of titanium with nitrogen in plasma with a concentration of n = 10¹⁰–10¹¹ cm⁻³ takes place at an ion current density on the cathode within 1.6–4.0 mA/cm². It is established that a key role in the process of metal saturation is played by atomic nitrogen. The experiments revealed the formation of a layer of gradient structure with a high microhardness (∼14 GPa) on the surface of nitrided titanium.     

Quasi-phase matching of third harmonic generation in corrugated discharge capillary

Quasi-phase matching third harmonic of Ti:sapphire laser was measured by propagation through corrugated discharge capillaries. The 1 cm long capillary with periodical varying inner radius was used with corrugation frequency of 200 μm. The longitudinal plasma density was periodically varied by a discharge current ablating the inner capillary walls, altering the refractive index accordingly. Average plasma density measured was 10¹⁸ cm⁻³ at minimum corrugation radius. Peak laser intensity was 10¹⁰ W/cm² allowing enough pondermotive energy to the electron for high harmonic generation.     

A mechanism of electron emission in an open discharge

The effect of an artificial UV emission from the drift space on the open discharge current, caused by an additional discharge operating between the anode and the electron collector, was studied. The experiments were performed in the continuous, quasicontinuous, and pulsed regimes of the electron beam generation in a range of currents from 1 mA/cm² to 10 A/cm². It was established that the energy efficiency of the additional discharge acting upon the beam current is greater than that of the beam proper. It is concluded that UV emission is the main factor providing for the supply of electrons to the open discharge.     

Roll-Pressed Silicon Anodes with High Reversible Volumetric Capacity Achieved by Interfacial Stabilization and Mechanical Strengthening of a Silicon/Graphene Hybrid Assembly

Application of Si anodes is hindered by severe capacity fading due to pulverization of Si particles during the large volume changes of Si during charge/discharge and repeated formation of the solid-electrolyte interphase. To address these issues, considerable efforts have been devoted to the development of Si composites with conductive carbons (Si/C composites). However, Si/C composites with high C content inevitably show low volumetric capacity because of low electrode density. For practical applications, the volumetric capacity of a Si/C composite electrode is more important than gravimetric capacity, but volumetric capacity in pressed electrodes is rarely reported. Herein, a novel synthesis strategy is demonstrate for a compact Si nanoparticle/graphene microspherical assembly with interfacial stability and mechanical strength achieved by consecutively formed chemical bonds using 3-aminopropyltriethoxysilane and sucrose. The unpressed electrode (density: 0.71 g cm⁻³) shows a reversible specific capacity of 1470 mAh g⁻¹ with a high initial coulombic efficiency of 83.7% at a current density of 1 C-rate. The corresponding pressed electrode (density: 1.32 g cm⁻³) exhibits high reversible volumetric capacity of 1405 mAh cm⁻³ and gravimetric capacity of 1520 mAh g⁻¹ with a high initial coulombic efficiency of 80.4% and excellent cycling stability of 83% over 100 cycles at 1 C-rate.     

Nonuniform microwave discharge in a nitrogen-hydrogen mixture

The method of optical emission spectroscopy is used to investigate the influence of additions of hydrogen on the emission characteristics of a highly nonuniform electrode microwave discharge in nitrogen at a pressure of 1 torr. It is demonstrated that the pattern of the influence made by hydrogen addition (zero to 50% with respect to flow rate of hydrogen) on the intensity of emission bands of nitrogen is different in different parts of the discharge. It is further observed that the influence of hydrogen on the vibrational distribution of nitrogen molecules in the C ³Π _u state is different C3?uin different parts of the discharge. Analysis is made of various processes involving hydrogen, which affect the emission of nitrogen bands. An inference is made that ion conversion is an important mechanism of such influence. One-dimensional simulation is performed in view of these processes, and it is demonstrated that the experimentally observed effects may be associated with this mechanism.     

Surface treatment of TiO2 films for dye-sensitized solar cells using atmospheric-pressure non-equilibrium DC pulse discharge plasma jet

In this paper, we report the utilization of the DC pulse discharge plasma jet technique as a means for the preparation of titanium oxide (TiO₂) films on fluorine dope tin oxide (FTO) coated glass substrates used for dye-sensitized solar cells (DSCs). The TiO₂ film made on these experimental bases exhibited the BET specific surface area of 95 m²/g, the pore volume of 0.3 cm²/g and the TEM particle size of ∼25 nm. The DSCs made by the TiO₂ film exhibited an energy conversion efficiency of 5.7% at 100 mW/cm² light intensity. Consequently, we believe that the optimization between the specific surface area and photocurrent density of TiO₂ film was achieved by the plasma surface treatment which also contributed to the improvement of energy conversion efficiency of DSCs.     

Mass transfer and crater geometry of a spark discharge in a hermetically sealed chamber

Results are presented of investigations of the dependence of crater diameter and depth and of transfer of electrode material for a spark discharge in transformer oil under an external pressure ranging from 1.01·10⁵ to 252.5·10⁵, N/m². The results obtained are discussed from standpoint of the role of the transient pressures and the surface and thermophysical properties of the liquid metal.     

Gasdynamic perturbations under conditions of surface microwave discharge in air

An investigation is performed of gasdynamic perturbations arising in the neighborhood of a dielectric antenna, on the external surface of which a microwave discharge is initiated at high pressures of air, where the electron-molecule collision frequency is much higher than the circular frequency of electromagnetic field. The time dependence of gas temperature is obtained for different values of power input, and it is demonstrated that, in the stage of formation of discharge at atmospheric pressure of air, the gas is heated at a rate of 30–70 K/μs. The electron concentration in plasma channels at atmospheric pressure does not exceed 10¹⁵–10¹⁶ cm⁻³. A study is made of the evolution of shock waves arising under conditions of surface micro-wave discharge at different pressures of surrounding gas, different durations of stimulation, and different power inputs to the discharge. It is demonstrated that the shock wave velocity in the vicinity of the antenna reaches a value of 1 km/s.     

Grid-controlled current switching in cathode-spot discharge

The first results of an investigation of the complete current switching (initiation and quenching) using a fine-mesh grid in discharge with a cathode spot on liquid cesium are reported. Experimental data show the possibility of using this method of control at current densities within 5–25 A/cm² in the grid plane.     

The role of fast electrons in the formation of a pulsed volume discharge at elevated gas pressures

A volume electric gas discharge was obtained using a pulsed inhomogeneous electric field without a preionization source in various gases (nitrogen, air, helium, neon, argon, krypton) at elevated pressures. In air at atmospheric pressure and nanosecond voltage pulses, the specific energy deposited in the gas amounted up to ∼1 J/cm³. The mechanism of the volume discharge formation is related to the appearance of fast (keV-energy) electrons emitted from plasma formations at the cathode. Fast electrons provide for the effective preionization of the gas in the interelectrode space and favor the formation of volume discharge. Under these conditions, the maximum voltage drop across the discharge gap is achieved in the quasi-stationary stage of discharge.     

Measurement of sputtered Mg particles in an MgO surface discharge

The experimental analyses of the surface erosion in an MgO surface discharge of an ac plasma display panels (PDPs) were performed. As the result of the surface observation on the MgO layer after accelerated discharge test, the erosion pattern of the MgO surface was spatially non-uniformed and a maximum erosion region existed near the electrode edge side in the MgO surface. To explain the localized erosion of the MgO layer, spatiotemporal distributions of Mg particles emitted from an MgO surface discharge were directly measured using the laser-induced fluorescence (LIF) method. The use of two-level scheme with fluorescence light of 285.2 nm (Mg 3¹P₁-3¹S₀) allowed us to perform measurements at 2 mm above the MgO surface under the condition of S/N (signal to noise ratio) > 3. The result of LIF measurement was found to explain the localized erosion profile obtained from the surface observation on MgO layer.     

Successively pulse plated cadmium selenide films and their photoelectrochemical behaviour

In successive pulse plating, the pulse deposition is repeated after a definite duration of plating preceded by a mild cleaning of the electrode and with a fresh deposition bath for the same duration. In this study, CdSe films were deposited on Ti substrates by successive pulse plating from a bath containing CdSO₄ and SeO₂ at a current density of 80 mA cm⁻² and a duty cycle of 3·3% for a duration of 30 min. The films heat-treated to 550°C for 20 min in argon atmosphere, were polycrystalline with a hexagonal structure. At an illumination of 60 mW cm⁻², a conversion efficiency of 4·5% for the photoetched film and 1·7% for the chemically etched one were determined.     

Production of H atoms in solid H2 by RF discharge

Hydrogen atoms have been produced by RF discharge at the surface of an H₂ crystal and studied by ESR techniques. The mean concentration at 4.2 K was estimated to be 10¹⁵ atoms per cm³ for about 14 h of source pulsing. This atom concentration was shown to be stable for long times. The results suggest that diffusion of atoms into the interior of the solid takes place very rapidly.