Bulletin of the American Physical Society
62nd Annual Gaseous Electronics Conference
Volume 54, Number 12
Tuesday–Friday, October 20–23, 2009; Saratoga Springs, New York
Session TR3: Plasma Chemistry |
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Chair: Robert Hicks, UCLA Room: Saratoga Hilton Ballroom 3 |
Thursday, October 22, 2009 1:30PM - 1:45PM |
TR3.00001: Manipulating Plasma Surface Interaction Stephan Reuter, Kari Niemi, Volker Schulz-von der Gathen, Timo Gans A low temperature rf-powered atmospheric pressure plasma jet (APPJ) operated with helium and a small oxygen admixture is investigated. The study aims at a better understanding of reactive oxygen species production and annihilation processes in the APPJ's effluent. Optical emission spectroscopy (OES) measurements reveal the existence of excited atomic oxygen even at considerable distance from the jet's nozzle. In order to gain insight into energy transport mechanisms from core plasma to the effluent, (V)UV-optical emission spectroscopy measurements and chemical model calculations are performed and oxygen species densities (O, O$_{3}$, O$_{2}$(b$^{1}\Sigma _{g}^{+}))$ derived from two-photon absorption laser-induced fluorescence (TALIF) spectroscopy [1], UV-absorption spectroscopy, and optical emission spectroscopy measurements are compared with the chemical model calculations, showing excellent agreement. The chemical model allows to investigate the possibility to influence the APPJ's chemistry and enhance the oxygen output -- e.g. by laser radiation. The ultimate prospect is to design the properties of a plasma according to the specifications required by respective surface treatment applications. \\[0pt] [1] S. Reuter, K. Niemi, V. Schulz-von der Gathen, and H. F. D\"{o}bele, Plasma Sources Sci. Technol., \textbf{18}, 015006 (2009) [Preview Abstract] |
Thursday, October 22, 2009 1:45PM - 2:00PM |
TR3.00002: Comparsion of mass spectra measurements and kinetic modelling of high pressure He-Air glow discharges K.R. Stalder, R.J. Vidmar, W.G. Graham, Y.A. Gonzalvo The results of a chemistry code are compared with mass spectrometry measurements of positive and negative ion species for helium-air systems excited in the 30-50 kHz range. A 6 mm O.D. DBD with a 1.0 mm diameter inner wire electrode, operated at a flow of helium 3-10 l.min$^{-1}$ into air was interfaced to a Hiden Analytical HPR-60 molecular beam mass spectrometer (MBMS). This consists of a quadruple mass spectrometer with a differentially pumped three-stage inlet system [1]. The kinetics of a parallel plate APGD, operating in static helium with 10000 ppm of air, have been modeled using a code [3,4] which includes 461 reactions and tracks 58 species including neutral atoms and molecules, metastable species, vibrationally-excited N$_{2}$ and O$_{2}$, electrons, positive and negative ions, and various water cluster ions. The results show interesting similarities with the main discrepancies existing in the effects of water clustering. [1] E.Stoffels et al., Plasma Sources Sci. Technol.15 501 (2006) [2] Y. Aranda-Gonzalvo et al J.Vac.Sci.Technol.A 24 55 (2006) [3] R.J. Vidmar, IEEE Trans. Plasma Sci. 18, 733 (1990) [4] K.R. Stalder et al., J.Appl. Phys. 99, 093301 (2006). [Preview Abstract] |
Thursday, October 22, 2009 2:00PM - 2:15PM |
TR3.00003: Partial modeling for plasma assisted combustion -- Turbine combustor application Boris Potapkin, Maxim Deminsky, Marina Strelkova, Irina Chernysheva, Igor Kochetov, Seyed Saddoughi, John T. Herbon, Timothy Sommerer Modern gas turbine combustors have to meet increasingly stringent emissions requirements at enlarged operability at conditions of lean-premixed natural gas combustors. This work is dedicated to analysis of possible plasma effect on natural gas combustion gas turbine operation via partial modeling approach. It was shown that plasma effect has potential to enhance the stability of premixed natural gas combustion by widening the lean-blowout limit and enabling operation at lower flame temperatures thus achieving lower emissions and higher turndown capability. [Preview Abstract] |
Thursday, October 22, 2009 2:15PM - 2:45PM |
TR3.00004: Effects of non-thermal plasmas and electric field on hydrocarbon/air flames Invited Speaker: Need to improve fuel efficiency, and reduce emission from hydrocarbon combustor in automotive and gas turbine engines have reinvigorated interest in reducing combustion instability of a lean flame. The heat generation rate in a binary reaction is H$_{Q }$=N$^{2 }$c$_{1}$c$_{2}$ Q exp(-E/RT), where N is the density, c$_{1}$ and c$_{2}$ are mol fractions of the reactants, Q is the reaction heat release, E is the activation energy, R is the gas constant and T is the average temperature. For hydrocarbon-air reactions, the typical value of E/R $\sim $20, so most heat release reactions are confined to a thin reaction sheet at T $\ge $1400 K. The lean flame burning condition is susceptible to combustion instability due to a critical balance between heat generation and heat loss rates, especially at high gas flow rate. Radical injection can increase flame speed by reducing the hydrocarbon oxidation reaction activation barrier and it can improve flame stability. Advances in nonequilibrium plasma generation at high pressure have prompted its application for energy efficient radical production to enhance hydrocarbon-air combustion. Dielectric barrier discharges and short pulse excited corona discharges have been used to enhance combustion stability. Direct electron impact dissociation of hydrocarbon and O$_{2}$ produces radicals with lower fuel oxidation reaction activation barriers, initiating heat release reaction C$_{n}$H$_{m}$+O $\Leftrightarrow $ C$_{n}$H$_{m-1}$+ OH (and other similar sets of reactions with partially dissociated fuel) below the typical cross-over temperature. Also, N$_{2 }$(A) produced in air discharge at a moderate E/n can dissociate O$_{2 }$leading to oxidation of fuel at lower gas temperature. Low activation energy reactions are also possible by dissociation of hydrocarbon C$_{n}$H$_{m}$+e $\to $ C$_{n}$H$_{m-2}$+H$_{2}$+e, where a chain propagation reaction H$_{2}$+ O$\Leftrightarrow $ OH+H can be initiated at lower gas temperature than possible under thermal equilibrium kinetics. Most of heat release comes from the reaction CO+OH$\to $ CO$_{2 }$+H, nonthermal OH production seem to improve combustion stability The effect of applied voltage in a flame below self-sustained plasma generation is known to enhance flame holding through induced turbulence. Review of recent results will be presented to show future research opportunities in quantitative measurements and modeling of hydrocarbon/air plasma enhanced combustion. [Preview Abstract] |
Thursday, October 22, 2009 2:45PM - 3:15PM |
TR3.00005: Ultrahigh quality amorphous silicon film deposition for solar cells employing novel plasma enhanced CVD Invited Speaker: Hydrogenated amorphous silicon (a-Si:H) is most widely employed as a top cell material in thin film Si tandem solar cells. The a-Si:H solar cells have three important problems to be solved: 1) a low stabilized efficiency below 10{\%}. 2) light induced decrease in efficiency around -20{\%} of the initial one. 3) a low deposition rate of 0.5 nm/s. In SiH$_{4}$ discharges employed for a-Si:H deposition, there coexist three deposition precursors; SiH$_{3}$ radicals, HOS radicals, and amorphous clusters [1]. SiH$_{3}$ radicals are the main deposition precursor for ``good'' quality films. Incorporation of clusters into a-Si:H films has been pointed out to cause the light induced degradation, whereas that of HOS radicals has not. To study effects of clusters on the light induced degradation and to control their deposition into films, we have employed a multi-hollow plasma CVD method to deposit films in which the incorporation of clusters is reduced in the upstream region with the gas flow that drive clusters toward the downstream region of the reactor [2, 3]. Films deposited in the upstream region tend to be more stable than those deposited in the downstream region; and the films deposited far from the discharges in the upstream region shows high stability, which indicates that the incorporation of clusters degrades the stability of a-Si:H films against light exposure. Our a-Si:H films deposited at 2.3 nm/s show a remarkably low stabilized defect density of 4x10$^{15}$ cm$^{-3}$. \\[4pt] [1] M. Shiratani, et al., Thin Solid Films 427 (2003) 1.\\[0pt] [2] W. M. Nakamura, et al., J. Phys.: Conference Series 100 (2008) 082018.\\[0pt] [3] W. M. Nakamura, et al., IEEE Trans. Plasma Sci. 36 (2008) 888. [Preview Abstract] |
Thursday, October 22, 2009 3:15PM - 3:30PM |
TR3.00006: Effect of acetylene portion on the properties of high frequency discharge in argon Irina Schweigert, Dmitry Ariskin The gas discharge in hydrocarbon mixtures is widely used for carbon film growth. These thin films are of great interest for a wide range of industrial applications due to their extraordinary material properties. Noble gases like argon and neon are often used as main background gases for hydrocarbon mixtures as their presence changes morphology of diamond like carbon films and leads to fewer crystalline defects. In this paper the numerical study of characteristics of high frequency discharge are performed with using PIC-MCC simulation for different portions of acetylene in the mixture with argon. We consider the formation of heavy ions and radicals which are precursors for nanoparticle growth in the discharge volume. The density of electrons, positive and negative ions are found to be nonmonotonic functions of the quantity of the acetylene in the mixture. The presence of the negative ions, the density of which is comparable with electron density, weakly affects the parameters of discharge. [Preview Abstract] |
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