Characteristics Of Glow Discharge Research Articles

Increasing the Surface Energy and Sterilization of Nonwoven Fabrics by Exposure to a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP)*

A technique for generating active species with the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been developed and used to sterilize and increase the surface energy, wettability and wickability of nonwoven fabrics. The OAUGDP is a non-thermal, fourth-state-of-matter plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. No vacuum system or batch processing is necessary, and a wide range of applications to fabrics and polymeric webs can be accommodated in a parallel plate plasma reactor. In addition to directly exposing webs and workpieces to active species for surface energy increase in a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. This technology is simple, produces many effects that can be obtained in no other way, generates minimal pollutants or unwanted byproducts, and is suitable for online treatment of webs, films, and fabrics. Early exposures of nonwoven fabrics to the OAUGDP required minutes to produce relatively small increases of surface energy. These durations appeared too long for commercial application to fast-moving webs. Recent improvements in OAUGDP power density, plasma quality and impedance matching of the power supply to the parallel plate plasma reactor have made it possible to raise the surface energy of a variety of polymeric webs (PP, PET, PE, etc.) to levels in the range of 60 to 70 dynes/cm with one second of exposure. In most cases these high surface energies were not durable, and fell off to 50 dynes/cm after periods of weeks to months. Here, we report the exposure of nonwoven fabrics made of PP and PET at the UTK Textiles and Nonwovens Development Center (TANDEC) to an impedance matched parallel plate OAUGDP for durations ranging from one second to several tens of seconds. Data will be reported on the surface energy, wettability and wickability as functions of time of exposure, and of the aging effect after exposure. We will report the use of a OAUGDP with air as the working gas to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a Remote Exposure Reactor to sterilize large workpieces 20 centimeters or more from the plasma-generating region, and a sterilizable air filter.

Subnormal glow discharge in a Xe/Cl2 mixture in a narrow discharge tube

Electrical and optical characteristics of a subnormal glow discharge in a short (L=10 cm) discharge tube with an inner diameter of 5 mm are investigated. The dependences of the discharge current-voltage characteristic, the energy deposition in the discharge, the plasma spectral characteristics in the 130-to 350-nm wavelength range, the emission intensities of the XeCl(D-X) 236-nm and XeCl(B-X) 308-nm bands, and the total emission intensity in the range 180–340 nm on the pressure and composition of the Xe/Cl2 mixture are studied. Two modes of glow discharge are shown to exist: the low-current mode at a discharge current of I ch ≤2 mA and the high-current mode at I ch >2 mA. The transition from one mode to another occurs in a stepwise manner. The increase in the chlorine content causes the discharge voltage and the energy deposition in the plasma to increase. At low pressures of the Xe/Cl2 mixture (P≤0.7 kPa), stationary strata form in the cathode region. The lower the discharge current, the greater the volume occupied by the strata. This longitudinal discharge acts as a powerful source of continuous broadband emission in the range 180–340 nm, which forms due to overlapping the XeCl(D, B-X) and Cl 2 * bands with edges at λ=236, 308, and 258 nm. The intensity of the 236-nm band is at most 20% of the total intensity of UV radiation. The maximum power of UV radiation (3 W at an efficiency of 8%) is attained at a xenon partial pressure of 250–320 Pa and a total pressure of the mixture of 2 kPa.

Apparent secondary-electron emission coefficient and the voltage-current characteristics of argon glow discharges.

The accuracy of secondary-electron emission coefficients, that are used as input data of discharge models, seriously influences the calculated discharge characteristics. As it is very difficult to consider all possible electron emission processes of a cold cathode separately, in most of the recent models an apparent secondary coefficient gamma is applied, which is often assumed to be constant, even for a wide range of discharge conditions. In contrast with this common assumption, the present calculations-based on a heavy-particle hybrid model-show that in abnormal glow discharges gamma varies considerably with changing discharge conditions: a factor of 3 change of gamma has been found in the range of reduced current densities (0.04 mA cm(-2) Torr(-2)< or =j/p(2)< or =4 mA cm(-2) Torr(-2)) covered in this study. The present simulations also confirm that ionization by heavy particles plays a significant role in the ion production at the abnormal cathode fall. Moreover, it is shown, that the fast heavy particles reflected from the cathode surface play the dominant role in the gas heating.

An atmospheric pressure glow discharge optical emission source for the direct sampling of liquid media.

A glow discharge optical emission spectroscopy (GD-OES) source that operates at atmospheric pressure is described. This device utilizes an electrolytic solution containing the analyte specimen as one of the discharge electrodes. The passage of electrical current (either electrons or positive ions) across the solution/gas phase interface causes local heating and the volatilization of the analyte species. Collisions in the discharge region immediately above the solution surface result in optical emission that is characteristic of the analyte elements. Operation of this device with the analyte solution acting as either the cathode or anode is demonstrated. Current-voltage (i-V) plots reveal abnormal glow discharge characteristics, with operating parameters being dependent on the electrolyte concentration (i.e., solution conductivity) and the gap between the solution surface and the counterelectrode. Typical conditions include discharge currents of 30-60 mA, and potentials of 500-900 V. Electrolyte solutions having pH, pNa, or pLi values of 0.5-2 and interelectrode gaps of 0.5-3 mm produce stable plasmas in which the analyte solutions flow at rates of up to 3.0 mL/min. Preliminary limits of detection are determined for the elements Na, Fe, and Pb to be in the range of 11-14 ppm (approximately 60 ng) for 5-microL sample volumes.

Voltage–current characteristics of high-current glow discharges

The voltage–current characteristics of glow discharges in gas mixture (N2:O2=8:2) at a pressure of 10 Torr were obtained with the discharge current up to 150 A. Parallel-plane electrodes with a diameter of 10.7 cm and a discharge chamber with co-axial geometry were used to produce glow discharge with high current. The glow discharge voltage was almost constant until the whole surface of the cathode was covered with glow, i.e., until the discharge current became 3.7 A in our experimental condition (a normal glow discharge mode). The voltage, however, increased with the current when the glow covered over the cathode (an abnormal glow discharge mode). The electron density in positive column of the high-current glow discharge was obtained to be 3×1011 cm−3 from Langmuir probe measurements.

Influence of the Emission of Charged Particles on the Characteristics of Glow Discharges with Oscillating Electrons

The influence of the extraction of charged particles on the conditions of sustaining and the characteristics of a glow discharge with oscillating electrons is considered. It is shown that there is some pressure-dependent optimum level for the extraction of ions at which the energy efficiency of the ion source reaches a maximum. Experimentally, it has been established that the sustaining of a discharge is adversely affected by the run-off of fast ionizing electrons from the discharge, whereas the emission of slow plasma electrons can facilitate the sustaining of the high-current variety of discharge and even lead to a stabilization of an unstable gas-discharge structure. It has been shown that due to the different character of the spatial distributions of fast and slow particles in discharges with electrons oscillating in a magnetic field it is possible to realize highly efficient electron emission without loss of discharge stability by extracting electrons from the near-anode region.

Multiwave Low‐Pressure Excimer Radiator

The excitation conditions and characteristics of a longitudinal glow discharge in a short tube of small diameter in Kr/Cl2 and Ar/Kr/Cl2 mixtures are investigated. It is shown that this discharge is a multiwave radiation source on systems of the 199/222/258 and 175/199/222/258 nm bands. Optimization of the pressure and composition of working mixtures most applicable for obtaining the approximately equal intensity of the ArCl(BX), KrCl(D, BX), and Cl2(D′A′) radiation bands is carried out in the discharge investigated. A multiwave UV‐VUV radiation source is of interest for use in photometry, microelectronics, photochemistry, and medicine.

Experimental study of a low-pressure glow discharge in air in large-diameter discharge tubes: I. conditions for the normal regime of a glow discharge

The initiation and characteristics of a low-pressure glow discharge in air in large-diameter discharge tubes are studied. A deviation from the Paschen law is observed: the breakdown curves Udc(pL) shift toward the higher values of Udc and pL as the interelectrode distance L increases. It is shown that the normal regime of a glow discharge is accompanied by gas ionization in the anode sheath. This takes place only for pL values lying to the right of the inflection point in the breakdown curve. The cathode-sheath characteristics in the normal and abnormal regimes of an air discharge for a duralumin cathode are determined. The axial profiles of the ion density, electron temperature, and plasma potential, as well as the anode voltage drop, are measured at various air pressures.

Optimising diamond nucleation via combined pre-treatments

Diamond thin film deposition on copper substrates has been carried out using hot filament chemical vapour deposition (HFCVD). Surface pre-treatment methods such as substrate polishing and biasing have been employed in order to maximise diamond grain density. We show that by combining substrate polishing and biasing there is an enhancement in the diamond grain density in comparison to the results obtained when each pre-treatment method is employed individually. After negatively biasing the substrate for 30 min, broad D- and G-bands of microcrystalline graphite were found to be present in the Raman spectrum. The graphite phase is essentially acting as the precursor for subsequent diamond deposition. It was found that this material, which consists of a network of amorphous carbon and microcrystalline graphite, was readily etched when exposed to the hydrogen plasma. Subsequent diamond deposition under standard CVD conditions completely covers the amorphous carbon layer with diamond until a uniform film is deposited. Interestingly, after diamond deposition for 5 h Raman spectra no longer displays the D- and G-bands of microcrystalline graphite. In this paper, the characteristics of the glow discharge which are expected to have a significant effect on diamond nucleation have also been studied.

Cathode layer characteristics of a low-pressure glow discharge in argon and nitrogen

Cathode layer characteristics were experimentally determined for a glow discharge in argon and nitrogen in a broad range of gas pressures. A normal glow discharge regime is observed only provided that the gas ionization takes place in the anode layer (on the right of the inflection point in the glow discharge initiation curve). Importance of using a correct method for the normal cathode voltage drop is emphasized.

Sterilization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.

Characteristics of a high-current transient glow discharge in dryair

The transition of a high-current glow to an arc and the energydissipation during the glow phase have been investigated in dry air by staticbreakdown. The measurements have been made for uniform-field gaps up to 2 cmat gas pressures of 1-20 Torr. A low-inductance capacitor of 1.89 µF and a discharge circuit with a coaxial system were used to produce atransient glow discharge with a current in excess of 400 A. The experimentalresults showed that the high-current glow discharge occurred at a cathodecurrent density of 3.2 A cm-2, which is almost two orderslarger than the value deduced from the formula for Cu-air normal glow;jn = 240×10-6p2, where jn and p are the current density and gaspressure, respectively. The transition from the glow to an arc starts todevelop in the discharge region near the cathode. The energies dissipated inthe discharge or in the cathode fall region during the glow phase depend onthe gas pressure and/or the electrode separation. However, the dissipatedenergy density in the cathode fall region during the glow phase is independentof the gas pressure and the electrode separation, and is approximately0.035 J cm-3 in the present experiment.

Surface-discharge characteristics of MgO-thin films prepared by reactive RF unbalanced magnetron sputtering

The performance of a.c. plasma display panels (PDP) is influenced strongly by the surface glow-discharge characteristics on the MgO-thin films. This paper deals with the surface glow-discharge characteristics and some physical properties of MgO-thin films prepared by reactive RF planar unbalanced magnetron sputtering in connection with a.c. PDP. The samples prepared with the d.c. bias voltage of −10 V showed lower discharge voltage, lower erosion rate by ion bombardment, higher optical transparency and higher crack resistance in the annealing process than those samples prepared by conventional magnetron sputtering or E-beam evaporation.

大電流パルスグロー放電の特性

Pulsed glow discharge is one of the candidates for the ion source plasma because it can easily generate large volume plasma even for a short time. This paper describes the characteristics of a transient glow discharge with high current using a low impedance circuit. A low inductance capacitor of 1.89μ F was used in this experiment. The voltage between electrodes and consumed energy were obtained by calculation of circuit equations and measurement of discharge current and static breakdown voltage. The gas used is dry air. As the experimental results, the transient glow discharge with high current above one hundred ampere was generated for several microseconds. It was clarified that cathode fall voltage under this experimental condition is approximately 320V which agrees with the value of normal glow discharge. The glow-to-arc transition occurs when the consumed energy in the cathode fall region reaches almost 35mJ in the present experimental conditions.

Investigations on the effect of constriction in the cathode region of argon glow discharges

We have investigated the effect of constriction on the characteristics of low-pressure glow discharges in argon. In a series of experiments four discharge tubes with plane-parallel electrodes of different diameters (D = 31.4, 20, 10 and 5 mm) and same electrode separation (L0 = 45 mm) were studied. The discharges were surrounded by floating-potential metal tubes. We measured voltage-current characteristics of the discharges and recorded the spatial intensity distribution of selected spectral lines (Ar-I 750.3 nm, 811.5 nm and Ar-II 476.5 nm) in the electrode gap at current densities 0.2 mA cm-2 j 1 mA cm-2. We also observed copper lines in the spectrum originating from the sputtering of the copper cathode, even at these relatively low discharge current densities. The `effective surface' of the cathode - that actively participates in discharge operation - is always smaller than the cathode surface. This results from the radial electric field formed in the cathode dark space due to the accumulation of charges on the metal tube surrounding the discharge. Using a simple model we could calculate the effective cathode diameter (which determines the current density for given current). Taking into account the current density obtained this way, the voltage of the tubes was found to obey the V = f(j/p2) scaling relation. The increasing loss of charge on the metal wall with decreasing tube diameter also resulted in structural changes in the discharge. While at large diameter the cathode dark space and the negative glow filled the interelectrode gap, at low D a positive column-like part was also formed.

Hollow cathode glow discharge in long tubes

An analysis is made of some burning characteristics of a hollow-cathode glow discharge with a long tube (L≫D) used as the cathode. It is shown that, as in the case L∼D, the main factor imposing a lower limit on the range of operating voltages is the drift of fast electrons through the aperture in the cavity. Assuming that the electrons move along the cavity as a result of diffusion, it was possible to calculate the critical pressure at which the discharge can no longer burn and to determine the optimum ratio L/D for which the discharge can be sustained at the lowest voltage. The calculations showed satisfactory agreement with the experiment.

Glow discharge in low-pressure excilamps

This paper presents a review of the principal publications devoted to the study of the spontaneous radiation sources operating in the uv region and discusses the properties of a low-pressure glow discharge in binary mixtures of inert gases with halides. It has been demonstrated that for variation of the excitation parameters over a wide range more than 10% emission efficiencies are realized for exciplex molecules and thatXeCl* andKrCl* molecules are formed in the main by the harpoon reaction. The current-voltage characteristics of glow discharges in cylindrical, coaxial, and planar excilamps and the parameters of the radiation ofXeCl*,KrCl*, andXeF* molecules generated on excitation of inert-gas-halide mixtures by normal and high-voltage glow discharges are presented. It is pointed out that low-pressure glow-discharge excilamps enable one to use simple power supplies.

Effects of MgO annealing process in a vacuum on the discharge characteristics of AC PDP

This paper deals with the relationships between various annealing conditions in a vacuum and the surface glow discharge characteristics on the MgO thin film prepared by e-beam evaporation method. The minimum discharge inception voltage is obtained for the sample annealed at 400°C for about 2 h in a clean vacuum. Above the annealing temperature of 430°C, cracks are founded on the MgO film, which results in higher discharge voltage. Moreover, the lower the annealing pressure, the lower the discharge voltage. The main factors that improves the discharge characteristics by annealing process is considered to be due to both the morphology changes or crystal structure of the MgO thin films and pumping impurities in the MgO film during the annealing process.

Effect of cathode surface state on the characteristics of pulsed hollow-cathode glow discharges

A study is made of the effect of pulse repetition rate (0.1−103 s−1) and average discharge current (0–1 A) on the breakdown delay time and burning voltage of low-pressure glow discharges (p<0.1 Pa) in an electrode system of the reverse magnetron type with a large cathode surface area (≈103 cm2). It is shown that increasing the repetition rate leads to a many-fold reduction in the statistical spread in the delay time and in the discharge formation time, while the average discharge current has a significant effect on the burning voltage. The mechanism for the observed phenomena is interpreted qualitatively in terms of the presence of thin dielectric films on the cathode surface.

パルスグロー放電を用いた大容量高密度プラズマの生成

Summary form only given. A new technique, Plasma Source Ion Implantation (PSII) for the surface modification of materials, was proposed by Conrad in 1989. This technique has been studied all over the world as Plasma Based Ion Implantation (PBII), Plasma Immersion Ion Implantation (Pm, PI3), IONCLAD (called by General Motors), PLAD (by Varian). In PBII, it is necessary to generate high density plasma with large volume. Pulsed glow discharge is one of the candidates for the ion source plasma because it can easily generate large volume plasma, although for a short time. This paper describes the characteristics of high current pulsed glow discharge generated using a low impedance circuit. A low inductance capacitor of 1.89 /spl mu/F was used in this experiment.