19 Matching Results

Search Results

Advanced search parameters have been applied.

Nucleation of nanocrystalline diamond by fragmentation of fullerene precursors.

Description: Growth of diamond films from C{sub 60}/Ar microwave discharges results in a nanocrystalline microstructure with crystallite sizes in the range 3-10 nm. Heterogeneous nucleation rates of 10{sup 10} cm{sup {minus}2} sec are required to account for the results. The nucleation mechanism presented here fulfills this requirement and is based on the insertion of carbon dimer, C{sub 2}, molecules, produced by fragmentation of C{sub 60}, into the n-bonded dimer rows of the reconstructed (100) surface of diamond. Density functional theory is used to calculate the energetic of C{sub 2} insertion into carbon clusters that model the (100) surface. The reaction of singlet C{sub 2} with the double bond of the C{sub 9}H{sub 12} cluster leads to either carbene structures or a cyclobutynelike structure. At the HF/6-31G* level, the carbene product has a C{sub 2v} structure, while at the B3LYP/6-31G* levels of theory, it has a C{sub s} structure with the inserted C{sub 2} tilted. No barrier for insertion into the C=C double bond of the C{sub 9}H{sub 12} cluster was found at the HF/6-31G* and B3LYP/6-31G* levels of theory. Thus, calculations including correlation energy and geometry optimization indicate that insertion of C{sub 2} into a C=C double bond leads to a large energy lowering, {approximately}120 kcal/mol for a C{sub 9}H{sub 12} cluster, and there is no barrier for insertion.
Date: May 4, 1998
Creator: Gruen, D. M.
Partner: UNT Libraries Government Documents Department

Plasma and Ion Sources in Large Area Coatings: A Review

Description: Efficient deposition of high-quality coatings often requires controlled application of excited or ionized particles. These particles are either condensing (film-forming) or assisting by providing energy and momentum to the film growth process, resulting in densification, sputtering/etching, modification of stress, roughness, texture, etc. In this review, the technical means are surveyed enabling large area application of ions and plasmas, with ion energies ranging from a few eV to a few keV. Both semiconductortype large area (single wafer or batch processing with {approx} 1000 cm{sup 2}) and in-line web and glass-coating-type large area (> 10{sup 7} m{sup 2} annually) are considered. Characteristics and differences between plasma and ion sources are explained. The latter include gridded and gridless sources. Many examples are given, including sources based on DC, RF, and microwave discharges, some with special geometries like hollow cathodes and E x B configurations.
Date: February 28, 2005
Creator: Anders, Andre
Partner: UNT Libraries Government Documents Department

Design of microwave vitrification systems for radioactive waste

Description: Oak Ridge National Laboratory (ORNL) is involved in the research and development of high-power microwave heating systems for the vitrification of DOE radioactive sludges. Design criteria for a continuous microwave vitrification system capable of processing a surrogate filtercake sludge representative of a typical waste-water treatment operation are discussed. A prototype 915 MHz, 75 kW microwave vitrification system or `microwave melter` is described along with some early experimental results that demonstrate a 4 to 1 volume reduction of a surrogate ORNL filtercake sludge.
Date: April 1, 1996
Creator: White, T.L.; Wilson, C.T.; Schaick, C.R. & Bostick, W.D.
Partner: UNT Libraries Government Documents Department

Ion energy distribution functions in inductively coupled RF discharges in mixtures of chlorine and boron trichloride

Description: Plasma discharges involving mixtures of chlorine and boron trichloride are widely used to etch metals in the production of very-large-scale-integrated circuits. Energetic ions play a critical role in this process, influencing the etch rates, etch profiles, and selectivity to different materials. The authors are using a gridded energy analyzer to measure positive ion energy distributions and fluxes at the grounded electrode of high-density inductively-coupled rf discharges. In this paper, they present details of ion energies and fluxes in discharges containing mixtures of chlorine and boron trichloride.
Date: February 1, 1997
Creator: Woodworth, J.R.; Nichols, C.A. & Hamilton, T.W.
Partner: UNT Libraries Government Documents Department

Time-resolved infrared absorption studies of the dynamics of radical reactions.

Description: There is very little information available about the dynamics of radical+radical interactions. These processes are important in combustion being chain termination steps as well as generating new molecular species. To study these processes, a new experimental apparatus has been constructed to investigate radical-radical dynamics. The first radical or atomic species is produced with a known concentration in a microwave discharge flow system. The second is produced by pulsed laser photolysis of a suitable photolyte. The time dependence of individual rovibrational states of the product is followed by absorption of a continuous infrared laser. This approach will allow the reaction of interest to be differentiated from other radical reactions occurring simultaneously. The experimental approach is highly versatile, being able to detect a number of molecular species of particular interest to combustion processes such as water, methane, acetylene etc. at the state specific level. State specific infrared absorption coefficients of radicals can be measured in situ allowing for the determination of the absolute concentrations and hence branching ratios for reactions having multiple reaction pathways.
Date: March 6, 1998
Creator: MacDonald, R. G.
Partner: UNT Libraries Government Documents Department

Electron density and collision frequency of microwave resonant cavity produced discharges. [Progress report]

Description: This progress report consists of an article, the abstract of which follows, and apparently the references and vita from a proposal. A review of perturbation diagnostics applied to microwave resonant cavity discharges is presented. The classical microwave perturbation technique examines the shift in the resonant frequency and cavity quality factor of the resonant cavity caused by low electron density discharges. However, modifications presented here allow the analysis to be applied to discharges with electron densities beyond the limit predicted by perturbation theory. An {open_quote}exact{close_quote} perturbation analysis is presented which models the discharge as a separate dielectric, thereby removing the restrictions on electron density imposed by the classical technique. The {open_quote}exact{close_quote} method also uses measurements of the shifts in the resonant conditions of the cavity. Thirdly, an electromagnetic analysis is presented which uses a characteristic equation, based upon Maxwell`s laws, and predicts the discharge conductivity based upon measurements of a complex axial wave number. By allowing the axial wave number of the electromagnetic fields to be complex, the fields are experimentally and theoretically shown to be spatially attenuated. The diagnostics are applied to continuous-wave microwave (2.45 GHz) discharges produced in an Asmussen resonant cavity. Double Langmuir probes, placed directly in the discharge at the point where the radial electric field is zero, act as a comparison with the analytic diagnostics. Microwave powers ranging from 30 to 100 watts produce helium and nitrogen discharges with pressures ranging from 0.5 to 6 torr. Analysis of the data predicts electron temperatures from 5 to 20 eV, electron densities from 10{sup 11} to 3 {times} 10{sup 12} cm{sup {minus}3}, and collision frequencies from 10{sup 9} to 10{sup 11} sec{sup {minus}1}.
Date: December 31, 1992
Creator: McColl, W.; Brooks, C. & Brake, M. L.
Partner: UNT Libraries Government Documents Department

Large-Volume Resonant Microwave Discharge for Plasma Cleaning of a CEBAF 5-Cell SRF Cavity

Description: We report the preliminary results on plasma generation in a 5-cell CEBAF superconducting radio-frequency (SRF) cavity for the application of cavity interior surface cleaning. CEBAF currently has {approx}300 of these five cell cavities installed in the Jefferson Lab accelerator which are mostly limited by cavity surface contamination. The development of an in-situ cavity surface cleaning method utilizing a resonant microwave discharge could lead to significant CEBAF accelerator performance improvement. This microwave discharge is currently being used for the development of a set of plasma cleaning procedures targeted to the removal of various organic, metal and metal oxide impurities. These contaminants are responsible for the increase of surface resistance and the reduction of RF performance in installed cavities. The CEBAF five cell cavity volume is {approx} 0.5 m2, which places the discharge in the category of large-volume plasmas. CEBAF cavity has a cylindrical symmetry, but its elliptical shape and transversal power coupling makes it an unusual plasma application, which requires special consideration of microwave breakdown. Our preliminary study includes microwave breakdown and optical spectroscopy, which was used to define the operating pressure range and the rate of removal of organic impurities.
Date: July 1, 2012
Creator: J. Mammosser, S. Ahmed, K. Macha, J. Upadhyay, M. Nikoli, S. Popovi, L. Vuakovi
Partner: UNT Libraries Government Documents Department

Atmospheric Pressure Plasma Process And Applications

Description: This paper provides a general discussion of atmospheric-pressure plasma generation, processes, and applications. There are two distinct categories of atmospheric-pressure plasmas: thermal and nonthermal. Thermal atmospheric-pressure plasmas include those produced in high intensity arcs, plasma torches, or in high intensity, high frequency discharges. Although nonthermal plasmas are at room temperatures, they are extremely effective in producing activated species, e.g., free radicals and excited state atoms. Thus, both thermal and nonthermal atmosphericpressure plasmas are finding applications in a wide variety of industrial processes, e.g. waste destruction, material recovery, extractive metallurgy, powder synthesis, and energy conversion. A brief discussion of recent plasma technology research and development activities at the Idaho National Laboratory is included.
Date: September 1, 2006
Creator: Kong, Peter C. & Myrtle
Partner: UNT Libraries Government Documents Department

High-intensity sources for light ions

Description: The use of the multicusp plasma generator as a source of light ions is described. By employing radio-frequency induction discharge, the performance of the multicusp source is greatly improved, both in lifetime and in high brightness H{sup +} and H{sup {minus}} beam production. A new technique for generating multiply-charged ions in this type of ion source is also presented.
Date: October 1, 1995
Creator: Leung, K.N.
Partner: UNT Libraries Government Documents Department

Advanced aircraft ignition CRADA final report

Description: Conventional commercial and military turbo-jet aircraft engines use capacitive discharge ignition systems to initiate fuel combustion. The fuel-rich conditions required to ensure engine re-ignition during flight yield less than optimal engine performance, which in turn reduces fuel economy and generates considerable pollution in the exhaust. Los Alamos investigated two approaches to advanced ignition: laser based and microwave based. The laser based approach is fuel ignition via laser-spark breakdown and via photo-dissociation of fuel hydrocarbons and oxygen. The microwave approach involves modeling, and if necessary redesigning, a combustor shape to form a low-Q microwave cavity, which will ensure microwave breakdown of the air/fuel mixture just ahead of the nozzle with or without a catalyst coating. This approach will also conduct radio-frequency (RF) heating of ceramic elements that have large loss tangents. Replacing conventional systems with either of these two new systems should yield combustion in leaner jet fuel/air mixtures. As a result, the aircraft would operate with (1) considerable less exhaust pollution, (2) lower engine maintenance, and (3) significantly higher fuel economy.
Date: March 1, 1997
Creator: Early, J.W.
Partner: UNT Libraries Government Documents Department

Photoionization-photoelectron research.

Description: In the broad sense of a general definition, the fundamental goal of this research program is to explore, understand, and utilize the basic processes of interaction of vacuum UV light with atoms and molecules. In practical terms, this program uses photoionization mass spectrometry and other related techniques to study chemically relevant transient and metastable species that are intimately connected to energy-producing processes, such as combustion, or play-prominent roles in the associated environmental issues. Some recent examples of species that have been studied are: CH{sub 3}, CH{sub 2}, CH{sub 3}O, CH{sub 2}OH, CH{sub 3}S, CH{sub 2}SH, HCS, HNCO, NCO, HNCS, NCS, the isomers of C{sub 2}H{sub 5}O, HOBr, CF{sub 3} and CF{sub 3}OH. The ephemeral species of interest are produced in situ using various suitable techniques, such as sublimation, pyrolysis, microwave discharge, chemical abstraction reactions with H or F atoms, laser photodissociation, on-line synthesis, and others. The desired information is obtained by applying a variety of suitable photoionization methods, which use both conventional and coherent light sources in the vacuum W region. The spiritus movens of our studies is the need to provide the chemical community with essential information on the species of interest, such as accurate and reliable thermochemical, spectroscopic and structural data, and thus contribute to the global comprehension of the underlying chemical processes. The scientific motivation is also fueled by the necessity to unveil useful generalities, such as bonding patterns within a class of related compounds, or systematic behavior in the ubiquitous autoionization processes. In addition, the nature of the results obtained in this program is such that it generates a significant impetus for further theoretical work. The experimental work of this program is coordinated with other related experimental and theoretical efforts of the Chemical Dynamics Group to provide a broad perspective on this area of science.
Date: March 6, 1998
Creator: Ruscic, B.
Partner: UNT Libraries Government Documents Department

Buckyball microwave plasmas: Fragmentation and diamond-film growth

Description: Microwave discharges (2.45 GHz) have been generated in C{sub 60}-containing Ar produced by flowing Ar over fullerene-containing soot. Optical spectroscopy shows that the spectrum is dominated by the d{sup 3}{Pi}g-a{sup 3}{Pi}u Swan bands of C{sub 2} and particularly the {Delta}v = {minus}2, {minus}1, 0, +1, and +2 sequences. These results give direct evidence that C{sub 2} is one of the products of C{sub 60} fragmentation brought about, at least in part, by collisionally induced dissociation (CID). C{sub 60} has been used as a precursor in a plasma-enhanced chemical vapor deposition (PECVD) experiment to grow diamond-thin films. The films, grown in an Ar/H{sub 2} gas mixture (0.14% carbon content, 100 Torr, 20 sccm Ar, 4 sccm H{sub 2}, 1500 W, 850{degree}C substrate temperature), were characterized with SEM, XRD, and Raman spectroscopy. Growth rate was found to be {approx} 0.6 {mu}/hr. Assuming a linear dependence on carbon concentration, a growth rate at least six times higher than commonly observed using methane as a precursor, would be predicted at a carbon content of 1% based on C{sub 60}. Energetic and mechanistic arguments are advanced to rationalize this result based on C{sub 2} as the growth species.
Date: August 1, 1993
Creator: Gruen, D. M.; Liu, Shengzhong; Krauss, A. R. & Pan, Xianzheng
Partner: UNT Libraries Government Documents Department

Ion energy and angular distributions in inductively driven RF discharges in chlorine

Description: In this paper, the authors report values of ion energy distributions and ion angular distributions measured at the grounded electrode of an inductively-coupled discharge in pure chlorine gas. The inductive drive in the GEC reference cell produced high plasma densities (10{sup 11}/cm{sup 3} electron densities) and stable plasma potentials. As a result, ion energy distributions typically consisted of a single peak well separated from zero energy. Mean ion energy varied inversely with pressure, decreasing from 13 to 9 eV as the discharge pressure increased from 20 to 60 millitorr. Half-widths of the ion angular distributions in these experiments varied from 6 to 7.5 degrees, corresponding to transverse energies from 0.13 to 0.21 eV. Ion energies gradually dropped with time, probably due to the buildup of contaminants on the chamber walls. Cell temperature also was an important variable, with ion fluxes to the lower electrode increasing and the ion angular distribution narrowing as the cell temperature increased. Plasmas discharges are widely used to etch semiconductors, oxides and metals in the fabrication of integrated circuits.
Date: March 1, 1996
Creator: Woodworth, J.R.; Riley, M.E. & Hamilton, T.W.
Partner: UNT Libraries Government Documents Department

Plasma chemistries for dry etching GaN, AlN, InGaN and InAlN

Description: Etch rates up to 7,000 {angstrom}/min. for GaN are obtained in Cl{sub 2}/H{sub 2}/Ar or BCl{sub 3}/Ar ECR discharges at 1--3mTorr and moderate dc biases. Typical rates with HI/H{sub 2} are about a factor of three lower under the same conditions, while CH{sub 4}/H{sub 2} produces maximum rates of only {approximately}2,000 {angstrom}/min. The role of additives such as SF{sub 6}, N{sub 2}, H{sub 2} or Ar to the basic chlorine, bromine, iodine or methane-hydrogen plasma chemistries are discussed. Their effect can be either chemical (in forming volatile products with N) or physical (in breaking bonds or enhancing desorption of the etch products). The nitrides differ from conventional III-V`s in that bond-breaking to allow formation of the etch products is a critical factor. Threshold ion energies for the onset of etching of GaN, InGaN and InAlN are {ge} 75 eV.
Date: April 1, 1996
Creator: Pearton, S.J.; Vartuli, C.B.; Lee, J.W.; Donovan, S.M.; MacKenzie, J.D.; Abernathy, C.R. et al.
Partner: UNT Libraries Government Documents Department

Experiments and modeling with a large-area inductively coupled plasma (ICP) source

Description: We describe initial experiments with a large (30 in.) plasma source chamber to explore the problems associated with large-area Inductively coupled plasma (ICP) sources to produce high density plasmas useful for processing 400 mm semiconductor wafers. Our experiments typically use a 25 in. diameter planar ICP coil driven at 13.56 MHz. Plasma and system data are taken in Ar and N{sub 2} over the pressure range 3--50 mtorr. R.F. Inductive power was run up to 2000W, but typically data were taken over the range 100--1000W. Diagnostics Include optical emission spectroscopy, Langmuir probes, and B-dot probes as well as electrical circuit measurements. The B-dot and E-M measurements are compared with models based on commercial E-M codes. Initial indications are that uniform plasmas suitable for 400 mm processing are attainable. We present a comparison between computer modeling and experimental results for this source. Computer simulations using the fluid code INDUCT94 are used to explain variations In the plasma density profile measurements as a function of Inductive power, gas pressure and gas composition. Both Argon and Nitrogen discharges are modeled. INDUCT94 solves the 2D time-dependent fluid equations for electrons, ions and neutrals Including effects of both Inductive and capacitive coupling. Detailed volume and surface chemistry reactions are treated. We discuss the effects of pressure and power on plasma uniformity.
Date: June 1, 1995
Creator: Benjamin, R.D.; DiPeso, G.; Egan, P.O.; Parker, G.J.; Richardson, R.A. & Vitello, P.
Partner: UNT Libraries Government Documents Department

Electrical characterization of rf plasmas

Description: Radio-frequency (rf) electrical sources are commonly used to generate plasmas for processing of industrial materials and for related experimental work. Published descriptions of such plasmas usually include generator-power measurements, and occasionally include plasma dc-bias measurements. One or both of these quantitites are also used in industrial feedback ccontrol systems for setpoint regulation. Recent work at Sandia an elsewhere with an experimental rf discharge device (the GEC RF Reference Cell'') has shown that power and dc-bias levels are often insufficient information for specifying the state of the plasma. The plasma can have nonlinear electrical characteristics that cause harmonic generation, and the harmonic levels can depend sensitively on the impedance of the external circuitry at harmonic frequencies. Even though the harmonics may be low in amplitude, they can be directly related to large changes in plasma power and to changes in optical emission from the plasma. Consequently, in order for a worker to truly master the plasma-generation process, it is necessary to understand, measure, and control electrical characteristics of the plamsa. In this paper we describe technique that have been developed from work with the Reference Cell for making electrical measurements on rf plasmas, and we describe surprising observations of harmonic behavior. 10 refs., 4 figs.
Date: August 1, 1991
Creator: Miller, P.A.
Partner: UNT Libraries Government Documents Department

Microwave production of hydrogen and sulfur from hydrogen sulfide wastes

Description: A waste-treatment process is being developed that uses ``cold`` microwave plasma-chemical reactions to split hydrogen sulfide into elemental hydrogen and sulfur. A clean sulfur product can be recovered and sold, while product gases are purified and separated into seams containing hydrogen, hydrogen sulfide for recycle, and the process purge containing carbon dioxide and water. Experiments with pure hydrogen sulfide at 0.5 to 1.5 L/min flow rates and microwave powers of 400 to 1000 W confirmed that conversions of over 90% per pass at process energy requirements approaching 5 kcal/mol are possible. Experiments with impurities typical of petroleum refinery waste hydrogen sulfide streams have demonstrated that these impurities are compatible with the plasma dissociation process and that they do not create new waste treatment problems. This technology has a long-term potential for saving 40 to 70 {times} 10{sup 12} Btu/yr in the refining industry, for an economic savings of $500 million to $1000 million annually. Although the microwave process should show particular advantages for the petroleum refining industry, the low capital costs and modular nature of the new process should make it economically attractive in connection with the small-scale waste-treatment technologies currently used in the natural gas industry. Currently, in the U.S.S.R., a 500-kW demonstration microwave hydrogen sulfide treatment unit operating at near atmospheric pressure is being tested at the natural gas fields in Orenberg. 3 refs.
Date: January 1, 1992
Creator: Harkness, J. B. L. & Doctor, R. D.
Partner: UNT Libraries Government Documents Department

Potential applications of a new microwave ECR (electron cyclotron resonance) multicusp plasma ion source

Description: A new microwave electron cyclotron resonance (ECR) multicusp plasma ion source using two ECR plasma production regions and multicusp plasma confinement has been developed at Oak Ridge National Laboratory. This source has been operated to produce uniform and dense plasmas over large areas of 300 to 400 cm{sup 2}. The plasma source has been operated with continuous argon gas feed and pulsed microwave power. The discharge initiation phenomena and plasma properties have been investigated and studied as functions of discharge parameters. Together with the discharge characteristics observed, a hypothetical discharge mechanism for this plasma source is reported and discussed. Potential applications, including plasma and ion-beam processing for manufacturing advanced microelectronics and for space electric propulsion, are discussed. 7 refs., 6 figs.
Date: January 1, 1990
Creator: Tsai, C.C.
Partner: UNT Libraries Government Documents Department

Microwave production of hydrogen and sulfur from hydrogen sulfide wastes

Description: A waste-treatment process is being developed that uses cold'' microwave plasma-chemical reactions to split hydrogen sulfide into elemental hydrogen and sulfur. A clean sulfur product can be recovered and sold, while product gases are purified and separated into seams containing hydrogen, hydrogen sulfide for recycle, and the process purge containing carbon dioxide and water. Experiments with pure hydrogen sulfide at 0.5 to 1.5 L/min flow rates and microwave powers of 400 to 1000 W confirmed that conversions of over 90% per pass at process energy requirements approaching 5 kcal/mol are possible. Experiments with impurities typical of petroleum refinery waste hydrogen sulfide streams have demonstrated that these impurities are compatible with the plasma dissociation process and that they do not create new waste treatment problems. This technology has a long-term potential for saving 40 to 70 {times} 10{sup 12} Btu/yr in the refining industry, for an economic savings of $500 million to $1000 million annually. Although the microwave process should show particular advantages for the petroleum refining industry, the low capital costs and modular nature of the new process should make it economically attractive in connection with the small-scale waste-treatment technologies currently used in the natural gas industry. Currently, in the U.S.S.R., a 500-kW demonstration microwave hydrogen sulfide treatment unit operating at near atmospheric pressure is being tested at the natural gas fields in Orenberg. 3 refs.
Date: January 1, 1992
Creator: Harkness, J.B.L. & Doctor, R.D.
Partner: UNT Libraries Government Documents Department