Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session QR2: Non-equilibrium Kinetics |
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Chair: Mirko Vukovic, Tokyo Electron Limited Room: Classroom 203 |
Thursday, October 25, 2012 10:30AM - 10:45AM |
QR2.00001: Reactive species in atmospheric pressure helium-oxygen plasmas with humid air impurities Tomoyuki Murakami, Kari Niemi, Timo Gans, Deborah O'Connell, William G. Graham In most applications helium-based plasma jets operate in an open air environment. The presence of humid-air in the plasma jet will influence the plasma chemistry and can lead to the production of a broader range of reactive species. We explore the influence of humid air on the reactive species in rf driven atmospheric-pressure helium-oxygen mixture plasmas (helium with 5000 ppm admixture of oxygen) for wide air impurity levels of 0-500 ppm with relative humidities of from 0 to 100{\%} using a zero-dimensional, time-dependent global model. Comparisons are made with experimental measurements in an rf driven micro-scale atmospheric pressure plasma jet and with one-dimensional semi-kinetic simulations of the same plasma jet. The evolution of species concentration is described for reactive oxygen species, metastable species, radical species and positively- and negatively-charged ions (and its clusters). Effects of the air impurity containing water humidity on electronegativity and chemical activity are clarified with particular emphasis on reactive oxygen species. [Preview Abstract] |
Thursday, October 25, 2012 10:45AM - 11:00AM |
QR2.00002: Influence of kinetic effects on the resonance behavior of the Multipole Resonance Probe Jens Oberrath, Thomas Mussenbrock, Ralf Peter Brinkmann Active plasma resonance spectroscopy is a well known diagnostic method. Many concepts of this method are theoretically investigated and realized as a diagnostic tool. One of these tools is the multipole resonance probe (MRP) [1]. The application of such a probe in plasmas with pressures of only a few Pa raises the question whether kinetic effects have to be taken into account or not. To address this question a kinetic model is necessary. A general kinetic model for an electrostatic concept of active plasma resonance spectroscopy has already been presented by the authors [2]. This model can be used to describe the dynamical behavior of the MRP, which is interpretable as a special case of the general model. Neglecting electron-neutral collisions, this model can be solved analytically. Based on this solution we derive an approximated expression for the admittance of the system to investigate the influence of kinetic effects on the resonance behavior of the MRP. \\[4pt] [1] M. Lapke et al., Plasma Sources Sci. Technol. 20, 2011, 042001\\[0pt] [2] J. Oberrath et al., Proceedings of the 30th International Conference on Phenomena in Ionized Gases, 28th August - 2nd September, 2011 [Preview Abstract] |
Thursday, October 25, 2012 11:00AM - 11:15AM |
QR2.00003: Influence of cross section set on the self-consistent electron and vibrational kinetics Gianpiero Colonna, Mario Capitelli Advanced models of elementary processes in plasmas are based on the self--consistent approach, solving at the same time the Boltzmann equation for free electrons and the master equation for the evolution of species concentration and the distribution of internal state. In some conditions, it is very important also to couple these models with the radiation transport, to consider non--local effects, because the radiation emitted in one location can be absorbed in a different position. This aspects is very important in high pressure, conditions met in high pressure pulsed discharges. The new set of e-molecule cross sections, extend the available data, considering processes for the whole vibrational ladder, has dramatic effects on the kinetics, increasing considerably the energy injected in internal degrees of freedom. This work is intended to investigate such effects, comparing results obtained by using old cross section set or recently calculated complete set. [Preview Abstract] |
Thursday, October 25, 2012 11:15AM - 11:30AM |
QR2.00004: Production and provision mechanisms of OH radical of an atmospheric-pressure helium plasma jet Seiya Yonemori, Ryo Ono, Tetsuji Oda An atmospheric-pressure helium plasma jet is getting much attention because of its low heat load. It is known that active species such as OH radical play important role in many plasma processes, for example, in plasma medical care or in plasma sterilization. When using the plasma jet for surface treatment, it is important that the amount of OH radical provided into objectives. We measured OH density in the vicinity of the surface of objectives using laser induced fluorescence (LIF). The plasma jet was generated when AC 8 kHz, 10 kV was applied. When the plasma jet extended onto the dry glass surface, the maximum OH density was 0.2 ppm. On the other hand, the maximum OH density was 1 ppm when the plasma jet extended onto the wet surface. In addition, time-evolution of OH density between two successive voltage pulses was measured. On the edge of the plasma jet, OH density was at maximum and rapidly decreased between two pulses. Those results suggest that there are three ways of OH production; first, the dissociation of H$_{2}$O included in discharge gas; secondly, the dissociation of H$_{2}$O included in the ambient air; finally, the dissociation of H$_{2}$O evaporates from the wet surface. [Preview Abstract] |
Thursday, October 25, 2012 11:30AM - 11:45AM |
QR2.00005: Thermal electron attachment to fluorocarbon radicals: Experiment and kinetic modeling Nicholas Shuman, Thomas Miller, Albert Viggiano Few experimental measurements of the kinetics of electron attachment to radicals exist due to the inherent difficulties of working with transient species. Electron attachment to small fluorocarbon radicals is particularly important, as the data are needed for predictive modeling of plasma etching of semiconductor materials. We have recently developed a novel flowing afterglow technique to measure several types of otherwise difficult to study plasma processes, including thermal electron attachment to radicals. Variable Electron and Neutral Density Attachment Mass Spectrometry (VENDAMS) exploits dissociative electron attachment in a weakly ionized plasma as a radical source. Here, we apply VENDAMS to a series of halofluorocarbon precursors in order to measure the kinetics of thermal electron attachment to fluorocarbon radicals. Results are presented for CF$_{2}$, CF$_{3}$, C$_{2}$F$_{5}$, CF$_{3}$, 1-C$_{3}$F$_{7}$, 2-C$_{3}$F$_{7}$, and C$_{3}$F$_{5}$ from 300 to 600 K. Both the magnitude and the temperature dependences of rate coefficients as well as product branching between associative and dissociative attachment are highly system specific. The data are analyzed using a kinetic modeling approach, allowing for physical insight into the systems as well as extrapolation to non-thermal conditions inaccessible to the experiment. [Preview Abstract] |
Thursday, October 25, 2012 11:45AM - 12:00PM |
QR2.00006: Ozone kinetics in low-pressure discharges Vasco Guerra, Daniil Marinov, Olivier Guaitella, Antoine Rousseau Ozone kinetics is quite well established at atmospheric pressure, due to the importance of ozone in atmospheric chemistry and to the development of industrial ozone reactors. However, as the pressure is decreased and the dominant three-body reactions lose importance, the main mechanisms involved in the creation and destruction of ozone are still surrounded by important uncertainties. In this work we develop a self-consistent model for a pulsed discharge and its afterglow operating in a Pyrex reactor with inner radius 1 cm, at pressures in the range 1-5 Torr and discharge currents of 40-120 mA. The model couples the electron Boltzmann equation with a system of equations for the time evolution of the heavy particles. The calculations are compared with time-dependent measurements of ozone and atomic oxygen. Parametric studies are performed in order to clarify the role of vibrationally excited ozone in the overall kinetics and to establish the conditions where ozone production on the surface may become important. It is shown that vibrationally excited ozone does play a significant role, by increasing the time constants of ozone formation. Moreover, an upper limit for the ozone formation at the wall in these conditions is set at 10(-4). [Preview Abstract] |
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