Search

This work provides a comparative analysis of the sensitivity of the two most widely used kinetic schemes in helium when simulating various modes of direct current discharges in helium: glow and arc. In particular, a kinetic scheme with the formation of three excited atomic states and one molecular state, as well as a scheme with five excited atomic states and two molecular states, are considered. It is shown that the two models yield different results in the glow discharge mode and similar results in the transition from glow to arc and in the arc mode. A study was carried out of the influence of recombination constants from various databases on the discharge characteristics. [ABSTRACT FROM AUTHOR]

Plasma decomposition reactions are used for various gas phase chemical processes including the decomposition of ammonia. In this work we show that pure ammonia can be effectively decomposed at atmospheric pressure and ambient temperature using a packed-bed plasma reactor moderated with BaTiO3 ferroelectric pellets without catalyst. The decomposition rate and energy efficiency of this ferroelectric barrier discharge reactor have been monitored as a function of applied voltage (up to a maximum value of 2.5 kV) and flow rate. For each operating condition reaction efficiencies have been correlated with the parameters defining the electrical response of the reactor. It is found that plasma current and volume inside the reactor and hence the energy efficiency of the process and the decomposition rate vary with the applied voltage and the flow of ammonia (a maximum decomposition rate of 14% and an energy efficiency of 150 LH2/kWh has been determined under optimized operation conditions). The role of back reactions (i.e. N2 + 3H2 → 2NH3) in decreasing reactor performance is another key effect affecting the overall efficiency for the ammonia decomposition. The possibilities of ferroelectric barrier discharge reactors to induce the decomposition of ammonia and the importance of keeping the operating temperature below the Curie temperature of the ferroelectric material are highlighted. [ABSTRACT FROM AUTHOR]

In this work, direct deposition of patterned thin films using immobilized dielectric barrier discharge (DBD) plasma filaments and pulsed sinusoidal excitation in argon/propargyl methacrylate (PMA) mixtures was investigated. Microdischarge ignition and deposition processes were studied in detail and compared with a continuous excitation scheme. In both cases, µm-thick circular areas ('spots', S) are deposited from the filaments and a thinner film ('between the spots', BS) is generated in between from the non-filament regions. Pulsed excitation was seen to better stabilize filaments than continuous excitation, resulting in milder deposition conditions and lower deposition rates between the spots. X-ray photoelectron spectroscopy (XPS), contact angle, profilometry, and optical microscopy measurements all show that pulsed excitation leads to better patterning (i.e., higher fidelity patterns with greater morphological contrast between S and BS regions), higher retention of PMA chemical functionalities, and less substrate damage. Moreover, by decreasing the deposition time in pulsed mode, area-selective deposition was achieved. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharges (DBDs) bring a long history of application and leave many interesting scientific questions. A positive streamer concept describes a temporal development of a microdischarge well, and memory charge effect explains spatially distributed microdischarges over the entire area of DBD. To properly model plasma chemistry occurring in a DBD, knowledge of microdischarges, distributed spatially and temporally, is essential. Here we present experimental result of multiple microdischarges, occurring successively and rooted at the same location. By employing a triangular waveform to a pointed electrode and a high conductivity layer at a surface of a dielectric barrier, a physical mechanism of the successive microdischarges was revealed: a slew rate of an external alternating current compensated a voltage drop caused by memory charges from a former microdischarge. A time interval between two neighboring microdischarges was inversely proportional to the slew rate, and the number of microdischarges depended primarily on an applied voltage. The number of microdischarges with an uncoated barrier was higher than that with an Ag-coated barrier; however, the charges delivered by each microdischarge were smaller in cases with an uncoated barrier. To investigate interactions between spatially separated microdischarges, this study will be extended to a configuration having multiple pointed electrodes. The effect of the successive microdischarges on plasma chemistry will also be a future study. [ABSTRACT FROM AUTHOR]

Dielectric barrier discharge (DBD) is used for many important applications in various sectors of science and technology. For example, for ozone generation, surface modification of polymers, in plasma medicine, and for decomposition of heavy volatile organic compounds. Nowadays, one of the actual problems is getting of uniformity of discharge distribution for high quality treatment of materials surfaces. To achieve uniform distribution of the discharge, several methods are available, one is to use different types of noble gases, and another is to use AC power supply with frequency varied in wide range. But besides this, another of the potential methods for obtaining a uniformly distributed discharge is to blow through the discharge gap flow of air. This method was used in this paper to conduct experiments which consisted of oscilloscoping voltage and current values, high-speed imaging, also gas flow simulation for comparison with the experiments. The obtained results show the dynamics of microdischarge motion in laminar and turbulent flow regimes, which supported by flow simulation. [ABSTRACT FROM AUTHOR]

Additive methods for manufacturing materials have recently emerged, particularly for the fabrication of three‐dimensional architectures. Because of their long history in thin‐film etching and deposition, plasmas offer unique advantages for many of the materials and surface processes associated with additive manufacturing. Here, we review recent efforts that have been primarily focused on the direct writing of patterned structures and the post‐treatment of printed materials. Different configurations, materials, and applications are presented. Current challenges and a future outlook are also provided. [ABSTRACT FROM AUTHOR]

• Catalysts clearly affect physical plasma behavior in dielectric barrier discharge. • Dry reforming of methane benefits from microdischarges and large plasma volume. • In contrast, ammonia synthesis benefits greatly from uniform plasma discharge. • The catalyst synthesis method defines how the catalyst affects the plasma. • Precise distribution of metal throughout support is crucial for plasma discharge. Plasma catalysis is a rapidly growing field, often employing a packed-bed dielectric barrier discharge plasma reactor. Such dielectric barrier discharges are complex, especially when a packing material (e.g., a catalyst) is introduced in the discharge volume. Catalysts are known to affect the plasma discharge, though the underlying mechanisms influencing the plasma physics are not fully understood. Moreover, the effect of the catalysts on the plasma discharge and its subsequent effect on the overall performance is often overlooked. In this work, we deliberately design and synthesize catalysts to affect the plasma discharge in different ways. These Ni or Co alumina-based catalysts are used in plasma-catalytic dry reforming of methane and ammonia synthesis. Our work shows that introducing a metal to the dielectric packing can affect the plasma discharge, and that the distribution of the metal is crucial in this regard. Further, the altered discharge can greatly influence the overall performance. In an atmospheric pressure dielectric barrier discharge reactor, this apparently more uniform plasma yields a significantly better performance for ammonia synthesis compared to the more conventional filamentary discharge, while it underperforms in dry reforming of methane. This study stresses the importance of analyzing the plasma discharge in plasma catalysis experiments. We hope this work encourages a more critical view on the plasma discharge characteristics when studying various catalysts in a plasma reactor. [ABSTRACT FROM AUTHOR]

This paper reports on theoretical studies of the role of the field emission effects in direct current nitrogen discharges between the electrodes separated from 0.5 μm up to 100 μm. The effect of the various parameters on the breakdown voltage curves and current densities was calculated by using a Breakdown Voltage and Current Density in Microgaps Calculator. The obtained results clearly show that the shape of the potential barrier depends on the gap size and the work function. The high electric fields generated in microgaps combined with the lowering of the potential barrier seen by the electrons in the cathode as an ion approaches lead to the onset of ion-enhanced field emissions and the lowering of the breakdown voltage. Therefore, electrical breakdown across μm gaps is initiated by the secondary emission processes instead of a gas avalanche process and occurs at voltages far below the minimum predicted by the standard scaling law. It was found that the gap size, the gas pressure, enhancement factor, and the effective yield affect both the breakdown voltage curves and the current density. Presented results provide better understanding of the electrical breakdown in microgaps. [ABSTRACT FROM AUTHOR]

Abstract In this work, we consider the rational design of a plasma catalysis system for the splitting of carbon dioxide (CO 2) via one-dimensional PIC/MCC simulations. We show that field emission-driven microdischarges (also called microplasmas) can selectively excite the asymmetric stretch mode, which is known to be more favorable to the dissociation of CO 2 , relative to the symmetric stretch mode. These results suggest that field emission-driven microdischarges could form the basis for intentionally coupling the plasma state with a catalyst for improving the performance of CO 2 reforming. Highlights • A theoretical study that explores how to design a microscale plasma catalysis system for the dissociation of CO 2. • Kinetic plasma simulations conducted to determine how to selectively excite CO 2 into a specific vibrationally-excited state. • Breaking of conventional scaling enables higher E/n conditions that favor selectivity toward the asymmetric vibration mode. • Field emission-driven microdischarges could be potentially applied to plasma catalytic dissociation of CO 2. [ABSTRACT FROM AUTHOR]

The use of low‐temperature plasmas for bio‐decontamination and sterilization has been gaining increased attention. In this study, a two‐dimensional array of integrated coaxial microhollow micro‐discharges generated in dry air at atmospheric pressure is used to treat metal surfaces (gas‐phase) and solution (liquid‐phase) contaminated with a known concentration of feline calicivirus (FCV). FCV acts as a surrogate for human norovirus, which is responsible for causing outbreaks of acute gastroenteritis in humans. The decontamination efficacy as well as the primary chemical pathways leading to virus inactivation in both the treatments are studied and compared. It is found that the humidity of the bio‐sample for gas‐phase treatment in dry air is required to achieve >5 log10 reduction in FCV titer within 3 min. The gas‐phase FCV inactivation is found to be due to a combination of ozone (O3) and reactive nitrogen species (RNS), most likely NOx. The liquid‐phase FCV inactivation mechanism is pH‐dependent and is primarily due to RNS, most likely acidified nitrites. O3 has a negligible effect on FCV suspended in solution. Previous studies performed in a batch reactor have shown that the inactivation pathways through O3 and RNS are mutually exclusive due to ozone poisoning at high NxOy concentrations. The present study employs a flow‐through system which avoids accumulation of reactive species and allows for the coexistence of NOx and O3 for the gas residence times used in this study, giving rise to these specific inactivation pathways. [ABSTRACT FROM AUTHOR]

In this paper, the results of measurements of the characteristics of the hydrogen microdischarges from direct current to radio frequencies are presented and discussed. Two types of the electrode configurations are used: electrodes with Bruce profile and glass melting electrodes separated between 2.5 and \mathrm 100~\mu m . The breakdown voltage values for low frequencies are similar to the direct current breakdown voltage data, while the high-frequency breakdown voltages are systematically lower. As the frequency increases, the breakdown voltage decreases in the case of glass melting electrodes and increases in the case of electrodes with Bruce profile. It is observed that the breakdown voltages that correspond to the melting glass electrodes are lower due to edge issues and inability to achieve a homogenous field. The effective yields estimated from the measured breakdown voltage curves are similar for both electrode configurations. In addition to the breakdown voltage curves and current–voltage waveforms, the images demonstrating the discharge development and propagation are also recorded. Presented results reveal that secondary electrons play an essential role in sustaining the discharge in microgaps, where the relationship between breakdown voltage and gap spacing is far away from the standard scaling law at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Non-equilibrium plasmas have been used as one of the principal technologies for development of microelectronics and they are the basis for the development of new generations of nano-electronics devices required for 65 and 40 nm technologies. Microdischarges recently have become more common in everyday life. Technology of plasma etching has enabled us to develop such discharges and the field of microdischarges has grown into the most interesting field of the physics of collisional non-equilibrium plasmas. Recently, an effort to fabricate microplasma sources that can be integrated with other MEMS devices to form larger Microsystems has been made. Plasma-based microsystems can find application in bio-microelectro- mechanical system (bio-MEMS) sterilization, small-scale materials processing and microchemical analysis systems. However, integrability requires not only a size reduction, but also an understanding of the physics governing the new small-scale discharges. In this paper, we have performed modeling of a breakdown voltage by using Particle-in-Cell/Monte Carlo collision (PIC/MCC) code taking into account the secondary electron emission due to a high field.

Pulsed microdischarges produced by dielectric barrier discharges (DBDs) in a submillimeter gap were investigated under 200 cycles of sinusoidal ac voltage at 5 kHz in this paper. The impulsive current in the external circuit was accurately measured by an oscilloscope with a bandwidth of 2.5 GHz and a maximum sampling rate of 40 GS/s to calculate the filamentary current in the discharge gap. The amplitude, pulse duration, and transferred charge of a single filamentary current and the microdischarge energy acquired over the 200 voltage cycles were statistically analyzed for different discharge gaps and gas pressures. The microdischarge parameters and ozone generation efficiencies for different conditions were compared. The ozone production efficiency was found to increase with increasing pressure from 1 to 2 bar absolute, and the gap length from 0.2 to 0.5 mm. The maximum ozone production efficiency achieved in the paper was 217 g/kWh, with a gap length of 0.5 mm, an absolute pressure of 2.0 bar, and an applied voltage of 5.5 kV at 5 kHz. [ABSTRACT FROM AUTHOR]

Microfabricated detectors can be used to provide first alert information about the presence of radiation sources. This paper describes a micromachined neutron detector that operates in the Geiger-Muller regime. It utilizes electrodes that are lithographically micromachined from 50- \mu \textm thick stainless steel #304 foil. The cathode is coated with a 2.9- \mu \textm thick layer of Gd on one side to convert thermal neutrons into fast electrons and gamma rays, which are then detected by ionization of the fill gas (Ar). Three electrodes are stacked in a cathode-anode-cathode arrangement, separated by 70- \mu \textm thick Kapton spacers, and assembled within a commercial TO-5 package. The detector diameter and height are 9 and 9.6 mm and it weighs 0.97 g. Detector performance is characterized using a 90 $\mu $ Ci 252Cf neutron source placed at a distance of 10 cm from the detector. Using Pb blocks between the source and detector to block gamma rays, the typical detector response at 285 V bias is \sim 8.7$ counts per minute (cpm), with background radiation count of 1.2 cpm. The typical dead time is 5.3 ms. Compared with commercial devices which operate at >900 V, have detector volumes of 2000–100000 mm ^{3} and can only detect a subset of radiation types (i.e., beta particles, gamma rays, and neutrons), this device offers lower operating voltages smaller volume and the ability to detect all three types of radiation. [ABSTRACT FROM PUBLISHER]

We studied statistical behavior of microdischarges of diffuse coplanar surface barrier discharge (DCSBD) operated in nitrogen atmosphere at two input voltage regimes. We measured spectrally unresolved discharge patterns together with discharge electrical parameters using highspeed iCCD camera and digital storage oscilloscope. External synchronization enabled us to measure the discharge pattern during positive and/or negative half-period of input high voltage in the single-shotmode of operation. The comparison of microdischarges behavior during positive, negative and both half periods of input high voltage was performed for two levels of input voltage, i.e. voltage slightly above ignition voltage and high above ignition voltage (“overvoltage”). The number of microchannels crossing discharge gap was counted and compared with number of microdischarge current peaks observed during corresponding half-period of input high voltage. The relations of those incidences was shown and discussed.

The gas breakdown processes in dc microdischarges with a zeolite cathode (ZC) have been investigated. The electric field has a pronounce effect on the electrical characteristics of the ZC. The effects of electric field and secondary emission were discussed in atmospheric plasmas (AP). A nanoporous surface used as microreactor could enhance the electron emission from the cathode surface, thus reducing the breakdown voltage ( UB). Results indicate that the UB decreases with increasing ZC diameter and decreasing with gap distance. Microdischarges in spatially confined geometries, such as the nanoporous structure of ZCs, present a promising method for the generation and maintenance of stable AP. [ABSTRACT FROM AUTHOR]

This paper reports a method for producing protein arrays on antifouling PEO-like coatings using a 'non-contact' atmospheric pressure helium microplasma array. ToF-SIMS characterization of PEO-like coatings after short plasma treatment revealed the antifouling plasma polymer was largely modified/removed within the microplasma-exposed regions. Incubation of microplasma-patterned PEO-like coatings with a fluorescently labeled streptavidin resulted in selective and uniform protein adsorption within the modified regions. A protein sensing application was demonstrated where a target red fluorescent protein (RFP) was only captured on the anti-RFP functionalized regions. This indicates the adsorbed antibody protein on the microplasma-treated PEO-like regions retained its bioactivity. [ABSTRACT FROM AUTHOR]

This paper contains results of experimental studies of the direct current breakdown voltage curves and volt-ampere characteristics of discharges generated in a system consisting of two plane-parallel tungsten and molybdenum electrodes at separations from 100 µ m to 1 µ m. The measurements were performed in the pressure range from 22.5 Torr to 738 Torr. The results are presented in the form of Paschen curves. Based on the measured breakdown voltage curves, the effective yields have been estimated in the case of different cathode materials. Differences between them are attributed to the influence of the work function of the cathode material on the current-voltage characteristics due to field emission effect in small gaps and high pressures. At low-pressures, however, vaporation of impurities from the electrodes material becomes significant. The present paper delivers new data on DC breakdown under these experimental conditions and conditions on the validity of the Paschen law in helium and provides better insight into the role of the field emission and the electrode materials on the breakdown voltage. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: We present a straightforward method for particle identification and background rejection in 3He proportional counters for use in neutron detection. By measuring the risetime and pulse height of the preamplifier signals, one may define a region in the risetime versus pulse height space where the events are predominately from neutron interactions. For six proportional counters surveyed in a low-background environment, we demonstrate the ability to reject alpha-particle events with an efficiency of 99%. By applying the same method, we also show an effective rejection of microdischarge noise events that, when passed through a shaping amplifier, are indistinguishable from physical events in the counters. The primary application of this method is in measurements where the signal-to-background for counting neutrons is very low, such as in underground laboratories. [Copyright &y& Elsevier]

Time series of pulsating microdischarges were analysed. The results showed that deterministic chaos is present in these series. The estimated values of the correlation coefficients indicated a strong chaotic discharge behaviour.

Recent studies have shown that, in microscale electrode gaps, the traditional Paschen's curve fails as the left branch sharply decreases with electrode spacing, thus resulting in the modified Paschen's curve. This deviation from Paschen's curve is attributed to ion-enhanced field emission and notably breaks pressure times distance (pd) scaling. Here, 1-D particle-in-cell/Monte Carlo collision simulations at moderately high pressures are used to predict breakdown and reproduce the modified Paschen's curve, which is in good agreement with existing theory. These simulations reveal that the net positive space charge that accumulates in the electrode gap enhances the electric field, subsequently enhancing field emission from the cathode. Because the emitted electrons generate additional ions in the discharge, a positive feedback mechanism occurs, where the field-emitted electrons produce the ions that enhance the electric field. It is revealed that this coupling between field emission and the discharge is necessary in order for breakdown to occur. [ABSTRACT FROM PUBLISHER]

Silicon oxide nanowires are synthesised below 523 K by a non-VLS mechanism on different substrates: Fe-0.5 wt.-%Si and Fe-1.5 wt.-%Si alloys and silicon wafers coated or not by 30-nm thick coatings of iron. An Ar-O2 micro-afterglow is used to feed the substrate with oxidising species over an area of ≈2 mm2. In this area, circular bundles of nanowires appear after 15 min and are randomly distributed. Each bundle diameter increases with time and reaches 50 µm. After several hours, bundles overlap and give a continuous carpet of nanowires. TEM analyses show that no iron is found in the nanowires, whatever the substrate. A growth mechanism, based on the emergence of a surface defect is proposed. [ABSTRACT FROM AUTHOR]

This paper contains experimental results of the direct current breakdown voltage curves in nitrogen, hydrogen, oxygen and dry air discharges formed between parallel-plane electrodes placed at distances ranging from 2.5 μm to 100 μm. Experimental results presented here clearly show that electrical breakdown across micron size gap may occur at voltages below the minimum predicted by the conventional scaling law. The observed breakdown voltage reduction maybe attributed to the long path breakdown. Experimental results satisfactorily agree with the available simulation results and can be useful for microelectronic devices in localized diagnostics of ICs during their manufacture, in choosing appropriate conditions for electromechanical micro systems which may eventually lead to nano-machining in localized treatment of materials and assembly of nano-structures and in micro- and nano-biological processing and diagnostics. [ABSTRACT FROM AUTHOR]

In this paper, a quartz coaxial dielectric-barrier-discharge tube operated at different gas pressures and frequencies has been studied. A sinusoidal voltage up to 2.4 kVp with frequencies 34.5 and 47.5 kHz has been applied to the discharge electrodes for the generation of microdischarges. The experimental results confirm the filamentary nature of discharges when operated at different pressures (300, 600, and 1000 mbar) and at different frequencies (34.5 and 47.5 kHz). The relative influence of the given pressures and applied voltage waveforms on the discharge parameters has been analyzed. An equivalent electrical circuit model representing the multipeak phenomenon in the discharge has been developed, which validates the characteristics of the filamentary behavior. A series of simulations has been carried out in order to obtain the internal discharge parameters including discharge impedance which is not measurable during the experimental process. A close agreement between the simulated and experimental results has been obtained. From the experimental results and equivalent electrical circuit model, the dynamic nature of equivalent capacitance has also been reported. [ABSTRACT FROM PUBLISHER]

The vacuum ultraviolet (VUV) emissions from 115 to 200 nm from the effluent of an RF (1.2 MHz) capillary jet fed with pure argon and binary mixtures of argon and xenon or krypton (up to 20%) are analyzed. The feed gas mixture is emanating into air at normal pressure. The Ar excimer second continuum, observed in the region of 120-135 nm, prevails in the pure Ar discharge. It decreases when small amounts (as low as 0.5%) of Xe or Kr are added. In that case, the resonant emission of Xe at 147 nm (or 124 nm for Kr, respectively) becomes dominant. The Xe second continuum at 172 nm appears for higher admixtures of Xe (10%). Furthermore, several N I emission lines, the O I resonance line, and H I line appear due to ambient air. Two absorption bands (120.6 and 124.6 nm) are present in the spectra. Their origin could be unequivocally associated to O2 and O3. The radiance is determined end-on at varying axial distance in absolute units for various mixtures of Ar/Xe and Ar/Kr and compared to pure Ar. Integration over the entire VUV wavelength region provides the integrated spectral distribution. Maximum values of 2.2 mW·mm-2·sr-1 are attained in pure Ar and at a distance of 4 mm from the outlet nozzle of the discharge. By adding diminutive admixtures of Kr or Xe, the intensity and spectral distribution is effectively changed. [ABSTRACT FROM AUTHOR]

This paper contains a simple theoretical prediction of the electrical breakdown characteristics of the rf capacitive plasma source. The Kihara equation has been applied in order to determine the breakdown voltage in helium rf microdischarges. It was found that the Kihara equation, with modified molecular constants, describes the breakdown process well even for gaps of the order of a few millimeters. The agreement between theory and the available experimental data over a wide range of parameters verifies the correctness of the approach. In addition, theoretically determined breakdown voltages involving gas-adjustable parameters are supported by the PIC/MCC simulation results. [ABSTRACT FROM AUTHOR]

The multifractal image analysis of Lichtenberg figures has confirrmed a self- similar arrangement of surface streamers belonging to the special case of electrostatic separation discharges propagating along a surface of polymeric dielectrics.

Abstract: It is well known that there are two basic parts of electromagnetic emissions from a thunderstorm cloud. The first one is due to a return stroke and the second is generated by microdischarges on the lightning preliminary stage and between successive return strokes. The purpose of this paper is to consider the second part of electromagnetic emissions from thunderstorm clouds in a frequency range from one to hundreds of MHz. A new approach is developed, which is based on a three-dimensional computer simulation of microdischarge activity in thunderstorm clouds. We suggest that microdischarges on the lightning preliminary stage are connected with the growth of internal electric cell structures in a thunderstorm cloud. The characteristic scale of cells ranges from ten to hundred meters. The source of these cells can be a beam-plasma-like instability in the thunderstorm cloud medium where microdischarges appear as a saturation mechanism for this instability. Interaction of neighboring cells leads to the formation of dynamic chains of microdischarges. Following step-by-step computer simulations, we calculate radio emissions from every microdischarge and sum up the wave amplitudes from all intracloud volume at the reception point. The standard model for a separate microdischarge current is adopted, and the electromagnetic radiation is estimated in the far zone. We obtain the waveforms of electromagnetic field, the temporal development of radiation and the number of electromagnetic pulses. We have found that signal statistics and calculated frequency spectra exhibit a universal power-law (fractal) behavior. The results of simulations are found to be in satisfactory agreement with the experimental data, because the model waveforms demonstrate a close similarity to the observed ones. Also the temporal development with the duration of pulse trains from ten to hundreds of microseconds and the microdischarge number rate up to hundreds of thousands per second are in agreement with the corresponding experimental data. [Copyright &y& Elsevier]

Emission spectroscopy of plasma-excited chemical species is widely used for generalized chemical analyses in bench-top systems. This paper explores the use of pulsed microdischarges between two and three electrode microstructures, which operate in air at atmospheric pressure, for use in handheld chemical analyzers. Pulsed microdischarges are fired between two-electrodes spaced apart by 0.2-2 mm. Synchronized optical sampling and time resolved spectroscopy are performed to capture the emission spectra from the microdischarge and its afterglow. The discharge spectra in air consist mainly of wide-band background spectra and line spectra from the nitrogen, and water vapor in air. The detection of vapors in air is limited by the relative strengths of representative lines compared to background spectra rather than by their absolute strength. The separate temporal characteristics of the line and background spectra present opportunities to improve detection. This concept is evaluated using isopropyl alcohol vapors (100 ppm) for which lines corresponding to CH fragments are detected with a handheld spectrometer despite the presence of air spectra. This paper also introduces a three-electrode (flashFET) configuration, which further reduces power consumption and electrode wear. Occupying an active area < 1 mm2, it employs a strategically located high-impedance gate electrode that permits the use of pulses < 100 V between the source and drain. The device consumes only 2.5 muJ/pulse at 140 Torr and 22.5 muJ/pulse at atmosphere, as compared to 470 muJ/pulse for two-electrode discharges. The operation of the flashFET as a gas sensor is evaluated using acetone vapors in air ambient. A response curve is obtained by measuring the 388.1 nm emission from acetone fragments for acetone concentrations ranging from 50 to 1000 ppm. [ABSTRACT FROM PUBLISHER]

Devices with micrometer and submicrometer gaps can face a serious challenge due to electrical breakdown during manufacturing, handling, and operation. Therefore, it is necessary to be aware of the breakdown voltage at different gaps. Since the Paschen's law is not valid for gaps smaller than several micrometers, modified Paschen curve should be used to predict breakdown voltage for microdevices. One of the possible mechanisms responsible for the reduction of the maximum operation voltage at small gaps is the field emission (FE). In this paper, particle-in-cell/Monte Carlo collision simulations, including the ejection of electrons from the cathode due to a high electric field, have been carried out to estimate the significance of the FE effect on the breakdown voltage in microgaps. [ABSTRACT FROM AUTHOR]

New problems associated with charging of aircraft are considered. The first problem concerns the aircraft charging dynamics and the analysis of the steady-state and transient processes of charge accumulation on the aircraft surface. Possibilities of controlling the aircraft charge using the active charge compensation principle are demonstrated. The second problem concerns the development of microdischarges (discharges of low intensity) on a charged aircraft surface. The microdischarges develop in the presence of elements with disturbed electric contact with the remaining surface and lead (when sufficiently numerous) to interference with the operation of the aircraft’s radionavigation equipment. A method of simulating the electric charge growth on these elements under laboratory conditions by blowing over them a gasdynamic jet with a unipolar ion charge flowing out from a specially created source is proposed and justified theoretically. Microdischarge recording methods (time-base sweeps and spectra of the electric discharge current and acoustic signals), which make it possible rapidly to determine these elements (points of “ demetallization” of the aircraft structure), are developed. Data on microdischarges from both metal elements and the composite elements now widely used in aircraft structures are obtained. [ABSTRACT FROM AUTHOR]

We have performed simulations on a coplanar structured alternating current plasma display panel cell sustained in the ternary He-Ne-Xe gas mixture and its discharge characteristics were compared with those of the conventional binary Ne-Xe mixture, by using the two-dimensional fluid model simulator. Since plasma display panels use micro-discharges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of discharge gas mixtures is one of the main factors that determine luminous efficacy and thus, intensive studies on discharge gas mixture are essential to optimize it. As the He concentration increases in the He-Ne-Xe mixture, luminance and luminous efficacy increase but power consumption decreases, which agrees well with the recent experimental findings. We have found that the enhanced ion mobilities in the gas mixture by adding He gas to the conventional Ne-Xe mixture play an important role in increasing luminous efficacy of a plasma display panel cell, by reducing the cathode fall potential. In addition, He atoms increase the number of Xe*(3P2) in the excited state and thus, the dimer emission is increased while the resonant line is reduced with the He content. As a result, the total vacuum ultraviolet emission is increased and higher luminance and higher luminous efficacy can be obtained. [ABSTRACT FROM PUBLISHER]

Plasma display panel emission measurements are correlated with panel efficacy trends, and directions for the improvement of the discharge efficiency are derived. An increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared indicates an increased Xe excitation efficiency. Also, the time dependence and the spatial distribution of the Xe emission are important discharge characteristics. Experiments reveal that a high panel efficacy is obtained, especially for design and driving conditions that govern a fast and spatially distributed discharge development. A high sustain voltage V>200 V causes a "high efficiency discharge mode." It is proposed that in this mode, the cathode sheath is not, or is incompletely, formed during the rise of the discharge current. Then the electric field in the discharge cell is dominated not by the space charges, but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe-excitation. Under the fast discharge buildup conditions also the electron-heating efficiency increases due to a decrease of the ion heating losses in the cathode sheath. A high sustain voltage combines well with a high Xe content gas mixture, that further increases the discharge efficiency. Changes in the phosphor to Xe- and Ne-emission ratio show that for higher Xe content, a lower electron temperature accounts for a more efficient Xe excitation. Further, the use of a TiO2-layer underneath the phosphor causes an increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared, i.e., an increased Xe excitation efficiency. As a result, a high efficacy of 5 lm/W and a high luminance of 5000 cd/m2 have been realized in a 4-in color plasma display test panel design with a 50% Xe in Ne gas mixture, a TiO2-layer underneath the phosphor, and a high sustain voltage 260-290 V. [ABSTRACT FROM PUBLISHER]

The problem of the optimization of properties for biocompatible coatings as functional materials requires in-depth understanding of the coating formation processes; this allows for precise manufacturing of new generation implantable devices. Plasma electrolytic oxidation (PEO) opens the possibility for the design of biomimetic surfaces for better biocompatibility of titanium materials. The pulsed bipolar PEO process of cp-Ti under voltage control was investigated using joint analysis of the surface characterization and by in situ methods of impedance spectroscopy and optical emission spectroscopy. Scanning electron microscopy, X-ray diffractometry, coating thickness, and roughness measurements were used to characterize the surface morphology evolution during the treatment for 5 min. In situ impedance spectroscopy facilitated the evaluation of the PEO process frequency response and proposed the underlying equivalent circuit where parameters were correlated with the coating layer properties. In situ optical emission spectroscopy helped to analyze the spectral line evolutions for the substrate material and electrolyte species and to justify a method to estimate the coating thickness via the relation of the spectral line intensities. As a result, the optimal treatment time was established as 2 min; this provides a 9–11 µm thick PEO coating with Ra 1 µm, 3–5% porosity, and containing 75% of anatase. The methods for in-situ spectral diagnostics of the coating thickness and roughness were justified so that the treatment time can be corrected online when the coating achieves the required properties. [ABSTRACT FROM AUTHOR]

Microscope photos of the microdischarges in dielectric barrier discharge microplasma were taken for the discharge gaps ranging from 30 to 100 \mu\m. The microdischarge formation phenomena in all the stages were observed for microplasma generated in \N2/\Ar mixture by a pulse power supply. A diffused glowlike microplasma was observed with the increase in Ar concentration in \N2/\Ar mixture. [ABSTRACT FROM PUBLISHER]

• A microplasma ball reactor is used to convert the JP-8 into the gaseous products. • Study of produced gases by JP-8 processing with specific energy input is discussed. • The gas product yields were analyzed and compared with other processes. • The nano-sec pulses and controlled energy per pulse are the key features of reactor. Non-equilibrium microplasma technology is used as a non-conventional processing tool to attain fuel conversion efficiency. The microplasma was generated in a reactor with metal balls bouncing between parallel electrodes allowing energy control in a discharge. The released energy, in the range of 20–100 μJ per discharge initiates chain scission reactions to generate shorter chain hydrocarbons. The system consists of 300 reactors and is scaled and optimized to maximize power density while maintaining high efficiency for applications to Jet Propellant 8 (JP-8) fuel. Experiments demonstrate the ability of controlled chemistry (JP-8 to lighter hydrocarbons fuel conversion) without allowing excessive heat and carbon production. Analysis of gas products produced by JP-8 processing with specific energy input of 1450 kJ/kg demonstrates product distributions of 20.9%, 39.4%, 31.7%, 2.5%, 3.5% 1.3% by mass of H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 , C 3 H 8 respectively and is 1.64% of the initial JP-8 mass (24 g). Soot production is only 0.07% of the JP-8 mass that results in a 35:1 product selectivity of gaseous compounds to soot. Calculated gas product yields of 11.7, 2.2, 0.99, 0.07, 0.07 and 0.02 molecules/100 eV for H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 , C 3 H 8 respectively were observed and are generally higher than existing non-equilibrium processing technology. [ABSTRACT FROM AUTHOR]

It has been recently demonstrated that microcathode sustained discharges (MCSD) are very efficient for the production of large fluxes of singlet delta oxygen (SDO). In this paper, a comparison between MCSD operation in \Ar/O2 and in \He/O2 mixtures is done. It is shown that, even if SDO production efficiency is theoretically much higher in \Ar/O2 mixtures, atmospheric pressure operation is only possible in He-based mixtures. [ABSTRACT FROM AUTHOR]

Stable microdischarges, ∼0.5-1 mm in length, are produced in atmospheric air by extracting plasma from a (50 μm)² inverted pyramidal Si microdischarge device which serves as a plasma cathode. Both metal and dielectric lips have been successfully tested as the extraction electrode and driving frequencies up to 20 kHz have been demonstrated. The plasma column, or conduit, generated is well behaved and essentially cylindrical with a diameter smaller than the width of the Si cathode device. [ABSTRACT FROM AUTHOR]

Arrays of microdischarge devices, 100 × 100 μm² in cross section, have been fabricated in a photodefinable glass, and electrically driven by interdigitated electrodes. Operated in Ne gas at pressures from 200 to 600 torr, 5 × 5 arrays of square microdise charge pixels are bright and draw a total current of 0.4-1.5 mA for direct current operating voltages of <200 V. [ABSTRACT FROM AUTHOR]

The breakdown voltage (Vs) for a discharge in Ar at pressures between 35 and 300 torr has been reduced significantly with an array of cylindrical microdischarge devices mounted behind the tungsten cathode. For PAr = 50 torr, Vs drops by approximately a factor of two, relative to that for a conventional discharge, when the microdischarge array is in operation. The injection of electron-ion pairs into the anode-cathode gap region by the array also decreases the formative and statistical time lags associated with the startup of a cold lamp. [ABSTRACT FROM AUTHOR]