Localized material growth by a dielectric barrier discharge

In this paper, we have reported a localized material growth method by dielectric barrier discharge (DBD) in a mixture of acetylene and argon. We found that, in the discharge, plasma polymerization takes place and the material growth rate is much higher along the discharge filaments than it is in other locations. Three layers of material, which correspond to three modes of discharge, are observed after the plasma polymerization. One layer is homogeneous, which corresponds to a glow-like discharge. The second layer is made of small and dense columns, which can be seen only under microscope, and this layer of material's growth corresponds to a corona-like discharge. The third layer is made of a few bigger columns, which can be seen visually, and they are grown along patterned discharge streamers. By scanning electron microscope (SEM), we see that the bigger columns are made of small ball-like material with the diameter of approximately 0.1 μm. A Fourrier transfer infra-red (FTIR) spectrum of the deposited material is also shown to confirm the polymerization.     

Metal surface oxidation by using dielectric barrier discharge

The surface oxidation of metal is investigated through plasma treatments with an atmospheric-pressure dielectric barrier discharge (DBD) for comparison with a conventional thermal oxidation process. After the plasma treatment of a copper plate, the Cu surface was noted to have abundant CuO and Cu(OH)₂ which act the part of hydrophilic functional elements. Highly improved wettability was also noted. When a greater amount of atomic oxygen is generated in the plasma by the DBD at a high applied voltage and a high O₂ additive concentration, the hydrophilic functional elements become more abundant and therefore enhance the wettability of the oxidized surface.     

Vortex flow formation during dielectric barrier discharge initiation in quiescent air

The structure of vortex flows generated by dielectric barrier discharge initiated in quiescent air at atmospheric pressure has been studied by the methods of particle image velocimetry and schlieren photography. The flow parameters have been measured as functions of the time past the electric discharge onset. A secondary vortex arising over the exposed electrode surface has been revealed for the first time. The influence of the electric parameters of discharge and the configuration of electrodes on the velocity and vorticity of the flow induced by the discharge in air has been determined.     

Degradation of diuron in aqueous solution by dielectric barrier discharge

Degradation of diuron in aqueous solution was conducted in a dielectric barrier discharge (DBD) reactor and the proposed degradation mechanism was investigated in detail. The factors that affect the degradation of diuron were examined. The degradation efficiency of diuron and the removal of total organic carbon (TOC) increased with increasing input power, and the degradation of diuron by DBD fitted first-order kinetics. Both strong acidic and alkaline solution conditions could improve diuron degradation efficiency and TOC removal rate. Degradation of diuron could be accelerated or inhibited in the presence of H2O2 depending on the dosage. The degradation efficiency increased dramatically with adding Fe2+. The removal of TOC and the amount of the detected Cl-, NO3- and NH4+ were increased in the presence of Fe2+. The concentrations of oxalic and acetic acids were almost the same in the absence and presence of Fe2+, but high concentration of formic acid was accumulated in the presence of Fe2+. The main degradation pathway of diuron by DBD involved a series of dechlorination-hydroxylation, dealkylation and oxidative opening of the aromatic ring processes.     

Surface modification of materials by dielectric barrier discharge deposition of fluorocarbon films

Dielectric barrier discharges have been used to deposit fluorocarbon (FC) films on various materials, such as paper, glass, and silicon substrates. The primary monomers used for plasma polymerization were difluoromethane (CH₂F₂), octafluoropropane (C₃F₈), and octafluorocyclobutane (C₄F₈). FC films were characterized using Fourier transform infrared spectroscopy, atomic force microscopy, static contact angle measurements, and scanning electron microscopy. Surface and structural properties of deposited films are strongly dependent on the plasma compositions and plasma parameters. FC films deposited on paper are to enhance its barrier properties and to achieve hydrophobic surfaces. Contact angle studies reveal that a minimum FC film thickness of about 200 nm on paper is required to completely cover surface and near-surface fibers, thereby providing the paper with long term hydrophobic character. In the C₃F₈ and C₄F₈ systems, the contact angles of the deposited films do not change appreciably with plasma parameters and are strongly dependent on the substrate roughness. Hydrogenated FC films deposited with CH₂F₂ plasmas show the relatively low contact angles due to the existence of CH_X (x = 1-3) groups.     

Effect of dielectric barrier discharge on wing-tip vortex formation

The formation of vortex trace behind a finite-span model airfoil has been studied by the method of stereoscopic particle image velocimetry. It is established that a dielectric barrier discharge initiated at the airfoil tip surface influences the wing-tip vortex formation.     

介质阻挡放电光电检测装置研究

采用光电倍增管(PMT)研制一种探测介质阻挡放电(dielectric barrier discharge,DBD)微弱光信号的光电检测装置。根据DBD微弱光信号的特点,进行光电检测装置设计,通过光纤排、光电转换电路、示波器放大并采集微弱光信号。使用新装置进行大气压下DBD的检测试验,验证该新型装置较传统的DBD检测装置具有灵敏度高、响应速度快、可有效区分放电与干扰信号、可同时采集多点信号等特点,为DBD的试验研究提供可靠的探测方法。     

Elemental determination of microsamples by liquid film dielectric barrier discharge atomic emission spectrometry

In this study, a new liquid-film dielectric barrier discharge (LFDBD) atomic emission source was developed for microsample elemental determination. It consists of a copper electrode, a tungsten wire electrode, and a piece of glass slide between them, which serves as the dielectric barrier as well as the sample plate. The sample solution with 1 mol L(-1) nitric acid, when deposited onto the surface of the glass slide, forms a thin liquid film. The plasma is generated between the tip of the tungsten wire electrode and the liquid film surface when alternating-current (ac) high voltage (peak voltage ~3.7 kV, frequency ~30 kHz) is applied on the electrodes. Qualitative and quantitative determinations of metal ions in the sample solution were achieved by atomic emission measurements in the plasma and were demonstrated in this study with elements Na, K, Cu, Zn, and Cd. Detection limits were in the range from 0.6 ng (7 μg L(-1)) for Na to 6 ng (79 μg L(-1)) for Zn. Repeatability, expressed as relative standard deviation from seven repetitive analyses of samples with analyte concentrations at 1 mg L(-1), varied from 2.1% to 4.4%. Compared with other liquid discharge systems that operate at atmospheric pressure, the current system offers several advantages: First, it eliminates the use of a sample flow system (e.g., syringe or peristaltic pump); instead, a small aliquot of sample is directly pipetted onto the glass slide for analysis. Second, it is a microanalysis system and requires sample volume ≤80 μL, a benefit when a limited amount of sample is available. Third, because the sample is applied in aliquot, there is no washout time, and the analysis can be easily extended to sample array for high-throughput analysis. The proposed LFDBD is promising for in-field elemental determination because of its simplicity, cost effectiveness, low power supply, and no inert gas requirement.     

Comparisons of discharge characteristics of a dielectric barrier discharge with different electrode structures

In order to analyze the homogeneous discharge of air dielectric barrier discharge (DBD) under ambient conditions, three different electrode structures are used in the paper. They are aluminum plane electrode, stainless mesh electrode and pure water electrode. The electrical characteristics are obtained and compared by using Lissajous figures, the waveforms of applied voltage and discharge current and the light emission images. The results show that the discharges of the different electrode structures are all filamentary discharges mode in ambient air and the discharge intensity of pure water electrode is much weaker than the other two electrodes.     

Feasibility of destruction of gaseous benzene with dielectric barrier discharge

Destruction of gaseous benzene (C(6)H(6)) by dielectric barrier discharge (DBD) was studied in both laboratory-scale and scale-up DBD systems. The effects of input power, gas flow rate as well as initial concentration on benzene decomposition and energy yield were investigated. In addition, qualitative analysis on byproducts and relatively detailed discussion on mechanisms were also presented in this paper. At last, we systematically illustrated the feasibility of benzene removal with DBD on basis of three aspects: estimation of treatment cost per unit volume, comparison with other plasmas, and problems existed in DBD system. The results will help impel actual application of DBD on waste gas containing benzene.     

Study for amorphous silicon etching process using dielectric barrier discharge

Characteristics of amorphous silicon (a-Si) etching using atmospheric pressure plasma discharge had been studied. Dielectric barrier discharge (DBD) plasma with nitrogen gas was employed for the study. The active chemical agent for etching was generated by mixing a small quantity of sulfur hexafluoride (SF₆) gas into the plasma. The two distinguishable plasma zones are generated with the specially designed DBD plasma generator. The one is the main discharge zone generated between the two parallel plate electrodes. And the other one is downstream plasma zone extracted from the main discharge zone through the holes perforated on the bottom electrode. A test specimen was etched located at the plasma zone and moved the zone several times for etching on a temperature controlled stage. The etch rate of a-Si and the selectivity to silicon nitride (SiNx) were improved by addition of hydrogen (H₂) or methane (CH₄) gas into the plasma. However, when the specimen temperature was lower than 100 °C with H₂ or CH₄ gas added plasma condition, a-Si layer was not etched at all, but in the range of 100-140 °C of specimen temperature, the a-Si layer started to be etched while the influence of the specimen temperature on etching of a-Si was ignorable in that temperature range. At the optimized condition, the a-Si etch rate was up to 3000 A/min in the downstream plasma zone with the 3 mm of the distance between the surface of the specimen and the bottom side of the DBD plasma generator module. And the etch rate ratio between a-Si and SiNx was more than 100:1.     

Simulataneous pentachlorophenol decomposition and granular activated carbon regeneration assisted by dielectric barrier discharge plasma

An integrated granular activated carbon (GAC) adsorption/dielectric barrier discharge (DBD) process was applied to the treatment of high concentration pentachlorophenol (PCP) wastewater. The PCP in water firstly was adsorbed onto GAC, and then the degradation of PCP and regeneration of exhausted GAC were simultaneously carried out by DBD. The degradation mechanisms and products of PCP loaded on GAC were analyzed by EDX, FT-IR and GC–MS. The results suggested that the CCl bonds in PCP adsorbed by GAC were cleaved by DBD plasma, and some dechlorination and dehydroxylation products were identified. The adsorption capacity of adsorption/DBD treated GAC could maintain relatively high level, which confirmed that DBD treatment regenerated the GAC for subsequent reuse. The adsorption of N₂, Boehm titration and XPS were used to investigate detailed surface characterizations of GAC. It could be found that DBD plasma not only increased the BET surface area and pore volume in micropore regions, but also had remarkably impact on the distribution of the oxygen-containing functional groups of GAC.     

Efficient decomposition of NO by ammonia radical-injection method using an intermittent dielectric barrier discharge

Although many NO decomposition systems have been developed using plasmas such as dielectric barrier discharges (DBDs), corona discharges, surface discharges, glow discharges, and microwave discharges, the present system is unique on the viewpoint of the use of an intermittent one-cycle sinusoidal power source to generate DBD plasma. There are several features of the system: (1) easy control of the electric power consumed in the DBD plasma, and (2) DBD-plasma generation used only for the production of ammonia radicals. The system employs a radical injection system, where the radicals are produced in a separate discharge chamber, called radical injector, from NO flow field. This enables an efficient production of ammonia radicals being appropriate for DeNOx. It is shown from the temperature dependence of NO removal (DeNOx) characteristics that the present system is a low-temperature DeNOx system compared to a conventional thermal DeNOx system, and NO decomposition is performed over a wide range of gas temperature containing NO. Surveying parametric characteristics of DeNOx, the energy efficiency is improved by a factor of 30% compared to the previously obtained result.     

Removal of ammonia from gas streams with dielectric barrier discharge plasmas

We reported on the experimental study of gas-phase removal of ammonia (NH3) via dielectric barrier discharge (DBD) at atmospheric pressure, in which we mainly concentrated on three aspects--influence of initial NH3 concentration, peak voltage, and gas residence time on NH3 removal efficiency. Effectiveness, e.g. the removal efficiency, specific energy density, absolute removal amount and energy yield, of the self-made DBD reactor had also been studied. Basic analysis on DBD physical parameters and its performance was made in comparison with previous investigation. Moreover, products were detected via ion exchange chromatography (IEC). Experimental results demonstrated the application potential of DBD as an alternative technology for odor-causing gases elimination from gas streams.     

Optimizing the efficiency of dielectric barrier discharge for creating synthetic jets

A study of synthetic jets created by dielectric barrier discharge of the symmetric actuator has been carried out. The parameter—specific thrust (thrust-to-power ratio)—is used for the first time. The current–voltage characteristics of the dielectric barrier discharge are obtained at different values of the ballast resistance. The dependence of the thrust-to-power ratio on the supply-voltage frequency is determined experimentally.     

Formation of a synthetic jet based on a dielectric barrier discharge

Specific thrust of a synthetic jet based on a dielectric barrier discharge generated by a symmetric actuator has been measured. The dependence of the specific thrust on the distance between exposed electrodes at various applied voltages has been studied. The role of convection at various distances between exposed electrodes has been qualitatively assessed by schlieren imaging of synthetic jets.     

Non-thermal dielectric barrier discharge plasma induces angiogenesis through reactive oxygen species

Vascularization plays a key role in processes such as wound healing and tissue engineering. Non-thermal plasma, which primarily produces reactive oxygen species (ROS), has recently emerged as an efficient tool in medical applications including blood coagulation, sterilization and malignant cell apoptosis. Liquids and porcine aortic endothelial cells were treated with a non-thermal dielectric barrier discharge plasma in vitro. Plasma treatment of phosphate-buffered saline (PBS) and serum-free medium increased ROS concentration in a dose-dependent manner, with a higher concentration observed in serum-free medium compared with PBS. Species concentration inside cells peaked 1 h after treatment, followed by a decrease 3 h post treatment. Endothelial cells treated with a plasma dose of 4.2 J cm^–2 had 1.7 times more cells than untreated samples 5 days after plasma treatment. The 4.2 J cm^–2 plasma dose increased two-dimensional migration distance by 40 per cent compared with untreated control, while the number of cells that migrated through a three-dimensional collagen gel increased by 15 per cent. Tube formation was also enhanced by plasma treatment, with tube lengths in plasma-treated samples measuring 2.6 times longer than control samples. A fibroblast growth factor-2 (FGF-2) neutralizing antibody and ROS scavengers abrogated these angiogenic effects. These data indicate that plasma enhanced proliferation, migration and tube formation is due to FGF-2 release induced by plasma-produced ROS. Non-thermal plasma may be used as a potential tool for applying ROS in precise doses to enhance vascularization.     

Atmospheric plasma-calcination of mesoporous tungsten oxide utilizing plasma dielectric barrier discharge

The fabrication of mesoporous tungsten oxide films by spin-coating method followed by an atmospheric plasma-calcination method is described and discussed here. For the calcination process the dielectric barrier discharge system generating homogenous atmospheric plasma discharge was designed and used. By this method, large surface area mesoporous films, with disordered pores of average diameter size of about 4 to 5 nm were synthesized. All the plasma-calcined films exhibit amorphous structure. The process of calcination was evaluated by FT-IR spectroscopy and in comparison with other methods a very high speed of calcination process was achieved.     

Nonlinear behaviors in a pulsed dielectric barrier discharge at atmospheric pressure

In this paper, the temporal nonlinear behaviors of pulsed dielectric barrier discharge in atmospheric helium are studied numerically by a one-dimensional fluid model. The results show that the common single-period pulsed discharge with two current pulses per single voltage pulse can take place over a broad parameter range. The rising and falling times of the voltage pulse can affect the discharge characteristics greatly. When the discharge is ignited by a pulse voltage with long rising and falling times, a single-period pulsed discharge with multiple current peaks can be observed. Under appropriate rising and falling times of the voltage pulse, a stable period-two discharge can occur over wide frequency and voltage ranges. Also this period-two discharge can exhibit different current and voltage characteristics with changing the duty cycle. With other parameters fixed, the pulsed DBD could be driven to chaos through period-doubling route by increasing either the falling time or the frequency of voltage pulse.     

Cold deposition of large-area amorphous hydrogenated silicon films by dielectric barrier discharge chemical vapor deposition

Amorphous hydrogenated silicon films were deposited on glass substrates at room temperature. This cold deposition process was operated in a dielectric barrier discharge CVD reactor with a fixed strip-shaped plasma matched with a moving substrate holder. The maximum film area was 300 × 600 mm². The film deposition rate as a function of applied peak voltage of DBD power was investigated under different hydrogen-diluted silane concentrations, and the film surface smoothness, continuity, and film/glass adherence were also studied. The maximum deposition rate was 12.2 Å/s, which was performed under the applied peak voltage of 16 kV and a hydrogen-diluted silane concentration of 50%. IR measurements reveal that the silane concentration plays a key role in determining the hydrogen-silicon bonding configurations. With increasing hydrogen-diluted silane concentration, the H-Si bonding configurations shift gradually from Si-H₃ to Si-H. The variation of photo/dark conductivity ratio and optical bandgap versus hydrogen-diluted silane concentration were investigated. The use of DBD-CVD for deposition of a-Si:H films offers certain advantages, such as colder substrate, faster film growth rate, and larger deposition area. However, the consumption of silane for the DBD-PECVD procedure is much greater than for the RF-PECVD process.