K. Yasuoka

Influence of electrode contact on luminescence from alumina ceramic surface under ac electric field in vacuum

The luminescence from a planar metal–alumina–metal structure was investigated under ac voltage application in vacuum. Two kinds of electrode contacts, i.e., with/without sputtered gold film, showed quite different optical phenomena. For the nonsputtered alumina samples, no luminescence was detected until extremely irregular light pulses resulted from partial discharges under higher voltage. While for the sputtered samples, from far lower applied voltage, there was faint but stable light emission due to electroluminescence (EL) observed. Based on the band theory of solids, we proposed a model to explain the interesting phenomena qualitatively. Taking account of the sputtering process, a marked reduction of the potential barrier between electrodes and alumina surface would result. Thus, charge carriers can be easily injected from the electrodes into the surface layer of alumina, and EL will emit due to the radiative recombination of electrons and holes. It is considered that EL has a significant influence o...

Investigation of Charge Injection in Gas-Impregnated Polyethylene by Measurement of Electroluminescence under AC Voltage

Electroluminescence (EL) in polyethylene (PE) impregnated with N2, O2 or SF6 gas has been measured under ac voltages to investigate the effect of impregnation gas on charge injection. EL is strongly dependent on the processes of electron injection and transport in the surface region of PE. The results of our measurements of EL indicate that the process of electron injection is greatly affected by the type of impregnation gas in PE. In particular, O2 gas which is electronegative and chemically reactive markedly affects the charge injection process, causing a reduction in EL inception voltage and barrier height at the electrode-polymer interface. The surface states induced by the presence of O2 gas or by oxidation of PE enhance the electron injection. However, electrons injected into such surface states likely contribute little to EL. N2 gas also causes a reduction in the EL intensity but does not induce a change in the EL inception voltage and the barrier height in comparison with those in the degassed case. N2 gas probably affects an electron transport process such as intermolecular conduction in the surface region of PE rather than the electron injection process.

SI-thyristor as a high power switching device for fast high voltage pulse generators

Characterization of SI-thyristors as a fast closing switch for pulsed power application was examined. Since the SI-thyristors employed in this study are normally on-state, a negative bias voltage is necessary at the gate electrode to establish hold-off-state. As a consequence, fast current rise rate can be strongly expected. A low impedance gate driving circuit built with MOSFETs improved turn-on characteristics. By adjusting anode voltage distribution and gate timing, carefully stacked SI-thyristors were successfully operated to make turn on. The highest di/dt obtained in this study is 55 kA//spl mu/s. A fast high voltage pulse generator with magnetic pulse compression scheme was built by using stacked SI-thyristors. To obtain a faster high voltage pulse a nonlinear transmission line as an additional circuit for pulse sharpening was employed.

Preflashover and flashover phenomena of silicon–vacuum system under pulsed excitation

Rectangular n+nn+-type silicon blocks with different surface treatments, i.e., one surface is chemically etched and the other is unetched, were used to investigate the characteristics of preflashover and flashover of semiconductor under a high voltage pulse in a vacuum. The metallic contacts were employed to keep a fine contact between the sample and the electrode. For unetched samples, the preflashover current obeyed Ohm’s law, and for etched samples, it was dominated by the space-charge limited current. After flashover shots, two kinds of silicon samples showed quite distinct tracks. It is considered that all the phenomena are attributed to the different density and distribution of surface states for two kinds of samples. The developing process of surface flashover across a semiconductor could be explained as the current filamentation which is induced by thermal effects. It is suggested that the flashover occurs in the interface layer of silicon butted to electrodes, and in the lateral layer of silicon ...

Pulsed power generator utilizing fast SI-thyristors for environmental applications

Fast SI-thyristor switching systems were designed and examined for environmental applications. The authors characterized three kinds of SI-thyristor with different device structures by using an extremely low inductance testing circuit, and confirmed the superiority of punch-through and flat-anode structures for fast turn-on characteristics. In order to accomplish fast turn-on operation, they developed a fast and high current gate-driving circuit for repetitive pulsed power applications. The SI-thyristors were successfully operated with a fall time of 35 ns and a current rising rate of 9.5/spl rlarr2/10/sup 10/ A/s. To clarify technical issues for higher voltage operation, they employed three SI-thyristors stacked in series to assemble the generator, which was operated with a repetition rate of 2 kHz.

Fast bipolar voltage pulse generator using nonlinear transmission line for exciting UV light source

Fast bipolar voltage pulses were generated for exciting a dielectric coated discharge system by using a nonlinear transmission line (NLTL) which included nonlinear capacitors. The energy transfer efficiency of a basic resonant circuit consisting of a nonlinear capacitor was evaluated from the viewpoint of efficient energy transfer. The simulation results of the pulsed laser discharge show that the nonlinear capacitor is effective both in increasing the peak voltage and shortening the pulse width. A bipolar voltage pulse was generated by a specially connected cable discharge system switched by an SI thyristor. The input pulse of 700 V, 130 ns(FWHM) was compressed to 1.4 kV, 30 ns (FWHM) at the 7th section. The N/sub 2/ gas was excited by these short pulses and showed light emission of 30 ns (FWHM).

Decomposition of perfluorooctane sulfonate in water using atmospheric plasma

Perfluorooctane sulfonate (PFOS) is widely used for industrial and commercial products due to its chemical stability and physical characteristics. Biopersistance and unexpected toxicity however, have raised environmental concerns. In this study, PFOS in water was decomposed using direct plasma methods such as DC plasma generated within oxygen bubbles in water and barrier discharge plasma generated on water surface.

The generation and application of micro discharge plasmas

Summary form only given. The dielectric barrier discharge lamp has been developed and commercially supplied as a tunable UV light source. However, a high-voltage (over several tens of kilovolts) is required to drive the device. We have attempted to reduce the driving voltages without reducing the light intensity by using new types of micro discharge plasmas, such as, micro-hollow cathode discharge (MHCD) and surface plasma produced by a ferroelectric electron emission (FEE). These plasmas can be driven with a relatively low voltage pulses at atmospheric pressure. We have studied how to generate and operate these micro discharge plasmas as UV excimer light sources.

Electroluminescence from polymeric halides subjected to an AC voltage

Electroluminescence (EL) from polymeric halides and hydrocarbons has been investigated under voltages to clarify the effect of halogens in the polymers on the EL. We used polymer films with semi-transparent gold electrodes, namely, polytetrafluoroethylene (PTFE), polyvinylchloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP). The light emission from PVC and PTFE started from lower fields and had a larger light intensity than that from LDPE and PP. However, the basic natures of the physical mechanisms of light emission involved seemed to be similar in all samples. The characteristics of light emission can be explained by considering the energy band structure of electron at the surface of polymer. The necessary condition of light emission will be the formation of long-term electron space-charges near the metal-polymer interface sufficiently enough to generate the reverse field for the hole injection. Halogens in the polymers act as strong trapping centers for injected electrons and enhance the formation of long-term electron space-charges. The light may be emitted dominantly by radiative recombination of electrons and holes.

Mass balance analysis of perfluorocompound decomposition by DC plasma generated in gas bubbles

Summary form only given. Perfluorooctane sulfonic acid (PFOS) can be decomposed efficiently by plasmas generated in gas bubbles. However, mass balance during the degradation of PFOS is not fully understood. Mass balance is quite important for commercial applications. Thus, the purpose of this study is to clarify the value of the mass balances of fluorine, carbon, and sulfur, and to understand the degradation process of PFOS. PFOS in water was decomposed by dc plasma generated in argon gas bubbles. The reactor was made of acrylic. A ceramics plate, which was 0.3 mm in thickness and had a micro hole of 0.3 mm diameter at the center, was attached on the bottom of the reactor. Argon gas was supplied through the hole to PFOS solution at a flow rate of 100 sccm. A stainless steel mesh (SUS304, 30mesh) was used as a high voltage electrode and attached on the back side of the ceramics plate. A grounded electrode was put into the reactor and immersed in the solution. High voltage was applied to the high voltage electrode through a ballast resister (250 kΩ) and plasma was generated in argon gas bubbles. A resister (1 kΩ) was used to measure the electric current, which was regulated at 10 mA. The concentration of carbon dioxide (CO2) in the gas released from the plasma reactor was measured using gas chromatography. Other components in the gas were analyzed using Fourier transform infrared spectroscopy (FT-IR). The solution was analyzed using liquid chromatography-mass spectroscopy (LC-MS) and ion chromatography. During the degradation of PFOS, the concentrations of PFOS, perfluorocarboxylic acids (PFCAs: CnF2n+1COOH) with shorter carbon chains (n = 1-7), fluoride ion, and sulfate ion in the solution, and CO2 in the gas were quantified. The mass balances of fluorine, carbon and sulfur were calculated using these concentrations, and were 59.1%, 44.6%, and 83.2% respectively after 365 min treatment. Tetrafluoro methane (CF4), trifluoro methane (CHF3), hexafluoro ethane(C2F6), and carbon monoxide (CO) were detected in the gas using FT-IR but the concentrations of them were not quantified yet. By the quantification of the concentrations of the gas components, it will be possible for the mass balances to amount to 100%.