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.     

Influence of electrode configuration on ozone synthesis and microdischarge property in dielectric barrier discharge reactor

Characteristics of a dielectric barrier discharge were investigated experimentally to clarify an influence of an electrode configuration on ozone synthesis and a microdischarge behavior. Three difference configurations: plane, trench and multipoint were employed as ground electrode. The alumina dielectric barrier coated plane electrode was used as a high-voltage electrode, to which a sinusoidal high-voltage was applied with 10 kHz frequency. Pure oxygen gas was fed into the reactor with gas flow rate of 5 L/min. The maximum yielding rate increased from 80 to 120 g/kWh by changing an electrode configuration from plane to multipoint, which has 528 number of a right-pyramid shape projection on a 6 cm × 22 cm plane electrode. The yielding rate was strongly dependent on a produced ozone concentration in the plane electrode case, whereas slightly depended on the concentration in the multipoint electrode case. The electrode configuration also affected a number of the microdischarges per one applied voltage cycle. The multipoint electrode showed the largest number of microdischarges at same input energy.     

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.     

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.     

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.     

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.     

Effect of liquid film on decomposition of CFC-12 using dielectric barrier discharge

Dichloro-difluoro-methane (CFC-12) was decomposed with non-thermal plasma generated by dielectric barrier discharge where one electrode was covered with liquid film which could provide oxidants such as OH and also absorb acid gases produced by the decomposition. The experimental results indicated that the conversion of CFC-12 and the selectivity of CO₂ were improved by the installation of the water film at low discharge voltage, however, the installation reduced the power efficiency for the decomposition. Sodium hydroxide solution enhanced the absorption of Cl and F produced by the decomposition, while the conversion of CFC-12 was not affected. The study concluded that the simultaneous decomposition of CFC-12 and recovery of the halogenous product could be achieved using dielectric barrier discharge with liquid film electrode.     

Effect of temperature on the decomposition of trifluoromethane in a dielectric barrier discharge reactor

This study investigated the decomposition of trifluoromethane (HFC-23) by using nonthermal plasma (NTP) generated in a dielectric barrier discharge (DBD) reactor. The main problem of the NTP process may be its low decomposition efficiency for fluorinated carbons, which can be resolved by introducing a catalyst and operating the process at elevated temperatures. The effect of temperature on the HFC-23 decomposition was examined with alumina or glass beads as the packing material in the NTP reactor. With other conditions kept constant, higher temperature resulted in higher HFC-23 decomposition efficiency, and it was shown that the NTP reactor packed with alumina beads acting as a catalyst decomposed HFC-23 more effectively than that with glass beads. When the reactor temperatures were 300 °C and 250 °C (flow rate: 60 L h^− 1; HFC-23 concentration: 2000 ppm), the decomposition efficiency in the presence of the alumina catalyst approached 100% at input powers of 60 W and 100 W, respectively. The main products from HFC-23 were CO and CO₂, which nearly accounted for the amount of HFC-23 decomposed. With respect to the decomposition efficiency, the combination of the NTP and the catalyst was more advantageous than using them separately.     

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.     

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.     

Decolorization of reactive textile dyes using water falling film dielectric barrier discharge

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0 mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H₂O₂, Fe²⁺ and Cu²⁺) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315 kJ/L) were studied. Influence of residence time was investigated over a period of 24 h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10 mM H₂O₂ in a system of 80.0 mg/L Reactive Black 5 with applied energy density of 45 kJ/L, after residence time of 24 h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism.     

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.     

Dielectric barrier discharge — properties and applications

Dielectric barrier discharge (DBD) is a typical non-equilibrium high-pressure ac gas discharge. Recently, two types of DBD arrangements are developed; volume discharge (VD) and surface discharge (SD). Such devices are beneficial for industrial acceptance, since vacuum can be got rid of and devices operated in atmospheric pressure region. DBD is an excellent source of ideal energetic electrons with 1–10 eV and high density. Its unique advantageous is to generate low excited atomic and molecular species, free radicals and excimers with several electron volt energy. In this paper, the properties of microdischarge in DBD are discussed with their simulation. Due to its attractive characteristics, DBD is recently widely studied for potential industrial applications. Ozone generators, excimer radiation sources, free radical generation and their applications in pollution control and monitor are also discussed.     

Surface modifications of polymethylmetacrylate films using atmospheric pressure air dielectric barrier discharge plasma

In this paper, polymethylmetacrylate (PMMA) films are modified using an atmospheric pressure non-thermal plasma generated by a dielectric barrier discharge (DBD) in air. The DBD is generated in a plane-parallel reactor, which is driven by a μs pulse power supply with amplitude of up to 25 kV and repetition rate of 1 kHz, and the plasma generated shows homogeneous mode discharge characteristics verified by electrical measurements and light emission images with 0.5 ms exposure time. The treatment time ranging from 0 to 60 s and the discharge power density ranging from 11.62 to 30.83 W/m² are used to study the effects of discharge parameters on the surface treatment, and the surface properties of PMMA films are studied using contact angle and surface energy measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). The study shows that, after the plasma treatment, the surface of PMMA film is etched, and oxygen-containing polar groups are introduced into the surface. These two processes can induce a remarkable decrease in water contact and a remarkable increase in surface energy, and the surface properties of PMMA films is improved accordingly. It is shown that the improvement of hydrophobicity depends on the discharge power density and treatment time, and there is a saturation treatment time at each discharge power density. Increasing discharge power density can induce more effective treatment of PMMA films, and less treatment time is needed to achieve the same level of surface treatment by increasing the discharge power density. Because more oxygen-containing polar groups are created and more obvious etching is occurred on the PMMA surface at higher discharge power density.     

常压介质阻挡放电对聚苯乙烯表面改性研究

鉴于介质阻挡放电(DBD)是工业上非常有前途的处理材料表面的环保技术,于是采用常压DBD产生的空气低温等离子体对聚苯乙烯(PS)薄膜进行了表面改性.通过接触角测量、原子力显微镜(AFM)观察和X射线光电子能谱(XPS)分析,研究了空气等离子体处理前后PS薄膜的表面性能的变化.结果表明,PS膜表面润湿性随处理时间的延长而提高,PS膜表面粗糙度增加,而且在表面10nm范围内引入了含氧和含氮的官能团.等离子体处理后PS薄膜润湿性改善的主要原因是由表面粗糙化和引入含氧、含氮极性官能团的复合作用造成的.     

电源对介质阻挡放电(DBD)激发准分子(XeCl*)辐射的影响

本文对电源参数如电压幅值、频率及正负电压对介质阻挡放电激发准分子XeCl 紫外 (30 8nm)辐射的影响进行了实验研究。结果表明 ,UV辐射随电压幅度的增加而增强 ,但效率下降 ;提高频率 ,增加了放电次数 ,导致UV辐射的增强 ;此外 ,在较高的频率下 ,电压上升沿变陡 ,使得电子获得的能量主要用于原子的激发和电离。正、负电压放电的不对称源于电极结构的不对称而引起的放电过程的差异 ,负电压内电极可向放电管中馈入更多的能量 ;比较发光光谱可判断生成准分子的等离子体化学过程没有明显的差别     

接地电极转动对电极不对称介质阻挡放电的影响

本文的目的是确定接地电极转动对介质阻挡放电的影响.采用不对称电极结构来降低外加的工作电压.实验的结果表明:接地电极静止或转动介质阻挡放电将呈现不同的放电形式和电流波形.文中对其原因进行了讨论.     

Improving tribological properties of bismaleimide nanocomposite filled with carbon nanotubes treated by atmospheric pressure filamentary dielectric barrier discharge

Atmospheric pressure filamentary dielectric barrier discharge (APDBP) treatment was adopted to modify the surface of the multi-walled carbon nanotubes (MWCNTs), altering the miscibility of MWCNTs with bismaleimide (BMI) matrix and the effects of this treatment on friction and wear properties of MWCNTs/BMI composites were investigated. Dynamic mechanical analysis (DMA), scanning electron microscope (SEM) images of the fractured surface and the worn surface were adopted to figure out the possible friction and wear mechanism of the composite. It is found that BMI composite with APDBD treated MWCNTs exhibits a lower friction coefficient value and a lower wear loss rate value than the composite with original MWCNTs, which can be related to the higher degree of crosslink of the resin and also better interfacial adhesion between MWCNTs and the BMI matrix.     

Simultaneous removals of NOx, HC and PM from diesel exhaust emissions by dielectric barrier discharges

The main target of this work is to characterize the abatements of particulate matter (PM), hydrocarbons (HC) and nitrogen oxides (NO_x) from an actual diesel exhaust using dielectric barrier discharge technology (DBD). The effects of several parameters, such as peak voltage, frequency and engine load, on the contaminant removals have been investigated intensively. The present study shows that for a given frequency, the removals of PM and HC are enhanced with the increase of peak voltage and level off at higher voltage, while in the range of higher voltages a decline of NO_x removal efficiency is observed. For a given voltage, the maximums of specific energy density (SED) and removal efficiency are attained at resonance point. The increase of peak voltage will result in a significant decrease of energy utilization efficiency of DBD at most engine loads. Alkanes in soluble organic fraction (SOF) are more readily subjected to removals than polycyclic aromatic hydrocarbons (PAHs).     

Chemical composition of plasma of dielectric barrier discharge at atmospheric pressure with a liquid electrode

The composition of active particles in a plasma was calculated for the conditions of dielectric barrier discharge at atmospheric pressure in oxygen from the measured waveforms of current and voltage using joint solution of the Boltzmann equation and the equations of chemical kinetics. Kinetic equations included the reactions involving O₂ and H₂O molecules (the main plasma gas), their dissociation products, and the excited states of molecules O₂ and atoms O. It is shown that the main neutral components of such plasma are molecules O₃, O₂(a ¹Δ _g ), H₂O₂, and OH. The mechanisms of formation and destruction of these components are studied.