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Etching Effects During the Chemical Vapor Deposition of (100) Diamond

Description: Current theories of CVD growth on (100) diamond are unable to account for the numerous experimental observations of slow-growing, locally smooth (100)(2x1) films. In this paper they use quantum mechanical calculations of diamond surface thermochemistry and atomic-scale kinetic Monte Carlo simulations of deposition to investigate the efficacy of preferential etching as a mechanism that can help to reconcile this discrepancy. This etching mechanism allows for the removal of undercoordinated carbon atoms from the diamond surface. In the absence of etching, simulated growth on the (100)(2x1) surface is faster than growth on the (110) and (111) surfaces, and the (100) surface is atomically rough. When etching is included in the simulations, the (100) growth rates decrease to values near those observed experimentally, while the rates of growth on the other surfaces remain largely unaffected and similar to those observed experimentally. In addition, the etching mechanism promotes the growth of smooth (100) surface regions in agreement with numerous scanning probe studies.
Date: August 2, 1999
Creator: Battaile, C.C.; Srolovitz, D.J.; Oleinik, I.I.; Pettifor, D.G.; Sutton, A.P.; Harris, S.J. et al.
Partner: UNT Libraries Government Documents Department

High-heat-load studies of silicon and diamond monochromators using the APS/CHESS prototype undulator

Description: The results of the latest high-heat-load studies made on the APS/CHESS prototype undulator are summarized. Four different crystals were tested: two slotted, symmetrically cut silicon crystals and a core-drilled, asymmetrically cut silicon crystal and a diamond crystal that was jet cooled using water. The purpose of the silicon crystal tests was to reevaluate the surface power loading at which appreciable degradation of the diffraction efficiency was observed. The diamond tests, allotted only a brief period of time during the testing period, were our first attempt at using diamonds for high-heat-flux x-ray monochromators and were performed primarily to gain first-hand experience with diamond monochromators. Measurements with the silicon crystal at 5 keV reconfirmed our previous measurements of performance degradation at around 4-6 watts/mm{sup 2} using liquid gallium with slotted coolant channels. A value of only 2 watts/mm{sup 2} was observed to cause a degradation of the diffraction performance at 15 keV with the same crystals due to the increased sensitivity to strain because of the reduced Darwin widths. The performance of the asymmetric crystal, with its core-drilled coolant channels, was not found to be as good as that of the slotted crystals. This was probably due to poorer heat transfer properties of the core-drilled geometry in combination with the narrowing of the rocking curves because of the asymmetric cut. Fabrication issues for construction of the gallium-cooled crystals is also discussed. Although the diamonds were only successfully tested at low total power the results were very encouraging and motivated us to accelerate our program on the use of diamonds for high-heat-load monochromators.
Date: September 16, 1994
Creator: Mills, D.M.; Lee, W.K.; Smither, R.K. & Fernandez, P.B.
Partner: UNT Libraries Government Documents Department

Ultrashort-pulse lasers machining

Description: A new type of material processing is enabled with ultrashort (t < 10 psec) laser pulses. Cutting, drilling, sculpting of all materials (biologic materials, ceramics, sapphire, silicon carbide, diamond, metals) occurs by new mechanisms which eliminate thermal shock or collateral damage. High precision machining to submicron tolerances is enabled resulting in high surface quality and negligible heat affected zone.
Date: January 22, 1999
Creator: Banks, P S; Feit, M D; Nguyen, H T & Perry, M D, Stuart, B C
Partner: UNT Libraries Government Documents Department

Shock Response of Diamond Crystals

Description: Sandia is investigating the shock response of single-crystal diamond up to several Mbar pressure in a collaborative effort with the Institute for Shock Physics (ISP) at Washington State University (WSU). This is project intended to determine (i) the usefulness of diamond as a window material for high pressure velocity interferometry measurements, (ii) the maximum stress level at which diamond remains transparent in the visible region, (iii) if a two-wave structure can be detected and analyzed, and if so, (iv) the Hugoniot elastic limit (HEL) for the [110] orientation of diamond. To this end experiments have been designed and performed, scoping the shock response in diamond in the 2-3 Mbar pressure range using conventional velocity interferometry techniques (conventional VISAR diagnostic). In order to perform more detailed and highly resolved measurements, an improved line-imaging VISAR has been developed and experiments using this technique have been designed. Prior to performing these more detailed experiments, additional scoping experiments are being performed using conventional techniques at WSU to refine the experimental design.
Date: December 1, 2001
Creator: KNUDSON, MARCUS D.; ASAY, JAMES R.; JONES, SCOTT C. & GUPTA, Y.M.
Partner: UNT Libraries Government Documents Department

Cylindrical Wire Electrical Discharge Machining of Metal Bond Diamond Wheels- Part II: Wheel Wear Mechanism

Description: The use of stereo scanning Electron Microscopy (SEM) to investigate the wear mechanism of the wire EDM true metal bond diamond wheel for ceramic grinding is presented. On the grinding wheel, a wedge-shape removal part was machined to enable the examination and measurement of the worn wheel surfaces using the stereo SEM. The stereo SEM was calibrated by comparing results of depth profile of a wear groove with the profilometer measurements. On the surface of the grinding wheel after wire EDM truing and before grinding, the diamond protruding heights were measured in the level of 35 {micro}m, comparing to the 54 {micro}m average size of the diamond in the grinding wheel. The gap between the EDM wire and rotating grinding wheel is estimated to be about 35 to 40 {micro}m. This observation indicates that, during the wire EDM, electrical sparks occur between the metal bond and EDM wire, which leaves the diamond protruding in the gap between the wire and wheel. The protruding diamond is immediately fractured at the start of the grinding process, even under a light grinding condition. After heavy grinding, the grinding wheel surface and the diamond protrusion heights are also investigated using the stereo SEM. The height of diamond protrusion was estimated in the 5 to 15 {micro}m range. This study has demonstrated the use of stereo SEM as a metrology tool to study the grinding wheel surface.
Date: January 22, 2002
Creator: McSpadden, SB
Partner: UNT Libraries Government Documents Department

Experimental Time Resolved Electron Beam Temperature Measurements Using Bremsstrahlung Diagnostics

Description: Electron beam temperature, {beta}{perpendicular} (= v{perpendicular}/v), is important to control for the development of high dose flash radiographic bremsstrahlung sources. At high voltage (> 5 MV) increasing electron beam temperature has a serious deleterious effect on dose production. The average and time resolved behavior of beam temperature was measured during radiographic experiments on the HERMES III accelerator (10 MV, 50 kA, 70 ns). A linear array of thermoluminescent dosimeters (TLDs) were used to estimate the time integrated average of beam temperature. On and off-axis photoconducting diamond (PCD) detectors were used to measure the time resolved bremsstrahlung dose rate, which is dependent on beam energy and temperature. The beam temperature can be determined by correlating PCD response with accelerator voltage and current and also by analyzing the ratio of PCD amplitudes on and off axis. This ratio is insensitive to voltage and current and thus, is more reliable than utilizing absolute dose rate. The data is unfolded using comparisons with Monte Carlo simulations to obtain absolute beam temperatures. The data taken on HERMES III show abrupt increases in {beta}{perpendicular} midway through the pulse indicating rapid onset of beam instability.
Date: June 25, 1999
Creator: Menge, P.R.; Maenchen, J.E.; Mazarakis, M.G. & Rosenthal, S.E.
Partner: UNT Libraries Government Documents Department

Corrosive Resistant Diamond Coatings for the Acid Based Thermo-Chemical Hydrogen Cycles

Description: This project was designed to test diamond, diamond-like and related materials in environments that are expected in thermochemical cycles. Our goals were to build a High Temperature Corrosion Resistance (HTCR) test stand and begin testing the corrosive properties of barious materials in a high temperature acidic environment in the first year. Overall, we planned to test 54 samples each of diamond and diamond-like films (of 1 cm x 1 cm area). In addition we use a corrosion acceleration method by treating the samples at a temperature much larger than the expected operating temperature. Half of the samples will be treated with boron using the FEDOA process.
Date: June 25, 2009
Creator: Prelas, Mark A.
Partner: UNT Libraries Government Documents Department

Protected Polycrystalline Diamond Compact Bits For Hard Rock Drilling

Description: Two bits were designed. One bit was fabricated and tested at Terra-Tek's Drilling Research Laboratory. Fabrication of the second bit was not completed due to complications in fabrication and meeting scheduled test dates at the test facility. A conical bit was tested in a Carthage Marble (compressive strength 14,500 psi) and Sierra White Granite (compressive strength 28,200 psi). During the testing, Hydraulic Horsepower, Bit Weight, Rotation Rate, were varied for the Conical Bit, a Varel Tricone Bit and Varel PDC bit. The Conical Bi did cut rock at a reasonable rate in both rocks. Beneficial effects from the near and through cutter water nozzles were not evident in the marble due to test conditions and were not conclusive in the granite due to test conditions. At atmospheric drilling, the Conical Bit's penetration rate was as good as the standard PDC bit and better than the Tricone Bit. Torque requirements for the Conical Bit were higher than that required for the Standard Bits. Spudding the conical bit into the rock required some care to avoid overloading the nose cutters. The nose design should be evaluated to improve the bit's spudding characteristics.
Date: October 31, 2000
Creator: Cardenas, Robert Lee
Partner: UNT Libraries Government Documents Department

A photoemission study of the diamond and the single crystal C{sub 60}

Description: This report studied the elctronic structure of diamond (100) and diamond/metal interface and C{sub 60}, using angle-resolved and core level photoemission. The C(100)-(2X1) surface electronic structure was studied using both core level and angle resolved valence band photoemission spectroscopy. The surface component of the C 1s core level spectrum agrees with theoretical existence of only symmetrical dimers. In the case of metal/diamond interfaces, core level and valence photoelectron spectroscopy and LEED studies WERE MADE OF B and Sb on diamond (100) and (111) surfaces. In the case of single-crystal C{sub 60}, photoemission spectra show sharp molecular features, indicating that the molecular orbitals are relatively undisturbed in solid C{sub 60}.
Date: March 1, 1994
Creator: Wu, Jin
Partner: UNT Libraries Government Documents Department

Molecular beam mass spectrometry studies of the chemical vapor deposition of diamond

Description: We have developed a novel molecular beam mass spectrometry technique that can quantitatively analyze the gas-phase composition in a CVD reactor. The technique simultaneously monitors a wide variety of radical and stable species, and their concentrations can be determined with sensitivities approaching 1 ppM. Measurements performed in a diamond deposition system have given us keen insights into the important phenomena that affect the growth environment. This paper first discusses the primary gas sampling design issues. In the second part, the details of the experimental results and their implications will be described.
Date: December 1, 1993
Creator: Hsu, Wen L.; McMaster, M. C.; Coltrin, M. E. & Dandy, D. S.
Partner: UNT Libraries Government Documents Department

Atomic structure modifications of diamond-like nanocomposite films: Observation by Raman spectroscopy, FTIR and STM

Description: Raman spectroscopy, FTIR and scanning tunneling microscopy (STM) were used to study diamond-like nanocomposite (DLN) and metal containing DLN (Me-DLN) films. The FTIR spectra showed no appreciable absorption from the C-H stretch vibration band in DLN when 1 kV rf bias voltage was applied. Thermal annealing (450{degrees}C for 2 hrs) of (a) DLN and Cr-DLN films caused no change in the Raman spectra while (b) for Pt-DLN films there was a blue shift of both the crystalline (G) and microcrystalline (D) graphite-like features, an increase in the I{sub D}/I{sub G} intensity ratio and a decrease in the linewidths. The changes observed were more pronounced in the film with the highest Pt concentration. The STM image of this Pt-DLN film revealed a structure of aromatic graphite rings.
Date: June 1, 1994
Creator: Dorfman, B.; Abraizov, M.; Pollak, F. H.; Yan, D.; Strongin, M.; Yang, X. Q. et al.
Partner: UNT Libraries Government Documents Department

Turning soot into diamonds with microwaves

Description: Growth of diamond films using fullerene precursors in an argon microwave plasma without the addition of hydrogen or oxygen has recently been accomplished. Microwave discharges (2.45 GHz) were generated in C{sub 60}-containing Ar. The gas mixtures were produced by flowing Ar over fullerene-containing soot at a variety of temperatures. Optical spectroscopy shows that the spectrum is dominated by the d{sup 3}{Pi}{minus}a{sup 3}{Pi}{sub u}. Swan bands of C{sub 2} and particularly the {Delta}{nu} = {minus}2, {minus}1.0, +1, and +2 sequences, that C{sub 2} is one of the products of C{sub 60} fragmentation brought about, at least in part, by collisionally-induced dissociation. The nanocrystalline films were characterized with scanning and high-resolution transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. 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: June 1, 1994
Creator: Gruen, D. M.; Krauss, A. R.; Luo, J.; Pan, X. & Liu, S.
Partner: UNT Libraries Government Documents Department

Plasma Sprayed Pour Tubes and Other Melt Handling Components for Use in Gas Atomization

Description: Ames Laboratory has successfully used plasma sprayed ceramic components made from yttria stabilized zirconia as melt pouring tubes for gas atomization for many years. These tubes have proven to be strong, thermal shock resistant and versatile. Various configurations are possible both internally and externally. Accurate dimensions are achieved internally with a machined fugitive graphite mandrel and externally by diamond grinding. The previous study of the effect of spray parameters on density was extended to determine the effect of the resulting density on the thermal shock characteristics on down-quenching and up-quenching. Encouraging results also prompted investigation of the use of plasma spraying as a method to construct a melt pour exit stopper that is mechanically robust, thermal shock resistant, and not susceptible to attack by reactive melt additions. The Ames Laboratory operates two close-coupled high pressure gas atomizers. These two atomizers are designed to produce fine and coarse spherical metal powders (5{mu} to 500{mu} diameter) of many different metals and alloys. The systems vary in size, but generally the smaller atomizer can produce up to 5 kg of powder whereas the larger can produce up to 25 kg depending on the charge form and density. In order to make powders of such varying compositions, it is necessary to have melt systems capable of heating and containing the liquid charge to the desired superheat temperature prior to pouring through the atomization nozzle. For some metals and alloys this is not a problem; however for some more reactive and/or high melting materials this can pose unique challenges. Figure 1 is a schematic that illustrates the atomization system and its components.
Date: April 1, 2011
Creator: Byrd, David; Rieken, Joel; Heidloff, Andy; Besser, Matthew & Anderson, Iver
Partner: UNT Libraries Government Documents Department

Primary carbonatite melt from deeply subducted oceanic crust

Description: Partial melting in the Earth's mantle plays an important part in generating the geochemical and isotopic diversity observed in volcanic rocks at the surface. Identifying the composition of these primary melts in the mantle is crucial for establishing links between mantle geochemical 'reservoirs' and fundamental geodynamic processes. Mineral inclusions in natural diamonds have provided a unique window into such deep mantle processes. Here they provide exper8imental and geochemical evidence that silicate mineral inclusions in diamonds from Juina, Brazil, crystallized from primary and evolved carbonatite melts in the mantle transition zone and deep upper mantle. The incompatible trace element abundances calculated for a melt coexisting with a calcium-titanium-silicate perovskite inclusion indicate deep melting of carbonated oceanic crust, probably at transition-zone depths. Further to perovskite, calcic-majorite garnet inclusions record crystallization in the deep upper mantle from an evolved melt that closely resembles estimates of primitive carbonatite on the basis of volcanic rocks. Small-degree melts of subducted crust can be viewed as agents of chemical mass-transfer in the upper mantle and transition zone, leaving a chemical imprint of ocean crust that can possibly endure for billions of years.
Date: July 1, 2008
Creator: Walter, M.J.; Bulanova, G.P.; Armstrong, L.S.; Keshav, S.; Blundy, J.D.; Gudfinnesson, G. et al.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of a nanocrystalline diamond aerogel

Description: Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas and ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding and intriguing challenge. Here we report the high-pressure, high-temperature synthesis of a diamond aerogel from an amorphous carbon aerogel precursor using a laser-heated diamond anvil cell. Neon is used as a chemically inert, near-hydrostatic pressure medium that prevents collapse of the aerogel under pressure by conformally filling the aerogel's void volume. Electron and X-ray spectromicroscopy confirm the aerogel morphology and composition of the nanodiamond matrix. Time-resolved photoluminescence measurements of recovered material reveal the formation of both nitrogen- and silicon- vacancy point-defects, suggesting a broad range of applications for this nanocrystalline diamond aerogel.
Date: July 6, 2011
Creator: Pauzauskie, Peter J.; Crowhurst, Jonathan C.; Worsley, Marcus A.; Laurence, Ted A.; Kilcoyne, A. L. David; Wang, Yinmin et al.
Partner: UNT Libraries Government Documents Department

Progress on diamond amplified photo-cathode

Description: Two years ago, we obtained an emission gain of 40 from the Diamond Amplifier Cathode (DAC) in our test system. In our current systematic study of hydrogenation, the highest gain we registered in emission scanning was 178. We proved that our treatments for improving the diamond amplifiers are reproducible. Upcoming tests planned include testing DAC in a RF cavity. Already, we have designed a system for these tests using our 112 MHz superconducting cavity, wherein we will measure DAC parameters, such as the limit, if any, on emission current density, the bunch charge, and the bunch length. The diamond-amplified photocathode, that promises to support a high average current, low emittance, and a highly stable electron beam with a long lifetime, is under development for an electron source. The diamond, functioning as a secondary emitter amplifies the primary current, with a few KeV energy, that comes from the traditional cathode. Earlier, our group recorded a maximum gain of 40 in the secondary electron emission from a diamond amplifier. In this article, we detail our optimization of the hydrogenation process for a diamond amplifier that resulted in a stable emission gain of 140. We proved that these characteristics are reproducible. We now are designing a system to test the diamond amplifier cathode using an 112MHz SRF gun to measure the limits of the emission current's density, and on the bunch charge and bunch length.
Date: March 28, 2011
Creator: Wang, E.; Ben-Zvi, I.; Burrill, A.; Kewisch, J.; Chang, X.; Rao, T. et al.
Partner: UNT Libraries Government Documents Department

Annual Scientific Progress Report: National Nuclear Security Administration Stewardship Stockpile: Academic Alliance Research Grant #DE-FG52-06NA26205

Description: The focus of this grant, entitled ''Experimental investigations of magnetic, superconducting, and other phase transitions in novel f-electron materials at ultra-high pressures using designer diamond anvils'', is to explore the novel properties of f-electron compounds under pressure, with a particular emphasis on the physics of superconductivity, magnetism, and their interactions. This report is a synopsis of the research that was undertaken from 6/2006-6/2007.
Date: July 26, 2007
Creator: Maple, M. Brian & Jeffries, Jason R.
Partner: UNT Libraries Government Documents Department

DIAMOND AMPLIFIED PHOTOCATHODES.

Description: High-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator. The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.
Date: November 26, 2007
Creator: SMEDLEY,J.; BEN-ZVI, I.; BOHON, J.; CHANG, X.; GROVER, R.; ISAKOVIC, A. et al.
Partner: UNT Libraries Government Documents Department

Turbodrilling in the Geothermal Environment

Description: Geothermal drilling, historically, has presented what seemed to be insurmountable barriers to the efficient and extended use of downhole drilling motors, especially those containing elastomeric bearing or motor components. In addition to being damaging to rubber, the typical temperatures of 177 to 371 C (350 to 700 F) create other operating problems as well. Recent innovations, specifically in turbodrill design, have opened heretofore unrealized potentials and allowed, for the first time, extended downhole drilling of geothermal wells. A considerable amount of experience has been obtained both in The Geysers and Imperial County areas of California primarily in directional drilling applications using insert, diamond, and polycrystallines diamond compact bits. Other hot-hole applications are currently being drilled successfully or planned in other states, both onshore and offshore. The turbodrill is devoid of any elastomers or other temperature-sensitive materials, hence, its capabilities are closely matched to the requirements of the industry. The bearing assembly can withstand the rigors found in the drilling of typical geothermal formations and provide the performance necessary to stay in the hole, thus providing increased penetration rates and, hence, more economical drilling. This paper presents case histories of recent turbodrill performances in all areas where used. Furthermore, data will be presented showing the performance of insert, diamond, and polycrystalline diamond bits as they relate to the turbodrill, together with forecasts as to the potential that turbodrills have to offer in accelerating and controlling the drilling of geothermal wells.
Date: January 1, 1981
Creator: Herbert, P.
Partner: UNT Libraries Government Documents Department

FY05 LDRD Final Report Chemical Dynamics At Interfaces

Description: At high pressure and temperature, the phase diagram of elemental carbon is poorly known. We present predictions of diamond and BC8 melting lines and their phase boundary in the solid phase, as obtained from first principles calculations. Maxima are found in both melting lines, with a triple point located at {approx} 850 GPa and {approx} 7400 K. Our results show that hot, compressed diamond is a semiconductor which undergoes metalization upon melting. In contrast, in the stability range of BC8, an insulator to metal transition is likely to occur in the solid phase. Close to the diamond/ and BC8/liquid boundaries, molten carbon is a low-coordinated metal retaining some covalent character in its bonding up to extreme pressures. Our results provide constraints on the carbon equation of state, which is of critical importance for devising models of Neptune, Uranus and white dwarf stars, as well as of extra-solar carbon-rich planets.
Date: February 9, 2006
Creator: Schwegler, E; Ogitsu, T; Bonev, S; Correa, A; Militzer, B & Galli, G
Partner: UNT Libraries Government Documents Department

Dynamic Diamond Anvil Cell (dDAC): A novel device for studying the dynamic-pressure properties of materials

Description: We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/sec ({approx}0.16 s{sup -1} for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.
Date: February 23, 2007
Creator: Evans, W J; Yoo, C; Lee, G W; Cynn, H; Lipp, M J & Visbeck, K
Partner: UNT Libraries Government Documents Department

The Origin of the Monochromatic Photoemission Peak in Diamondoid Monolayers

Description: Recent photoemission experiments have discovered a highly monochromatized secondary electron peak emitted from diamondoid self-assembled monolayers on metal substrates. New experimental data and simulation results are presented to show that a combination of negative electron affinity and strong electron-phonon scattering is responsible for this behavior. The simulation results are generated using a simple Monte Carlo transport algorithm. The simulated spectra contain the main spectral features of the measured ones.
Date: October 31, 2008
Creator: Clay, William A.; Liu, Zhi; Yang, Wanli; Fabbri, Jason D.; Dahl, Jeremy E.; Carlson, Robert M.K. et al.
Partner: UNT Libraries Government Documents Department