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常压射频容性放电氩等离子体中活性气体对放电特性的影响

Influence of Active Gas Mixed in Atmospheric-pressure Radio-frequency Capacitively Coupled Argon Plasma on the Discharge Characteristics

作者: 专业:等离子体物理 导师:李寿哲 年度:2010 学位:硕士  院校: 大连理工大学

Keywords

Radio-Frequency Atmospheric Pressure Glow Discharge, Electrical Measurements, Optical Diagnosis, Electron Density

        大气压射频辉光放电冷等离子体由于摆脱了真空腔的限制,在等离子体辅助刻蚀、灰化、薄膜沉积、材料表面清洗、消毒灭菌、战地生化等领域有着非常广阔的应用前景。目前,采用具有裸露金属电极结构等离子体发生器实现大气压下氧气/氩气、氮气/氩气等廉价气体的稳定射频a模式辉光放电是一项具有挑战性的工作。本文采用13.56 MHz的射频电源和双级联平板形电极在大气压下成功实现了氩/氧、氩/氮等混合气体的均匀稳定的α模式辉光放电,并采用电学测量与光谱学诊断等方法对其进行了研究。在研究Ar/O2放电中,纯氩气在不同电极间距下放电击穿机制为电子迁移控制击穿机制和电子扩散控制击穿机制。纯氩气击穿后,形成均匀稳定a模式放电,然后通过调节匹配器来适当加入氧气,氧气和氩气的最大混合比例可达到0.9 vol%。实验发现掺入氧气的含量越大,放电表现的越不稳定,放电从正常的辉光放电过渡到反常辉光放电所需的功率密度就越大。进而,我们分析了纯氩气下整个放电过程中的模式转化及相应的伏安特性曲线,纯氩气击穿后,随着输入功率的不断增加,放电形态由α放电模式转化成a-γ共存模式,最后演变成γ模式。在氧氩混合比为0.%、0.3%和0.6%的条件下,放电电压和电流随着输入功率的增加而增加,以电压、电流和功率的变化曲线为依据,应用等效电路模型估算出电子密度的数量级在1011cm-3,并且随着输入功率增加而增大,随着氧气含量的增大反而减小。用约化能量守恒方程估算出电子温度在1.4 eV左右,随着输入功率的增加,电子温度变化幅度很小。在光谱诊断方面,利用LIFBASE光谱拟合软件和玻耳兹曼斜率法对OH(306-310nm)自由基进行拟合,可以准确估测气体温度。实验发现,气体温度随着输入功率的增加而增大。此外,应用光化线强度的方法得出氧原子浓度在掺入氧气的浓度为0.35%附近达到极大值。由于氩/氧等离子体中富含活性很强的氧原子、臭氧等,在功率为150W时处理玻璃基片上的炭黑粉末,处理时间达3.5min,处理效果良好,为大气压氩/氧放电等离子体应用领域提供了可行性依据。在氩/氮射频辉光放电中,我们得到了稳定的α模式辉光放电,而且掺氮含量高于1%,实验中发现,随着掺入氮气含量的变化,放电颜色发生了明显的变化,由白色变为紫色。选用发射光谱仪,测量了300~900nm范围内的谱线,并且分析了氮分子的第二正带系。采用顺序组带的方法,估算了振动温度随氮气流量的变化,在氮气含量为0.8%时,振动温度约为1811K。从定性的角度分析了氮气分子在337nm、380nm、405nm处的谱线强度随功率的变化趋势,发现随功率的增加而增加。
    Radio-frequency atmospheric pressure glow discharge (RF APGD) cold plasmas have widespread applications in different fields, including plasma-aided etching, deposition, material surface cleaning and ashing, sterilization and biological warfare agents due to the removal of the vacuum system. At the present time, it is a challenging task to obtain Ar/O2, or Ar/N2 RF APGD in the a mode using the plasma generators with bare metallic electrodes. In this paper, a homogeneous and stable Ar/O2 and Ar/N2 glow discharge in a mode is generated at atmospheric-pressure in a parallel bare metal plate reactor with a radio frequency (13.56 MHz) power supply by introducing a dielectric strip in the inlet of the gas flow. The discharge characteristics with oxygen-argon and nitrogen-argon mixtures are investigated by the electrical measurements and optical diagnostics.In the study of Ar/O2 RF APGD, two different breakdown mechanisms were found to be responsible for argon plasma ignition at various electrode gaps. Stable and uniform RF APGD plasma in a mode was observed after argon breakdown. Oxygen can be added into argon by adjusting matching network and the allowable oxygen-to-argon ratio reached 0.9 vol%. With increasing oxygen-to-argon ratio, the Ar/O2 discharge plasma became unstable. Depending on the input power, normal and abnormal glow regimes were observed in a mode. The discharge started as a normal glow and then became an abnormal glow as the input power was increased. It was found that the power density of the plasma operated in an abnormal glow increased with the increase of oxygen content. And the voltage-current characteristic, representing the whole discharge process from the ignition with pure argon to a stable and uniform plasma in the y mode is analyzed. Meanwhile, the a and y mode andα-γcoexisting mode were observed in the whole process. The curves of voltage and current versus input power were recorded in rms values in the glow discharge region at 0.0%,0.3% and 0.6 vol%. With increasing input power, both RF current and voltage increased. The electron density and electron temperature were estimated on the basis of the electrical experiment data using the equivalent circuit model and the reduced energy balance equation. The results showed that the electron density of the Ar/O2 discharge in the abnormal glow regime was approximately 1011 cm-3 and increased with input power, however it decreased while increasing the fraction of oxygen, as oxygen is an electronegative gas and the attachment processes are loss channels of electrons. The electron temperature of Ar/02 was approximately 1.4 eV and changed slightly as input power increased. Furthermore, the gas temperature has been determined by the fitting of experimental and simulated spectra of OH band with LIFBASE software and using the Boltzmann plot method, which is in good coincidence. With increasing input power, the gas temperature of Ar/02 increased at oxygen-to-argon ratios of 0.0,0.3 and 0.6 vol%. When mensurating the oxygen atom generated in Ar/02 plasma by optical actinometry, it was found that an optimal value of oxygen density (0.35 vol%) existed in the production of oxygen radicals. Moreover, the carbon black on the slide glass was completely removed by an oxidation in 3.5 min. Base on the results, it is expected that the Ar/O2 plasma can be effectively utilized to material treatment due to enough chemically active species.In the study of Ar/N2 RF APGD, a stable and uniform plasma in a mode was also obtained and the allowable nitrogen-to-argon ratio reaches more than 1.0 vol%. The color of the discharge plasma changed from white to purple when the nitrogen was added into the argon plasma. In addition, Emission spectrum of the N2 (C3Πu→B3Πg) was observed by measuring the spectrum of 300-900 nm in mixture gas. And the vibrational temperature of N2 was calculated by the measurements of the sequences of vibrational bands of N2 second positive system. The vibrational temperature was approximately 181 IK at nitrogen-to-argon ratio of 0.8 vol% and an input power of 150W. We analyzed qualitatively the optical emission spectrum of the N2 (C3Πu→B3Πg). It was found that the peaks at 337,380 and 405nm increased with the increase of input power.
        

常压射频容性放电氩等离子体中活性气体对放电特性的影响

摘要4-5
Abstract5-6
1 绪论9-21
    1.1 等离子体概述9-10
    1.2 大气压辉光放电产生方式及应用10-17
        1.2.1 电晕放电与应用11-12
        1.2.2 介质阻挡放电与应用12-14
        1.2.3 大气压射频容性耦合放电及其应用14-17
    1.3 研究背景和内容17-21
2 实验装置及大气压射频冷等离子体发射光谱诊断原理21-32
    2.1 射频辉光放电实验装置21-26
    2.2 射频辉光放电发射光谱诊断原理26-32
        2.2.1 氧原子的光化线强度测定27-28
        2.2.2 玻耳兹曼斜率法测量转动温度28-30
        2.2.3 顺序带组法测量振动温度原理30-32
3 大气压氩/氧射频辉光放电32-60
    3.1 大气压氩气射频容性放电的击穿机制32-35
        3.1.1 实验设置32
        3.1.2 主要结论及讨论32-35
    3.2 氩/氧放电的实验现象及讨论35-36
    3.3 电学特性分析36-39
    3.4 电子密度和电子温度的估算39-42
    3.5 光谱分析42-48
        3.5.1 氩/氧射频等离子体中氧原子的光化线强度测定42-43
        3.5.2 氩/氧辉光放电的气体温度及炭黑的灰化效果43-48
    3.6 对氩气/氧气等离子体源的设计方案及放电特性的进一步分析48-58
        3.6.1 放电结构的设计和改进48-50
        3.6.2 氧气在氩等离子体中的掺杂对射频辉光放电特性的影响50-58
    3.7 小结58-60
4 大气压氩/氮射频辉光放电的初步研究60-66
    4.1 不同放电模式下混合气体的放电图像60-61
    4.2 氩/氮放电的电压电流波形图61-62
    4.3 氩/氮射频辉光放电的发射光谱诊断62-66
结论66-68
参考文献68-73
致谢73-74
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