Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session SW: Poster Session II |
Hide Abstracts |
Chair: I. Langmuir Room: Doubletree Hotel Fir/Oak 4:00-6:00pm |
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SW.00001: CAPACITIVELY COUPLED PLASMAS
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SW.00002: Study of a capacitive discharge driven by three frequencies using inline RF metrology Steven Shannon, Joel Blackburn, Daniel Hoffman, Valery Godyak, Jang Gyoo Yang, Stephen Rosenblum A capacitive discharge driven by a combination of 2MHz, 13.56MHz, and 60MHz is analyzed using voltage, current, and phase measurements taken at the interface between the electrode and the matching network. The electrode measurements are taken at 2MHz and 13.56MHz using an Advanced Energy Z-Scan{\texttrademark} RF sensor. Using these measurements and combining rigorous RF characterization of the process chamber, discharge impedances are calculated. These impedances are input into a discharge model to calculate electron density and time averaged sheath thickness above the electrode. Over 450 combinations of pressure and power were measured to study the interaction of these three frequencies with regard to plasma parameters. Trends in electron density and sheath parameters over this experiment matrix, with particular attention to the impact of mixing of the 2MHz and 13.56MHz, will be presented. [Preview Abstract] |
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SW.00003: Diagnostics of a large size cylindrical CCP reactor Nevena Pua\v{c}, Gordana Malovi\'c, Antonije Djordjevi\'c, Zoran Petrovi\'c Cylindrical CCP reactor was built for treatment of textile, biological samples and polymers. It is a cylinder 1.2 m in diameter and 2 m long. Central electrode is powered and it is 2 cm in diameter. A stable uniform plasma is produced at 13.56 MHz and for powers in the range from 20 W to several hundred watts. We have used current and voltage probes to measure voltage and current waveforms and obtain the real power transmitted to the plasma. We will show how these waveforms depend on the power, gas, and pressure. In a smaller chamber of a similar geometry increasing the power led to a smaller percentage of the power transmitted to the plasma while in this case the percentage of transmitted power is constant and reasonably high. [Preview Abstract] |
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SW.00004: Secondary electron effects in dual frequency discharges Miles M. Turner Secondary electron effects are often characterized by an effective emission coefficient for each ion arriving at an electrode surface. This approach acknowledges that processes such as the photoelectric effect and fast neutral impact may be important, without representing them explicitly. However, the relative importance of these processes may vary with time during a radio-frequency period and may change as the discharge conditions change. In such cases, a fixed effective secondary emission coefficient is not satifactory. In this paper, we present particle-in-cell simulations including a detailed secondary emission model [1]. These simulations show that under typical dual-frequency capacitive discharge conditions, these issues are significant. Among other things, the effective secondary emission coefficient varies greatly with time, and can reach a maximum of 0.6, which considerably exceeds the values usually assumed. Consequently, secondary emission effects are of considerable significance and have a large effect on the discharge parameters. [1] A. V. Phelps and Z. Lj. Petrovic, Plasma Sources Sci. Technol. 8, R21 (1999). [Preview Abstract] |
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SW.00005: Measurements of power dissipation in a capacitive sheath David Gahan, Michael B. Hopkins, Albert R. Ellingboe An experimental system is presented to investigate collisionless power coupling through a capacitively coupled rf sheath. An electrode is mounted in the downstream region of an inductively coupled discharge and driven using a separate power source. The frequency of the power delivered to the electrode is sufficiently different to that of the plasma power source to avoid interference. A DC power supply is used to bias the electrode slightly more negative than the self bias and hence alter the sheath electron density profile to exclude losses at the end of the rf cycle. This enables comparison with theoretical collisionless heating models which assume no electron loss [1] and a recent model [2] which suggests that there is a significant difference in power coupling if electron loss is included or not. The power absorbed by the plasma is measured using a customised current / voltage sensor which enables both time averaged and phase resolved power measurements. Initial results show that the collisionless power decreases as electrons are retarded while the rf electrode voltage is held constant. The phase resolved measurements confirm that the drop in power occurs in the region where electron loss is expected, consistent with the latter model mentioned above. References: [1] M. A. Lieberman, IEEE Trans. Plasma Sci., vol 16, p. 638, 1988 [2] G. Gozadinos {\em et al}, Phys. Rev. Lett., vol 87(13), 2001 [Preview Abstract] |
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SW.00006: Ignition conditions for peripheral plasma in a grounded chamber connected to a dual frequency capacitive discharge Sungjin Kim, M.A. Lieberman, A.J. Lichtenberg, J.T. Gudmundsson A capacitive discharge connected through a slot to a peripheral grounded pumping region is a configuration of both theoretical and practical interest. It is used in commercial dual frequency capacitive discharges with one frequency higher than the usual industrial frequency of 13.56 MHz, with application to dielectric etching. In some configurations a dielectric slot surrounding the substrate separates the main plasma from a peripheral pumping region. Ignition of the peripheral plasma produces detrimental effects on processing performance. Discharge models for diffusion and plasma maintenance in the slot have been developed to obtain conditions for ignition of the plasma in the periphery. We found that, depending on the discharge conditions, either maintenance of the slot plasma or the periphery plasma determines the loss of confinement in the system. An experiment has been constructed to compare with and validate theoretical predictions of ignition conditions. We observed a significant hysteresis in the loss of confinement and ignition of the peripheral and slot plasmas, which can be explained qualitatively by our model theory. Support provided by Lam Research, the state of California MICRO program, NSF Grant ECS-0139956, and UC Discovery Grant from IUCRP. [Preview Abstract] |
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SW.00007: Stochastic heating in RF capacitive discharges E. Kawamura, M.A. Lieberman There are two main mechanisms for heating electrons in RF capacitive discharges: ohmic and stochastic heating. Plasma resistivity due to electron-neutral collisions leads to ohmic heating while momentum transfer from high voltage moving sheaths leads to stochastic heating. Thus, ohmic heating is mainly a bulk phenomena while stochastic heating is localized in the sheaths areas. We try to understand the nature of stochastic heating and how it depends on various parameters such as pressure, sheath velocity, frequency and density profiles. We are particularly interested in the case of dual frequency discharges in which the high frequency controls the ion flux while the low frequency controls the ion mean energy. We conduct a series of fixed ion particle-in-cell simulations of RF capacitive discharges in order to investigate the electron heating mechanisms. [Preview Abstract] |
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SW.00008: Modeling of a 2f-CCP in SF$_6$/O$_2$ for high-speed MEMS processiong Fukutaro Hamaoka, Takashi Yagisawa, Toshiaki Makabe MEMS (Micro Electro Mechanical Systems) device processing has been developed on the basis of the techniques utilized in microelectronic device fabrications. For a MEMS processing, Si etching with high-speed ($>$ 100 $\mu$m min$^{-1}$) and high-selectivity ($>$ 100) is required due to the large scale of trench/hole profiles with several hundred $\mu$m in width and depth, as compared with semiconductor devices. In the etching of a large scale structure on a wafer, the sheath tends to wrap around the corner of the structure (plasma molding), which strongly affects the ion flux, energy and angular distribution. In the present study, a self-consistent modeling of a 2f-CCP in SF$_6$/O$_2$ practically used in industry will be performed at 300 mTorr. We will mainly focus on the 2D-t structures SF$_6$/O$_2$ plasma under the presence of large scale structure on a wafer. We use a small spatio-mesh at the vicinity of the wafer in order to predict the distorted sheath structure in a self-consistent system of 2f-CCP. That is, the sheath is distorted on the large-scale trench corner and is radially nonuniform on the wafer. [Preview Abstract] |
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SW.00009: Driving frequency effect on the heating mode transition in capacitive discharge ShinJae You, SungSik Kim, HongYoung Chang The evolution of the electron energy distribution function (EEDF) with various driving frequencies is investigated in capacitive discharge. While increasing the driving frequency, a significant change of the EEDF is found, the bi-Maxwellian electron energy distribution changes drastically to the Druyvesteyn-like one. This observed result can be understood as an electron heating mode transition from the collisionless to collisional heating induced by driving frequency. [Preview Abstract] |
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SW.00010: Time resolved investigations of hydrogen DFC-CCP plasma sheaths in afterglow discharge Cezar-Mihai Gaman, Albert R. Ellingboe This paper reports the results of time resolved measurements of ion energy distribution function in an afterglow discharge for a hydrogen DFC-CCP (dual-frequency confined capacitively coupled plasma). The experiments were carried out in the CIRIS device which consists of two flat, parallel-plate electrodes. The plasma is confined in the volume between the powered and grounded electrodes by a quartz tube, which shields the plasma from the grounded chamber walls, resulting in a symmetric discharge. In the grounded electrode is mounted a energy resolved mass spectrometer. The experiment was performed in a dual frequency mode (2$\sim$Mz and 27.12 MHz). The pressure range was 5 -- 25 Pa and the working domain of the power of radio frequency in on phase was 15 -- 150 W. We have measured IEDFs (Ion Energy Distribution Functions) of the dominant ion in this discharge -- H$_3^+$, in the afterglow with steps of 1 $\mu$s. Further into the afterglow, we find that the sheath potential does not fully collapse to zero, and, after a transient phase, a constant ion energy of about 5 eV is maintained. This suggests that the electron temperature does not full collapse in the afterglow, but is maintained at approximately 1 eV. [Preview Abstract] |
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SW.00011: Mechanism of Electron Heating in Radio Frequency (RF) Capacitive Discharges Alan Wu Using a fixed ion background to focus on the electron physics, an investigation is conducted to examine the heating mechanisms of the electrons using PIC simulation. The pressure is varied and after running the simulations to steady-state, necessary data are gathered in order to calculate the effective collision frequency. The pressure dependence of collision frequency depends upon the heating mechanism: ohmic heating results in a collision frequency proportional to pressure, and stochastic heating results in a collision frequency independent of pressure. The heating mechanism that occurs is important in understanding how to control the heating in the plasma. Results are as expected for normal operating ranges, with abnormalities that must be resolved at really high and low pressures. [Preview Abstract] |
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SW.00012: Optical Emission Measurements of Dual Frequency Capacitively Coupled Plasmas Eric Benck, Kristen Steffens Dual frequency capacitively coupled plasma sources are becoming increasingly important in semiconductor manufacturing processes. By having the two frequencies separated sufficiently far apart, it is possible to essentially independently control the plasma density and ion energies impacting wafers. This significantly increases the operating range and etching control over that of a single frequency CCP. An imaging spectrometer combined with a high speed intensified CCD camera is utilized to obtain spatially and temporally resolved measurements of the optical emissions from dual frequency fluorocarbon plasmas created in a Gaseous Electronics Conference (GEC) reference reactor. Plasma behavior is characterized for a variety of operating conditions. In particular, the influence of a single vs. multiple powered electrodes will be presented. [Preview Abstract] |
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SW.00013: Electron density measurement in a dual frequency confined capacitive coupled plasma (DFC-CCP) processing tool using a floating hairpin resonance probe S.K. Karkari, A.R. Ellingboe The DFC-CCP's are widely used in industries for etching metals, insulators and semiconductor materials. In a symmetric DFC-CCP plasma tool [Exelan{\textregistered}, Lam Research Corporation] the discharge is electro-statically confined within a narrow gap (12 mm), which causes large plasma potential oscillation (1KV) of the two fundamental frequencies and their harmonics with the mean potential floating at several hundreds of volts above the ground. Therefore for plasma diagnostics, the RF compensated Langmuir probes are not suitable since appropriate resonant filters are practically difficult to design and also the bulky probe construction highly perturb the discharge. To overcome such limitations, we have designed a ``floating hairpin probe'' for measuring the electron density in Exelan{\textregistered}. This technique is based on Piejak's directly coupled hairpin probe operated in the reflection mode [presented in the 56$^{th}$ and 57$^{th}$ GEC conference], however with the hairpin probe electrically isolated from the loop antenna. Using this probe we have measured the time-averaged electron plasma density at the mid-plane of the discharge electrodes in Ar/O$_{2}$/C$_{4}$F$_{8}$ gas mixtures. The spatial and the phase-resolved measurements of the electron densities are presently being carried out and the results shall be presented in the conference. [Preview Abstract] |
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SW.00014: PLASMA DIAGNOSTICS II
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SW.00015: Asymmetry reversal of ion collection by Mach probe in flowing unmagnetized plasma Eunsuk Ko, Xu Wang, Noah Hershkowitz, Gregory Severn Mach probes derive ion drift velocity in flowing plasma from the asymmetry of ion current collection by measuring upstream and downstream flux. Intuitively it is expected that the ion flux density on the upstream side of the Mach probe is higher compared to the downstream side. Hutchinson's numerical calculation\footnote{I. H. Hutchinson, Plasma Phys. Control. Fusion \textbf{45}, 1477 (2003)} of a sphere in unmagnetized plasma found unexpected result that the downstream flux was higher than the upstream flux for relatively low drift velocity v$_{d}$, comparable Debye length $\lambda _{D}$ to the probe size r$_{p}$, high probe bias V$_{p}$. We found experimental evidence for such a reversal when $\lambda _{D}$/r$_{p}$ $\sim $ 0.18, v$_{d} \quad <$ 2.7c$_{s}$, where c$_{s}$ is the ion sound velocity, and V$_{p} \quad >$ 20T$_{e}$. The experiments were performed in a double plasma system with v$_{d} \quad \le $ 4.5c$_{s}$ and Ar pressure range of 0.3 $\sim $ 0.6mTorr and a plasma density range of 10$^{8} \quad \sim $ 10$^{10}$cm$^{-3}$. The supersonic ion drift was determined from ion beam detection\footnote{Wim. J. Weber, Richard J. Armstrong, and Jan Trulsen, J. Appl. Phys. \textbf{50 }(7), 4545 (1979)} using the upstream planar Mach probe, and the ion beam energy was found to agree with Ion energy analyzer measurements. [Preview Abstract] |
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SW.00016: Plasma Potential Fluctuation Measured by an Emissive Probe in Processing Plasma Dongsoo Lee, Noah Hershkowitz Measuring the plasma potential is very important not only to the fundamental understanding of plasma parameters but also to industrial development of plasma systems such as semiconductor etchers because the plasma potential determines the ion energy to wafers. One weakly perturbing technique for measuring the plasma potentials is the use of emissive probes for evaluating the inflection points of the I-V characteristics in the limit of zero emission. When RF power is coupled to the plasma, difficulties can arise in the measurement due to potential fluctuations by harmonic RF fields and deposition on the probe by reactive gases. In this study, we provide experimental data of plasma potential fluctuations measured in an inductive and a helicon processing tool using a fluorocarbon gas (CF$_{4}) $. The fluctuations give the minimum and maximum values of the fluctuating plasma potential. Deposition effects on the probes are also investigated. [Preview Abstract] |
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SW.00017: Electron Number Density Decay in Nitrogen Afterglow Using a Microwave Hairpin Resonator Nicholas Siefert, Biswa Ganguly, Greg Hebner A microwave hairpin resonator probe has been built to measure the decay of the electron number density in nitrogen afterglow (p = 0.25 {\&} 0.75 Torr). In order to operate at these pressures, it was necessary to make corrections for both sheath and collisional damping. In order to measure the change in electron number density in the afterglow, it was necessary to convert the hairpin resonator probe from a steady-state diagnostic tool into a time-dependent one. The results presented in this work will show that both the steady state and time dependent electron density measurements are reasonably accurate up to a pressure of 0.75 Torr, but only over a limited range of electron number densities (5x10$^{8}$ cm$^{3} \quad <$ n$_{e} \quad <$ 5x10$^{9}$ cm$^{3})$. For pressures at or below 0.75 Torr, the error due to electron-neutral collisions is less than three percent. Using the e-folding decay time of the electron number density, we solve the ambipolar diffusion equation to determine the mean electron temperature in the afterglow. We estimate that the electron temperature stays between 0.7 eV and 1.3 eV for up to a few hundred microseconds after the discharge is switched off. [Preview Abstract] |
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SW.00018: Electric field measurements by fluorescence-dip Stark spectroscopy Erik Wagenaars, Gerrit Kroesen, Mark Bowden We used Stark spectroscopy with fluorescence-dip detection to quantitatively measure electric field strengths in the sheath region of a dc glow discharge in xenon. Our laser spectroscopic technique is based on the observation of Stark mixing of Rydberg energy levels in an atom due to external electric fields. In order to quantify the electric field strength, the measured spectra are matched to a theoretical calculation. A 2+1 photon excitation scheme is used to excite xenon atoms from the ground state, through an intermediate 6p state, to high-lying Rydberg levels. During this two-step process, fluorescence light at 828 nm is measured. When scanning the wavelength of the second laser, a reduction (dip) of the fluorescence intensity indicates excitation to a Rydberg state. The theoretical calculation of the Stark shifts and splitting of xenon energy levels is based on solving the Schr\"{o}dinger equation of a system with a perturbation due to the dipole interaction of the atom with an electric field. In order to test our experimental arrangement we used a simple dc glow discharge. This consisted of two parallel electrodes separated by a 1 cm gap in 800 Pa xenon gas. The applied dc voltage was about 300 V. Axial profiles of the electric field strength in the sheath region were determined by measuring Stark spectra of several {\it ns} and {\it nd} levels of xenon atoms in the discharge. [Preview Abstract] |
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SW.00019: Population Distribution of Atmospheric Pressure Argon Discharge Based on CR Model Hiroshi Akatsuka We carried out numerical study on the population densities of excited states of argon atoms under atmospheric pressure discharge for the basis of OES measurement of electron temperature and density. As a numerical code, we applied collisional radiative model (CR model) to calculate excited populations as a function of the electron temperature, density, gas temperature and total pressure. As a preliminary stage, we assumed the EEDF to be Maxwellian in the present study. The CR model included not only electron collisional/radiative processes but also atomic collisional processes and optical escape factors. We found that the highly excited states for the recombining plasma are not in the state of LTE, which were generally considered to be the case for the low-pressure discharge. Excitation temperature became closer to the gas temperature when we applied the levels with the same principal quantum number. On the other hand, it became closer to the electron temperature when the levels with the same angular momentum states were used. Consequently, there is possibility to obtain electron temperature by line intensity measurement. [Preview Abstract] |
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SW.00020: Measurement of Radical Density in an Atmospheric Plasma by Molecular Beam Mass Spectrometry Yolanda Aranda Gonzalvo, Alan Rees, Peter Hatton, Dave L. Seymour, Ian D. Neale Radical species produced in an atmospheric discharge have been measured by appearance potential mass spectrometry (APMS) using a Hiden EQP differentially pumped mass/energy analyser. The non-thermal discharge was generated by a radio frequency driven atmospheric plasma source.\footnote{E. Stoffels et\textit{ al}., Plasma Sources. Sci. Technol.11(2002) 383-388} Species were sampled from atmospheric pressure using a triple stage differentially pumped molecular beam inlet system. The discharge was generated mainly in Helium and, for the present investigation, different percentages of Oxygen, Nitrogen, Nitrous oxide, Carbon dioxide and Carbon monoxide gases were added to the plasma discharge. Radical densities produced in the atmospheric discharge were studied as a function of the power and the distance between the plasma source and the entrance to the analyser. Other species observed from the Oxygen/ Helium and Nitrogen/Helium mixtures were NO radicals formed by recombination. [Preview Abstract] |
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SW.00021: Measurement of electric fields in plasma using Stark spectroscopy of krypton atoms Tao Jiang, M.D. Bowden, E. Wagenaars, G.M.W. Kroesen The electric field is one of the most important discharge parameters. In glow discharges, it is the driving force behind many processes at the plasma boundary. But it is difficult to measure, because of perturbation problems. We report a spectroscopic method for the measurement of the electric field in a glow discharge in krypton. The method to determine the electric field is based on the comparison of the results of experimental laser opto-galvanic (LOG) spectra and theoretical calculations, obtained by solving the Schrödinger equation of krypton atoms in an electric field. For high electric fields, there is a good agreement between experiment and calculation for excitation from 5s to f states of krypton atoms in an electric field. For lower electric fields, the resolution of the technique is lower using f state. However, excitation from 5s to p-states results in a larger LOG signal and larger Stark shifts were observed. Therefore, the resolution of the technique is better using p-states for low electric fields. [Preview Abstract] |
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SW.00022: Biased hairpin probes Nicholas Braithwaite, Fred Haas, Jafar Al-Kuzee A hairpin probe is an open, quarter-wave transmission line. When immersed in a plasma its resonant frequency can directly and immediately provide a measure of local electron density, through the plasma's dielectric response. The sheath around the hairpin wires can be relatively large, either at low electron density or when deliberately baised to several times the mean electron energy. A model the hairpin resonance has been developed incorporating sheaths with positive and negative bias, including electron space charge in the former and taking account of the radial geometry. To date, in using the hairpin is has been presumed that its behaviour is well modelled without any independent test, though comparisons with Langmuir probes are certainly favourable. The variation of resonant frequency with bias is an important test of the hairpin concept. Calculations show that, as expected, negative bias lowers the resonant frequency monotonically. Positive bias shows a different trend with an initial sharp increase in resonant frequency at small bias settling into a weakly declining trend at larger bias. The latter behaviour is traced to radial convergence of electrons near the probe wires. Experimental results show similar trends with notable differences that highlight the shortcomings of the model. [Preview Abstract] |
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SW.00023: GLOWS II
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SW.00024: Self-consistent kinetic study of abnormal glow discharge plasmas Florian Sigeneger, Detlef Loffhagen The axial structure of abnormal glow discharge plasmas is analysed by means of a self-consistent hybrid approach. The investigations have been performed in plane parallel geometry for inert gases at pressures of some Torr. This approach couples the solution of Poisson's equation and a fluid description of electrons, ions and excited atoms with a kinetic treatment of the electron component. The system of Poisson's and time-dependent fluid equations is solved by a semi-implicit method. Using the electric field course determined from Poisson's equation and the excited atom densities from the fluid equations, the space-dependent electron Boltzmann equation is solved. This approach avoids the separation in fast and slow electrons and yields the axial profiles not only of rate coefficients but also of the transport coefficients. Starting from a space-independent electric field, the fluid and kinetic parts of the model are iteratively solved until a stationary state is reached. The results show a distinct separation between the cathode fall with a strongly decreasing electric field and the negative glow with a very low or even reversed electric field. The pronouncedly non-local behaviour of the electrons in this strongly changing field results in remarkable spatial alterations of their collision rate and transport coefficients. [Preview Abstract] |
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SW.00025: Optical and Electrical Characteristics of AC Glow Discharge Plasma in N$_{2}$O H. Mart$\acute{i}$nez, F.B. Yousif, A. Robledo, F. Castillo, A.B. Mondrag\'{o}n This paper considers the optical and electrical characterization of AC glow discharge plasma in the abnormal glow mode used for optical emission spectroscopy. The total discharge current and applied voltage are measured using conventional techniques. Optical emission spectroscopy was used to determine the main emission lines of the glow discharge plasma of $N_{2}O$ at pressures between $0.5$ and $4.0 Torr$. It shows that the discharge emission range is mainly within $300-400$ $nm$. The emission lines at $315.98$, $337.55$, $354.20$, $357.24$, $380.09$ and $391.42$ $nm$ corresponding to $NO$, $O_{2}$, and $O_{2}^{+}$ are the dominant lines in the glow discharge plasma in the present study. Intensity of the emission lines show linear increase with the discharge current up to $0.6$ $A$ followed by saturation at higher currents. The emission consists of $NO$, $O_{2}^{+}$ and $O_{2}$ narrow peaks. No emission lines were identified with the atomic oxygen leading us to conclude that the atomic oxygen is produced either in the $O(^{5}S)$ state that is sufficiently energetics and most likely is lost collisionally, or produced in its ground state $O(^{3}P)$ or themetastable state $O(^{1}D)$ that is quenched in collisions with $N_{2}$ resulting in $O(^{3}P)$ . [Preview Abstract] |
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SW.00026: Dispersion of a Stationary Acoustic Shock in a Supersonic Flowing Afterglow Dereth Janette Drake, Reza Biazaran, Svetozar Popovic, Leposava Vuskovic Experimental studies of shock wave dispersion in weakly ionized gas have been mostly performed on traveling shock waves [1,2]. Inability to fully characterize transient phenomena in the shock layer interacting with electric discharge has produced some ambiguity in the interpretation of the phenomenon of dispersion. In the attempt to elucidate the role of excited states in the dispersion, we employed a supersonic microwave flowing afterglow apparatus with a blant solid body suppressing the flow to generate a stationary shock. Commercial microwave generator, operating in S-band, was used to sustain a cylindrical cavity discharge in argon and nitrogen at power density between 3.5 and 7 W/cm$^{3}$. The discharge was sustained downstream of the cavity by the traveling microwave field using the quartz tube as the wave guide. Therefore, this plasma generator differs from conventional d.c. flowing afterglow in the ability to sustain ionized gas over a longer distance. As a consequence, electron density was higher, in the range of (1-3)$\times $10$^{13 }$cm$^{-3}$, which was determined by the Stark broadening technique. Gas temperature was constantly below 800 K that was determined by thermocouple measurements, Doppler component of the observed line profiles, and rotational spectra of nitrogen molecules. Excited state population in argon was measured with combined emission and absorption spectroscopy using the absolute intensities of (4p- 4s) spectral lines. Dispersion effect was observed in the form of a double- peaked distribution of intensities in front of the model. Interpretation of the results will be presented at the conference. [1] P. Bletzinger, B. N. Ganguly, Phys. Lett. A \textbf{258} (1999) 342. [2] S. Popoviæ and L. Vu\v{s}koviæ, Physics of Plasmas \textbf{7} (1999) 1448. [Preview Abstract] |
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SW.00027: Investigations of argon hollow cathode discharge with iron cathode J.F. Behnke, H. Scheibner, H. Kersten, H. Lieder The formation of argon metastable and resonance state densities and of iron ground state densities by ion sputtering are studied experimentally by absorption spectroscopy and LIF in the plasma of a cylindrical hollow cathode discharge (Fe, R = 0.4 cm l = 3.0 cm, p0 = 160 Pa argon). The intensity of iron spectral lines has been measured by means of the emission spectroscopy. The EEDF in the negative glow were determined from the second derivative of the probe characteristic and the charge carrier density from the ion saturation probe current. The densities of the sputtered iron atoms in the ground and excited states in dependence of discharge current have been calculated by a simple model of the sputter process and the excitation kinetic via measured EEDF and electron densities. The discharge current characteristics were calculated via the POISSON equation in the cathode fall region considering the electron multiplication and secondary emission of electrons by ions and resonance photons at the cathode. [Preview Abstract] |
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SW.00028: Investigation of a Micro-Hollow Cathode Discharge stability in different gases Xavier Aubert, Antoine Rousseau Micro-hollow cathode discharge (MHCD) are of interest for the plasma generation near atmospheric pressure at a relatively low voltage [1-3]. MHCD are generated in the hole (typically few hundreds of micrometers) made in a conductor-dielectric-conductor sandwich. We report the characterization of such plasmas in argon, helium and air and show that the electrical behaviour is different from air to noble gases. Current/ voltage characteristics performed under various hole diameter and gas pressure show that highly reproducible self pulsing regime exists when the plasma expends towards the backside cathode region. The influence of such a self-pulsing regime on the discharge stability in a multi-hole configuration is also reported. Finally, the possibility of generation of a microplasma in a three electrodes configuration is studied. Production of oxidized species such as nitrogen oxides in air is also reported. \newline \newline [1] K. H. Schoenbach, R. Verhappen, T. Tessnow, F. E. Peterkin, W. W. Byszewski, Appl. Phys. Lett. 68 (1996) 13 \newline [2] D.D. Hsu and D. B. Graves J. Phys. D: Appl. Phys. 36 (2003) 2898 \newline [3] J. P. Boeuf, L. C. Pitchford, K. H. Schoenbach, Appl. Phys. Lett. 86 (2005) 71501. [Preview Abstract] |
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SW.00029: Dynamics of striations formed in a hollow anode covered by a dielectric layer V.N. Khudik, A. Shvydky, C.E. Theodosiou The dynamics of the charging of a cylindrical hollow anode (covered with a dielectric layer) by an electron current is studied via 3-dimensional Particle-in-cell/Monte-Carlo kinetic simulations. For the first time, it is shown that this process is accompanied by the successive formation of striations in the plasma created by the electron impact ionization of the background noble gas. The dynamics of the formation of striations can be quite different depending on the gas pressure, the cylinder radius, the thickness of the dielectric layer, and the magnitude of the current from the emitter. A number of specially designed numerical experiments are performed to further explore the nature of this phenomenon. An experimental set-up where this type of striations should be observed is suggested. [Preview Abstract] |
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SW.00030: Expansion of a Dynamic Cathode Fall along the Dielectric Surface A. Shvydky, V.N. Khudik, V.P. Nagorny, C.E. Theodosiou The dynamics of the expansion of a cathode fall along the plane cathode covered with dielectric layer is studied via Particle-in-cell/Monte-Carlo kinetic simulations. It is shown that the spreading progresses in a wave-like manner with a quite pronounced wave front where most of ionizations of the background noble gas take place. Different mechanisms of the ionization wave propagation are discussed. The role of the electron and ion diffusion is elucidated. It is found that the wave propagates over very thin dielectrics as well as very thick ones. The dependence of the wave velocity on the dielectric layer parameters and on the potential difference between the plasma and the cathode is determined. [Preview Abstract] |
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SW.00031: PLASMA DIAGNOSTICS I
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SW.00032: Imaging spectrometer based on Fabry-Perot interferometer Aleksandr Kravchenko, Anatoly Khakhaev, Lidia Luizova, Aleksei Solovev The aim of this work is to construct a research complex, which will allow to investigate spatial distribution of parameters of inhomogeneous plasma such as distribution of atomic temperature, density of atoms in different states and others by spectrum line profiles in certain parts of plasma; and then to investigate real plasma sources to determine their parameters and internal processes. In our setup, the light from the source, placed in a focus of focusing lenses, passes through the Fabry-Perot interferometer. The superposition of a source image and interference rings is drawn by the drawing lenses on the entrance slit of the spectrometer. In this setup, the spectrometer is used for picking out a definite spectral line. Having carried out the experiment with interferogram obtainment, we try to model interferograms obtained in the experiment. We set desired plasma characteristics using models with few parameters and calculate light intensity distribution along the entrance slit of the spectrometer taking into account the spread function of the Fabry-Perot interferometer. Varying parameters, we achieve the best agreement between experimental and calculated light intensity distribution. [Preview Abstract] |
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SW.00033: Experimental Details on Air-Plasma Measurements of Electron Density and Ozone Concentration Robert Vidmar, Kenneth Stalder, Megan Seeley Details on the measurement of electron density and ozone concentration in air plasma are presented. Air plasma is generated by a 100-kV10- 20 mA electron beam for approximately 1 ms in a 400-liter test cell filled with air under atmospheric conditions from sea level to 300,000 ft. An electron-density measurement technique based on RF absorption and phase shift at X-band using a null-based differential measurement system is used. A White's cell topology is used to measured ozone concentration using absorption at 254 nm. System sensitivity, time response, engineering details, and representative data for both systems are quantified. This material is based on research sponsored by the Air Force Research Laboratory, under agreement numbers FA9550-041-1-0015 and FA9550-04-1-0444. [Preview Abstract] |
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SW.00034: A measurement of F metastables by laser absorption spectroscopy in a two frequency CCP Kenji Hayashi, Takeshi Ohmori, Takumi Akaike, Takeshi Kitajima, Toshiaki Makabe Fluorine-containing plasmas are used in SiO$_{2}$ etching. The degree of dissociation of CF$_{4}$ is a critical factor for bottom etching and sidewall polymer deposition and determines the absolute density of F atom. Relative density is of F atom in metastables and grand state are experimentaly reported in an ECR plasma[1]. In the present study, we have observed the absolute density of F metastables by using a tunable diode laser absorption spectroscopy(LAS) in a capacitively-coupled plasma (CCP) in Ar/CF$_{4}$. The transition line used for absorption spectroscopy of F metastables is $3s4p_{3/2}-3p4D_{5/2}$ at 690.25nm. The metastable density, $6.0\times10^{9}cm^{-3}$ on the center of electrodes is measured at conditions that the CCP is sustained at 100MHz with 50W and a pressure of 100mTorr. Consequently we performed a measurement of absolute density of F metastables in the low and middle-density plasma.\newline [1]Kazuki Takizawa, Koichi Sasaki and Kiyoshi Kadota. Jpn. J. Appl. Phys. Vol40(2001)pp. 5130-5133 [Preview Abstract] |
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SW.00035: Optical emission CT for an effect of LF-bias voltage on a 2f-CCP for etching Takumi Akaike, Takeshi Ohmori, Kenji Hayashi, Mikio Ishimaru, Takeshi Kitajima, Toshiaki Makabe It is essential to control and optimize 2-dimensional ion velocity and radical distributions under a strong sheath dynamics in front of an oxide wafer biased deeply by a low frequency source in a 2f-CCP, because high energy ions have a responsibility for oxide etching in RIE. In our previous work, we have performed a design of the functional separation in a 2f- CCP sustained at VHF and biased at LF source. Experimental evidence was limited to a low bias voltage of the LF at the wafer[1]. In this work, by using the CT image of the optical emission from the short-lived Ar($2p_{1}$) and Ar($2p_{9}$) as the probe of the transport of electrons with energy greater than $13.48$ eV and $1.53$ eV, we spatiotemporally investigate the influence of the high voltage LF bias on the 2f-CCP in Ar. The degree of a collapse of electrons from the bulk plasma at the instantaneous anode phase, and that of an ionization growth of the secondary electrons emitted at the wafer by high energy ions at the instantaneous cathode are experimentally shown in the CT images as a function of 2D space and time.\newline [1] T.Kitajima, Y.Takeo, N.Nakano and T.Makabe : J. Appl. Phys. 82, 5928 (1998) [Preview Abstract] |
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SW.00036: Investigation of Pulse-Modulation Effect in Electron Beam Excited Plasma with Time Resolved Optical Emission Spectroscopy Keigo Takeda, Takayuki Ohta, Masafumi Ito, Masaru Hori Micromachining of optical devices attracts much attention. In the process, the fast atomic-beam etching or the ion-beam etching has been employed, since the conventional reactive plasma etching can't be employed as the radio-frequency self-biasing is not efficiently supplied to the thick dielectric materials. However, a pulse-modulated electron-beam- excited plasma (EBEP) has a potential to realize the high etching rate without any additional bias power supply. Therefore, we have investigated the effect of pulse-modulation of EBEP using time resolved optical emission spectroscopy. Plasma was generated at a pressure of 0.27Pa and the fed gases were C$_{4}$F$_{8}$/Ar, a discharge current of 25A and an electron acceleration-voltage of 65V with a pulse-modulation frequency of 50kHz. It was found that CF$_{2}$ optical emission intensity at the 50{\%}-duty ratio was involved in two lifetimes of $\tau _{1}$=3 and $\tau _{2} $=19.8$\mu $s compared with Ar optical emission intensity. Moreover, CF$_ {2}$ radical density was evaluated by using Actinometry in order to compare with F atom density. F atom density increased with the increase of duty ratio, but CF$_{2}$ radical density decreased. Therefore, the dissociation degree of C$_{4}$F$_{8}$ was controlled by the duty ratio of electron acceleration voltage. [Preview Abstract] |
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SW.00037: F$^-$ detection by CRDS in a dual-frequency capacitive plasma in Ar/C$_4$F$_8$/O$_2$ Cormac Corr, Garrett Curley, Jean-Paul Booth Dual-frequency capacitively coupled plasmas in Ar/fluorocarbon mixtures are widely employed for etching of holes in SiO$_2$-based dielectrics in integrated circuit manufacture. Negative ions can dominate the structure and dynamics of discharges if their density is high enough, yet no experimental data is available for dual-frequency plasmas. They may also play a role in etching if they can reach the surface. The determination of the negative ion density via the detection of photo-detached electrons is difficult to implement in such reactors due to the large RF fluctuations of the plasma potential. Therefore we have implemented the cavity ring-down spectroscopy (CRDS) technique to measure the density of fluorine negative ions in a customized industrial dual-frequency capacitive etch reactor operating with Ar/C$_4$F$_8$/O$_2$. A pulsed laser beam from a tuneable dye laser was scanned over the wavelength range 340 to 360 nm and injected into an optical cavity formed by two high-reflectivity concave mirrors ($>$ 99.95 \%). The temporal behaviour of the decaying pulse at the cavity exit allows the density of absorbing F$^{-}$ ions to be determined from the known photo-detachment cross-section. The negative ion density will be investigated as a function of input power and gas mixture. [Preview Abstract] |
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SW.00038: Characterization of the Lam 9100TCP plasma through atomic argon spectral lines Vladimir Milosavljevi\'{ c}, Albert R. Ellingboe Argon as one of most frequently used gas in RF discharge. Determination of plasma parameters through analysis of argon emission would be a powerful tool. Four argon lines have been measured from two different transitions. From the 4s--4p transition the 750.387 nm and 751.561 nm spectral lines are recorded and also from 4p--4d transition the 687.129 nm and 751.041 nm Ar\,I spectral lines are recorded. These four Ar\,I spectral lines each belong to the different multiplets and therefore have the different upper energy level. The difference of upper energy levels among these argon spectral lines is greater than 1.5 eV. Also, the 751.041 nm spectral line of Ar\,I have an upper energy level very close to ionized limit for atomic argon. Data is collected for a range of operator contribution in an Ar-O$_2$--C$_4$F$_8$ gas mixture discharge, by high resolution spectrometers Carl Zeiss PGS--2 with 60 pm instrumental width. The emission strengths and profile shapes are found do be dependent on RF power settings, gas mixture and pressure. Correlation of plasma internal state will be presented. [Preview Abstract] |
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SW.00039: Local Stochiometry Distortions in a Rotatable Magnetron Sputter Source measured by True 2D Imaging Spectroscopy Till Wallendorf, Swen Marke, Falk Milde Reactive sputter processes are widely being used for large scale optical glass coating. Even though there is a strong push towards the use of ceramic target materials at the moment, also in the future reactive sputtering will play an important role. Process control is of very high importance for reactive sputtering especially for the transition mode, where working points are not stable by nature. By use of a new type true 2D imaging spectrograph we demonstrate, how to acquire the spatial intensity distribution of selected emission lines. This true 2D imaging spectrograph combines wide wavelength range, excellent wavelength resolution, and good spatial resolution with a short sample time. The observations presented in this paper may serve as a starting point for systematic optimization of the appropriate choice of position and properties of the optical collimation hardware. [Preview Abstract] |
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SW.00040: Magnetic field measurements for N$_{2}$ and H$_{2}$ discharges from a low frequency RF inductively coupled plasma source Chandan Kumar Chakrabarty The electric field due to a strong capacitive coupling between the induction coil and the walls of the plasma chamber is quite large despite the discharge being in the H-mode in N$_{2}$ and H$_{2}$ gases. And as such, this field will interfere with the measurement of the magnetic field thus causing a higher degree of measurement error. This paper hence describes the use of a centre-tapped coiled magnetic probe for the measurement of magnetic field profiles in 1-D in the low frequency RF inductively coupled plasma source. From these profiles, an independent method to determine the average electron density is shown. [Preview Abstract] |
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SW.00041: BIOLOGICAL, ENVIRONMENTAL, AND OTHER INNOVATIVE APPLICATIONS
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SW.00042: Investigation of Bacterial Biofilm Destruction Using Gas Discharge Plasma N. Abramzon, J. Bray, J.C. Joaquin, G. Brelles-Mari\~{n}o Biofilms are bacterial communities embedded in an exopolysaccharidic matrix with a complex architectural structure. Bacteria in biofilms show different properties from those in free life thus, conventional methods of killing bacteria are often ineffective with biofilms. The use of plasmas potentially offers an effective alternative to conventional sterilization methods since plasmas contain a mixture of charged particles, chemically reactive species, and UV radiation. 4 and 7 day-old biofilms were produced using two bacterial species. Gas discharge plasma was produced by using an AtomfloTM reactor (Surfx Technologies) and bacterial biofilms were exposed to it for different periods of time and different plasma conditions. For each plasma condition, cell counts were plotted against the time of treatment, which allow us to calculate D-values and compare various plasma treatments quantitatively. Optical emission spectroscopy was used to study plasma composition and temperature which was then correlated with the effectiveness of killing. \newline This Work was supported partly by CSUPERB. [Preview Abstract] |
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SW.00043: Investigation of Sporicidal Effect of Gas Discharge Plasma Shawn Tseng, Wei-Jen Lin, Nina Abramzon Bacteria spores are the most resistant form of life and have been a major threat to public health and food safety. In this study, helium- based plasmas were used to treat spores of various bacteria including \textit {Bacillus} and \textit{Clostridium}. Gas discharge plasma was produced by using an AtomfloTM reactor (Surfx Technologies). The spore species tested include \textit{B. subtilis,} \textit{B. stearothermophilus C. sporogenes, C. perfringens}, and \textit {C. difficile.} Also, the bactericidal effects of plasmas are tested against vegetative cells of \textit{B. subtilis, }the gram positive rods, and the gram negative rods, \textit{Escherichia coli}. The D-values for spores range from 2 to 10 minutes, in comparison with the D-values of vegetative cells, ranged from 20 to 50 seconds. Our results show the effectiveness of using plasmas to sterilize vegetative bacterial cells as well as bacterial spores of various types. Optical emission spectroscopy was used to study plasma composition which was then correlated with the effectiveness of killing. The sporicidal mechanisms of various plasma species will be characterized morphologically and molecularly in future studies. \newline This Work was supported partly by CSUPERB. [Preview Abstract] |
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SW.00044: Purification of Gaseous Pollutant using Secondary Emission Electron Beam generated by Wire Discharge Plasma Source Masato Watanabe, Yusuke Sakai, Eiki Hotta It is well known that the non-thermal plasma processes using electrical discharge or electron beam are effective for the environmental pollutant removal. Especially, the electron beam can efficiently remove pollutant, because a lot of radicals which are useful to remove pollutant can be easily produced by high-energy electrons. We have developed a compact 100kV secondary emission electron gun to apply several gaseous pollutant removals. The device offers several inherent advantages such as compact in size, wide and uniform electron beam. Besides, the device offers good capability in high repetition rate pulsed operation with easy control compared with glow discharge or field emission control cathode guns. In present study, the NOx removal characteristics have been studied under the increased gun voltage, varied pulsed electron beam parameters such as current density and pulse width as well as gas flow rate. The experimental results indicate a better NOx removal efficiency comparing to other high-energy electron beam and electrical discharge processing. [Preview Abstract] |
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SW.00045: Infrared laser diagnostics of the plasma-photocatalyst interaction in a pulsed low pressure discharge Olivier Guaitella, Frederic Thevenet, Antoine Rousseau, Chantal Guillard, Gabi Stancu, Jurgen Roepcke The combination of a plasma with a porous semi-conductor surface (TiO$_{2}$ photocatalytic material) has been recently reported to oxidize volatiles organic compounds (VOC) at a low energy costs [1]. However, activation mechanisms of the photocatalytic surface by the plasma are not clearly identified to the day. In order to improve the understanding of the synergy of the plasma-photocatalysis combination for C$_{2}$H$_{2}$ removal, time resolved in-situ measurements of infrared laser absorption spectroscopy are performed in a low pressure pulsed DC discharge in air containing less than 1000 ppm of C$_{2}$H$_{2}$. The time resolution of the infrared lead-salt diode laser is about 1ms. Time resolved measurements are carried out during a series of single pulses (10 to 100 ms) in a closed plasma reactor. It is shown that the combination of TiO$_{2}$ with external UV irradiation leads a strong enhancement of the C$_{2}$H$_{2}$ oxidation rate under plasma exposure. Similarly, adsorption/desorption characteristic time of C$_{2}$H$_{2}$ on TiO$_{2}$ is modified by the presence of the plasma. \newline [1] S. Futamura, H. Einaga, H. Kabashima, L.Y. Hwan, Catal. Today 89, 89 (2004). [Preview Abstract] |
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SW.00046: Production of Syngas via Biomass Pyrolysis in Thermal Hydrogen/Oxygen Plasma Milan Hrabovsky, Michal Hlina, Milos Konrad, Vladimir Kopecky The plasma reactor for pyrolysis of waste materials with dc arc gas/water plasma torch was operated at arc power up to 140 kW using wood as a model substance. High enthalpy, low-density hydrogen/oxygen plasma generated in the torch interacted with a flow of treated material in a reactor volume. The experimental results prove that homogeneous heating of volume of plasma reactor and proper mixing of plasma with treated material was ensured despite of very low plasma mass flow rate and constricted form of plasma jet. The conditions within the reactor ensured complete destruction of tested substance. Synthetic gas with high content of hydrogen and carbon monoxide and low concentration of carbon dioxide was produced. Due to composition of plasma and its very low mass flow rate the composition of reaction gases was close to stechiometric composition of cellulose fully dissociated to hydrogen and carbon monoxide with their concentrations exceeding 40{\%}. The authors gratefully acknowledge the support of this work by the Grant Agency of the Czech Republic under the project No. 202/05/0669. [Preview Abstract] |
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SW.00047: Spectroscopic study for abatement system for the global warming gases using VAWP Jiankun Wang, Ryohei Itatani, Tohru Yasuda A unique abatement system for the global warming gases such as PFCs, HFCs and CFCs was developed. This, called as VAW(Vertical Aqua Wall) plasma system, consists of a vertical straight tube, from the top of which the target gases are introduced with the water covering the inner wall of the tube. A stable long arc in atmospheric pressure is produced between a cathode above the tube and an anode covered by thin water film in the lower part of the tube through which the arc current flows. More than 99{\%} of decomposition efficiency with 300sccm CF4 diluted by 15slm N2 was achieved by this system. Here, in order to investigate the structure of this exotic plasma, we observe the distribution of OES along both vertical and radial directions of the plasma column. The results will be shown in the presentation. [Preview Abstract] |
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SW.00048: Model Study of the Pulsed Discharge Nozzle W.J.M. Brok, B.H.P. Broks, J. Remy, J.J.A.M. van der Mullen The characteristics of the plasma generated by a pulsed discharge slit nozzle (PDN) are investigated. The PDN source was designed to produce and cool molecular ions, creating an astrophysically relevant environment in the laboratory. A discharge model is applied to this system to provide a qualitative as well as a quantitative picture of the plasma. We find that the plasma's properties and behaviour are characteristic of that of a glow discharge. The model describes the electron density and energy, as well as the argon ion and metastable atom number density. The results reveal a high abundance of metastable argon atoms in the expansion region, which is more than one order of magnitude higher than the abundance of electrons and ions. These findings confirm experimental observations, which concluded that large molecular ions are dominantly formed through Penning ionization of the neutral molecular precursors seeded in the supersonic expansion of argon gas. The simulations presented here will help optimise the yield of formation of molecular ions and radicals in the PDN source; they will also provide key physical insight into the characteristics of interstellar molecules and ions analogs in laboratory experiments. [Preview Abstract] |
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SW.00049: Surface dielectric barrier discharges as actuators for flow control Y. Lagmich, G. Hagelaar, L.C. Pitchford, J.P. Boeuf Surface discharges created in Dielectric Barrier Discharge (DBD) configurations have been proposed as actuators for flow control in aerodynamic applications. Using a two-dimensional model of the surface dielectric barrier discharge in pure nitrogen we study the time evolution of the plasma and calculate the electrohydrodynamic force acting on the gas flow. The results show that this force is due to the momentum transfer from the ions to the neutral molecules in the sheath that propagates along the dielectric layer surface. The calculations also confirm that the asymmetry of the electrode configuration is responsible for the existence of a non-zero averaged force parallel to the surface. We present a parametric study of the discharge and calculated electrohydrodynamic force as a function of geometry and applied voltage. We also discuss the possible effect of photoemission from the dielectric surface on the discharge properties. Finally, the discharge model is coupled to the Navier Stokes equations for the gas flow to evaluate the effect of the surface discharge on the boundary layer. [Preview Abstract] |
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SW.00050: Measurement of the Absolute Concentration of Molecular Oxygen in a Capacitively-Coupled RF Discharge in a Martian Simulant Gas George Brooke We will be presenting the results of an experiment to measure the absolute concentration of molecular oxygen in a capacitively-coupled RF discharge in a Martian simulant gas using cavity ring-down spectroscopy (CRDS). The goal of this work is an efficient, low-power oxygen generator for use on the surface of Mars. Previous experiments have demonstrated the ability to produce and extract molecular oxygen using an RF discharge but were unable to measure the absolute concentration within the discharge volume. Using the CRDS technique we have measured the absolute concentration of molecular oxygen in the discharge with respect to RF power and two different electrode configuration (planar and solonoidal) at a fixed pressure of 5 Torr. [Preview Abstract] |
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SW.00051: ARCS AND BREAKDOWN
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SW.00052: Model Study of Breakdown in Low-Pressure Argon between Parabolic Electrodes W.J.M. Brok, E. Wagenaars, J.J.A.M. van der Mullen, M.D. Bowden Breakdown between two electrodes in argon at 3.5 Torr is investigated by means of a fluid model and a fluid-particle hybrid model. The cylindrically symmetric electrodes have a parabolic cross section and are placed in a vacuum chamber with their axis aligned and tips separated by 3.3 mm. Experimental observations of visible emission have shown a pre-breakdown light flash near the anode before the applied voltage reached the static breakdown voltage of the setup. After the breakdown voltage had been reached, an ionisation wave was observed to travel from anode to cathode and subsequently to envelope the cathode. The phenomena related to the pre-breakdown flash are investigated with a fluid-particle hybrid model and the results account for the stratified emission near the anode. By modelling this setup with a fluid model, the observed breakdown phenomena can be explained by means of buildup of space charge and the resulting evolution of the electric field. [Preview Abstract] |
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SW.00053: Experimental study of breakdown in low-pressure argon between parabolic electrodes Erik Wagenaars, Niels Perri\"{e}ns, Gerrit Kroesen, Mark Bowden Plasma breakdown phenomena in low-pressure argon gas were investigated by making time-resolved images of the plasma light emission, using an intensified charge coupled device (ICCD) camera. The breakdown arrangement consisted of 2 electrodes mounted inside a vacuum chamber creating a 3.3 mm discharge gap. A flow of argon gas was directed through the system, while a needle valve maintained the pressure at 465 Pa (3.5 torr). The electrodes were cylindrically symmetric and had a parabolic cross section. A repetitive, quasi-dc breakdown was created by applying voltage pulses with an amplitude of about 350 V, a duration of 100 $\mu$s and a repetition rate between 10 and 2000 Hz. Our measurements show a general breakdown behavior consistent with the Townsend breakdown theory. Additionally, we observed the appearance of a light flash near the anode at a time when the applied voltage was below the static breakdown voltage. This phenomenon could not be explained by Townsend theory and was investigated further by varying the rise time, repetition rate, polarity and shape of the applied voltage pulses. It was concluded that this feature was the result of charges close to the discharge volume, left over from the previous discharge cycle. These charges created weak electron avalanches at low applied voltages, before the main breakdown phase started. [Preview Abstract] |
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SW.00054: Characterization of Anode Boundary Layer of a High Intensity Arc with Cross Flow Guang Yang, Joachim Heberlein, Emil Pfender Anode boundary layers of high intensity arcs are characterized by large gradients in temperature, electrical potential and velocity. They determine anode life time and processing efficiency in many industrial applications. It has been shown that when a strong cold cross flow is applied to a high intensity arc, a new anode arc attachment mode can be formed, with a larger anode boundary layer area and thus smaller thermal load to the anode. In this study, we have used Langmuir probe and laser Thomson scattering diagnostics to measure the electron temperature and electron density in the anode boundary layer for this attachment mode for an atmospheric pressure argon arc. The arc is operated with working gas flow rates from 2 slpm to 18 slpm, and with currents from 50A to 100A. Argon and nitrogen are used as cross flow gases, and they have been shown to have quite different effects on the anode attachment. Our results indicate a strong effect of the attachment mode on the electron temperature and steeper electron density gradients than predicted by models. [Preview Abstract] |
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SW.00055: Optical Emission Spectroscopy of an Atmospheric Arc Russell Rhoton, Mary Brake An arc plasma was generated in atmospheric air between two carbon electrodes powered by a high voltage transformer controlled by a variable input source. A voltage of up to 12,000 V and current of 30 mA was delivered to an arc about 1.5 cm long. The diameter of the arc is estimated to be 0.1 cm, giving a current density of 4 A/cm$^{2}$. Optical emissions spectroscopy from 250 nm to 800 nm revealed a variety species ranging from molecular species like OH and N$_{2}^{+}$ to atomic lines of oxygen and nitrogen. When the arc is first ignited, molecular lines dominate while atomic lines begin to grow in intensity the longer the arc runs and as the gas heats up. Thermal equilibrium calculations between nitrogen atoms and molecules suggest that the plasma gas temperature is no more than 4500 K. The electron density is estimated to be about 10$^{12}$ {\#}/cm$^{3}$ based upon the relationship between current density and electron density in Ref. [1]. The spectral evolution of the discharge as a function of time will be discussed with respect to heating mechanisms. [1] Lan Yu et al., J. Appl. Phys., 91(5) 2678, 2002 [Preview Abstract] |
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SW.00056: An Experimental Study of Cold Helium Arc-Jet Flowing along Diverging Magnetic Field Hiroshi Akatsuka, Toshiaki Kanuma, Haruaki Matsuura, Mitsuo Matsuzaki We experimentally examined plasma parameters of a supersonic cold helium arc jet accelerated along diverging magnetic field from a uniform magnetic channel, particularly relationship between plasma potential and ion Mach number. The atmospheric pressure arc plasma is generated and ejected into a rarefied gas wind tunnel with a uniform longitudinal magnetic field of 0.16 T. The strength of the magnetic field decreases to 0.01 T at 20 cm down from the end of the coils. The longitudinal velocity of the plasma jet was measured by Mach probes. At the maximum gradient of the magnetic field, the peak of the Mach number 3.1 of the flow velocity was observed. We found lowering of the plasma potential at the exit of the nozzle from $2.5$ to $0.4$~V. The radial measurement shows that the lowest plasma potential was situated along the centerline of the plasma jet. It is well explained that he acceleration was caused by the change in the plasma potential rather than fluid dynamic effect. It is also found that the MHD effect like Hall acceleration ($j_\theta B_r$) or pumping force ($j_\theta B_z$) is insignificant. In addition, the swirl acceleration due to the conservation of the magnetic moment $\mu_{\mathrm{m}}=mv_\perp^2/(2B)$ is also less significant than the electrostatic acceleration. [Preview Abstract] |
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SW.00057: ELECTRONEGATIVE PLASMAS
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SW.00058: Modelling electronegative plasmas separated by an internal sheath Nicolas Plihon, Cormac S. Corr, Pascal Chabert, Jean-Luc Raimbault, Allan J. Lichtenberg It has experimentally been shown that in an ICP with an expanding chamber, adding a small concentration of SF$_6$ to argon can lead to the formation of a stationary double layer [1] separating two plasmas: a high density electropositive plasma in the source, and a low density, high electronegativity plasma downstream. This double layer periodically forms and propagates when increasing the the electronegativity [2]. We present calculation of the discharge equilibrium in the stationary double layer case based on a 1D description of the discharge. The source plasma appears to be only sligthly affected by the downstream plasma. The particles densities downstream are set by the incoming flux of positive ions from the source and attachment ocurring in the downstream volume. Our calculations show fairly good agreement to our experimental data. \newline [1] Plihon \textit{et al.} 2005 \textit{App. Phys. Lett} \textbf{86} 091501 \newline [2] Plihon \textit{et al.} 2005 \textit{J. Appl. Phys.} to be published [Preview Abstract] |
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SW.00059: Hairpin probes: time-resolution and electronegative plasma Nicholas Braithwaite, Eva Vasekova, Jafar Al-Kuzee, Mark Bowden A hairpin probe is an open, quarter-wave transmission line. When immersed in a plasma its resonant frequency measures local electron density directly and immediately through the plasma's dielectric response. At low electron density the sheath around the hairpin wires can be relatively large so it is necessary to allow for this. The use of a hairpin in photodetachment studies is explored: issues of time, electronegativity and spatial sensitivity are addressed. Temporal response is expected be limited by the time to establish resonance and the time for the sheath to equilibrate. The resonance is typically $\sim $~GHz so the former limit is $\sim $~10~ns. The latter limit applies when the sheath is wide. Experimentally, in pulsed RF plasmas (eg He), a fully-floating hairpin is seen to have $\sim $~100~ns resolution in the after-glow. In electronegative plasmas the effect of negative ions on the sheath structure is important. Test show that the hairpin functions with adequate sensitivity in the highly electronegative environment of SF$_{6}$; it is even possible to track the effects of fluorine-based etching of the hairpin wire (W). The spatial sensitivity of the hairpin peaks close to the open end. A dielectric rod has been used to mimic a photodetachment trail indicating that photodetachment signals will be a only a few {%} of full volume detachment. [Preview Abstract] |
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SW.00060: Negative Ions in Rare Gas/Oxygen Discharges M. Katsch, A. Wagner The temporal behavior of negative oxygen ions in argon-, krypton- and neon/oxygen mixtures is investigated in a pulsed inductively excited GEC reactor. The negative ion densities are measured by laser photodetachment of negative ions in combination with a Langmuir probe. In the early afterglow an unexpected high density of negative oxygen ions is found in mixtures with a high content of rare gas. These findings are in contrast to the predictions of our global model. It is, therefore, necessary to invoke an additional production channel for the negative ions, in order to explain the observed high negative ion density. It is likely that additional negative ions are generated by dissociative attachment of highly excited oxygen molecules. It is also possible that Rydberg states of the oxygen molecules are excited via collisions with metastable rare gas atoms. These excited Rydberg molecules may also lead to a generation of negative oxygen ions. Comparative measurements show that it is unlikely that Rydberg states are responsible for the enhanced generation of negative ions. [Preview Abstract] |
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SW.00061: Negative ion formation and motion in a mixture of $CCl_{4}$ and $Ar$ F.B. Yousif, H. Mart\'{i}nez, A.B. Mondrag\'{o}n This work deals with the measurement of the mobility of negative ions in the mixtures of $CCl_{4}$ with $Ar$ with the $CCl_{4}$ ratio up to $33.3\%$. The Pulsed Townsend Technique was employed to produce an integrated ionic avalanches over a range of the density-reduced electric field $E/N$ for which ionization is either negligible or absent, and attachment processes are dominant, leading to the formation of mostly $CCl_{4}^{-}$. The $E/N$ range of measurement was 1 to $50$ $Td$ (1$Td = 10^{-17} Vcm^{2})$ and gas pressure of $80 Torr$. Our measurements strongly suggest that attachment is the dominant process and only negative ions are formed. The characteristics of the measured transients, indicating that there is only one drifting ionic species. That, and the low $E/N$ values used, led to the assumption that the majority ion species under investigation is $CCl_{4}^{-}$. This method proved to be highly sensitive for detecting negative ion signals even for small amounts of $CCl_{4}$ in the mixture. The relevance of electron attachment processes in these gas mixtures are desirable and it is our hope that the present data are of use for gas discharge simulation and complex ion chemistry of $CCl_{4}/Ar$ mixtures. [Preview Abstract] |
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SW.00062: Global Model of Electronegative Discharges for Neutral Radical Control Sungjin Kim, M.A. Lieberman, A.J. Lichtenberg, J.T. Gudmundsson Control and reduction of the ratio of neutral radical flux to ion flux at the wafer surface is required for the next generation plasma etching processes in the microelectronics industry. To explore these processes, the electronegative plasmas driven by steady power and by time-modulated power, with oxygen as the feedstock gas, have been investigated utilizing volume-averaged (global) models of a cylindrical plasma discharge. The variations of the time-average flux ratio of oxygen neutrals to O$_{2}^{+}$ ions depending on the chamber geometry and power modulation conditions were examined using a simple model with uniform spatial profiles and a new model with non-uniform spatial profiles, and the results from the models were compared. In both models, at a fixed duty-ratio, the flux ratio of neutrals to ions is found to have a minimum value as the pulse period is varied, with the minimum value decreasing as the duty-ratio decreases. The flux ratio is reduced in the chamber geometry with lower aspect ratio, and the pulse period that yields minimum value also decreases. In future work, we will compare the simulation results with measured experimental results. [Preview Abstract] |
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SW.00063: IONIZATION OF ATOMS AND MOLECULES
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SW.00064: An Electron Momentum Spectroscopy, Density Functional and Greens Function Theories study of the Outer Valence Electronic Structure of Bicyclo[2.2.1]heptane-2,5-dione Michael Brunger, Darryl Jones, Stefan Knippenberg, Jean-Pierre Francois, Michael Deleuze, Saumitra Saha, Feng Wang, Rolf Gleiter, Johannes Bueber, Dave Winkler We report our preliminary results for an electron momentum spectroscopy (EMS) study of the outer valence electronic region of bicyclo[2.2.1]heptane-2,5-dione. The measured binding energy spectra are presented for the azimuthal angles 0$^{\circ}$, 10$^{\circ}$ and 0$^{\circ}$+10$^{\circ}$ and are compared to new He(I$\alpha )$ photoelectron spectroscopy results. These data are then compared with results from theoretical computations, using Greens Function theories. Derived momentum distributions are compared against those obtained by calculations which employ the plane-wave impulse approximation. These calculations use basis sets obtained from Density Functional Theory calculations at the triple zeta valence polarization level with a collection of different exchange correlation functionals. [Preview Abstract] |
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SW.00065: Electron Impact Ionization of Silicontetrachloride (SiCl$_{4})$ Ralf Basner, Michael Gutkin, Jenny Mahoney, Vladimir Tarnovsky, Hans Deutsch, Kurt Becker We measured absolute partial cross sections for the formation of various singly charged and doubly charged positive ions produced by electron impact on silicon tetrachloride (SiCl$_{4})$ using two different experimental techniques, a time-of-flight mass spectrometer (TOF-MS) and a fast-neutral-beam apparatus. The energy range covered was from the threshold to 900 eV in the TOF-MS and to 200 eV in the neutral beam apparatus. The results obtained by the two different experimental techniques were found to agree very well (better than their combined margin of error). The SiCl$_{3}^{+}$ fragment ion has the largest partial ionization cross section with a maximum value of slightly above 6 x 10$^{-20}$ m$^{2}$ at about 100 eV. The cross sections for the formation of SiCl$_{4}^{+}$, SiCl$^{+}$, and Cl$^{+}$ have maximum values around 4 x 10$^{-20}$ m$^{2}$. Some of the cross section curves exhibit an unusual energy dependence with a pronounced low-energy maximum at an energy around 30 eV followed by a broad second maximum at around 100 eV. The maximum cross section values for the formation of the doubly charged ions, with the exception of SiCl$_{3}^{++}$, are 0.05 x 10$^{-20}$ m$^{2}$ or less. [Preview Abstract] |
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SW.00066: Formation of positive ions of quadricyclane C.Q. Jiao, C.A. DeJoseph, Jr., R.H. Lee, A. Garscadden Quadricyclane (QC) is one of the strained hydrocarbons that have potential as high-energy density materials used as aerospace fuel or as additives to kerosene rocket fuel. We have studied the formation of positive ions of QC by electron impact and by charge-transfer reactions, using Fourier-transform mass spectrum (FTMS) techniques. The electron ionization cross sections in the energy range of 10-200 eV have been measured. The total cross section reaches a maximum of 2.3x10$^{-15}$ cm$^{2}$ at 60 eV. Parent ion C$_{7}$H$_{8}^{+}$ and 21 fragment ions including C$_{5}$H$_{6}^{+}$ and C$_{5}$H$_{5}^{+}$ that dominate the dissociation channels at low energies ($<$25 eV) are observed. Ar$^{+}$ charge-transfer reaction with QC produces C$_{5}$H$_{5}^{+}$ and C$_{7}$H$_{7}^{+}$ as the major ionic species. Some selected hydrocarbon ions, i.e., C$_{3}$H$_{3}^{+}$, C$_{5}$H$_{3}^{+}$, C$_{5}$H$_{5}^{+}$ and C$_{5}$H$_{6}^{+}$, which are formed from QC by electron ionization, are found to react with QC forming C$_{7}$H$_{7}^{+}$ and C$_{7}$H$_{8}^{+}$ as the major product ions, while the latter two ions are unreactive with QC. The relative rates of the hydrocarbon ion reactions, compared to the Ar$^{+}$ charge-transfer reaction, are rather low; while the rate for C$_{3}$H$_{3}^{+ }$is less than 20 percent of the Ar$^{+}$ reaction rate, the rates for C$_{5}$H$_{3}^{+}$, C$_{5}$H$_{5}^{+}$ and C$_{5}$H$_{6}^{+}$ are less than 3 percent. [Preview Abstract] |
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SW.00067: Approximating the Green's Function in Evaluating Second-Order Amplitudes Zhangjin Chen, Don Madison, Klaus Bartschat It is well established that second-order effects are often important for electron impact ionization processes. Due the complexity of evaluating second order amplitudes, approximations are typically made in their evaluation. One of the approximations that have been used is accounting only for the imaginary part of the Green's function, so that the second-order amplitude reduces to a sum of products of two first-order terms. To check the validity of this approximation, we performed second-order distorted-wave calculations, in which the first-order amplitudes were evaluated by a convergent $R$-matrix with pseudostates (close-coupling) model to describe the initial bound state and the ejected-electron--residual-ion interaction. The results obtained without making any approximations are compared with those obtained by simplifying the Green's function for electron impact ionization of helium to He$^{+}$(1s) and He$^{+}$(2s,2p). The approximation is found to be reasonably good for direct ionization to He$^{+}$(1s) at incident energies greater than about 600 eV. The accuracy decreases with decreasing incident electron energy. [Preview Abstract] |
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SW.00068: Electron-impact Fully Differential Cross Sections of Helium for Simultaneous Excitation- Ionization M. Foster, D.H. Madison, J.L. Peacher, A.L. Harris We have examined fully differential cross sections for electron- impact ionization of helium with simultaneous excitation of the atomic electron to either the 2s or 2p state. This process has attracted considerable attention due to the fact that second order effects are known to be very important and there have been several studies within the framework of the second Born approach which treats the projectile-atom interaction to second order. We will report results for a complete quantum mechanical four-body model known as the 6DW (six-distorted-wave) model. The 6DW model takes all two particle Coulomb interactions (six in total) into account exactly which means that all two-particle interactions are taken into account to all orders of perturbation theory. One of the advantages of this approach is that the importance of each two-particle subsystem can be independently studied. 6DW results will be compared with experimental data and other theoretical approaches. [Preview Abstract] |
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SW.00069: Experimental and Theoretical study of the Fully Differential Cross Section both in and out of the Scattering Plane for Electron-Impact Ionization of Magnesium M. Foster, D.H. Madison, J.L. Peacher, A. Walters, R. VanBoeyen, M. Coplan Most of the experimental and theoretical studies of electron- impact ionization of atoms, normally referred to as (e,2e), have concentrated on the scattering plane defined by the initial and final momentum vectors of the projectile. The assumption has been that all the important physical effects will be observable in the scattering plane. However, very recently it has been shown that, for C$^{6+}$-helium ionization, experiment and theory are in nice agreement in the scattering plane and in very bad agreement out of the scattering plane. This lack of agreement between experiment and theory has been explained in terms of higher order scattering effects between the projectile and ion which would never be seen in the scattering plane. In this paper we will examine electron-impact ionization of magnesium to see if similar higher order effects might be present here as well. [Preview Abstract] |
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SW.00070: Proton Impact Transfer-Ionization of Helium D.H. Madison, M. Foster, J.L. Peacher, M. Schoeffler, R. Doerner For the first time experimentally all the final state particles in the process of transfer ionization are measured in triple coincidence\textbf{. }Transfer-ionization is the process in which one electron is transferred to a fast proton and the other electron is ionized into the continuum. In this paper, we will present fully differential transfer-ionization cross section (FDTICS) for 630 keV p + He $\to $ H$^{0}$ + He$^{2+}$ + e$^{-}$. In order to fully understand the electronic correlation in atoms such as helium, we will present a complete quantum mechanical four-body model known as the 6DW (six-distorted-wave) model. The 6DW model takes all two particle Coulomb interactions (six in total) into account on equal footing. The 6DW approach also allows for the probing of high level electronic correlation effects in atoms such as helium. The atomic correlation effects can be studied in great detail through various types of (e, 2e) and ion impact collisions. The first of the impact collisions that will be examined is referred to as transfer-ionization. Preliminary results will be reported for both transfer-ionization of helium. [Preview Abstract] |
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SW.00071: Ionization of silicon, germanium, tin, and lead by electron impact Philip Stone, Yong-Ki Kim We continue our investigation of electron impact ionization of neutral atoms that are important in modeling of low temperature plasmas and gases. Cross sections for ionization have been calculated for ionization from ground levels and low-lying metastable levels of Si, Ge, Sn and Pb. We use the binary-encounter-Bethe approximation (BEB) for direct ionization and scaled plane-wave-Born approximation for dipole- and spin-allowed transitions to autoionizing levels.$^{1,2}$ Multiconfiguration Dirac-Fock wavefunctions have been used for the atomic structure. The calculated values are in agreement with the few experimental results available for comparison. It is clear that autoionization is important in these elements and must be included accurately. These results complement earlier calculations of H, He, Li, B, C, N, O, Al, Ga, and In. The results for these atoms, along with ionization cross sections for many molecules are being made available on a NIST web site.$^{3}$ \newline \newline Work supported in part by the U.S. DOE Office of Fusion Sciences. \newline $^{1}$ Kim Y-K and Desclaux JP, Phys. Rev. A 2002; \textbf{66}; 012708. \newline $^{2}$ Kim Y-K and Stone PM, Phys. Rev. A 2001; \textbf{64}; 052707. \newline $^{3}$ \href{http://physics.nist.gov/ionxsec}{http://physics.nist.gov/ionxsec} (2005). [Preview Abstract] |
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SW.00072: Ionization of neutral W and W$^+$ ion by electron impact Duch-Hee Kwon, Yong-Joo Rhee, Yong-Ki Kim Ionization cross sections for the neutral W and W$^+$ ion by electron impact are being calculated using binary-encounter- Bethe (BEB) model for the direct ionization and scaled Born cross sections for excitation-autoionization as was done successfully for the ionization of C, N, and O.\footnote{Y.-K. Kim and J. P. Desclaux, Phys. Rev. A {\bf 66}, 012708 (2002).} Two sets of experimental data for W$^+$ are available in the literature, while there are no experimental data for the neutral W. Both sets of the experimental data indicate the presence of metastable W$^+$ ions in their target beams, but the magnitude and shape are comparable to our preliminary results for W$^+$ ion in the ground level. Theoretical results that include cross sections for both direct ionization and excitation-autoionization of W and W$^+$ will be reported at the conference. [Preview Abstract] |
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