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Nanoparticle synthesis in pulsed low temperature discharges

Description: Silicon nitride powders with an average size as low as 7 nm are synthesized in a pulsed radio frequency glow discharge. The as-synthesized silicon nitride powder from a silane/ammonia plasma has a high hydrogen content and is sensitive to oxidation in air. Post-plasma heating of the powder in a vacuum results in nitrogen loss, giving silicon-rich powder. In contrast, heat treatment at 800 C for 20 minutes in an ammonia atmosphere (200 Torr pressure) yields a hydrogen-free powder which is stable with respect to atmospheric oxidation. Several approaches to synthesizing silicon carbide nano-size powders are presented. Experiments using silane/hydrocarbon plasmas produce particles with a high hydrogen content as demonstrated by Fourier transform infrared analysis. The hydrogen is present as both CH and SiH functionality. These powders are extremely air-sensitive. A second approach uses a gas mixture of methyltrichlorosilane and hydrogen. The particles have a low hydrogen content and resist oxidation. Particle morphology of the silicon carbide is more spherical and there is less agglomeration than is observed in the silicon nitride powder.
Date: June 1, 1996
Creator: Buss, R.J.
Partner: UNT Libraries Government Documents Department

Mechanical properties of melt-derived erbium oxide

Description: Erbium oxide (Er{sub 2}O{sub 3}) is a rare earth oxide that is chemically and thermally stable and has a melting point of 2,430 C. There is relatively little information available regarding single crystal growth of erbia or the properties of erbia. In this study, erbia single crystals have been grown in a Xenon Optical Floating Zone Unit (XeOFZ) capable of melting materials at temperatures up to 3,000 C. Erbia was melt synthesized in the XeOFZ unit in a container less fashion, proving for little chance of contamination. Crystals were grown in compressed air and in reducing atmospheres. A recurring problem with melt synthesis of erbia is the appearance of flakes at the edges of the melt zone during growth; these flakes disrupt the growth process. The processing details and an initial survey of the physical properties of erbia single crystals is discussed.
Date: December 31, 1998
Creator: Neuman, A.D.; Blacic, M.J.; Platero, M.; Romero, R.S.; McClellan, K.J. & Petrovic, J.J.
Partner: UNT Libraries Government Documents Department

Conveyor with rotary airlock apparatus

Description: This invention is comprised of an apparatus for transferring objects from a first region to a second region, the first and second regions having differing atmospheric environments. The apparatus includes a shell having an entrance and an exit, a conveyer belt running through the shell from the entrance to the exit, and a horizontally mounted `revolving door` with at least four vanes revolving about its axis. The inner surface of the shell and the top surface of the conveyer belt act as opposing walls of the `revolving door`. The conveyer belt dips as it passes under but against the revolving vanes so as not to interfere with them but to engage at least two of the vanes and define thereby a moving chamber. Preferably, the conveyer belt has ridges or grooves on its surface that engage the edges of the vanes and act to rotate the vane assembly. Conduits are provided that communicate with the interior of the shell and allow the adjustment of the atmosphere of the moving chamber or recovery of constituents of the atmosphere of the first region from the moving chamber before they escape to the second region.
Date: January 1, 1993
Creator: Kronbert, J.W.
Partner: UNT Libraries Government Documents Department

Implantation activation annealing of Si-implanted gallium nitride at temperatures > 1,100 C

Description: The activation annealing of Si-implanted GaN is reported for temperatures from 1,100 to 1,400 C. Although previous work has shown that Si-implanted GaN can be activated by a rapid thermal annealing at {approximately}1,100 C, it was also shown that significant damage remained in the crystal. Therefore, both AlN-encapsulated and uncapped Si-implanted GaN samples were annealed in a metal organic chemical vapor deposition system in a N{sub 2}/NH{sub 3} ambient to further assess the annealing process. Electrical Hall characterization shows increases in carrier density and mobility for annealing up to 1,300 C before degrading at 1,400 C due to decomposition of the GaN epilayer. Rutherford backscattering spectra show that the high annealing temperatures reduce the implantation induced damage profile but do not completely restore the as-grown crystallinity.
Date: June 1, 1997
Creator: Zolper, J.C.; Han, J. & Biefeld, R.M.
Partner: UNT Libraries Government Documents Department

Coherent V{sub 2}O{sub 3} precipitates in {alpha}-Al{sub 2}O{sub 3} co-implanted with vanadium and oxygen

Description: The oxides of vanadium VO{sub 2} and V{sub 2}O{sub 3} are of fundamental and practical interest since they undergo structural phase transitions during which large variations in their optical and electronic properties are observed. In the present work, the authors report the formation of buried precipitates of V{sub 2}O{sub 3} in sapphire by ion implantation and thermal annealing. It was found that the co-implantation of oxygen and vanadium was required in order to form nanophase V{sub 2}O{sub 3} precipitates. Additionally, these precipitates, which formed only following an anneal of the co-implanted sample under reducing conditions, are coherent with the sapphire lattice. Two epitaxial relationships were observed: (0001)V{sub 2}O{sub 3}//(0001) {alpha}-Al{sub 2}O{sub 3} and (11--20)V{sub 2}O{sub 3}//(0001) {alpha}-Al{sub 2}O{sub 3}. This finding is in agreement with results obtained elsewhere for thin films of V{sub 2}O{sub 3} deposited on c-axis-oriented sapphire.
Date: December 31, 1994
Creator: Gea, L.A.; Boatner, L.A.; Budai, J.D. & Rankin, J.
Partner: UNT Libraries Government Documents Department

Comparative hot carrier induced degradation in 0.25 {micro}m MOSFETs with H or D passivated interfaces

Description: Hot electron induced degradation in 0.25 {micro}m, n-channel MOSFETs annealed in H{sub 2} or D{sub 2} containing atmospheres is reported. Threshold voltage and channel transconductance variations correlate with the growth of the interface state density. The spectral density of the stress induced interface states in the Si bandgap does not depend upon the anneal gas but the transistor lifetime (for a 20% transconductance variation) is {approximately} 40 times shorter for H{sub 2} as opposed to D{sub 2} annealed devices.
Date: March 1, 1997
Creator: Autran, J.L.; Devine, R.A.B.; Warren, W.L. & Vanheusden, K.
Partner: UNT Libraries Government Documents Department

Wafer bonding of GaAs, InP, and Si annealed without hydrogen for advanced device technologies

Description: In this paper the authors report on the direct bonding of compound semiconductors and silicon annealed at low temperatures (400 C) using hydrogen and nitrogen. Pressure and temperature relationships on interface characteristics were investigated with high resolution transmission electron microscopy and energy dispersive x-ray spectroscopy. It was found that no morphology differences existed between hydrogen and nitrogen annealed samples. applying the N{sub 2} bonding process, 850nm bottom emitting vertical cavity surface emitting lasers (VCSELs), were bonded to a transparent AlGaAs substrate. Finally, high anneal temperatures (up to 450 C) and shear stress values (> 1.6 MPa) were obtained for GaAs bonded to Si using a dry (plasma) activation technique.
Date: October 1, 1997
Creator: Roberds, B.E.; Choquette, K.D.; Geib, K.M.; Kravitz, S.H.; Twesten, R.D. & Farrens, S.N.
Partner: UNT Libraries Government Documents Department

Environmental microcracking of [NZP] type ceramics

Description: NZP ceramics (sodium zirconium phosphate and its crystal structure analogs) have very low thermal expansion through a large temperature range. Some compositions, with a high degree of thermal expansion anisotropy, are prone to microcracking upon cooling to room temperature. The onset of microcracking is a function of sintering temperature and hence grain size. Subsequent thermal cycling affects the thermal expansion behavior of highly anisotropic compositions due to microcrack healing. Recently it has been determined that this microcracking behavior can be delayed or enhanced by controlling the atmosphere in which the ceramic is heated and cooled. The effects of various atmospheres on the thermal expansion of isotropic and anisotropic [NZP] compositions are presented.
Date: December 31, 1994
Creator: Jackson, T.B. & Porter, W.D.
Partner: UNT Libraries Government Documents Department

Need for a contamination control textbook

Description: Since the authors have become associated with contamination control technology they have repeatedly found themselves searching for technical information that was either never documented and therefore never reached a technical journal or was too specific to appear in a technical article. On countless occasions they have found other workers frustrated over the same lack of concise and up to date information in the relatively broad and interdisciplinary field of surface science, surface cleaning, and clean room operation and design. It is for these reasons that the authors wish to suggest formally that those engineers, chemists, technicians, and surface scientists working in this field collectively create a textbook that they may use as their first reference and teaching book. The text of this paper suggests a topical outline for a book and gives examples of the kinds of information that it should contain and the types of questions it should address. Included is an extensive bibliography recently collected showing the diversity of disciplines that those working in contamination control must be knowledgeable of and the variety of publications and journals in which these reports and articles are generally found.
Date: January 1, 1980
Creator: Stowers, I.F.; Patton, H.G. & Guntrum, S.K.
Partner: UNT Libraries Government Documents Department

Evidence for the Tribochemical Generation of Hydrogen From Higher Rank Coals

Description: Analysis of gases in sealed ampoules of higher rank Argonne Premium Coal Samples over a period of years has revealed the presence of significant (up to about 18%) constant amounts of hydrogen and increasing amounts of carbon dioxide. Comparison with the gas contents of sealed 55 gallon drums which have not been pulverized indicates that these gases came from activity following the collection of the samples. Several hypotheses are examined. The evidence indicates a possible tribochemical reaction involving fresh surface generated during pulverizing in the nitrogen atmosphere. It is probable that water reacts with the coal surface to release hydrogen. The oxygen from the water appears to bound to active sites, and later diffusion leads to formation and release of carbon dioxide.
Date: February 1994
Creator: Vorres, Karl S.
Partner: UNT Libraries Government Documents Department

The effect of selective absorption on coal conversion, October--December 1991

Description: The objectives of this report are to (1) determine the importance of the presence of added hydrogen donor compounds within the coal in the first stage of direct liquefaction processes; (2) determine the composition of the solvent absorbed by and present within the coal in the first stage of direct coal liquefaction.
Date: May 1, 1992
Creator: Larsen, J. W.; Lazarov, L. & Amui, J.
Partner: UNT Libraries Government Documents Department

Refractory metal welding using a 3.3 kW diode pumped Nd:YAG laser.

Description: Recent developments in multi-kilowatt continuous wave lasers allow fiber optic delivery to high-purity controlled atmosphere chambers and challenge electron beam welding with improvements in cost, complexity, beam quality and flexibility. Questions remain with respect to the performance of these lasers for refractory alloy welding regarding damaging back reflections, laser-plume interactions, and sufficiency of beam intensity and coupled energy. System performance for the welding of various refractory metal alloys and comparisons to electron beam welds will be presented.
Date: January 1, 2001
Creator: Carpenter, R. W. (Robert W.); Piltch, M. S. (Martin S.); Nemec, R. B. (Ronald B.) & Milewski, J. O. (John O.)
Partner: UNT Libraries Government Documents Department

Low Beam Voltage, 10 MW, L-Band Cluster Klystron

Description: Conceptual design of a multi-beam klystron (MBK) for possible ILC and Project X applications is presented. The chief distinction between this MBK design and existing 10-MW MBK's is the low operating voltage of 60 kV. There are at least four compelling reasons that justify development at this time of a low-voltage MBK, namely (1) no pulse transformer; (2) no oil tank for high-voltage components and for the tube socket; (3) no high-voltage cables; and (4) modulator would be a compact 60-kV IGBT switching circuit. The proposed klystron consists of four clusters containing six beams each. The tube has common input and output cavities for all 24 beams, and individual gain cavities for each cluster. A closely related optional configuration, also for a 10 MW tube, would involve four totally independent cavity clusters with four independent input cavities and four 2.5 MW output ports, all within a common magnetic circuit. This option has appeal because the output waveguides would not require a controlled atmosphere, and because it would be easier to achieve phase and amplitude stability as required in individual SC accelerator cavities.
Date: May 1, 2009
Creator: Teryaev, V.; Yakovlev, V. P.; Kazakov, S. & Hirshfield, J. L.
Partner: UNT Libraries Government Documents Department

TVA pilot greenhouse for waste heat research

Description: A pilot facility for evaluating the use of waste heat from power plants, both fossil-fueled and nuclear, to heat a greenhouse was designed and built at the TVA reservation at Muscle Shoals, Ala. The simulation of waste heat was from an electric hot water heater. The subjects to be evaluated included: greenhouse environmental control system operation during one year period under wide range of climatic conditions and the crop performance, i.e., yield and disease control under various controlled-environment conditions and with various rooting media conditions. The facility design, control instrumentation, tests performed, and operating conditions obtained for airflow, air temperature, and humidity are described. No information is included on the crops produced. It is concluded that the pilot facility is providing valuable guidelines for the design of a larger demonstration plant to be located at an operating power plant. (LCL)
Date: January 1, 1973
Creator: King, L.D. & Furlong, W.K.
Partner: UNT Libraries Government Documents Department

Effect of ambient gas pressure on pulsed laser ablation plume dynamics and ZnTe film growth

Description: Epitaxial thin films of nitrogen-doped p-ZnTe were grown on single-crystal, semi-insulating Ga-As substrates via pulsed laser ablation of a stoichiometric ZnTe target. Both low pressure nitrogen ambients and high vacuum were used. Results of in situ reflection high energy electron diffraction (RHEED) and time-resolved ion probe measurements have been compared with ex situ Hall effect and transmission electron microscopy (TEM) measurements. A strong correlation was observed between the nature of the film`s surface during growth (2-D vs. 3-D, assessed via RHEED) and the ambient gas pressures employed during deposition. The extended defect content (assessed via cross-sectional TEM) in the region >150 mn from the film/substrate interface was found to increase with the ambient gas pressure during deposition, which could not be explained by lattice mismatch alone. At sufficiently high pressures, misoriented, columnar grains developed which were not only consistent with the RHEED observations but also were correlated with a marked decrease in Hall mobility and a slight decrease in hole concentration. Ion probe measurements, which monitored the attenuation and slowing of the ion current arriving at the substrate surface, indicated that for increasing nitrogen pressure the fast (vacuum) velocity distribution splits into a distinct fast and two collisionally-slowed components or modes. Gas controlled variations in these components mirrored trends in electrical properties and microstructural measurements.
Date: December 1, 1995
Creator: Rouleau, C.M.; Lowndes, D.H.; Geohegan, D.B.; Allard, L.F.; Strauss, M.A.; Cao, S. et al.
Partner: UNT Libraries Government Documents Department

A design guide for energy-efficient research laboratories

Description: This document--A Design Guide for Energy-Efficient Research Laboratories--provides a detailed and holistic framework to assist designers and energy managers in identifying and applying advanced energy-efficiency features in laboratory-type environments. The Guide fills an important void in the general literature and compliments existing in-depth technical manuals. Considerable information is available pertaining to overall laboratory design issues, but no single document focuses comprehensively on energy issues in these highly specialized environments. Furthermore, practitioners may utilize many antiquated rules of thumb, which often inadvertently cause energy inefficiency. The Guide helps its user to: introduce energy decision-making into the earliest phases of the design process, access the literature of pertinent issues, and become aware of debates and issues on related topics. The Guide does focus on individual technologies, as well as control systems, and important operational factors such as building commissioning. However, most importantly, the Guide is intended to foster a systems perspective (e.g. right sizing) and to present current leading-edge, energy-efficient design practices and principles.
Date: September 24, 1996
Creator: Wishner, N.; Chen, A.; Cook, L.; Bell, G.C.; Mills, E.; Sartor, D. et al.
Partner: UNT Libraries Government Documents Department

Deposition of mullite and mullite-like coatings on silicon carbide by dual-source metal plasma immersion. Topical report, October 1995--September 1996

Description: Mullite and mullite-like coatings on silicon carbide have been produced by a Metal Plasma Immersion Ion Implantation and Deposition (Mepiiid) technique based on two cathodic vacuum arc sources and concurrent pulse biasing of the substrate in an oxygen atmosphere. The deposition was carried out at oxygen partial pressures of between 0.66 and 3.33 Pa. The Al:Si ratio in the films varied from 1:1 to 8:1 and was controlled by varying the pulse duration of the separate plasma guns. High bias voltage was used early in the deposition process in order to produce atomic mixing at the film-substrate interface, while lower bias voltage was used later in the deposition; low ion energy allows control of the physical properties of the film as well as faster deposition rates. The as-deposited films were amorphous, and crystalline mullite was formed by subsequent annealing at 1,100 C for 2 hours in air. Strong adhesion between the mullite and the SiC was achieved, in some cases exceeding the 70 MPa instrumental limit of the pull-tester.
Date: April 1, 1997
Creator: Brown, I.G. & Monteiro, O.R.
Partner: UNT Libraries Government Documents Department

Laser welding of aluminum alloys

Description: Recent interest in reducing the weight of automobiles to increase fuel mileage has focused attention on the use of aluminum and associated joining technologies. Laser beam welding is one of the more promising methods for high speed welding of aluminum. Consequently, substantial effort has been expended in attempting to develop a robust laser beam welding process. Early results have not been very consistent in the process requirements but more definitive data has been produced recently. This paper reviews the process parameters needed to obtain consistent laser welds on 5,000 series aluminum alloys and discusses the research necessary to make laser processing of aluminum a reality for automotive applications.
Date: March 1, 1997
Creator: Leong, K.H.; Sabo, K.R.; Sanders, P.G. & Spawr, W.J.
Partner: UNT Libraries Government Documents Department

Brookhaven National Laboratory free-air carbon dioxide enrichment forest prototype -- Interim report

Description: A variety of approaches have been used in fumigation experiments to quantify the effects of increasing atmospheric carbon dioxide concentration ([CO{sub 2}]{sub atm}) on plants. Mot of these approaches, reviewed elsewhere (Allen 1992), entail some type of enclosure or chamber. Chambers provide containment of the CO{sub 2}-enriched air and in this way reduce the amount of CO{sub 2} required for the experiment. At the same time, chambers alter microclimate conditions in a variety of ways so that there is a significant chamber effect on the plants within. Free-air carbon dioxide enrichment (FACE) is an alternative experimental strategy in which CO{sub 2}-enriched air is released into the ambient environment in such a way as to provide effective experimental control over [CO{sub 2}]{sub atm} without causing any change in other environmental variables. Early types of free-air exposure systems were built in the Netherlands and England for exposing vegetation to elevated concentrations of atmospheric trace gases. The FACE Program at Brookhaven National Laboratory (BNL) considered these original ideas in designing the BNL FACE systems. The purpose of the current BNL project in the Duke Forest is to develop a FACE system that can provide adequate control over [CO{sub 2}]{sub atm} in a tall forest setting. This report is a preliminary overview of the data and much remains to be done in the analysis.
Date: August 1, 1994
Creator: Hendrey, G.R.; Lewin, K.F. & Nagy, J.
Partner: UNT Libraries Government Documents Department

Hot forging of graphite-carbide composites. Final report

Description: This project was aimed at hot shaping of titanium carbide/graphite and vanadium carbide/graphite composite materials by heating them to above 2000 degrees celsius and pressing into an electrographite die. The sample was to be a preformed cylinder of powdered graphite mixed with powdered titanium or vanadium, lightly sintered. The preform would be heated in a hot press and the titanium or vanadium would react with some of the graphite to form titanium or vanadium carbide. The remaining (excess) graphite would form a composite with the carbide, and this could then be deformed plastically at temperatures well below the onset of plasticity in pure graphite. There were to be two major thrusts in the research: In the first, an electron beam furnace at Sandia Laboratory was to be used for rapid heating of the sample, which would then be transferred into the press. The second thrust was to be entirely at Alabama A and M University, and here they intended to use a heated, controlled atmosphere press to forge the graphite/carbide preforms at a steady temperature and measure their viscosity as a function of temperature. This report discusses the progress made on this project.
Date: July 15, 1998
Creator: Jenkins, G.M. & Holland, L.R.
Partner: UNT Libraries Government Documents Department

Photosynthetic acclimation to elevated carbon dioxide: Basis for variability among plants. Final technical report, September 1, 1988--April 30, 1992

Description: The objective of this research was to investigate the acclimation phenomena involved in plants as they adjust to a CO{sub 2} enriched atmosphere. Plants were grown under various CO{sub 2} concentrations in the controlled chambers of the Duke University Phytotron. Soil nutrients, irradiance, temperature, soil water, and atmospheric relative humidity were controlled. Photosynthesis, leaf structure, leaf biomass of photosynthetic leaves or leaflets and of growth points that are not assimilating CO{sub 2} were measured to determine contributions of carbon source tissues to sink tissues. Export and import rates following movement of plants into atmospheres of higher carbon dioxide concentration were specifically examined.
Date: March 30, 1998
Creator: Cure, J.
Partner: UNT Libraries Government Documents Department

Long term drift studies of Sandia H{sub 2} sensor in reducing atmospheres

Description: A study of the drift in Pd/Ni alloy hydrogen sensitive resistor and transistor responses is presented. The sensors were monitored for a period of 6 months in a reducing atmosphere of 0.1% H{sub 2} in N{sub 2} with periodic calibration exposures. A comparison of a resistor film with an adhesion layer showed considerable improvement in diminishing the drift.
Date: April 1, 2000
Creator: JENKINS,MARK W.; HUGHES,ROBERT C. & PATEL,SANJAY V.
Partner: UNT Libraries Government Documents Department

Growth of highly doped p-type ZnTe films by pulsed laser ablation in molecular nitrogen

Description: Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N{sub 2} ambient without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range were obtained for a range of nitrogen pressures The maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. The highest hole mobilities were attained for nitrogen pressures of 50--100 mTorr ({approximately}6.5-13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N{sub 2} do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg > 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe{sub l-x}S{sub x} films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.
Date: April 1, 1995
Creator: Lowndes, D.H.; Rouleau, C.M.; Budai, J.D.; Poker, D.B.; Geohegan, D.B.; Zhu, Shen et al.
Partner: UNT Libraries Government Documents Department