Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session MWP1: Poster Session II |
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Room: Doubletree Crystal City Crystal Ballroom C, 4:00pm - 6:00pm |
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MWP1.00001: OPTICAL EMISSION |
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MWP1.00002: Models of H$\alpha$ Doppler profiles from a hydrogen-filled drift tube at high E/N A.V. Phelps Doppler profiles are calculated for the H$\alpha$ line excited in collisions of fast atoms, ions, molecules, and electrons with H$_2$ in a low-current, uniform-electric-field drift tube at high E/N, where E is the electric field and N is the gas density. Starting with a multi-beam model of the particle fluxes and energy distributions and assumed angular distributions of particles approaching and reflected by the cathode, we calculate the velocity distributions of excited atoms relative to an observer. Spectral profiles are compared with measurements parallel to the tube axis, e.g., for $E/N = 10$ kTd (1 Td $= 10^{-21}$ V m$^2$) at 0.15 Torr and 4 cm electrode separation.\footnote{Z. Lj. Petrovi\'c, B. M. Jelenkovi\'c and A. V. Phelps, Phys. Rev. Lett. {\bf 68}, 325 (1992).} Spectrally integrated intensity measurements are normalized to electron excitation data at low $E/N$. Excitation is principally by fast H + H$_2$ $\rightarrow$ fast H(n=3) + H$_2$. The calculated magnitude, high degree of profile asymmetry, large change in emission by reflected atoms with cathode material, and change in integrated intensity with E/N agree well with experiment. Predictions are made for observations perpendicular to the tube axis and for a simplified cathode fall model. [Preview Abstract] |
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MWP1.00003: Hydrogen Balmer-Line Broadening in a Water-Vapor Microwave Plasma Source Elena Tatarova, Francisco Dias, Boris Gordiets, Carlos Ferreira Emission spectroscopy was used for the diagnostic of a large-scale, slot-antenna excited microwave (2.45 GHz) plasma source operating in water vapor at low-pressures (1 mbar). The Doppler temperatures corresponding to the broadening of the $H_\beta $ line at 486.1~nm are in the range 2,500-3,000 K, and much higher than the rotational temperatures ($\sim $500 K) determined from the Q-branch (in the wavelength range 600-610~nm ) of the Fulcher-$\alpha $ band [$d^2\Pi _u (v=0)\to a^3\Sigma _g^+ (v=0)$]. Kinetic considerations demonstrate that the electron-ion and ion-ion recombination processes, respectively $H_3 O^++e\to H_2 O+H_{hot}^\ast +\Delta E_1 $ and $H_3 O^++OH^-\to H_2 O+H_2 +O_{hot}^\ast +\Delta E_2 $ can be the source of ``hot'' hydrogen and oxygen atoms provided H$_{3}$O$^{+}$ is the main positive ion in the water plasma. ``Hot'' atoms were also detected in the far remote plasma zone of the source up to 30 cm away from the slot-antennas. Acknowledgment: This study was funded by FCT/FEDER in the framework of the project ``Ecological Plasma Engineering Laboratory'' POCI/FIS/61679/2004. [Preview Abstract] |
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MWP1.00004: H$_{\alpha}$ and H$_{\beta}$ Line Broadening in Microplasma Jet at Atmospheric Pressure Jayr Amorim, Jorge Souza Corr\^ea, Carlos Oliveira, Bogos Sismanoglu, Marcelo Gomes Microplasma jets of argon/hydrogen mixture were generated by radio-frequency waves at 144 MHz with powers ranging from 5W to 50W. Microjets with length of 15.0 mm were created at atmospheric pressure. Electrons and ions present in the plasma may induce broadening of Balmer lines due to Stark effect. This effect is the most important one in the H$_{\beta}$ line broadening, although contribution from Resonance and Doppler effects should be taken into account. Through the analysis of H$_{\beta}$ line the electron density was measured as a function of power and position in the jet. Broadening of H$_{\alpha}$ line may be mainly due to Doppler, Resonance and Stark effects. Through a careful analysis the influence of each one was evaluated, as a function of electron density and gas temperature in order to estimate the atomic temperature. Analyzing the fine structure splitting of H$_{\alpha}$ line, the H atom temperature at nozzle jet exit was around 23000 K in the Ar/H$_{2}$ micro plasma at atmospheric pressure. [Preview Abstract] |
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MWP1.00005: Dependence of the emission intensities with the flow in pulsed $N_2$ dc discharges Lucio Isola, Bernardo J.A. Gomez, Jorge N. Feugeas, Vasco Guerra This work presents an experimental investigation of the behavior of the emission bands of the first negative and second positive systems of nitrogen in the negative glow of a pulsed dc discharge. The discharge current, applied voltage and gas temperature were measured as well. The experiments were carried out at a fixed cathode temperature equal to 705 $^{\circ}$K, the pressure was varied between 2.6 and 3.4 Torr, whereas the gas flow was in the range 30-100 ml/min. At constant pressure, the emission intensities pass through a minimum as the gas flow increases. On the other hand, at fixed gas flow all the emissions decrease as the pressure increases. It is shown that the increase in the flow contributes to a departure from quasi- neutrality conditions in the negative glow. Moreover, a decrease in the ionization degree with pressure is observed, as expected. [Preview Abstract] |
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MWP1.00006: Doppler broadening of atomic-hydrogen lines in DC and capacitively coupled RF plasmas Kamran Akhtar, J.E. Scharer, R.L. Mills The extraordinary broadening of Balmer lines of hydrogen admixed with Ar or He as opposed to Xe in DC glow and capacitively coupled rf discharges is studied over a wide range of pressure and gas compositions. High-resolution optical emission spectroscopy is performed parallel to (end-on) and perpendicular (side-on) to the electrode axis along with Langmuir probe measurements of plasma density and electron temperature for the RF capacitive discharge case. A broad and symmetric (Gaussian) Balmer emission line corresponding to 20-60 eV hydrogen atom temperatures is observed in Ar/H$_{2}$ and He/H$_{2}$ plasmas. Energy is transferred selectively to hydrogen atoms whereas the atoms of admixed He and Ar gases remain cold ($<$0.5 eV). In the field acceleration model [e.g., Cvetanovic et. al. J. App. Phys., Vol. 97, 033302-1, 2005] there apparently is no preferred species to which energy is coupled and according to the model one should observe enhanced temperatures of hydrogen and helium atoms in He/H$_{2}$ discharges where the atomic mass is more comparable (4:1). We also briefly examine the experimental results using the Resonance Transfer Model of hydrogen heating [Mills et. al \textit{IEEE Trans. Plasma Sci., }31, 338, 2003] as the source of broadening. [Preview Abstract] |
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MWP1.00007: Doppler broadening of atomic-hydrogen lines in low E-field plasmas R.L. Mills, Kamran Akhtar, J. He, M. Nansteel, B. Dhandapani, Z. Chang, W. Good, Y. Lu Substantial broadening of the H$_{\alpha}$ lines of hydrogen admixed with preionized atoms is observed in filament heated and inductively coupled plasmas where the applied electric field is quite low. These filament heated hydrogen plasmas forms at low temperatures (e.g.) and low field strength ($\sim $1-2 V/cm) when argon and strontium were present with atomic hydrogen, exhibit H$_{\alpha}$ line broadening ($\sim $24 eV). H$_{\alpha }$ line broadening (20-24 eV) is also observed in inductively coupled plasma where the voltage drop across the plasma sheath is small. Moreover, the selective transfer of energy to H atom and the absence of comparable hot helium atoms ($<$0.5 eV) where the atomic mass ratio is 4:1 along with the absence of hot H atoms in Xe/H$_{2}$ plasmas are also inconsistent with the field acceleration model [e.g., Cvetanovic et. al. J. App. Phys., 97, 033302-1, 2005]. Plasma diagnostics include high-resolution optical emission spectroscopy, Langmuir probe and millimeter wave interferometeric measurements. The model of an energetic chemical reaction of hydrogen [Mills et. al \textit{IEEE Trans. Plasma Sci., }31, 338, 2003] as the source of broadening can explain the observation that certain plasmas exhibit the selective extraordinary broadening. [Preview Abstract] |
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MWP1.00008: Modeling of Electronegative Discharges Derek D. Monahan, Miles M. Turner Modeling electronegative discharges has been a persistently contentious topic for several years past. In this paper, we show results from an extensive simulation survey of electronegative discharges, spanning a wide range of collisionality, electronegativity and negative ion destruction mechanism. We further consider how these simulation results are best represented by simple zero-dimensional formulations with the character of global models. Various transport models have been proposed for these conditions. We show that one of the simplest such models is mostly adequate, and indeed that considerations such as the form of the electron energy distribution function, and other factors usually neglected, such as the negative ion temperature, are usually more significant that the details of the transport model. [Preview Abstract] |
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MWP1.00009: Modeling and simulation of electromagnetic effects in capacitive discharges Michael Lieberman We present a self-consistent two-dimensional axisymmetric model and simulation strategy for predicting radial plasma uniformity in large-area high-frequency capacitive discharges. The model couples Maxwell equations, fluid plasma equations and a sheath model with stochastic heating effects taken into account, solving the equation using the finite element method (FEM). Electromagnetic effects (e.g. standing wave and skin effects) as well as the electrostatic edge effect appear in our simulation, whose results are in agreement with recent experiments. The model highlights differences between the edge effect and the skin effect, both of which can cause strong plasma production near the radial reactor edge. At higher frequencies and high pressures, we observed the `stop band' where waves are highly damped as they propagate from the discharge edge into the center. The model enables an investigation into the transition from global-to-local power deposition as the pressure varies. The use of a FEM-based simulation allows for treatments of irregular geometries, as well as the addition of equations describing fluid flow, heat and mass transfer, and chemical kinetics, although we do not include these effects here. [Preview Abstract] |
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MWP1.00010: Microwave gas breakdown instabilities in the presence of external magnetic field Mohammad Ghorbanalilu, Babak Shokri The electron distribution function (EDF) formed in the interaction of high-frequency microwave (MW) pulsed fields with a rarefied neutral gas is obtained in the presence of the static magnetic field. It is expected that this system undergoes the various instabilities because of the anisotropic structure of the EDF. Making use of the EDF the dielectric permittivity tensor is derived and the general dispersion relation is found in the adiabatic approximation. Analyzing the dispersion relation in the weakly and strongly magnetized regimes for propagation along and across the magnetic field it is shown that the plasma is unstable in the both regimes. [Preview Abstract] |
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MWP1.00011: Low-pressure breakdown in fluorocarbon gases Dragana Mari\'c, Nikola \v{S}koro, Gordana Malovi\'c, Marija Radmilovi\'c-Radjenovi\'c, Zoran Petrovi\'c Fluorocarbon plasmas are typically considered for applications in plasma etching and therefore systems operating in rf fields are studied. However, one needs a lot of information from the basic dc discharges and gas breakdown in order to understand and test the kinetics of secondary electron production at electrodes and to describe the non-local electron kinetics in the cathode fall. We will present experimental and modelling results of breakdown and low current discharge properties obtained for fluorocarbons CHClF$_2$, CF$_4$ and CF$_4$-Ar mixtures, in the range of pressures from 100~mTorr to 1~Torr. Experimental measurements in the pulsed mode of operation were used to obtain the basic experimental data especially the spatio-temporal profiles of emission obtained by using ICCD. Particle in cell (PIC) code which includes proper description of secondary electron yield [1] was used to obtain the theoretical data and properties of low current discharges. In addition, we have used a standard Monte Carlo Code [2] to study the the non-hydrodynamic region close to the cathode and also the effective electron multiplication coefficients. [1] Radmilovi\'c-Radjenovi\'c, J.~K.~Lee, F.~Iza and G.~Y.~Park, \textit{J. Phys.} D, \textbf{38} (2005) 950. [2] G.~Malovi\'c, A.~Strini\'c, S.~\v{Z}ivanov, D.~Mari\'c and Z.~\mbox{Lj.} Petrovi\'c, \textit{Plasma Sources Sci. Technol.} \textbf{12} (2003) S1. [Preview Abstract] |
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MWP1.00012: PLASMA APPLICATIONS FOR NANOTECHNOLOGY |
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MWP1.00013: Plasma-grown high-surface-coverage nanoislanded Ni Catalyst Films for Dense Nanotube Arrays Amanda Rider, Kevin Chan, Igor Levchenko, Kostya (Ken) Ostrikov Dense carbon nanotube (CNT) arrays are usually grown on surfaces covered with islanded films of Ni, Co or Fe catalyst particles. Adsorbed atoms diffusing about the substrate surface penetrate through the catalyst and form a CNT on the Ni surface. Thus, parameters of the catalyst particles (density and size, distribution function and spatial location) directly determine the characteristics of the final CNT forest. Processes such as self-assembly and island transformations can't be modeled without calculating the real adatom concentration field (ACF). Dissolution of an island can initiate abrupt rearrangement of the ACF resulting in a significant change in rate of growth of the neighboring islands. Displacement of island may lead to the same effect. Some successful attempts at modeling surface phenomena such as island shape transformation are known. In our work we model dissolution, displacement and coalescence of the islands. Our approach is based on direct calculation of the adatom concentration field on the surface. Our simulation results can be used to control and optimize the density, size and distribution of CNT nucleation sites, a critical but yet unresolved issue of nanofabrication [1]. \newline [1] K. Ostrikov, IEEE Tran. Plasma Sci. 35, 127 (2007) [Preview Abstract] |
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MWP1.00014: Effect of Atomic Hydrogen and Ions on Carbon Nanotube Growth in PECVD Kostya (Ken) Ostrikov, Igor Denysenko A surface diffusion model for multi-wall carbon nanotube (MWCNT) growth in plasma-enhanced chemical vapor deposition (PECVD) is developed. It is assumed that growth is due to deposition of hydrocarbon (HC) molecules, ions and an etching gas (atomic hydrogen) from plasma. The model accounts for reactions of HC neutrals and carbon atoms with an etching gas, decomposition of absorbed particles due to ion bombardment, decomposition of HC ions on MWCNT surface, thermal decomposition of HC neutrals on MWCNT surface, in addition to the film growth between MWCNTs, etching of the film and carbon sputtering. Using the model, MWCNT growth rates are calculated for different substrate temperatures and HC, hydrogen and ion fluxes on the substrate. It is shown that at low substrate temperature the MWCNT growth is mainly due to reactions of ions with HC neutrals and the decomposition of HC ions on the MWCNT surface. Meanwhile, at large ion and low hydrogen fluxes on the substrate the film growth between MWCNTs can dominate over the MWCNT growth. The model reveals that the growth rate is dependant on substrate temperature which has a maximum (T$_{max})$ that agrees well with experimental data on MWNT growth. T$_{max}$ increases with an increase of the hydrogen atom flux, the ion and HC fluxes. [1] K.Ostrikov, A. B. Murphy, J. Phys. D:Appl. Phys. 40, 2223 (2007) [Preview Abstract] |
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MWP1.00015: Modeling of plasma-assisted fabrication of polymer-nanotube photovoltaic solar cells Igor Levchenko, Kostya (Ken) Ostrikov, Amanda Rider, Eugene Tam Given the increasing interest in renewable energy, photovoltaic devices are of great significance. Intensive research efforts are centred on finding a cost-effective, powerful solar cell. One possible solution is polymer/nanotube (CNT)-based solar cells. These devices possess promising characteristics, yet their method of production is intricate and unreliable. Traditionally, CNTs are produced by arc discharges, this is followed by a number of complex manual manipulations to create a dense, perfectly aligned CNT array in a polymer matrix. Here, we present a numerical simulation of polymer/nanotube photovoltaic cell production. Production of a composite nanotube-based solar cell by a single continuous process involving fabrication of ordered arrays of self-assembled single-walled carbon nanotubes, their treatment, activation, functionalization, in addition to construction of the polymer matrix, all via plasma deposition is an excellent example of the versatility of plasmas as nanofabrication tools [1]. [1] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2005) [Preview Abstract] |
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MWP1.00016: Silicon nanocrystal synthesis in microplasma reactor Tomohiro Nozaki, Tomohisa Ogino, Takashi Nakamuta, Kenji Sasaki, Ken Okazaki Atmospheric-pressure microplasma reactor was developed for the fabrication of tunable photoluminescent silicon nanocrystals. A mixture of Ar, H2, and SiCl4 was activated by capacitively-coupled non-equilibrium plasma generated in a capillary glass with a volume less than 1 $\mu $l. The microplasma efficiently realizes supersaturated silicon vapor that leads to gas phase crystal nucleation via three-body collision, followed by rapid termination of crystal growth due to short-residence-time reactor. The room temperature photoluminescence (PL) of as-synthesized material with H2 = 0.7{\%} exhibited intense visible light emission with peak intensity around 670 nm. The TEM analysis of the red-luminescent material revealed crystalline particles with sizes around 3 nm and amorphous silicon oxide shell which surrounds the crystalline core. The PL spectrum was blue-shifted to 520 nm with increasing H2 content. The green-luminescent materials were readily oxidized upon exposure to air, and the PL capability attributing to silicon nanocrystal was extinguished within a few hours. The PL spectrum was well stabilized by adding a trace amount of CH4. The surface structure of silicon nanocrystals might be modified by inserting hydrocarbon capping. [Preview Abstract] |
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MWP1.00017: Quasi-2D nanostructures: Growth in low-temperature plasmas Eugene Tam, Igor Levchenko, Kostya (Ken) Ostrikov, Amanda Rider, Sergey Vladimirov, Shuyan Xu Quasi-two-dimensional nanostructures, such as nanowalls, are currently the subject of enormous research interest. Gas-based synthesis methods follow either a neutral- or ionized gas (plasma)-based route to fabricate structures of reduced dimensionality [1]. Here, we present a multiscale hybrid numerical simulation which demonstrates the superiority of the plasma route in controlling the morphology of quasi-two-dimensional surface nanopatterns. It was found that the nanowall width uniformity was the best in high-density plasmas, becoming more non-uniform in lower-density plasmas. The neutral gas-based process resulted in the worst nanowall width uniformity. This effect is the result of the focusing of ion fluxes by irregular electric fields in the vicinity of the plasma-grown nanostructures on a biased substrate, and the differences in the 2D-adatom diffusion fluxes in the ionized gas and neutral gas-based processes. Our simulation results are in good agreement with available experimental results concerning the effect of plasma process parameters on the sizes and shapes of relevant nanostructures. [1] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2005); K. Ostrikov, A. B. Murphy, J. Phys. D: Appl. Phys. 40, 2223 (2007) [Preview Abstract] |
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MWP1.00018: Generation of surface preparation species in an Ar+H$_{2}$ plasma discharge Kostya (Ken) Ostrikov, Hyun-Jin Yoon, Amanda Rider Deposition surfaces must be carefully prepared before nanoassembly can take place. Therefore, understanding how the surface preparation species or `working units' (WUs), responsible for surface activation and passivation are generated in a plasma discharge is an important step towards creating reliable and robust plasma-aided nanofabrication methods [1,2]. Here, a two-dimensional fluid simulation of the number densities of WUs in a low-temperature, low-pressure, non-equilibrium Ar+H$_{2}$ plasma is conducted. Parameters such as operating pressure, H$_{2}$ partial pressure and power were varied in order to observe the effect on production of the argon ion and atomic hydrogen, species responsible for surface activation and passivation respectively. Delicate balances are required between these parameters in order to ensure high number densities of Ar$^{+}$ and H species, and thus to achieve acceptable rates of surface activation and passivation. This paper contributes to the improvement of the controllability and predictability of plasma-based nanoassembly processes. [1] K. Ostrikov et al, Plasma Process. Polym. 4, 27 (2007) [2] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2005) [Preview Abstract] |
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MWP1.00019: A plasma-based pre-treatment for low temperature bonding of silicon wafers Nicholas Braithwaite, Jan Kowal, Tony Rogers In the fabrication of micro and nano electromechanical systems (MNEMS), there is a demand for adhesive-free, low-temperature wafer bonding. These constraints arise from the need to avoid issues relating to thermal strain and to unacceptability of high temperature processes late in the manufacturing sequence. It has been known for some time that high strength wafer bonding can be achieved by exposure to oxygen plasmas for a few minutes followed by a 200 deg C, 60 minute anneal step. Low pressure and atmospheric pressure routes have been demonstrated commercially. Our studies show that a more effective pre-treatment involves exposure radicals generated in an oxygen plasma, avoiding deleterious effects of excessive ion bombardment and UV flux. In the present configuration the plasma source is an annular arrangement that surrounds a pair of wafers; plasma excitation uses mesh electrodes, and mains frequency voltage. Neutral species diffuse from the source across the surface of the wafer, where they activate the bonding process; the mechanism is yet to be fully elucidated, but has been shown to work effectively. [Preview Abstract] |
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MWP1.00020: Low-temperature Plasma Enhanced Chemical Vapour Deposition of Nanodevice-grade nc-3C-SiC Kostya (Ken) Ostrikov, Qijin Cheng, Shuyan Xu, Jidong Long The development of robust fabrication techniques that are capable of achieving a synergy of essential structure-, composition-, function/property-, application-, and process-related requirements in the same material is the ultimate goal of Materials Science [1]. Despite the outstanding chemical, mechanical, optical and thermal properties of bulk SiC, applications of nanocrystalline silicon carbide (nc-SiC)[2] in nanodevices are hampered by a substantial lack of such synergy. Here we report on the plasma-based synthesis of nanodevice-grade nc-3C-SiC films, with very high growth rates (7-9 nm/min) at low and ULSI technology-compatible process temperatures (400-550 $^{o}$C), featuring: high nanocrystalline fraction (67{\%} at 550 $^{o}$C); good chemical purity; excellent stoichiometry throughout the entire film; wide optical band gap (3.22-3.71 eV); refractive index close to that of single-crystalline 3C-SiC; and clear, uniform, and defect-free Si-SiC interface. The counter-intuitive low SiC hydrogenation in a H$_{2}$-rich plasma process is explained by hydrogen atom desorption-mediated crystallization. [1] K. Ostrikov, Rev. Mod. Phys. 77, 489 (2007) [2] Q. J. Cheng, S. Xu, J. D. Long, K. Ostrikov, Appl. Phys. Lett. 90, 173112 (2007) [Preview Abstract] |
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MWP1.00021: ELECTRON AND PHOTON COLLISIONS WITH ATOMS AND MOLECULES |
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MWP1.00022: Excitation of the 3p$^{5}$5p levels of Argon from the 3p$^{5}$4s metastable levels Rajesh Srivastava, Lalita Sharma, Allan Stauffer In the light of recent experimental results of Jung et al [1] we have extended our relativistic distorted wave (RDW) calculations [2] to the electron impact excitation of the ten higher-lying fine-structure levels of the 3$p^{5}$5$p$ configuration of argon from the lowest metastable states (the J = 0, 2 levels of the 3$p^{5}$4$s$ configuration). We compare our theoretical results with their experimental results and discuss the differences from the similar excitation to the 3p$^{5}$4p levels from the same metastable states [2]. [1] R. O. Jung, J. B. Boffard, L; W; Anderson and C. C. Lin, Phys. Rev. A \textbf{75}, 052707 (2007). [2] R. Srivastava, A. D. Stauffer and L. Sharma, Phys. Rev. A \textbf{74}, 012715 (2006). [Preview Abstract] |
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MWP1.00023: Excitation of atomic oxygen by electron impact Rajesh Srivastava, Lalita Sharma, Allan Stauffer We have carried out relativistic distorted-wave calculations for the excitation of atomic oxygen from its ground (2p)$^{4} \quad ^{3}$P state to the excited (2p)$^{3}$3s $^{3}$S, $^{3}$P and $^{3}$D states and to the (2p)$^{3}$3d $^{3}$D state in the energy range from 15 to 100 eV. We compare our results for the differential cross sections with both experimental measurements and other theoretical calculations for these transitions and find our calculations agree very well with them. We have also compared our integrated cross sections for the excitation of (2p)$^{3}$3s $^{3}$S for which extensive theoretical and experimental data have been reported. [Preview Abstract] |
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MWP1.00024: Electron impact excitation cross sections into (3p)$^{5}$5p levels from the (3p)$^{5}$4s metastable level of Ar by the Kim B-E-f Scaling method. M.A. Ali, P.M. Stone We present results for electron impact excitation cross sections from (3p)$^{5}$4s,1s$_{5}$ and 1s$_{3}$ metastable states of Ar to (3p)$^{5}$5p, 3p$_{1}$ to 3p$_{10}$ states, which are dipole allowed by the use of the Kim B-E-f Scaling procedure [1]. We use the experimental excitation energy for E-scaling and accurate f values of Zatsarinny and Bartschart [2] for f- scaling. We compare our results with apparent excitation cross sections recently reported by Jung et al. [3]. Our results suggest that cascade contributions for the upper levels are substantial. To gauge the accuracy of B-E-f scaling, we also present similar results for (3p)$^{5}$4s, 1s$_{5}$ and 1s$_{3}$ metastable states to (3p)$^{5}$4p, 2p$_{1}$ to 2p$_{10}$, dipole allowed states and compare with the distorted wave results of Srivastava et al. [4]. \newline [1] Y-K. Kim, Phys. Rev. A 64 032713 (2001). [2] O. Zatsarinny and K. Bartschart J. Phys. B: At. Mol. Phys. 39 2145 (2006). [3] R. O. Jung, J. B. Boffard, L. W. Anderson, and C. C. Lin Phys. Rev. A 75 052707 (2007). [4]R. Srivastava, A. D. Stauffer, and L. Sharma Phys. Rev. A 74 012715 (2006). [Preview Abstract] |
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MWP1.00025: Electron impact ionization of metastable states of He, Ne, Ar, Kr and Xe. M.A. Ali, P.M. Stone Electron impact ionization cross sections of rare gases are important quantities needed for modeling of rare gas discharges, lighting and plasma displays. We present ionization cross sections of (np)$^{5}$ (n+1)s $^{3}$P (J=2 and 0) metastable states calculated within the Binar-Encounter-Bethe (BEB) model of Kim and Rudd [1]. These are compared with very scant experimental data available for He, Ne, and Ar and other theoretical data using advanced methods, where available. Our results compare favorably with results using sophisticated methods but share similar disagreement with experimental data as do results of advanced method calculations. The BEB ionization cross sections of J=2 and 0 states for Ne, Ar, Kr and Xe are virtually identical. \newline [1] Y-K.Kim and M. E. Rudd, Phys. Rev. A 50 3954 (1994) [Preview Abstract] |
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MWP1.00026: Studies into electron-water scattering and transport phenomena Michael Brunger, William Morgan, Penny Thorn We have developed an integral cross section data base for electron scattering from water. This data base is self-consistent with available total cross section measurements, as will be demonstrated at the meeting. In addition we have used this data base in conjunction with Boltzmann and Monte Carlo swarm coefficient calculations, in order to further check its self-consistency against measured transport coefficients. Finally, the present cross sections are employed to calculate the atmospherically important quantities: (1) electron energy transfer rates and (2) electron impact excitation rates. All these data will also be presented at the meeting. [Preview Abstract] |
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MWP1.00027: Low energy elastic scattering and vibrational excitation of THF Violaine Vizcaino, James Sullivan, Stephen Buckman, Jason Roberts, Michael Brunger Tetrahydrofuran is a reasonable model for the deoxy-ribose part of the DNA backbone and it has attracted much recent attention in the context of electron-induced radiation damage. In this paper we extend recent measurements of absolute elastic electron scattering cross sections to energies below the shape resonance (6.5 eV) and also provide measurements of vibrational excitation for energies below 10 eV. [Preview Abstract] |
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MWP1.00028: Near-threshold electronic excitation of N2 Subhendu Mondal, Tyler Raeside, Stan Newman, Julian Lower, Stephen Buckman Absolute cross sections for the electron impact excitation of low lying electronic states of N2 are measured using a position sensitive, time-of-flight technique. This technique employs a pulsed, monochromatic electron beam and a large area channelplate detector and delay-line anode which can detect all scattered electrons, elastic and inelastic, over an angular range of $\sim $ 20\r{ }. The transmission of the detector is uniform in energy and the absolute cross sections for inelastic processes are obtained directly from the measurement of the elastic to inelastic scattering ratio and the well-known absolute elastic scattering cross sections. The incident energy range of interest is 10-15 eV. [Preview Abstract] |
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MWP1.00029: Transport Coefficients and Cross Section Set for Electron Scattering in Mixtures $CF_4$ and $CF_2$ Zeljka Nikitovic, Vladimir Stojanovic, Zoran Petrovic We present transport coefficients for electrons in mixtures of $CF_4$ with $CF_2$ for conditions such as those found in plasma assisted technologies for semiconductor production. We used a two term numerical solution of the Boltzmann equation and we tested the accuracy of the results by using a Monte Carlo simulation. Mixtures of radicals with $CF_4$ were constructed by using the cross sections of Tennyson and coworkers [1]. We selected a wide range of abundances of radicals from $0.01\%$ to $10\%$ in the mixture. For low $E/N$ large deviations from values for total electron attachment for pure $CF_4$ are obtained for mixtures of $CF_4$ and its radicals if abundances are sufficiently high. The effect of radicals on electron kinetics is relatively small for abundances below 1\%. For higher abundances all transport coefficients, mean energies and rate coefficients are affected to a degree which could affect the operating conditions in plasmas. \newline \newline [1] I. Rozum, P. Limao-Vieira, S. Eden, and J. Tennyson, N.J. Mason, J. Phys. Chem. Ref. Data, Vol. 35, No. 1, (2006) 267. [Preview Abstract] |
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MWP1.00030: Electron-impact ionization rates for BF$_{3}$ and its fragments M. Raskovic, S. Popovic, L. Vuskovic We have calculated the electron-impact ionization rates of BF$_{3}$ and its fragments for electron energy distribution present in sheath mode of the repetitively pulsed d.c. diode system. Data are required for BF$_{3}$ discharge modeling. BF$_{3}$ and its fragments are reactive species used to interact with niobium surface in order to remove oxides and other impurities from the surface in the form of volatile compounds. This cleaning and smoothening treatment of bulk niobium improves the performance of the superconducting radiofrequency cavities used for particle accelerators. In our calculation electronic structures of BF$_{3}$ and its fragments were described with several empirical basis sets. After geometry optimization using density functional method B3LYP, MO parameters were calculated with UHF, CCSD(T) and OVGF methods. Electron-impact ionization cross-sections were calculated employing the Binary-Encounter-Bethe approximation and results were compared with available experimental data. Relative calculation errors were estimated, which were especially important for the cross-sections obtained with CEP-31G basis set, necessary to describe system containing niobium samples. These cross-sections are used to calculate rates for electron energy distributions of BF$_{3}$ plasmas. [Preview Abstract] |
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MWP1.00031: Theoretical Differential Cross Sections for Transfer-Excitation in Proton-Helium Collisions A.L. Harris, J.L. Peacher, D.H. Madison Theoretical differential cross sections will be compared with experimental results for transfer-excitation occurring in proton-helium collisions. In the experiment, the incident proton captures one electron from a helium atom, and the remaining electron is left in an excited bound state of the helium ion. These experiments have been performed in Rolla, MO. The theoretical approach we use is a full four-body approach, taking each particle into account. This results in a nine dimensional integral to evaluate the T-matrix. A fully correlated Hylleraas wavefunction is used for the initial state helium atom, and hydrogenic wavefunctions are used for the projectile hydrogen atom and the residual helium ion in the final state. [Preview Abstract] |
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MWP1.00032: Total ionization cross sections for Benzene, Furan and Tetrahydro furan on electron impact C.G. Limbachiya, M. Vinodkumar, S. Gangopadhyay, K.N. Joshipura Industrial society has increased human exposure to thousands of chemicals in the environment e.g. Benzene (C$_{6}$H$_{6})$, Furan (C$_{4}$H$_{4}$O) and Tetrahydrofuran (C$_{4}$H$_{8}$O). Of particular concern is the potential hazard of these chemicals to produce cancer. The molecules are thus biologically and industrially important. In this paper we have examined scattering of electrons (from threshold to 5 keV) from these targets and calculated the total ionization cross sections. We used complex optical potential formalism (SCOP) [1, 2] to calculate total inelastic cross section Q$_{inel}$. We have developed a method, Complex Scattering Potential -- ionization contribution (CSP-ic) to extract ionization cross sections Q$_{ion}$ from calculated Q$_{inel}$. \newline \textbf{Ref. }[1] M.Vinodkumar, K.N.Joshipura, C.G.Limbachiya {\&} B.K.Antony, Eur. J. Phys. D. \textbf{37} (2006) 67 \newline [2] M.Vinodkumar, K.N.Joshipura, C.G.Limbachiya {\&} B.K.Antony, Phys. Rev A \textbf{74 }(2006) 022721 [Preview Abstract] |
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MWP1.00033: Electron Impact Excitation of Atmospheric Species C.P. Malone, P.V. Johnson, J.W. McConkey, J.M. Ajello, I. Kanik Electron collisions with neutral molecular targets, such as O$_{2}$, H$_{2}$, and N$_{2}$, have been investigated. Resulting fluorescence was probed using various monochromator-detector combinations. Line and band intensities were investigated as a function of wavelength and incident electron energy. The emission cross sections for these atmospheric species will be presented. In the case of O$_{2}$, previous values in the literature, such as [J.M. Ajello and B. Franklin, J. Chem. Phys. \textbf{82}, 2519 (1985); O. Wilhelmi and K.-H. Schartner, Eur. Phys. J. D \textbf{11}, 79 (2000)], demonstrated significant discrepancies and provided a strong impetus for this work. The present results are compared to available cross sections. [Preview Abstract] |
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MWP1.00034: Integral Cross Sections for the Electron Impact Excitation of Molecular Nitrogen C.P. Malone, P.V. Johnson, I. Kanik, S. Wang, M.A. Khakoo Integral cross sections (ICSs) for the electron impact excitation of the X $^{1} \Sigma_{g}^{+}$ (v$^{\prime\prime}$=0) ground level to the a$^{\prime\prime}$ $^{1}\Sigma$$_{g}^{+}$, b $^{1}\Pi _{u}$, c $^{1}\Pi _{u}$, o $^{1}\Pi _{u}$, b$^{\prime}$ $^{1}\Sigma$$_{u}^{+}$, c$_{4}^{\prime}$ $^{1}\Sigma$$_{u}^{+}$, G $^{3}\Pi _{u}$, and F $^{3}\Pi_{u}$ states of N$_{2}$ are reported at incident energies of 17.5eV, 20eV, 30eV, 50eV, and 100eV. The ICSs were obtained from integrating recent differential cross sections, which were obtained by unfolding new energy-loss spectra taken at electron scattering angles ranging from $2^{\circ}$ to $130^{\circ}$. The analysis of the spectra followed a different algorithm from that employed in a previous study of N$_{2}$ for the valence states by Khakoo \textit{et al.} [Physical Review A \textbf{71}, 062703 (2005)], since the $^{1}\Pi_{u}$ and $^{1}\Sigma $$_{u}^{+}$ states form a strongly-interacting Rydberg-valence series. The present results are compared to existing cross sections. [Preview Abstract] |
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MWP1.00035: Electron impact excitation of xenon Oleg Zatsarinny, Klaus Bartschat We have used the $B$-spline $R$-matrix (close-coupling) method with non-orthogonal sets of orbitals~[1] to calculate angle-integrated and angle-differential cross sections, as well as spin-polarization and coherence parameters for electron impact excitation of xenon. A total of 31 physical and two pseudo target states were included in the close-coupling expansion, with the latter chosen to account for the dipole polarizability of the ground state. Relativistic effects were accounted for perturbatively through the most important correction terms in the Breit-Pauli Hamiltonian. In light of the very complex structure of xenon, characterized by strong mixing of states with different principal configurations, the use of term-dependent one-electron orbitals was critical for obtaining an acceptable target description, which could still be used in the subsequent collision calculation. We are also in the process of developing a full-relativistic version of the computer code. The progress and the latest results will be reported at the conference. \par\noindent [1] O.~Zatsarinny, Comp.~Phys.~Commun. {\bf 174} (2006) 273. [Preview Abstract] |
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MWP1.00036: Multiscale analysis in perturbation dynamics for the two-dimensional wake Sau Bal A three-dimensional initial-value problem to study the linear stability of the two-dimensional wake by means of a multi space and time scale description is presented. The viscous perturbation analysis is carried out so that, by imposing arbitrary three-dimensional perturbations in terms of the vorticity, both the early transient as well as the asymptotic behavior can be considered (Criminale \& Drazin 1990, 2000). Analytical Navier-Stokes asymptotic expansions are used to describe the base flow. Non-parallel effects, as non linear convection and both streamwise and transversal diffusion, are directly included (Tordella \& Belan 2003). After a Fourier decomposition in the $x-z$ plane, a complex and a real wavenumber in $x$ and $z$ directions are introduced, respectively (Scarsoglio, Tordella \& Criminale 2007). The polar wavenumber is the small parameter of the regular perturbation scheme. The limit of small wavenumbers as well as the the more general problem with larger wavenumbers are studied and results are asymptotically compared with spatio-temporal normal mode analyses (Tordella, Scarsoglio \& Belan 2006; Belan \& Tordella 2006). [Preview Abstract] |
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MWP1.00037: LIGHTING PLASMAS: GLOWS, ARCS, FLAT PANELS, NOVEL SOURCES, OTHERS |
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MWP1.00038: RF Noise Generation in High-Pressure Short-Arc DC Xenon Lamps Olga Minayeva, Douglas Doughty Continuous direct current xenon arcs will generate RF noise under certain circumstance, which can lead to excessive electro- magnetic interference in systems that use these arcs as light sources. Phenomenological observations are presented for xenon arcs having arc gaps $\sim$1 mm, cold fill pressures of $\sim$2.5 MPa, and currents up to 30 amps. Using a loop antenna in the vicinity of an operating lamp, it is observed that as the current to the arc is lowered there is a reproducible threshold at which the RF noise generation begins. This threshold is accompanied by a small abrupt drop in voltage ($\sim$0.2 volts). The RF emission appears in pulses $\sim$150 nsec wide separated by $\sim$300 nec - the pulse interval decreases with decreasing current. The properties of the RF emission as a function of arc parameters (such as pressure, arc gap, electrode design) will be discussed and a semi-quantitative model presented. [Preview Abstract] |
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MWP1.00039: Quantitative X-ray Absorption Imaging of Density Distributions in HID Lamps John J. Curry Quantitative x-ray absorption imaging of gases is possible with an optical digital array detector, such as a charge-coupled device (CCD), combined with an x-ray phosphor. The linearity and low dark current of a CCD enable the sensitivity needed to image gases quantitatively. X-ray absorption imaging is useful in the high-pressure Hg discharges of HID lamps because Hg has a relatively large x-ray absorption cross-section. However, inversion of a 2-dimensional projected image to obtain a 3-dimensional distribution is not directly solvable when the x-ray source has a broad spectrum and detection is not energy-resolved. Given that the energy-dependent Hg absorption cross-section varies by nearly a factor of 4 over the 15 keV to 25 keV spectral range typical of an x-ray tube source, as much as a factor of 2 error in the measured Hg density can result. The problem is further complicated by the fact that the x-ray spectrum inevitably varies with position in the image because of spectral filtering by the arc tube. A solution of sufficient accuracy can be obtained by determining, \textit{a priori}, an effective absorption cross-section based on the spectral distribution and energy-dependent response of the CCD/phosphor system. Progress on determining such cross-sections for a range of parameters will be presented. [Preview Abstract] |
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MWP1.00040: Development of light source using micro hollow cathode plasma for monitoring absolute densities of metal atoms in magnetron sputtering Takayuki Ohta, Yoshihiro Tachibana, Masafumi Ito, Seigo Takashima, Yasuhiro Higashijima, Hiroyuki Kano, Shoji Den, Masaru Hori The quantitative analysis of metal atoms is important for understanding the chemistry and controlling the conditions in sputtering process. The light source, which emits multi-atomic lines simultaneously, is required for diagnostics of behaviors of many kind of metallic atom at the same time. In this study, a multi-micro hollow cathode lamp for simultaneous monitoring of multi-metal atoms in sputtering process was developed. The emissions of Cu, Zn, Fe, and Mo for analysis were simultaneously obtained from 4 hollows. The Cu and Mo densities in the magnetron sputtering were measured using absorption spectroscopy employing the multi-micro hollow cathode lamp. Those densities were measured to be from 10$^{9}$ to 10$^{10}$ cm$^{-3}$ in the RF power range from 0 to 100 W at a pressure of 5 Pa. The simultaneous measurement of the atomic densities in the sputtering plasma has been performed. [Preview Abstract] |
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MWP1.00041: A Survey of Infrared Continuum verses Line Radiation from Metal Halide M. Kato, M.T. Herd, J.E. Lawler Near-infrared radiation (near-IR) losses from the arc of six commercial Metal Halide High Intensity Discharge (MH-HID) lamps with various power levels and with both Na/Sc and rare earth doses were surveyed in this paper. A radiometrically calibrated Fourier transform infrared spectrometer was used. Lamps with rare earth doses have appreciably better Color Rendering Indices (CRI's) than lamps with Na/Sc doses. The ratios of near-IR continuum emission over near-IR line emission from these six lamps were compared. The near-IR continuum dominates near-IR losses from lamps with rare earth doses and the continuum is significant, but not dominant, from lamps with Na/Sc doses. There was no strong dependence of this ratio on input power or Color Temperature (Tc). Total near-IR losses were estimated using absolutely calibrated, horizontal irradiance measurements. Estimated total near-IR losses were correlated with CRI. The lamps with rare earth doses yield the best CRI's, but have appreciably higher near-IR losses due primarily to continuum processes. One of these rare earth MH-HID lamps was used in a more detailed study of the microscopic physics of the continuum mechanism[M. T. Herd {\&} J. E. Lawler, J. Phys. D 40, 3386 (2007)]. [Preview Abstract] |
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MWP1.00042: MAGNETICALLY-ENHANCED PLASMAS: ECR, HELICON, MAGNETRON, OTHER |
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MWP1.00043: Effect of the magnetic field divergence on the ion velocity distribution in the expanding region of an argon helicon plasma Ioana A. Biloiu, Earl Scime, Costel Biloiu, Samuel Cohen Laser induced fluorescence (LIF) observations downstream from a helicon source-diffusion chamber junction revealed bimodal ion velocity distribution functions (ivdf) along diverging magnetic field lines for 1.5 mTorr argon plasma. By increasing the magnetic field divergence in the expansion region, the speed of the faster component of the distribution function increases, reaching a maximum of $\sim$ 10 km/s. The speed of the slower component is essentially zero. Upstream the junction, i.e., at the end of the helicon source, the distributions are also bimodal but no effect of the magnetic field divergence on fast or slow component is observed. LIF tomography observations of the 2D ivdf in the expansion region show the presence of the fast ion component including slight ion conics with cone angle of 2$\theta$ = 64\r{ }. The strong ion acceleration and the ion conics are strong evidence of weak ion collisionality as the plasma flows out along the diverging magnetic field. The parallel velocity of the fast ions increases as a result of acceleration by the potential drop across the electric double layer at the end of the helicon source and acceleration by the magnetic moment conserving $\mu \nabla $B force. [Preview Abstract] |
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MWP1.00044: Suppression of High-Energy Backscattered Species in Magnetron Sputter Plasma with Cylindrical Cathode Hirotaka Toyoda, Yusuke Takagi, Hideo Sugai Recent application of magnetron plasma to nano-scale devices requires high-quality films, e.g., magnetic multilayer films with nano-scale flat interface and with no mixing of atomic components at the interface. In general, surface qualities of sputter deposited films are influenced by incidence of particles with kinetic energies much higher than bond energies of deposited materials. Recently, we have shown abundant flux of high energy (100-200 eV) Ar atom and Ar$^{+}$ ion those are produced by backscattering of Ar$^{+}$ on the target, i.e., ejection of high-energy Ar atom from target. In this paper, we propose a new magnetron source to suppress high energy Ar and Ar$^{+}$ flux using a cylindrical cathode instead of planar cathode. Energy distribution function (EDF) of Ar$^{+}$ is measured by a QMA with an energy analyzer. It is shown that a quantity of energetic Ar$^{+}$ is much less than that of a conventional plane type cathode. In parallel with the measurement of the Ar$^{+}$ EDFs, a Monte Carlo code which simulates Ar and Ar$^{+}$ EDFs is developed. The simulation well explains the Ar$^{+}$ EDFs and shows that a quantity of the energetic Ar atom is considerably small compared with the plane type cathode. Experimental and simulation results suggest that incidence of energetic particles on the substrate is suppressed in the cylindrical magnetron sputter source. [Preview Abstract] |
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MWP1.00045: Drift Phenomena in an Inductively Coupled Magnetic Neutral Loop Discharge Dragos Crintea, Dirk Luggenhoelscher, Deborah O'Connell, Timo Gans, Uwe Czarnetzki The neutral loop discharge is a magnetically enhanced plasma source applicable between 10$^{-2}$~Pa and 10~Pa with electron densities of a few times 10$^{10}$~cm$^{-3}$ to 10$^{12}$~cm$^{-3}$. A magnetic quadrupole is bent into a torus in which the magnetic field vanishes and is therefore called the neutral loop (NL). The NL is located close to a planar inductive coupling antenna separated from the plasma by a quartz cylinder and operated at 13.56~MHz. The NL confines the electrons and randomizes their trajectories, which leads to an increased heating at low pressures. In addition, the electron pressure gradients in the magnetic field cause a diamagnetic drift. With Thomson scattering the electron velocity distribution is measured and allows the determination of the diamagnetic drift of the electrons along the NL in the range of 10$^{4}$~m/s to 10$^{5}$~m/s. With an ICCD camera the temporal modulation of the emission is measured and from this the drift velocity is also determined and compared to the laser measurement. Both results agree well over three orders of magnitude in pressure with a simple fluid-dynamic drift-collision model. Drift and confinement are closely related as is also represented by the low transversal electric field measured by a Langmuir probe. [Preview Abstract] |
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MWP1.00046: The plasma parameters in a high power impulse magnetron sputtering discharge (HiPIMS) J.T. Gudmundsson, P. Sigurjonsson, D. Lundin, U. Helmersson The time evolution of the electron density and electron temperature in a high power impulse magnetron sputtering discharge (HiPIMS) are explored with a Langmuir probe. A high-density plasma is created by applying a high power pulse with short duty cycle and low repetition frequency to a planar magnetron discharge [1]. The electron density in a HiPIMS discharge is very high $\sim 10^{19}$ m$^{-3}$ in the substrate vicinity [2,3] and remains high for a while after the pulse is off. The electron energy distribution function (EEDF) in the substrate vicinity during and shortly after the pulse can be represented by a bi-Maxwellian like distribution indicating two energy groups of electrons. Here the time evolution of the two electron groups is monitored. \newline \newline [1] U. Helmersson, M. Lattemann, J. Bohlmark, A.P. Ehiasarian, and J.T. Gudmundsson, Thin Solid Films 513, 1 (2006) \newline [2] J. T. Gudmundsson, J. Alami, and U. Helmersson, Appl. Phys. Lett. 78, 3427 (2001) \newline [3] J. Bohlmark, J. T. Gudmundsson, J. Alami, M. Lattemann, and U. Helmersson, IEEE Trans. Plasma Sci. 33, 346 (2005) [Preview Abstract] |
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MWP1.00047: PLASMA CHEMISTRY: ATMOSPHERIC, GAS, PHASE, SURFACE |
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MWP1.00048: Dissociative ionization of JP-10 in a cross-flowing Ar/Xe plasma expansion Charles Jiao, Biswa Ganguly, Alan Garscadden JP-10 (C$_{10}$H$_{16})$, a synthetic fuel composed almost exclusively of exo-tetrahydrodicyclopentadiene, has been widely used in missiles, supersonic-combustion ramjets and pulse-detonation engines. Although many combustion research studies have been carried out on JP-10, its detailed combustion mechanism remains to be explored. As plasma-assisted ignition and combustion have been of great interest in recent years, and topics on the roles played by charged species in ignition/combustion are being revisited, it is appropriate to study charged particle collisions with the fuel molecule. Previously we have investigated the electron impact ionization of JP-10. In the current study we examine the formation of ion fragments from JP-10 by adding the fuel to a nozzle-formed expansion of Ar or Xe plasma. Dependences of fragment ion intensities on the rf-power will be presented. Mechanisms for the ion formation will be discussed based on the interpretation of the ion intensity profiles showing both exothermic and endothermic characteristics, and on results from additional measurements including optical emission and plasmas with Ar/N$_{2}$ mixtures in the same configuration. [Preview Abstract] |
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MWP1.00049: Measurement of Ground State Oxygen Radical [O($^{3}$P)] in Surface Cleaning Process Employing Nonequilibrium Atmospheric-Pressure Pulsed Remote Plasma Masahiro Iwasaki, Keigo Takeda, Masaru Hori, Masafumi Ito, Eiji Miyamoto, Takuya Yara, Tsuyoshi Uehara Plasma surface cleaning technology using the nonequilibrium atmospheric-pressure plasma has the advantages of non-vacuum system, high throughput, and scalability for large area in-line processing. In this study, the surface cleaning on an indium tin oxide film was investigated by using a nonequilibrium atmospheric-pressure pulsed plasma. It was found that a remarkably high cleaning efficiency was realized by plasma treatment with additions from 0.025 to 0.1{\%} O$_{2}$ to N$_{2}$. The densities of the ground state oxygen radical [O($^{3}$P)] and ozone [O$_{3}$] were measured using vacuum UV laser absorption spectroscopy and UV absorption spectroscopy, respectively. It was found that the key factor for the surface cleaning was the scission of carbon bonds of organic compounds due to UV emissions, and subsequent oxidation due to O($^{3}$P) and O$_{3}$. [Preview Abstract] |
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MWP1.00050: PLASMA-SURFACE INTERACTIONS |
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MWP1.00051: Study of the influence of collisions between physisorbed atoms on the surface recombination probability Vasco Guerra A dynamical Monte-Carlo method was developed to study the surface kinetics of a simple system. The kinetic scheme comprises physisorption, thermal desorption from physisorption sites, chemisorption, Eley-Rideal recombination, surface diffusion of physisorbed atoms, and Langmuir-Hinshelwood recombination. The model provides the time-evolution of the fractional coverage of both physisorption and chemisorption sites, the recombination probability, and the contribution of each elementary process to recombination. Different grid sizes and averaging procedures were used to optimize the Monte Carlo algorithm. The results were compared with a previously developed mean-field model. The effect of collisions between physisorbed atoms, could not be described within the previous model, was investigated in detail. Evidently, they become important and can change significantly the results in the domain of low surface temperatures, corresponding to a high occupancy of physisorption sites. [Preview Abstract] |
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MWP1.00052: Production and loss of rovibrationally excited H$_{2}$ molecules: Expanding Hydrogen plasmas in experiment and model Richard Engeln, Onno Gabriel, Daan Schram, Peter Vankan The rovibrationally resolved density distributions of molecular hydrogen are measured in expanding thermal hydrogen plasmas by means of laser induced fluorescence in the vacuum-UV range (VUV-LIF). The results reveal a non-Boltzmann distributions, where the low rotational states (J~=~1-6) follow a temperature of 700~K, while the higher rotational states are overpopulated compared to these lower states and follow higher temperatures up to 4500~K. Experiments were performed under variation of the surface area in the plasma source by varying the nozzle length. We assume surface association processes of atomic hydrogen at the surface of the nozzle, producing rovibrationally excited H$_{2}$ molecules. While the atomic hydrogen flow decreases with increasing surface areas, the H$_{2}^{rv}$ distribution shows a more pronounced non-Boltzmann behaviour. A simple 0D model of (de)excitation processes by collisions with electrons and neutrals results in additional information about the formation of the measured H$_{2}^{rv}$ distributions. [Preview Abstract] |
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