Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session FTP1: Poster Session I |
Hide Abstracts |
Room: Doubletree Crystal City Crystal Ballroom C, 7:30pm - 9:30pm |
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FTP1.00001: HIGH PRESSURE GLOW DISCHARGES |
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FTP1.00002: Mechanisms of Atomic Oxygen Generation and Destruction in the Effluent of an RF-Excited Atmospheric Pressure Plasma Jet (APPJ) S. Reuter, K. Niemi, V. Schulz-von der Gathen, H.F. D\"obele The aim of this study is to gain a better insight into the mechanisms of atomic oxygen generation and destruction in the effluent of an atmospheric pressure plasma jet (APPJ). The APPJ is a 13.56 MHz RF-excited atmospheric pressure plasma source operated with 2 m$^{3}$/h helium feed gas plus $\sim $1vol{\%} molecular oxygen admixture. The effluent contains very few charged particles and a high oxygen radical density in the order of 10$^{16}$ cm$^{-3}$. The space resolved ground state atomic oxygen density is measured with two-photon absorption laser induced fluorescence (TALIF) spectroscopy. Optical emission spectroscopy (OES) measurements reveal the existence of excited atomic oxygen even at 10 cm distance to the jet's nozzle. UV-OES measurements and chemical model calculations are performed to understand energy transport mechanisms into the effluent. [Preview Abstract] |
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FTP1.00003: Study of a 2.45 GHz microwave micro-plasma in air J. Gregorio, P. Synek, L.L. Alves, C. Boisse-Laporte, P. Leprince, O. Leroy, L. Teul\'e-Gay This paper studies a 2.45 GHz microwave micro-plasma source, working in air at atmospheric pressure. The discharge, similar to the one developed by Kono \textit{et al }[1], is sustained within a slit (50-200 $\mu$m wide and 1.4cm width) delimited by two metallic blades placed at one end of a microstrip line. At the other end, a movable short circuit works as an impedance matching unit. The plasma source is placed inside a microwave absorbent box. The power coupling is analyzed theoretically by using the commercial software CST Microwave Studio{\textregistered}, and experimentally by taking the ratio of the reflected to incident power, with and without plasma and for different slit sizes. A spatially resolved optical emission spectroscopy study was also realized, using the SPECAIR{\textregistered} software [2] to deduce the gas temperature $T_{g}$ along the plasma width. In general, $T_{g}$ is found between 650 and 1650 K, for 60-140W input power and 50-200 $\mu$m slit size. \newline [1] A. Kono, T. Sugiyama, T. Goto, H. Furuhashi, Y. Uchida, \textit{Jpn. J. Appl. Phys. }Vol. 40 (2001) pp. L238-L241 \newline [2] http://www.specair-radiation.net/ [Preview Abstract] |
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FTP1.00004: Electrical and Optical Measurements in an RF-Driven Micro-Discharge Source C.M.O. Mahony, T. Gans, W.G. Graham, P.D. Maguire, Z.Lj. Petrovic Microdischarge properties are distinctly different to those of larger sources, leading to potential applications such as: high density tailored plasmas, local heating, fast material processing and scale up to large area sources. Hollow cathode operation is unlikely in micro-hollow cathode devices of diameter~$\le $~100~$\mu $m$^{[1]}$ because short mean free paths inhibit pendular electron motion. Thus diameters as small as 10~$\mu $m may be required for HC operation, a critical stability challenge. We report radio frequency operation in micro-hollow cathode structures for diameters as small as 25$\mu $m. The sources are operated in argon and helium at pressures of 20 to 600 Torr and ignite readily at $\sim $20 W, operating stably at powers $<$10W. Measurements of breakdown characteristics, rf current and voltage and optical emission were recorded. A number of operating modes have been observed in these sub-100$\mu $m dimensions and OES of argon and helium discharges indicates there is less sputtering with helium. Positive dc bias has been observed in the cathode potential under rf operation, similar to that reported by Guo {\&} Hong$^{[2]}$ at a diameter of 300~$\mu $m. [1] Kushner, J. Phys. D: Appl. Phys. 38 (2005) 1633 [2]Guo {\&} Hong, Jpn. J. Appl. Phys. 42 (2003) 6598 [Preview Abstract] |
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FTP1.00005: Study of the transition between MicroHollow Cathode Discharge and MicroCathode Sustained Discharge in a 3-electrode system L.C. Pitchford, K. Makasheva, Th. Callegari, J.P. Boeuf, J. Santos Sousa, V. Puech MicroHollow Cathode Discharges (MHCDs) are known to be good sources for production of DC non-thermal plasmas at high gas pressure. Using them as a cathode in a system with third positivly biased electrode, placed at distance of about 1 cm from the MHCD, allows the ignition of a stable, larger volume plasma in the MicroCathode Sustained Discharge (MCSD). The aim of our study is to investigate the electrical properties of the discharge when it is sustained in different gases (He, Ne, Ar or O$_{2})$. The voltage-current (V-I) characteristics of the MCSD were measured for gas pressures in the range $p$~=~50~--~200~Torr, varying gas flow $Q$~=~50~--500~sccm and gas composition. The MHCD is a sandwich type, consisting of 100~$\mu $m thick molybdenum electrodes glued on each side of 500~$\mu $m thick Al$_{2}$O$_{3}$ plate, with a 800~$\mu $m diameter hole. The transition between the MHCD and MCSD, defined as the point where the third electrode collects all the electron current, is rather abrupt and depends on the operating conditions. Results from model calculations will also be presented to help clarify the phenomena occuring during the transition. [Preview Abstract] |
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FTP1.00006: Reactivity in microplasma operating at medium pressure X. Aubert, A. Pipa, J. Ropcke, D.L. Marinov, Y. Ionikh, A. Rousseau IR Tunable Diode Laser Absorption Spectroscopy (TDLAS) and UV broad band absorption spectroscopy measurements are used to detect O$_{3}$, NO and NO$_{2}$ produced by a microplasma made of a micro-hollow cathode geometry. The gas flows through the microplasma; an additional plasma plume may be ignited on the microplasma anode region using an auxiliary anode. The microplasma may be operated in continuous or self-pulsing mode [1]. The current density in the microplasma is about 3 orders of magnitude higher than in the plume and may reach 1000 A/cm$^{2 }$ in a self pulsing mode. It is shown that NO and NO$_{2}$ densities scale as a function of the specific energy (J/l). The effect of the plume ignition is to lower the production of these species. Experimental results are compared with an experimental modeling. \newline \newline [1] A. Rousseau and X. Aubert J. Phys.D~: Appl. Phys. \textbf{39} (2006) 1619--1622. [Preview Abstract] |
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FTP1.00007: Pulsed plasma bubble located in a water capillary P. Ceccato, A. Rousseau Several studies have investigated water discharges for hydroxyl radical generation and organic compound removal for water cleaning [1]. We report preliminary results concerning the generation of plasma in a water capillary and the influence of rise time, water conductivity on the plasma injected power, using electric measurement probes and on the plasma propagation, using CCD camera. The plasma may be generated directly in the water after the formation of a gas bubble due to the ohmic heating or, it can be created in an pre-injected bubble. Bubble expansion and plasma current is monitored. The plasma formation occurs at the water/plasma interface where the electric field is higher. Streamer length and initiation time lag have been measured. \newline \newline [1] A. T. Sugiartoa et al. Journal of Electrostatics 58 (2003) 135--145. [Preview Abstract] |
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FTP1.00008: Fabrication process and electrical characterization of direct current parallel micro-discharges in helium M. Mandra, R. Dussart, J.-B. Lee, M. Goeckner, T. Dufour, P. Lefaucheux, P. Ranson, L. Overzet Micro Hollow Cathode Discharges (MHCD) have been fabricated. They are round holes through 250 $\mu$m or 500 $\mu$m thick Nickel-Alumina-Nickel surfaces. The base surfaces are constructed from 7.5 X 7.5 cm alumina wafers, which are vacuum baked then coated with chromium and copper seed layers and finally patterned. Nickel film, 5-6 um thick, is then deposited on either side of the alumina wafer using the process of electroplating. Single and multi cavity micro discharges are then laser drilled with diameters ranging from 130 $\mu$m to 300 $\mu$m and spacing between the cavities ranging from 245 $\mu$m to 315 $\mu$m. Breakdown vs. pressure measurements show that smaller diameter cavities (130 $\mu$m) have higher breakdown voltages than cavities with larger diameter (300 $\mu$m). In addition, the difference between the breakdown voltage and the operating voltage is substantially larger. Current-voltage measurements for single hole MHCD devices indicates that they operate in the normal glow regime with decreasing discharge voltage as discharge current is increased. [Preview Abstract] |
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FTP1.00009: Atmospheric-pressure microgap plasma produced by 10-GHz microwave excitation A. Kono, M. Kobayashi, M. Aramaki Atmospheric pressure high-density glow discharge can be sustained continuously in the microgap (100-$\mu $m wide) between two knife-edge electrodes by microwave excitation. Detailed characterizations of a microgap plasma produced by 2.45-GHz microwave excitation were reported previously, including electron density and temperature measurements using laser Thomson scattering, gas temperature measurements under the influence of gas flow, etc. In the present study, we investigate the effect of microwave frequency on the electron density, in view of the analogy with the fact of increasing electron heating efficiency with increasing driving frequency in usual rf low-pressure capacitively coupled discharge. Preliminary studies on three different electrode configurations and microwave driving schemes indicate that the electron density do not reach that in the case of 2.45-GHz excitation, suggesting a large radiation loss of the microwave power in 10-GHz excitation. A discharge structure to reduce the radiation loss is being pursued. (Work supported by Grant-in-aid 15075205 from MEXT Japan.) [Preview Abstract] |
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FTP1.00010: Spatio-temporal development of atmospheric pressure plasma filaments: influence of surface memory effects. S. Celestin, O. Guaitella, G. Canes-Boussard, A. Rousseau, A. Bourdon It has been recently shown in a cylindrical DBD that the current amplitude distribution function shows two different peak populations during positive half periods of the 50Hz high voltage (when the metallic inner electrode is positive) [1]. The high current population is caused by the simultaneous propagation of plasma filaments, the so called collective effect. In the present study, CCD imaging is coupled to electrical measurements; we show that, in a pin to plan DBD, the spatial shape of the plasma filaments in the gas gap depends strongly on the ``history'' of the events. The first peak impacts the dielectric surface close to the center (minimum pathway from the metallic electrode) and then propagates radially on the surface. The following peaks impact the dielectric with a larger radius. The branching of the plasma filament is also highly dependant on the ``history'' and increases with the current pulse. \newline \newline [1] O. Guaitella, F. Thevenet, C. Guillard, A. Rousseau J. Phys. D~: appl. Phys (2006). [Preview Abstract] |
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FTP1.00011: Shock Wave Drag Coefficients in Argon Glow Discharge Plasma Nirmol K. Podder, Anastasia V. Tarasova, Ralph B. Wilson IV Mach 2 shock waves are launched into a weakly ionized dc glow discharge plasma. Four pairs of laser beams are setup across the plasma and spaced over the entire positive column. Laser deflections caused by the gradient in the shock wave gas density are recorded on an oscilloscope to obtain the time history of the shock wave propagation through plasma. In this way, multipoint shock wave velocities are measured over a range of operating argon gas pressure from 3-15 Torr and discharge current from 0-70 mA. The shock wave propagation velocity in plasma is seen to increase with increasing discharge current. Shock wave drag coefficients are determined from the functional dependence of the velocity on the position. [Preview Abstract] |
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FTP1.00012: Modelling gas plasma interactions in driven systems C.S. MacLachlan, D.A. Diver, H.E. Potts We explore numerically the impact of collisions in gas plasma systems and possible ways to exploit plasma chemistry in different experimental contexts. \textbf{Electron Avalanches}: We investigate the early stages of the initiation of a high pressure discharge paying particular attention to the production of excited neutral species. This highly non-equilibrium initiation is a Townsend-like avalanche created by electron impact ionisation and occurs on a sub-nanosecond timescale. Understanding this stage of the discharge could identify a technique for the non-steady production of metastables for high-activation energy chemistry without full plasma ignition. \textbf{Electronegative Instabilities}: Instabilities manifesting as variations in light emission and number density have been reported in electronegative discharges. Here electron attachment and detachment drives a radiative instability in a pre-formed RF discharge. We propose a simple model that captures the physics behind the experimental phenomena. [Preview Abstract] |
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FTP1.00013: DIELECTRIC BARRIER DISCHARGES, DISPLAYS |
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FTP1.00014: Backscattering of secondary electrons to the cathode in the oblique electric field in dielectric barrier discharge systems. Vladimir Khudik, Joel Pendery, Alexander Shvydky, Constantine Theodosiou In contrast to electric field lines in gas discharge systems with bare electrodes, electric field lines in dielectric barrier discharge systems, where the cathode is covered with the dielectric layer, may cross the dielectric surface at an oblique angle. The secondary electrons emitted from this surface either return to the cathode due to collisions with background gas atoms or eventually escape from the region near the cathode. Using the diffusion P1-approximation to the kinetic equation for electrons, we have found analytically the electron escape factor k for different limiting cases. Monte-Carlo simulations of backscattering of electrons have been performed for noble gases and the dependence of the escape factor on the angle between the electric filed lines and the dielectric surface have been found. The analytical theory has been used to explain unexpected peculiarities in results of Monte-Carlo simulations. [Preview Abstract] |
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FTP1.00015: Effects of overvolting on direct electron impact and heavy particle excitations of Ar and N$_{2}$ electronic states in a pulsed DBD Robert Leiweke, Biswa Ganguly The pressure dependence of direct electron impact and heavy particle resonant energy transfer kinetics within a pulsed- excited N$_{2}$/Ar DBD have been studied using two different pulsed applied voltage rise times ($\sim $20 ns and $\sim $150 ns) in order to measure the effects of over volting upon direct electron impact and heavy particle excitation efficiencies. The DBD was operated from 15-500 Torr, up to 8{\%} N$_{2}$, 7.75 kV total applied voltage, and 5 kHz repetition rate. Time-resolved emission spectroscopy was used to obtain the relative intensities of the N$_{2}^{+}$ (B-X), Ar$^{+}$ (4P-4D), Ar (2p$_{1}$-1s$_{2}$), N$_{2}$ (C-B) transitions which have differing excitation thresholds of $\sim $19 eV, 19 eV, 13.5 eV, and 11 eV, respectively. Absolute total Ar metastable (Ar$^{M}$, 11 eV) column densities were obtained using Diode Laser Spectroscopy. The Ar$^{M}$ column densities can be used to calibrate the relative emission intensities from the other four excited state species, once the pressure scaling for the pure argon case has been established. These reported results will show that the relative excitation efficiencies peak at different pressures depending upon both the excitation thresholds and overvolting, except for the Ar$^{M}$ + N$_{2}\to $Ar + N$_{2}$(C-B) excitation. [Preview Abstract] |
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FTP1.00016: ABSTRACT WITHDRAWN |
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FTP1.00017: PLASMA BOUNDARIES: SHEATHS, BOUNDARY, LAYERS, OTHER |
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FTP1.00018: Spatial Plasma Oscillations - Physical Phenomenon or Computational Artefact? Raoul Franklin Often when attempting to solve problems involving a bounded active plasma, the expedient is adopted of assuming plausible initial values and then integrating the full fluid equations including generation, collisions, and Poisson's equation, until the wall conditions are met. This procedure generates spatial plasma oscillations of decreasing magnitude. This paper examines a number of different cases and ranges over a wide variation of parameters. It seeks to show that such spatial oscillations arise from the approximations made. The oscillations have been the subject of interest in published papers from time to time, and thus we seek to make workers aware of these `spurious' results in electropositive plasmas. On the other hand we also give results for electronegative plasmas where it is well-established that such oscillations are expected to occur in the vicinity of the core-plasma interface. However there is as yet, so far as I am aware, no experimental evidence for their existence. [Preview Abstract] |
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FTP1.00019: Role of Secondary Electrons in Anode Sheath Gilles Cartry, Loic Schiesko, Jean-Marc Layet, Marcel Carrere We study electron attracting sheath (anode sheath) both experimentally and theoretically. Experiments are conducted in a low-pressure (0.05 and 0.1 Pa) helicon reactor. A positively biased Cu sample faces a mass and energy analyser. Plasma electrons are accelerated towards sample and ionize background gas creating Ar$^{+}$ ions. These ions in turn are accelerated towards the mass and energy analyser and are detected according to their energy. The energy at which an ion is detected corresponds to local electrical potential at which the ion has been created. Measurements show that no ion is detected with full energy. We explain this considering secondary electrons emitted from surface upon primary electron impacts. These secondary electrons are trapped by potential, accumulate near the sample, and cause a very fast potential variation close to the sample. This fast variation occurs on a too short distance to observe a significant ionization signal and consequently no ion is detected with full energy. Measurements are compared with a numerical model solving Poisson equation including secondary electrons and computing ion energy distribution. [Preview Abstract] |
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FTP1.00020: Neutral energy distribution in the cathode fall of direct-current glow discharges Tsuyohito Ito, Mark Cappelli Energetic neutrals are formed in the cathode fall of dc glow discharges through collisions with accelerated ions. These energetic neutrals contribute to secondary electron emission, electrode erosion, and discharge gas heating. In this study we describe direct measurements and Monte Carlo simulations of the energy distribution of energetic neutrals in an argon dc glow discharge. The measurements are performed by time-of-flight analysis of neutrals escaping through a cathode orifice. The experimental results are found to be in good agreement with the Monte Carlo simulations. A preliminary sensitivity of the MC simulations to angular scattering in ion-neutral collisions suggests that improved agreement can be obtained by including more complex modeling of the charge exchange collision processes. The results also indicate that commonly-used theories for the production of energetic neutrals through charge exchange in the cathode fall do not capture the neutral energy distribution over the range of discharge voltage studied. [Preview Abstract] |
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FTP1.00021: Xenon ion Laser-Induced Fluorescence using a tunable diode laser near 680nm Greg Severn, Dongsoo Lee, Noah Hershkowitz Xe ion laser-induced fluorescence (LIF) measurements in low temperature Xe II plasmas ($T_e \sim 1 eV, T_i \sim 1/40 eV$,n$_i \sim 10^9$ cm$^{-3}$) have been achieved. The transition studied involves the metastable state $(^3P_1)5d[3]_{7/2}$, at 108423.07 cm$^{-1}$. The excited states that compose this LIF scheme, which involve excitation at 680.574nm (air) and fluorescence at 492.15nm (air), have been missidentified in the past. This is due in part to the realization that the energy level structure of Xe II is somewhat better described by $jk$ coupling than by $LS$ coupling. LIF measurements of a room temperature iodine gas cell were used to monitor the wavelength of the laser during the measurements, and these are compared with the molecular iodine absorption spectrum measurements of Gerstenkorn \& Luc and of Salami and Ross. These studies have permitted measurements of the ion velocity distribution functions for both ions in a two ion species, Ar+Xe plasma, something never before accomplished, so as to make possible the first experimental test of the Generalized Bohm Criterion. [Preview Abstract] |
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FTP1.00022: NEGATIVE ION PLASMAS |
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FTP1.00023: Sheath and presheath in ion-ion plasmas via particle-in-cell simulation Albert Meige, Gary Leray, Jean-Luc Raimbault, Pascal Chabert A full particle-in-cell simulation is developed to investigate electron-free plasmas constituted of positive and negative ions under the influence of a DC bias voltage. It is shown that high-voltage sheaths following the classical Child-law sheaths form within a few $\mu s$ after the DC voltage is applied. Although a characteristic screening length can be defined in the vicinity of the electrodes, the bulk plasma does not appear to be in Boltzmann equilibrium and a Debye length would be more difficult to define. It is also shown that there exists the equivalent of a Bohm criterion with the corresponding presheath accelerating ions collected at one of the electrodes to the sound speed before entering the sheath. [Preview Abstract] |
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FTP1.00024: Production of negative ions at graphite surface in hydrogen plasmas Gilles Cartry, Loic Schiesko, Jean-Marc Layet, Marcel Carrere Production of hydrogen negative ions is of great interest for controlled fusion. Indeed neutralized beams of negative ions are used to heat plasma in fusion reactors. Up to now, negative ion sources use cesium surfaces but an important research effort is undertaken to go towards cesium free sources. Dissociative attachment on vibrationnally excited hydrogen molecules is known to be the main H$^{-}$ formation mechanism. Graphite surfaces are expected to give an important vibrationnal excitation through H recombination. Therefore graphite is a good candidate for next generation negative ion sources. In this work we show that under positive ion bombardment, a huge number of negative ions are produced on graphite surface. Our goal is to understand this unexpected negative ion production mechanism. In this aim, we put a graphite sample (HOPG) in a helicon reactor, in front of a EQP300 mass spectrometer. The sample is negatively biased with respect to plasma and negative ions energy distribution functions are recorded and analysed versus sample bias, plasma power and pressure, percentage of hydrogen in H$_{2}$-Ar mixtures. [Preview Abstract] |
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FTP1.00025: Numerical investigation on capacitively coupled chlorine discharge. Taesang Lee, Choongseock Chang PIC methods using Monte Carlo collision have been extensively used for the study of chlorine plasma. In our study we introduce a self-consistent particle model for capacitively coupled chlorine discharge which considers motions and collisions of neutral species as well as of charged particles. Chlorine discharge is highly electro-negative which requires long discharge time for steady state where the negative ion population dominates over that of electrons. Multi-scale simulation technique is developed to simulate both plasma steady state and steady state of plasma to neutral gas dynamics. Precise structure of multi-scale simulation method and preliminary results will be shown. [Preview Abstract] |
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FTP1.00026: Investigations of negative oxygen ions in pulsed rf plasmas Michael Katsch, Alexander Wagner, Michael Kr\"amer The spatial and temporal distributions of electrons and ions in ICP GEC reference cell and a large diffusion chamber connected to a helicon plasma source were investigated. The investigations were focussed on the production and loss processes of negative oxygen ions in argon-oxygen mixtures. Laser-induced photodetachment of the negative oxygen ions using of a frequency-doubled Nd:Yag laser along with a Langmuir probe was applied to detect the O$^{-}$ ions. An increase of the negative ion density in the early afterglow is found at high plasma densities in the GEC cell as well in the diffusion chamber. There is, apparently, a formation channel for negative ions that becomes efficient with reduced electron temperature. Dissociative attachment of electrons to highly excited metastable oxygen molecules are suggested as a negative oxygen ion source. Comparative measurements of the temporal behavior of the negative ions in Ar/O$_{2}$, Kr/O$_{2}$ and Ne/O$_{2}$ mixtures indicate that metastable noble gas atoms do not play an essential role in the formation process of negative ions during the afterglow. A simple global model supports the experimental results. [Preview Abstract] |
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FTP1.00027: Negative Ions and Neutral Beams in Plasma Etching Vladimir \v{S}amara, Nicholas Braithwaite, Mark Bowden A major problem in etching processes for future nanoscale devices is charge build-up due to the electron shading phenomenon. One possible solution of this problem is to use beams of energetic neutral atoms instead of positive ions in etching. The neutral beam can be produced by generating negative ions which are accelerated toward a substrate and then neutralized$^{1}$. This paper presents research aimed at diagnosing and understanding electronegative plasmas. Techniques for measuring negative ion density by laser photodetachment and electrical probes are presented together with preliminary results in SF$_{6}$ pulsed rf plasmas. The results will be compared with those from a global model$^{2}$. \newline \newline $^{1}$ S. Samukawa, Jpn. J. Appl. Phys. \textbf{45}, 2395 (2006). \newline $^{2}$ Y. T. Lee, M. A. Lieberman, A. J. Lichtenberg, F. Bose, H. Baltes, and R. Patrick, J. Vac. Sci. {\&} Tech. A \textbf{15}, 113 (1997). [Preview Abstract] |
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FTP1.00028: PLASMA INSTABILITIES |
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FTP1.00029: Influence of the cross field drift on stability of plasma systems: electrostatic and electromagnetic study Dragana Petrovic, Annemie Bogaerts A general dispersion relation is derived for the coupled electron drift-driven and kinetic Alfven modes in a strongly collisional, weakly ionized plasma that includes the effects of cross field drift, parallel dynamics and ionisation. It is shown that the kinetic Alfven mode is totally damped without cross-field electron drift. A finite electron drift decreases the influence of the collisions and results in a weaker damping of the mode, enabling its appearance in the system. However, the kinetic Alfven mode is still damped and cannot become unstable due to this electron drift. The instability of the system thus originates only from the electron-drift driven mode which is destabilized when the cross-field drift exceeds some critical threshold value. It is shown that the ionisation of neutrals, as the dominant plasma production process, destabilize the plasma system, while the electron parallel dynamics has the opposite effect. The model and equations derived in the study are valid for any partially ionised plasma comprising a substantial amount of neutral atoms. [Preview Abstract] |
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FTP1.00030: DISTRIBUTION FUNCTIONS AND TRANSPORT COEFFICIENTS: ELECTRONS, IONS |
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FTP1.00031: Non-monotonous excitation profiles in positive column of DC nitrogen discharge due to the electron distribution non-locality Eugene Bogdanov, Anatoly Kudryavtsev, Semen Popugaev, Lev Tsendin Because of the presence of very different energy scales caused by elastic collisions, excitation of vibrational and electronic states, the nonlocal character of the electron distribution function (EDF) manifests itself in various ways in its different parts. As different parts of EDF have different electron energy relaxation lengths, surprising phenomena were revealed in [L. D. Tsendin, E. A. Bogdanov, A. A. Kudryavtsev. Phys. Rev. Lett., v.94, 015001, 2005] for DC positive column (PC) plasmas in atomic gases: the peaks of the profiles of the excitation rates shift from the discharge axis toward the periphery as the pressure increases. In this report we present the results of kinetic simulations of PC in molecular nitrogen in different pressures and analyze radial distributions of plasma parameters for different conditions. We have found that non-monotonic distributions exist not only for electronic states, but also for vibrational levels. The work was supported by the RFBR grant N 06-02-17317. [Preview Abstract] |
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FTP1.00032: Effect of H$_{2}$ and N$_{2}$ Impurities in Argon on the Kinetics of Electrons Nuno Pinhao, Mario Pinheiro, Zoltan Donko The presence of small amounts of gas impurities in argon glow discharges used for optical emission spectrometry (GDOES) has strong implications on the accurate calibration of GDOES. To circumvent these difficulties, the intentional admixture of controlled amounts of H$_{2}$ or N$_{2}$ to argon has been practiced [1]. The understanding of the electron kinetics in these mixtures is valuable for the characterization and calibration of the cell. In this work the electron velocity distribution function, rate coefficients and transport parameters are computed in Ar + xH$_{2}$ and Ar + xN$_{2}$ mixtures, with 0{\%} $\le $ x $\le $ 10{\%}, for pulsed Townsend discharge conditions. Different computational techniques are used: a classical two-term expansion, a modified finite elements method applied to the density gradients representation, and a Monte Carlo simulation at the same discharge conditions. Two different set of cross sections for H$_{2}$ are used [2,3], allowing a comparison between them. \newline [1] Hodoroaba \textit{et al.} J. Anal. At. Spectrom. 18, 521 (2003) \newline [2] [http://jilawww.colorado.edu/$\sim $avp] \newline [3] Loureiro \textit{et al.} J. Phys. D: Appl. Phys. \textbf{22} 1680 (1989) [Preview Abstract] |
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FTP1.00033: HEAVY PARTICLE INTERACTIONS: ION-ATOM, ION-MOLECULE, NEUTRAL-NEUTRAL, OTHER |
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FTP1.00034: Double Ionization of Helium by Fast Proton Impact Matthew Foster, James Colgan, Mitch Pindzola We present total cross sections for single and double ionization of helium by various charged ion impact. A non-perturbative time-dependent close-coupling method (TDCC) has been developed to treat the correlated dynamics of ionized electrons by bare-ion impact. The two-electron helium wavefunction is subject to a time-dependent projectile interaction. The projectile-atom interaction is constructed as a multipole expansion that includes monopole, dipole, quadrupole, and octopole terms. For proton, antiproton, and alpha particle impact, good agreement is obtained between our calculations and experimental measurements of total single and double ionization cross sections. We will also report on our progress in using the TDCC method to extract differential cross sections for double ionization by fast protons. [Preview Abstract] |
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FTP1.00035: DISSOCIATION, RECOMBINATION, AND ATTACHMENT |
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FTP1.00036: A pulsed nitrogen discharge: A global (volume averaged) model study E.G. Thorsteinsson, J.T. Gudmundsson A time dependent global (volume averaged) model is applied to study a pulsed low pressure (1 - 100 mTorr) high density nitrogen discharge. The electron density, electron temperature and the density of ions and neutral species is evaluated for various discharge pressures, pulse frequencies and duty cycles. In particular the dissociation of the nitrogen molecule and the role of metastable nitrogen molecules N$_2$(A) and metastable nitrogen atoms N($^2$D) and N($^2$P) is explored. The density of the metastable nitrogen atoms N($^2$D) and N($^2$P) is found to be significant. Furthermore, we explore how the neutral/ion flux ratio $\Gamma_{\mathrm{N}}/\Gamma_+$ varies with duty cycle and pulse frequency. [Preview Abstract] |
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FTP1.00037: COMPUTATIONAL METHODS FOR PLASMAS |
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FTP1.00038: 2D Electromagnetic and hydrodynamic models of a microwave plasma torch R. Alvarez, L. Marques, L.L. Alves This work reports simulation results for a microwave (2.45 GHz) plasma reactor, operated by an axial injection torch (TIA). The study is based on a two-dimensional electromagnetic (EM) and hydrodynamic description of the TIA-reactor system. The EM model [1] solves Maxwell's equations, yielding the distribution of the EM fields and the averaged power absorbed, for a given spatial profile of the plasma density (with maximum values in the range 10$^{14}-$10$^{15}$ cm$^{-3}$, according to experimental measurements). Perfect-conductor boundary conditions are satisfied at the reactor walls, and absorbing boundary conditions are used at the open-end of the coaxial waveguide powering the system. The hydrodynamic model solves the Navier-Stokes equations for the flowing neutral gas, yielding the distribution of mass density, pressure and velocities. The input surface (about 1{\%} of the output surface) has a radius of 0,5mm. The boundary conditions impose the input gas flow ($\sim $1000 sccm), the output gas pressure (atmospheric pressure) and no-slip conditions at reactor walls. Simulations are used to provide general guidelines for device optimisation. \newline [1] R. \'{A}lvarez, L.L. Alves, J. Appl. Phys. 101, 103303 (2007) [Preview Abstract] |
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FTP1.00039: $H_{\alpha}$ emission in pure hydrogen Townsend discharge obtained by a Monte Carlo simulation Vladimir Stojanovic, Zeljka Nikitovic, Zoran Petrovic We calculated $H_{\alpha}$ emission profiles from Townsend discharges in pure hydrogen between two parallel electrodes focusing on details of heavy particle interaction with the cathode surface. The basic data were provided by A. Phelps [1]. Monte Carlo simulation technique employing null collision method was used to follow electrons and heavy particles between collisions with $H_2$ or with surface for the conditions of a high electric field $(E)$ to gas density $(N)$ ratios $E/N$. Trajectories of reaction fragments are followed after the collision until their neutralization or thermalization down to the threshold of $H_{\alpha}$ excitation. For the conditions of Phelps and Petrovi\'{c}'s experiment [2], we obtained spatially resolved emission profiles and Doppler broadened line profiles. Intensity of Doppler profile wing showing $H_{\alpha}$ emission of particles emerging from the cathode direction is obtained assuming that the reflection coefficient of fast H atoms depends on the incident angle and on energy of the incident particle. Some effects of collision dynamic of heavy particles with $H_2$ on Doppler broadened profile are discussed. \newline [1] A.V. Phelps to be published. \newline [2] Z.Lj. Petrovi\'{c} and A.V. Phelps to be published. [Preview Abstract] |
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FTP1.00040: Computational Methods in Plasma Nanoscience Eugene Tam, Amanda Rider, Igor Levchenko, Kostya (Ken) Ostrikov Ion-assisted techniques have been shown in the past to be superior in processing dense arrays of vertically aligned nanostructures to their neutral specie counterparts [1,2]. However, predicting the final outcomes is difficult and requires precise knowledge of the plasma and substrate parameters required. Here, the dynamics of ion-assisted deposition of various ion species onto two-dimensional nanostructure arrays are simulated using a variety of numerical tools including multi-scale hybrid numerical simulations. We have found that important factors in post-processing nanostructures include the plasma sheath width, the aspect ratio of the pre-patterned structures and the density of the array. We also show how increasing the level of complexity of the model, for example, including the effects of multiple species which may exhibit different behaviors, affects the simulation results. The results of this work are generic and can be applied to a broader range of nanostructures and materials. Computational investigations such as these are directly relevant and crucial to the development of deterministic strategies towards precise and cost-efficient plasma-aided nanofabrication. [1] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2005) [2] E. Tam et al, Phys. Plasmas. 14, 033503 (2007) [Preview Abstract] |
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FTP1.00041: PLASMAKIN: A chemical kinetics library for plasma physics modeling Nuno Pinhao PLASMAKIN is a package to handle physical and chemical data used in plasma physics modeling and to compute kinetics data from the reactions taking place in the gas or at the surfaces: particle production and loss rates, photon spectra and energy exchange rates. It has no limits on the number of species and reactions that can be handled, is independent of problem dimensions and can be used in both steady-state and time-dependent problems. A broad range of species properties and reaction types are supported: gas or electron temperature dependent rate coefficients, vibrational and cascade levels, branching ratios, superelastic and other reverse processes, three-body collisions, radiation imprisonment and photoelectric emission. Non-standard rate coefficient functions can be handled by a user-supplied shared library. Reaction data is supplied in text files and is independent of the user's program. Recent additions include the simulation of emission spectra taking line broadening into account; reactions with excited ionic species; 3-body reactions with species with different efficiencies as 3rd body; a species properties database and a Python interface for rapid scripting and debugging. [Preview Abstract] |
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FTP1.00042: CAPACITIVELY COUPLED PLASMAS |
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FTP1.00043: Modes of low-pressure longitudinal combined discharge Valeriy Lisovskiy, Nadiia Kharchenko, Vladimir Yegorenkov We studied in experiment the longitudinal combined (RF/DC) discharges. We applied across the electrodes the RF voltage and additionally DC voltage Udc simultaneously. Experiments were performed at the nitrogen pressure of p=0.01--5 Torr within the range of amplitude values of the RF voltage Urf $<$ 2000 V, DC voltage Udc $<$ 600V and f=13.56 MHz. The combined RF/DC discharges might exist in three modes. At low RF voltages the additional DC voltage makes a small contribution to the ionization rate of gas molecules within the plasma volume, and we observe the first mode of the combined RF/DC discharge -- ``non self-sustained RF discharge perturbed by the DC voltage''. When the RF voltage and the DC voltage are sufficiently large to induce the breakdown of the ``cathode'' layer, the discharge experiences the transition to the second mode -- ``combined discharge''. Just this mode is of considerable interest for plasma technology. The third mode may be obtained applying a small RF voltage to the burning DC discharge. We will call it conditionally ``non self-sustained DC discharge perturbed by the RF voltage''. [Preview Abstract] |
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FTP1.00044: A global model of a dual frequency capacitive discharge considering the nonlinearity of the sheath and a bulk-chemistry Philipp Mertmann, Thomas Mussenbrock, Ralf Peter Brinkmann, Peter Awakowicz A global model of a capacitive coupled low pressure plasma which considers the nonlinear behavior of a boundary sheath and a bulk chemistry, excited by two frequencies is developed. On the basis of certain assumptions the global model for the plasma bulk is derived. The bulk model, which can be solved for its own, is combined with a sheath model to get a self-consistent global model. By that, not the bulk power but the radio frequency voltages over the whole discharge are input parameters of the model, which is close to the experiment. Results for different voltages of the two frequencies and a variation of the pressure are presented. [Preview Abstract] |
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FTP1.00045: Effect of the driving frequency on a VHF capacitively coupled plasma Hiroyuki Takahashi, Takashi Yagisawa, Toshiaki Makabe In the next-generation ULSI process, a capacitively coupled VHF (UHF) plasma will be employed in order to obtain higher plasma density with large size of electrodes ($\sim $ m). Then the system will be subject to the strong electromagnetic effect, such as a standing wave and a skin effect. The effect of the standing wave causes nonuniformity along the radial direction to the capacitively coupled plasma (CCP), when the size of the electrode is comparable to the wavelength of the VHF(UHF) voltage source on the electrode. In the present study, nonuniformity of the potential distribution is numerically investigated on a large electrode in the VHF-CCP in Ar in the cylindrical coordinate system ($r$, $z$) by using the combination between the transmission line model (TLM) and the relaxation continuum (RCT) model. The influence of potential nonuniformity on the plasma structure will be discussed in detail. [Preview Abstract] |
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FTP1.00046: Analytical Model for Self-Excited Plasma Series Resonances. Uwe Czarnetzki, Julian Schulze, Brian Heil, Dirk Luggenhoelscher Self-excited plasma series resonances are observed in CCP discharges as high frequency oscillations superimposed on the normal RF current. This high-frequency contribution is generated by the interaction between the capacitive sheath and the inductive (due to inertia) and ohmic bulk. The non-linearity of the sheath is essential for the whole effect. In a previous work we have described the effect in the frame of a simple one-dimensional model [1]. It could be shown that at low pressures common in etching applications, PSR can play an important role for both, the actual current waveform and the power transferred to electrons. Here the model is extended to include electron temperature and electrode area ratio effects. Both effects can lead to a reduction of the high-frequency amplitude but have no effect on the frequency itself that is within reasonable limits approximately given by $\omega _{PSR} \quad \approx $ 2/3 (s/L)$^{1/2}$ $\omega _{pe}$, where s is the maximum sheath extension, L the characteristic length of the plasma bulk and $\omega _{pe}$ the electron plasma frequency. The derived analytical approximations agree well with numerical solutions of the model. First comparisons with experiment and a fluid-dynamic simulation including an extensive sheath model also show excellent agreement. [1] U. Czarnetzki, T. Mussenbrock, and R.P. Brinkmann, Phys. Plasmas 13, 123503 (2006) [Preview Abstract] |
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FTP1.00047: Comparison between measured and simulated breakdown characteristics in micro discharges in argon Zoran Petrovic, Marija Radmilovic-Radjenovic, Paul Maguire, Charles Mahony, Nikola Skoro, Dragana Maric Devices with micron and sub-micron gaps can face a serious challenge due to electrical breakdown during manufacturing, handling and operation. Therefore, it is necessary to be aware of the breakdown voltage for different gaps. Gas breakdown and Volt-Ampere characteristics are studied in an atmospheric pressure argon discharges. Experimental results are compared with the results obtained by using PIC/MCC code in order to establish whether the standard micro discharges operate in Townsend regime or in Glow Regime. The code is adjusted to include field emission effect in microgaps. It is applied manly for the breakdown stage but may also follow the formation of the space charge. The measurements of Volt-Ampere and breakdown characteristics of micro discharges were performed down to 20\,$\mu$m gaps at pressures up to 400\,Torr. Paschen curves reveal that very tight geometry is required to avoid long path breakdown at the left hand side of the Paschen curve. It is critical to measure width of the discharge to test the scaling and regime of operation of micro discharges. [Preview Abstract] |
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FTP1.00048: Harmonics excitation in capacitive rf discharges: A spatially resolved nonlinear model Dennis Ziegler, Martin Lapke, Thomas Mussenbrock, Ralf Peter Brinkmann The excitation of harmonics in capacitively coupled plasmas is a phenomenon that arises from an interaction between the linear behavior of the plasma bulk and the nonlinear behavior of the plasma sheath. Recent research has investigated the phenomenon by studying models which couple either a global or a spatially resolved description of the bulk to sheath models where the charge-voltage relation $V=V(Q)$ was approximated as a quadratic form with constant coefficients.\footnote{T. Mussenbrock, D. Ziegler, and R.P. Brinkmann, Phys. Plasmas {\bf 13}, 083501 (2006).}$^{,}$\footnote{T. Mussenbrock and R.P. Brinkmann, Plasma Sources Sci. Technol. {\bf 16}, 377 (2007).} In this contribution, we improve the model by replacing that quadratic form with a more realistic charge voltage relation that is calculated on the basis of a self-consistent sheath model. [Preview Abstract] |
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FTP1.00049: Nonlinear electron resonance heating vs. the Herlofson paradox Jens Oberrath, Martin Lapke, Dennis Ziegler, Thomas Mussenbrock, Ralf Peter Brinkmann In the regime of low gas pressure, capacitive rf discharges exhibit resonant behavior which can have a profound impact on the energy budget. This contribution compares two scenarios of resonance-related electron heating known as, respectively, ``nonlinear electron resonance heating'' (NERH) and ``the Herlofson paradox''. NERH arises from the self-excitation of the plasma series resonance by harmonics generated via the nonlinearity of the plasma sheath. $^{1}$ The Herlofson paradox, on the other hand, is a linear phenomenon that occurs at points where the electron plasma frequency is locally equal to the rf frequency. $^{2,3,4}$ This contribution intended to point out similarities and differences of the two scenarios. $^1$ T. Mussenbrock and R.P. Brinkmann, Appl. Phys. Lett. {\bf 88}, 151503 (2006), $^2$ F.W. Crawford and K.J. Harker, J. Plasma Phys. {\bf 8}, 261 (1972), $^2$ V.P.T. Ku, B.M. Annaratone, and J.E. Allen, J. Appl. Phys {\bf 84}, 6536 (1998), $^3$ V.P.T. Ku, B.M. Annaratone, and J.E. Allen, J. Appl. Phys {\bf 84}, 6546 (1998), $^4$ F.W. Crawford and K.J. Harker, J. Plasma Phys. {\bf 8}, 261 (1972). [Preview Abstract] |
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FTP1.00050: The nonlinear characteristic of the plasma boundary sheath: Results from a self-consistent model Mustafa Bayrak, Dennis Ziegler, Thomas Mussenbrock, Ralf Peter Brinkmann The phase-resolved voltage drop across an rf modulated plasma boundary sheath is calculated on the basis of a self-consistent fluid model. The situation is described in terms of a nonlinear charge voltage relation $V(t)=V(Q(t))$, where $Q(t)$ is the instantaneous charge of the sheath. It is found that the form of the curve $V(Q)$ is approximately quadratic. The coefficients of that form, however, are not constant but strongly dependent on the amplitude of the modulation itself. An effective model is constructed which captures this behavior in terms of simple algebraic formulas, and which may be used for a consistent analysis of the nonlinear behavior of capacitively coupled plasmas as a whole. [Preview Abstract] |
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FTP1.00051: Plasma ionisation in the low pressure operating regime of capacitively coupled radio-frequency plasmas D. O'Connell, A. Meige, T. Gans, E. Semmler, P. Awakowicz, R. Boswell Fundamental plasma sustaining mechanisms in the low pressure operation regime of a single frequency capacitively coupled plasma are investigated with radio-frequency (rf) excitation at 2 MHz. Both hydrogen and rare gas discharges are explored. The discharge is operated at relatively low voltages to prevent plasma sustainment through secondary electron emission. Two pronounced ionisation mechanisms are observed; one as the retreating sheath approaches the electrode and a second as the advancing sheath expands towards the plasma bulk. The ionisation during the phase of the retreating sheath dominates in the low pressure operation limit (approx. 1 Pa) of all investigated gases. This mechanism is caused by an electric field accelerating electrons towards the electrode. It is believed that the electric field builds up due to inertia preventing electrons following the rapidly retreating sheath over the relatively large sheath width of a few centimetres correlated to the very low plasma density. In the case of rare gases ionisation during the sheath expansion phase becomes more important with increasing pressure and dominates above 5 Pa. Funding: SFB 591, ProInno II, GRK 1051, EPSRC. [Preview Abstract] |
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FTP1.00052: Computational Study of the Dual Frequency Capacitive Discharge Selma Cetiner, Seth Veitzer, Peter Stoltz Capacitively coupled radio frequency discharges have many applications including the plasma processing of microelectronic devices, where sputtering, plasma deposition, etching and other surface treatments are utilized. The primary factors that influence many of these processes are the ion energy and flux impinging the target material. Dual frequency discharges generate much interest due to their ability to control these elements independently. The high frequency voltage controls the ion flux through its influence on the electron energy which determines the plasma generation rate by electron impact ionization while the low frequency component determines the average ion impact energy. An investigation of the discharge using kinetic particle-in-cell simulations generated by VORPAL is presented. VORPAL is a plasma simulation framework developed at the University of Colorado at Boulder and Tech-X corporation. Its capabilities include one, two or three dimensions, a choice of kinetic, fluid of hybrid models and the ability to run in serial or parallel. [Preview Abstract] |
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FTP1.00053: A hybrid, one-dimensional simulation for studying electron kinetics and electron heating by the RF plasma boundary sheath B.G. Heil, J. Schulze, D. Luggenh\"olscher, U. Czarnetzki, T. Mussenbrock, R.P. Brinkmann A one-dimensional, hybrid, simulation has been developed for investigating electron kinetics and electron heating due to the capacitive sheath of Radio-Frequency (RF) discharges. The simulation calculates the time dependent electric field due to displacement current in the sheath region and the electric field due to conduction current throughout the entire discharge. It includes a simple bulk model and an equivalent electrical model. These elements are combined into a Monte-Carlo simulation which calculates the time resolved Electron Distribution Function (EDF). The model shows excellent agreement when compared against electric fields measured using Fluorescence Dip Spectroscopy (FDS), and when phase resolved plasma emissions are compared against emissions calculated using EDFs from the Monte-Carlo simulation. The simulation shows beams of electrons that have been accelerated by the plasma sheath travelling through the discharge. This supports the hypothesis that the stochastic heating of electrons is similar to Fermi heating. However this model calculates realistic electric fields instead of using the common step or hard wall model of the sheath. \\Supported by the DFG through: SFB591 and GK1051, and Andor Technology. [Preview Abstract] |
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