Bulletin of the American Physical Society
2005 58th Gaseous Electronics Conference
Sunday–Thursday, October 16–20, 2005; San Jose, California
Session FM: Poster Session I |
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Chair: I. Langmuir Room: Doubletree Hotel Fir/Oak |
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FM.00001: MATERIAL PROCESSING |
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FM.00002: Low Pressure PECVD of SiO$_{x}$N$_{y}$ Thin Films with Electron-Beam Generated Plasmas Darrin Leonhardt, Scott Walton The deposition of thin films of SiO$_{2}$/SiO$_{x}$N$_{y}$ is an integral part of flexible displays/electronics, medical implant bio-functionalization, as well as a robust barrier layer ideal for space applications. In all of these applications, such insulating layers must be uniform and defect free over large areas. In this work, modulated electron beam-generated plasmas were used to produce SiO$_{x}$/SiO$_{x}$N$_{y}$ films from organic precursors (TEOS or HMDSO) with Ar/O$_{2}$/N$_{2}$ gases. The inherent low electron temperature of these plasmas results in low plasma fields and potentials, which in turn provide low energy ($<$ 3 eV) ions to the substrate. Film properties (electrical, optical and chemical) with respect to gas mixtures, substrate temperature and ion energy will be presented. The incorporation of ion energy during deposition was critical in producing films with lower defect densities than typical deposition processes. Using the ion energy as an additional process control `knob' the film composition ranged from stoichiometric SiO$_{2}$ to heavily hydrolyzed films. The incorporation of additional ion energy showed more dramatic effects at higher than anticipated values ($\sim $50 eV vs. 15 eV). Ion fluxes and energies to the substrate determined by mass spectrometry measurements will be correlated to the process variables, final film composition and recent studies in other plasma sources. [Preview Abstract] |
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FM.00003: Niobium surface modification in a microwave discharge Marija Raskovic, Svetozar Popovic, Leposava Vuskovic Surface preparation techniques for Niobium superconducting RF cavities commonly employ chemical or electrochemical polishing. With wet chemical polishing and the final dry air treatment, the formation of a non-superconductive Niobium oxide layer is unavoidable since oxidation starts as soon as the chemical process stops. For that reason a dry surface modification is highly desirable. Plasma etching may provide a unique opportunity to explore oxide-free surfaces by directly testing a cavity surface after processing without exposure to air. We studied the effects of a cavity microwave discharge in Ar and Ar-Cl$_{2}$ mixtures on removal of oxide layer of an electrically biased Niobium samples. Results on discharge characterization during the process will be presented at the conference. [Preview Abstract] |
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FM.00004: Anisotropic fluorocarbon plasma etching of Si/SiGe heterostructures Ruhang Ding, Amy Wendt, Levente Klein, Mark Eriksson Fluorocarbon plasma etching of SiGe heterostructures for fabrication of quantum devices is investigated. The heterostructures consist of layers of silicon and SiGe, and anisotropic etching of the heterostructures using plasmas to isolate device elements is an attractive approach to fabricating devices. A challenge that has limited the use of fluorocarbon etching is the difference in Si and Ge etch rates. Preferential etching of SiGe can lead to undercutting beneath the top silicon layer, causing a reduction in critical device dimensions of unknown magnitude. To improve anisotropy of the etch process, we propose the use of flourocarbon etch gases with higher carbon content, making use of fluorocarbon sidewall passivation to improve the anisotropy of etched feature profiles by preventing lateral etching of SiGe. Initial etch results in a C$_4$F$_8$/Ar/N$_2$ gas mixture show a straight sidewall profile through the layers of the heterostructure. Furthermore, control of the energy distribution of bombarding ions has been implement to enhance etch selectivity to PMMA used as an etch mask. [Preview Abstract] |
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FM.00005: Industrial Carbon-Doped SiO$_2$ (CDO) Film Etching in Ar/O$_2$/c-C$_4$F$_8$ High Density Plasmas A. Islyaikin, V. Krastev, I. Reid, G. Hughes, A.R. Ellingboe Etching of Si samples covered by a carbon-doped SiO$_2$ (CDO) film was performed using high-density Ar/c-C$_4$F$_8$/O$_2$ plasmas produced in an industrial TCP reactor under a wide range of plasma conditions. Mass spectral diagnostics were used for analysis of the chemical composition of the plasma neutral components and dominant etching products. A complete dissociation of c-C$_4$F$_8$ was found for all the experimental conditions. Analysis of chemical composition of the surface layer as well as the depth elemental distributions in the bulk of the CDO layers were performed by means of X-ray photoelectron spectroscopy (XPS). Deposition of a thin fluorocarbon surface layer was recorded. Correlation between the plasma characteristics and results of the plasma processing is the object of current investigation. [Preview Abstract] |
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FM.00006: Three-dimensional etching profile simulation using level set methods Gon Jun Kim, Sung Jin Kim, Branislav Radjenovic, Jae Koo Lee Surface evolution in plasma etching and deposition is a significant challenge for numerical methods. A level set method is a robust and accurate computational technique for moving interfaces. We have developed 2D/3D simulators for etching profile evolution using level set methods. A sparse field method, which is an alternative to the usual combination of narrow band and fast marching procedures for computationally effective solutions, is applied for solving the level set equation in the 3D etching profile simulation. In the level set equation, a speed function represents etching rate and depends on physical and chemical reactions. Thus, we find out the speed function, considering reactions of injected ions and redicals. Kinetic information of injected ions is obtained by one-dimensional particle-in-cell Monte Carlo collision (PIC-MCC) simulations. Charge-up potential is calculated during surface evolution. Ion reflections which have influence on etching profiles such as trenching and bowing are included to the 3D etching profile simulation. Etching profiles are investigated in respect to injected particles and physical and chemical reactions. *This work is supported by the national program for Tera-level nanodevices in Korea Ministry of Science and Technology. [Preview Abstract] |
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FM.00007: Ti Surface Oxidization by Microwave Discharge Oxygen Plasma and Plasma Parameters Satoru Kakizaka, Takeshi Sakamoto, Haruaki Matsuura, Hiroshi Akatsuka We made an experimental study on Ti surface oxidization by microwave discharge oxygen plasma, which was generated in a cylindrical quartz tube (26 mm id.) with its discharge pressure 0.5 - 10.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. The gas flow rate was set at about 0.01 -- 1.6 l/min. The titanium sheet (15 $\times $15$\times $0.2 mm$^{3})$ was set at the position 60 mm down from the centerline of the microwave guide. The treatment time was 1 hour. We measured basic parameters of microwave oxygen plasma, such as electron density ($N_{e})$, electron temprature ($T_{e})$ by a double probe, vibrational and rotational temperatures ($T_{v}$, $T_{r})$ by OES. It was found that the $N_{e }\sim $ 10$^{11 }$cm$^{-3}$,$ T_{e }\sim $ 5 eV, $T_{r }\sim $ 0.14 eV and $T_{v} \quad \sim $ 0.25 eV, respectively, at a low discharge pressure. Only the rutile pattern was found for the samples by XRD. We are examining the effect of admixture of noble gases with oxygen. [Preview Abstract] |
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FM.00008: Plasma CVD of a-C:F Films Using C$_8$F$_{18}$ and Characterization of their Properties Yosuke Sakai, Shota Tazawa, Yoshiyuki Suda, Hirotake Sugawara We have composed low-$k$ amorphous fluorocarbon (a-C:F) dielectric films on the surface of spherical Al electrodes using a C$_8$F$_{18}$ plasma CVD for development of a composite insulation system. The relative dielectric constant $k$ of the a-C:F films was less than 2.5. An a-C:F film of the thickness of 1~$\mu$m on the electrode enhanced the insulation tolerance of sphere-to-sphere electrodes systems in Ar, N$_2$ and He about 700~V around the $pd$ values of their Paschen minima. The C$_8$F$_{18}$ plasma was analyzed with optical emission spectroscopy and mass spectrometry. It was found that CF$_3$ was one of the major fragment species derived from C$_8$F$_{18}$. The intensity of the CF$_3$ appearance was 6--10~times as much as that of CF$_2$, which was considered to be a primary precursor of a-C:F\@. In addition, C$_2$F$_4$ ($=100$), C$_2$F$_5$ ($=119$), C$_3$F$_5$ ($=131$), C$_3$F$_7$ ($=169$) and C$_4$F$_7$ ($=181$) were detected by the mass spectrometry done in a molecular weight range $\le200$. An FT-IR measurement showed that =CF$_2$ bonds more than $\equiv$CF bonds were involved in the deposited a-C:F films. The F/C ratio measured by an XPS observation was 1.4--1.5, and this ratio seemed independent of the CVD condition in the range of the C$_8$F$_{18}$ pressure of 0.2--0.4~Torr and the input power of 80--100~W\@. The deposition rate was over 300~nm/min. This work was in part supported by a Grant-in-Aid of JSPS\@. [Preview Abstract] |
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FM.00009: Noninvasive Measurement of Ion Energy Distributions in a Plasma Etching System SeJin Oh, ChinWook Chung, SungHo Cha, GiChung Kwon A monitoring of ion energy distributions is important during plasma etching processes. A commercial invasive ion energy analyzer is not well-suited to measure ion energy distributions because of various difficulties. A noninvasive monitoring technique in inductively coupled plasmas has been developed by M.A Sobolewski. We applied this technique to a plasma etching system. Plasma characteristic parameters and the rf bias dependent plasma potential were deduced by using the equations of power balance and particle balance to maintain completely noninvasive processes. The effects of source power, rf bias frequency, rf bias power, pressure and gas composition were measured. The experimental results agreed well with the predicted ion energy distributions. [Preview Abstract] |
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FM.00010: Laser Ablation Plasma Deposition and Ion Implantation of Hafnium and Hafnium-Oxide Thin Films* Nicholas M. Jordan, Ron Gilgenbach, Michael Jones, Lumin Wang, Sha Zhu, Michael Atzmon, Dongchan Jang, Y.Y. Lau Experiments are underway to deposit and implant films of hafnium and hafnium-oxide on silicon substrates. A KrF laser (400 mJ @ 248 nm) ablates solid Hf foils or sintered pellets of hafnium-oxide. Silicon substrates can be negatively biased (either pulsed or DC) by voltages up to 10 kV for ion implantation. Ablation plasma plumes are characterized by optical emission spectroscopy, dye laser resonance absorption photography, resonant/non-resonant interferometry, and Langmuir probe diagnostics. Composition and morphology of deposited films are analyzed by Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Energy Dispersive Spectroscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Thin film adhesion is also being tested. X-ray diffraction is being use to determine if the Hf films are amorphous or crystalline. Deposition rates are estimated to be on the order of 0.05 nm/pulse at a deposition rate of 20 pulses/s. [Preview Abstract] |
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FM.00011: MAGNETICALLY ENHANCED PLASMAS |
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FM.00012: Resolving the Plasma Sheath Layer in Two--Dimensional Magnetized Discharges Mark Carter, Philip Ryan, Daniel Hoffman The nonlinear physics of sheaths is important to study, not only for the constructive use of sheaths in semi--conductor processing, but also for their destructive tendencies in high power RF fusion applications. The disparity in device--to--sheath scale lengths often allows semi--analytical sheath models to be applied locally in a sheath layer, but whole--system models of realistic devices must be at least two--dimensional (2D) and require a consistent implementation of the sheath models. Whole--system models must also consider sources and transport of plasma outside the sheath layer, electromagnetic coupling throughout the entire RF circuit, and neutral gas flows through the system. In this paper, we present results from joining 2D models of plasma transport and RF power coupling (including static magnetic fields) with locally consistent sheath models using the Modular Oak Ridge RF Integeration Code (MORRFIC). Nonlinear power coupling is accounted for by modifying the local dielectric inside the sheath when resolving the layer. Relatively modest 64--bit computing facilities are used to iterate the RF sheath and nonlinear dielectric properties to be consistent with the RF global solution. [Preview Abstract] |
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FM.00013: Biased substrate effects on ion characteristics in magnetized inductively coupled plasma Sanghyun Jun, Hong Young Chang Biased substrate can affect the plasma parameters related to ion heating. We suggest that bulk ions accelerated through sheath become energetic neutrals at the surface, and the neutrals may heat bulk ions again. DC bias is coupled to the substrate parallel and perpendicular to the magnetic field. The velocity distribution functions of the heated ions can be measured by diode LIF(Laser Induced Fluorescence) technique at 668.6nm for argon ion metastable LIF in magnetized~ICP. We can take ion temperature, density and drift velocity from the velocity distribution functions. [Preview Abstract] |
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FM.00014: Time-Resolved Optical Emission Studies of Pulsed DC Magnetron Plasmas Jose Lopez, WeiDong Zhu, Abraham Belkind, Kurt H. Becker Pulsed DC unbalanced magnetron sputtering is a well-developed deposition technique for coatings and thin films and is widely used in industry to deposit thin films such as alumina, Al$_{2}$O$_{3}$ and titania, TiO$_{2}$. The pulsed modulation of the direct current (DC) has been demonstrated to create plasmas that solve many of the arcing problems observed in DC magnetrons which can lead to non-uniform removal of material from the anode resulting in poor or unusable thin films for high-tech applications. The intense photon emission from the pulsed DC magnetron sputtering plasmas allows for the investigation of the optical plasma emissions with a fast intensified CCD (ICCD) camera. The non-intrusive diagnostic methods of time-resolved optical emission spectroscopy (TR-OES) and time- resolved imaging were used to study the temporal behavior of the various plasma species. [Preview Abstract] |
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FM.00015: INDUCTIVELY COUPLED PLASMAS |
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FM.00016: Model and Measurements for Closed Loop Control of an Inductively Coupled Plasma Source Bernard Keville, Petar Iordanov, Declan Doherty, Michael B. Hopkins, Ronan Faulkner Process analysis and design and simulation of closed loop control algorithms require lumped parameter or low order models of plasma sources which reveal the essential dynamics of the system. Empirical models do not facilitate the simulation of process disturbances and hence an approach based on first principles is preferable. A physically-based, control-oriented model consisting of a global model of the plasma chemistry, together with a model of power deposition and models of the mass flow controllers and throttle valve has been used in the design and simulation of closed loop control algorithms for an inductively coupled plasma source with internal intenna. Multivariable closed loop control of an Argon/ Oxygen plasma has been demonstrated experimentally and the use of a number of different sensors for feedback control has been investigated. [Preview Abstract] |
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FM.00017: Investigation of inductively coupled CF$_4$/O$_2$ discharges by Langmuir probe method and optical emission spectroscopy Takashi Kimura, Masahisa Noto The oxygen content dependence of the plasma parameters in inductively coupled CF$_4$/O$_2$ plasmas was investigated by Langmuir probe and optical emission spectroscopy. Plasma was produced in the cylindrical stainless steel chamber with 160 mm in inner diameter and 75 mm in length. Experiment was performed at three total pressures of 8m, 15m and 25 mTorr. The electron energy probability functions (EEPFs) were approximately Maxwellian at any oxygen content, although a slight enhancement of EEPF with respect to a Maxwellian distribution was observed at the energy region lower than 2-3 eV for the oxygen content lower than 70\%. The electron density decreased in the oxygen content below 20\%, beyond which it remained nearly constant. On the other hand, the measured electron temperature did not depend strongly on the content. The densities of fluorine and oxygen atoms were also investigated by actinometry method. The fluorine atom density increased markedly as oxygen was mixed to CF$_4$ discharges, and then reached the maximum around the oxygen content of 20 - 30\%, beyond which it decreased with increasing oxygen content. The oxygen atom density increased with the increase in the oxygen content and saturated at about 50\% oxygen content. A global model for electronegative plasma was used in order to study the dependence of the plasma parameters on the oxygen content assuming the Maxwellian electron energy distribution. [Preview Abstract] |
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FM.00018: Improvement in Uniformity of Linear Inductively Coupled Plasma for Large Area Processing S.M. Choi, S.H. Lee, J.K. Lee, K.N. Kim, G.Y. Yeom The external planar ICP sources with low pressure high density plasma have limited scale-up capabilities due to its high impedance accompanied with the large antenna size. The novel internal-type linear inductive antenna system (1020mm×830mm×437mm) is investigated to improve both the plasma density and the uniformity of LAPS for FPD processing. Until now, we have observed the characteristics of LAPS under various conditions to overcome the problems stated above. The total length of antenna is comparable to the driving rf wavelength to cause the plasma non-uniformity and so the uniformity is improved by reducing the standing wave effect. We will show the effects of various antenna shapes and permanent magnet that reduce standing wave effect, electron loss to chamber wall and finally the effects of the parallel resonance antenna that controls the current at each segment of antenna with a variable capacitor. To describe the discharge phenomenon we have utilized a magnetized two-dimensional fluid simulation. [References] 1. S.E.Park, B.U.Cho, Y.J.Lee, and G.Y.Yeom, and J.K.Lee, ``The Characteristics of Large Area Processing Plasmas,'' IEEE Trans. Plasma Sci., Vol.31, No.4(2003) 2. K.N.Kim, S.J.Jung, Y.J.Lee, and G.Y.Yeom, S.H.Lee and J.K.Lee, ``Low-impedance internal linear inductive antenna for large-area flat panel display plasma processing,'' J. Appl. Phys. 97, 063302(2005) [Preview Abstract] |
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FM.00019: Chlorine atom measurements in Ar:Cl$_{2}$ discharges. F.G. Marro, W.G. Graham Two-photon Laser Induced Fluorescence has been used to measure the chlorine atom density in an inductively coupled discharge. A 233.3nm beam was focused into a 130$\mu $m waist 2-3 cm above the lower electrode pumping the ground state 3s$^{2}$3p$^{5}(^{2}$P$^{0}_{3/2})$ to the excited level 3s$^{2}$3p$^{4}$4p($^{4}$S$^{0}_{3/2})$. From the three radiative decay channels at 725.6, 754.7 and 774.5nm, the strongest one, 725.6nm, was monitored. The UV photons were obtained from mixing an Nd:YAG fundamental (1064nm) and the second harmonic of a DYE laser. Relative and total measurements were performed in pure chlorine and in Ar:Cl$_{2}$ mixtures. A calibration based on CCl$_{4}$ photolysis was used. The estimated dissociation shows values as high as 33{\%} near the transition between the capacitive and the inductive coupling. An unexpected decay of the atom density with power was observed in the inductive mode. The dependence of the atom density as chlorine is introduced into an argon discharge is linear. Doppler broadening was estimated from the lineshape, suggesting that the atomic temperature rises a few hundred Kelvin in the inductive mode. A kinetic model has been developed which shows that gas heating and the surface recombination coefficient have an important effect on the dissociation. [Preview Abstract] |
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FM.00020: Study of non-local electron kinetics in a low-pressure afterglow argon plasma Sergey Gorchakov, Florian Sigeneger, Dirk Uhrlandt Non-isothermal pulsed plasmas are widely used for technological applications. The specific properties of these plasmas could be adjusted by appropriate choice of operation conditions. In particular, the switch-off period of a discharge has a strong influence on the time-averaged plasma properties. In this contribution results of theoretical investigations of the early afterglow, i.e. the range of few microseconds after switching off the power input, in an argon plasma of an inductively coupled discharge at pressures of few Pa are presented. Under these conditions the kinetic behaviour of the electron component dominates the plasma properties. The plasma is studied by means of a self-consistent model which includes the non-local electron kinetic approach taking, in particular, the impact of electron-electron collisions and of electron cooling due to ambipolar losses to the walls (diffusive cooling) into account. The results for temporal evolutions of the velocity distribution function, density and mean energy of electrons and the space-charge potential are discussed in comparison with recent experimental data. Good agreement has been found. The analysis confirms the significant influence of the diffusive cooling on the plasma properties and shows a marked impact of electron-electron collisions on the afterglow behaviour. [Preview Abstract] |
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FM.00021: Optical emission and self mode transition of low frequency inductively coupled plasmas driven by crossed internal oscillating currents YuPing Ren, Pavlo Rutkevych, JiDong Long, QiJin Cheng, ShuYan Xu, Kostya Ostrikov Optical emission and self induced electrostatic (E)-to-electromagnetic (H) mode transition in a newly-developed plasma reactor are investigated. Volume uniform, high density Ar/N2 plasmas are generated by means of transverse unidirectional currents driven by a low frequency RF power of 460 kHz in a 23 cm height and 32 cm diameter reactor. Plasma properties are investigated using a high-resolution optical emission spectroscope. The measurements reveal that the spatial profiles of the excited atomic naturals and singly ionized ions feature a high degree of uniformity in radial and axial directions. A spatially homogeneous E-mode discharge is observed at a power level as small as 40 W. At RF power exceeding a transition threshold of 230 W, the integral emission intensity suddenly jumps to approximately one order of magnitude (H-mode). Further increase of RF power results in a gradual rise of the optical emission intensity. This phenomenon is reproducible for all discharges under the investigation. Furthermore, a spontaneous E-$>$H mode transition (``self-transition'') is observed at input power slightly below the conventional transition threshold value. [Preview Abstract] |
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FM.00022: Neutral gas collisional heating and the 0D/1D modeling in a semiconductor plasma reactor Masashi Shimada, George R. Tynan The significant neutral gas temperature increase has been observed in various noble gases in the center of an inductively coupled plasma (ICP) chamber and the actual neutral gas pressure has been obtained by considering the thermal transpiration effects with this neutral gas increase. A plate which consists of 8 vertical optical ports with collimating lens and a movable optical fiber probe have been developed and used to measure axial and radial profile of gas temperature in an inductively coupled plasma reactor respectively. The rotational temperature obtained from the second positive band of Nitrogen molecule has been compared with the Doppler broadening translational temperature of the noble gas (Ar/He) emission line in a various partial pressure of $\mathrm{N_2}$ in $\mathrm{Ar/N_2}$ and $\mathrm{He/N_2}$ mixture, and both temperature have been observed to be in equilibrium in the conditions of our plasma experiment. 0D/1D neutral gas heating model have been developed and compared with experimental results. Monte Carlo simulation have been carried out to model the ion acceleration by pre-sheath electric field. [Preview Abstract] |
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FM.00023: PLASMA BOUNDARIES |
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FM.00024: Consistent matching of plasma and sheath Karl-Ulrich Riemann Due to the sheath edge singularity, the asymptotic ($\epsilon\sim\lambda_D/L \to 0$) plasma- and sheath solutions cannot be matched smoothly. The sheath edge singularity, however, can be bridged by an intermediate scale analysis accounting in lowest order both for plasma processes (e.g. collisions, ionization, and non-planar geometry) and space charge. The possibility to construct a uniformly valid matched asymptotic expression from the plasma -, intermediate -, and sheath solutions was questioned in the literature. Problems arise from the asymptotic singularities and from the ionization eigenvalue problem of bounded plasmas (plasma balance). To clarify the topic we analyze the plasma-sheath problem both analytically and numerically. We show that the validity of the intermediate scale analysis is limited to a very narrow vicinity ($|\Delta \varphi| \leq 0.1$) of the sheath edge and formulate a matched asymptotic expression uniformly valid from the plasma core to the wall. The approximations obtained by matching are compared with exact solutions and discontinuities in the derivatives are investigated analytically. [Preview Abstract] |
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FM.00025: A bounded active magnetized plasma over a wide range of collisionality Raoul Franklin At the last GEC Sternberg gave a treatment of this problem in the collisionless limit, and with the magnetic field at a variable angle to the wall. This is extended to include the effect of collisions on the ion motion in the constant collision frequency for momentum model $\nu _{i}$. The relevant parameters are $\omega _{ci}$, the ion cyclotron frequency, the plasma half size L, the central Debye length $\lambda _{D0}$, and the ionization frequency Z. For $\nu _{i}$ = 0 the results of Sternberg and Poggie are recovered and the dimensionless quantities used in the description of the results here are $\lambda _{D0}$/L, $\omega _{ci}$/Z, $\nu _{i}$/Z and the angle $\Psi $. The eigenvalue is ZL/c$_{s}$. As $\nu _{i}$/$\omega _{ci}$ becomes greater than 1 the effect of the magnetic field is nullified, as is to be expected on physical grounds. Sternberg N and Poggie J (2004) IEEE Trans. Plasma Science \textbf{32}, 2217. [Preview Abstract] |
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FM.00026: Investigation of a Planar Langmuir Probe Orientated Parallel to the direct of Flow in a Laser Ablation Plasma Peter Sheerin, Miles M. Turner, Brendan Doggett, James G. Lunney Langmuir probes are a well established tool for investigating the characteristics of laser produced plasmas. Such plasmas typically take the form of highly directed plumes, with flow velocities that are supersonic with respect to the ion sound speed. The behaviour of planar Langmuir probes in such conditions are dependant on both the plasma parameters and the orientation of the probe with respect to the flow. The theory for such probes in supersonic flowing plasmas is not well developed. This limits their usefulness as diagnostic tools in the various applications where such conditions are encountered. The adaptations made to the associated theory of plasma ion implantation (PIII) to describe the I-V characteristics of the planar Langmuir probe in a flowing plasma are discussed. The resultant analytical theory when used in combination with one dimensional particle in cell simulations is shown to provide an excellent description of the behaviour of the planar Langmuir probe in a flowing plasma at early times. [Preview Abstract] |
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FM.00027: Energy Distributions of Ion Drift to the Cathode in a DC Microdischarge Tsuyohito Ito, Mark Cappelli The cathode sheath serves many important functions in a discharge. A DC microdischarge has a relatively high ratio of cathode surface area to volume. Understanding the structure of the sheath and its associated physical phenomena is even more critical to the understanding of microdischarges. In this study, the ion energy distributions (IED) in the cathode sheath of a DC microdischarge were measured. The pressure-gap distance product was fixed at 1 cmTorr with a pressure from 2 Torr to 20 Torr. The measured IED was analyzed by the expanded theory of Davis and Vanderslice. The results indicate that a scaling law of pressure-normalized current density is no longer applicable. The background gaseous temperatures expected from IED and the collisional Child law is seen to increase with increasing current. Moreover, the expected temperature shows good agreement with that estimated by Doppler broadening via laser absorption spectroscopy. Given this result, it is concluded that the expanded theory might accurately describe microdischarges at least over the discharge conditions studied here. [Preview Abstract] |
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FM.00028: Different modes of arc attachment at HID cathodes: Simulation and comparison to measurements Oliver Langenscheidt, Lars Dabringhausen, Stefan Lichtenberg, Juergen Mentel, Peter Awakowicz Based on a model for the plasma boundary layer of high intensity discharge (HID) cathodes simulations are performed and compared to experimental results. To solve the power balance of the cathode body 1D, 2D and 3D finite-element calculations are used. The simulations are done for cylindrical tungsten cathodes operated in different pure noble gas discharges (0.1 . . . 1.0MPa) and with currents between 0.5A to 10A. Under these conditions different modes of arc attachment are found both in simulations and experiments. For the diffuse mode of arc attachment an excellent quantitative agreement between measurements and the simulations is obtained reflecting an improved accuracy of measurements and of simulation. In addition different spot modes are found. At least one of these modes is also observed in the experiment. Also for this spot mode the agreement between measurements and simulation for the integral quantities is good but there are still some open questions concerning the spot mode of cathodic arc attachment. Evaluating the cathode fall characteristics regions of existence for the different modes are found, which are similar to the experiments. [Preview Abstract] |
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FM.00029: Studies of sheath physics in two ion species plasmas with diode laser LIF Greg Severn, Noah Hershkowitz, M.M. Turner Recent diode laser based Laser-Induced Fluorescence (LIF) measurements of Ar ion flows at the sheath-presheath boundary in single and multiple ion species plasmas have confirmed that the usual Bohm Criterion holds for the single ion species plasma but must be generalized for multiple ion species plasmas to include the possibility that the ions may reach the sheath edge traveling either faster or slower than its individual ion sound speed. These results are in accord with the Generalized Bohm Criterion and PIC code simulation results for the experimental case of two ion species plasmas which are relatively collisionless and of low temperature (ArI+HeI plasmas, $\:P_{ArI} \sim 0.1mTorr, \: 0 \leq P_{He}/P_{Ar} \leq 25$, and $\lambda_{Debye} \ll \lambda_{mfp}, \: T_e \leq 2 eV$). Both experimental and numerical simulation results will be presented concerning the details of the ion velocity distribution functions (ivdfs) near the sheath edge in two ion species plasmas for the cases of He and Xe ions as the other ion species besides Ar. Our goal is ultimately to diagnose both ion species in a two ion species plasma with diode laser LIF, some thing which is still difficult to do, but which would significantly extend the range of possible experiments that test existing theory. [Preview Abstract] |
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FM.00030: Effect of bombarding ion energy distribution on ion/surface interaction during fluorocarbon plasma etching Amy Wendt, Shuntel Williams, Yuk-Hong Ting, Satoshi Hamaguchi In earlier studies, etch rate measurements in fluorocarbon plasmas showed a surprisingly significant dependence of fluorocarbon etch/deposition rate on the energy {\it distribution} of bombarding ions (IED). Understanding this result has implications for the many etch processes that depend on selective fluorocarbon deposition to control etch selectivity. Toward this end, an analysis was conducted of the nonlinear effects resulting from ions of different energies interacting with a surface simultaneously. The analysis made use of available data on the interaction between fluorocarbon ion beams of single fixed energy interacting with a silicon surface. The outcome was a simple model that illustrates and quantifies an important nonlinear effect: specifically, that the effect of ions of a particular energy on the substrate is sensitive to the presence of ions of other energies. The etch/deposition rate resulting from ions of different energies reaching the substrate simultaneously is not just the linear combination of the rates resulting from ions of each energy interacting with the surface on their own. The nonlinearity arises from differences in the chemical composition of the interaction region at the surface of the substrate, resulting from changes in the IED. [Preview Abstract] |
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FM.00031: Photoresist covered wafer charging effects in pulsed plasma assisted ion implantation Ji Hyun Hur, Gyung Soo Keum, Jae Hyung Won, Jae Joon Oh, Jai Kwang Shin Ion implantation is a process in which energetic, high flux ions are directly introduced into a substrate such as silicon, poly silicon, and photoresist covered wafers. As a wafer is being implanted, ions can lead to positive charge build-up on the wafer. Especially for a low conductivity wafer like silicon dioxide or photoresist covered wafer, charging issue becomes more severe. Such charge build-up can cause two major problems. One is altering plasma conditions which results in reduction of ion energy and ion flux so that implantation condition is shifted lower energy/current process. And the other is wafer surface arcing owing to the large potential difference between wafer surface and powered electrode. We studied wafer charging effects in pulsed plasma assisted doping(P2LAD) for photoresist covered wafers by means of fluid plasma simulations. The results are discussed in comparison with experimental results. [Preview Abstract] |
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FM.00032: GLOWS I |
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FM.00033: A multi-beam model for low-current, very high E/N discharges in hydrogen. A.V. Phelps The multi-beam model of Helm and St\"{o}ri\footnote{D. Helm and H. St\"{o}ri, J. Appl. Phys. {\bf 72}, 3330 (1992).} has been applied to the motion and reactions of H$^+$, H$_2^+$, H$_3^+$, fast H$_2$, and fast H in H$_2$ for a uniform electric field. Plots of most of our analytic expressions for the cross sections are available\footnote{A. Bogaerts and R. Gijbels, Spectrochim. Acta Part B {\bf 57}, 1071 (2002).}. Elastic scattering of non-identical particles is modelled with an energy loss for backward scattering in center-of-mass and the elastic momentum transfer cross section. For identical particles, we use the energy loss for 90$^\circ$ scattering and the elastic viscosity cross section. Calculated rates of excitation of H$_\alpha$ and the uv continuum versus distance and pressure are compared with experiments\footnote{H.A.M. Blasberg and F.J. de Hoog, Physica {\bf54}, 468 (1971).}$^,$\footnote{Z.Lj. Petrovi\'c, B.M. Jelenkovi\'c, and A.V. Phelps, Bull. Am. Phys. Soc. {\bf 37}, 1951 (1992).}. Calculated ion and fast neutral fluxes at the cathode will be compared with calculations using Monte Carlo methods\footnote{T. \v{S}imko, Z. Donk\'o, and K. R\'ozsa, 23rd Intl'l. Conf. on Ionization Phenomena in Gases, (Univ. Paul Sabatier, Toulouse, 1997), p. II-64.}. [Preview Abstract] |
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FM.00034: NO kinetics in pulsed DC low-pressure discharge: influence of TiO$_{2}$ surface Lina Gatilova, Olivier Guaitella, Antoine Rousseau, Yury Ionikh, Stefan Welzel, Jurgen Roepcke NO, NO$_{2}$, N$_{2}$O are readily formed in air discharge plasma. The study of their formation and destruction in plasma are of interest for environmental protection from industrial emissions. This interest has stimulated extensive experimental and theoretical investigations devoted to studying of air plasmas kinetics. Recently, measurements performed in the afterglow of a pulsed DC discharge showed that NO density scales as a universal function of the averaged power for a very wide set of pulse duration, repetition rate and current; this was analysed using a simple model of the NO$_{x}$ kinetics [1]: the main source of NO formation is the reaction of N$_{2}$*(A$^{3}\Sigma _{u}^{+})$ with atomic oxygen O. In the present work, time-resolved absorption spectroscopy measurements of NO concentration were performed in-situ the positive column of a low-pressure pulsed DC discharge in order to validate this model. It is first shown that NO production during one single plasma pulse is a linear function of the Ixt product where I is the pulse peak current and t the pulse duration.Then, we show that the presence of porous semi-conductor material (TiO2) inside the plasma region leads to a strong decrease of the NO production. \newline [1] A. Rousseau, L. Gatilova, J. R\"{o}pcke, A. V. Meshchanov, Y. Ionikh Appl. Phys. Lett 86, 211501 (2005). [Preview Abstract] |
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FM.00035: Benchmark simulations of electronegative discharges Derek Monahan, Miles M. Turner There has recently been much interest--and some controversy--concerning the structure of electronegative discharges. These discharges can exhibit complicated spatial structures including stratification into electropositive and electronegative regions. Moreover, there are appreciable differences between discharges where the dominant negative ion destruction mechanism is detachment and those where it is recombination. In this paper we present benchmark particle-in-cell simulations for discharges in Ar/O$_2$ mixtures. These simulations cover a wide range of conditions in terms of collisionality, electronegativity, and negative ion destruction mechanism. We will discuss the changes in the spatial structure of the discharge that occur as the conditions change, including the appearance of structures such as double layers. [Preview Abstract] |
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FM.00036: Critical Evaluation of the Global Model Approximation Derek Monahan, Miles M. Turner The assumptions and simplifications typically associated with volume-averaged, or global, plasma chemistry models greatly limit the parameter domain over which they may be reliably applied. Well defined boundaries to these domains, however, have not been established and often only minimal model validation is offered in the literature. The aim of this project is to critically evaluate the performance of a global model over a range of parameters and gas compositions by comparing such a model to a more elaborate one dimensional kinetic simulation. The motivation for this work has arisen from the need for reliable and computationally inexpensive qualitative models in real time freedback control applications. In this paper initial findings are presented. It is found, as expected, that the most significant limitation of such a model appears to be the assumption of a Maxwellian electron energy distribution. The propensity of capacitively coupled discharges to develop energy distributions which are significantly non-Maxwellian, is well known. However, we have observed similarly restrictive behaviour in PIC simulations of a low pressure inductively coupled argon plasma. In our simulations the electrons appear to develop a bi-Maxwellian like distribution as pressure is increased above $\sim$ 10 mTorr. The volume averaged mean electron energy is then found to rise slowly with increasing pressure beyond this point. This is in direct contradiction with simple global model arguments. The source of this high energy tail is currently being investigated. [Preview Abstract] |
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FM.00037: Characterization of pulsed discharges for next-generation plasma processes Sang-Hun Seo, Shin-Jae You, Dong-Seok Lee, Sang-Won Lee, Hong-Young Chang As the device size is rapidly shrunk, various issues have been encountered in plasma etching processes for manufacturing of semiconductor with feature size of few tens nm. In particular, the deep contact hole etching with high aspect ratio becomes more and more difficult with reducing the contact-hole size and the serious distortions of contact profile are observable. Although several mechanisms on the distortion of contact profile, especially bowing and necking, have been suggested, any solutions on the basis of these mechanism have not been proposed. In this study, we concerned about the local pressure around the etched hole and propose new mechanism on bowing, tilting, and necking. In small and high-aspect-ratio contact, ions incident to the contact hole can give an amount of pressure to the by- products which are formed inside the contact hole and pumped out outside the contact hole, resulting in the increase of local pressure around the contact hole. We call this the ion-pressure effect. For the relief of the ion pressure, we investigated the pulse-modulation of rf power in ICP and CCP as the preliminary work and found that the modulation of bias power instead of source power is needed to relieve the incident ion pressure. [Preview Abstract] |
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FM.00038: Observations of Ionization Waves in Argon Glow Discharges using a Microwave Hairpin Resonator Nicholas Siefert, Biswa Ganguly We use optical and electrical diagnostic tools, as well as the hairpin resonator, to observe large-amplitude fluctuations in light emission, electric field and electron number density due to traveling ionization waves in argon glow discharges. The location of maximum production of ionization and the location of maximum electron number density are over 180$^{o}$ out of phase in ionization waves under our discharge conditions. The production rates of electrons peaks where the electric field is greatest; however, the electrons accumulate where the electric field is near its minimum. To measure the changing electron number density in these waves, we have revisited the hairpin resonator technique [R.L. Stenzel Rev. Sci. Instrum. 47, 603 (1976)]. We solve the wave equation with electron-neutral collisions and show that correction to the electron number density is less than 5{\%} for pressures at or below 1 Torr. The wave frequency varies from 2 kHz to 5 kHz, depending on pressure and current. The data shows that both the light emission and the electric field are in phase with each other, but they are out of phase with the electron number density by 185$^{o}$-265$^{o}$. This is consistent with the current continuity equation. The effect of pressure and current on both the phase difference and the peak electron number density will be presented. [Preview Abstract] |
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FM.00039: ELECTRON AND POSITRON COLLISIONS WITH ATOMS AND MOLECULES |
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FM.00040: Benchmark calculations for electron collisions with FeII Oleg Zatsarinny, Klaus Bartschat We have applied the $B$-spline $R$-matrix method~[1] to study electron collisions with Fe$^+$ over an energy range from threshold to 10$\,$Ry. A major challenge for this astrophysically important collision system is the very complex target structure, with a strong term-dependence in the individual orbitals. Using a multi-configuration Hartree-Fock method with non-orthogonal orbitals, we generated a target description of unprecedented accuracy in collision calculations. Our results for individual cross sections and effective collision strengths are in qualitative agreement with the predictions by Ramsbottom {\it et al.}~[2]. A few significant discrepancies are found in the low-energy regime, which is dominated by resonance structures. [1] O. Zatsarinny and C. Froese Fischer, J. Phys. B~{\bf 33}, 313 (2000). [2] C.A. Ramsbottom, C.J. Noble, V.M. Burke, M.P. Scott and P.G. Burke, J. Phys. B~{\bf 37}, 3609 (2004). [Preview Abstract] |
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FM.00041: Ground and Excited State Cross Sections for Electron Impact on Cesium William McConkey, Michal Lukomski, TImothy Reddish, Sean Sutton, Wladek Kedzierski We report some of the most interesting results of our ongoing [1,2] investigation of electron collisions with cesium atoms localized in a Magneto-Optical Trap (MOT). The trap loss technique used was pioneered by Lin and co-workers [e.g. 3], and does not require knowledge of the absolute target density. The choice of an appropriate pulsing scheme has enabled total cross sections for the ground (Cs 6 $^{2}$S$_{1/2})$ and 6 $^{2}$P$_{1/2}$ excited states to be determined. Furthermore, preliminary results of total ionization cross sections will also be presented. Our earlier studies [1] covered a 100-400eV energy range for the incident electrons. Recent significant modifications to the apparatus have resulted in a more efficient data acquisition rate and have enabled us to extend the energy range down to 5eV. This low energy capability is important as in this region the discrepancies with other experimental work and with theory become apparent. \newline \newline [1] J. A. MacAskill et al, J. Elect. Spect. and Rel. Phen., \textbf{123}, 173 (2002). \newline [2] M Lukomski et al, J Phys B, \textbf{38}, (2005), Submitted. \newline [3] R. S. Schappe et al, Europhys. Lett., \textbf{29}, 439, (1995). [Preview Abstract] |
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FM.00042: Optical potential calculation of elastic electron scattering from heavy noble gases Allan Stauffer, Robert McEachran We have developed a complex optical potential within the framework of the Dirac equations to account for the absorption of flux into the inelastic channels for electron scattering at intermediate energies. We have used Dirac-Fock wave functions to represent the fine-structure excited states of the atomic target. Detailed results will be given for elastic scattering from argon, krypton and xenon. [Preview Abstract] |
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FM.00043: A New, High-Resolution Positron Beamline James Sullivan, Violaine Vizcaino, Jens Huft, Gerard Atkinson, Adric Jones, Stephen Buckman A new positron beamline has been constructed based on the techniques established by the Surko group at UCSD. The beamline uses a buffer gas trap system to trap and cool positrons before producing a pulsed high resolution positron beam, for the study of atomic and molecular collision processes [1]. The system has been designed to take advantage of the techniques developed in San Diego for studying scattering in a magnetic field, which have revolutionised the study of low energy positron collisions. However, experiments on helium are impossible on the San Diego system, due to the use of cryopumps for maintaining vacuum. To allow for experiments on helium, the new experiment uses turbopumps. In addition, a charge sensitive detection system is also in place, enabling the use of electrons in the system. This not only provides for a direct comparison with well known electron cross sections, but also will allow the new techniques to be applied to electron scattering, in particular with regards to total excitation cross sections, where measurements have been difficult using conventional scattering techniques. [1] Gilbert et al., Appl. Phys. Lett. \textbf{70}, 1944 (1997) [Preview Abstract] |
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FM.00044: Elastic and Vibrational Cross Sections in Methane and Cyclopropane Michael Allan There is a general agreement about the elastic cross sections in methane in the literature, but substantial discrepancies exist about the vibrational cross sections. This work measures absolute differential elastic and vibrational cross sections from nearly threshold to 20~eV. The cross sections are measured over a large angular range using the magnetic angle changer. All four vibrations are resolved at low energies. Earlier relative measurements \{(M. Allan and L. Andri\' c, {\it J. Chem. Phys.} {\bf 105}, 3559 (1996)\} have revealed large differences in the shapes of the cross sections in propane and cyclopropane due to an $l=3$ shape resonance made possible by the $C_3$ axis in cyclopropane. The present work extends the existing measurements and presents absolute cross sections. [Preview Abstract] |
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FM.00045: Measurement of the Elastic and Vibrational Cross Sections in N$_2$ Over a Wide Angular Range Michael Allan The poster will report on the recent improvements of the techniques to measure elastic and inelastic electron-molecule cross sections. Emphasis will be given on the measurement of the cross sections as a function of scattering angle over a large angular range using the `magnetic angle changer' (MAC) invented by Frank Read and co-workers and on the measurements at low energies. It will be shown that measurement of cross sections in general and the use of the MAC device in particular require complex strategies to control instrumental drift and to determine the instrumental response function over wide ranges of energies and scattering angles, and that the results may to some degree depend on the details of these strategies. The procedures will be illustrated with measurement of elastic and vibrational cross sections in N$_2$. The $v=0\rightarrow 1$ cross section in the resonance region was measured in the full angular range $0^\circ - 180^\circ$, elastic cross sections were in the range of about $10^\circ - 180^\circ$, the lower limit being dependent on the electron energy. The results agree well with the high quality theoretical results of Morrison, Sun and Hao. The integral and momentum transfer cross sections derived from the differential data agree well with swarm data. [Preview Abstract] |
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FM.00046: Rydberg-Like Feshbach Resonances in Dissociative Electron Attachment to Amines and Alcohols Michael Allan, Bogdan Ibanescu, Svetlana Zivanov, Olivier May, Patric Oulevey The dissociative electron attachment (DEA) spectra of saturated compounds ($i.e.$, without double and triple bonds) containig the O and N atoms have recently been shown to be generally dominated by Feshbach resonances with double occupation of Rydberg-like orbitals around a cationic core \{T. Skalick\' y and M. Allan, {\it J. Phys.} B {\bf 37}, 4849 (2004)\}. The Feshbach resonance serves as a doorway state anf is predissociated by a repulsive valence state of the anion. These resonances shift to lower energies with alkyl substitution, in contrast to the shape resonances, and are found at surprisingly low energies in amines because of their low ionization energies. Feshbach resonances have been identified already earlier as being responsible for DEA in water, amonia, and other molecules. We continue this work with the aim of gaining fundamental insight into the dynamics of dissociation of saturated organic compounds by electron impact. We study the dependence of the dissociation patterns on the energy of the resonance and the type of alkyl substitution of the amines. [Preview Abstract] |
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FM.00047: A method for measuring optical cross sections for electron impact excitation from metastable states C.A. DeJoseph, Jr., V.I. Demidov We present a method for determining optical cross sections of states which are excited by electron impact from metastable levels. The method utilizes the afterglow of a low pressure, pulsed (100\% modulated) rf-driven plasma. Following termination of the rf power, the average electron energy decreases rapidly to a few tenths of an eV, which, for the rare gases, is well below the inelastic threshold for excitation from the ground and metastable states. At the same time, metastable atoms can react to create fast electrons through pooling reactions, which produce ionization, and collisions of the second kind with slow electrons. The energy of these fast electrons depends on the specific production mechanism. These fast electrons can, in tern, collide with metastables leading to excitation and subsequent optical emission from higher lying states. At the low pressures of this experiment ($\sim$20 mTorr) emission from three body recombination is negligible. We demonstrate the method using a pulsed ICP in argon over the pressure range of 10-20 mTorr. Specifically, we present relative data for a number of lines from the Ar $3p^54p$ manifold, where optical cross sections have been measured, and from the $3p^55p$ manifold, such as the 420.1 and 419.8 nm lines where measurements are unavailable. [Preview Abstract] |
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FM.00048: A global (volume averaged) model of a nitrogen discharge Jon T. Gudmundsson, Narfi T. Snorrason, Sungjin Kim, Michael A. Lieberman 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. The dissociation mechanism in the nitrogen discharge is investigated as a function of power and pressure. The dissociation fraction is of the order of a few precent and increases with increased applied power. Furthermore, we explore and compare the reaction rates for the creation and destruction of the positive ions N$^+$ and N$_2^+$. [Preview Abstract] |
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FM.00049: Electron excitation coefficients in oxygen \v{Z}eljka Nikitovi\'c, Vladimir \v{S}amara, Gordana Malovi\'c, Zoran Petrovi\'c We have presented measurements of electron excitation coefficients for the level leading to 777 nm radiation of oxygen. Measurements were performed in a drift tube. The drift tube consists of a pair of plane electrodes, with a diameter of 79 mm at a distance of 14.7 mm, placed inside a close fitting quartz tube. The cathode was made of stainless steel and the anode of graphite so that backscattering of electrons from the anode is minimized. The self-sustained Townsend discharge between 600 Td and 24000 Td was maintained by running low current discharges at pressures between 2.2 Torr and 0.09 Torr, respectively. The absolute electron excitation coefficients were determined from the measurements of the optical signal at the anode. The spatial profiles of emission provide us with information on heavy particle excitation, on non-hydrodynamic behaviour of the discharge and on the reflection of electrons from the anode. The absolutely calibrated spatial profiles of emission may be used to separate the effects of electron and heavy particle excitation at high $E/N$ values and obtain the cross sections for fast neutral excitation. [Preview Abstract] |
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FM.00050: HIGH PRESSURE PLASMA PHYSICS AND CHEMISTRY |
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FM.00051: Experimental study on atmospheric pressure RF capacitive He/O$_2$ discharges Takashi Kimura, Yosuke Hattori, Takamasa Hanai The discharge voltage-current characteristics, and the densities of the active species such as oxygen atom and ozone were investigated in the capacitively coupled RF (13.56MHz) He/O$_2$ discharges at atmospheric pressure. The discharges were produced between two planar aluminum electrodes of 40mm-$\phi$ in the discharge gap range from 0.5mm to 2.0mm. The flow rates of helium and oxygen were controlled using the mass flow controllers, keeping the total flow rate at 10.0 $\ell$/min. The oxygen content was changed from 0 to 5$\%$. With increasing the applied voltage, the discharge current and the power dissipated in the discharge monotonically increased until the glow discharges turned into the arc discharges. But the slope of the voltage with respect to the current was less than linear. The small amount of argon (=10 sccm) was fed into the discharge in order to estimate the density of oxygen atom by the actinometry method, where the optical emission intensities of 844.6 nm and 750.4 nm were used. The ozone concentration was detected by an optical absorption of 254 nm line using the Lambert-Beer law. The oxygen atom density was higher than the ozone density. The densities of oxygen atom and ozone were on the order of 10$^{15}$ - 10$^{17}$ cm$^{-3}$ in the power range lower than 100 W. This work is partially supported by Grant-in-Aid from the Japan Society for the Promotion of Science. [Preview Abstract] |
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FM.00052: Gas Temperature and Metastable Density Measurements in Ar/H$_{2 }$DBD Using Diode-Laser Absorption Spectroscopy Robert Leiweke, Biswa Ganguly Short-pulse excited DBDs are viable sources of UV, VUV radiation and radical flux at low gas temperatures for material processing applications. In this work, a 20{\%} H$_{2}$/Ar short-pulse (15 ns FWHM) excited DBD was operated between 5-50 Torr, 6-8 kV, and 5 kHz repetition rate. Diode-Laser Absorption Spectroscopy was used to obtain Ar 1s$_{3}\to $2p$_{2}$ transition profiles near 772.4 nm for bulk gas temperature and metastable line density measurements which are important for estimating both the power deposition efficiency into electronic states and the E/n. Absorption profiles obtained below 30 Torr were used to extract gas temperature, collisional Lorentzian linewidth, and absolute Ar line densities using standard iterative lineshape fitting techniques. In accordance with Lindholm-Foley T$^{0.3}$ scaling law for van der Waals interactions, we used the Lorentzian linewidths to obtain the pressure broadening coefficient for this gas mixture, which was found to be in agreement with the value for pure argon. Temperature and Ar* density were extracted from the pressure-broadened 50 Torr profile using an accurate method which self-consistently incorporates knowledge of the collisional line broadening parameter, the Doppler component, and the Voigt linewidth. At 50 Torr, we also estimated the energy deposition efficiency of direct electron impact metastable production based upon time-resolved power measurements and absolute Ar metastable line density. [Preview Abstract] |
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FM.00053: Two-dimensional numerical study of atmospheric pressure glows in helium Peng Zhang, Uwe Kortshagen Atmospheric pressure glow discharges (APGs) have attracted significant attention due to their spatially homogenous plasma properties. Unfortunately, at atmospheric pressure a glow discharge has a strong tendency to transform into a non-uniform filamentary dielectric barrier discharge (DBD). The transition between filamentary DBDs and uniform APGs is studied by a two-dimensional fluid model. The results show that the discharge structure is affected by many operating parameters, including the dielectric constant and the thickness of the barriers, the driving frequency, and the voltage amplitude. For instance, an increase in the applied low-frequency voltage leads to an increase in the number of plasma filaments. In addition, the influence of the gas properties such as the ionization coefficient, and the mobility and diffusion coefficients of charge carriers is investigated. It is found that a uniform glow discharge is more easily achieved in a gas with higher ionization coefficient at a relatively low electric field. The ion transport properties have a larger influence on the discharge structure than those of the electrons. [Preview Abstract] |
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FM.00054: On the mechanism of hollow-needle to plate atmospheric-pressure DC discharge Milan Simek, Stanislav Pekarek Hollow needle to plate electrical discharge at atmospheric pressure with a supply of gaseous medium through the needle electrode is frequently studied for a variety of ecological applications. We explored various combinations of the mass flow and DC driving voltage in order to find limits of stable discharge operation. In pure nitrogen, we observed only two basic discharge modes. In the case of the needle biased negatively and at low energy dissipated between electrodes, the discharge is restricted to the small area surrounding the needle cathode. It takes the shape of a short continuous luminous jet, which is directed towards anode. At higher dissipated energy, the discharge is more complex. The luminous jet becomes longer and, simultaneously, the gap between the tip of the jet and the anode surface is frequently bridged by very thin filamentary discharges. In the case of the needle biased positively and at low dissipated energy, the discharge resembles a diffuse weekly luminous cone bridging completely the gap. With increasing energy, the continuous cone is superimposed with pulsed luminous filamentary discharges. [Preview Abstract] |
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FM.00055: Experimental and computational study of gas temperature characteristics for atmospheric-pressure microgap discharge Akihiro Kono, Tomoyuki Shibata, Mitsutoshi Aramaki We are studying microwave-excited atmospheric-pressure high-density nonthermal plasma produced in the microgap between knife-edge electrodes, aiming at an application to VUV light source. The gas temperature is an important parameter for such an application and has been studied experimentally (from optical emission) and computationally for air and He discharges. In a previous presentation [1], we reported that a gas dynamic simulation indicates the existence of strong convection caused by a large temperature difference between the plasma center and the wall. However, detained reanalysis indicated that this convention was an artifacts caused by a particular discretization method of the pressure term. Here, we show, reanalysis of the previous results by a new code and extend the work to include Ar plasmas as well as to include the case of using new electrode system, in which gas blows out from the edge of the electrode. (Work supported by Grant-in-aid 15075205 from MEXT Japan)\newline \newline [1] A. Kono, GEC2004, Bul. Am. Phys. Soc. 49, 76 (2004). [Preview Abstract] |
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FM.00056: Time-Resolved Studies of Fast-Pulsed Dielectric Barrier Discharges Jose Lopez, Robert J. Leiweke, Peter Bletzinger, James M. Williamson, Abraham Belkind, Kurt H. Becker, Biswa N. Ganguly Dielectric Barrier Discharges (DBDs) produce highly non- equilibrium plasmas that allow for the effective generation of ions, excited species, and radicals from energetic electron-driven processes. In an effort to improve the production of the excited species, radicals, and UV radiation, which is strongly influenced by the reduced electric field, it is more effective to use a pulsed high voltage of very short duration, particularly if the aim is to keep the gas temperature low. In order to better understand this physical phenomenon, time-resolved electrical measurements in conjunction with the established methods of time-resolved optical emission spectroscopy (TR-OES) and time-resolved diode laser absorption spectroscopy (TR-DLAS) were utilized to characterize the fast-pulsed discharge. As an additional investigative method, an ICCD camera was used for time-resolved imaging studies. [Preview Abstract] |
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FM.00057: Electrical properties of TiO$_{2}$ in a dielectric barrier discharge Olivier Guaitella, Antoine Rousseau The efficiency of plasma and photocatalyst (TiO$_{2})$ combination for volatile organic compounds removal is now proved in atmospheric pressure DBD in air [1]. This efficiency may be due to chemical activity of TiO$_{2}$ as well as geometry of the surface or electrical properties of this material. A complete study of electrical properties is performed to check how TiO$_{2}$ changes discharge current in a DBD. The average injected energy is compared in plasma, plasma + UV lamp, plasma + TiO$_{2}$, plasma + TiO$_{2}$ + UV. Then, a statistical study of current peak amplitudes is carried out at different times during one period of the sinusoidal power supply (50Hz). Several populations of current peaks are observed during the positive half period and the negative one. These populations change with and without TiO$_{2}$ even for the same averaged injected energy and may be a reason for the depolluting efficiency of plasma/TiO$_{2}$ combination. [1] Kang et al, \textit{Journal of Molecular Catalysis} (\textbf{2002}) [Preview Abstract] |
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FM.00058: Microdischarge-assisted ignition of large volume dielectric barrier atmospheric pressure glow (DB-APG) discharge Jichul Shin, Laxminarayan Raja Ignition of large-volume dielectric-barrier discharge (DBD) in the presence of dc microdischarges is studied with pure helium and pure nitrogen gas. A hybrid configuration that consists of a classical parallel-plate DBD and an array of microdischarges is used in this study. Microdischarges provide seed species (charged and radical) that allow for a low voltage (non-classical) breakdown of the dielectric-barrier gap. With microdischarges being turned on, both helium and nitrogen DBD ignite with a confined discharge that is localized above the microdischarge holes at as low as 50 {\%} of breakdown voltage without the presence of microdischarges. In nitrogen gas, the localized discharge is much more confined than helium. Intensified CCD image provides an understanding of the structure of localized discharge. I-V characteristics suggest that the localized discharge has a glow-like character, with estimated electron densities ($\sim $10$^{17 }$m$^{-3})$ that are typical of a regular DB-APG discharge. Higher microdischarge power makes the localized discharge slighly more intense and the geometric configuration of microdischarge array gives some effect with increasing packing densities of localized discharge resulting in a lower DBD breakdown voltage. This study suggests that low-voltage (less than a regular DB-APG), large-volume operation of DB-APG is possible using an array of microdischarges that covers the entire electrode plane. [Preview Abstract] |
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FM.00059: Secondary ionization coefficient and electron reflection coefficient of MgO electrode Susumu Suzuki, Haruo Itoh Secondary ionization coefficient $\gamma $ of MgO in Ar was determined using the Townsend's criterion[1] and the starting voltage of self- sustaining discharge between MgO electrodes in the plasma display panel (PDP) cell. Electron transport characteristics in the cell were also investigated under the driving condition of the PDP cell by the Monte Carlo Simulation (MCS). In this condition, the nonequilibrium electron energy distributions were recognized in the results. Therefore, the secondary ionization coefficient was about 20{\%} larger than that in the case of energy equilibrium. In addition, $\gamma $ slightly became small with an increase in initial energy of electron emitted from the cathode[1]. The secondary ionization coefficient was defined as the product of the secondary electron emission coefficient in vacuum and the electron transmission coefficient $T $in gases. We investigate on the influence of the electron reflection at the cathode and anode on the secondary ionization coefficient and electric power injection in the PDP cell. The result is shown that the secondary ionization coefficient is independent of the electron reflection at the electrode. Furthermore, the increases in electron reflection coefficient at the cathode and the anode give high values of the electric power injection and the delay of the time response of the electron flux at the anode, respectively. \newline [1] S.Suzuki and H.Itoh: Jpn.J.Appl.Phys., \textbf{43}, 10 (2004) 7234-7239. [Preview Abstract] |
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FM.00060: Observation of N$_{4}^{+}$ recombination at near atmospheric pressure S.F. Adams, C.A. DeJoseph, Jr., J.M. Williamson We previously reported our initial modeling results of the N$_{4}^{+}$ + e$^{-}$ recombination observed by monitoring the time-resolved N$_{2}$ emission (GEC03, paper SRP 24). The N$_{2}$ 2nd positive (C $^{3}\Pi _{u}$ -- B $^{3}\Pi _{g})$ and N$_{2}^{+}$ 1$^{st}$ negative (B$^{2}\Sigma _{u}^{+}$-X$^{2}\Sigma _{g})$ emission was measured following laser resonance-enhanced multi-photon ionization (REMPI) of N$_{2}$ at near-atmospheric pressure. N$_{4}^{+}$ is produced by the three-body association reaction of N$_{2}^{+}$ + N$_{2}$ which occurs rapidly at these pressures. Two types of fluorescence are observed following irradiation of N$_{2}$ by the laser pulse. A ``prompt'' fluorescence composed primarily of emission from the N$_{2}^{+}$ 1$^{st}$ negative system (B $^{2}\Sigma _{u}^{+}$-X $^{2}\Sigma _{g})$ followed by a ``delayed'' fluorescence form the aforementioned N$_{2}$ (C-B). The preliminary modeling presented previously has been extended to include other key N$_{2}$ neutral and ionic species as well as the important loss channel of N$_{4}^{+}$ by laser photodissociation which had been neglected. The improved model along with additional N$_{2}^{+}$ LIF and N$_{4}^{+}$ UV photolysis results will be presented. [Preview Abstract] |
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FM.00061: Control of ionic species composition in complex plasmas dominated by charge exchange collisions Kostya Ostrikov A generic approach towards tailoring of ion species composition in reactive plasmas used for nanofabrication of various functional nanofilms and nano-assemblies, based on a simplified model of a parallel-plate rf discharge, is proposed. The model includes a reactive plasma containing two neutral and two ionic species interacting via charge exchange collisions in the presence of a microdispersed solid component (``dust''). It is shown that the number densities of the desired ionic species can be efficiently controlled by adjusting the dilution of the working gas in a buffer gas, rates of electron impact ionization, losses of plasma species on the discharge walls and surfaces of fine particles, charge excahnge rates, and efficiency of three-body recombination processes in the plasma bulk. The results are relevant to plasma-assisted fabrication of ordered patterns of carbon nanotip and other carbon-based nanostructures. [Preview Abstract] |
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FM.00062: Kinetic Modeling of Electric Discharge in a Preformed Air-Plasma Channel Tzvetelina Petrova, Harold Ladouceur, Andrew Baronavski Recent experimental studies of atmospheric discharges in a pre-existing plasma show that electrical breakdown occurs at relatively low electric fields ($\sim $5.7 kV/cm). This breakdown at such low fields cannot be explained in terms of the classical Paschen theory. To understand the physical mechanism of this phenomenon an extensive self-consistent collisional-radiative model for air plasma was developed. The model is based on the electron Boltzmann equation for the electron energy distribution function self-consistently coupled with the electron balance equation. The balance equations for various nitrogen and oxygen species in ground and excited states, as well as various atomic and molecular ions are incorporated. The model includes a variety of chemical reactions and plasma processes such as direct excitation and de-excitation, quenching, dissociation, ionization, attachment and detachment, charge exchange, and radiation. This system of equations was solved in a quasi-stationary regime and the self-consistent breakdown electric field and other plasma parameters were determined as a function of the initial degree of ionization. * NRC-NRL Postdoc Supported by Office of Naval Research. [Preview Abstract] |
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FM.00063: LIGHTNING PLASMAS |
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FM.00064: Basic Study of Discharge Simulation with Relaxation Process of Electron Swarm for Plasma Display Panel Yukio Murakami, Keiichi Kondo Plasma display panels (PDPs) with a thin profile and a wide screen are widely used in displays for digital high-definition television broadcasting, etc. For further popularization of PDPs, the vacuum ultraviolet (VUV) radiation mechanism in microdischarge cells is determined by discharge simulation with the aim of achieving a lower power consumption. Although in ordinary discharge simulations, a fluid model with local field approximation (LFA) is widely used, the possibility of new analysis considering the relaxation process of electron swarms for high-precision analysis under a markedly changing electric field in a cell- like alternating current (AC) type PDP or radio-frequency field is examined. The time-dependent Boltzmann equation, which is transformed to the matrix representation of the Burnett basis function, is used for the analysis of the relaxation processes. For rare and mixed gases, relaxation processes of electron energy distribution function (EEDF) and its swarm parameters, such as drift velocity and mean energy, in applying step and repetitive pulsed electric fields under the condition of conventional PDPs were calculated. Considering these relaxation processes in the near future, a high-precision simulation will be developed in which the analysis of the short time evolution of the EEDF is possible, and the VUV radiation mechanism will be clarified in detail expecting advancement in the search of the high-efficiency new discharge mode. [Preview Abstract] |
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FM.00065: Near IR Continuum Radiation From Metal Halide HID Lamps J.E. Lawler, M.T. Herd A recent study demonstrated that the near IR continuum from pure Hg High Intensity Discharge (HID) lamps is primarily due to electron- atom bremsstrahlung over a pressure range from 8 bar to more than 200 bar [1]. The study compared absolute spectroradiometric measurements to radiation transport simulations using new (larger) electron-Hg atom bremsstrahlung coefficients. The absence of significant molecular radiation in the near IR from 230 bar Ultra High Pressure lamps was unexpected. Near IR losses from Metal Halide (MH) HID lamps are typically 20 to 30{\%} of input power. A quantitative, microscopic understanding of these losses is very desirable since MH lamps are more and more widely used for general illumination. The near IR from MH lamps is emitted by the arc core. It is composed of a strong continuum, many weak atomic lines, and negligible molecular radiation. In an effort to understand the Near IR losses from MH lamps, we are mapping the spatial and spectral dependence of this radiation. The maps are being compared to radiation transport simulations. Additives provide most of the free electrons in MH lamps, and additive segregation complicates the analysis of near IR emission. Our approach to this problem and progress to date will be described. \newline [1] J. E. Lawler, A. Koerber, and U. Weichmann, J. Phys. D: Appl. Phys., in press (2005). [Preview Abstract] |
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FM.00066: Development of a compact arc discharge light source for measurement of radicals Haruhiko Ito, Seigo Takashima, Hiroyuki Kano, Masaru Hori To measure the radicals in plasma processes by using ultraviolet absorption spectroscopy, the light source that has a continuous emission spectrum in ultraviolet range is necessary. However, the size of the light source that has been used so far is generally large. So, the installation of the measurement system to the process chamber was very difficult. Therefore, the miniaturization of the light source was required. In this study, the compact light source using an arc discharge has been developed. The size of the electrode of light source was 30mm or less in the diameter. The small slit on the cathode electrode could act as enhancement to keep arc discharge. However, when the arc discharge time became long, the fluctuation of arc discharge point at time was caused because the insulator was consumed, and stability was low. To improve the stabilization of the arc discharge, the insulator was removed. The decrease in the stability of the arc discharge caused by the consumption of the insulator could be evaded and so the stability of the light source was greatly improved. [Preview Abstract] |
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FM.00067: COMPUTATIONAL METHODS FOR PLASMAS |
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FM.00068: Convergence of particle-in-cell simulations Miles M. Turner Particle-in-cell simulations are widely used for benchmarking other simulation methods and other purposes where a highly accurate representation of the physics is desired. In such cases, it is necessary to establish, among other things, that the simulation is fully converged with respect to all numerical parameters. There are generally accepted criteria or rules of thumb for selecting the numerical parameters to be used in particle-in-cell simulation. In this paper, we show that there are cases where the usual rules of thumb do not deliver satisfactory convergence, and indeed that such convergence is difficult to achieve at all. These issues are associated with a degradation of the kinetic properties of the particle-in-cell simulation that occurs when Monte Carlo collisions are introduced. In particular, the rate of numerical thermalization is greatly increased when the frequency of Monte Carlo collisions is large. Since this thermalization rate is a function of the number of simulation particles, it follows that a much greater number of particles may be required than is commonly assumed. [Preview Abstract] |
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FM.00069: Spectroscopic characterization of an ultrashort laser driven Ar cluster target incorporating both Boltzmann and particle-in-cell models Manolo Sherrill, J. Abdallah, G. Csanak, E. Dodd, Y. Fukuda, Y. Faenov A model that solves simultaneously both the electron and atomic kinetics was used to generate a synthetic He$_{\alpha}$ and satellite X-ray spectra to characterize a high intensity ultrashort laser driven Ar cluster target experiment. In particular, level populations were obtained from a detailed collisional-radiative model where collisional rates were computed from a time varying electron distribution function obtained from the solution of the zero dimensional Boltzmann equation. In addition, a particle-in-cell simulation was used to model the laser interaction with the cluster target and provided the initial electron energy distribution function (EEDF) for the Boltzmann solver. This study suggests that an average high density of N$_{a}=3.2\times 10^{20}$ cm$^{-3}$ was held by the system for a time of 5.7 ps, and during this time the plasma was in a highly non-equilibrium state in both the EEDF and the ion level populations. Finally, this work provides evidence that cluster targets could produce X-ray radiation in the 100 femtosecond time scale. [Preview Abstract] |
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FM.00070: PLASMA AND NANOSTRUCTURAL MATERIALS |
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FM.00071: Nanofabrication of single-crystalline flat panel display microemitter arrays: a ``plasma-building unit'' approach Ken Ostrikov, Shuyan Xu This contribution is focused on PECVD systems used for nanofabrication of flat panel display microemitter arrays based on ordered patterns of single-crystalline carbon nanotip structures (CNSs). The fundamentals of the plasma-based nanofabrication of CNSs and other nanofilms and nanostructures are critically examined and compared with CVD processes. Specific features, challenges, and potential benefits of using the reactive plasma-based systems for relevant nanofabrication processes are analyzed by using the ``plasma-building unit'' approach that builds up on extensive experimental data on plasma diagnostics and nanofilm/nanostructure characterization, and numerical simulation of the species composition in the plasma (fluid models), ion interaction with ordered carbon nanotip patterns (MC simulation), and computations of chemical structure of single crystalline carbon nanotips (DFT technique). This approach is also applicable for nanoscale assembly of other carbon nanostructures, polymorphous silicon films, semiconductor quantum dot structures, and nano-crystalline bioceramics. Special attention is paid to control strategies of the building units in the plasma phase and on nanostructured deposition surfaces. The issues of tailoring the plasma and development of plasma nanofabrication facilities are also discussed. [Preview Abstract] |
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FM.00072: Simulation of ion deposition in nanofabrication of single-crystalline carbon nanotip electron field emitters Igor Levchenko, Ken Ostrikov Three-dimensional topography of microscopic ion fluxes in the reactive hydrocarbon-based plasma-aided nanofabrication of ordered arrays of vertically aligned single crystalline carbon nanotip microemitter structures is simulated by using a Monte-Carlo technique. The ion trajectories are computed by integrating the equations of motion in the electric field of a biased substrate. It is shown that the ion flux focusing onto carbon nanotips is more efficient under conditions of low potential drop U across the plasma sheath. Under low-U conditions, the ion current density onto the surface of nanotips is higher for higher-aspect-ratio nanotips and can exceed the mean ion current density onto the nanopattern in up to 5 times. This effect becomes less pronounced with increasing the substrate bias, with the current enhancement not exceeding 1.7. This value is higher in denser plasmas and behaves differently with the electron temperature depending on the substrate bias. When the substrate bias is low, the ion current decreases with the electron temperature, with the opposite tendency under high-U conditions. The results are relevant to the PECVD of ordered large-area nanopatterns of vertically aligned carbon nanotips, nanofibers, and nanopyramidal microemitter structures for flat panel display applications. [Preview Abstract] |
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