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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

Melting of Copper and Nickel at high pressure: the role of d-electrons

Description: Melting curves of Cu and Ni were measured to 97 GPa (3800 K) and 60 GPa (2970 K), respectively, in the laser-heated diamond cell. The measured melting temperatures of Cu are in good agreement with recent theoretical calculations. The melting slope (dT/dP) of Cu, which has a filled d-electron band, is about 2.5 times steeper than for Ni, which with one less electron, has a partially unfilled d-electron band. The relatively low melting slope obtained for Ni, measured using identical experimental methods as for Cu, is consistent with our previous measurements for other transition metals with partially filled d-bands, which are in serious disagreement with theoretical estimates. The present results confirm the key role d-shell electrons play in determining the high pressure melting curves.
Date: April 11, 2005
Creator: Japel, S; Boehler, R & Ross, M
Partner: UNT Libraries Government Documents Department

A Steinberg-Guinan model for High-Pressure Carbon, Diamond Phase

Description: Since the carbon, diamond phase has such a high yield strength, dynamic simulations must account for strength even for strong shock waves ({approx} 3 Mbar). We have determined an initial parametrization of two strength models: Steinberg-Guinan (SG) and a modified or improved SG, that captures the high pressure dependence of the calculated shear modulus up to 10 Mbar. The models are based upon available experimental data and on calculated elastic moduli using robust density functional theory. Additionally, we have evaluated these models using hydrodynamic simulations of planar shocks experiments.
Date: July 27, 2007
Creator: Orlikowski, D; Correa, A; Schwegler, E & Klepeis, J
Partner: UNT Libraries Government Documents Department

Final Report. IUT No. B560420 with UC Berkeley. Organic Chemistry at High Pressures &Temperatures

Description: We have successfully completed the research outlined in our proposal: Organic Chemistry at High Pressures and Temperatures. We have experimentally determined a phase diagram which documents the phases and reaction regimes of cyanuric acid , H{sub 3}C{sub 3}N{sub 3}O{sub 3} (1,3,5-triazine-2,4,6-trione), from 300 - 750 K and 0 - 8.1 GPa. We utilized a comparatively new technique to study thin samples of cyanuric acid in the diamond anvil cell in order to collect ambient temperature, high pressure FTIR and Raman data as well as the high-pressure, high-temperature data used in the phase diagram. These experiments made use of the CMLS High-pressure lab's diamond anvil facilities as well as the FTIR and Raman systems.
Date: March 20, 2007
Creator: Montgomery, W; Crowhurst, J C; Zaug, J M & Jeanloz, R
Partner: UNT Libraries Government Documents Department

Asymptotic Diffusion-Limit Accuracy of Sn Angular Differencing Schemes

Description: In a previous paper, Morel and Montry used a Galerkin-based diffusion analysis to define a particular weighted diamond angular discretization for S{sub n}n calculations in curvilinear geometries. The weighting factors were chosen to ensure that the Galerkin diffusion approximation was preserved, which eliminated the discrete-ordinates flux dip. It was also shown that the step and diamond angular differencing schemes, which both suffer from the flux dip, do not preserve the diffusion approximation in the Galerkin sense. In this paper we re-derive the Morel and Montry weighted diamond scheme using a formal asymptotic diffusion-limit analysis. The asymptotic analysis yields more information than the Galerkin analysis and demonstrates that the step and diamond schemes do in fact formally preserve the diffusion limit to leading order, while the Morel and Montry weighted diamond scheme preserves it to first order, which is required for full consistency in this limit. Nonetheless, the fact that the step and diamond differencing schemes preserve the diffusion limit to leading order suggests that the flux dip should disappear as the diffusion limit is approached for these schemes. Computational results are presented that confirm this conjecture. We further conjecture that preserving the Galerkin diffusion approximation is equivalent to preserving the asymptotic diffusion limit to first order.
Date: November 5, 2009
Creator: Bailey, T S; Morel, J E & Chang, J H
Partner: UNT Libraries Government Documents Department

Defect-related internal dissipation in mechanical resonators and the study of coupled mechanical systems.

Description: Understanding internal dissipation in resonant mechanical systems at the micro- and nanoscale is of great technological and fundamental interest. Resonant mechanical systems are central to many sensor technologies, and microscale resonators form the basis of a variety of scanning probe microscopies. Furthermore, coupled resonant mechanical systems are of great utility for the study of complex dynamics in systems ranging from biology to electronics to photonics. In this work, we report the detailed experimental study of internal dissipation in micro- and nanomechanical oscillators fabricated from amorphous and crystalline diamond materials, atomistic modeling of dissipation in amorphous, defect-free, and defect-containing crystalline silicon, and experimental work on the properties of one-dimensional and two-dimensional coupled mechanical oscillator arrays. We have identified that internal dissipation in most micro- and nanoscale oscillators is limited by defect relaxation processes, with large differences in the nature of the defects as the local order of the material ranges from amorphous to crystalline. Atomistic simulations also showed a dominant role of defect relaxation processes in controlling internal dissipation. Our studies of one-dimensional and two-dimensional coupled oscillator arrays revealed that it is possible to create mechanical systems that should be ideal for the study of non-linear dynamics and localization.
Date: January 1, 2007
Creator: Friedmann, Thomas Aquinas; Czaplewski, David A.; Sullivan, John Patrick; Modine, Normand Arthur; Wendt, Joel Robert; Aslam, Dean (Michigan State University, Lansing, MI) et al.
Partner: UNT Libraries Government Documents Department

Electrical Conductivity of the Lower-Mantle Ferropericlase

Description: Electrical conductivity of the lower-mantle ferropericlase-(Mg{sub 0.75},Fe{sub 0.25})O has been studied using designer diamond anvils to pressures over one megabar and temperatures up to 500 K. The electrical conductivity of (Mg{sub 0.75},Fe{sub 0.25})O gradually rises by an order of magnitude up to 50 GPa but decreases by a factor of approximately three between 50 to 70 GPa. This decrease in the electrical conductivity is attributed to the electronic high-spin to low-spin transition of iron in ferropericlase. That is, the electronic spin transition of iron results in a decrease in the mobility and/or density of the charge transfer carriers in the low-spin ferropericlase. The activation energy of the low-spin ferropericlase is 0.27 eV at 101 GPa, similar to that of the high-spin ferropericlase at relatively low temperatures. Our results indicate that low-spin ferropericlase exhibits lower electrical conductivity than high-spin ferropericlase, which needs to be considered in future geomagnetic models for the lower mantle. The extrapolated electrical conductivity of the low-spin ferropericlase, together with that of silicate perovskite, at the lower mantle pressure-temperature conditions is consistent with the model electrical conductivity profile of the lower mantle.
Date: April 19, 2007
Creator: Lin, J F; Weir, S T; Jackson, D D; Evans, W J; Vohra, Y K; Qiu, W et al.
Partner: UNT Libraries Government Documents Department

Tuning magnetic frustration on the diamond lattice of the A-site magnetic spinels CoA12-xGax04: lattice expansion versus site disorder

Description: The spinels CoB{sub 2}O{sub 4} with magnetic Co{sup 2+} ions on the diamond lattice A site can be frustrated because of competing near-neighbor (J{sub 1}) and next-near neighbor (J{sub 2}) interactions. Here we describe attempts to tune the relative strengths of these interactions by substitution on the non-magnetic B-site. The system we employ is CoAl{sub 2-x}Ga{sub x}O{sub 4}, where Al is systematically replaced by the larger Ga, ostensibly on the B site. As expected, Ga substitution expands the lattice, resulting in Co atoms on the A-site being pushed further from one other and thereby weakening magnetic interactions. In addition, Ga distributes between the B and the A site in a concentration dependent manner displacing an increasing amount of Co from the A site with increasing x. This increased inversion, which is confirmed by neutron diffraction studies carried out at room temperature, affects magnetic ordering very significantly, and changes the nature of the ground state. Modeling of the magnetic coupling illustrates the complexity that arises from the cation site disorder.
Date: January 1, 2008
Creator: Proffen, Thomas E; Melot, Brent C; Page, Katharine; Seshadri, Ramzy; Stoudenmire, E M; Balents, Leon et al.
Partner: UNT Libraries Government Documents Department

Preliminary numerical modeling results - cone penetrometer (CPT) tip used as an electrode

Description: Figure 1 shows the resistivity models considered in this study; log10 of the resistivity is shown. The graph on the upper left hand side shows a hypothetical resisitivity well log measured along a well in the upper layered model; 10% Gaussian noise has been added to the well log data. The lower model is identical to the upper one except for one square area located within the second deepest layer. Figure 2 shows the electrode configurations considered. The ''reference'' case (upper frame) considers point electrodes located along the surface and along a vertical borehole. The ''CPT electrode'' case (middle frame) assumes that the CPT tip serves as an electrode that is electrically connected to the push rod; the surface electrodes are used in conjuction with the moving CPT electrode. The ''isolated CPT electrode'' case assumes that the electrode at the CPT tip is electrically isolated from the pushrod. Note that the separate CPT push rods in the middle and lower frames are shown separated to clarify the figure; in reality, there is only one pushrod that is changing length as the probe advances. Figure 3 shows three pole-pole measurement schemes were considered; in all cases, the ''get lost'' electrodes were the leftmost and rightmost surface electrodes. The top frame shows the reference scheme where all surface and borehole electrodes can be used. The middle frame shows two possible configurations available when a CPT mounted electrode is used. Note that only one of the four poles can be located along the borehole at any given time; electrode combinations such as the one depicted in blue (upper frame) are not possible in this case. The bottom frame shows a sample configuration where only the surface electrodes are used. Figure 4 shows the results obtained for the various measurement schemes. The white lines ...
Date: December 19, 2006
Creator: Ramirez, A L
Partner: UNT Libraries Government Documents Department

The structure of a-C: What NEXAFS and EXAFS see

Description: Mechanically hard ha-C and soft sa-C amorphous carbon films of 2.9 and 2.2 g cm-3 approximate densities were prepared by filtered cathodic arc deposition and analyzed by near-edge x-ray absorption spectroscopy NEXAFS and extended x-ray absorption spectroscopy EXAFS to determine their structure. The analysis observed an insignificant level of pi bond conjugation in both kind of films. EXAFS distinguished two types of atomic environments in them: one semiordered with well defined bond lengths, and the other with so strong bond disorder that its contribution to EXAFS was undetectable. The proportion of atoms in the semiordered atomic environments was of less than 40percent in both films. Their bond lengths were similar to those of diamond in the ha-C films and to graphite in the sa-C. NEXAFS spectra analysis was based on the linear relation between sigma* energy and bond length. It served to quantify the proportion of sp3 bonded atoms in a-C, to deduce the average bond length of the atoms undetected by EXAFS, and to determine the level of bond conjugation in the films. The sp3 concentration estimated with the proposed method was of 44percent in the ha-C films and 10percent in the sa-C films. These values were consistent with the EXAFS results, but disagreed with those obtained based on the traditional pi*/sigma* intensity ratio method which overestimated sp3 concentrations. Annealing of the ha-C films up to its almost complete graphitization caused a gradual reduction in bond length of the semiordered environments with no differentiation between two phases, diamondlike and graphitelike, at any temperature. This resultsupport models that explain sp3 bond promotion in a-C as caused by the high compressive stress attained by a strongly disordered sp2 dense structure during film deposition.
Date: August 1, 2006
Creator: Hussain, Zahid; Diaz, J.; Monteiro, O.R. & Hussain, Z.
Partner: UNT Libraries Government Documents Department

DIAMOND SECONDARY EMITTER

Description: We present the design and experimental progress on the diamond secondary emitter as an electron source for high average power injectors. The design criteria for average currents up to 1 A and charge up to 20 nC are established. Secondary Electron Yield (SEY) exceeding 200 in transmission mode and 50 in emission mode have been measured. Preliminary results on the design and fabrication of the self contained capsule with primary electron source and secondary electron emitter will also be presented.
Date: October 9, 2005
Creator: BEN-ZVI, I.; RAO, T.; BURRILL, A.; CHANG, X.; GRIMES, J.; RANK, J. et al.
Partner: UNT Libraries Government Documents Department

Recovery of CVD Diamond Detectors using Laser Double Pulses

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 associated electronics. In a first experiment, the laser beam energy was increased from a few tens of a pJ to about 100 {micro}J, 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 (E{sub bandgap} = 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: September 27, 2005
Creator: Dauffy, L S; Lerche, R A; Schmid, G J; Koch, J A & Silbenagel, C
Partner: UNT Libraries Government Documents Department

Static High Pressure Structural studies on Dy to 119 GPa

Description: Structural phase transitions in the rare-earth metal Dysprosium have been studied in a Diamond Anvil Cell (DAC) to 119 GPa by x-ray diffraction. Four transformations following the sequence hcp {yields} Sm-type {yields} dhcp {yields} hR24 (hexagonal) {yields} bcm (monoclinic) are observed at 6, 15, 43, and 73 GPa respectively. The hexagonal to monoclinic transformation is accompanied by a 6% reduction in volume, which is attributed to delocalization of the 4f electrons, similar to that seen in Ce, Pr, and Gd.
Date: November 12, 2003
Creator: Patterson, J R; Saw, C K & Akella, J
Partner: UNT Libraries Government Documents Department

ELECTRON AMPLIFICATION IN DIAMOND.

Description: We report on recent progress toward development of secondary emission ''amplifiers'' for photocathodes. Secondary emission gain of over 300 has been achieved in transmission mode and emission mode for a variety of diamond samples. Techniques of sample preparation, including hydrogenation to achieve negative electron affinity (NEA), have been adapted to this application.
Date: July 10, 2006
Creator: SMEDLEY, J.; BEN-ZVI, I.; BURRILL, A.; CHANG, X.; GRIMES, J.; RAO, T. et al.
Partner: UNT Libraries Government Documents Department

First Observation of an Electron Beam Emitted from a Diamond Amplified cathode

Description: We observed, for the first time, the emission of an electron beam from a hydrogenated diamond in the emission mode on a phosphor screen. Our experimental device is based on the following concept: the primary electrons of a few keV energy generate a large number of secondary electron-hole pairs in a hydrogenated diamond, and then the secondary electrons are transmitted to the opposite face of the diamond and emitted from its negative-electron-affinity (NEA) surface. Under our present conditions, the maximum emission gain of the primary electron is about 40, and the bunch charge is 50pC/0.5mm{sup 2}. Our achievement led to new understanding of the hydrogenated surface of the diamond. We propose an electron-trapping mechanism near the hydrogenated surface. The probability of electron trapping in our tests is about 70%. The hydrogenated diamond was demonstrated to be extremely robust. After exposure to air for days, the sample exhibited no observable degradation in emission.
Date: May 4, 2009
Creator: Chang,X.; Ben-Zvi, I.; Burrill, A.; Kewisch, J.; Rao, t.; Smedley, J. et al.
Partner: UNT Libraries Government Documents Department

DIFFERENTIAL THERMAL ANALYSIS OF IRRADIATED DIAMOND AND SILICON CARBIDE

Description: It was demonstrated by differential thermal analysis (DTA) that: 1. Catastrophic amounts of energy can be stored in diamond. 2. Even at low irradiations, the release takes place over several hundred degrees, indicating a spectrum of activation energies. 3. At higher irradiations, the stored energy release is considerably less than the increased energy content and seems not to have been completely released even at the highest temperatures reached. 4. There is some indication of an increased heat capacity below the temperature of stored energy release. It was shown by DTA that large amounts of energy can be stored in silicon carbide on irradiation. The release was found to be spread out over a greater range of temperatures than in diamond and indicated a larger and higher group of activation energies. Catastrophic release was not achieved. The amount of stored energy released over the range of temperatures used was 140 cal/g in a sample irradiated in a water-cooled testhole at HEW for an exposure of 265 Mwd/aT. (auth)
Date: December 1, 1954
Creator: Primak, W.
Partner: UNT Libraries Government Documents Department