Showing papers on "Diamond published in 1986"

Crystal data for high-pressure phases of silicon

Abstract: X-ray-diffraction data have been obtained on Si in a diamond anvil cell to pressures of \ensuremath{\sim}50 GPa. Crystallographic data are presented in phase I (cubic, diamond), II (tetragonal, \ensuremath{\beta}-Sn), V (simple hexagonal), VII (hexagonal close-packed), and the metastable phase III [body-centered-cubic (BC8)] and on the coexistence of the phases. Comparison is made between these data and the predictions of ab initio calculations for these structures and their equations of state.

Diamond genesis in a multiply-constrained model

Abstract: Thermal cracking of primordial carbon gas species in depleted and reduced Archaean subcratonic lithosphere is proposed for the nucleation of micro- and ultramafic macrodiamonds. Growth was mainly by solid-state diffusion, although crystallization of the eclogitic diamond suite was from sulphide-immiscible melts. Lateral and vertical heterogeneities and the geometry of the lithosphere can account for a variety of second-order variables such as diamond type, colour, crystal morphology and dissolution characteristics.

Rock bit with diamond tip inserts

Abstract: A percussion rock bit comprises a steel body having means for connection to a drill string at one end and having a plurality of inserts at the other end for crushing rock at the bottom of a hole being drilled. The inserts have a cemented tungsten carbide body partially embedded in the steel bit and at least two layers at the protruding drilling portion of the insert. The outermost layer contains polycrystalline diamond. The remaining layers adjacent the polycrystalline diamond layer are transition layers containing a composite of diamond crystals and precemented tungsten carbide, the composite having a higher diamond crystal content adjacent the polycrystalline diamond layer and a higher precemented tungsten carbide content adjacent the tungsten carbide layer. Another embodiment of rock bit has three cones with tungsten carbide inserts in the cutting structure of each cone. The gage row inserts have a layer of polycrystalline diamond on the converging portion protruding from the surface of the cone. One or more transition layers are provided between the tungsten carbide insert body and the polycrystalline diamond layer. Such a transition layer comprises diamond and precemented tungsten carbide.

Electronic and structural properties of BN and BP.

Abstract: We present a pseudopotential study within the local-density formalism of the structural and electronic properties of zinc-blende BN and BP. The ground-state properties of these systems such as bulk moduli, lattice constants, cohesive energies, and frequencies of the TO phonon mode are in good agreement with experimental results. The valence charge density of BP shows two local maxima along the bond, which is similar to the case of diamond. In contrast, the charge density of BN is similar to that of a typical III-V compound semiconductor. The resulting band structures have some important features which are in disagreement with previously published work. Like most III-V compound semiconductors, the fundamental gap in BP decreases with decreasing volume. The corresponding gap in BN, however, increases with decreasing volume as was also found in diamond.

C 1 s excitation studies of diamond (111). I. Surface core levels

Abstract: By comparing the C 1s photoemission intensities from a clean diamond (111) surface to those obtained from a fluorine-covered surface, we conclude that a single (111) layer of atoms participates in the diamond 2\ifmmode\times\else\texttimes\fi{}1 surface reconstruction. The data interpretation presented does not rely on assuming an electron mean free path, but, in fact provides an independent measurement of its value. For clean diamond (111) a surface core-level peak is observed at 0.80\ifmmode\pm\else\textpm\fi{}0.05 eV lower binding energy than the bulk-C 1s peak at 285.0 eV below ${E}_{F}$. After fluorine exposure a single chemically shifted carbon peak is observed at 1.85\ifmmode\pm\else\textpm\fi{}0.05 eV higher binding energy than the bulk peak, indicating the presence of CF units at the surface.

Pseudopotential total-energy study of the transition from rhombohedral graphite to diamond.

Abstract: The path maintaining rhombohedral symmetry in the transition from graphite to diamond which minimizes the energy at each value of the bond length between layers is determined. The energy barrier for this path is found to be 0.33 eV. The total energy of the solid is calculated using local-density-functional theory with ab initio pseudopotentials. Results are presented for the charge density and density of states along the transition path. In contrast to recent extended-H\"uckel-theory results, throughout most of the transition the structure is found to remain semimetallic or semiconducting. A final rapid opening of the gap to the insulating diamond phase develops as the interlayer carbon-carbon bonds form. The behavior of rhombohedral graphite under conditions of isotropic pressure is also examined. We predict that rhombohedral graphite will transform to diamond, without thermal or catalytic activation, at an isotropic pressure of 80 GPa if it maintains its rhombohedral symmetry. Our analysis moreover suggests that, in general, cross linking of hexagonal-ring carbon compounds leading to local tetrahedral coordination should be favored when the interlayer distance between hexagonal rings is between 2.1 and 2.3 A\r{}.

High-Pressure Ruby and Diamond Fluorescence: Observations at 0.21 to 0.55 Terapascal

Abstract: A diamond-anvil, high-pressure apparatus was used to extend the upper pressure limit of static laboratory experiments. Shifts of the R(1) strong fluorescent line of ruby were observed that correspond to static pressures of 0.21 to 0.55 terapascal (2.1 to 5.5 megabars) at 25 degrees C. Sensitive spectroscopic techniques in the pressure range 0.15 to 0.28 terapascal were used to observe ruby and diamond fluorescence separately; these two fluorescent emissions overlap strongly at high pressures. At pressures greater than approximately 0.28 terapascal, the diamond fluorescence diminished and the ruby fluorescence reappeared strongly. Pressure was determined by extrapolation of the calibrated shift of the ruby R(1) line.

Optical phonons and elasticity of diamond at megabar stresses

Abstract: The optical \ensuremath{\Gamma} phonon and the stress-strain relations in diamond are investigated for general uniaxial and hydrostatic stresses up to several megabar. Theoretical calculations are carried out using ab initio pseudopotentials within local-density-functional theory. Second-, third-, and fourth-order elastic constants are evaluated, including the internal-strain effect. The splittings and shifts of the \ensuremath{\Gamma} phonon are predicted up to cubic order in the macroscopic strain. A number of quantities are predicted, and where experimental results are available good agreement is found. At large uniaxial stresses (\ensuremath{\sim}4 Mbar) the electronic band gap collapses, and a phonon instability of the metallic diamond structure is found for compressions along the [110] and [111] crystal axes.

Polycrystalline diamond and CBN cutting tools

Abstract: A cutting tool comprised of a polycrystalline layer of diamond or cubic boron nitride which has a cutting edge and at least one straight edge wherein one face of the polycrystalline layer is adhered to a substrate of cemented carbide and wherein a straight edge is adhered to one side of a wall of cemented carbide which is integral with the substrate, the thickness of the polycrystalline layer and the height of the wall being substantially equivalent.

Excimer-laser etching of diamond and hard carbon films by direct writing and optical projection

Abstract: Excimer‐laser patterning of monocrystalline diamond was performed in the direct writing and in the optical projection modes. The etching mechanism employs combined photochemical/thermal transformation of the initial crystal to graphite followed by sublimation or reaction of the transformed solid. In optical projection, linewidths as narrow as 0.13 μm were etched with patterning possible using single 0.193 μm (wavelength) laser pulses. Etch rates of 2000 A/pulse were achieved. The morphology of the etched features was optimized by introducing gases which reacted chemically with the hot graphitic layer generated in the process of etching. Patterning of diamond‐like carbon thin films was accomplished and the effectiveness of these films as resists for submicrometer‐resolution lithography of semiconductors was demonstrated.

Finite element analysis of the diamond anvil cell: Achieving 4.6 Mbar

Abstract: We have performed a comprehensive finite element analysis of the diamond anvil cell. Our analysis shows how beveled diamonds and material properties of the gasket affect diamond anvil cell performance. Using the results of the analysis, we have achieved 4.6 Mbar experimentally, which is the highest static pressure reported to date. Possible methods to increase the pressure further are discussed.

Thermal Conductivity of Diamond Films Synthesized by Microwave Plasma CVD

Abstract: A measurement method is developed for the thermal conductivity of thin films in the direction parallel to the surface. Measurements are made between 100°C and 130°C for diannond films from 7 µm to 30 µm thick that are synthesized from a gas phase of methane/hydrogen mixture by microwave plasma chemical vapor deposition, The thermal conductivity of diamond films increases rapidly with decreasing concentration of methane. The highest thermal conductivity ever obtained in this experiment is about 1000 Wm-1 K-1. The thermal conductivity and Raman spectrum are compared under different synthesis conditions.

Process for synthesis of diamond by CVD

Abstract: A synthesizing process for diamond by the chemical vapor phase growth method, characterized by converting an organic compound containing carbon, hydrogen and at least one of oxygen and nitrogen, to a gas phase, mixing the gas with hydrogen gas, decomposing the mixed gas by an energy of heat, electron beam, light, direct current glow discharge, alternating current glow discharge, or direct current arc discharge, and introducing the decomposed gas to the surface of a heated substrate (5) to deposit diamond on the surface of the substrate.

Synthesis of diamond by laser‐induced chemical vapor deposition

Abstract: Diamond has been obtained by ArF excimer laser‐induced chemical vapor deposition. The reaction was carried out by use of C2H2 diluted with H2 as a source gas and at the pressure range of 8–75 Torr. The products were characterized by scanning electron microscopy and reflection electron diffraction. Deposits prepared in the temperature range of 40–800 °C, which were measured by the thermocouple attached to the substrate, show several lines of diamond in the reflection electron diffraction photographs. The fact that the laser beam must be concentrated for the diamond formation to occur strongly suggests that the reaction proceeds through a multiple photon process.

An Application of Surface-Enhanced Raman Scattering to the Surface Characterization of Carbon Materials

Abstract: Surface-enhanced Raman scattering (SERS) has been successfully applied to the surface characterization of carbon materials such as highly oriented pyrolitic graphite, pyrolitic graphite, glassy carbon, diamond, and carbon fibers by the evaporation of Ag island films onto the surface. The surface chemical and morphological structure of carbon materials has been parallelly characterized by electron energy loss spectroscopy, x-ray photoelectron spectroscopy, and field-emission scanning electron microscope. Raman scattering from the outermost surface of carbon materials is found to be remarkably enhanced by the presence of Ag island films (50-100 A). The chemical and crystal structure change of graphite and diamond by argon-ion etching has also been studied by the enhanced Raman spectra. The obtained results demonstrate the possibility of using SERS with the Ag overlayer method as a new high-sensitivity surface probe for various kinds of industrial materials.

Polycrystalline abrasive grit

Abstract: Diamond or CBN polycrystalline abrasive grit useful in tools for grinding or cutting is made by size reducing and leaching non-diamond or non-CBN material from a compact greater than 1,000 microns in diameter to provide polycrystalline abrasive grit having a size of from about 1 to about 1,000 microns in diameter and having a network of inter-connected, empty pores dispersed throughout.

Fine diamond turning of KDP crystals.

Abstract: Frequency doubling optical components for the Nova laser system are made from single-crystal potassium dihydrogen phosphate (KDP). While developing a manufacturing process for these components, we found that single-point diamond turning could be used to directly produce finished parts with no need for additional surface polishing. A surface roughness of better than 8-A rms and 36-A P-V was measured on a test sample generated with certain machine and tool parameters. Further improvement in surface finish may be possible by employing refined diamond turning procedures and equipment.

Diamond coated scaler dental instrument for ultrasonic operation

Abstract: The invention is an improved dental instrument for scaling by ultrasonic operation. The scaler is coated with diamond particles to overcome the patient discomfort associated with the prior art chipping and dislodgement procedures. Four unique and novel scaler configurations are provided for various aspects of dental work, each is diamond coated and fitted for ultrasonic operation at lower power settings than present prior art instruments.

Textural Characterization of Porous Carbons by Physical Adsorption of Gases

Abstract: The carbons involved in many industrial applications take many diverse forms ranging from well-developed crystalline structures, such as graphite and diamond, to the so-called amorphous varieties such as carbon blacks, cokes, chars, activated carbons.

Cooling networks for pcd bearing surfaces

Abstract: Polycrystalline diamond wear surfaces (17) in bearing structures (11) are maintained at temperatures that prevent thermal degradation in spite of exceptionally high loads. This temperature control is accomplished by segmenting the diamond wear surface to provide interrupt channels (13, 15) through which the energy build-up at the diamond wear surface is maintained below the thermal degradation level. Cooling fluid may be caused to flow through the interrupt channels, the higher the velocity of fluid flow around the diamond bearing surface, the greater the cooling effect.

Surface graphitization of diamond at high temperatures

Abstract: Graphitization of diamond powders has been studied experimentally in a vacuum in the temperature range 1700 – 2100 K. The existence of two graphitization regions with different activation energies has been established. An increase in the specific graphitization rate with an increase in the size of the diamond powder particles, the so-called dimensional effect, has been established at temperatures above 1900 K. The stationary distribution of vacancies in small-size diamond particles explains the observed effect.

Improvements in or relating to cutting elements for rotary drill bits

Abstract: A method of producing a thermally stable polycrystalline diamond compact comprises placing in a high pressure/high temperature apparatus a mass of polycrystalline diamond particles, the mass having a front face and a rear face, and a mass of catalyst metallic material, and then subjecting the masses to high pressure and temperature such that the metallic material infiltrates the mass of diamond particles so as to form, on subsequent cooling, a solid composite compact. The grain size and/or packing density of the polycrystalline diamond particles is varied between said front face and rear face in such manner that, in the finished compact, material nearer the rear face is less wear resistant than material nearer the front face, so that the compact is self-sharpening in use. Alternatively or additionally, the wear resistance is varied by including an additive with the diamond particles, the proportion of the additive varying between the front face and rear face.

Member coated with diamond and its production

Abstract: PURPOSE:To improve the adhesion properties for a base body of a diamond film and to increase the quality and the reliability by forming the diamond film on the base body via a middle layer having a carbon component or the like CONSTITUTION:After providing a base body to the inside of a reaction chamber, the gas contg the constituting elements of the base body and the gas contg carbon are introduced into the reaction chamber to perform the gas phase growth A middle layer having the base body components and carbon components is formed on the base body and thereafter a diamond film is formed on the middle layer