Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session FTP1: Poster Session I (19:00-21:30) |
Hide Abstracts |
Chair: I. Langmuir Room: Salon F-J |
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FTP1.00001: INDUCTIVELY COUPLED PLASMAS This abstract not available. [Preview Abstract] |
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FTP1.00002: Probe measurements and optical emission spectroscopy in inductively coupled RF Ar/C$_4$F$_8$/O$_2$ discharges Takashi Kimura, Hatsuyuki Hanaki Measurements with a Langmuir probe and optical emission spectroscopy combined with actinometry are carried out in inductively coupled RF Ar/C$_4$F$_8$/O$_2$ discharges at the total pressure lower than 30mTorr for the Ar content ranging from 60$\%$ to 90$\%$. Plasmas are produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 80 mm in length, where the power injected into the plasma is 140W. The structure of the measured electron energy probability functions can be changed from a Druyvesteyn distribution to a Maxwellian one as the Ar content decreases. The electron density measured at each fixed Ar content gradually decreases with increasing the O$_2$ content, whereas the measured effective electron temperature is not sensitive to the O$_2$ content. The atomic fluorine density measured at each fixed Ar content has the local maxima when the ratio of the O$_2$ content to C$_4$F$_8 $ one is 0.3 and 0.7-0.8, whereas it has the local minimum when the ratio is about 0.6. The atomic oxygen density measured at each fixed Ar content decreases with the decrease in the O$_2$ content, and then can not be deduced from the optical emission spectroscopy when the O$_2$ content is lower than C$_4$F$_8$ content. This work is partially supported by Grant-in-Aid from the Japan Society for the Promotion of Science. [Preview Abstract] |
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FTP1.00003: Effect of Oxygen on Ar metastables in inductively coupled plasma in O$_2$/Ar Yuichiro Hayashi, Christian Scharwitz, Toshiaki Makabe Oxygen plasma is widely used in material processing, and oxygen gas diluted by rage gases is employed for many practical reasons. In the present work we experimentally investigate the influence of the rare gas Ar in admixture of Oxygen and Ar by using optical emission and absorption spectroscopy. We have measured the density of Ar metastables (1s5, 1s3) in ICP at 13.56 MHz in O$_2$/Ar at 100 mTorr as functions of mixture ratio of O$_2$ (0-20 \%) and dissipated power (50-150 W) by using laser absorption spectroscopy. The density of Ar metastables has a peak as a function of gas mixture at any power condition, and each of peak values has a similar magnitude of $1.8 \times 10^{11}$ cm$^{-3}$. At low percentage of Oxygen the density decreases with increasing the power, while at higher Oxygen content the density increases with increasing the power. The characteristics will imply that the collision and reaction processes for Ar metastable will differ at both of regions in the ICP. [Preview Abstract] |
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FTP1.00004: A reverse-blocking effect of antiparallel magnetic fields on electron transport in gas Hirotake Sugawara In order to analyze fundamental features of electron conduction in a magnetically neutral loop discharge (NLD) plasma, electron transport in CF$_4$ at 0.67~Pa along a magnetically neutral channel (NC) between gradient antiparallel \textbf{\textit{B}} fields were simulated by a Monte Carlo method. The \textbf{\textit{B}} field was set as $(B_x,B_y,B_z)=(0,0,\hat{B}x)$ ($\hat{B}=\mbox{const}>0$) to let the $y$-$z$ plane be the NC as a simplified model of the electron path in the NLD plasma, and the \textbf{\textit{E}} field was applied as $(E_x,E_y,E_z)=(0,E,0)$ ($E=\mbox{const}$). Two modes of electron transport were observed. When $E<0$, the electrons drifted in the -\textbf{\textit{E}} direction. They were confined near the NC and their spatial distribution $f(x)$ was a Gaussian with a standard deviation $\sigma_x\propto\hat{B}^{-1/2}$. The values of the mean electron energy $\bar{\varepsilon}$, the effective ionization frequency $\nu_{\rm i}$, the average velocity $W_{\rm v}$ and the centroid drift velocity $W_{\rm r}$ were close to those in dc $E$ fields without \textbf{\textit{B}} field at the same $E/N$. The diffusion coefficients $D_y$ and $D_z$ were also close to the longitudinal and transverse diffusion coefficients $D_{\rm L}$ and $D_{\rm T}$ in the dc \textbf{\textit{E}} field, respectively, but $D_x\simeq0$. In contrast, when $E>0$, the electrons were led into the regions of stronger \textbf{\textit{B}} field by the \textbf{\textit{E}}$\times$\textbf{\textit{B}} drift away from the NC and they hardly drifted in the $-\textbf{\textit{E}}$ direction because of the gyration. The parameters decreased slowly and their equilibrium values were not available in a trace up to 7.3~$\mu$s, but only $D_x$ had its equilibrium value $E/\hat{B}$. [Preview Abstract] |
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FTP1.00005: Interaction Analysis of Multi-frequency RF powers in Dual Coil Inductively Coupled Plasma Etcher Heeyeop Chae, Haegyoo Chang, Kun Joo Park, Robert Kim In commercial plasma etching systems, more than one radio-frequency (RF) frequency powers are introduced to increase the controllability of the degree of dissociation, ion density, ion energy, uniformity and so on. In this work, the interaction within multiple RF frequency was analyzed in a dual coil inductively coupled plasma system. 2MHz and 27MHz dual RF powers were introduced to the bottom electrode and 13.56MHz RF power was introduced to the dual coil on the top of the plasma chamber. Plasma density was determined by noninvasive plasma probe and ion energy was determined by measuring voltage waveform. The blanket silicon dioxide film was etched by Ar plasmas and photoresist film was etched by O2 plasmas. Based on the physical and chemical analysis of blanket film analysis, the interaction of multi-frequency RF powers was analyzed in various process regimes. [Preview Abstract] |
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FTP1.00006: Spatio-temporal studies of argon metastables at the mode transition in an inductively coupled plasma A.M. Daltrini, S.A. Moshkalev, T.J. Morgan, R.B. Piejak, W.G. Graham Time and space resolved images of emission at 750.4 nm, 425.9 nm and 425 nm from an argon inductively coupled plasma in a GEC reference cell are reported. From line intensity ratio's information about the dynamic behaviour of the argon metastables atoms can be derived. Laser induced fluorescence has been used to determine the metastable atom densities. Maximum metastable densities are observed close to the coil and in the centre of the discharge and in the vicinity of transitions between low density (E, capacitively coupled) and high density (H, inductively coupled) modes. A rapid increase in the Ar metastable density with decreasing power was observed near the H to E mode transition. Electron temperature measurements based on line ratio measurements and Langmuir probe measurements, coupled to a model which incorporates metastable diffusion, are used to demonstrate how the spatio-temporal behaviour of the Ar metastable population influences the E-H mode transition. [Preview Abstract] |
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FTP1.00007: Real-time measurement of electron temperatures and ion densities using self-bias effect in argon inductively coupled plasma Kwang-Tae Hwang, Ik-Jin Choi, Chin-Wook Chung AC bias voltage was applied through a DC blocking capacitor between a probe and a signal generator. Self-bias potentials were changed with the amplitude of AC bias voltage, electron temperatures and ion densities. The electron temperature and ion density were measured from the variations of the self-bias potentials at various RF powers (100-500W) and pressures (5-50mTorr). The experimental results were in good agreement with those from Langmuir probes. [Preview Abstract] |
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FTP1.00008: Real time feedback control of plasma density by using a floating probe in inductively coupled plasmas Sung-Ho Jang, Jin-Sung Kim, Min-Hyong Lee, Chin-Wook Chung A real time feedback control of plasma density was carried out experimentally in inductively coupled plasma (ICP). The plasma density was measured by a floating probe (P{\&}A Solutions, Wise probe$^{TM})$ which can measure the plasma density in real time without plasma perturbation installed on a chamber wall, and the measured information was fed back to actuator to influence the plasma density. This plasma control system allowed the plasma density to reach and keep the desired densities below 0.1{\%} of the state error. To describe External disturbances, the pressure of the chamber was dropped from 10 mTorr to 5 mTorr by using a molecular flow controller. At the pressure disturbance, the density decreases, and recovers with 1.5{\%} of the maximum error and 10 s of the settling time. In the comparison of active and inactive control with pressure disturbance, the maximum state errors were 1.5{\%} and 40{\%} respectively. [Preview Abstract] |
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FTP1.00009: Experimental investigation on Edge-to-Center density ratio in an inductively coupled plasma Gun-Ho Kim, Sung-Ho Jang, Chin-Wook Chung The plasma densities at the edge and center of a chamber in an inductively coupled plasma were measured by using a floating-type probe [1], which can measure ion density without changing sheath formation on the chamber edge. Measurements have been done in argon gas ranging in gas pressure between 5mTorr and 30mTorr. The ratios between edge and center density has been compared with theoretical ones. The Measured edge-to-center density ratios agree well with the tendency of theoretical values. It was found that the edge density has maximum values at 10mTorr, regardless of input powers. This can be understood by considering the dependence of the edge to center density ratio and center density on pressure. [1] M. H. Lee, S. H. Jang, C.W. Chung, J. of Applied Physics, 101, 033305 (2007) [Preview Abstract] |
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FTP1.00010: MATERIAL PROCESSING IN LOW PRESSURE PLASMAS: ETCHING, DEPOSITION, NEW MATERIALS |
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FTP1.00011: Correlation between plasma OES and properties of B-doped polycrystalline diamond films Alexander Pal, Maxim Belousov, Viktor Krivchenko, Pavel Minakov, Alexander Rakhimov, Nikolay Suetin, Vasily Sen' Boron is effective ligand creating p-type conductivity in diamond. If diamond film has been created by MWPECVD, the doping process can be realized by adding B-contained substance to the working mixture. At the same time morphology and doping level in many respects depend on processes occurring in MW plasma during film growth. These processes may be controlled by in-situ diagnostics of optical emission spectra (OES) of plasma. In this work we in-situ investigated OES of MW plasma in the region from 200 to 800 nm during B-doped polycrystalline diamond films (PDF) growth. Special attention was given to analysis of intensity of 249.7 nm line corresponding to 3s-2p transition of B atom. Relative intensity of this line allowed to measure amount of B in plasma. Hydrogen combined with ethanol and additives of trimethylborate was used as gas working mixture. All samples were grown on Si substrate (100) orientation. The morphology and B doping level of grown films were investigated by Raman spectroscopy using 532 nm laser radiation with power of 40 mW. Correlation dependences between OES features and Raman spectra along with temperature estimation of MW plasma were defined. [Preview Abstract] |
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FTP1.00012: Remote Plasma Assisted, Low-Temperature SiO$_{2}$ growth on SiC for MOS Device Applications J.M. Williamson, B.A. Tolson, S.F. Adams, J.D. Scofield SiC is an attractive material for semiconductor device applications in environments too harsh for normal Si-based semiconductors. It has high thermal conductivity and breakdown electric field strength enabling high power and temperature operation. SiO$_{2}$ is readily grown on SiC by high-temperature ($\sim $1200\r{ }C) thermal oxidation, but defect densities in the SiO$_{2}$/SiC interface limits device performance. Plasma-assisted oxidation of SiC is being investigated as a low-temperature alternative to thermal SiC oxidation to produce MOS devices with lower defect densities. SiC wafers were oxidized with a remote microwave plasma in an O$_{2}$ / Ar gas mixture at temperatures much lower than thermal oxidation. Recent results of the plasma assisted oxide growth process have shown significant improvement, with SiO$_{2}$ layers in excess of 600 {\AA} at growth temperatures near 300\r{ }C. Results will be presented of the plasma assisted SiC oxidation including plasma optical diagnostics and oxide layer characterization. [Preview Abstract] |
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FTP1.00013: Modeling the direct injection of binary liquid droplets into low-pressure environments and plasmas Iqbal Saraf, Daisuke Ogawa, Matthew Goeckner, Lawrence Overzet We will present simulation results obtained from a model describing binary droplet evaporation in low pressure plasmas. The time required for a droplet to evaporate is a function of background pressure, initial T, droplet-vapor interactions, solute mole fraction and initial droplet size. A 25$\mu $m radius droplet of hexane evaporates in less than 3 seconds at 100mTorr without plasma. The addition of plasma can decrease the evaporation time by more than an order of magnitude. We find that the evaporation time depends weakly on background pressure, gas temperature and electron temperature in presence of plasma; however, it strongly depends upon the plasma density. In addition, the model predicts that the temperature of the injected droplet first decreases by evaporative cooling (to $\sim $200K for hexane); however, once the solvent has fully evaporated, the plasma heats any remaining solute. As a result, the temperature can first fall to 200K then rise to nearly 700K in less than a second at a plasma density of 10$^{11}$cm$^{-3}$. [Preview Abstract] |
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FTP1.00014: Inductively coupled plasma assisted RF magnetron sputtering synthesis of $n$-/$p$-type ZnO Qijin Cheng, Shuyan Xu, Shiyong Huang, Bishuang Chua, Jidong Long, Eugene Tam, Kostya Ostrikov Al- and N-doped ZnO thin films have been deposited on glass substrates using an inductively coupled plasma assisted RF magnetron sputtering deposition system. The electrical, optical and structural properties of the deposited films have been investigated using various characterization tools. At the optimum deposition conditions, room-temperature Hall effect measurements show that Al-doped ZnO is $n$-type with an electron concentration of 3.74 x 10$^{18}$ cm$^{-3}$ and mobility of 1.42 cm$^{2}$V$^{-1}$s$^{-1}$, while the N-doped ZnO is $p$-type with a hole concentration of 3.32 x 10$^{18}$ cm$^{-3}$ and mobility of 1.31 cm$^{2}$V$^{-1}$s$^{-1}$. XRD measurements show that both of Al- and N-doped ZnO films are polycrystalline with the hexagonal structure, having a strong (002) preferential growth orientation. The two-layer structured ZnO $p-n$ homojunctions have been fabricated on a glass substrate by depositing the Al-doped $n$-type ZnO film on the N-doped $p$-type ZnO film. The current-voltage measurements reveal a typical diode characteristic with a turn-on voltage at about 1.2 V under forward-biased voltage and a low leakage current under reverse-biased voltage. [Preview Abstract] |
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FTP1.00015: Mechanism of Niobium Etching in Ar/Cl$_{2}$ Microwave Discharge J. Upadhyay, M. Raskovic, S. Popovic, L. Vuskovic, L. Phillips, A.-M. Valente-Feliciano Plasma based Nb surface treatment provides an excellent opportunity to eliminate surface imperfections [1] and increase cavity quality factor in important applications such as particle accelerators and cavity QED, as well as Josephson junctions [2]. We used a microwave glow discharge in Ar/Cl$_{2}$ mixture to remove impurities and mechanical damages from the surface of bulk niobium samples. The high etching rates, in the order of 1 $\mu$m/min were obtained using a less than 3{\%}Vol concentration of Cl$_{2}$ gas. The etching rate dependence on discharge parameters such input power density, pressure and Cl$_{2}$ concentration was determined. Simultaneously, plasma emission actinometry was used to estimate the absolute densities of Cl, Cl$^{+}$ and Cl$_{2}$ in the variable plasma conditions. This results, combined with results of discharge diagnostics, were used to determine the plasma etching mechanism. [1] M. Raskovic, et al., Nuclear Instruments and Methods in Physics Research A 569 663--670 (2006). [2] S. Gleyzes, et al., Nature 446, 297 (2007). [Preview Abstract] |
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FTP1.00016: Novel Helmholtz-Inductively Coupled Plasma Source for Nano-scale MOSFETs Kun-Joo Park, Kee-Hyun Kim, Won-Mook Lee, Heeyeop Chae, In-Shik Han, Hi-Deok Lee As the minimum feature size of MOSFET was continuously scaled down to the nano-scale regime, fine pattering using plasma etching process has become crucial in fabricating ULSI devices. Novel Helmholtz coil inductively coupled plasma (H-ICP) etcher is proposed and characterized for deep nano-scale CMOS technology. Various hardware split tests such as the distance between top and bottom coils, the distance between chamber ceiling and wafer, and the chamber height are applied for optimal design of the chamber or process condition. The uniformity is significantly improved using the optimum conditions. The plasma density obtained with H-ICP source was about 5$\times $10$^{11}$ /cm$^{3}$, and electron temperature was about 2$\sim $3eV. The etching selectivity of polysilicon gate to ultra-thin gate oxide is 482:1 with 10sccm of HeO$_{2}$. In this work, a novel H-ICP source was proposed for plasma etching with high uniformity and high selectivity suitable for nano-scale semiconductor devices.. Various kinds of split were applied and the optimum condition was successfully applied for formation of nano-scale poly gates. The proposed H-ICP is successfully applied for formation of under 60 nm gate layers. [Preview Abstract] |
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FTP1.00017: Meter-Scale Microwave Plasma Production and its Application to Silicon Thin Film Deposition Hirotaka Toyoda, Yudai Takanishi, Hirotaka Endo, Tatsuo Ishijima There has been a great need for meter-scale plasma sources for giant materials processing, such as thin film transistor manufacturing for meter-size liquid crystal display (LCD), deposition of silicon thin films for photovoltaic power generation and so on. Recently, we have developed a new technology for production of surface wave excitation [1]. In this paper, we demonstrate production of meter-scale large-area plasma with multiple waveguide lines. In the experiment, microwave power ($<$30 kW) is coupled to the plasma through power divider, multiple waveguide lines and slot antennas. Optical and Langmuir probe measurements of Ar/H$_{2}$ plasma show production of very uniform plasma at a plasma density of 3.4 x 10$^{11}$ cm$^{-3}$ and a variance of 2{\%} within an area of 0.9 m x 0.9 m. With use of carefully-designed gas manifold, microcrystalline silicon films are deposited on sample substrates. Deposition rate of $\sim $0.3 nm/s with a variance of less than 10 {\%} is obtained within an area of 0.6 m x 0.7 m. Uniformity of film quality such as film crystallinity is also confirmed. \textbf{[}1] H. Sugai, Y. Nojiri, T. Ishijima and H. Toyoda, 6$^{th}$ Int. Conf. on Reactive Plasmas and 23$^{rd}$ Symp. on Plasma Processing, (Matsushima, 2006), p.17. [Preview Abstract] |
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FTP1.00018: Effects of High Energy Ar Ions on Synthesis of Carbon Nanowalls Shingo Kondo, Olivera Stepanovic, Makoto Sekine, Masaru Hori, Koji Yamakawa, Shoji Den, Mineo Hiramatsu Carbon nanowalls (CNWs) are composed of graphene sheets standing vertically on the substrate. In order to apply CNWs to various industrial fields, clarification of the growth mechanism is strongly required. In this study, the new apparatus of two radical sources with an ion source was constructed in order to understand the fundamental studies of growth of CNWs. In particular, we have focused on which radicals or ions contributed to the CNWs formation. The Si substrate heated at 580$^{\circ}$C was exposed to fluorocarbon (CF$_{X})$ and H radicals, which were generated from C$_{2}$F$_{6}$, H$_{2}$ gases, in addition to Ar ions. In the case of Ar ion irradiation at an acceleration of 200 V with CF$_{X}$ and H radicals at 2.5 Pa, CNWs of 30 nm in height were formed in 25 min. On the other hand, the CNW growth was not confirmed in the cases without Ar ion irradiation and with Ar irradiation at 100 V. From these results, it was found that the threshold of ion energy bombardment for synthesis of CNWs was 100 V. The effects of Ar ions on CNWs formation will be presented. [Preview Abstract] |
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FTP1.00019: Deposition of single and layered amorphous fluorocarbon films by C$_8$F$_{18}$ PECVD Tatsuya Yamauchi, Kouichiro Mizuno, Hirotake Sugawara Amorphous fluorocarbon films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using C$_8$F$_{18}$ in closed system at C$_8$F$_{18}$ pressures 0.1--0.3~Torr, deposition times 1--30~min and plasma powers 20--200~W\@. The layered films were composed by repeated PECVD processes. We compared `two-layered' and `intermittently deposited' films, which were made by the PECVD, respectively, with and without renewal of the gas after the deposition of the first layer. The interlayer boundary was observed in the layered films, and that of the intermittently deposited films showed a tendency to be clearer when the deposition time until the interruption of the PECVD was shorter. The film thickness increased linearly in the beginning of the PECVD and it turned down after 10--15~min, that was similar between the single and intermittently deposited films. It was considered that large precursors made at a low decomposition degree of C$_8$F$_ {18}$ contributed to the film deposition in the early phase and that the downturn was due to the development of the C$_8$F$_{18}$ decomposition. This explanation on the deposition mechanism agrees qualitatively with our experimental data of pressure change and optical emission spectra during the deposition. This work is supported by Grant-in-Aid from Japan Society for the Promotion of Science. [Preview Abstract] |
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FTP1.00020: Modeling the chemistries of technical molecular plasmas James J. Munro, Jonathan Tennyson, Daniel B. Brown, Hemal N. Varambhia, Natasha Doss Plasma chemistries, especially for molecular gases, are complicated. With a limited amount of molecular data available, it is hard to model these plasmas accurately; just a couple of feedstock gases can lead to a minimal model containing perhaps dozens of gas-phase species. The possible gas-phase and surface reactions that can occur could be in the tens of thousands; less than a hundred are typically used in chemistry models. Understanding the importance of various species and reactions to a chemical model is vital. Here we present the progress on constructing a package (Quantemol-P)[1] to simplify and automate the process of building and analyzing plasma chemistries e.g. SF$_6$/O$_2$, CF$_4$/O$_2$ and O$_2$/He. [1] J.J. Munro, J. Tennyson, J. Vac. Sci. Tech. A, accepted [Preview Abstract] |
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FTP1.00021: Surface Layers Modification of Tungsten-Cobalt Alloy by Low Pressure RF Plasmas Ilgizar Sagbiev, Ildar Abdoullin, Victor Zheltoukhin, Roustem Sharafeev A process of surface layer modification of tungsten-cobalt alloy by low pressure RF plasmas is investigated. Analysis of materials from 10 up to 700 nm by thickness was studied by both X-ray and auger electrons spectroscopy. There are three sublayers within the surface layer after plasma action. The outer sublayer is from 10 up to 500 nm by thickness. One consists of carbon of unordered or diamond like structure, contents of tungsten and cobalt is decreased monotonous up in surface. The transitional sublayer is from 150 up to 200 nm by thickness. Carbon state in this one correspondence to mix of C-C and C-W bonds, concentration of tungsten and cobalt is fluctuating. The modifying layer is raising to some limit at increasing the time of plasma action. [Preview Abstract] |
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FTP1.00022: Characterization of PET Samples Processed in an RF Oxygen Discharge Russell L. Rhoton, Mary L. Brake A radio frequency plasma (13.56 MHz) was used to modify the surface of poly(ethylene terephthalate) (PET). Optical emission spectroscopy (OES) was used to characterize the plasma and the Sessile drop method was used to determine surface changes after processing. The OES changed depending upon the pressure of the plasma. Molecules of OH and atomic oxygen were observed at low pressures ($\sim $0.1 torr) whereas CO and atomic hydrogen were observed at higher pressures ($\sim $ 1 torr). There was an observable change in the PET samples after processing; in particular, the surface was degraded. The Sessile drop method was used to determine the relative change in the wettability of the surface along a continuum from hydrophobic to hydrophilic. [Preview Abstract] |
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FTP1.00023: ARCS, JETS AND TORCHES |
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FTP1.00024: Supersonic flow and electric potential of argon arc jet along open-field magnetic line Hiroshi Akatsuka, Yoh Nagahara, Kazuyuki Yoshida, Tomohiko Shibata, Haruaki Matsuura, Atsushi Nezu We report plasma parameters of argon arc jet along open-field magnetic line. The argon arc plasma is generated under atmospheric pressure, and ejected through an anode-nozzle into a rarefied wind tunnel continuously with a uniform magnetic channel of 0.16 T. The anode-nozzle is sufficiently choked to flow the plasma at its acoustic velocity. The plasma is further accelerated into supersonic flow through the open-field line. We experimentally measure ion acoustic Mach number, 2-dimensional ion velocity, plasma space potential, electron temperature and density by a para-perp and a 4-tip Mach probes. We find electric potential drop, increase in ion Mach number up to about 3, and following velocity reduction to subsonic flow. We conducted numerical modeling, where we assume the divergence of the magnetic field was equivalent to the increase in the cross sectional area of flowing channel. We introduced the deceleration model with collisions between ions and neutral particles. The model simulates the deceleration of the plasma at downstream region much better than isentropic model. [Preview Abstract] |
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FTP1.00025: Study of the Anodic Region of Electric Arcs by a Two-Temperature Model Margarita Baeva, Sergey Gorchakov, Dirk Uhrlandt Electric arcs are widely used in such industrial applications as welding, cutting and waste treatment. In order to optimize the device parameters and operation conditions, amongst others understanding of the discharge physics in the boundary regions near the electrodes is necessary. The discharge properties in these regions are influenced by evaporating material and the plasma shows strong deviations from the local thermodynamic equilibrium. For the study of the arc-anode interaction a two-temperature, multi-component model for the anodic region has been developed and applied. The non-equilibrium mixture composition, corresponding transport coefficients and thermodynamic functions of the mixtures of gas and metal vapor were determined for the parameter range of interest. The energy balance of the anode has been derived by taking into account heat fluxes from the plasma, evaporation, as well as Ohmic heating of the anode. The properties of the non-equilibrium sheath near the anode are evaluated. Results for an argon arc in the presence of copper or iron vapor are presented and discussed. [Preview Abstract] |
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FTP1.00026: 3D-simulation of an ICP torch and outside vapor deposition of $SiO_{2}$ Margarita Baeva, Dirk Uhrlandt A three dimensional model of an inductively coupled plasma torch and a moving target has been developed to describe the process of $SiO_{2}$-deposition during the manufacturing of preforms for optical fibers. The model is based on the customized CFD-ACE+ commercial package. The steady state continuity, momentum and enthalpy equations are solved assuming local thermal equilibrium and laminar flow, and optically thin plasma. The energy coupling to the plasma accomplished through the electromagnetic field of an induction coil and the radiation losses from the plasma are accounted for in the discretized fluid enthalpy equation as source terms. The surface reaction governing the deposition process is included to serve as a boundary condition for the species mass fractions in the fluid. The equation of heat transfer in the substrate has been completed to account for the real motion (both translation and rotation) of the substrate. The model developed supplies information about the flow, temperature, electromagnetic field, and the deposition rate on the target surface and torch walls for real geometries. It can be applied to study the influence of various operating parameters on the deposition rate as well as optimization of equipment and productivity. [Preview Abstract] |
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FTP1.00027: Comparative simulation studies of a magnetically rotating arc Margarita Baeva, Dirk Uhrlandt Magnetically rotating arcs have been increasingly adopted in DC arc plasma devices for diagnostics and material processing, modern circuit breakers, etc. The need to study arc behavior has motivated modeling activities based on computational fluid dynamics coupled with electromagnetics. A three-dimensional model of a DC plasma torch at atmospheric pressure has been developed based on the customized CFD-ACE+ commercial package. It is applied to study the behavior of a magnetically rotating arc in argon. The simulation studies are performed comparatively in terms of 1) two- temperature description (different electron $T_{e}$ and heavy particle ($T$) temperatures) and 2) local thermal equilibrium (LTE) ($T_{e} =T$). Temperature discrepancies between electron and heavy particles are found in the arc fringes and near the gas inlet. In the presence of axial magnetic field, the gas temperature gets lower in the arc core. The electron temperature profile is wider than the gas temperature one. Apart from the differences between 2-T and LTE model results, both models yield the same qualitative arc behavior. With increasing external axial magnetic field, the high temperature plasma region constrains in axial direction and expands in radial direction. [Preview Abstract] |
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FTP1.00028: ABSTRACT WITHDRAWN |
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FTP1.00029: ABSTRACT WITHDRAWN |
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FTP1.00030: Modeling the Transport Phenomena in the Solution Precursor Plasma Spraying Yanguang Shan Solution precursor plasma spraying has been used to produce finely structured ceramic coatings with nano- and sub-micrometric features. This process involves the injection of a solution spray of ceramic salts into a DC plasma jet under atmospheric condition. During the process, the solvent vaporizes as the droplet travel downstream. Solid particles are finally formed due to the precipitation of the solute, and the particle are heated up and accelerated to the substrate to generate the coating. This work describes a 3D model to simulate the transport phenomena and the trajectory and heating of the solution spray in the process. The jet-spray two-way interactions are considered. A simplified model is employed to simulate the evolution process and the formation of the solid particle from the solution droplet in the plasma jet. O'Rourke's droplet collision model is used to take into account of the influence of droplet collision. The influence of droplet breakup is also considered by implementing TAB droplet breakup models into the plasma jet model. The temperature and velocity fields of the jet are obtained and validated. The particle size, velocity, temperature and position distribution on the substrate are predicted. [Preview Abstract] |
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FTP1.00031: Effects of Geometry and Excitation Frequency on Plasma Torch Temperature Douglas Scott, Il Gyo Koo, Kazunari Sato, Cameron Moore, George Collins Temperatures of atmospheric pressure plasma jet effluent were measured spectroscopically in argon with 2{\%} hydrogen under conditions of constant delivered power. Different inner diameters of the mm-size plasma tube, excitation frequencies from several MHz to $>$ 100 MHz, and gas velocities resulted in measurements that indicate each of these parameters strongly affect temperature of the effluent plume. The data suggest that energy either flows in the plume or two the tube wall: plume and tube temperature are complementary. We present a heat flow model and analysis that agrees with experimental data, and from these data we estimate the diameter of the plasma in the upstream tube. We also present spatially resolved measurements along the plasma axis. [Preview Abstract] |
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FTP1.00032: MAGNETICALLY ENHANCED PLASMAS This abstract not available. [Preview Abstract] |
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FTP1.00033: Studies on spatial structures of plasma localization under various external magnetic field and geometry parameters in capacitively coupled neutral loop discharges Murat Vural, Fatih Sirin, Ralf Peter Brinkmann The neutral loop discharge (NLD) is an RF driven low pressure discharge with three magnetic coils placed coaxially outside the vacuum chamber, generating an axissymmetric magnetic field that vanishes at the so-called magnetic neutral loop (NL). In a capacitively coupled neutral loop discharge (CCP-NLD), the accelerating electrical field is generated by applying an RF potential to external electrodes; the corresponding electric field lines are co-planar to the magnetic field lines but perpendicular to the NL. The reactor chamber has the form of a regular cylinder of different radii and constant height. This paper studies the impact on the electron density and electron energy of variations in the reactor dimensions and external magnetic field parameters in a CCP-NLD by means of spatially resolved particle-in-cell/Monte Carlo simulations. The influence of the reactor geometry and neutral gas pressures between 0.5 Pa and 10 Pa on the homogenity and heating mechanism are also shown. [Preview Abstract] |
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FTP1.00034: The spatial and temporal variation of potentials in the HiPIMS discharge Pall Sigurjonsson, Petter Larsson, Daniel Lundin, Ulf Helmersson, Jon Tomas Gudmundsson We describe measurements of the plasma parameters in a high power impulse magnetron sputtering (HiPIMS) discharge. A Langmuir probe is used to determine the plasma parameters, such as the electron temperature $T_{\mathrm{eff}}$, the electron density $n_{\mathrm{e}}$, the floating potential $V_{\mathrm{fl}}$ and the plasma potential $V_{\mathrm{pl}}$, as well as the electron energy distribution function (EEDF). The spatial and temporal variation of the plasma parameters and electron energy distribution function are recorded in the pressure range $3 - 20$ mTorr. The electron density peaks at $5 \times 10^{18}$ m$^{-3}$ for $40 - 80$ mm distance from the target surface for all pressures investigated. The electron temperature reaches its peak value of $1.5 - 3$ V roughly $80~\mu$s after pulse initiation, in the pressure range $5 - 20$ mTorr. The plasma potential and the floating potential peak at the end of the pulse. We will in particular describe the spatial variation of the plasma and floating potentials at various times during the discharge. [Preview Abstract] |
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FTP1.00035: The 2nd Harmonic ECR Microplasma for Low Pressure Condition Hiroshi Fujiyama, Akihiro Yukishige, Ke Yan, Masanori Shinohara, Tatsuyuki Nakatani Plasma generation in narrow closed space has been succeeded for the pressure of 0.01Torr and gap length of 500 $\mu$m in xenon gas for the 2$^{nd}$ harmonic Electron Cyclotron Resonance (2$^{nd}$ harmonic ECR). Resonant confinement of electrons at the 2$^{nd}$ harmonic ECR leads to interesting micro plasma characteristics: the higher electron density, the lower plasma potential, the lower electron temperature and the effective power absorption against with the well-known ECR plasma. PIC-MC simulation of low pressure micro plasma supported such interesting plasma characteristics obtained by the experiments. It was also investigated on the plasma density and temperature for various ratio of Surface Dimensions/Volume of plasma. In the experiments, it was found that the typical micro plasma characteristics: the higher electron density, the lower plasma potential, the lower electron temperature became remarkable. The ionization degree for the 2$^{nd}$ harmonic ECR plasma in the present research, showed about 10$^{-3}$ by 2 order higher than that of PDP micro plasma. [Preview Abstract] |
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FTP1.00036: LASERS: BREAKDOWN AND SPARKS |
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FTP1.00037: ABSTRACT WITHDRAWN |
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FTP1.00038: Breakdown Behavior in Air and n-Butane Mixtures Leading to Combustor Ignition Modeled using Effective Ionization Coefficients S.F. Adams, A.A. Kudryavtsev, S.M. Popugaev, V.I. Demidov, C.Q. Jiao The process of electron attachment in electronegative air-hydrocarbon gas mixtures can be an impediment to the arc ignition process in a combustion engine. The optimized conditions to produce ignition include a gas mixture with a minimal ionization coefficient. Data on ionization rates and ion reactions in various air-hydrocarbon mixtures is necessary, though, for a proper theoretical analysis of the ignition process. The known set of cross-sections and rate constants for simple methane (CH$_{4})$ is often used and results extrapolated to heavier hydrocarbons. Recently, experimental data on cross-sections, ionization rates and ion reactions in n-butane (n-C$_{4}$H$_{10})$ were reported which allow for reliable models of ignition in more complex fuel mixtures. This paper presents an analysis of breakdown and ignition using air and n-butane mixtures. [Preview Abstract] |
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FTP1.00039: Frequency Effect on RF Gas Breakdown Valeriy Lisovskiy, Vladimir Yegorenkov, Jacques Jolly, Jean-Paul Booth We registered rf breakdown curves of the parallel-plate capacitive discharge in the range of frequency values from 13.56 MHz to 105 MHz with the inter-electrode gap of 3 cm and in the hydrogen pressure range of values from 0.001 to 1 Torr. Rf breakdown curves for the frequencies up to 40 MHz possess the diffusion-drift branch with a multi-valued section, then with lowering the pressure the Paschen and multipactor branches are observed. For higher frequency values the diffusion drift branch assumes a U-shaped form, it does not possess a multi-valued section and transforms directly to the multipactor branch. On increasing the frequency the rf breakdown voltage of the multipactor branch grows linearly, and the minimum of the diffusion-drift branch is shifted to the range of higher gas pressure and rf voltage values. [Preview Abstract] |
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FTP1.00040: The effect of the ion-enhanced field emission on the $CF_4$ discharges in microgaps Marija Radmilovic-Radjenovic, Branislav Radjenovic Recently, much attention has been paid to studies on $CF_4$ due to its practical utility as a feed gas for plasma etching in the semiconductor industry. In order to reduced feature sizes on microelectronic devices, it is necessary to determine the breakdown voltage in microgaps. In this paper, semi-empirical expression for the breakdown voltage based on the numerical solutions of the equation that describes the DC breakdown criteria in $CF_4$ microdischarges has been suggested. [Preview Abstract] |
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FTP1.00041: Two-dimensional Effects in High Power Microwave Breakdown Sang Ki Nam, Chul-hyun Lim, John Verboncoeur A major limiting factor in transmission of high power microwave radiation is dielectric window breakdown. A one-dimensional particle-in-cell/Monte Carlo collision (PIC/MCC) model was used to study dielectric window breakdown from vacuum multipactor to collisional microwave discharge for noble gases [1]. It showed that multipactor on the dielectric window drives breakdown at low pressure, and volumetric collisional ionization is the main mechanism for breakdown at high pressure. A Monte Carlo (MC) model was also used to investigate dielectric window breakdown in two-dimensionals, including spatial variation of the microwave electric field in transverse direction [2]. The breakdown times were consistent with their experiment data and also showed the interesting feature of electron clusters above the window. MC, however, is not self-consistent and neglects the space charge effect resulting from the charge build-up. In this work, two-dimensional PIC/MCC was employed to investigate the breakdown in oxygen including the space charge effect. [1] H.C. Kim, and J.P. Verboncoeur, Phys. Plasmas, 13, 123506(2006). [2] J.T. Krile, A.A. Neuber, and H. G. Krompholz, Appl. Phys. Lett., 89, 201501(2006). [Preview Abstract] |
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FTP1.00042: Simulation of a streamer breakdown in air Sergey Pancheshnyi, Aicha Flitti, George Naidis A numerical code that uses an adaptive grid refinement strategy for the computation of filamentary discharges within the diffusion-drift approximation in 2D and 3D geometry was applied for streamer simulation. The numerical discretization are based on finite volume methods and have 2nd order accuracy in space and time. The main stages of streamer discharge development in air are presented up to the moment of spark formation. In the case of fast breakdown, the plasma conductivity increases thanks to the accumulation of active particles that changes the balance between the rates of generation and loss of electrons due to the acceleration of processes such as detachment, stepwise, and associative ionization, etc. The evolution of plasma composition after the channel bridges the gap has been simulated using ZDPlasKin library in 0D approach; the kinetic model includes 14 components and 48 reactions. This approach exhibits a good agreement with measurements and can be easily applied for other gases and conditions. [Preview Abstract] |
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FTP1.00043: Branching Patterns in Multi-Atmospheric Pressure Corona Discharges With Positive and Negative Bubbles Natalia Yu. Babaeva, Mark J. Kushner The branching of streamers occurs in most high pressure gases and liquids. One mechanism for streamer branching may be inhomogeneities in the path of the streamer -- a solid particle, aerosol or a region of different density, one extreme being a bubble in a liquid. To lend insights into how positive (an included volume of higher density) or negative (volume of lower density) bubbles might produce branching in high pressure gases, we computationally investigated the role of randomly distributed bubbles on the propagation of a streamer in atmospheric (and greater) pressure humid air. The plasma hydrodynamics model, \textit{nonPDPSIM}, uses an unstructured mesh to simultaneously resolve reactor scales and bubbles. Radiation transport, and photoionization in bubbles are included by implementing a Green's function propagator. Positive streamers encountering a single slightly negative bubble in its path tends to converge into the bubble that has a higher rate of ionization. Streamers encountering slightly positive bubbles tend to branch around the regions of lower ionization. Photoionization producing electrons in remote highly negative bubbles which have a proportionally larger E/N can lead to remote sources of plasma that launch their own streamers. If the bubbles are within a few photon absorption lengths of the streamer (or other bubbles), these streamers may link together. [Preview Abstract] |
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FTP1.00044: Kinetic Model of a Nanosecond Afterglow in Air Sara Abbate, Denis Packan, Alain Broc, Christophe Laux In recent decades an active interest has been shown for applications of non equilibrium plasmas to combustion. Many laboratories~in Europe, US and the former Soviet Union have achieved combustion improvements by using plasma technologies, in particular nanosecond discharges due to their energy-efficient excitation of mixtures. Major effects have been noticed in the reduction of the delay time of combustible mixtures, along with auto ignition and stabilisation of flame in lean mixtures. Different mechanisms have been proposed in the literature to explain the observed effects and to build on the experiments, but a complete understanding of the principles is still lacking. The aim of our work is to develop a tool for the numerical simulation of the discharge and after-glow phenomena in a pulsed discharge scheme, with an emphasis on kinetics and plasma phenomena, in order to understand the role of plasmas in the combustion processes. Since recent experiments have demonstrated the fundamental role played by electronically and vibrationally excited air species to enhance combustion [1], we develop a complete vibrationally-specific kinetic scheme in air environment. The kinetic model is validated by mean of experimental measurements. [1] G. Pilla, C. Laux PhD Thesis 21/01/08 [Preview Abstract] |
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FTP1.00045: GLOWS: DC, PULSED, RF, MICROWAVE, INDUCTIVE, OTHERS |
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FTP1.00046: Experiment and global model of inductively coupled RF Ar/N$_2$ discharges Takashi Kimura, Hiroki Kasugai Plasmas containing N$_2$ have been attracted as a source of active species such as the active atomic nitrogen and the excited nitrogen molecules in the field of material science. In this study, measurements with a Langmuir probe and optical emission spectroscopy are carried out in inductively coupled RF (13.56 MHz) Ar/N$_2$ discharges in the total pressure range from 20mTorr to 100mTorr, changing the N$_2$ content from 5$\%$ to 50$\%$. Plasmas are produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 40 mm in length, where the power injected into the plasma is 200W. The structure of the measured electron energy probability function (EEPF) can be approximated as a Druyvesteyn-like distribution at any N$_2$ content. The electron density, which is on the order of 10$^{16} $-10$^{17}$(m$^{-3}$), increases with increasing the Ar content, whereas the effective electron temperature slightly decreases. The vibrational and rotational temperatures can be estimated from the optical emission spectroscopy of N$_2$ second positive system. The vibrational temperature is higher than 10000K at any experimental condition, and the rotational temperature monotonically increases from 500K to 1000K with the increase in the Ar content. Moreover, the N$_2$ dissociation rate, which corresponds to the density ratio of N to N$_2$, can be estimated by actinometry. The dissociation rate reaches the maximum when the Ar content is about 85$\%$. [Preview Abstract] |
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FTP1.00047: Fluid modelling and analysis of the constriction of the dc positive column in argon Mykhaylo Gnybida, Detlef Loffhagen, Dirk Uhrlandt A self-consistent fluid model describing the positive column of a DC argon discharge was developed. This model consists of the coupled solution of balance equations for the charge carriers, excited species, mean electron energy, and gas temperature in the plasma, Poisson's equation for the radial potential, and a current balance determining the axial electric field. Different assumptions concerning the electron energy distribution function (EEDF) were adapted to calculate electron transport and rate coefficients as a function of the electron mean energy. Simulations were carried out for currents from 1 to 100 mA and pressures from 100 to 500 Torr. The predicted voltage-current characteristics and electron density profiles are used to identify the transition from glow to constricted mode of the argon discharge. The results are compared with data from experiments. The impact of the various assumptions for the EEDF (Maxwellian, Druyvesteyn, solution of 0D Boltzmann equation with and without inclusion of electron-electron collisions) is discussed. The influence of cumulative ionization, electron-electron collisions, and gas heating in forming the EEDF as well as electron-ion recombination are found to be main reasons for the constriction of the glow discharge. [Preview Abstract] |
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FTP1.00048: Normal Mode of DC Glow Discharge Valeriy Lisovskiy, Nadiia Kharchenko, Vladimir Yegorenkov We registered the normal current density j of the dc glow discharge in the nitrogen pressure range p = 0.3 - 10 Torr and determined the quantity j/p$^{2}$. Experiments were carried out in a T-shaped tube, the cathode was located at one end of the horizontal part of T, whereas another electrode (anode at the bottom of T) was grounded. Photos were taken through a window at the opposite end of the horizontal part of T exposing the cathode and the images were digitized. According to a generally accepted opinion this quantity j/p$^{2}$ had to remain constant on varying the current I in the normal mode. This proved to be valid only for p $<$ 1 Torr. At higher pressure values the current growth was accompanied with a decrease of the quantity j/p$^{2}$. In a plasma column of small cross section the current density is larger to compensate for the increased loss of charged particles from the discharge volume. [Preview Abstract] |
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FTP1.00049: VI characteristics and spatial emission profiles of hollow cathode discharge N. \v{S}koro, D. Mari\'c, G. Malovi\'c, Z. Lj. Petrovi\'c, V. Mihailov, R. Djulgerova Our aim is to relate electrical properties of the hollow cathode devices to the spatial structure of the discharge, including discharge formation period. Special attention was given to the development of the hollow cathode effect. Commercial hollow cathode lamp sealed at 3.5 Torr (Ne) with cylindrical Mn cathode with bottom and a ring shaped anode was used. We measured VI characteristic and using emission profile images established current dependence of the peak emission intensity of the discharge. According to our data, hollow cathode discharge can be represented as a combination of discharges between parallel plates and inside the cavity. As the hollow cathode effect develops, the discharge moves from the cathode edge into the cavity, while the current density and emission intensity increase significantly. At the same time, the discharge voltage decreases. We were able to trace in time the discharge formation in several distinctive regimes of operation. Thus, we could connect certain points in transient phase with discharge spatial structure, revealing the discharge behavior. [Preview Abstract] |
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FTP1.00050: Temperature Effects on Propagating Shock Waves in Glow Discharge Plasmas* Nirmol Podder, Aaron LoCascio The time-history of the shock wave propagation in glow discharge plasma starting from the plasma switch-on or switch-off is produced. After a few tens of ms of the plasma switch-on, the photo acoustic deflection (PAD) profiles of the laser beams produced by the shock-front gas density gradients show increased signs of broadening, and both the shock wave propagation velocity and the laser deflection width start to increase nonlinearly as the temperature of the discharge is expected to rise from its room temperature value, and quickly reach their relatively fixed steady-state values at about 120 ms after the switch-on of the glow discharge at fixed discharge current 35 mA and gas pressure 15 Torr. At the plasma switch-off, the trend in the propagation velocity is reversed linearly, and that in the deflection width non-linearly as the afterglow plasma cools rapidly to its room temperature. [Preview Abstract] |
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FTP1.00051: Characteristics of a Propagating Shock Wave in Gas Discharges Aaron LoCascio, Nirmol Podder, Lane Roquemore Acoustic shock waves are launched in both neutral and ionized gases and their properties are measured with pressure sensors, laser beams, and a high-speed camera. The pressure sensors yield information on the total gas pressure, the deflection of the laser beams gives an indication of the gas density, and the high-speed camera captures the dynamics of the propagating shock wave. Shock wave propagation velocities ($\sim$ Mach 2) are determined from all three methods and compared well with one another. The emission characteristic and structure of the shock-front are obtained from the laser beam deflection signals and the camera images. [Preview Abstract] |
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FTP1.00052: Kinetic dispersion relation for electrostatic electron waves in a low-pressure collisional plasma J. Oberrath, R.P. Brinkmann For the kinetic description of plasma waves a number of approaches are common: 1) the Vlasov equation is discussed, if collisions between particles can be neglected, 2) the BGK collision term is used in a weakly ionized plasma to take collisions into account, and 3) the Fokker-Planck approach is applied to describe waves in Coulomb collision dominated plasmas. We investigate electrostatic electron waves in a weakly ionized low-pressure plasma dominated by electron-neutral collisions. We assume an isotropic collision term with a constant collision frequency instead of the BGK term because of the huge mass difference between electrons and neutrals. This allows the derivation of the dispersion relation from the linearized Boltzmann-Poisson system for homogeneous longitudinal waves. In contrast to established dispersion relations our relation is able to describe the influence of collisions on the electrostatic wave propagation of electrons. The dispersion relation including the dispersion function for a Maxwell distribution is a special case of our result. A similar description is given in [1], where the distribution function is expand to spherical harmonics in velocity space and terms of higher orders are neglected. We do not resort to such an expansion but treat the electron distribution function in full. [1] S.B. Biragov et al, Radiophys. Quantum Electron. 28 (1985) 743-748 [Preview Abstract] |
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FTP1.00053: Non-local effects in spatial distribution of excitation rates in positive column of glow discharge plasma of molecular gases Anatoly Kudryavtsev, Eugene Bogdanov, Lev Tsendin At simulations of gas-discharge plasmas the electron distribution function (EDF) is usually calculated using a local approximation (LA) which is applicable only when electron energy relaxation length \textit{le} $< \quad R -- $plasma size. For atomic gases \textit{le} $> \quad 100l$ ($l$ -- electron free-path-length), so the LA for EDF is not valid up to high pressures. By contrast, in molecular gases due to strong vibrational excitation with low energy threshold, the length \textit{le} is small \textit{le$\sim $l}. And so it is assumed everywhere that the LA for EDF calculation in molecular gases is valid in any cases when diffusive approximation $R $>$ l $ is applicable. In this report it is shown that in molecular gases local approximation is inapplicable on the discharge periphery, where ambipolar field exceeds longitudinal field. A heating of fast electrons in ambipolar field gives rise to excitation constants from centre to periphery of discharge. [Preview Abstract] |
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FTP1.00054: The Monte-Carlo get finished in hollow cathode theory -- a source equation is incoming! Vladimir Gorin The \textit{hollow cathode effect} (HCE) in glow discharge occurred rather hard bean for theoreticians. Classical local Engel and Shtenbek cathode dark space theory does not work under conditions of HCE because it is not possible to neglect inertia of electron here. The electron distribution function has many features and it is far from Maxwellian one. The absence of non-local source model from Paschen invention of a hollow cathode in 1916 till today forced to use Monte-Carlo methods. It meant an absence of any equation for a source of ionization in a hollow cathode! Time to find this equation is coming. It is an integral equation, which is derived from kinetic equation and determines a non-local dependence of ionization source on electric field through phase trajectories of electron motion. When simplification of local dependence is possible, the equation can be transformed into ordinary differential equation and then it is coincident with a continuity equation of classical Engel-Shtenbek model. In joining with field equations the source equation enables to calculate current voltage characteristics of simple glow and hollow cathode discharge and see the HCE in mathematical simulation. [Preview Abstract] |
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FTP1.00055: PLASMA CHEMISTRY |
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FTP1.00056: Hydrogen Sulfide Decomposition in Pulsed Corona Discharge Reactors S. John, G.B. Zhao, J.J. Zhang, J.C. Hamann, S.S. Muknahallipatna, S. Legowski, J.F. Ackerman, M.D. Argyle Hydrogen sulfide (H$_{2}$S) decomposition was carried out in each of four balance gases (Ar, He, N$_{2}$ and H$_{2})$ in a wire-in-tube pulsed corona discharge reactor. H$_{2}$S conversion rates and H$_{2}$S decomposition energy efficiencies depend on the balance gas and H$_{2}$S concentrations. H$_{2}$S conversion in monatomic balance gases, like Ar and He, is more efficient than in diatomic balance gases like N$_{2}$ and H$_{2}$. Low pulse forming capacitance, low charge voltage, and high pulse frequency operation produces the highest energy efficiency for H$_{2}$S conversion at constant power. H$_{2}$S conversion is more efficient in Ar-N$_{2}$ gas mixture than in Ar or N$_{2}$. These results can be explained by corona discharge observations, the electron attachment reactions of H$_{2}$S and the proposed reaction mechanism of H$_{2}$S dissociation. The results reveal the potential for energy efficient H$_{2}$S decomposition in pulsed corona discharge reactors. [Preview Abstract] |
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FTP1.00057: A Simulation of Gas Temperature Distribution in a Microcell Plasma in Ar by Considering Ion Impact on and Radiation Heat Transfer from a Chamber Wall Hisahito Mitsuhashi, Takashi Yagisawa, Toshiaki Makabe Microcell plasma has been attracting our attention to an emission device, conductive device and reactive plasma source for processes etc. Microcell plasma has intrinsic characteristics, i.e., wall controlled high density plasma. Then, it will be important for us to investigate the flow of the external electrical energy to the neutral gas molecule and surface of the microcell for the purpose of the control of the efficiency for plasma production, ion acceleration, and wall heating etc. In the present work, we simulate the spatial temperature distribution of neutral Ar in capacitively coupled microcell plasma sustained at 13.56 MHz by the consideration of the energy conservation equation of gas molecules under the heat transfer on and radiation from the electrode and wall. We mainly discuss the heating of the chamber wall by the impact of energetic ions and the heating of feed gases in the chamber. The dependence of the gas density on the gas heating will be also discussed. [Preview Abstract] |
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FTP1.00058: Plasma-enhanced catalysis at atmospheric pressure, using a dielectric barrier discharge. J.A. Rees, D.T. Lundie, D.L. Seymour, T.D. Whitmore The combination of plasmas and catalysis under moderate temperatures is an emerging area. The techniques are commonly combined in one of two ways. In the first of these the catalyst is introduced into the plasma while in the second, the catalyst is placed down-stream of the discharge. The introduction of a plasma to a catalysis system may produce a change in the distribution or type of reactive species available for reaction or a change of catalyst properties, such as an increase in dispersion or a change in catalyst structure. In the present work, a micro-reactor that allows the study of catalysis using temperature-programmed techniques. The reactor also allows a dielectric barrier discharge (DBD) to be generated over the whole length of the catalyst region or to precede it. The DBD produces a cool plasma at atmospheric pressure and generates surface modifications of the catalyst and is a source of ions and radicals for reaction processes. Test reactions have been studied to show differences in reaction product distributions and activation temperatures when compared with the catalyst alone. Reaction product distributions were measured using a Hiden, capillary-inlet, mass spectrometer. A molecular beam inlet, mass/energy spectrometer was also used to study the constituents of the DBD plasma. [Preview Abstract] |
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FTP1.00059: Low temperature conversion of molecular species via a hybrid plasma discharge -- catalytic process Ed Barnat Various avenues are being perused towards developing more sustainable energy sources to meet current and future energy requirements. Central to these energy surety related concerns is the efficiency of a given processes (chemical reaction) employed for synthesis of these fuels or energy sources. We present results from our preliminary studies on using low-temperature non-equilibrium discharges, coupled to active surfaces as a means of efficiently dissociating key molecular species that may be used towards fuel synthesis. Specifically, we focus on dissociating carbon dioxide to form carbon monoxide which is used in conjunction with hydrogen to generate syngas and higher hydrocarbons. While studies have been performed using various plasma sources, we primarily use a ``hybrid'' plasmas with tuned E/N that has been demonstrated to efficiently dissociate carbon dioxide[1]. \newline [1] S. N. Andreev et. al, Spectrochimica Acta A \textbf{60}, 3361 (2004). [Preview Abstract] |
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FTP1.00060: Molecules production/losses on surfaces under plasma exposure O. Guaitella, D. Marinov, A. Rousseau The production/losses of molecules on surfaces such as walls plasma reactors is interesting for numerous applications but especially for plasma/catalyst coupling used in air treatment devices. The processes like adsorption, desorption, surface production or destruction of molecules on different surfaces are crucial to understand the kinetics of molecule oxidation by air plasma. These mechanisms are studied for C$_{2}$H$_{2}$, NO and NO$_{2}$ molecules in a low pressure discharge (1mbar) in a 50 cm long tube with IR tunable diodes to perform time resolved in situ measurements during the plasma ``on'' phase as well as after switching off the plasma.Surfaces are treated by different plasmas (capacitive or DC discharge) in Ar, O$_{2}$, N$_{2}$ or air, for several pretreatment durations, injected powers, with pulsed or continuous plasma. These parameters are used to separate cleaning of adsorption sites from adsorption of reacting species which could both induce losses of molecules considered on surface. After these different pre-treatment procedures, two kinds of experiments are made:i)the study of molecule losses on pre-treated surfaces by introducing a controled amount of molecules in the closed tube reactor; this gives information about the adsorption of the introduced molecule on vacant sites or its reactivity with species already adsorbed during the pre-treatment ii)the production of molecules by a N$_{2}$ or O$_{2}$ plasma reacting with species adsorbed on wall during pretreatment. [Preview Abstract] |
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FTP1.00061: Comparison Study of Methane Conversion in Low Temperature DC Plasma Reactor with Catalytic High Temperature Fixed Bed Reactor Hamid Reza Bozorgzadeh, Naser Seyed-Matin, Amin Aziznia, Morteza Baghalha This work reports the results of oxidative coupling of methane in the presence of a Na$_{2}$WO$_{4}$/Mn/SiO$_{2}$ catalyst within the temperature range of 1023--1123 K and a low temperature, atmospheric co-axial cylinder DC corona discharge reactor. Catalytic high temperature reactions were conducted in a quartz tube reactor with Na$_{2}$WO$_{4}$/Mn/SiO$_{2}$ catalyst. A methane/oxygen feed ratio of 4:1 with argon as a diluent gas with total flow of 100, 130, 170 {\&} 200 ml/min has been studied in this investigation for both methods. The plasma reactor was a 15 cm stainless steel co-axial cylinder which cylinder is grounded. Acetylene and hydrogen were the major products of co-axial cylinder DC corona reactor. In the catalytic reactor, ethylene has the highest selectivity and no trace of acetylene was found. The comparison between two methods is also discussed. [Preview Abstract] |
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FTP1.00062: Interconnected Microcavity Plasma Arrays: New Opportunity For Microplasma Chemical Reactors Sung-Jin Park, Tyler Anderson, Jeffrey Ma, Jie Zheng, Cherk Lam, J. Gary Eden Various microchemical reactors consisting of parallel, linear arrays of interconnected cylindrical microcavity plasma devices have been fabricated by replica molding in ultraviolet-curable polymer. Tests of 10 $\times $ 10 arrays of 400 $\mu $m dia. devices with 125 $\mu $m wide gas flow channels have been conducted in rare gas and Ar/CS$_{2}$ flows and excitation of the array with a sinusoidal voltage. Visible chemiluminescence ($\lambda \sim $505 nm) resulting from the A $\to $ X transition of CS$_{2}^{+}$ and the deposition of a (C -- S)$_{n}$ microstructured polymer have been observed in the Ar/CS$_{2}$ flow experiments. Microplasma properties in a restricted gas flow and the potential of these arrays for microchemical applications will be discussed. [Preview Abstract] |
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FTP1.00063: PLASMA DIAGNOSTICS |
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FTP1.00064: Controllable optical emission spectroscopy plasma diagnostic system P.L. Stephan Thamban, Jimmy Hosch, Daniel Self, Matthew Goeckner Optical emission spectroscopy (OES) does not always produce signals useful for plasma diagnostics, including endpoint detection. Fluctuations in plasma power or deposition on walls, cause the OES signal to drift. To overcome such shortcomings, we have developed a method and tool that allows independent control of both electron energy (E$_{e})$ and density (n$_{e})$. A description of the method and resulting tool will be presented. We will show how we can alter the operation of the system to change just E$_{e} $ but not n$_{e}$. Thus, we can preferentially probe specific transitions of a given species, or across multiple species. Such ability allows one to probe specific species for use in endpoint detection. We will also show that we can correlate electrical measurements to OES data. Here, the OES signal can be directly correlated to the anode current, a measure of n$_{e}$. Finally, we will show how this system can be adapted for use on numerous plasma systems as either an endpoint tool or an advanced diagnostic, allowing the collection of data that has not been possible to date. [Preview Abstract] |
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FTP1.00065: Self-trapping of fast electrons and spectral measurements in short constricted discharge with cold cathode J.C. Blessington, S.F. Adams, V.I. Demidov, B.A. Tolson, M.E. Koepke It is known that the effect of self-trapping of the fast electrons in a plasma [1] can be used to regulate plasma properties and be useful for technological applications. It has been demonstrated experimentally that this effect is well pronounced in the cathode region of discharges. The measured wall potential in this discharge region is much higher than a few kT{\_}e, where T{\_}e is the electron temperature (average energy). The measurements have been conducted in short constricted discharges with a cold cathode in argon. Application of additional voltage to the discharge walls causes a redistribution of fast electron fluxes to the boundaries and changes in the intensities of argon spectral lines. Measurements of the relative intensities of spectral lines with wavelengths of 419.8 nm and 420.1 nm give a simple estimation of metastable argon atom distribution [2], which depends on the discharge configuration. 1. C. A. DeJoseph, V. Demidov, J. Blessington, and M. Koepke, Euro Phys. News, 38, {\#}6, 21 (2007). 2. C. A. DeJoseph, J. Phys. B: At. Mol. Opt. Phys., 38, 3805 (2005). [Preview Abstract] |
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FTP1.00066: The use of a hairpin resonator probe and emission spectroscopy to determine instabilities during silicon etching David Kavanagh, Mohammed Morshed, Stephen Daniels The hairpin resonator probe is a diagnostic method which determines electron density. The probe was placed in a capacitively coupled plasma SF$_{6}$ plasma during the etching of silicon and the steady state electron density determined. Due to the absence of substrate cooling, the temperature increase in the chamber as the etch process progressed begins to heat and damage the photoresist. As a result the photoresist begins to desorb and outgas, releasing organic polymers into the discharge. These effluents react with the bulk plasma chemistry and have the effect of reducing the electron density measured by the probe. Optical emission spectroscopy was also used to monitor emissions from the plasma. Emissions from non process gasses were also observed as a result of the photoresist heating. These results allow for the consideration of the hairpin resonator probe as a diagnostic for plasma process monitoring [Preview Abstract] |
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FTP1.00067: Characterization of the Basic Operational Properties of the Capillary Plasma Electrode (CPE) Discharge Jose Lopez, WeiDong Zhu, Margaret Figus, Kurt Becker Various approaches have been pursued to create stable atmospheric pressure discharges by extending the lifetime of the diffuse phase of the discharge to hundreds of microseconds. Previous research showed that the stability of the diffuse mode is dependent on the frequency (in the kHz range), gas type, power, mode of the excitation, and geometrical confinement. The Capillary Plasma Electrode (CPE) discharge is able to produce stable atmospheric pressure nonequilibrium plasmas. The CPE is similar in design to a barrier-electrode discharge, but has perforated dielectrics. This configuration, aside from exhibiting a diffuse mode of operation, also exhibits the so-called ``capillary jet'' mode, in which the capillaries ``turn on'' and a bright plasma jet emerges from the capillaries. The capillary jets from adjacent capillaries overlap so that the discharge appears uniform when the electrode contains an array of holes. There appears to be a threshold frequency for the capillary jet formation, which is strongly dependent on the L/D ratio of the capillaries, where D is the diameter of a capillary and L its length. This current work explores these modes of operation of the CPE by characterizing the electrical and optical emission properties of this discharge. [Preview Abstract] |
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FTP1.00068: Effect of multiphoton ionization of metastable and ground-state molecules in laser Thomson scattering diagnostics A. Kono, K. Fukuyama, M. Aramaki In laser Thomson scattering diagnostics of low temperature plasmas, the probe laser beam is focused to obtain a sufficient signal to noise ratio, and the laser energy density in the focal region is very high. Therefore, one must be certain that possible electron production due to multiphoton ionization is negligible in comparison with the unperturbed plasma electron density. We are carrying out a systematic study of determining multiphoton ionization efficiency in the focal region of frequency-double Nd:YAG laser (532 nm). The laser beam is focused between the electrodes of a small dc-biased parallel-plate probe, whose current due to the collected charge arising from multiphoton ionization is detected by a digital oscilloscope. Preliminary results indicate the following. For 200-mJ laser pulse focused with a f=400 mm lens, metastable Ar atoms are ionized with a high probability, while no significant ionization occurs for ground-state Ar atoms. Ground-state O$_{2}$ molecules give rather large multiphoton ionization signal and Thomson scattering measurements for medium pressure (1$>$Torr) O$_{2}$ plasma would require careful control of laser energy density in the focal region. Measurements for other gases are in progress. [Preview Abstract] |
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FTP1.00069: Phase resolved measurement of anisotropic electron velocity distribution functions in a radio frequency discharge Dirk Luggenhoelscher, Dragos Crintea, Viktor Kadetov, Christopher Isenberg, Uwe Czarnetzki In inductively coupled radio frequency discharges the electron velocity distribution function is harmonically modulated in time and this is equivalent to the oscillating current density generated in the plasma by the induced electric field of the antenna. This oscillation is measured temporally resolved by Thomson scattering~with a frequency doubled Nd:YAG laser with a pulse length of 8~ns which determines the temporal resolution. From the measured electron velocity distribution the electron temperature and the density can be derived. The displacement of the distribution shows the drift of the electron ensemble along the direction of the induced field. Further, we will introduce a novel phase resolved emission spectroscopic technique that allows absolute measurement of the same quantity by analyzing the modulation of the atomic excitation by electron collisions. The experiment is carried out in an ICP (f = 13,56~MHz) with a planar antenna of 10~cm radius in argon at low pressures in the Pa regime. [Preview Abstract] |
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FTP1.00070: Optical diagnostics of Ar plasmas using $3p^55p \rightarrow 3p^54s$ emissions with consideration of excitation out of metastable levels R.O. Jung, John B. Boffard, Chun C. Lin, A.E. Wendt For argon plasmas, optical emissions corresponding to $3p^54p \rightarrow 3p^54s$ (668-1150~nm) are often exploited for diagnostic purposes. Metastable atoms, having large electron-impact excitation cross sections and potentially high densities in a plasma can contribute significantly to these emissions. At high densities however, $3p^54p \rightarrow 3p^54s$ emissions can be strongly reabsorbed by metastable atoms, misleading results. In a 600~W, 1~mTorr ICP, our white light absorption measurements give a metastable density of $\sim 2 \times 10^{10}$ cm$^{-3}$. Here the observed $2p_6 \rightarrow 1s_5$ branching fraction is 0.24 in contrast to the expected value of 0.71 in the absence of radiation trapping. This discrepancy is resolved by accounting for radiation trapping. Emissions from $3p^55p \rightarrow 3p^54s$ (395-470~nm) however, are less affected by radiation trapping, making them favorable candidates for optical diagnostics. We have combined our $3p^55p \rightarrow 3p^54s$ optical emission, metastable density, and Langmuir probe measurements for a series of ICP conditions (1-25~mTorr, 10-800~W) with previously measured cross sections in order to develop a self-consistent model. [Preview Abstract] |
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FTP1.00071: Laser Thomson Scattering Diagnostics in the Low-Temperature Plasmas Hyun-Jong Woo, Kyu-Sun Chung Laser Thomson Scattering (LTS) is the non-invasive method for measuring the electron temperature and its density, which can be used for the calibrations of electric probes within collisional and magnetized plasmas. For LTS diagnostics in the low-temperature plasmas, one need to special optics for detection of the scattered light with restricting the Rayleigh and Stray lights. For this, one uses the Triple Grating Spectrometer (TGS), which is composed of Rayleigh block (notch filter for Rayleigh light) and double grating filter (DGF). All focusing lenses are used with achromatic doublet configuration for reducing the non-linear optical effects such as spherical aberration, coma, etc. The specifications of the grating and achromatic doublet lens are 1800 gr/mm with the dimensions of 84 mm $\times$ 84 mm and 400 mm of focal length with the diameter of 100 mm, respectively. In this configurations, the linear dispersion is given as 1.006 nm/mm. Considering the dimension of Charged Coupled Device (CCD) with the linear dispersion, the LTS system can be measure the electron temperatures of less than 10 eV (in most laboratory plasmas). The initial measurement of LTS measurement and comparative study with single probe are done in Divertor Plasma Simulator (DiPS) with the following plasma parameters; plasma density of $10^{11}-10^{13}$ cm$^{-3}$, electron temperature of 1-4 eV, and the magnetic field of 0.2-1 kG, respectively. [Preview Abstract] |
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FTP1.00072: Electron energy distribution function in low-pressure argon plasmas sustained by surface waves L. Stafford, D. Lapierre, N. Eddine, R. Khare, V. Donnelly Surface wave (SW) plasmas have attracted considerable attention because of their interest in materials processing. In such plasmas, the spatially averaged plasma frequency $\omega _{p}$ is larger than the wave frequency $\omega $ and this ensures the condition for SW propagation. However, due to a spatial plasma density inhomogeneity, local plasma resonances at which $\omega _{p}=\omega $ can occur over the density profile close to the discharge walls. This can result in large and sharp peaks of the SW electrical field. Through kinetic modeling, it was found that this effect can result in fast electron generation. However, this was never observed experimentally. We used trace-rare-gas-optical-emission-spectroscopy to measure the electron temperature ($T_{e})$ and electron energy distribution function (EEDF) in a 50 mTorr Ar plasma operating at 2.45 GHz and sustained in a 8~mm quartz tube. By selecting Ne, Ar, Kr, and Xe lines excited from the ground state which are characteristic of the high energy portion of the EEDF, we found that $T_{e}$ increased from 5 to 10 eV as the observation point was moved away from the launcher. On the other hand, a constant value of $T_{e}$ = 3.1 $\pm $ 0.6 eV was obtained using Ar, Kr and Xe lines excited to a significant extent through impact with lower energy electrons. Such high-energy tail was not observed in 600 MHz plasmas sustained in a 26~mm tube. [Preview Abstract] |
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FTP1.00073: Measurement of pulse mode ICP plasma using multi-frequency floating probe Myung-Sun Choi, Seok-Hwan Lee, Gon-Ho Kim Recently in plasma process, pulse mode operation of plasma source is getting popular for various processing products and it interests more in the in-situ property of pulse mode plasma. Newly a floating probe method which uses harmonic distortion of current has been introduced for in-situ plasma monitoring with a minimum perturbation and it may suit to pulse mode plasma measuring. Harmonic distortion of probe current due to sheath nonlinearity which is a strong function of electron temperature is analyzed in the frequency domain by Fast Fourier Transform(FFT), and the plasma density is obtained from the Bohm current model. To eliminate the sheath displacement current and stray current, multi-frequency correction is used which draws out the sheath conduction current by extrapolation of current-frequency relation. This multi-frequency floating probe method is evaluated with the Langmuir probe data in CW and pulse mode ICP argon plasma. The work on pulse mode plasma characteristic such as an EEDF and the transitions of plasma density and electron temperature and its effect to the floating probe measurement will be discussed. [Preview Abstract] |
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FTP1.00074: New method to measure the electron temperature in Ar/He mixture capacitive discharge Hyo-Chang Lee, Min-Hyong Lee, Chin-Wook Chung The electron temperatures were obtained in Ar or Ar/He capacitive discharge by using the new method to measure the electron temperature from a floating potential and a substrate potential [1]. In Ar discharge, as the gas pressures decrease the electron temperatures decrease from 4.0 eV to 1.2 eV, and as the input RF powers increase the electron temperatures slightly decrease from 3.5 eV to 2.8 eV. In the Ar/He discharge, the electron temperatures do not change linearly with the mixing ratio. However the electron temperatures increase abruptly near P$_{He}$/P$_{Ar+He }$= 1. These results agree well with electron temperatures measured by a floating type probe [2]. [1] Min-Hyong Lee, Ik-Jin Choe, and Chin-Wook Chung, J. Korean Phys Soc. 51, 1307 (2007). [2] Min-Hyong Lee, Sung-Ho Jang, and Chin-Wook Chung, J. Appl. Phys. 101, 033305 (2007). [Preview Abstract] |
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FTP1.00075: Experimental measurements of the total energy loss in low pressure inductively coupled argon plasma Young-Kwang Lee, Min-Hyong Lee, Chin-Wook Chung Total energy lost per electron-ion pair lost ($\varepsilon _{T})$ was measured experimentally in a low pressure inductively coupled argon plasma. $\varepsilon _{T}$ represents not only the elastic and inelastic collision energy loss of electron-neutral but also the kinetic energy loss when the electron and ion escape to the wall. In order to determine $\varepsilon _{T}$, the modified power balance of a global model (spatially-averaged) is properly derived using some assumptions. A floating-type probe working at very low bias voltage ($\sim $1.0 V) was applied to obtain the electron temperature and plasma density at the plasma-sheath boundary. At 10 mTorr, the measurement shows that the measured $\varepsilon _{T} \sim $100 V gradually decreased with absorbed power and began to saturate. These $\varepsilon _{T}$ are consistent with the theoretical results by Lee \textit{et al} [1]. [1] Min-Hyong Lee, Sung-Ho Jang and Chin-Wook Chung, Phys. Plasmas, 13, 053502 (2006) [Preview Abstract] |
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FTP1.00076: Dielectric thickness monitoring method by using dual frequency in processing plasmas Sung-Ho Jang, Gun-Ho Kim, Chin-Wook Chung The wall condition of a chamber lead to change in plasma state, and therefore it can be very important factor in processing plasmas.Real time measurement method of dielectric film thickness on the wall was developed. This method used the impedance difference of the coated dielectric material because the impedance is a function of the frequency of applying voltage. The experiment was conducted at various pressures and rf powers. The experimental result showed that the thickness of aluminum oxide (Al$_{2}$O$_{3})$ film could be obtained well. And the changes in the thickness of the deposited dielectric film on the wall in processing plasmas were observed in real time. [Preview Abstract] |
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FTP1.00077: Thermal, Electrical, and Optical Measurements of Electrical Discharges in Saline Cameron Moore, Arlen Ward, Kazunari Sato, George Collins We report measurements of electrical discharges in saline that are electrically excited at 100 kHz from a commercial electrosurgical system. Using a one-dimensional thermocouple array, we estimate that these discharges in saline, in contrast to prior work, induce local temperatures $>$ 100 C. Simultaneous measurement of voltage, current, and optical emission of Na* at 589 nm show that these discharges have frequent arcs, and that these arcs dominate energy flow into the saline. Finally we present measurements of Stark splitting of the sodium D1 and D2 resonant emission lines and from these data estimate the thickness of sheath-like region where most of the applied voltage is dropped. [Preview Abstract] |
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FTP1.00078: Mode transitions in radio-frequency plasmas Deborah O'Connell, Kari Niemi, Timo Gans, Bill Graham Inductively coupled radio-frequency plasmas can be operated in two distinct modes. At low power and comparatively low plasma densities the plasma is sustained in capacitive or so-called E-mode. As the plasma density increases a transition to inductive H-mode is observed. This transition region is of particular interest and governed by non-linear dynamics and under certain conditions can result in structure formation with strong spatial gradients in the light emission. The two modes show pronounced differences is various measureable quantities e.g. electron densities, electron energy distribution functions, ion energy distribution functions, dynamics of optical light emission. Thus, the synergy of employing various diagnostics simultaneously yields improved understanding of the non-linear dynamics during the mode transition. The electron and ion energy distribution functions exhibit different characteristic shapes in each mode. The two distinct operation modes can be identified through the higher harmonic components of both the current and optical light emission. [Preview Abstract] |
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FTP1.00079: A simple analysis method for the I-V curve of Single Langmuir Probes Ikjin Choi, Chin-Wook Chung In single Langmuir probes, the derivation of the electron temperatures from I-V characteristics is not easy and simple because of the difficulties in obtaining ion currents. The electron temperatures are usually found from a logarithm slope of the election current that the ion current was subtracted from the probe current. In this paper, a simple method regardless of ion currents will be introduced and demonstrated. If electrons are in a Maxwellian distribution, the electron temperature is simply given by Ip / (dIp/dV) at a plasma potential where Ip and V are the probe current and the bias voltage. In this case, ion current theories were not needed because the ion current becomes zero at the plasma potential. The electron temperatures from this method are used to derive plasma densities from electron saturation currents. This simple analysis was a good agreement with that from the electron energy distribution measurement when the electron distribution was a Maxwellian. This analysis was applied in Bi-Maxwellian electron distributions and some discussion will be presented. [Preview Abstract] |
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FTP1.00080: Mass and energy spectroscopy of fluorocarbon plasmas. J.A. Rees It is helpful for many processing plasmas which are operated using fluorocarbon and similar gases to have available information on the nature of the ions generated in the plasma and on the energies with which they impact on surfaces exposed to the plasma. To illustrate the range of data which may be obtained using a Hiden mass/energy spectrometer attached to a plasma reactor, measurements for RF plasmas in CF$_{4}$ CF$_{3}$I, CCl$_{2}$F$_{2}$, and CHClF$_{2}$ in a parallel-plate reactor are outlined. Of particular interest, are the data obtained for the production of negative ions. For the experiments carried out with a 10 Watt plasma in CHClF$_{2}$, the dominant negative ions were H$^{-}$, Cl$^{-}$ and F$^{-}$ . For each of these species, the relative rates of production from the parent gas and the mixture of neutral fragments produced by dissociation in the plasma were determined for electron energies of between 0.5 and 30eV. In the presence of a plasma, the contributions to the negative ion population of electron attachment to the dissociation fragments are also clearly seen. In the absence of a plasma, the electron attachment rates measured for the production of CF$_{3}^{-}$ ions from the parent CF$_{4 }$,$_{ }$show clearly the contributions of two formation pathways via the ground and excited states of the temporary CF$_{4}^{-}$ ions first formed in the electron/molecule collisions. The ability of the mass/energy analyser to observe the energies of the attachment products is helpful. [Preview Abstract] |
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FTP1.00081: Improvement of copper vapor laser characteristics by zinc additive Yurij Shpenik, Volodymyr Kelman, Yurij Zhmenyak The influence of Zn atom additive on ``pure'' copper vapor laser output characteristics was studied. Two-section discharge tube (DT) with an external heated Zn reservoir placed at the center between ceramic sections with Cu pieces was elaborated. The pulsed periodical longitudinal discharge was excited in the DT with Cu-Zn-Ne admixture by a traditional circuit using thyratron generator with resonant overcharge of a storage capacitor. Experimental investigations established that the width, energy and power of laser pulses increased when Zn atoms at appropriate temperature $\sim$ 500 $^{\circ}$C of zinc containing reservoir diffuse into discharge. The registered increasing of pulse energy was up to 50{\%} comparatively with the energy without additive with peak energy at $\sim$ 600 $^{\circ}$C. Additional absorption experiments and modeling the absorption of Zn atom resonant line in the DT (taking into account Doppler and dispersion line broadening) consistent with the conclusion that not only optical resonant pumping by 213.9 nm Zn atom line, but other processes also might be taken into account to explain the influence effects (second kind collisions between resonance state zinc and metastable copper state atoms). [Preview Abstract] |
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FTP1.00082: Extraction of electron energy distribution functions from Langmuir probes using integrated step function response and regularized least squares solver Ahmed ElSaghir, Steve Shannon Electron energy distribution function (EEDF) extraction from Langmuir probe data is an ill-posed problem due to the integral relationship between electron current and EEDF with respect to probe voltage. Curve fitting solutions to extract this EEDF assume a specific type of distribution. Point by point extraction of the second derivative relationship uses a small fraction of the integrated data to extract the EEDF. Recently EEDF extraction techniques have been evaluated using regularized solutions to the integral problem.\footnote{Guti\'{e}rrez-Tapia and Flores-Llamas, Phys. Plasmas \textbf{11} 5102 (2004)} These techniques do not assume any mathematical representation of the EEDF and solve the integral problem for any function that best represents the EEDF. In this paper the electron current for arbitrary functions is derived assuming that the electron density is a sum of step functions representing such a function. This technique for EEDF extraction is validated by adding noise to numerically generated data and using a regularized least squares method to calculate the original function by solving for the individual step function contribution to the total electron current. The methodology, reconstruction, and comparison to current best-known methods will be presented. [Preview Abstract] |
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FTP1.00083: Analysis of spectral line shapes in HID plasmas Hartmut Schneidenbach, Steffen Franke, Martin Wendt, Margarita Baeva The optical emission spectroscopy is widely used for the temperature determination in high-intensity discharge plasmas. The spectral lines are in general strongly reabsorbed around the line centre at high pressures. The plasma parameters can be determined by fitting the measured spectral radiances with radiation transport calculations where the knowledge of the line profile and broadening mechanisms is required. For sufficiently strong reabsorption spectral lines become self-reversed. Bartels and Karabourniotis developed methods which make use of the special features of the spectral radiance at the reversal maxima. The plasma layer properties are approximately represented by an inhomogeneity parameter. The application of these approximations for fitting measured spectral radiances is proposed. High-pressure mercury discharges without and with metal halide additives have been analyzed. The different methods for the temperature determination have been compared and their applicability has been discussed for different spectral lines. [Preview Abstract] |
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FTP1.00084: Optical emission spectroscopy diagnostic of pure vapor Ni plasma Cornel Porosnicu, Ana Mihaela Lungu, Catalin Ticos, Cristian P. Lungu The method studied expensively in our group for materials processing is based on the thermionic vacuum arc (TVA) principle. In TVA, the high-density plasma is localized above the anode, whereas the substrates are placed away from the core of the plasma. This enables thin films deposition to be carried out at low substrate temperatures even for the highest melting point materials. Also, although it is arc plasma, the TVA can be used to prepare particle free films of pure materials. The TVA plasma parameters were evaluated using the analysis of the optical emission radiation of the plasma running in pure vapors. The plasma parameters obtained are anode (Ni pool) temperature, vapor pressure, evaporation rate and electron temperature (evaluated by using the ratio of the atomic emission lines) as function of the dissipated power between electrodes. It was found that plasma parameters are increasing with the power and during arc plasma have relatively constant values. [Preview Abstract] |
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FTP1.00085: Langmuir probe measurements in a VHF dielectric plasma etcher Leonid Dorf, Kartik Ramaswamy, Ken Collins, Walter Merry Langmuir probe (LP) measurements in a realistic VHF CCP discharge are complicated by a number of factors, such as absence of a well-defined DC ground reference and unpredictable behavior of standard electronic components at VHF. The VHF source can produce plasma very efficiently; therefore, to reach the same plasma density, VHF discharges require lower power than HF discharges. Nevertheless, even at low source power ($\sim $100--200W with N$_{e} \quad \le $ 10$^{10}$ cm$^{-3})$, RF potential in a VHF CCP discharge can be large, especially compared to that in an ICP discharge with similar parameters. Uncompensated RF potential distorts both electron and ion parts of the measured V-I characteristic, resulting in unrealistic plasma parameters. Here, we present preliminary results of our work to develop a LP system suitable for measurements in a 162 MHz dielectric plasma etcher. The probe design employs many previously developed RF compensation techniques. Furthermore, all electronic components of the probe and the measuring circuit were characterized using a network analyzer to select adequate values. The probe was used to study the effects of magnetic field, input power, pressure, and other operating conditions on electron and ion density profiles. Electron temperature was found to be in the range of 1.8 -- 3.5 eV, and the shape of ion saturation curve was found to be in agreement with OML theory. [Preview Abstract] |
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FTP1.00086: INTERACTION OF PHOTONS WITH ATOMS AND MOLECULES |
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FTP1.00087: Controlling and stopping vibrational wave packets in $D_2^+$ with fs laser pulses Uwe Thumm, Thomas Niederhausen Ionization of neutral $D_2$ molecules by a short pump laser pulse may create a vibrational wave packet on the lowest ($1s\sigma_g^+$) adiabatic potential curve of the $D_2^+$ molecular ion. We investigated the possibility of manipulating the bound motion, dissociation, and vibrational--state composition of $D_2^+$ nuclear wave packets with a sequence of ultra--short, intense, near infrared control laser pulses. Our numerical results show that a single control pulse with an appropriate time delay can quench the vibrational state distribution of the nuclear wave packet by increasing the contribution of a selected stationary vibrational state of $D_2^+$ to more than 50\%. We also demonstrate that a second control pulse with a carefully adjusted delay can further squeeze the vibrational-state distribution, suggesting a multi--pulse control protocol for preparing stationary excited nuclear wave functions. With the subsequent fragmentation of the molecular ion with a probe pulse, we suggest a scheme for experimentally assessing the degree at which the nuclear motion in small molecules can be controlled, cf., Phys. Rev. {\bf 77}, 013407 (2008). [Preview Abstract] |
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FTP1.00088: Time-series analysis of vibrational nuclear wave packet dynamics Uwe Thumm, Thomas Niederhausen, Bernold Feuerstein We discuss the extent to which measured time-dependent fragment kinetic energy release (KER) spectra and calculated nuclear probability densities can reveal 1) the transition frequencies between stationary vibrational states, 2) the nodal structure of stationary vibrational states, 3) the ground-state adiabatic electronic potential curve of the molecular ion, and 4) the progression of decoherence induced by random interactions with the environment. We illustrate our discussion with numerical simulations for the time-dependent nuclear motion of vibrational wave packets in the $D_2^+$ molecular ion caused by the ionization of its neutral $D_2$ parent molecule with an intense pump laser pulse. Based on a harmonic time-series analysis, we suggest a general scheme for the full reconstruction, up to an overall phase factor, of the initial wave packets based on measured KER spectra, cf., Phys. Rev. A {\bf 77}, 063401 (2008). [Preview Abstract] |
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FTP1.00089: A Fully Relativistic B-Spline R-Matrix Method for Electron and Photon Collisions with Atoms and Ions Oleg Zatsarinny, Klaus Bartschat We have extended our $B$-spline $R$-matrix (close-coupling) method~[1] to fully account for relativistic effects in a Dirac-Coulomb formulation. Our numerical implementation of the close-coupling method enables us to construct term-dependent, non-orthogonal sets of one-electron orbitals for the bound and continuum electrons. This is a critical aspect for complex targets, where individually optimized one-electron orbitals can significantly reduce the size of the multi-configuration expansions needed for an accurate target description. Core-valence correlation effets are treated fully {\it ab initio}, rather than through semi-empirical model potentials. The method is described in detail and will be illustrated by comparing our theoretical predictions for e-Cs collisions~[2] with benchmark experiments for angle-integrated and angle-differential cross sections~[3], various spin-dependent scattering asymmetries~[4], and Stokes parameters measured in superelastic collisions with laser-excited atoms~[5]. [1]~O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). [2]~O.~Zatsarinny and K. Bartschat, Phys. Rev. A~{\bf 77}, 062701 (2008). [3]~W.~Gehenn and E.~Reichert, J. Phys. B~{\bf 10}, 3105 (1977). [4]~G.~Baum {\it et al.}, Phys. Rev. A~{\bf 66}, 022705 (2002) and {\bf 70}, 012707 (2004). [5]~D.S.~Slaughter {\it et al.}, Phys. Rev. A~{\bf 75}, 062717 (2007). [Preview Abstract] |
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FTP1.00090: Differential Cross Sections of Two-Photon Double Ionization of He From Time-Independent and Time-Dependent Calculations Daniel Horner, Alicia Palacios, Thomas Rescigno, C. William McCurdy The method of exterior complex scaling allows us to compute numerically converged time-independent and time-dependent wave functions describing two unbound electrons on a large, but finite volume. With these wave functions, using formally exact integral methods, we are able to extract the observable cross sections. We present total, single differential, and fully differential cross sections for two-photon double ionization of helium above and below the threshold for sequential ionization (54.4 eV). The sequential, two step, double ionization mechanism produces characteristic features seen in the total and differential cross sections. Furthermore, the fully differential cross section shows that even below the sequential ionization threshold two-photon double ionization is largely a process where each electron absorbs a single photon and then correlation between the electrons leads to double ionization. [Preview Abstract] |
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FTP1.00091: Quantum-beat Spectroscopy of Molecular Dynamics in Ultrashort Laser Fields Uwe Thumm, Thomas Niederhausen, Bernold Feuerstein, Thorsten Ergler, Artem Rudenko, Robert Moshammer, Joachim Ullrich Reaction Microscope-based, complete, and time-resolved Coulomb explosion imaging of vibrating and dissociating $D_2^+$ molecules with femtosecond time-resolution allowed us to perform an internuclear distance (R-)dependent Fourier analysis of the corresponding wave packets. Our wave packet propagation calculations demonstrate that the obtained two-dimensional R-dependent frequency spectra enable the complete characterization of the wave packet dynamics and directly visualize the field-modified molecular potential curves in intense, ultrashort laser pulses, cf., Phys. Rev. Lett. {\bf 99} 153002 (2007) and Phys. Rev. A {\bf 77}, 063401 (2008). [Preview Abstract] |
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FTP1.00092: POSITRON ATOM/MOLECULE COLLISIONS |
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FTP1.00093: Elastic electron and positron scattering from argon Allan Stauffer, Robert McEachran In order to obtain accurate elastic differential cross sections for electron and positron scattering from the noble gases at intermediate energies, the effect of the open inelastic channels must be taken into account. We have developed a complex optical potential which does this [1] and have applied this to scattering from argon. Detailed results will be shown. \newline [1] S. Chen, R.P. McEachran and A.D. Stauffer, J. Phys. B 41, 025201 (2008). [Preview Abstract] |
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FTP1.00094: High Resolution Studies of Low Energy Positron Collisions with Helium Stephen Buckman, James Sullivan, Peter Caradonna, Adric Jones, Casten Makochekanwa, Daniel Slaughter, Mark Stevenson, Birgit Lohmann A high resolution, trap-based beam of positrons has been used to study total scattering, positronium formation and direct ionization of He atoms. The energy resolution of the positron beam is typically 65 meV, and measurements have been carried out at incident positron energies between 1 and 60 eV. The experimental arrangement consists of a pulsed beam of positrons from a Surko trap combined with a gas cell containing the helium target gas and a retarding potential analyzer (RPA). ~The beam is confined radially using a 500 gauss magnetic field and the RPA allows absolute cross sections to be obtained by measuring the scattering rate for each process. Normalisation depends only on a measurement of the target gas pressure (in the milliTorr range) and ~the length of the scattering cell. Results will be compared with previous measurements and contemporary theory. [Preview Abstract] |
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FTP1.00095: Role of multimode excitations and inelastic escape channels in positron-molecule attachment C.M. Surko, J.A. Young Experiments have shown that positrons, like electrons, can attach a variety of molecules via vibrational Feshbach resonances (VFR). Because of the positron's unique annihilation channel, one can probe particularly short-lived resonances by examining features in the positron energy-resolved annihilation spectra. We discuss here energy-resolved annihilation spectra for a variety of molecules and relate these results to theory [1]. In particular, we examine the role of multi-mode excitations, which are found to produce VFR in a number of small molecules [2] and may participate in the enhancement of single-mode resonances in large molecules [3]. Also discussed is how fluorine substitution in a large hydrocarbons produces a strong inelastic escape channel. This, in turn, limits resonance lifetimes and decreases the magnitudes of the annihilation resonances above the inelastic threshold [3]. \\ ~[1] G. F. Gribakin \& C. M. R. Lee, \textit{Phys. Rev. Lett.}, \textbf{97}, 193201 (2006). \\ ~[2] J. A. Young, C. M. Surko, G. F. Gribakin, \& C. M. R. Lee, \textit{Phys. Rev. A}, in press (2008). \\ ~[3] J. A. Young \& C. M. Surko, \textit{Phys. Rev. A}, \textbf{77}, 052704 (2008). [Preview Abstract] |
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FTP1.00096: Positron-molecule binding energies measured via resonances in annihilation J.A. Young, C.M. Surko Measurements of positron-molecule annihilation using a monoenergetic positron beam have revealed distinct features due to vibrational Feshbach resonances (VFR). The presence of these features implies the existence of positron-molecule bound states. The shifts in the energies of the resonant peaks from those of the vibrational modes provides a measure of the binding energies. In this paper, we present positron-molecule affinity data for thirty molecular species, which range from $<1$~meV for small molecules such as ethane and ethylene to more than 300 meV for hexadecane and naphthalene. We relate these positron affinities to various physical parameters such as polarizability, ionization potential and dipole moment [1]. We also describe recent results of a quantitative theoretical model for VFR-mediated positron attachment to small molecules [2, 3]. \\ ~[1] J. A. Young \& C. M. Surko, \textit{Phys. Rev. A}, \textbf{77}, 052704 (2008). \\ ~[2] G. F. Gribakin \& C. M. R. Lee, \textit{Phys. Rev. Lett.}, \textbf{97}, 193201 (2006). \\ ~[3] J. A. Young, C. M. Surko, G. F. Gribakin, \& C. M. R. Lee, \textit{Phys. Rev. A}, in press (2008). [Preview Abstract] |
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FTP1.00097: ELECTRON MOLECULE COLLISIONS |
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FTP1.00098: Thermalization of High Energy Electrons in Nitrogen Vladimir Stojanovic, Zeljka Nikitovic, Zoran Petrovic Electron thermalization in pure nitrogen and in air (N2/O2) is studied by Monte Carlo technique for electron energies from 20 eV up to 10 keV. Spatially resolved emission is accounted for by counting number of specific emissions at pressures 1 Torr and 760 Torr. Relaxation of electron energy is followed by using a set of data for nitrogen and oxygen including elastic and inelastic collisions and realistic energy partitioning in ionizing collisions. The secondary electrons born in ionization events are found to affect significantly emission of the $2^{+} $ band. The energy dependences of the effective collision (and emission) probabilities for 391.4 nm and 337.1 nm emission lines and ionization are calculated. These data are used in attempts to use atmospheric fluorescence due to cosmic rays to detect very high energy elementary particles. [Preview Abstract] |
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FTP1.00099: Electron Impact Single Ionization of Atoms and Molecules: Three-Dimensional Images for the Electron Emission XueGuang Ren, Thomas Pflueger, Arne Senftleben, Alexander Dorn, Joachim Ullrich While electron impact ionization for the simplest atomic species hydrogen and helium can be handled well by theory, more heavy atoms and molecules pose severe challenges. Presently we are performing systematic (e,2e) experiments in the impact energy range below 200 eV for various atomic targets as Ne and Ar, and for molecular species as H$_{2}$, Ar$_{2}$, N$_{2}$, O$_{2}$ and CO$_{2}$. The goal is to provide benchmark cross sections covering the full solid angle and a large range of ejected electron energies and momentum transfers by applying an experimental multi-particle imaging technique (Reaction Microscope). [Preview Abstract] |
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FTP1.00100: Fragmentation studies of CF$^+$ and HF$^+$ ions in collisions with cold electrons Oldrich Novotny, S. Altevogt, M.H. Berg, D. Bing, H. Buhr, H. Fadil, M. Froese, J. Hoffmann, B. Jordon-Thaden, C. Krantz, M. Lange, M. Lestinsky, M. Mendes, S. Novotny, D.A. Orlov, A. Petrignani, A. Shornikov, T. Sorg, J. Stuetzel, A. Wolf, A.S. Jaroshevich The fundamental molecules composed of atoms from the second row of the periodic table (C,N,O,F) have a rich structure of excited potential curves that can be probed at high energy resolution by observing fragmentation processes following collisions with quasi-monochromatic electrons. Experiments of this type are performed in merged electron and ion beams at the ion storage ring TSR in Heidelberg, Germany. Using a cold, photocathode-produced electron beam, experiments on the system CF$^+$ yield rich structure in the collision energy dependence of both dissociative recombination (DR) and excitation (DE). The fragment-imaging technique shows a strong collision energy dependence of final ground and excited states of DR products. Moreover, an angular anisotropy of DR is observed for elevated collision energies. DR of HF$^+$ displays extremely low kinetic energy release of neutral fragments yielding resolution on initial rotational states of the ions. This predestines HF$^+$ to be used as ``molecular thermometer.'' [Preview Abstract] |
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FTP1.00101: ABSTRACT WITHDRAWN |
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FTP1.00102: On the reaction rates in the low pressure nitrogen discharge Jon Tomas Gudmundsson, Eythor Gisli Thorsteinsson We use a global (volume averaged) model to study the dissociation of the nitrogen molecule and the role of metastable species in a low pressure (1 - 100 mTorr) high density nitrogen discharge. The collisional energy loss per electron ion pair created is evaluated for the nitrogen atom and the nitrogen molecule. We explore and compare the reaction rates for the creation and destruction of the positive ions N$^+$ and N$_2^+$, the atomic nitrogen in the ground state N($^4$S), the metastable atom N($^2$D) and the metastable molecule N(A$^3\Sigma_u^+$). Furthermore, the dissociation mechanism in the nitrogen discharge is investigated as a function of power and pressure. The discharge is dominated by atomic nitrogen at low pressure and by molecular nitrogen at the higher pressures. [Preview Abstract] |
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FTP1.00103: ION SWARMS |
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FTP1.00104: Arrival Time Spectra of Heavy Particles in Hydrogen Discharge Vladimir Stojanovic, Zeljka Nikitovic, Zoran Petrovic Arrival time spectrum of electrons and heavy particles in Townsend discharge at very high E/N is determined by using Monte Carlo technique. Three dimensional Monte Carlo codes are used for simulation of coupled kinetics of electrons, ions and fast neutrals. The electron collisions are represented by the anisotropic cross section set with available data for energy partitioning. Heavy particle collisions are represented by latest cross section set compiled by Phelps. Trajectories of $H^ {+}$, $H_2^+$ and $H_3^+$ ions, fast H and fast H2 are followed up to the electrodes where arrival time is recorded. Energy relaxation of the neutral particles is followed down to the energy limit of 5 eV. These results are used to obtain the integrated particle flux data that can be compared either to experimental emission integrated data or to data obtained by current integration. The results of simulation allow us separation of different contributions and tests of models of interactions. [Preview Abstract] |
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FTP1.00105: Models of H$\alpha$ Doppler emission profiles from cathode fall discharges in hydrogen A.V. Phelps Doppler profiles are calculated for the H$\alpha$ line excited in collisions of fast atoms, ions, molecules, and electrons with H$_2$ in the cathode fall of low-pressure, moderate-current hydrogen discharges. We use a multi-beam model of the particle fluxes and energy distributions, assumed angular distributions of particles approaching and reflected by the cathode, and a simplified cathode fall model. Spectral profiles are compared with measurements parallel and perpendicular to the tube axis for the conditions reported by Cvetanovi\'c et al.\footnote{N. Cvetanovi\'c, M. M. Kuraica, and N. Konjevi\'c, J. Appl. Phys. {\bf 97}, 033302 (2005).} Excitation is principally by fast H atom collisions with H$_2$ as they approach and leave the cathode and by the electrons leaving the cathode. The calculated relative magnitudes of the wings and core of the parallel and perpendicular H$\alpha$ line profiles and the sensitivity of the emission produced by reflected atoms to cathode material are in agreement with experiment. [Preview Abstract] |
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FTP1.00106: Ion flux energy distributions in a hydrogen-filled drift tube at high E/N Arthur Phelps Ion flux energy distributions are calculated for H$^+$, H$_2^+$, and H$_3^+$ ions in H$_2$ for low-current, uniform-electric-field drift tubes at 1 kTd $< E/N < 10$ kTd and $5\times10^{20} \leq N d \leq 3\times10^{21}$ m$^2$, where E is the electric field, N is the gas density, and $d$ is the electrode separation. We use updated cross sections in a multi-beam model of the spatial and energy dependent particle fluxes. Calculated distributions at the cathode are compared with experiments by Rao et al.\footnote{M. V. V. S. Rao, R. J. Van Brunt, and J. K. Olthoff, ESCAMPIG '96.} and detailed theory by Bretagne et al.\footnote{J. Bretagne, G. Gousset, T. \v{S}imko, M.V.V.S. Rao, R. J. Van Brunt, Y. Wang, J. K. Olthoff, B. L. Peko and R. L. Champion, ESCAMPIG '96.} Hypothetical large increases in the total momentum transfer cross sections for H$^+$ and H$_3^+$ at 100 to 1000 eV yield approximate fits to the relative experimental distributions at high energies at moderate $E/N$. However, these fitted distributions are much too small at low ion energies. Similar discrepancies occur for analytic solutions of the Boltzmann equations using simplified reaction cross sections and the almost free-fall conditions for H$^+$ at 10 kTd. [Preview Abstract] |
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FTP1.00107: HEAVY PARTICLE COLLISIONS |
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FTP1.00108: Alignment relaxation of Ne*(2p$_{i}$[J=1]) atoms due to collisions with He(1s$^{2}$) atoms Vaibhav Khadilkar, Hiraku Matsukuma, Masahiro Hasuo, Cristian Bahrim Alignment relaxation of atoms induced by collisions offers accurate information regarding the anisotropic atom-atom potentials and has many applications in atomic and plasma physics. Here we report the energy-averaged cross sections for destruction of alignment $\sigma ^{(2)}$ and the rate coefficients for disalignment K$_{DA}$ of Ne$^{\ast }$(2p$^{5}$ 3p; 2p$_{i}$ [J=1]) atoms due to He atom collisions using a many-channels close-coupling method based on a modified model potential for the HeNe$^{\ast }$(2p$^{5}$ 3p) system [1]. Comparison with measurements using laser-induced fluorescence spectroscopy (LIFS) [2] and Hanle signals [3] is reported. The LIFS method measures K$_{DA}$ due to intra-multiplet transitions, while the analysis of Hanle signals gives $\sigma ^{(2)}$, which incorporates both the intra- and inter-multiplet transitions. Good agreement between theory and experiments was found for the 2p$_{2}$, 2p$_{5}$, and 2p$_{7}$ states at 77 K $<$ T $<$ 350 K when a static polarizability for each Ne$^{\ast }$(2p$_{i})$ state is added to the long-range potentials of the HeNe$^{\ast }$(2p$^{5}$ 3p) system given in Ref.[4]. [1] Bahrim C and Khadilkar V 2008 \textit{J. Phys. B }\textbf{41} 035203 [2] Seo M, Shimamura T, Furatani T, Hasuo M, Bahrim C and Fujimoto T 2003 \textit{J. Phys. B }\textbf{36} 1885 [3] Carrington C G and Corney A 1971 \textit{J. Phys. B }\textbf{4} 869 [4] Bahrim C, Kucal H and Masnou-Seeuws F 1997 \textit{Phys. Rev. A} \textbf{56} 1305 [Preview Abstract] |
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FTP1.00109: Ionization of Atomic Hydrogen by 75keV Proton Impact Aaron LaForge, Michael Schulz, Jadon Alexander The dynamics and interactions of the few-body problem is one of the most fundamental problems in physics due to the fact that the Schr\"{o}dinger equation is not solvable in closed form for more than two mutually interacting particles. A proton colliding with atomic Hydrogen is a particularly important system to study the few-body problem for its simplicity (only three particles involved), and the underlying force, electromagnetism, being completely known. We performed a kinematically complete experiment to study ionization in this collision system. The fully momentum analyzed recoil ions and scattered projectiles were measured in coincidence so that the ejected electron momentum can be deduced from momentum conservation. As a result, it is possible to extract the maximum information about the collision dynamics for this benchmark system. Multiple differential cross sections will be compared to data obtained recently for p + He collisions, for which serious discrepancies to theory were found [1]. [1] N.V. Maydanyuk et al., Phys. Rev. Lett. \underline {94}, 243201 (2005) [Preview Abstract] |
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FTP1.00110: He Single Ionization in Collisions with ``Fixed-in-Space'' MeV H$_2^+$ Ions Shaofeng Zhang, Jan Suske, Daniel Fischer, Kai-Uwe Kuehnel, Siegbert Hagmann, Michael Schulz, Alexander Voitkiv, Bennaceur Najjari, Andreas Krauss, Xinwen Ma, Robert Moshammer, Joachim Ullrich Two center effects in collisions of fast ions with H$_2$ molecules have been studied intensively. We investigated in a kinematical complete experiment the ionization of He in collisions with H$_2^+$-molecular ions at 0.5 and 1.0 MeV at the Max Planck Institute for Nuclear Physics at Heidelberg. The momenta of the recoiling He ions and the electrons produced in the collisions were measured using a ``Reaction Microscope.'' The fragments of the H$^2_+$ were separated by a dipole magnet after the interaction region and detected by two position sensitive MCP detectors. From this information the orientation and the internuclear distance of the molecular ion at the instance of the collision could be determined. Pronounced structures are found both in the experimental data and theoretical calculations, indicating that the emitted He electron shows a slight preferential emission parallel to the molecular axis. According to our theoretical calculations the effects are due to two-center interference, which turned out to be strongly dependent on the type of approximated molecular wave function used in the calculations. [Preview Abstract] |
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FTP1.00111: Single Electron Capture by C4+ from Atomic and Molecular hydrogen at low energies Dwayne Joseph, Bidhan Saha Electron Capture is well known to be an important collision process in nearly all types of plasma environments from terrestrial laboratories [1] to solar system atmospheres [2] to astrophysical sources. Ion-molecule collisions have received less attention both theoretically and experimentally than its atomic counterpart due to extra degree of freedom. We report here our calculation using ab initio structure calculations. We compare our findings with other available theoretical and experimental results. [1] R. K. Janev, in ``Atomic and Molecular Processes in Fusion Edge Plasmas'' (Plenum Press, NY, 1995), p1. [2] T. E. Cravens, Science 296, 1042 (2002). [Preview Abstract] |
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