482 Matching Results

Search Results

Advanced search parameters have been applied.

Diamonds and Conflict: Background, Policy, and Legislation

Description: This report discusses issues surrounding "conflict diamonds" -- i.e., diamonds that have been mined and sold to support armed conflict -- as well as resulting U.S. policy responses. Policy makers' attention has also increasingly focused on the possible role that diamonds may play in the financing of terrorist operations.
Date: July 16, 2003
Creator: Cook, Nicolas
Partner: UNT Libraries Government Documents Department

Hydrogen Storage in Nano-Phase Diamond at High Temperature and Its Release

Description: The objectives of this proposed research were: 91) Separation and storage of hydrogen on nanophase diamonds. It is expected that the produced hydrogen, which will be in a mixture, can be directed to a nanophase diamond system directly, which will not only store the hydrogen, but also separate it from the gas mixture, and (2) release of the stored hydrogen from the nanophase diamond.
Date: October 13, 2008
Creator: Ghosh, Tushar K
Partner: UNT Libraries Government Documents Department

HFCVD of diamond at low substrate and low filament temperatures

Description: It has been discovered that the addition of a small amount of oxygen to the CH{sub 4} and H{sub 2} feed gas permits HFCVD of diamond at significantly lower filament and substrate temperatures. The effective O/C ratio here is much lower than that used in most studies of the oxygen effect. Careful control of the O/C and C/H ratios were found to be crucial to success. The effects of substrate and filament temperatures on growth rate and film quality were studied. Optimum conditions were found that gave reasonable growth rates ( {approximately}0.5 {mu}m/h ) with high film quality at filament temperatures below 1750{degrees}C and substrate temperatures below 600C. As a result, low temperature deposition has been realized. Power consumption can be reduced 50%, and the filament lifetime is extended indefinitely.
Date: March 8, 1995
Creator: Tolt, Z. L.; Heatherly, L.; Clausing, R. E.; Shaw, R. W. & Feigerle, C. S.
Partner: UNT Libraries Government Documents Department

THERMAL EMITTANCE MEASUREMENT DESIGN FOR DIAMOND SECONDARY EMISSION.

Description: Thermal emittance is a very important characteristic of cathodes. A carefully designed method of measuring the thermal emittance of secondary emission from diamond is presented. Comparison of possible schemes is carried out by simulation, and the most accessible and accurate method and values are chosen. Systematic errors can be controlled and maintained at small values, and are carefully evaluated. Aberration and limitations of all equipment are taken into account.
Date: June 25, 2007
Creator: WU,Q.; BEN-ZVI, I.; BURRILL, A.; CHANG, X.; KAYRAN, D.; RAO, T. et al.
Partner: UNT Libraries Government Documents Department

Measurements and Calculations of Halfraum Radiation Drives at the Omega Laser

Description: Thin walled gold halfraums are a common choice for producing x-ray drives in experiments at high-power laser facilities. At the Omega Laser, we use 10 kJ of laser energy in a two-pulse sequence to generate halfraum drive temperatures of 160-190 eV for {approx}3ns. This type of drive is well characterized and reproducible, with characterization of the drive radiation temperature typically performed using the Dante diagnostic. Additionally, calibrated Photoconductive Diamond Detectors (PCDs) are used to measure the drive when it is desirable to utilize the Dante elsewhere in the experiment. Measurements of halfraum drives from both Dante and PCDs are compared with calculations, with good agreement. This agreement lends the calculations a predictive capability in designing further experiments utilizing halfraum drives.
Date: January 6, 2005
Creator: MacLaren, S A; Back, C A & Hammer, J H
Partner: UNT Libraries Government Documents Department

Wire Electrical Discharge Truing of Metal Bond Diamond Grinding Wheels

Description: Cylindrical wire EDM profile truing of the metal bond diamond wheel for precision form grinding of ceramics is presented in this report. First a corrosion-resistant, precise spindle with the high-electrical current capability for wire EDM truing of grinding wheel was fabricated. An arc profile was adopted in order to determine form tolerances capabilities of this process. Results show the wire EDM process can generate {micro}m-scale precision form on the diamond wheel efficiently. The wheel, after truing, was used to grind silicon nitride. Grinding forces, surface finish of ground components, and wheel wear were measured. The EDM trued wheel showed a reduction in grinding force from that of the stick dressed wheel. Surface finishes between the two truing methods were similar. In the beginning of the grinding, significant wheel wear rate was identified. The subsequent wheel wear rate stabilized and became considerably lower.
Date: January 24, 2002
Creator: McSpadden, SB
Partner: UNT Libraries Government Documents Department

Stability of the graphite and diamond phases of finite carbon cluster

Description: The stability of particulate carbon formed in the detonation of high explosives has been investigated with first principles and semiempirical molecular orbital calculations carried out on carbon clusters. The dangling surface bonds were capped wit/r hydrogen atoms and the surface contributions to the cohesive energy were removed by extrapolation as a function of the cluster size. Comparison of the calculated heat of formation of graphite and diamond particles as a function of size predicts that the graphite phase becomes more stable for IO<sup>4</sup> -10<sup5</sup> carbon atoms. Calculations were also carried out on geometry optimized carbon clusters without capping atoms, resulting in reconstructed cluster surfaces that may be a more realislic model for particulate carbon formed under the extreme conditions of detonation. The calculated energy barrier for tbe conversion of a graphitic cluster to the cubic diamond structure was in good agreement with calculations on b
Date: August 28, 1998
Creator: Ree, F & Winter, N W
Partner: UNT Libraries Government Documents Department

Testing of Critical Features of Polysilicon MEMS

Description: The behavior of MEMS devices is limited by the strength of critical features such as thin ligaments, oxide cuts joining layers, pin joints and hinges. Devices fabricated at Sandia's Microelectronic Development Laboratory have been successfully tested to investigate these features. A series of measurements were performed on samples with gage lengths of 15 to 1000 microns, using conventional and tungsten coated samples as well as samples that include the critical features of standard components in the test section. Specimens have a freely moving pin joint on one end that anchors the sample to the silicon die to allow rotation to reduce effects of bending. Each sample is loaded in uniaxial tension by pulling laterally with a flat tipped diamond in a computer-controlled Nanoindenter. Load is calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. The specimen cross section and gage length dimensions were verified by measuring against a standard in the SEM. Multiple tests can be programmed at one time and performed without operator assistance allowing the collection of significant populations of data.
Date: December 2, 1999
Creator: LAVAN,DAVID A. & BUCHHEIT,THOMAS E.
Partner: UNT Libraries Government Documents Department

TEM study of diamond films grown from fullerene precursors

Description: Transmission Electron Microscope (TEM) techniques are applied to study the microstructure of diamond films grown from fullerene precursors. Electron diffraction and electron energy loss spectra (EELS) collected from the diamond films correspond to that of bulk diamond. Microdiffraction, high resolution images and EELS help determine that the first diamond grains that nucleate from fullerene precursors generally form on a thin amorphous carbon interlayer and seldom directly on the silicon substrate. Grain size measurements reveal nanocrystalline diamond grains. Cross section TEM images show that the nanocrystalline diamond grains are equiaxed and not columnar nor dendritic. The microstructure of small equiaxed grains throughout the film thickness is believed responsible for the very smooth surfaces of diamond films grown from fullerene precursors.
Date: November 1, 1995
Creator: Csencsits, R.; Gruen, D.M.; Krauss, A.R. & Zuiker, C.
Partner: UNT Libraries Government Documents Department

Conflict Diamonds: Agency Actions Needed to Enhance Implementation of the Clean Diamond Trade Act

Description: A letter report issued by the Government Accountability Office with an abstract that begins "In 2003, the United States and other countries began implementing the Kimberley Process Certification Scheme (KPCS) to curtail the trade of rough diamonds that had fueled severe conflicts in Africa, known as conflict diamonds. CDTA provides the statutory framework for U.S. implementation of the KPCS. As mandated in CDTA, this report (1) describes the institutional framework established to implement the act, (2) examines implementation of the domestic provisions of the act and challenges it faces, and (3) examines how the United States has helped to strengthen the KPCS and challenges it faces."
Date: September 27, 2006
Creator: United States. Government Accountability Office.
Partner: UNT Libraries Government Documents Department

A machining parameter study to select best conditions for SPDT of large single-crystal silicon optics

Description: The interdependence of process parameters on diamond turning of single-crystal silicon is poorly understood. An experimental design technique based on methods of statistical analysis permits the determination of a specific parameter's influence and its co-dependence on other factors. This design technique enables the creation of an experimental matrix, considering all input parameters (surface velocity; feed rate; depth of cut; tool radius; tool rake/skew angle; cutting fluid), while substantially decreasing the overall number of experiments. After an initial survey the significant parameters for a subsequent response surface methodology (RSM) study can be selected. From measurements of tool wear, surface finish and sub-surface damage (SSD) the optimum parameter settings for the diamond turning process can then be determined.
Date: March 18, 1999
Creator: Carr, J W; Davis, P J; Haack, J K; Krulewich, D A; McClellan, M R & Zimmermann, M
Partner: UNT Libraries Government Documents Department

The laser interferometer system for the large optics diamond turning machine

Description: The purpose of this report is to describe the Laser Interferometer System designed for the Large Optics Diamond Turning Machine (LODTM). To better understand the laser interferometer system, it is useful to begin with an overview of the LODTM metrology system.
Date: June 29, 1999
Creator: Baird, E D; Donaldson, R R & Patterson, S R
Partner: UNT Libraries Government Documents Department

Nanodiamonds: Their Structure and Optical Properties

Description: Nanometer sized diamond is a constituent of diverse systems ranging from interstellar dusts and meteorites [1] to carbonaceous residues of detonations [2] and diamond-like films [3-5]. Many of the properties of bulk diamond have been well understood for decades, those of nanodiamond are mostly unexplored. We present a combined theoretical and experimental study showing that diamond has unique properties not only as a bulk material but also at the nanoscale, where size reduction and surface reconstruction effects are fundamentally different from those found, e.g. in Si and Ge.
Date: May 14, 2002
Creator: Raty, J.-Y.; van Buuren, T. & Galli, G.
Partner: UNT Libraries Government Documents Department

Development of Designer Diamond Anvils for High Pressure-High-Temperature Experiments in Support of the Stockpile Stewardship Program

Description: The focus of this program at the University of Alabama at Birmingham (UAB) is to develop the next generation of designer diamond anvils that can perform simultaneous joule heating and temperature profile measurements in a diamond anvil cell. A series of tungsten-rhenium thermocouples will be fabricated onto to the anvil and encapsulated by a chemical vapor deposited diamond layer to allow for a complete temperature profile measurement across the anvil. The tip of the diamond anvil will be engineered to reduce the thermal conductivity so that the tungsten-heating coils can be deposited on top of this layer. Several different approaches will be investigated to engineer the tip of the diamond anvil for reduction in thermal conductivity (a) isotopic mixture of 12C and 13C in the diamond layer, (b) doping of diamond with impurities (nitrogen and/or boron), and (c) growing diamond in a higher concentration of methane in hydrogen plasma. Under this academic alliance with Lawrence Livermore National Laboratory (LLNL), PI and his graduate students will use the lithographic and diamond polishing facility at LLNL. This proposed next generation of designer diamond anvils will allow multi-tasking capability with the ability to measure electrical, magnetic, structural and thermal data on actinide materials with unparallel sensitivity in support of the stockpile stewardship program.
Date: May 12, 2005
Creator: Vohra, Yogesh K.
Partner: UNT Libraries Government Documents Department

RECENT PROGRESS ON THE DIAMOND AMPLIFIED PHOTO-CATHODE EXPERIMENT.

Description: We report recent progress on the Diamond Amplified Photo-cathode (DAP). The use of a pulsed electron gun provides detailed information about the DAP physics. The secondary electron gain has been measured under various electric fields. We have achieved gains of a few hundred in the transmission mode and observed evidence of emission of electrons from the surface. A model based on recombination of electrons and holes during generation well describes the field dependence of the gain. The emittance measurement system for the DAP has been designed, constructed and is ready for use. The capsule design of the DAP is also being studied in parallel.
Date: June 25, 2007
Creator: CHANG,X.; BEN-ZVI, I.; BURRILL, A.; GRIMES, J.; RAO, T.; SEGALOV, Z. et al.
Partner: UNT Libraries Government Documents Department

Saturation of CVD Diamond Detectors

Description: A 5 x 0.25 mm Chemical Vapor Deposited (CVD) diamond detector, with a voltage bias of + 250V, was excited by a 400 nm laser (3.1 eV photons) in order to study the saturation of the wafer and its surrounding electronics. In a first experiment, the laser beam energy was increased from a few tens of a pJ to about 100 ┬ÁJ, and the signal from the diamond was recorded until full saturation of the detection system was achieved. Clear saturation of the detection system was observed at about 40 V, which corresponds with the expected saturation at 10% of the applied bias (250V). The results indicate that the interaction mechanism of the 3.1 eV photons in the diamond (Ebandgap = 5.45 eV) is not a multi-photon process but is linked to the impurities and defects of the crystal. In a second experiment, the detector was irradiated by a saturating first laser pulse and then by a delayed laser pulse of equal or smaller amplitude with delays of 5, 10, and 20 ns. The results suggest that the diamond and associated electronics recover within 10 to 20 ns after a strong saturating pulse.
Date: January 1, 2005
Creator: Dauffy, Lucile S.; Lerche, Richard A.; Schmid, Greg J.; Koch, Jeffrey A. & Silbernagel, Christopher
Partner: UNT Libraries Government Documents Department

Secondary-electron emission from hydrogen-terminated diamond

Description: Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in the vacuum level due to the Schottky effect. We demonstrated that the decrease in the secondary electrons average emission gain was a function of the pulse width and related this to the trapping of electrons by the effective NEA surface. The findings from the model agree well with our experimental measurements. As an application of the model, the energy spread of secondary electrons inside the diamond was estimated from the measured emission.
Date: May 20, 2012
Creator: E., Wang; Ben-Zvi, I.; Rao, T.; Wu, Q.; Dimitrov, D.A. & T. Xin, T.
Partner: UNT Libraries Government Documents Department

An Industry/DOE Program to Develop and Benchmark Advanced Diamond Product Drill Bits and HP/HT Drilling Fluids to Significantly Improve Rates of Penetration

Description: A deep drilling research program titled 'An Industry/DOE Program to Develop and Benchmark Advanced Diamond Product Drill Bits and HP/HT Drilling Fluids to Significantly Improve Rates of Penetration' was conducted at TerraTek's Drilling and Completions Laboratory. Drilling tests were run to simulate deep drilling by using high bore pressures and high confining and overburden stresses. The purpose of this testing was to gain insight into practices that would improve rates of penetration and mechanical specific energy while drilling under high pressure conditions. Thirty-seven test series were run utilizing a variety of drilling parameters which allowed analysis of the performance of drill bits and drilling fluids. Five different drill bit types or styles were tested: four-bladed polycrystalline diamond compact (PDC), 7-bladed PDC in regular and long profile, roller-cone, and impregnated. There were three different rock types used to simulate deep formations: Mancos shale, Carthage marble, and Crab Orchard sandstone. The testing also analyzed various drilling fluids and the extent to which they improved drilling. The PDC drill bits provided the best performance overall. The impregnated and tungsten carbide insert roller-cone drill bits performed poorly under the conditions chosen. The cesium formate drilling fluid outperformed all other drilling muds when drilling in the Carthage marble and Mancos shale with PDC drill bits. The oil base drilling fluid with manganese tetroxide weighting material provided the best performance when drilling the Crab Orchard sandstone.
Date: June 30, 2007
Creator: TerraTek
Partner: UNT Libraries Government Documents Department