Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session MR1: Poster Session III (8:00-9:30AM) |
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Room: Ballroom Foyer |
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MR1.00001: PLASMA-SURFACE INTERACTIONS |
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MR1.00002: An experimental study of secondary electron emission in the limit of low electron energy V.I. Demidov, I.D. Kaganovich, M.E. Koepke Study of secondary electron emission (SEE) from solid surfaces is important for many areas of science and technology, including but not limited to the formation of electron clouds in particle accelerators, plasma measurements by electrostatic probes and operation of Hall plasma thrusters [1]. The measurements at low incident electron energy below 2eV are very challenging. The goal of this work is to measure SEE coefficient for molybdenum surface in contact with plasmas. In this study nearly mono-energetic electrons arising in plasma-chemical reactions like pair collisions of metastable atoms have been used for the measurements. Variation of the target voltage and measurement of the corresponding electron current from the mono-energetic electrons allows us to obtain the SEE coefficient. It is experimentally demonstrated that the coefficient is close to zero (less than 0.1) for clean targets and may have much higher value for contaminated targets with some absorbed gas on the surface.\\[4pt] [1] J. Cazaux. J. Appl. Phys. 111 (2012) 064903. [Preview Abstract] |
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MR1.00003: Energy dissipation in plasma treated Nb and Secondary Electron Emission for modeling of multipactor discharges Ana Samolov, Svetozar Popovic, Leposava Vuskovic, Milos Basovic, Filip Cuckov, Yevgeny Raitses, Igor Kaganovich Electron-induced Secondary Electron Emission (SEE) is important in many gas discharge applications such as Hall thrusters, surface and multipactor discharges. Often they present the inhibiting phenomena in designing and operating of these systems, examples being the Superconducting Radio Frequency (SRF) accelerator cavities. The multipactor discharges depend on the resonant field configuration and on the SEE from the cavity surface. SEE is proportional to the energy dissipated by the primary electrons near the surface. Our analysis of energy spectra of secondary electrons indicates that the fraction of dissipated energy of primary electrons in solid reaches the maximum at the primary energies that produce the maximum yield. The better understanding of this mechanism is crucial for successful modeling of the multipactor discharge and design of vacuum electronic devices. We have developed an experimental set up to measure energy distribution of SEE from Nb coupons under different incident angles, since Nb is used for manufacturing of SRF accelerating cavities. Samples are placed in carousel target manifolds which are manipulated by robotic arm providing multiple degrees of freedom of a whole target system. [Preview Abstract] |
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MR1.00004: Characterization of a Helicon Plasma Source for Plasma Material Interactions Peter Fiflis, Davide Curreli, Kyle Lindquist, David Ruzic A helicon plasma device has been constructed at the Center for Plasma Material Interactions at the University of Illinois Experiments for the purpose of plasma material interaction studies. A MORI 200 helicon source is used to generate the plasma at 13.56 MHz. Measurements of the DC magnetic field provided by a Helmholtz coil were performed and are presented here as well as Langmuir probe measurements of the density and temperature. Radial and axial scans are performed to generate a profile of the plasma. A moveable stage for material substrates coupled with the experimental suite of material characterization devices at the Material Research Lab at the University of Illinois as well as this full characterization of the device will enable higher fidelity plasma material interaction studies, and potentially allow investigation of such phenomena as tungsten fuzz production. [Preview Abstract] |
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MR1.00005: FALCON Ion Source Focusing System Optimization for Effective Beam Impurities Mass-Separation Oleksii Girka, Stanislav Herashchenko, Ivan Bizyukov, Aleksander Bizyukov, Konstantin Sereda The numerical and experimental investigation of the intrinsic capability for impurities mass-separation of FALCON ion source [1-2] was carried out. Optimal distance between the ballistic focusing cathodes and the magnetic lens was obtained via numerical calculations to provide maximum ion flux impurities separation. New magnetic lens for FALCON ion source was designed and manufactured as a result of calculations. A set of experiments on high-flux ion beam impurities mass-separation was carried out. Cyclohexane was used as a working gas. Cyclohexane molecule dissociated at gas discharge. As a result, there were hydrogen H$^{+}$ ions and C$_{\mathrm{X}}$H$_{\mathrm{Y}}$ group ions. Polished SS304 samples coated with TiN were irradiated. Irradiation experiments showed that impurities are mass-separated and form the circle of a radius from 0.6 to 1.3 cm. There is free of impurities hydrogen only ion beam into this circle. Optimized FALCON ion source with closed drift provides particle and heat fluxes per unit surface of the target which are by the order of magnitude higher in comparison with existing ion sources designed for the plasma-surface interaction study.\\[4pt] [1] O. Girka, I. Bizyukov, K. Sereda, A. Bizyukov, M. Gutkin, V. Sleptsov, Rev. Sci. Instr., 83, (2012) 083501;\\[0pt] [2] M. Gutkin, A. Bizyukov, V. Sleptsov, I. Bizyukov, and K. Sereda, U.S. Patent US 7622721 B2 (2009) [Preview Abstract] |
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MR1.00006: Using Low Temperature Plasma as a Method of Decontamination of Fruits Soheila Mohades, Richard Jonas, Nazir Barekzi, Mounir Laroussi Non-thermal atmospheric pressure plasmas have been investigated in biomedical applications as well as surface decontamination [1]. The characteristics of the helium plasma generated by the plasma pencil have been elucidated using spectroscopy methods, which revealed the formation of radical and metastable states [2]. The plasma pencil generates biologically tolerant plasma (BTP) that is not thermally harmful to biological living tissues. In addition, there are no persistent chemical residues as compared to the use of cleaning solutions. The rational for this study is that the low thermal load and the reactive species can be exploited in decontaminating fruit surfaces. The BTP is evaluated in the killing of bacteria in solution and on the surface of food. The focus of this paper is to evaluate the efficacy of decontaminating surfaces of plants such as green peppers. The doses of plasma, media and growth conditions, as well as the general effect of plasma on fruit without bacteria are investigated using bacterial killing assays and spectroscopy.\\[4pt] [1] Laroussi M, Tendero C, Lu X, Alla S, and Hynes W L, 2006, \textit{Plasma Processes and Polymers}. 3(6-7): p. 470-473.\\[0pt] [2] Jarrige J, Laroussi M, and Karakas E, 2010, \textit{Plasma Sources Science and Technology}. 19(6): p. 1-11. [Preview Abstract] |
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MR1.00007: Experimental and computational study of plasma bullet reignition behind a thin dielectric slab Pietro Ranieri, Natalia Babaeva, John Foster Ionization waves (IWs) propagating through plasma jets and helium channels are often observed as luminous fronts of the IWs and conventionally termed as plasma bullets. The preliminary experiments show that if a thin dielectric slab is placed in the helium channel as an obstacle for the bullet propagation, the discharge may reignite below the slab. This process is perceived as though the bullets propagate through the obstacle. The goal of this work is to find conditions under which the bullet can reignite behind the dielectric. The experimental setup consists of a corona discharge, with a single metal electrode, within a quartz tube. We study the influence of the dielectric constant, thickness and the length of the mica slab on the plasma jet behavior. We show that after the impact on the mica surface, the bullet partially reflects from the surface and plasma spreads along the surface. Depending on the location of the mica relative to the tube exit, its capacitance and opacity to photoionizing radiation, a second bullet can emerge below the slab. The computational model used in this work, \textit{nonPDPSIM}, is a plasma hydrodynamics model in which continuity, momentum and energy equations are solved for charged and neutral species with solution of Poisson's equation for the electric potential. [Preview Abstract] |
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MR1.00008: Plasma surface kinetics studies of silicon dioxide etch process in inductively coupled fluorocarbon plasmas Won-Seok Chang, Dong-Hun Yu, Deog-Gyun Cho, Yeong-Geun Yook, Poo-Reum Chun, Se-Ah Lee, Deuk-Chul Kwon, Yeon-Ho Im With continuous decrease of nanoscale design rule, plasma etching processes to form high aspect ratio contact hole still remains a challenge to overcome their inherent drawbacks such as bowing and twisted feature. Due to their complexities there still exist big gaps between current research status and predictable modeling of this process. To address this issue, we proposed a surface kinetic model of silicon nitride etch process under inductively coupled fluorocarbon plasmas. For this work, the cut-off probe and quadrapole mass spectroscopy were used for measuring electrical plasma properties, the ion and neutral radical species. Furthermore, the systematic surface analysis was performed to investigate the thickness and chemical bonding of polymer passivation layer during the etch process. The proposed semi-global surface kinetic model can consider deposition of polymer passivation layer and silicon nitride etching self-consistently. The predicted modeling results showed good agreement with experimental data. We believe that our research will provide valuable information to avoid the empirical development of plasma etching process. [Preview Abstract] |
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MR1.00009: Injection of micron size droplets into vacuum Caroline Liu, John Poulose, Daisuke Ogawa, Matthew Goeckner, Lawrence Overzet Previous experiments using direct liquid injection into plasma for film deposition produced films that had unwanted voids. We believe that the uneven deposition of polymer film is due to injected liquids not completely evaporating into the plasma and landing on the surface of the substrate instead. To address this issue, we chose to improve upon the previous film deposition chamber setup by modifying the injector to decrease the injected liquid droplet sizes. The literature presents multiple theories on liquid breakup into air and resultant droplet sizes but to the best of our knowledge, there is not much research on droplet breakup dynamics or resultant droplet sizes when liquid is injected into low pressure ($<$ 20mTorr) or vacuum. The literature states that liquid breakup in vacuum is caused by surface tension only and that the resulting droplet sizes produced by this mechanism are linearly dependent upon the orifice size. In our poster, we will describe previous work done, experimental setup along with experimental data on droplet sizes produced by orifices of various sizes when liquid is injected into low pressure. [Preview Abstract] |
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MR1.00010: PLASMA MODELING AND SIMULATIONS II |
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MR1.00011: Kinetic global modeling of the rotating ionization regions in HiPIMS Sara Gallian, Ralf Peter Brinkmann, William N.G. Hitchon High Power Impulse Magnetron Sputtering often develops a characteristic slowly rotating high emissivity region. This highly ionized region -or spoke- shows a stationary behavior in the current plateau region and rotates with $\Omega \approx$ 80 kHz.\footnote{A. Hecimovic et al. (2013), submitted} It is argued that these spoke-like structures determine the overall plasma density, carry most of the discharge current and are responsible for anomalous cross field electron transport. It is therefore fundamental to understand their formation and relevance in order to characterize the system behavior. First we develop a phenomenological fluid model\footnote{S. Gallian et al. (2013), submitted} and we analytically solve for the electron and neutral densities in a rotating steady state situation. Then, we develop a global model specifically for the spoke region that solves for the electron energy distribution function self-consistently with the rate equations for Ar and Al species. The fluxes of neutrals resulting from the movement of the volume are obtained self consistently from the phenomenological fluid model. We evolve the system employing a relaxation method, until convergence. [Preview Abstract] |
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MR1.00012: Modeling of capacitively and inductively coupled plasma for molecular decontamination Diana Mihailova, Gerjan Hagelaar, Philippe Belenguer, Christopher Laurent, Juslan Lo, Bruno Caillier, Laurent Therese, Philippe Guillot This project aims to study and to develop new technology bricks for next generation of molecular decontamination systems, including plasma solution, for various applications. The contamination control in the processing stages is a major issue for the industrial performance as well as for the development of new technologies in the surface treatment area. The main task is to create uniform low temperature plasma inside a reactor containing the object to be treated. Different plasma sources are modeled with the aim of finding the most efficient one for surface decontamination: inductively coupled plasma, capacitively coupled plasma and combination of both. The model used for testing the various plasma sources is a time dependent two-dimensional multi-fluid model. The model is applied to a simplified cylindrically symmetric geometry in pure argon gas. The modeling results are validated by comparison with experimental results and observations based on optical and physical diagnostic tools. The influence of various parameters (power, pressure, flow) is studied and the corresponding results are presented, compared and discussed. [Preview Abstract] |
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MR1.00013: Fully-kinetic Particle-in-Cell Simulations of Gas Switches Carsten Thoma, Dale Welch, David Rose, William Zimmerman, Craig Miller, Robert Clark We describe a fully-kinetic electromagnetic particle-in-cell Monte Carlo (PICMC) computational model for the modeling of breakdown phenomena in electrophilic gases such as SF$_6$ and air which has been implemented into the hybrid-PIC code LSP. We present the results of 2D and 3D gas closing switch simulations in which all species are treated kinetically. We demonstrate that this PICMC approach can be used to follow the entire evolution of the switch, from the initial avalanche and streamer formation up to the fully conducting phase. We utilize an 18-species chemistry model for air which is shown to agree with swarm parameters (breakdown threshold, drift velocity) obtained by experiment. Photon transport and photo-ionization are also included to permit the modeling of phenomena such as cathode-directed streamers. This computational model will be used to help design closing switches for pulsed-power systems. [Preview Abstract] |
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MR1.00014: Generation of super-thermal electrons by intense electron beam in a dc discharge D. Sydorenko, I.D. Kaganovich, A.V. Khrabrov, P.L.G. Ventzek, L. Chen Experimental measurements of electron energy distribution function in a rf dc discharge with 800 V dc voltage reveal the presence of a peak of super-thermal electrons with energy in the range of 40-400 eV [1]. The cathode in the experimental device could emit electrons thus producing an electron beam. We used a particle-in-cell code [2] to investigate acceleration of plasma electrons by an electron beam in a dc discharge with parameters close to those of Ref. [1]. The beam excites electron plasma waves via the two-stream instability. Simulations show that the two-stream instability is intermittent, with quiet and active periods. During the quiet periods, the beam propagates through the plasma with minimal perturbations. During the periods of activity of the two-stream instability, the beam interacts with the plasma most intensively at locations where the global frequency of instability matches the local electron plasma frequency. There may be two resonance areas with intense oscillations usually near the edges of the plasma. These intense localized plasma oscillations produce peaks in the velocity distribution function similar to the ones measured in the experiment. \\[4pt] [1] L. Xu et al., Appl. Phys. Lett. 93, 261502 (2008).\\[0pt] [2] D. Sydorenko et al., Phys. Plasmas 13, 014501 (2006). [Preview Abstract] |
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MR1.00015: Modeling of recovery mechanism of ozone zero phenomenaby adding small amount of nitrogen in atmospheric pressure oxygen dielectric barrier discharges Haruaki Akashi, Tomokazu Yoshinaga Ozone zero phenomena [1-3] in an atmospheric pressure oxygen dielectric barrier discharges have been one of the major problems during a long time operation of ozone generators. But it is also known that the adding a small amount of nitrogen makes the recover from the ozone zero phenomena. To make clear the mechanism of recovery, authors have been simulated the discharges with using the results of ref.3. As a result, the recovery process can be seen and ozone density increased. It is found that the most important species would be nitrogen atoms. The reaction of nitrogen atoms and oxygen molecules makes oxygen atoms which is main precursor species of ozone. This generation of oxygen atoms is effective to increase ozone. The dependence of oxygen atom density ($n_{\mathrm{O}})$ and nitrogen atom density ($n_{\mathrm{N}})$ ratio was examined in this paper. In the condition of low $n_{\mathrm{N}}$/$n_{\mathrm{O}}$ratio case, generation of nitrogen oxide is low, and the quenching of ozone by the nitrogen oxide would be low. But in the high ratio condition, the quenching of ozone by nitrogen oxide would significant. This work was supported by KAKENHI(23560352).\\[4pt] [1] K.H. Voigt, et al.: Proc. Am. Water Works. Assoc. Ann. Conf., pp.885-900(1994)\\[0pt] [2] M. Taguchi et al, Plasma Process Polym., pp.719-727(2007)\\[0pt] [3] G.Takahashi and H.Akashi, IEEE Trans. Plasma Sci. 39, pp.2234-2235(2011) [Preview Abstract] |
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MR1.00016: Numerical studies of collisionless scattering of an electron beam propagating in background plasma Erinc Tokluoglu, Alexander Khrabrov, Igor Kaganovich Beam-plasma systems are an important area of study for their application in plasma sources used in plasma processing. However the streaming of beam particles against a stationary plasma excite the two-stream instability. In 1D systems the result of this interaction is axial electrostatic Langmuir waves. However in real systems oblique modes can be excited, resulting in transverse electric fields which lead to the collisionless scattering of beam particles. In this work, using PIC code LSP we study the interaction of a 30eV e-beam with a background plasma using an electrostatic 2D model. By tracking the scalar potential, the beam density, the particle phase space and using Fourier transform techniques, we look for evidence of oblique modes with both parallel and perpendicular wave numbers, study their time evolution and the consequent transverse scattering of beam electrons. [Preview Abstract] |
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MR1.00017: Plasma-chemical simulation of negative corona near the inception voltage Francisco Pontiga, Francisco J. Duran-Olivencia, Antonio Castellanos The spatiotemporal development of Trichel pulses in oxygen between a spherical electrode and a grounded plane has been simulated using a fluid approximation that incorporates the plasma chemistry of the electrical discharge. Elementary plasma processes, such as ionization, electron attachment, electron detachment, recombination between ions and chemical reactions between neutral species, are all included in a chemical model consisting of 55 reactions between 8 different species (electrons, O$_2^+$, O$_2^-$, O$_3^-$, O$^-$, O$_2$, O, O$_3$). Secondary emission at the cathode by the impact of positive ions and photons is also considered. The spatial distribution of species is computed in three dimensions (2D-axysimmetrical) by solving Poisson's equation for the electric field and the continuity equations for the species, with the inclusion of the chemical gain/loss rate due to the particle interaction. The results of the simulation reveal the interplay between the different negative ions during the development of every Trichel pulse, and the rate of production of atomic oxygen and ozone by the corona discharge. [Preview Abstract] |
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MR1.00018: Non-Equilibrium Reaction Kinetics of an Atmospheric Pressure Microwave-Driven Plasma Torch: a Global Model Guy Parsey, Yaman G\"{u}\c{c}l\"{u}, John Verboncoeur, Andrew Christlieb In the context of microwave-coupled plasmas, within atmospheric pressure nozzle geometries, we have developed a kinetic global model (KGM) framework designed for quick exploration of parameter space. Our final goal is understanding key reaction pathways within non-equilibrium plasma assisted combustion (PAC). In combination with a Boltzmann equation solver, kinetic plasma and gas-phase chemistry are solved with iterative feedback to match observed bulk conditions from experiments; using a parameterized non-equilibrium electron energy distribution function (EEDF) to define electron-impact processes. The KGM is first applied to argon and ``air'' systems as a means of assessing the soundness of made assumptions. The test with ``air'' greatly increases the complexity by incorporating a plethora of excited states (e.g. translational and vibrational excitations) and providing new reaction pathways. The KGM is then applied to plasma driven combustion mechanisms (e.g. H2 or CH4 with an oxidizer source) which drastically increases the range of reaction time-scales. As the reaction mechanisms become more complex, availability of data will begin to hinder model physicality, requiring analytical and/or empirical treatment of gaps in data to maintain completeness of the reaction mechanisms. [Preview Abstract] |
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MR1.00019: Silicon oxide surface reaction modeling coupled with global bulk plasma model in inductive coupled fluorocarbon plasmas Se-Ah Lee, Poo-Reum Chun, Yeong-Geun Yook, Kwang-Sung Choi, Deog-Gyun Cho, Dong-Hun Yu, Won-Seok Chang, Deuk-Chul Kwon, Yeon-Ho Im Ultra-high deep contact-hole etching is one of the critical issues in fabrication processes of the nanoscale devices. The fluorocarbon plasmas have been used to obtain the ideal etch profiles. As an effort to address this issue, we developed a predictable global plasma model that is coupled strongly with surface reaction and bulk plasma chemistry under fluorocarbon plasmas. For this work, bulk plasma diagnostics in inductively coupled fluorocarbon plasma was performed by quadruple mass spectrometry, Langmuir probe, and cut-off probe. Based on bulk plasma diagnostic data and SiO$_{2}$ etch rates, key information such as rate coefficient and reaction paths for realistic bulk plasma and surface chemistry could be obtained in this work. Furthermore, global plasma model was strongly coupled with surface reaction model to capture the realistic plasma phenomena. Finally, the predicted modeling results of etch rate as functions of plasma conditions showed good agreement with experimental data of SiO$_{2}$ etching. We believe that this model approach can provide useful and effective route to predict the complex plasma phenomena for oxide etching process in fluorocarbon plasma. [Preview Abstract] |
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MR1.00020: GPU based 3D feature profile simulation of high-aspect ratio contact hole etch process under fluorocarbon plasmas Poo-Reum Chun, Se-Ah Lee, Yeong-Geun Yook, Kwang-Sung Choi, Deog-Geun Cho, Dong-Hun Yu, Won-Seok Chang, Deuk-Chul Kwon, Yeon-Ho Im Although plasma etch profile simulation has been attracted much interest for developing reliable plasma etching, there still exist big gaps between current research status and predictable modeling due to the inherent complexity of plasma process. As an effort to address this issue, we present 3D feature profile simulation coupled with well-defined plasma-surface kinetic model for silicon dioxide etching process under fluorocarbon plasmas. To capture the realistic plasma surface reaction behaviors, a polymer layer based surface kinetic model was proposed to consider the simultaneous polymer deposition and oxide etching. Finally, the realistic plasma surface model was used for calculation of speed function for 3D topology simulation, which consists of multiple level set based moving algorithm, and ballistic transport module. In addition, the time consumable computations in the ballistic transport calculation were improved drastically by GPU based numerical computation, leading to the real time computation. Finally, we demonstrated that the surface kinetic model could be coupled successfully for 3D etch profile simulations in high-aspect ratio contact hole plasma etching. [Preview Abstract] |
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MR1.00021: Plasma Sheath Properties at Gas-Dielectric Interface Ashraf Farahat Microdischarges have numerous properties that have been investigated in a number of applications including microdischargers for small spacecraft and plasma displays. A two dimensional flowing gas-plasma model is developed to investigate microdischarges properties near dielectric surfaces. The model consists of electrons, ions and metastable species conservation equations and the Poisson equation and is applied to a 1.2 mm length, 0.2 mm height argon filled microdischarger including anodes and a cathode separated by a dielectric material. Initial electron swarm is assumed to be uniform in the volume and equal to 10$^{8}$ m$^{-3}$. Secondary emission due to ions and excited particles impact is considered with a coefficient equal to 0.05. We present early nanoseconds charge development near the dielectric surface and at the electrodes -- dielectric boundaries. Two-dimensional plots of the charged and excited-species densities are presented and discussed. Electrons' temperature reaches 11.7 eV after 580 ns. Positive dielectric surface charges results in an anode virtual expansion which help in the formation of an ion sheath that gradually decreases the potential gradient between electrodes. [Preview Abstract] |
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MR1.00022: Investigation of Isentropic Coefficient in Non-LTE Hydrogen Thermal Plasma Rohit Sharma, Kuldip Singh The isentropic coefficient in non-LTE hydrogen plasma has been examined in the temperature range from 6000K to 60000K at pressures of 1, 10 and 100 atm for different values of non-equilibrium parameters $\theta $ by taking into account the influence of electronically excited states. The two cases of hydrogen thermal plasma have been considered (i) the ground state (GS), in which all the plasma species are assumed to be in the ground state and (ii) the excited state (ES), in which all the species are distributed in the various possible excited states. It has been observed that isentropic coefficient for hydrogen thermal plasma remains almost constant at 1.16 when degree of ionization varies from 0.1 to 0.8 with some dependence on the non-equilibrium parameter $\theta $. Further, it is inferred that electronically excited states play a significant role at high pressure in affecting the isentropic coefficient of hydrogen thermal plasma. [Preview Abstract] |
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MR1.00023: INDUCTIVELY COUPLED PLASMAS |
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MR1.00024: Effect of Radio Frequency Bias on the Plasma Density and Electron Heating in Inductive Discharge Hyo-Chang Lee, Chin-Wook Chung We show experimental observations of the radio frequency (RF) bias effect on the plasma density and electron heating in RF biased inductively coupled plasma (ICP). When the ICP power is relatively small or the discharge is in capacitive mode, the plasma density increases considerably with the bias power, while decrease in the plasma density is observed when the discharge is in inductive mode. The change of the plasma density can be explained by the balance between total power absorption and power dissipation. With small RF bias powers in the ICP, the electron energy distribution (EED) evolves from bi-Maxwellian distribution to Maxwellian distribution by enhanced plasma bulk heating. In the capacitive RF bias dominant regime, however, high energy electrons by the RF bias are heated on the EEDs in the presence of the ICP. The collisionless heating mechanism of the high energy electrons transits from collisionless inductive heating to capacitive coupled collisionless heating by the electron bounce resonance in the RF biased ICP. [Preview Abstract] |
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MR1.00025: Inductive and Capacitive Power Deposition of Anti-parallel Current Source using Plasma Modeling Kallol Bera, John Forster, Shahid Rauf, Umesh Kelkar Inductive and capacitive power deposition to plasma for anti-parallel current carrying conductors as plasma source has been investigated at different frequency and pressure using plasma modeling. In our model capacitive electric field is calculated by solving scalar potential, $\varphi $, in Poisson equation. In addition, induced magnetic and electric fields have been solved based on coil current. The power deposition to electrons includes both inductive and capacitive power deposition. The coupled set of equations governing the scalar potential, $\varphi $, momentum equation for ions and drift-diffusion equations for electrons are solved implicitly in time. The characteristic discharge dimension we considered is a few cm. The rf current and voltage are applied to the rod. At intermediate pressure of a few Torr at 13.5 MHz, it is found that ICP-only operation requires very high current. In this condition the skin depth being large the inductive coupling is not effective. With increase in frequency to 60 MHz, the skin depth decreases, the inductive coupling improves and current requirement decreases. At lower pressure the current requirement decreases as the inductive coupling improves due to smaller skin depth. The inductive and capacitive power couplings to the plasma at different operating frequency and pressure have been characterized for the plasma source. [Preview Abstract] |
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MR1.00026: E to H Heating Mode Transition and Hysteresis in Inductively Coupled Plasma Hyo-Chang Lee, Chin-Wook Chung Inductively coupled plasma has been known to have two distinct modes, capacitive mode (E mode) and inductive mode (H mode), and the dramatic changes in the plasma parameters and the hysteresis has been observed on the E to H and H to E heating mode transitions. In this work, we investigate two main points: 1) origin of the hysteresis by considering impedance matching circuit, 2) smooth transition of the plasma density through a comparison between argon and helium. From our experimental effort, it is found that the E to H heating mode transition and the hysteresis are caused by both the system power loss and the nonlinear behaviors of the plasma. [Preview Abstract] |
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MR1.00027: Evolution of Electron Temperature and Coupling between Electron Temperature and Power Absorption Hyo-Chang Lee, SeungJu Oh, Young-Cheol Kim, Chin-Wook Chung Power absorption to plasma is a fundamental and core issue in the field of ionized gases and plasma physics, and it is generally known that in the thermal equilibrium plasma with Maxwellian electron distribution, the power absorption in global model is decoupled to electron temperature (T$_{\mathrm{e}})$. However, we show experimentally and theoretically that T$_{\mathrm{e}}$ is quite coupled to the power absorption. With increase in the power absorption to the plasma, the power absorption and the T$_{\mathrm{e}}$ are abnormally evolved due to a competition between the step-ionizations and the gas heating. [Preview Abstract] |
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MR1.00028: A study of increasing radical density and etch rate using remote plasma generator system Jaewon Lee, Kyunghyun Kim, Sung-Won Cho, Chin-Wook Chung To improve radical density without changing electron temperature, remote plasma generator (RPG) is applied. Multistep dissociation of the polyatomic molecule was performed using RPG system. RPG is installed to inductively coupled type processing reactor; electrons, positive ions, radicals and polyatomic molecule generated in RPG and they diffused to processing reactor. The processing reactor dissociates the polyatomic molecules with inductively coupled power. The polyatomic molecules are dissociated by the processing reactor that is operated by inductively coupled power. Therefore, the multistep dissociation system generates more radicals than single-step system. The RPG was composed with two cylinder type inductively coupled plasma (ICP) using 400 kHz RF power and nitrogen gas. The processing reactor composed with two turn antenna with 13.56 MHz RF power. Plasma density, electron temperature and radical density were measured with electrical probe and optical methods. [Preview Abstract] |
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MR1.00029: Measurement of electron energy distribution functions in a low pressure and low density inductively coupled plasma Hyun-Ju Kang, Yu-Sin Kim, Dong-Hwan Kim, Chin-Wook Chung Electron energy distribution functions (EEDFs) and electron densities versus RF power were measured in a low-pressure argon discharge. The measurement was performed with an RF compensated single Langmuir probe, accurate measurement circuits and improved data acquisition algorithms in order to obtain the high quality EEDFs. As power increases, the EEDF evolves from a bi-Maxwellian distribution to a Maxwellian distribution. In low density region, a bi-Maxwellian distribution is clearly observed and their density is higher than the estimated density with a Maxwellian distribution. Energetic electrons and their high temperature that are directly related to collisional energy loss for creating one electron--ion pair can explain these results. [Preview Abstract] |
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MR1.00030: MICRODISCHARGES: DC, RF, MICROWAVE |
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MR1.00031: Study of the maximum length of atmospheric pressure microplasma jets Anne Bourdon, Francois Pechereau, Jaroslav Jansky Since a few years, atmospheric pressure microplasma jets formed by pulsed helium discharges ignited in thin dielectric tubes have received considerable interest due to their potential for biomedical applications. At the tube exit, in most experimental set-ups, the maximum length of the microplasma jet is related to the helium-air mixing. Indeed, the discharge front is usually tubular at the tube exit and its radius decreases during its propagation, as the discharge is constrained to propagate in the region with a sufficient helium concentration. However, when a voltage pulse with a short decrease time is used in experiments, the maximum length is related to the voltage decrease with a decrease of the emission of the discharge front. As the discharge front stops propagating, an increase of emission is observed in the tube. In this work, we propose to simulate in 2D the discharge dynamics and to study the influence of the voltage decrease time on the maximum length and discharge structure of a microplasma jet. Results will be compared with experiments. Finally, we propose to simulate in 2D the interaction of two counter propagating microplasma jets to study the influence of the polarity of discharges and of the dielectric tube radius on the length of both plasma jets. [Preview Abstract] |
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MR1.00032: Measurement of electric fields in a helium micro-hollow cathode discharge by forbidden transitions Shinichi Namba, Daisuke Maki, Ken Takiyama Micro-hollow cathode discharges operated at high pressure has been attracting a great deal of interest for various application, such as, excimer light sources, medical/biological fields and microchemical reactor. In the plasmas, the electric ($E)$ field in the sheath region plays an important role to generate and sustain the plasmas. In order to determine the $E$ field in the He microplasma, the emissions of allowed (He I 2P-4D: 492.19 nm) and forbidden (2P-4F: 492.06 nm) lines were observed. The cathode and anode were both made of brass, and ceramic disks were used to electrically insulate the electrodes. The cathode disk had inner hole diameter of 1.0 mm (length: 2.0 mm). The gas with a flow rate was 1.0 L/min. The discharge was operated at voltages of 250 V, currents of 8 mA and gas pressures up to 100 kPa. The plasmas in the cathode opening were observed using a visible spectrometer. The forbidden line associated with the level mixing of upper levels was observed in the cathode surface, indicating that the high $E$ field was formed. As the intensity ratio of forbidden to the allowed lines is a function of the $E$ field which is calculated by perturtabation theory, we derived the field strength of 18 kV/cm at1.0 mm cathode surface. [Preview Abstract] |
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MR1.00033: Electron dynamics in dual frequency operation of a helium-based radio frequency atmospheric discharge Laura Cox, Colm O'Neill, Andrew Gibson, Bill Graham, Timo Gans, Deborah O'Connell The effects of dual frequency operation on the electron energies in a capacitively coupled radio frequency discharge of a plasma jet were studied. The device consists of two stainless steel electrodes of area 1 x 30 mm, spaced 1 mm apart. The gap spacing is bounded on each side by quartz glass windows. A gas mixture of 1 slm helium, 5 sccm oxygen and 1 sccm argon is flowed through. The top electrode was operated at a frequency of 13.33 MHz and the lower at 39.99 MHz, each with a voltage of approximately 200V$_{\mathrm{p-p}}$. The phase relationship between the two was varied in 30 degree steps. Phase and space resolved optical emission spectroscopy was used to observe the spatio-temporal behavior of higher energy electrons involved in excitation throughout one 75.02 ns RF period. Images were taken at 1 ns intervals. Optical filters at 706 nm and 750 nm were used to view emission from the He (3s$^{\mathrm{3}}$S -- 2p$^{\mathrm{3}}$P) and Ar (2p$_{\mathrm{1}}$ -- 1s$_{\mathrm{2}})$ transitions, corresponding to excitation energies above 22 eV and 13 eV respectively. The results show a change in excitation structures and relative intensity dependent on the phase relationship between the two frequencies. The results are compared with simulation results under these conditions, which allows further insight into the plasma behavior. [Preview Abstract] |
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MR1.00034: Comparison of kinetic, fluid and global modeling of rf discharges at amospheric pressure Torben Hemke, Denis Eremin, Ralf Peter Brinkmann, Thomas Mussenbrock Modeling and simulation of microplasmas is an important key for understanding their physical properties. In particular, not all available plasma diagnostics are applicable to the small dimensions of microplasmas. Thus, theoretical approaches offer in many cases the only way to gain physical insight. The general modeling simulation techniques are kinetic, fluid and global models. In this order they decrease in computational effort, but also in physical accuracy. The computational costs have espescially to be taken into account when dealing with large sets of particle species and chemical reactions. In this contribution, we report on different implementations of the three different modeling approaches for (1d) rf driven micorplasmas at atmospheric pressure in a helium-nitrogen mixture. In conclusion, we show the benefits and limitations of each simulation technique. [Preview Abstract] |
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MR1.00035: Hollow radial electron density profiles in surface wave discharges. An inside job? Manuel Jimenez-Diaz, Sara Rahimi, Emile A.D. Carbone, Jan van Dijk In many microwave excited plasmas, there is a part of the discharge (tube) hidden from optical access e.g. because of the metal parts that cover it; it is the region where the transformation occurs between the EM modes found in the (metal) waveguide to modes in the plasma (waveguide). Because in most of cases optical access is not an option here, studies of this region remain scarce. Regardless of this, it is a well-known fact that the discharge tube can easily break due to the high temperatures inside the launcher of surfaguide discharges, which means the temperature is higher there than in other regions of the plasma. In this work, we use a 2D model to show how the inner region changes for increasing power absorbed and electromagnetic wave frequency. The shaping of the EM coupling into the plasma region by the cavity is explored as well. We discuss when the hollow radial profiles for the electron density appear in a surfaguide plasma, and how they are related to the radial inhomogeneity of the EM fields and the plasma properties (e.g gas temperature). All these results were obtained using the modeling platform Plasimo. [Preview Abstract] |
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MR1.00036: Self-Organized Patterns of Spots In DC Glow Microdischarges in Krypton WeiDong Zhu, Pedro G.C. Almeida, Mikhail S. Benilov, Diego F. Santos, Prajwal Niraula Self-organized patterns of cathodic spots have been observed in DC microdischarges in xenon. Modeling of microdischarges in xenon has revealed existence of multiple solutions. Some of the solutions describe normal discharges, others describe 2D patterns of cathodic spots, and others describe 3D patterns similar to those observed in experiments. A very interesting question is why modes with self-organized patterns have been observed in DC microdischarges in xenon but not in other gases. Modeling suggests that self-organized patterns can be observed in gases other than xenon provided that conditions are right. In the present work, self-organized patterns of spots observed in DC microdischarges in krypton are reported. The experiments are guided by modeling and the discharge device employed in the experiments consists of a molybdenum foil as the anode, an aluminum oxide plate as the dielectric spacer and another molybdenum foil as the cathode. Each layer of the device is 0.25 mm thick. Circular openings of 0.75 mm in diameter are prepared on both anode and dielectric spacer and are aligned. The whole device is assembled by Torr Seal epoxy. Research grade krypton is used to fill the chamber to a pressure of 200-1200 Torr. [Preview Abstract] |
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MR1.00037: THERMAL PLASMAS, ARCS, JETS, SWITCHES, OTHERS |
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MR1.00038: Simulation Research of Influence of Retarded Axial Magnetic Fields on Vacuum Arc in DC Interruption Process Lijun Wang, Shenli Jia, Lilan Hu, Ling Zhang, Zongqian Shi, Shuwei Fan In this paper, based on magnetic-hydrodynamic dynamic (MHD) model, the influence of retarded axial magnetic fields (AMFs) on vacuum arc characteristics in fast direct current (DC) interruption process was simulated and analyzed. Magnetic field calculation results showed that the faster current decreased, the more obviously AMF lagged behind arc current. On one hand, higher AMF strength can restrain the contraction of vacuum arc more efficiently, so that the distribution of current density in arc column region was more homogeneous; on the other hand, higher AMF strength restrained plasma diffusion in current zero stage, which made residual plasma density between electrodes at current zero moment keep higher value, and the possibility of arc re-ignition increased as well. By weakening AMF strength at current dropping stage, DC arc can be more easily interrupted successfully. The correctness of simulation results also was verified by experimental results. In artificial crossing-zero stage, as current decreased, the decrease of light intensity and arc diameters were consistent with those in experimental results. [Preview Abstract] |
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MR1.00039: Flow Dynamics from a Nonequilibrium Atmospheric-Pressure Arc Discharge Jet Juan Trelles Plasma jets are used as directed sources of energy, momentum and excited species fluxes in diverse technologies, such as spray coating, chemical synthesis, waste treatment and pyrolysis. The fluid, thermal and electromagnetic dynamics from the jet produced by a direct-current non-transferred arc plasma torch are explored using time-dependent three-dimensional simulations encompassing the dynamics of the arc inside the torch, the development of the jet through the outside environment, and the later impingement of the jet over a substrate. The plasma flow is described mathematically by a chemical equilibrium and thermodynamic nonequilibrium (two-temperature) model and numerically by a coupled fluid-electromagnetic transport model and a Variational Multiscale Finite Element Method. Simulation results uncover various aspects of the flow dynamics, including the jet forcing due to the movement of the arc, the prevalence of deviations between heavy-species and electron temperatures in the plasma fringes, the development of shear flow instabilities around the jet, the occurrence of localized regions with high electric fields far from the arc, the fluctuating expansion of the gas ejected from the torch, and the formation and evolution of coherent flow structures. [Preview Abstract] |
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MR1.00040: PLASMA ETCHING |
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MR1.00041: Reduction of Aspect Ratio Dependency in Silicon Trench Etch Robert Bates The etch rate of deep features in silicon, such as trenches and vias, can vary significantly with the changing aspect ratio (AR) of the feature. This work focused on using a continuous plasma process utilizing a gas mixture of SF$_{6}$-C$_{4}$F$_{8}$-Ar to produce trenches of varying widths and depths. Optical and electrical diagnostics of percent flow, total flow and RF bias on trench profiles were investigated. Experiments were also performed to show that the etch rate of low AR features can be reduced through the deposition of a passivation layer and thereby allow larger AR features to ``catch up''. It is also possible to invert the ARDE in certain circumstances. [Preview Abstract] |
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MR1.00042: Plasma Processing of Large Curved Nb Surfaces with Application to SRF Cavities Janardan Upadhyay, Do Im, Frederick Miller, Svetozar Popovic, Leposava Vuskovic, Larry Phillips, Anne-Marie Valente-Felliciano Surface modification of superconducting radio-frequency (SRF) cavities are a promising alternative to the wet etching technologies that are currently applied to Nb cavities. We have built a Nb etching cylindrical discharge chamber, comparable by volume to 1.5 GHz resonant cavity with 8 observation ports for holding the Nb samples, spectral observations, and electric probe measurements. Several asymmetric discharge configurations were tested with a variety of pressure, power and gas composition combinations. All discharges have been operated in Ar/Cl$_{2}$ gas mixtures with Cl$_{2}$ content up to 15{\%}. Plasma parameters were evaluated using a Langmuir probe, and an optical emission spectroscopy based on the relative intensities of two specific Ar 5p-4s lines at 419.83 and 420.07 nm, respectively. We have also carried out a systematic study of atomic and molecular spectra during Nb etching in order to determine the most appropriate process signature. The effects of discharge conditions and parameters are intended to be used as guidelines for optimal design of SRF cavity etching processes. [Preview Abstract] |
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MR1.00043: Development of Magnet-Free Sputtering System for Dielectric Film Deposition with Surface-Wave Excited Plasma Tomonori Noda, Toshiya Hagihara, Hirotaka Toyoda In various thin film deposition technologies such as plasma-enhanced chemical vapor deposition or vacuum evaporation, plasma sputtering is known as one of common technology because of its applicability to the deposition of high-melting-point materials on glass or polymer substrates. However, degradation of interface and/or and crystalline quality due to impingement of high-energy-particles is sometimes one of issues for sputter deposited films. In our previous study, we have shown that high energy negative ions are localized not at high plasma density regions but at low plasma density regions in the case of dielectric RF sputtering. This fact suggests that the movement of the magnet (and the plasma) that is common in industrial sputtering system results in non-uniform irradiation of high energy negative ions on the depositing film surface. To solve such problem, we propose uniform sputtering of dielectric materials without using magnets, i.e., using uniform surface-wave excited plasma and RF biasing. With use of a microwave-plasma coupling antenna that can sustain plasma at low pressures less than 1 Pa, uniform sputtering of dielectric materials will be demonstrated. [Preview Abstract] |
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MR1.00044: Dynamics of pulsed laser deposition plasmas Kim Peerenboom, Jan van Dijk, Rik Groenen, Kasper Orsel, Bert Bastiaens Pulsed laser deposition has proven to be a successful technique to deposit complex materials with atomic precision. In the first stage of the pulsed laser deposition process, target material is ablated by irradiation with a high power pulsed laser. This ablated material develops into a plasma plume which expands and is finally deposited on a substrate. Although the pulsed laser deposition technique itself is simple, the physical processes behind it are rather complex. As a result of this complexity, up to now understanding of the pulsed laser deposition process is limited to empirical knowledge. To establish the link between the experimental parameters (e.g. laser pulse duration, background pressure) and the deposited film, quantification of the species fluxes in the plasma plume is crucial. As a first step towards such a quantification, we will present a numerical simulation studying the influence of the background gas on the dynamics of the plasma plume. [Preview Abstract] |
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MR1.00045: Cluster incorporation during amplitude modulated VHF discharge silane plasmas Susumu Toko, Yeonwon Kim, Yuji Hashimoto, Yoshinori Kanemitu, Hyunwoong Seo, Giichiro Uchida, Kunihiro Kamataki, Naho Itagaki, Kazunori Koga, Masaharu Shiratani VHF discharge silane plasmas have been widely used to deposit hydrogenated amorphous silicon (a-Si:H) films. In this plasma process, while the higher VHF power brings about the higher deposition rate, it also results in generating a lot of Si clusters, which are mainly responsible for light degradation of a-Si:H thin films. Therefore, it is important to clarify a growing process and behavior of clusters and to develop a method for suppressing cluster incorporation into films. Here we investigated effects of amplitude modulated VHF discharge silane plasmas on cluster incorporation into Si thin films by in-situ measurements with quartz crystal microbalances (QCM). Experiments were carried out in a multi-hollow discharge plasma CVD reactor with QCM [1,2]. The amount of cluster incorporation in initial phase and steady state is found to be controlled by modulation level and frequency of the amplitude modulation.\\[4pt] [1] Y. Kim, et al., Jpn. J. App. Phys. 52 (2013) 01AD01.\\[0pt] [2] K. Koga, et al., J. Vac. Sci. Technol. A22 (2004) 1536. [Preview Abstract] |
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MR1.00046: A study on the characteristics of Ti and C thin film prepared by Modulated Sputtering System (MSS) Tae-Hwan Kim, Dae Chul Kim, Yonghyun Kim, Young-Woo Kim, Ho Jun Lee, Seunghee Han In this work, newly designed bipolar pulsed DC power supply (Modulator) for MSS was developed to improve the properties of thin films. During the pulse on-time of the modulator driven by external TTL pulse, a negative voltage is applied to deposit the thin films on the substrate. Also, a positive voltage is applied while the pulse off-time of the modulator, and then ion beams are generated from the plasma and driven away to the substrate. Experiment was performed for various bias voltage, frequency and duty cycle. We also observed Ti thin films deposited by the MSS. The crystal structure, surface roughness, and thickness were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), alpha step and scanning electron microscopy (SEM) measurement, respectively. The crystal orientation of the Ti films changes from a (002) preferred orientation to an entirely (100) orientation with increasing the ion beam energy. Also, we investigated bonding structure, sheet resistance, and thickness of carbon thin film by using micro-Raman spectroscopy, thin films resistor analyzer, and alpha step. In the case of the sheet resistance of carbon films, sheet resistance was decreased by increased ion beam energy. And then, it was increased again through continuously ion beam energy increasing more than 100eV. [Preview Abstract] |
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MR1.00047: Thin Film Deposition of MAX Phase Nb-Al-C Compounds on Stainless Steel Substrates Using a Magnetized Sheet Plasma Source Janella Mae Salamania, Henry Ramos Thin films of the Nb-Al-C system were deposited on stainless steel substrates through the magnetron sputtering mode of the Magnetized Sheet Plasma Facility from elemental source of Nb, Al metals and reactive gas CH$_{4}$. Niobium and aluminum targets were first sputtered using argon plasma and were deposited together with CH$_{4}$ gas onto the substrates. Various parameters such as target bias, time, filling pressure and extraction current were varied. Synthesized thin films were then characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX) and Raman Spectroscopy. XRD spectra of the samples show that MAX phases of the Nb-Al-C family are present on the films, specifically, the 413 phase (Nb$_{4}$AlC$_{3})$. EDX and Raman spectra confirm the presence of the elemental niobium, aluminum and carbon in the films. Raman spectra show that excess carbon formed fine graphite crystallites. SEM surface images show that the resulting films follow the contours of the SS substrate. The cross-sectional images show micron scale thickness deposited above the SS substrates. [Preview Abstract] |
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MR1.00048: Parameter manipulation in the Synthesis of Ti-Cd-C Films via Reactive Sputtering in a Magnetized Sheet Plasma Facility Matthew Bryan Villanueva, Henry Ramos Titanium-cadmium-carbon (Ti-Cd-C) deposits were achieved through reactive sputtering in a magnetized sheet plasma facility (MSPF). Titanium and cadmium metals (99.9{\%} purity) were used as sputter targets, and high purity methane as the reactive gas. Parameters investigated were target bias, deposition duration, filling pressure, gas ratio, gas type such as acetylene, and magnetic configuration. Through X-ray diffractometry, peak signals at 2$\theta =$23.3$^{\circ}$ for the treatment which implemented an independent sputtering step at -200 V target bias, and 2$\theta =$12.34$^{\circ}$ for direct reactive sputtering only with -800 V target bias were recorded. Both XRD results are indicative of the formation of Ti$_{2}$CdC, a theorized solid solution of M$_{\mathrm{n+1}}$AX$_{\mathrm{n}}$ phase variety. [Preview Abstract] |
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MR1.00049: PLASMA DEPOSITION |
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MR1.00050: Ar/N2 Magnetron Sputtering Discharges to Control Growth of Transparent Conducting Oxide Films Koichiro Oshikawa, Iping Suhariadi, Daisuke Yamashita, Hyunwoong Seo, Kunihiro Kamataki, Giichiro Uchida, Kazunori Koga, Masaharu Shiratani, Naho Itagaki Here we demonstrate advantageous application of Ar/N2 discharges to magnetron sputtering deposition of ZnO films for crystal growth control [1]. Optical emission spectroscopy reveals that atomic nitrogen in Ar/N2 discharges plays important roles in determining the crystal grain density as well as the surface morphology of ZnO films. By utilizing 10-nm-thick ZnO films fabricated in Ar/N2 discharges as buffer layers, we have succeeded in fabricating low-resistive ZnO:Al (2wt.{\%}) films, the properties of which are superior to those of conventional ZnO:Al films fabricated without N2. The resistivity of ZnO:Al films with buffer layers is a constant low value of 2.6x10$^{-4}$ $\Omega \cdot$cm in the thickness range 20-200 nm, whereas the resistivity of conventional ZnO:Al films increases from 6.3x10$^{-4}$ to 1.5x10$^{-3}$ $\Omega \cdot$cm with decreasing the thickness from 200 nm to 20 nm. Effects of Ar/N2 discharges on other transparent conductive oxides including In2O3:Sn will be discussed at the conference.\\[4pt] [1] N. Itagaki, et al., Appl. Phys. Express 4 (2011) 011101. [Preview Abstract] |
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MR1.00051: Growth of Amorphous Silicon Nitride Films on Silicon Wafer by Atmospheric Pressure Plasma Jet Xueqiang Zhang, Sylwia Ptasinska Atmospheric pressure plasma jets (APPJ) possess favorable advantages including low temperature, low cost and the potential to be applied in areas such as coating and material functionalization. Silicon nitride is the most important non-oxide ceramics and multi-methods have been employed to grow silicon nitride, but its application has been limited by its high production cost. Here we demonstrate a method in which APPJ was used to grow amorphous silicon nitride films on a silicon wafer. Hydrofluoric acid pretreated Si wafers were treated by the helium APPJ at ambient air conditions. X-ray photoelectron spectroscopy (XPS) showed that silicon nitride species with binding energy at 398 eV are formed on the Si surface. XPS spectra taken from different areas of Si wafers indicate that the formation of nitrides is highly localized due to direct interactions with the plasma jet. This can also be verified by XPS 2-D mapping of N1s signal. Other gases such as N$_{2}$, N$_{2}$O, NO, NH$_{3}$ were doped into the helium stream and it was found that nitrogen and ammonia gas mixed with helium produced the highest intensity of a nitride signal. Optical emission spectra of APPJ were measured in order to understand the nitride formation mechanism. [Preview Abstract] |
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MR1.00052: BIOLOGICAL AND BIOMEDICAL APPLICATIONS OF PLASMAS |
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MR1.00053: Reaction mechanism between cell membranes of P. digitatum spores and oxygen radicals Masafumi Ito, Hiroshi Hashizume, Takayuki Ohta, Keigo Takeda, Kenji Ishikawa, Masaru Hori P. digitatum spores were exposed to oxygen radicals 10 and 20 mm downstream from our developed atmospheric-pressure oxygen-radical source. Treated spores were stained by 1,1'-dioctadecyl-3,3,Y,3'-tetramethyl indocarbocyanine perchlorate (DiI), which has been used for investigation for functions of cell membranes. For control spores, DiI is not permeable into cells because cell membranes have selective permeability. Stained spores were observed by confocal laser microscopy. At 10 mm distance, 84{\%} of total spores were intracellularly stained with 1.5-minute oxygen radical treatment. On the other hand, at 20 mm distance, about 80{\%} of the total spores were intracellularly stained at least with 3-minute oxygen radical treatment. Based on the results of inactivation rates of \textit{P. digitatum} spores and oxygen-radical densities, the results indicated that the increase of ratio of the number of intracellularly stained spores was correlated with the density of O($^{3}$P$_{\mathrm{j}})$ rather than O$_{2}(^{1}\Delta_{\mathrm{g}})$. These results and SEM observations suggest that O($^{3}$P$_{\mathrm{j}})$ plays an important role as an inactivation factor by disturbing the normal function of cell membranes and influencing intracellular organelles without major deformation of the membranes. [Preview Abstract] |
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MR1.00054: Air surface microdischarge-photon synergy in antibacterial plasma-activated water David Graves, Mathew Pavlovich, Hung-Wen Chang, Yuki Sakiyama, Douglas Clark We show that the antibacterial effects of air plasma on water can be amplified by synergy with ultraviolet (UV) photons. We use the surface microdischarge configuration (SMD) in atmospheric air adjacent to bacteria-laden water coupled with UVA (360 nm) photons from a light emitting diode (LED) to demonstrate this synergy. Air SMD, especially if operated in a confined space, can operate in different modes: low power mode ($<$ 0.1 W/cm2) generates primarily O3 whereas higher powers generate mainly nitrogen oxides; we focus here on the latter. The nitrogen oxide mode creates a powerful antibacterial mixture in water, including NO2-, NO3- and H2O2. Although these species alone can be strongly antibacterial, especially at low pH, we show that addition of UVA photons greatly amplifies the antibacterial effect. We first measured log reductions with only photons and then only plasma. Only when UVA exposes water after plasma does the synergy appear. Synergy appears to be due to UVA photolysis of plasma-generated NO2- to form NO and OH. We conclude that combining plasma-generated chemical species with activating photons can amplify and strengthen plasma effectiveness in many biological and other applications. [Preview Abstract] |
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MR1.00055: The interaction of atmospheric pressure plasma jets with cancer and normal cells: generation of intracellular reactive oxygen species and changes of the cell proliferation and cell cycle Tae Hun Chung, Hea Min Joh, Sun Ja Kim, Sun Hee Leem The possibility of atmospheric pressure plasmas is emerging as a candidate in cancer therapy. The primary role is played by reactive oxygen species (ROS), UV photons, charged particles and electric fields. Among them, intracellular ROS induced by plasma are considered to be the key constituents that induce cellular changes and apoptosis. In this study, the effects of atmospheric pressure plasma jet on cancer cells (human lung carcinoma cells) and normal cells (embryonic kidney cells and bronchial epithelial cells) were investigated. The plasma treatment was performed under different working gases, applied voltages, gas flow rates, and with and without additive oxygen flow. Using a detection dye, we observed that plasma exposure leads to the increase of the intracellular ROS and that the intracellular ROS production can be controlled by plasma parameters. A significant ROS generation was induced by plasma exposure on cancer cells and the overproduction of ROS contributes to the reduced cell proliferation. Normal cells were observed to be less affected by the plasma-mediated ROS and cell proliferation was less changed. The plasma treatment also resulted in the alteration of the cell cycle that contributes to the induction of apoptosis in cancer cells. The selective effect on cancer and normal cells provides a promising prospect of cold plasma as cancer therapy. [Preview Abstract] |
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MR1.00056: DNA damage induced by low energy electron collision and new experimental setup for further studying DNA damage by plasma Yeunsoo Park, Leon Sanche, Richard Wagner Low energy electrons (LEEs; below 10 eV) are the most abundant among the radiolytic species generated along the high energy radiation track in living cell. And these electrons are also one of major components with ions and photon in plasma. Interestingly, it has turned out that LEEs can create DNA damages such as base release, single- and double- strand breaks (SSB and DSB) via indirect action named dissociative electron attachment (DEA). The purposes of this study are to further find out exact mechanisms of DNA damage by LEEs at the molecular level and to verify new DNA damage like structural alteration on DNA subunits. And we will expand our study to DNA damage by plasma source to develop plasma-based new medical and biological applications. We are currently setting new experimental system for reaching our goals. We will show some recent results about new finding DNA modification damage and some experimental designs and working principles. [Preview Abstract] |
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MR1.00057: Low Temperature Plasma Kills SCaBER Cancer Cells Nazir Barekzi, Lucas Van Way, Mounir Laroussi Squamous cell carcinoma of the bladder is a rare type of bladder cancer that forms as a result of chronic irritation of the epithelial lining of the bladder. The cell line used in this study is SCaBER~(ATCC\textregistered ~HTB-3\texttrademark ) derived from squamous cell carcinoma of the human urinary bladder. Current treatments of bladder cancer include surgery, radiation and chemotherapy. However, the cost of these treatments, the potential toxicity of the chemotherapeutic agents and the systemic side-effects warrant an alternative to current cancer treatment. This paper represents preliminary studies to determine the effects of biologically tolerant plasma (BTP) on a cell line of human bladder cancer cells. Previous work by our group using the plasma pencil [1] revealed the efficacy of BTP on leukemia cells suspended in solution [2]. Based on these earlier findings we hypothesized that the plasma exposure would elicit a similar programmed cell death in the SCaBER cells. Trypan blue exclusion and MTT assays revealed the cell killing after exposure to BTP. Our study indicates that low temperature plasma generated by ionizing helium gas and the reactive species may be a suitable and safe alternative for cancer therapy. [1] Laroussi M and Lu X. 2005. \textit{Applied Physics Letters}, \textbf{87}(113902):1-3. [2] Barekzi N and Laroussi M. 2012. \textit{Journal of Physics D: Applied Physics}. \textbf{45}(42): p.422002. [Preview Abstract] |
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MR1.00058: Atmospheric pressure dielectric barrier discharges interacting with liquid covered tissue Wei Tian, Mark J. Kushner Tissue treated by atmospheric pressure dielectric barrier discharges in plasma medicine are often covered by a thin layer of liquid, water with dissolved gases and proteins. The liquid processes the plasma produced radicals and ions prior to their reaching the tissue. We report on a computational investigation of the interaction of DBDs with a thin liquid layer covering tissue. The simulations were performed with \textit{nonPDPSIM}, a 2-D plasma hydrodynamics and radiation transport model. The liquid is treated identically to the gas as a partially ionized substance but with a higher density. Liquid evaporates into the gas with a source given by its saturated vapor pressure. Transport of gas phase species into the liquid is determined by Henry's Law considerations. The tissue is treated as a dielectric and the species fluxes onto the tissue are recorded. The liquid layer, typically hundreds of microns thick, is water containing dissolved O$_{2}$ and alkane-like hydrocarbons (RH). In the model, the DBDs are operated with multiple pulses at 100 Hz followed by a 1 s afterglow. Gas phase reactive oxygen and nitrogen species (RONS) intersect the water vapor saturated air above the liquid and then solvate when reaching the liquid. The photolysis of water by plasma produced UV/VUV plays a significant role in the radical production. Without RH, O$_{2}^{-}$ and hydronium (H$_{3}$O$^{+})$ dominate the water ions with H$_{3}$O$^{+}$ determining the pH. The dominant RONS in the liquid are O$_{3}$, H$_{2}$O$_{2}$, and HNO$_{x}$. With RH, ROS are largely consumed, leaving R\textbullet (alkane radical) to reach the tissue. [Preview Abstract] |
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MR1.00059: The injection of microorganisms into an atmospheric pressure rf-driven microplasma P.D. Maguire, C.M.O. Mahony, D. Diver, D. Mariotti, E. Bennet, H. Potts, D.A. McDowell The introduction of living organisms, such as bacteria, into atmospheric pressure microplasmas offers a unique means to study certain physical mechanisms in individual microorganisms and also help understand the impact of macroscopic entities and liquid droplets on plasma characteristics. We present the characterization of an RF-APD operating at 13.56MHz and containing microorganisms in liquid droplets emitted from a nebulizer, with the spray entrained in a gas flow by a gas shroud and passed into the plasma source. We report successful microorganism injection and transmission through the plasma with stable plasma operation of at least one hour. Diagnostics include RF electrical characterization, optical emission spectrometry and electrostatic deflection to investigate microorganism charging. A close-coupled Impedans Octiv VI probe indicates source efficiencies of 10 to 15{\%}. The introduction of the droplets/microorganisms results in increased plasma conductivity and reduced capacitance, due to their impact on electron density and temperature. An electrical model will be presented based on diagnostic data and deflection studies with input from simulations of charged aerosol diffusion and evaporation. [Preview Abstract] |
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MR1.00060: Comparison of an APPJ discharge characteristics to internal properties of living cells Pietro Ranieri, Sarah Gucker, John Foster, Aniruddha Ray, Raoul Kopelman, Leshern Karamchand Plasma medicine is quickly developing into a novel research field for decontamination and treatment for both wounds and disease. A common question between the research efforts is the effect of plasma both around the cell and within it. This study aims to discover the effect of an atmospheric pressure plasma jet on the internal properties of living cells as a function of treatment time. Through the use of nanoparticles, relative changes in pH and singlet oxygen both inside the cells and the cell media have been determined for various plasma exposure times. Further diagnostic tests on the plasma discharge will allow this effort to compare the results from changes inside the cell to those in the surrounding atmosphere to gain further insight on the reaction of the cell to plasma treatment. [Preview Abstract] |
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MR1.00061: Plasma jets for biomedical applications: PAPS control of the rare gas jets Jean-Michel Pouvesle, Vanessa Sarron, Eric Robert, Jerome Fontane, Thibault Darny, Delphine Ries, Sebastien Dozias, Laurent Joly The development of atmospheric pressure plasma biomedical applications led number of teams to develop various types of rare gas plasma jets. It's generally thought that the plasma plume expanding in air, where most of the reactive species are produced, just follow the rare gas canal which is produced at the outlet of the plasma reactor capillary. Depending on Reynolds number (i.e. capillary diameter, gas flow rate), the rare gas flow will undergo a laminar or turbulent regime. This directly affects the reactive species distribution at the plasma/target interface, thus potentially having an influence on the realized treatment. In this work, not only we demonstrate that PAPS (Pulsed Atmospheric pressure Plasma Stream) production parameters (frequency, capillary length) directly affect the rare gas flow structure in addition to flow parameters mentioned above, but that the PAPS themselves control the gas column development outside the capillary. At low flow rate, there exists a real build up of the gas column within the first hundred of pulses and a rapid return to initial situation as soon as the plasma is off. This allows a very precise modulation of plasma application. Conversely, it can lead to misinterpretations if not taken into account properly in the treatment protocol. [Preview Abstract] |
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MR1.00062: The electrodynamics of aerosols and bacteria in a microplasma P.D. Maguire, C.M.O. Mahony, D. Diver, D. Mariotti, E. Bennet, H. Potts, D.A. McDowell The physics of living organisms is considered a grand challenge of science. Plasma interactions with living organisms, particularly at atmospheric pressure, offer a unique opportunity to study the physical mechanisms and surface electrodynamics of individual microorganisms. The impact on the plasma of such macroscopic entities is itself important; the dynamics of non-spherical and non-rigid nano-/micro-scale structures have received little attention. Also the plasma interaction with water, from molecules to droplets, is becoming increasingly significant due to induced chemistries that differ considerably from conventional plasma chemistry. We investigate the bulk and surface physical properties of individual microorganisms, particularly bacteria, through electrical and visco-mechanical excitation. Individual organisms are transported by water droplets to an rf microplasma. Their impact on the plasma is determined by imaging, optical and electrical diagnostics. We report, using imaging, electrostatics and simulation, on (i) fluid stability under evaporative stress of charged microbe-carrying macroscopic droplets, (ii) impact of the plasma on the stochastic component of motion and (iii) the acquired charge distribution and transfer from liquid to lipid surface. [Preview Abstract] |
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MR1.00063: Application of Surface Micro-Discharge plasma to spacecraft component decontamination Satoshi Shimizu, Simon Barczyk, Petra Rettberg, Tetsuji Shimizu, Tobias Klaempfl, Julia Zimmermann, Peter Weber, Gregor Morfill, Hubertus Thomas In the field of extinct or extant extraterrestrial life research on other planets and moons, the prevention of biological contamination through spaceprobes is one of the most important requirements, and its detailed conditions are defined by the COSPAR planetary protection policy. Currently, a dry heat microbial reduction (DHMR) method is the only applicable way to satisfy the demand, which could, however, damage the sophisticated components like integrated circuits. In this study, cold atmospheric plasma based on the Surface Micro-Discharge technology was investigated for inactivation of different types of bacteria and endospores as an alternative method. After 90 min of plasma gas exposure, 3-6 log reductions were observed for the vegetative bacteria \textit{Escherichia coli }and \textit{Deinococcus radiodurans} and several types of bacterial endospores - including \textit{Bacillus atrophaeus},\textit{ B. safensis, B. megaterium, B. megaterium 2c1} and \textit{B. thuringiensis E24}. Furthermore, the applicability of the system for spacecraft decontamination was checked by studying the inactivation homogeneity, the temperature at the area of interest and the effects of the plasma gas exposure on different materials. [Preview Abstract] |
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MR1.00064: Applications of plasma sources for nitric oxide medicine Victor Vasilets, Anatoly Shekhter, Alexander Pekshev Nitric oxide (NO) has important roles in the function of many tissues and organs. Wound healing processes are always accompanying by the increase of nitric oxide concentration in wound tissue. These facts suggest a possible therapeutic use of various NO donors for the acceleration of the wound healing and treatment of other diseases. Our previous studies [1] indicated that gaseous NO flow produced by air-plasma generators acts beneficially on the wound healing. This beneficial effect could be caused by the mechanism involving peroxynitrite as an intermediate. As a result of mobilization of various antioxidant reactions more endogenous NO molecules become available as signaling molecules. to regulate the metabolic processes in wound tissue. In this paper different air plasma sources generated therapeutic concentrations of NO are discussed. The concentration of NO and other therapeutically important gas products are estimated by thermodynamic simulation. Synergy effects of NO with other plasma components are discussed as a factor enhancing therapeutic results. Some new medical application of plasma devices are presented. [Preview Abstract] |
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MR1.00065: HEAVY PARTICLE COLLISIONS |
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MR1.00066: Enhancement of Limb Growth by Non-Thermal Plasma Generated Reactive Species N. Shainsky, M. Steinbeck, G. Fridman, A. Fridman, G. Friedman, T. Freeman Introduction: The goal of this investigation was to examine the effect of Dielectric Barrier Discharge plasma on mouse autopod differentiation and growth. In this study we hypothesized that NT-plasma can be used to promote redox dependent changes in differentiation pathways and enhance developmental signaling? Methods: Approximately 1 hour after isolation, NT-plasma or sham plasma treatment was applied to the right or left limb, respectively. The medium was changed daily thereafter for the 4-6 days of culture. NT-plasma treatment: pulsed (1000 Hz) voltage of 17 - 25 kV magnitude (peak to peak), a 1 $\mu$s pulse width and a rise time of 5 V/ns between the quartz-insulated high voltage electrode and the sample undergoing treatment. Results: A single 10 second NT-plasma treatment promoted development of mouse autopods as compared to the sham control contralateral limb. NT-plasma accelerated digit growth in both E14.5 and E12.5 autopods. Inhibitors were used to determine the role of ROS and RNS in mediating NT-plasma accelerated autopod development. Treatment with these agents stunted autopod morphogenesis NT-plasma treatment partially rescued development. Discussion: Our findings highlight the capability of NT-plasma to activate ROS-dependent cell signaling cascades within developing autopod tissue. In fact, the effect of NT-plasma may indeed extend beyond ROS sensitive signaling as NT-plasma exposure seems to stimulate some growth even in the presence of antioxidant induced stunting. [Preview Abstract] |
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MR1.00067: Mean-field description of B$^{2+}$-Ne collisions with active target and projectile electrons Tom Kirchner, Gerald Schenk, Marko Horbatsch We apply an independent electron model to study $q$-fold target charge state production in 25--600~keV/u B$^{2+}$-~Ne collisions. Projectile and target electrons are treated on the same footing using a common potential and a single-determinant wave function for the combined system [1]. For the sake of comparison we also perform a reduced calculation in which the projectile electrons are frozen in their initial state. Results are compared with recent experimental and theoretical data for positive ion production as well as for Ne$^{q+}$ production obtained in coincidence with an unchanged projectile charge state [2]. We find that the total cross sections obtained from our full calculation agree well with experiment for $q=1,\ldots,4$, while the reduced calculation produces pronounced discrepancies for $q\ge 2$. This suggests that the projectile electrons participate actively even in processes, in which the projectile charge state does not change. At the conference, we will demonstrate that direct projectile electron loss with and without simultaneous transfer of a target electron can explain the observed features. \\[4pt] [1] T.~Kirchner and M.~Horbatsch, Phys.~Rev.~A~\textbf{63}, 062718 (2001)\\[0pt] [2] W.~Wolff et al, Phys.~Rev.~A~\textbf{84}, 042704 (2011) [Preview Abstract] |
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MR1.00068: Synthesis and characterization of SnS2 Arturo Mendez, Mauricio Ortega, Jorge Contreras Tin disulfide (SnS$_{2})$ nanoparticles were successfully prepared by colloidal chemistry using the hot-injection approach, starting of tin(II) chloride, sulfur and oleylamine. The phase composition and morphology were analyzed by X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM). The results show that the synthesis produces nearly-spherical SnS$_{2}$ nanoparticles around 20-50 nm in size, crystallizing in the hexagonal structure. The elemental analysis carried out by EDAX indicated that the obtained nanoparticles are nearly stoichiometric SnS$_{2}$. A representative Raman spectrum reveals a sharp peak at 313 cm$^{-1}$, which characterizes the hexagonal phase of SnS$_{2}$. [Preview Abstract] |
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MR1.00069: Basis-generator-method study of ionization and fragmentation of water molecules by multiply-charged ion impact Tom Kirchner, M. Horbatsch, M. Murakami, T. Pausz, H.J. L\"udde In a recent series of publications we have described the adaptation of the basis generator method (BGM), originally developed for ion-atom collisions, to molecular targets and have reported on results for proton and He$^{+}$-ion impact on H$_2$O molecules [1]. The microscopic collision calculations were complemented with a semi-phenomenological fragmentation model [2], which in contrast to previous models takes multiple electron removal processes into account. This turned out to be crucial for obtaining reasonable agreement with experimental data for the production of singly charged fragment ions. In this contribution, we report on results obtained from using the same methodology for bare helium, lithium, and carbon ion impact on H$_2$O in the 20--5000 keV/amu regime and compare them with experimental data and previous calculations where available. In addition, we will discuss the usefulness of ternary plots [3] to provide a somewhat more general view on fragmentation in ion-water-molecule collisions. \\[4pt] [1] M. Murakami {\em at al}, Phys. Rev. A {\bf 85}, 052704 (2012); {\bf 86} 022719 (2012).\\[0pt] [2] M. Murakami {\em at al}, Phys. Rev. A {\bf 85}, 052713 (2013). [3] E. C. Montenegro, J. Phys.: Conf. Ser. {\bf 194}, 012049 (2009). [Preview Abstract] |
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MR1.00070: Numerical simulations of N$_{2}$-N$_{2}$ quasi-complex formation in binary collisions Anatoly Napartovich, Alexander Kurnosov It's known that atomic and molecular collisions in a gas at low temperatures may result in formation of the unstable quasi - complexes (QC). The specific feature of these complexes is rather long life time. The QCs are of interest for researchers since they can play an active role in various physical and chemical processes. Stabilization of a QC results in formation of molecular dimer. Numerical simulation of dynamics of the QCs requires detailed data about interaction potential. In particular, in [1] studies were done on sensitivity of the characteristics of Ar-CO$_{2}$ QC to a form of potential energy surface. No information exists about dynamics of bimolecular QCs. The purpose of our study is numerical simulations of a QC formation in bimolecular collisions. Of particular interest is formation of N$_{2}$-N$_{2}$ QC since the molecular nitrogen is the widespread species. We used the semi-classical coupled-state method described in [2] with the same intermolecular potential function. The rate constants for the N$_{2}$-N$_{2}$ QC formation will be presented.\\[4pt] [1] S. V. Ivanov, Molecular Physics, 2004, v.102, p.1871\\[0pt] [2] M. Cacciatore, A. Kurnosov, A. Napartovich, Journal of Chemical Physics, 2005, v.123, p.174315 [Preview Abstract] |
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MR1.00071: DISSOCIATION, RECOMBINATION AND ATTACHMENT |
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MR1.00072: Computational Study on Chemical Reaction Properties of C$_{4}$F$_{8}$ Plasma Molecules Heechol Choi, Young C. Park, Kyoung K. Baeck, Yoon S. Lee Of many perfluorocarbons(PFCs), C$_{4}$F$_{8}$ species attract special attention because of their potential for decreasing global warming gas emissions and their high CF$_{2}$ radical levels in commercial plasma treatments. Several experimental and theoretical studies of these species have been conducted, although only the geometries at their stationary states and their adiabatic electron affinities have been determined. However, this information is not sufficient for a deep understanding of all the possible fates and roles of C$_{4}$F$_{8}$ species and their fragments in plasma phases. So a careful additional assessment of the reliability of DFT functionals for the study of PFCs is highly required. First, in order to find a DFT method appropriate to PFCs, the geometry, energy, and chemical reaction properties of C$_{4}$F$_{8}$ were calculated and compared with reference data. Second, based on variational transition-state theory, the rate constants of dissociations and isomerizations of C$_{4}$F$_{8}$ species were computed for a deep insight into their mechanisms. [Preview Abstract] |
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MR1.00073: Dissociative electron attachment to the monocyclic azines pyrimidine, pyridazine, pyrazine and 1,3,5-triazine Thomas Gilmore, Thomas Field, Nathan Agnew, Andreas Mauracher, Samuel Z\"{o}ttl, Ewelina Szymanska Observations of dissociative electron attachment to Pyrimidine, Pyrazine, Pyridazine ($C_4H_4N_2$) and 1,3,5-Triazine ($C_3H_3N_3$) are reported in the electron energy range 0-12eV. Pyrimidine is the building block of the nucleobases Cytosine, Thymine and Uracil. Dissociation of the nucleobases caused by low energy electrons, eg. released by the Auger effect in radiation therapy, has been studied over the last decade. Resonances presented here will be compared to those observed in nucleobase experiments. CN- is identified as the main product of dissociative electron attachment to the azine molecules. Resonances occur near 5.1eV and 8.2eV for all molecules. A comparison to R-matrix calculations by Masin and Gorfinkiel show reasonable agreement to experiment. Absolute cross sections for dissociative electron attachment have been estimated: pyrimidine has a maximum negative ion formation cross section of 8 x 10$^{-3}$ {\AA}$^2$ at 5.1 $\pm$ 0.2eV. The cross sections on resonance for negative ion formation in dissociative electron attachment to the other molecules are all within a factor of two of this peak value for pyrimidine.The absence of hydrogen fragments,reported as dominant in nucleobase studies,is also investigated. [Preview Abstract] |
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MR1.00074: DISTRIBUTION FUNCTIONS AND TRANSPORT COEFFICIENTS FOR ELECTRONS AND IONS |
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MR1.00075: Updates on the freeware electron Boltzmann equation solver BOLSIG$+$ G.J.M. Hagelaar, L.C. Pitchford In 2005, we released BOLSIG$+$, a user-friendly and free computer application solving the Boltzmann equation for electrons in uniform electric fields in order to obtain electron transport coefficients and rate coefficients from cross section data. The physical principles of BOLSIG$+$ were described in a journal article [Plasma Sources Sci. Technol. 14, 722-733 (2005)]. Since then BOLSIG$+$ has grown into a standard tool in research on collisional gas discharges. This paper discusses a number of BOLSIG$+$ extensions/improvements that were added over the years but were never published in the official literature, including anisotropic diffusion coefficients. We also show comparisons with Monte-Carlo calculations in order to evaluate possible errors due to the two-term approximation (of the angular dependence of the distribution function) used by BOLSIG$+$. These errors are smaller than is generally thought and are in fact insignificant over a wide range of conditions, provided that proper attention is paid to the consistency of the input data and the definition of the transport coefficients. [Preview Abstract] |
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MR1.00076: Electron swarm transport coefficients in H2O - He mixtures: Experiment and calculations J. de Urquijo, A.M. Ju\'arez, J.L. Hern\'andez-\'Avila, E. E. Basurto, K.F. Ness, R.E. Robson, Ron White, M.J. Brunger In this presentation we report recent measurements of electron swarm transport coefficients using the pulsed-Townsend technique for mixtures of water and helium over the range of applied fields E/N from 0-200Td. Comparison is made with transport coefficients calculated using a multi-term Boltzmann equation solution and recently proposed electron-water cross-section sets. This represents a new and more discriminative test on the accuracy and consistency of such sets. Negative differential conductivity is observed for a small window of mixture ratios, even though the pure gases themselves do not demonstrate NDC. Similar interesting effects are observed in the ionization rates as a function of the mixture ratios. The origin of these behaviours will be discussed. [Preview Abstract] |
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MR1.00077: OTHER ATOMIC AND MOLECULAR COLLISION PHENOMENA |
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MR1.00078: Momentum transfer cross sections for the heavy noble gases Allan Stauffer, Robert McEachran We have used our relativistic optical potential method [1] to calculate the momentum transfer cross sections for Ar, Kr and Xe from threshold to 1000 eV. The target ground state as well as the open excited and ionization channels used in the optical potential have been calculated using the MCDF program [2]. We have included 17 excitation channels for Ar, 26 for Kr and 15 for Xe. In the ionization channels, ionization of the outer p, s and d shells were included for Kr and Xe while for Ar all electrons were allowed to be ionized. Comparisons with previous calculations and experimental measurements will be included. We also include analytic fits to our cross sections to aid in plasma modelling studies.\\[4pt] [1] S. Chen, R. P. McEachran and A. D. Stauffer, J. Phys. B 41 025201 (2008)\\[0pt] [2] I. P. Grant, B. J. McKenzie, P. H. Norrington, D. F. Mayers and N. C. Pyper, Comput. Phys. Commun. 21 207 (1980) [Preview Abstract] |
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MR1.00079: Static potentials for electron-molecule scattering: the case of water Allan Stauffer, Tapasi Das, Rajesh Srivastava Molecular wave functions are commonly represented by Gaussian orbitals which have a simple form. We have derived a scheme to calculate spherically-averaged static potentials for electron-molecule scattering which is analytic except for the inclusion of the error function which can be easily calculated using existing algorithms. Although the asymptotic form of these potentials falls off too rapidly, the scattering potential is dominated by the long range polarization potential in this region. Including an exchange potential produces a result which is realistic representation of the electron-molecule interaction. Details of the method will be presented as well as an application to electron scattering from water. Our method produces results in good agreement with existing calculations and experimental measurements. The extension of this method to more complex molecules is straightforward. [Preview Abstract] |
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MR1.00080: Two-center approach to fully differential positron-impact ionisation of hydrogen A.S. Kadyrov, I. Bray The two-center approach to positron-impact ionisation of atomic hydrogen is shown to follow from the exact {\em post} form of the breakup amplitude [Kadyrov {\em et al.}, Phys. Rev. Lett. 101, 230405 (2008)]. In such approaches distinct ionization amplitudes arise from each center for the same ionization process. The fully differential cross section for positron-impact breakup of atomic hydrogen is calculated including direct ionisation of the target and electron capture into the positronium continuum. We show that the coherent combination of the amplitudes leads to unphysical oscillations in the differential cross sections, whereas the incoherent combination does not. On this basis it is concluded that two-center approaches to the problem should assume incoherent combination of the amplitudes from direct ionisation of the atom and positronium formation in the continuum. The latter is also consistent with the unitarity of the close-coupling formalism. [Preview Abstract] |
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MR1.00081: Monte Carlo simulation of rotating wall positron cloud compression Srdjan Marjanovic, Ana Bankovic, Milovan Suvakov, Sasa Dujko, Zoran Lj. Petrovic We have used our standard Monte Carlo code and applied it to electric potential setup that models the conditions inside the rotating wall apparatus. This model has allowed us to investigate the mechanisms behind the compression and to determine the types of collisions responsible for compression. Our results show that both ``high threshold'' losses, like ionization or electronic excitation, as well as ``low threshold'' losses, like vibrational and rotational excitations, play a role in compression. Parts of the positron ensemble that are further away from the axis are heated by the rotating field much stronger than the particles that are closer. Without the ``high threshold'' processes trajectories of these particles become unstable after several collisions. On the other hand, these ``high threshold'' processes do not provide strong enough cooling for fast compression. That is why ``low threshold'' processes are necessary to compress the positron beam to widths several orders of magnitude smaller. In addition we will report on frequency scan for compression rates, as well as compression rates for different values of the applied rotating electric field, magnetic field, and background gas pressure conditions. [Preview Abstract] |
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MR1.00082: Correlated n$^{1,3}$S states for two-electron atoms in screened potentials Lorenzo Ugo Ancarani, Karina V. Rodriguez, Gustavo Gasaneo We investigate two-electron atoms placed in a plasma environment, and consider both exponential cosine screened Coulomb potentials (ESCP) [1] and Debye-H\"{u}ckel or screened Coulomb potentials (SCP), for which the screening parameter $\lambda $ is related to the plasma frequency. Using highly correlated Hylleraas-type expansions, Ghoshal and Ho [2] have published the first calculations of the ground states of H$^{-}$ and He in ECSCP and SCP for a wide range of $\lambda $ values. We have confirmed these results with relatively simpler wave functions within a Configuration Interaction approach with explicitly correlated basis functions satisfying exactly all two-body Kato cusp conditions [3]. The main aim of the present contribution is to extend the findings of Ghoshal and Ho in various directions: (i) we evaluate the energy for the ground and the first $^{1,3}$S excited states, and provide analytical fits of the energy E($\lambda )$; (ii) we further extend the investigation to the iso-electronic series considering higher values of the nuclear charge Z and provide a double fit E($\lambda $,Z) -- thus a practical estimation tool for plasma applications; (iii) we make a systematic investigation of the $\lambda_{0}$ value for which the ground state ceases to exist. \\[4pt] [1] P K Shukla and B Eliasson 2008 Phys. Lett. A 372, 2897\\[0pt] [2] A Ghoshal and Y K Ho 2009 J. Phys. B 42, 075002; 42, 175006\\[0pt] [3] L U Ancarani and G Gasaneo 2007 Phys. Rev. A 75, 032706; 2008 Phys. Rev. A 77, 012705 [Preview Abstract] |
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MR1.00083: Positron transport in gases in electric and magnetic fields crossed at arbitrary angles Ana Bankovic, Sasa Dujko, Srdjan Marjanovic, Ronald D. White, Zoran Lj. Petrovic The knowledge of positron transport in gases under the influence of electric and magnetic fields is of key importance in optimizing positron traps. In this work we apply a multi term solution of Boltzmann's equation to study positron transport in gases under the influence of electric and magnetic fields crossed at arbitrary angles. Calculations are performed over a range of E/N and B/N values, and angles between the fields for positrons in N2, H2 and H2O. Values of mean energy, drift velocity, diffusion tensor, energy gradient vector, and temperature tensor and rate coefficient for positronium (Ps) formation are reported in this work. It is demonstrated that the difference between the bulk and flux transport coefficients resulting from the explicit effects of Ps formation can be controlled either by the variation in the magnetic field strengths or by the angles between the fields. Special attention is paid to synergistic effects of Ps formation and angle between the fields on the Ps-induced NDC phenomenon for positrons in H2 and H2O. The results presented in this work represent the first multi term solution of the non-conservative Boltzmann equation for positrons in varying configurations of electric and magnetic fields. [Preview Abstract] |
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MR1.00084: Quasi-Sturmian approach to two- and three-body continuum Coulomb problems Jessica A. Del Punta, Marcelo J. Ambrosio, Gustavo Gasaneo, Lorenzo Ugo Ancarani, Dario M. Mitnik, S.A. Zaytsev, M.S. Aleshin In this work we present new two-body basis functions to be used when solving atomic physics scattering problems. We name them Quasi Sturmian (QS) because of the resemblance of their generating equation with that of Generalized Sturmian (GS) sets [1]. They can be thought of a generalization of the Green function as they satisfy a non-homogeneous Schr\"{o}dinger equation where the delta function is replaced by any element of a $L^2$ basis set. The QS functions are regular at the origin, form a complete basis set with scattering asymptotic form and, by construction, solve the interactions appearing in the original Schr\"{o}dinger equation. Once a set of QS is generated, it can be used to expand a scattering solution. In comparison with well established GS functions, our numerical investigations showed that the proposed QS possess convergence superiority. Initially set for two-body interactions, the proposal can be easily extended to three-body problems. For a two-body Coulomb scattering problem, and taking Laguerre basis functions as $L^2$ basis set, the QS functions can be expressed analytically. As a consequence, when QS are applied to three-body scattering calculations, analytical expressions result for all necessary matrix elements. Furthermore, the properties of the two-body basis functions allow one for an analytical study of the three-body wave function itself. [1] Mitnik et al, Comp. Phys. Comm. 182, 1145 (2011) [Preview Abstract] |
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MR1.00085: Modeling Positron Transport in Gaseous and Soft-condensed Systems with Kinetic Theory and Monte Carlo G. Boyle, W. Tattersall, R.E. Robson, Ron White, S. Dujko, Z. Lj. Petrovic, M.J. Brunger, J.P. Sullivan, S.J. Buckman, G. Garcia An accurate quantitative understanding of the behavior of positrons in gaseous and soft-condensed systems is important for many technological applications as well as to fundamental physics research. Optimizing Positron Emission Tomography (PET) technology and understanding the associated radiation damage requires knowledge of how positrons interact with matter prior to annihilation. Modeling techniques developed for electrons can also be employed to model positrons, and these techniques can also be extended to account for the structural properties of the medium. Two complementary approaches have been implemented in the present work: kinetic theory and Monte Carlo simulations. Kinetic theory is based on the multi-term Boltzmann equation, which has recently been modified to include the positron-specific interaction processes of annihilation and positronium formation. Simultaneously, a Monte Carlo simulation code has been developed that can likewise incorporate positron-specific processes. [Preview Abstract] |
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MR1.00086: A Review of recent theoretical development for Coulomb explosion and stopping power of energetic molecular ions and clusters in plasmas Guiqiu Wang, Younian Wang We summarize our recent theoretical study for Coulomb explosion and stopping power of energetic molecular ions and clusters in plasmas. It's an interesting topic because the potential use of cluster ion beams in fusion research. In particular, there exists a promising inertial confinement fusion scheme in which a plasma target is radiated simultaneously by both an intense laser beam and an intense ion beam. In this paper, the emphasis is laid on the dynamic polarization and correlation effects of the constituent ions within the cluster in order to disclose the role of the vicinage effects on the Coulomb explosion and energy deposition of the molecules and clusters in plasma. On the other hand, affecting of a strong laser field on the cluster propagating in plasma is considered, the influence of a large range of laser parameters and plasma parameters on the Coulomb explosion and stopping power are discussed. Furthermore, in order to indicate the effects of different cluster sizes on the stopping power, a comparison is made for hydrogen clusters and carbon clusters. In addition, the deflection of molecular axis for diatomic molecules during the Coulomb explosion are also discussed for the cases both in the presence of laser field and laser free. [Preview Abstract] |
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MR1.00087: Neutral Resonant Ionization in Hydrogen Anion Production John Vogel Dissociative ionization of molecules causes gas phase H$^{-}$ but fails to explain anion intensity. Atomic collisions on surfaces with reduced work function give anions, but also fail to explain intensity, lowered electron density, and diagnostics. Neutral resonant ionization of H(2s) atoms to ion pairs is here predicted with a very high cross section. H(2s,p) atoms are resonant with numerous short-lived excited states (``resonances'') of H$^{-}$ as well as the putative doubly-excited stable state of H$^{-}$ which resists production by other means. This state decays through $^{1}\Sigma_{u}^{+}$ (2s $\sigma _{u}^{2})$ to a singly excited ion pair, leaving both proton and anion with 3.8 eV energy. H(2s,p) atoms arise from dissociative recombination of trihydrogen ion (H$_{3}^{+})$ which dominates ion content of hydrogen plasmas. Initial H(2s,p) are resonantly produced by ground state Cs atoms or excited Ar, Kr, and Xe atoms, but these initiators are not needed to sustain anion production. This theory may explain the intense ion source at Cal Tech that produced 1.5 mA/cm$^{2}$ H$_{3}$ in the mid-1980's (1). A full CRM calculation is not complete, but equilibrium calculations suggest that \textgreater 1 mA/cm$^{2}$ H$^{-}$ may be predicted. \\[4pt] [1] J. F. Garvey and A. Kuppermann, Rev. Sci. Instrum. 57, 1061 (1986). [Preview Abstract] |
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MR1.00088: POST-DEADLINE ABSTRACTS |
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MR1.00089: Soliton and Double layer in multi-component plasma Karima Annou, Nadia Saoula, Rabah Tadjine In the present work, an investigation of double layer formation in four-component plasmas is made. Assuming that the constituents of plasma are electrons, ions, and an admixture of dynamics ions with negative and positive charge. It is shown that stationary solutions of the fluid equation combined with Poisson`s equation can be expressed in terms of the energy integral of a classical particle with a Sagdeev Potential. Furthermore, the four-fluid plasma system provides the possibility of generation of ion acoustic solitary waves (namely: Solitons), as well as double layers. Additionally, conditions under which double layer arise are given, and their profiles are display graphically. [Preview Abstract] |
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MR1.00090: Self-organized electrode processes in the carbon arc discharge for nanotube synthesis Jonathan Ng, Yevgeny Raitses The atmospheric pressure carbon arc in helium is an important method for nanotube production [1]. Typical arcs operate in a dc mode between a graphite anode, which is consumed, and a lower melting temperature cathode (e.g. copper [2, 3]). It is accepted that electrons from the cathode are emitted by thermionic field emission [2,4], requiring the cathode to be above the melting temperature of its material. Yet, the cathode usually remains undamaged by the arc, raising the question about how the electron current in the arc is supported. Our experiments with copper, stainless steel and aluminum cathodes have revealed that thermo-field emission is the source of most of the arc current at the cathode, but emission is from the carbon deposit formed on the cathode in the course of the arc operation. Due to its low heat conduction, the cathode does not reach its melting temperature and remains undamaged. The evaporation of the graphite anode and formation of the carbon deposit on the cathode are self-organized to maintain the current conduction in the arc.\\[4pt] [1] Journet et. al. Nature 388:756 (1997)\\[0pt] [2] Keidar and Beilis, J. Appl. Phys 106, 103304 (2009)\\[0pt] [3] Fetterman et al, Carbon 46, 1322 (2008)\\[0pt] [4] Hantzsche, Beitr. Plasmaphys., 22, 325(1981) [Preview Abstract] |
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MR1.00091: Measurement of negative ion mobility with a trace moisture analyzer in O$_{2}$ Yui Okuyama, Susumu Suzuki, Haruo Itoh We have been investigated the effects of impurities on the negative ion mobility in O$_{2}$ at high pressures including atmospheric pressure using a high-pressure ion drift tube with a positive point plate gap that acts as a negative ion detector [1]. When a small admixture of impurities such as N$_{2}$ and CO$_{2}$ from atmosphere are existed in O$_{2}$, negative ion mobility is increased at $E$/$N$ \textgreater 1.77 Td due to formations of NO$_{2}^{-}$, NO$_{3}^{-}$, CO$_{3}^{-}$, CO$_{4}^{-}$ as impurity ions. In addition, existence of H$_{2}$O in O$_{2}$ leads to decrease negative ion mobility because O$_{2}^{-}$$\cdot$(H$_{2}$O)$_{n}$ forms by ion-molecule between O$_{2}^{-}$ or O$_{4}^{-}$ and H$_{2}$O [2]. In this work, we describe the experimental results on the measurement of negative ion mobility in ultrahigh-purity O$_{2}$ with a trace moisture analyzer (HALO-H$_{2}$O). The ion drift tube is mounted in the stainless steel chamber with stainless steel pipes to connect the trace moisture analyzer and O$_{2}$ bottle of 99.99995{\%} purity with a gas defecator (MICROTORR: MC200-203). Mobility measurements were carried out after gas flowing, baked and pumped the chamber and gas lines at least two months due to remove impurities. During the measurements, O$_{2}$ were flowed through the chamber at 0.5 L/min. As the results, a constant mobility 2.39 cm$^{2}$/V$\cdot$s was observed at H$_{2}$O concentration between 30 and 100 ppb. This value is good agreement with the polarization limit of mobility for O$_{4}^{-}$.\\[4pt] [1] Y. Okuyama et al, J. Phys. D: Appl. Phys., 45, 195202 (2012). [2] Y. Okuyama et al, 65th Annual Gaseous Electronic Conference, 57, 8, MW2.00006 (2012). [Preview Abstract] |
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MR1.00092: Magnetically insulated baffled probe for measurements in complex magnetized plasma diagnostics Chenggang Jin, Raitses Yevgeny, Vladimir Demidov When the magnetic field is parallel to the probe surface, the electron-repelling sheath can be significantly reduced as the magnetic field also impedes the cross-field electron flow and therefore, a smaller sheath voltage is needed to maintain the zero current balance to the floating probe. This is the basic idea of the magnetically insulated baffled (MIB) probe, which offers the advantages of direct measurements of the plasma potential in magnetized plasmas while being non-emitting and electrically floating [1]. A simplified MIB probe was constructed by retracting the conducting pin of a classical Langmuir probe inside an insulating tube placed perpendicular to the magnetic field lines. The retracting distance \quad of the collector inside the ceramic tube was calculated assuming classical and anomalous mechanisms of the electron cross-field diffusion and taking into account particles losses inside the tube. The results of MIB probe measurements in a Penning-type cross-field discharge are presented. \\[4pt] [1] V. I. Demidov et al., Rev. Sci. Instrum. 81, 10E129 (2010). [Preview Abstract] |
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MR1.00093: Simultaneous Filtered and Unfiltered Light Scattering Measurements in Laser Generated Air Sparks Christopher Limbach, Richard Miles Elastic laser light scattering may be used to measure the thermofluidic properties of gases and plasmas, including but not limited to density, temperature and velocity. Most of this information is contained within the spectra of the scattered radiation. This may be measured directly through dispersion or indirectly, by passing the light through an atomic or molecular vapor filter with known absorption features. In this work, filtered and unfiltered laser light scattering is used to diagnose air sparks generated by a 1064nm Q-switched laser. The probe laser consists of a second Q-switched Nd:YAG laser frequency doubled to 532nm. Simultaneous unfiltered and filtered images of the scattering are captured by a Princeton Instruments ICCD camera by using a 50mm diameter concave re-imaging mirror. The filter consists of a well-characterized molecular Iodine cell. In the shock wave formed by the laser spark, spatially resolved measurements of density, temperature and radial velocity are extracted and compared with theory and models. Measurements in the spark core probe the ion feature of the electron Thomson scattering, from which $n_e$ and $T$ can be extracted with the assumption $T_e=T_i$. [Preview Abstract] |
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MR1.00094: Sheath induced instabilities in plasmas with E0 x B0 drift Andrei Smolyakov, Winston Frias, Igor Kaganovich, Yevgeny Raitses It is shown that ion acoustic waves in plasmas with $\mathbf{E}_0 \times \mathbf{B}_0$ electron drift become unstable due to the closure of plasma current in the chamber wall. Such unstable modes may enhance both near-wall conductivity and turbulent electron transport in plasma devices with $\mathbf{E}_0 \times \mathbf{B}_0$ electron drift and unmagnetized ions. It is shown that the instability is sensitive to the wall material: a high value of the dielectric permittivity (such as in metal walls) reduces the mode growth rate by an order of magnitude but does not eliminate the instability completely. [Preview Abstract] |
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MR1.00095: Plasma-induced crystallization of silicon nanoparticles Nicolaas Kramer, Rebecca Anthony, Meenakshi Mamunuru, Eray Aydil, Uwe Kortshagen The ability to form crystalline group IV nanoparticles makes plasma synthesis an attractive production mechanism.$^{\mathrm{\thinspace }}$However, temperatures that are significantly higher than the gas temperature are required for crystallization of these materials to occur. The nanoparticle heating mechanism therefore remains one of the poorly understood aspects of the plasma synthesis technique. In the current study, we investigate the crystallization of nanoparticles using a tandem plasma configuration, characterizing both the nanoparticles and the plasma. Amorphous silicon nanoparticles, 3-5 nm in diameter, are formed in a low-power upstream plasma and then injected directly into a separate secondary plasma which is operated with variable power. \textit{Ex situ} characterization of the nanoparticles using X-ray diffraction, Raman spectroscopy and transmission electron microscopy showed that crystallization occurs at powers of 20 W to 40 W, depending on the nanoparticle size. The second step is an in-depth plasma characterization. We performed optical emission spectroscopy on the secondary plasma to obtain the electron temperature and hydrogen density, and capacitive probes for ion density measurements during nanoparticle crystallization. These plasma conditions are used in a nanoparticle heating model to simulate the nanoparticle heating in the second plasma. Calculations show that nanoparticles obtain temperatures much higher than the gas temperature. [Preview Abstract] |
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MR1.00096: Landau damping of the dust acoustic surface waves in a Lorentzian complex plasma containing elongated and rotating dust grains Myoung-Jae Lee, Kyu-Sun Chung, Seungjun Lee We investigate the stability of dust acoustic surface waves propagating at the plasma-vacuum interface of semi-infinity Lorentzian plasma containing elongated and rotating dust particles. The dispersive properties of complex plasma are kinetically analyzed by employing Vlasov-Maxwell equations and the specular boundary condition. The result exhibits that the Landau damping rates of the dust acoustic surface wave can be evaluated for various parameters such as the Lorentzian spectral index, rotational frequency of dust particles, etc. It has been found that the high rotational frequency reduces the Landau damping rate in general. For the case of k$_{\mathrm{x}}\lambda_{\mathrm{e}}$ \textgreater 1 where k$_{\mathrm{x}}$ is the wave number and $\lambda_{\mathrm{e}}$ the electron Debye length, the damping rate decreases as the wavelength of the wave decreases and vice versa for the case of k$_{\mathrm{x}}\lambda _{\mathrm{e}}$ \textless \textless 1. [Preview Abstract] |
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MR1.00097: \textit{Ab initio} molecular dynamics study of liquid Li and interactions with deuterium and tritium Mohan Chen, Emily Carter We investigate the structure of liquid Li and its interaction with deuteriumand tritium atoms using PROFESS (PRinceton Orbital-Free Electronic Structure Software) [1]. This linear-scaling orbital-free density functional theory method is a very fast quantum mechanics technique that allows one to perform ab initio molecular dynamics of metals for a large number of atoms and fairly long time. We predict 434 K as the melting temperature of Li [2], which compares well with an experimental melting point of 453 K [3]. Key properties of liquid Li will be presented and discussed, such as its diffusion coefficients and static structure factors, etc. We will also present some preliminary results of simulations of deuterium and tritium atom adsorption on liquid L. This work provides new insights into understanding the bulk and surface structure and reactivity of liquid Li using large-scale ab initio molecular dynamics methods.\\[4pt] [1] Hun, C. Huang, I.Shin, G. H, V. L. Lignere, and E. A. Carte, Compu. Phy. Com., 181, 2208 (2010).\\[0pt] [2] M. Chen, L. Hung, C. Huang, J. Xia, and E. A. Carter, ``The Melting Point of Lithium: An Orbital-Free First-Principles Molecular Dynamics Study,'' Molecular Physics, in press (2013).\\[0pt] [3] . Boehler, Phy. Rev. B. 2, 6754 (1983) [Preview Abstract] |
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MR1.00098: Formation and Decomposition of Lithium Deuteride Films on Mo(100) Angela Capece, John Roszell, Oluseyi Fasoranti, Charles Skinner, Bruce Koel Lithium-conditioned plasma-facing components have improved plasma performance by reducing the recycling of hydrogenic species; however, this process is not well understood in the complex tokamak environment. Ultrahigh vacuum surface science experiments are used to investigate the processes that occur at the plasma-surface interface by probing surface chemistry and composition while independently controlling vacuum conditions, surface temperature, and D atom/ion flux. In this work we have investigated the formation and decomposition of lithium deuteride films on a Mo(100) single crystal using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD). [Preview Abstract] |
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MR1.00099: Improving Efficiency of Ion Generation in Ion Source with Saddle Antenna Vadim Dudnikov, Sydnei Murrey, Terry Pinnisi, Chip Piller, Manuil Santana, Martin Stockli, Robert Welton, Rolland Johnson Extraction of positive and negative ions from a saddle antenna radio-frequency surface plasma source (SA RF SPS) are considered. Several versions of new plasma generators with different antennas and magnetic field configurations were tested in the small Test Stand. The efficiency of positive ion generation in plasma has been improved up to $\sim$ 0.2 A/cm$^{2}$ per 1 kW. For cesiation was used a heating of the cesium chromate cartridges. A small oven for cesium compounds and alloys decomposition by heating was developed and tested. After cesiation a current of negative ions to the collector was increased from $\sim$ 1 mA to 10 mA with RF power $\sim$ 1.5 kW in the plasma and longitudinal magnetic field B$_{l}$ $\sim$ 250 Gauss. A specific efficiency of H- production was increased up to $\sim$ 20 mA/ cm$^{2}$ kW from previous $\sim$ 2.5 mA/ cm$^{2}$ kW. [Preview Abstract] |
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