Thin film deposition using a plasma source with a hot refractory anode vacuum arc

Vacuum arc generated plasma was used to deposit metallic Al, Zn, and Sn coatings on glass substrates. An arc mode with a refractory anode and an expendable cathode (the “hot refractory anode vacuum arc”), overcomes macroparticle (MP) contamination experienced in other arc modes. I = 100–225 A arcs were sustained between a water-cooled coating source cathode and an anode, which was heated by the arc, separated from each other by a 10-mm gap, for times up to 150 s. The distance from the arc axis to the substrate (L) was 80–165 mm. Film thickness was measured with a profilometer. It was found that the deposition rate increased with time to a peak, and then decreased to a steady-state value. The peak occurred earlier when using short anode (9 mm long), e.g., with the Al cathode, L = 110 mm, and I = 200 A, the peak was at t _p = 15 s after arc ignition while with the long anode t _p = 45 s. t _p decreased with I, from 45 s with I = 100 A, to 10 s with I = 225 A with the short anode. The peak is believed to appear due to initial condensation of cathode material (including MPs) on the cold anode, and its subsequent evaporation as the anode heated. In the later HRAVA steady state, a balance between condensation and evaporation on the anode is established. The deposition rate peak was significant with low melting temperature Al and Zn cathodes, which produce many MPs, and negligible with Cu and Ti cathodes.     

Effect of nitrogen pressure on the energy of runaway electrons generated in a gas diode

The energy spectra of runaway electrons generated in a gas diode under the action of voltage pulses with a front width of ∼300 ps and amplitude of ∼140 kV have been studied using a time-of-flight spectrometer at nitrogen pressures in a range of 0.1–760 Torr. The delay of runaway electron beam pulse relative to the driving voltage pulse has been determined. The electron energy depends in a complicated manner on the nitrogen pressure in the gas diode and on the cathode geometry. A minimum breakdown voltage for a gap between tubular cathode and flat anode has been observed at a nitrogen pressure of ∼100 Torr. A decrease in the nitrogen pressure below 100 Torr leads to an increase in the maximum of voltage drop on the gap and the energy of the main fraction of electrons.     

Optimization of field emission properties of carbon nanotubes cathodes by electrophoretic deposition

Cold cathodes of carbon nanotubes (CNTs) were deposited on the glass substrate by the electrophoretic deposition (EPD) method. The cathodes were tested in the diode construction with the cathode–anode gap of 170 μm in vacuum. The emission characteristics of the CNTs film cathodes have as good properties as those by screen printing and better emission uniformity. The influence of the voltage between electrodes in the electrophoretic process of flat cold cathode fabrication on the uniformity of the CNTs film distribution was studied. The results indicate that the uniformity of CNTs film cathode by EPD depends on the voltage between electrodes during the electrophoretic deposition. The uniformity of CNTs film and optimized emission properties of the cathode have been achieved when the voltage is 25 V.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).     

Breakdown in planar magnetron discharges of argon on copper

In magnetrons the magnetic field confines partially the electron swarm in a trap near the cathode increasing sputtering yield and deposition rates. The magnetic field also decreases the ignition voltage even at relatively low pressures thus allowing sputtering at lower pressures. Under this conditions fewer collisions, less diffusion and less thermalization of the sputtered atoms occur during the transport to the substrates. Atoms arrive at substrates with larger energy and at higher rates.We present an experimental study of the magnetic field influence on the breakdown voltage in planar magnetron abnormal glow discharges for argon on copper. A magnetron cathode was constructed, with a finely tuneable magnetic configuration. The experimental curves of the breakdown voltage as a function of the discharge pressure at constant “confinement power” show minima similar to those occurring in Paschen's law. At lower pressures the breakdown voltage has a strong dependence on magnetic configuration and changes from 750 to 250 V can be found. At higher pressures the breakdown voltage is less sensitive to the magnetic field.Paschen's law could not be fitted to the experimental results and as alternative an empirical expression is proposed and its parameters discussed.The results can be understood by the increased length of the average electron path both in helical and cycloid type trajectories near the cathode and by the reduction of the electron drift towards the anode and the walls of the chamber. In the Townsend regime, before breakdown and fixed voltage the electron density near the cathode increases with the confinement power. This causes a higher flux and energy of the ions that strike on the cathode for the same applied voltage. The voltage needed to get the self-sustained discharge is strongly reduced.     

Operating characteristics of the hollow anode glow discharge ion source

In this work, a new shape of a glow discharge ion source with axial extraction has been designed and constructed. High output ion beam current can be extracted axially in a direction normal to the discharge region without using extraction system. Optimization of the distance between the anode and the cathode has been determined using argon gas. It is found that the optimum gap distance between the anode and the cathode is equal to 3.5 mm, where stable discharge current and maximum output ion beam current can be obtained. The discharge characteristics of the ion source at different operating gas pressures have been measured at this optimum distance between the anode and the cathode. A disk of Teflon insulator has been put between the anode and the cathode. This disk was covering the cathode area and reducing the discharge area on the cathode surface for discharge confinement, therefore, a higher output ion beam current could be obtained.     

Two-dimensional axisymmetric simulations and the heating effects associated with DC atmospheric pressure discharges during the post-streamer stage

Numerical results are presented for the development of the post-streamer discharge stage in atmospheric pressure air. The model used comprises Poisson, charged-particle continuity and Navier-Stokes equations developed in two-dimensional cylindrical axisymmetric co-ordinates. Applied direct current voltage of 20% above the breakdown threshold is applied in a 1 mm gap between two parallel plate electrodes. Starting from a single electron as the initial condition, the transitory regime from the streamer to the glow discharge is analysed, and the glow discharge is shown to consist of the cathode fall, negative glow, positive column and anode regions. The positive column is shown to propagate in the form of a return wave towards the anode. The very fast redistribution of the electric field just after the streamer hits the cathode is presented. Furthermore, the current density at the cathode fall and anode regions is shown to increase and extend radially outwards, justifying the inclusion of a two-dimensional axisymmetric model to study the radial effects in the discharge. Neutral gas heating starts to occur with the initiation of the post-streamer discharge stage, and the neutral gas temperature increases at the cathode by approximately 180 K     

Electromigration-enhanced intermetallic growth and phase evolution in Cu/Sn–58Bi/Cu solder joints

This paper presents some experimental observations relative to the influence of elevated current densities on the intermetallic growth and phase evolution in Cu/Sn–58Bi/Cu solder joints. Three samples were stressed with different current densities of 10⁴, 1.2 × 10⁴, and 1.4 × 10⁴ A/cm², respectively, for 80 h. The abnormal polarity effect of electromigration (EM) on chemical reactions at the cathode and the anode was investigated as well as the effect of EM on phase segregation in the two-phase eutectic microstructure. Results indicate that electric current enhances the growth of IMC layer at the cathode and retards it at the anode due to the Bi accumulation acting as a barrier layer with current density of 10⁴ A/cm². However, when current density increases, the electrical force dissolves the IMC at the cathode into the solder. More and more intermetallic precipitates formed due to the dissolution of Cu into the solder at the cathode side with increased current densities, leading to a very different morphology at the anode and the cathode interfaces, one being planar and the other being very irregular. It can be concluded that the chemical force and the electrical force are the main driving forces contributing to the IMC growth at both interfaces.     

Battery in the form of a cement-matrix composite

Reported here is a battery in the form of a cement-matrix composite, with cement paste as the matrix, the pore solution in cement as the electrolyte, zinc particles dispersed in the matrix as the anode, manganese dioxide particles dispersed in the matrix as the cathode, and carbon black dispersed in the matrix as the conductive additive in both anode and cathode regions. The electrolyte is continuous throughout the battery, which consists of successively cast and co-cured anode, electrolyte and cathode layers. The anode layer (4 mm thick) comprises cement and zinc particles. The cathode layer (8 mm thick) comprises cement and manganese dioxide particles. The electrolyte layer (2 mm thick) is cement with an embedded piece of tissue paper for drying shrinkage control. The battery attained open-circuit voltage up to 0.72 V, current up to 120 μA (current density up to 3.8 μA/cm²), power output up to 1.4 μW/cm², capacity up to 0.2 mA h, and fraction of zinc consumed up to 5 × 10^?5.     

Synthesis and blue electroluminescent properties of zinc (II) [2-(2-hydroxyphenyl)benzoxazole]

This study reports on the properties of organic light-emitting diodes (OLEDs) with zinc (II) [2-(2-hydroxyphenyl)benzoxazole] as a hole-blocking layer. OLEDs devices are prepared in a conventional OLEDs structure (i.e., anode/HTL/EL/HBL/cathode and anode/HTL/HBL/EL/cathode). The luminescence efficiencies and the turn-on voltage are significantly affected by the existence of the hole-blocking layer. This is attributed to an excellent hole-blocking property, which is in turn due to the high HOMO energy level (6.5 eV). The device showed luminous efficiency 2.46 lm/W at 5 V. The maximum luminance of about 10,000 cd/m² is obtained, and the turn-on voltage (2.5 V) is affected by the existence of the hole-blocking layer.     

Generalization of volt-ampere characteristics of the electric arc in a double-jet plasmatron with tubular single-chamber electrode units

On a double-jet plasmatron with cylindrical single-chamber electrode units, an experimental study of volt-ampere characteristics of the electric arc is conducted at current 105–550 A, voltage 400–1320 V, total flow rate of the plasma-forming gas (air) (0.76–9.83)∙10⁻³ kg ⁄ s, angle between the cathode and anode parts 45–62°, distance between the cathode and anode axes at the outlet from nozzles 0.07–0.2 m, and outlet pressure of ~0.1 MPa. Correlations for these characteristics are obtained.     

Electrical breakdown in nonuniformly heated gases and the upper temperature limit of the applicability of Paschen’s law

The electrical breakdown of nonuniformly heated gas-discharge gaps with a uniform electric field at temperatures of 1200–3600 K is studied experimentally. It is found that the thermionic emission from the cathode has an effect on the breakdown parameters. This effect starts manifesting itself at the critical density of the emission currentJ _cr ∽ 10⁻⁸ A/cm² attained in experiments with a tungsten cathode at a temperatureT _CT ∼ 1700 K. The increase of the cathode temperature to -2200 K results in a decrease of the breakdown voltageU _br by more than an order of magnitude due to the thermionic emission. The heating of the anode to a temperature of up to 3600 K does not result in a decrease of the breakdown voltage below the values defined by the gas density. In this case, the decrease of the values ofU _br is due only to the change of the gas density distribution along the gap length and obeys the generalized law of similarity. The existence of a critical temperatureT _T is predicted, above which one should expect a drastic decrease of the breakdown voltage due to the thermal ionization of gas. The value ofT _T depends on the configuration of the thermal field between the electrodes and the type of gas. In the thermal fields typical of our experimental conditions involving the heating of one of the electrodes, the critical temperature for xenon is about 4700 K. The studies were carried out in argon, krypton, and xenon.     

A Molecularly Engineered Cathode Lithium Compensation Agent for High Energy Density Batteries

Prelithiating cathode is considered as one of the most promising lithium compensation strategies for practical high energy density batteries. Whereas most of reported cathode lithium compensation agents are deficient owing to their poor air-stability, residual insulating solid, or formidable Li-extracting barrier. Here, this work proposes molecularly engineered 4-Fluoro-1,2-dihydroxybenzene Li salt (LiDF) with high specific capacity (382.7 mAh g⁻¹) and appropriate delithiation potential (3.6–4.2 V) as an air-stable cathode Li compensation agent. More importantly, the charged residue 4-Fluoro-1,2-benzoquinone (BQF) can synergistically work as an electrode/electrolyte interface forming additive to build uniform and robust LiF-riched cathode/anode electrolyte interfaces (CEI/SEI). Consequently, less Li loss and retrained electrolyte decomposition are achieved. With 2 wt% 4-Fluoro-1,2-dihydroxybenzene Li salt initially blended within the cathode, 1.3 Ah pouch cells with NCM (Ni92) cathode and SiO/C (550 mAh g⁻¹) anode can keep 91% capacity retention after 350 cycles at 1 C rate. Moreover, the anode free of NCM622+LiDF||Cu cell achieves 78% capacity retention after 100 cycles with the addition of 15 wt% LiDF. This work provides a feasible sight for the rational designing Li compensation agent at molecular level to realize high energy density batteries.     

Electromigration-induced cracks in eutectic SnPb solder reaction couple at room temperature

Electromigration (EM) of 63Sn–37Pb solder reaction couple was studied under high current density of 5 × 10³ A/cm² at room temperature. There was non-uniform distribution of current density across the linear specimen, and the dissimilar interface of two different materials could trigger current crowding especially at the edge of the interface. Though the atoms/ions of Sn and Pb would migrate along the direction of electron flow pushed by electron wind force, the Sn atoms were observed to be the principal diffusion entities at room temperature. Depletion of mass at cathode side induced the tensile stress along parallel direction of the specimen cross-section, while the accumulation of mass at anode side induced the compressive stress along the perpendicular direction of the specimen cross-section. Crack initiation and propagation in both cathode and anode side was found to be strongly dependent on the current density distribution.     

Improved version of the triode electron gun

Results of the triode electron gun which delivers 500 mA current pulses of 2 μs duration at an energy of 40 keV are presented. This new gun uses LaB₆ cathode as emitter indirectly heated by a tungsten filament, a focusing electrode, non-intercepting modulating anode and anode. Various improvements and additions carried out to the earlier gun which delivered only 120 mA current pulses is described.     

Perturbation solutions for steady direct and inverse electrochemical machining problems

The steady state electrochemical machining process gives rise to both the direct problem which consists of determining the anode shape resulting from a specified cathode shape, and the inverse problem in which the cathode shape required to produce a given anode shape is sought. These two problems are solved by a perturbation scheme in which the perturbation parameter is the square of the ratio between the “wavelength” of the variation in the anode or cathode surfaces and the inter-electrode gap.     

Discharge current and ultrashort avalanche electron beam current in a volume nanosecond gas discharge in inhomogeneous electric field

The moment of generation of an ultrashort avalanche electron beam (UAEB) relative to the discharge current pulse front has been determined in a volume discharge formed upon nanosecond breakdown of an air gap at atmospheric pressure in an inhomogeneous electric field. The UAEB current reaches maximum on the front of the discharge current pulse, ～100 ps before the peak of this current. Bias currents with amplitude above 1 kA have been observed. The amplitude of this current increases due to the charging of a capacitor formed by the flat metal anode and a dense discharge plasma expanding from the cathode.     

硫酸阳极氧化槽中阴极的改进

硫酸阳极氧化用铝阴极替代铅阴极可以减少压降损失1～2 V,铅电导率仅为铝的10%～15%.使用铝阴极可减少氧化槽热量的产生,节能30%.6063T6铝阴极在硫酸中(180g/L)因溶解的损失率仅1 mm/a,阴阳极面积比最佳为1:3,特殊情况可控制在1:5,阴阳极之间最小距离25 cm较为合适.     

Rational Design of a High-Loading Polysulfide Cathode and a Thin-Lithium Anode for Developing Lean-Electrolyte Lithium–Sulfur Full Cells

Lithium-sulfur cells are attractive energy-storage systems because of their high energy density and the electrochemical utilization rates of the high-capacity lithium-metal anode and the low-cost sulfur cathode. The commercialization of high-performance lithium–sulfur cells with high discharge capacity and cyclic stability requires the optimization of practical cell-design parameters. Herein, a carbon structural material composed of a carbon nanotube skeleton entrapping conductive graphene is synthesized as an electrode substrate. The carbon structural material is optimized to develop a high-loading polysulfide cathode with a high sulfur loading capacity (6–12 mg cm⁻²), rate performance (C/10–C/2), and cyclic stability for 200 cycles. A thin lithium anode based on the carbon structural material is developed and exhibits long lithium stripping/plating stability for ≈2500 h with a lithium-ion transference number of 0.68. A lean-electrolyte lithium–sulfur full cell with a low electrolyte-to-sulfur ratio of 6 µL mg⁻¹ is constructed with the designed high-loading polysulfide cathode and the thin lithium anode. The integration of all the critical cell-design parameters endows the lithium–sulfur full cell with a low negative-to-positive capacity ratio of 2.4, while exhibiting stable cyclability with an initial discharge capacity of 550 mAh g⁻¹ and 60% capacity retention after 200 cycles.     

Determination of the cathode erosion and temperature for the phases of high voltage discharges using FEM simulations

A discharge produces an energy input in the cathode material, which causes the erosion of the material surface. The principal mechanism of erosion is the formation of craters mainly due to melting. From calorimetric results published in the literature, the amounts of energy delivered to the cathode for the different phases of the discharge (breakdown, arc and glow discharge) were calculated. A FEM model was developed to simulate the temperature distribution and the phase transitions, which allows the definition of molten and evaporated zones. These zones were compared with the volumes of craters done in Pt-samples at air with pressures ranging between 1 and 9 bar and static electrode gaps of 2 mm. The breakdown energy is enough to melt an amount of material, which is responsible for the formation of very flat craters. The formation of deeper overlapped craters observed in experiments can not be produced during the breakdown; they are produced by the arc phase of the discharge. The assumption of the crater area as the area for the energy exchange between plasma and material gives the best results in the simulation. The glow discharge produces only a light heating of the cathode, without any significant erosion.