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开发了氢气甚高频(60MHz)容性耦合放电的PIC/MC模型.在模型中考虑了带电粒子(e,H+,H2+,H3+)与H2的21种碰撞反应过程,模拟了氢气甚高频放电射频电场和电势分布以及电子和氢离子(H+,H2+,H3+)粒子密度和平均能量分布,并与频率为13.56MHz的放电结果进行了比较.结果表明,相对于频率13.56MHz的放电,氢气甚高频放电等离子体电势增高,导致两电极附近的电场增强;另外,两鞘层厚度变窄并且电子和H3+离子平均能量减小,其总密度却增加.H3+离子为氢气甚高频放电空间的主要离子,H2+离子密度比H3+离子小约2～3个数量级.     

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采用PIC-MC自洽模型,模拟了氮气电容性耦合射频放电的微观等离子体过程及带电粒子(e,N2+,N+)的行为。结果表明,离子(N2+,N+)的运动状态滞后瞬时射频电场的变化;在两极附近,N2+具较高密度,但能量较低,N+具较低的密度但能量较高,两者的密度差6倍左右。两种离子轰击射频电极的能量分布变化规律类似,随放电参数变化,离子(N2+,N+)能量变化显著,其密度变化不明显。模拟的电子能量几率分布与测量结果一致。     

离子(N2+, N+)在氮辉光放电等离子体光辐射中的作用

采用氮辉光放电等离子体电子与重粒子综合的Monte Carlo模型,研究了离子(N2+,N+)与氮分子碰撞产生光辐射的强度分布及其 在氮辉光放电等离子体光辐射中的作用。两种离子产生的各种碰撞激发和辐射都分布在鞘层区内,光辐射强度向阴极方向逐渐 增加,且总强度随放电电压增加而增强。相对于电子产生的碰撞激发辐射,离子(N2+,N+)引起的辐射在阴极附近引起次最大 光强,且原子离子N+的作用较分子离子N2+大。当电压较低时,离子(N2+,N+)引起的辐射可以忽略。模拟结果很好解释了两 种典型的N2辉光放电光学发射谱的实验结果,为等离子体诊断研究中的光谱数据分析提供参考。     

氮直流辉光放电活性粒子(N~+,N)的产生率

在氮直流辉光放电等离子体中采用快电子和离子(N+2,N+)混合的蒙特卡罗模型,模拟研究了e+N2→N+ N+N+2e e和N+2+N2→N++N+N2过程中粒子(N+,N)产生率的轴向分布随放电参数(工作气压、放电电压和温度)的变化规律。结果表明:两种离解过程中氮活性粒子(N+,N)的产生率都随气压和电压的增加而增大,随放电气体温度的升高而降低;但N+2-N2离解碰撞主要发生在阴极附近。电压较高时,阴极处的离子N+主要由N+2-N2离解过程产生;电压较低时,N+2-N2离解过程可忽略。中性原子N主要由电子碰撞离解过程产生。     

双频容性耦合等离子体相分辨发射光谱诊断

采用相分辨发射光谱法, 对双频容性耦合纯Ar和不同含O₂量的Ar-O₂混合气体放电等离子体的鞘层激发模式进行了探究. 在射频耦合电源上极板的鞘层区域处观察到两种电子激发模式: 鞘层扩张引起的电子碰撞激发模式和二次电子引起的电子碰撞激发模式; 并发现这两种激发模式均受到低频射频电源周期的调制. 在纯Ar放电等离子体中, 两种激发模式的激发轮廓相似; 而在Ar-O₂混合气放电等离子体中, 随着含O₂量的增加, 二次电子的激发轮廓变弱. 此外, 利用相分辨发射光谱法对不同含O₂量的Ar-O₂混合气放电下Ar的 750.4 nm谱线的平均低频电源周期轴向分布进行了研究, 得到了距耦合电源上极板约3.8 mm处为双频容性耦合射频等离子体的鞘层边界. 关键词： 双频容性耦合等离子体 等离子体鞘层 发射光谱     

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采用粒子模拟与蒙特卡罗模型相结合(PIC/MCC)的方法,建立了氮分子气体辉光放电自洽的混合模型,其中带电粒子在电场中的运动及其产生的自洽场由PIC方法的静电模型描述,粒子间的碰撞过程由MC方法描述。模拟了放电过程及带电粒子(e、N2+、N+)在整个放电空间的行为及与之对应的自洽电场和电势的分布,通过计算带电粒子在负辉区的几率分布函数,讨论了带电粒子(e、N2+、N+)在负辉区的行为和分布特征。计算的分子离子密度与实验结果一致。     

大气压Ar／NH3介质阻挡辉光放电的仿真研究

为了研究火气压下氩气（Ar）中掺杂氨气（NH3）的Ar／NH3介质阻挡辉光放电的放电机理,通过建立一‘个多粒子的自洽耦合流体模型,采用有限元方法进行数值计算,得到了气体间隙压降、介质表面电荷密度、放电电流密度随时间的周期变化波形,以及带电粒子、中性粒子与空间电场强度的时空分布．仿真计算结果表明：气体间隙的周期击穿过程主要由气隙电压控制,并受气隙两侧介质极板上积聚的表面电荷的影响．气隙间带电粒子密度和电场强度的时空分布表明本文的放电过程存在阴极位降区、负辉区、法拉第暗区、等离子体正柱区等辉光放电的典型区域,放电模式为大气压辉光放电．在Ar/NH3等离子体中,主要的正离子为NH＋,其次为Ar2＋,主要的负离子为NHi：NH3分解产生的主要的激发态分子为NH,NH2和N2H3,而最终的稳态产物主要是N2和H2．     

N+2离子在氮直流辉光放电中碰撞离解的作用

采用氮辉光放电等离子体快电子和各种重粒子（N＋２，N＋，Nf）的混合Monte Carlo模型，从不同放电条件的离解碰撞率，快原子态粒子（N+，Nf）在阴极鞘层区的输运过程及轰击阴极的能量及角分布三个方面研究了 N＋２+N２→N+＋N+N2f反应在氮气直流辉光放电中的作用.该过程在电压较高时为阴极鞘层区的重要离解过程， 且主要发生在阴极附近，其碰撞率随电压和气压增加而增加；阴极表面附近的活性粒子（N＋，Nf）主要由该离解过程产生（而不是e--N2离解电离过程），而且这些粒子具有中等的平均能量且小角入射，是 关键词： 氮直流辉光放电 Monte Carlo模拟 N＋２-N２碰撞离解     

射频容性耦合等离子体放电特性的光谱诊断

利用流体模型模拟和发射光谱实验诊断相结合的方法,研究了中等气压、中等功率下射频容性耦合等离子体的放电特性。理论上,采用基于流体模型的COMSOL软件仿真,建立一维等离子体放电模型,以Ar气为工作气体,研究了不同气压以及不同射频输入功率下等离子体电子温度和电子密度的分布规律。实验上,依据仿真模型设计制作了相同尺寸的密闭玻璃腔体和平板电极,采用13.56 MHz射频放电技术电离腔体内的工作气体Ar气,测量了不同气压、不同射频输入功率时放电等离子体的发射光谱。通过分析和选择适当的Ar Ⅰ和Ar Ⅱ的特征谱线,分别利用玻尔兹曼斜率法以及沙哈-玻尔兹曼方程计算了等离子体的电子温度与电子密度,并结合模拟仿真结果对光谱诊断结果进行了修正。结果表明：当气体压强为300~400 Pa、输入功率为600~800 W时,等离子体近似服从玻尔兹曼分布,此时利用光谱法得到的等离子体参数与仿真结果相符合。仿真模拟与光谱实验诊断相结合的方法可初步诊断出中等气压下等离子体的放电参数,增加了玻尔兹曼斜率法和沙哈-玻尔兹曼方程在等离子体放电中的使用范围,扩大了光谱法在低电子密度容性耦合等离子体参数诊断的应用场合,为中等气压容性耦合等离子体在工业与军事上的应用研究提供了重要物理状态的分析手段。     

氮直流辉光放电活性粒子（N^＋，N）的产生率

在氮直流辉光放电等离子体中采用快电子和离子(N2^ ，N^ )混合的蒙特卡罗模型，模拟研究了e N2→N^ /N N 2和N2^ N2→N^ N N2过程中粒子(N^ ，N)产生率的轴向分布随放电参数(工作气压、放电电压和温度)的变化规律。结果表明：两种离解过程中氮活性粒子(N^ ，N)的产生率都随气压和电压的增加而增大，随放电气体温度的升高而降低；但N2^ —H2离解碰撞主要发生在阴极附近。电压较高时，阴极处的离子N^ 主要由N2^ —N2离解过程产生；电压较低时，N2^ —N2离解过程可忽略。中性原子N主要由电子碰撞离解过程产生。     

N_2-H_2容性耦合等离子体电非对称效应的particle-in-cell/Monte Carlo模拟

H_2-N_2混合气体电容性耦合射频放电在有机低介电系数材料刻蚀中具潜在研究意义.采用paxticle-incell/Monte Carlo模型模拟了双频(13.56 MHz/27.12 MHz)电压源分别接在结构对称的两个电极上的H_2-N_2容性耦合等离子体特征,研究了其电非对称效应.模拟结果表明,通过调节两谐波间的相位角θ,可以改变其电场、等离子体密度、离子流密度的轴向分布及离子轰击电极的能量分布.当相位角θ为0°时,低频电极(晶片)附近主要离子(H_3~+)的密度最小,离子(H_3~+,H_2~+,H~+)轰击低频电极的流密度及平均能量最高;当θ从0°变化90°时,低频电极的自偏压从-103V到106V近似线性增加,轰击电极的离子流密度变化约±18%,H~+离子轰击低频电极的最大能量约减小2.5倍,轰击电极的平均能量约变化2倍,表明氢离子能量和离子流几乎能独立控制.     

宏观放电参数对快原子态氮(N+,Nf)的影响

采用氮直流辉光放电等离子体中快电子和重粒子(N₂⁺,N⁺,N_f)混合的蒙特卡罗方法,模拟研究了快原子态粒子(N⁺,N_f)的产生率及轰击阴极的能量分布随宏观放电参数(P,V)的变化规律.结果表明,存在一最佳放电条件,使阴极壁处粒子(N⁺,N_f)的粒子数密度大且能量高;当电压大于800V时,轰击阴极的活性粒子(N⁺,N_f),主要由N₂⁺-N₂离解过程产生,电压小于300V时,主要由e^--N₂离解过程产生,模拟结果与实验结果相符合.     

大气压甲烷针-板放电等离子体中粒子密度和反应路径的数值模拟

甲烷针-板放电与重油加氢耦合形成甲烷转化重油加氢,可实现重油高效加氢并增产高附加值低碳烯烃,有实践应用前景和科学研究意义.建立二维流体模型,对大气压甲烷针-板放电等离子体进行数值模拟,得到电场强度、电子温度和粒子密度的空间与轴向分布,总结反应产额并提炼生成各种带电和中性粒子的关键路径.模拟结果表明,CH_3~+和CH_4~+密度与电场强度和电子温度的轴向演化接近且密切相关;CH_5~+和C_2H_5~+密度沿轴向先增大后减小;CH_3与H密度的空间和轴向分布几乎相同;CH_2,C_2H_4与C_2H_5的粒子密度分布在靠近阴极的区域内明显不同而在正柱区内较为相像;电子与CH_4发生电子碰撞电离生成的CH_3~+和CH_4~+,CH_3~+和CH_4~+分别与CH_4发生分子碰撞解离生成C_2H_5~+和CH_5~+;电子与CH_4间的电子碰撞分解是生成CH_3,CH_2,CH和H的主导反应;CH_2与CH_4和电子与C_2H_4发生的反应分别是生成C_2H_4和C_2H_2的关键路径;电子与CH_4间的电子碰撞分解反应和CH_2与CH_4发生的反应的产额各占H_2总产额的52.15%和47.85%.     

Particle simulation of radio-frequency plasma discharges of methanefor carbon film deposition

Particle-in-cell/Monte Carlo (PIC/MC) simulations of capacitively coupled radio-frequency (RF) glow discharges were carried out for low pressure CH₄ plasmas. The present computational scheme includes the motions and collisions of both neutral and charged particles. The CH₄ plasma is modeled by combining a one-dimensional PIC/MC method with a polyatomic particle collision scheme. The model considers the motions of CH₄, CH₄⁺, CH₃, C₂H₅, H₂, H, and electrons. Space and time dependent results show ionization rate is high at the sheath region. The dissociation rate of CH₄ is found to be high at the sheath as well as in the plasma bulk. Deposition rate of carbon film is calculated by sampling impinging particles at at the powered electrode. The calculations show that neutral radicals are the major depositing species for the cases studied. Ion energy impinging to the electrode was found to be strongly dependent on the “imposed” dc bias (as opposed to self-bias) voltage for a given RF voltage. Deposition rate was found to be almost independent of the “imposed” dc bias voltage as the RF voltage remained constant     

N2流量对N掺杂MgZnO薄膜结构和性能的影响

利用射频磁控溅射方法,使用Mg_{0. 04}Zn_0.96O 陶瓷靶材,选用不同流量比的氮气和氩气混和气体作为溅射气体,在石英基片上生长N掺杂Mg_xZn_1-xO合金薄膜。研究了氮流量比对薄膜组分、结构、形貌、电学性质和拉曼光谱的影响。结果显示：随着溅射气氛中氮流量比的增加,薄膜中Mg含量增加,薄膜表面颗粒尺寸减小,结晶质量变差,电阻率逐渐增大,导电类型发生转变。在氮流量比为20%时,获得了最好的p型导电薄膜。另外,随着氮流量比的增加,拉曼光谱中与N_O相关的位于272 cm^-1、642 cm^-1左右的振动峰逐渐增强,表明N_O的浓度随着氮流量比的加大而有所增加。     

Active species in microwave postdischarge for steel-surfacenitriding

Production of nitrogen atoms has been studied in a 2.45-GHz flowing postdischarge in N₂ and N₂-H₂ gas mixtures with Ar as a buffer gas in the high-pressure regime (5×10³ to 6.5×10⁴ Pa). N atom densities have been measured by NO titration in the 10¹⁴-10 ¹⁵ cm³ range and monitored by the first positive emission resulting from the N atom recombination. The rate coefficient of the N+N+N₂ recombination has been found to be _k=6×10^-33 cm⁶ atom^-2 s ^-1 at T₀=300 K, which agrees with previously published data. The N atom production (or degree of N/N₂ dissociation) in front of an Fe-0.1%C substrate correlates well with the thickness of a γ' Fe₄N layer produced by the postdischarge treatment. The H₂ gas was first introduced in the initial phase of treatment to remove surface oxidizing and then was cut off to keep high densities of N atoms. It is deduced that N atoms are more active nitriding species than NH-type radicals     

Physical aspects of dust–plasma interactions

Low-pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle-forming plasmas, where the dust-induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle-resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state-of-the-art understanding of such complicated, discharge-type-specific phenomena as dust-induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.     

Effects of fly ash on NOx removal by pulsed streamers

NO_x removal methods using plasma chemical reactions in nonthermal plasmas have been widely studied. In this paper, the effects of the addition of fly ash on NO_x removal using short-pulsed discharge plasmas are described. Fly ash which had been collected from a coal-burning thermal electrical power plant was used. Experiments were performed using four different mixtures of gases which included NO. These were (N₂+NO), (N₂+NO+O₂), (N₂+NO+H₂O), and (N₂+NO+O₂+H ₂O). These gas mixtures were used either with or without the addition of fly ash. The initial concentration of NO was fixed at 200 ppm (NO parts per million of the gas mixture), The study of the NO_x (NO+NO₂) removal was performed with the fly ash, as it is relevant to real situations in coal power plants. The results show that the presence of fly ash decreased the NO_x removal rate slightly in the case of dry gas mixtures while it increased the NO_x removal rate substantially in the case of wet gas mixtures. These results suggest that the presence of fly ash in the flue gases, which also contain a few percentages of moisture, would be advantageous to the treatment of flue gases emitted from thermal power plants for the removal of nitrogen oxides