Showing papers on "Diamond published in 1971"

Diamond tools for machining

Abstract: Diamond tools and superpressure processes for the preparation thereof are described wherein the diamond content is present either in the form of a mass comprising diamond crystals bonded to each other or of a thin skin of diamond crystals bonded to each other. In each instance the diamond content is supported on and directly bonded to an extremely stiff sintered carbide substrate in order to provide mechanical support therefor to more effectively utilize the high elastic modulus of the diamond.

The nature of the acceptor centre in semiconducting diamond

Abstract: A precision study has been made of the temperature dependence of the Hall effect and resistivity in five carefully selected natural semiconducting diamonds. The donor and acceptor concentrations in each sample have been calculated from the Hall effect data, and the acceptor concentrations are shown to correlate excellently with the intensities of the acceptor infrared absorption spectrum in each diamond. The behaviour of the resistivity is characteristic of a single acceptor centre, and the much lower activation energy observed at low temperatures is attributed to the tunnelling of electrons from ionized to neutral acceptor centres. The aluminium concentration in each crystal has been measured by slow neutron activation analysis and found to be substantially lower than the acceptor concentration in every case. Aluminium therefore cannot form the acceptor centre as was previously thought. Boron is the only group III element that neutron activation analysis has not eliminated as a possible acceptor, and the results of other workers point to boron as a likely candidate. The revised interpretation, that the acceptor centre in semiconducting diamond is definitely not aluminium and probably boron, is discussed, and its significance to previous publications is critically considered.

Cubic boron nitride/sintered carbide abrasive bodies

Abstract: Abrasive bodies comprising combinations of cubic boron nitride crystals and sintered carbide are disclosed. These composite bodies are prepared by superpressure processes. Cubic boron nitride contents of up to about 99 volume percent have been successfully employed in certain constructions. Similar abrasive bodies have been prepared from mixtures of cubic boron nitride, diamond and carbide powder.

Determination of the occupancy of valence bands in graphite, diamond and less-ordered carbons by X-ray photo-electron spectroscopy

Abstract: The profile of the occupied parts of the valence-band of elemental carbon in a number of distinct forms has been estimated by measuring the intensity of the photo-electrons emitted as a result of AlKα and MgKα irradiation. The widths of the bands for graphite (31 ± 2 eV), for diamond (33±3 eV), and for the less-ordered forms (carbonized poly-vinylidene chloride cellulose char, carbon fibre (PAN), vitreous carbon, powdered nuclear-grade graphite) are larger than expected theoretically, and on the basis of previous soft X-ray spectroscopic measurements. In line with recent views on the consequences of “amorphization”, it is established that the major part of the density-of-states curve is largely unaltered in going from the crystalline to the disordered solid. It is also established that the valence band of coronene is very similar to that of graphite. Our measurements of the binding energies of core electrons yield two main conclusions: (i) the C1s binding energies in diamond and graphite are very similar, the respective values being 284.0 ± 0.3 and 284.3 ± 0.5 eV; (ii) chemisorption of oxygen at prismatic (but not at basal) faces of single-crystals of graphite is readily detectable from the O1s peak, the width of which indicates that at least two types of chemical linkages exist for the bound oxygen.

Window‐Heat Sink Sandwich for Optical Experiments: Diamond (or Sapphire)‐Semiconductor‐Indium Sandwich

Abstract: A fixture for mounting thin semiconductor samples for luminescence and stimulated emission experiments is described. This fixture, a sandwich configuration, consists of a diamond or sapphire window, a thin (1–5 μ) experimental sample, and indium wetted onto copper. In comparison with previous methods for mounting thin samples for optical pumping, the new sandwich fixture affords higher heat dissipation capability (∼103 W/cm2) and total reflection at the sample edges and back surface, thus improving the sample Q and optical performance.

Sintered Diamond Compacts with a Cobalt Binder

Abstract: Diamond powder can be successfully cemented with cobalt. At 62 kilobars the sintering occurs over the temperature range from 1570 degrees to 1610 degrees C. The maximum microhardness of the compact ( 3000 kilograms per square millimeter on the Knoop scale) is obtained with a mixture of 20 percent cobalt (by volume) and a diamond particle size of 1 to 5 micrometers.

The dielectric function in zincblende semiconductors

Abstract: The dielectric function epsilon (q) is calculated by the empirical pseudopotential method for fourteen semiconductors with the diamond and zincblende structures. The predictions of the static limit epsilon (0) are in excellent agreement with experiment. The form of the screening in real space is also given.

Lattice distortion near vacancies in diamond and silicon. I

Abstract: A dynamical relaxation procedure, coupled with a valence force potential, has been used to calculate the distortion around point defects in a diamond-type crystal. The method has been applied to the vacancy in diamond and silicon. The response of the lattice to symmetrized forces on the nearest neighbours to the vacancy was calculated. The results can be used in estimates of point defect properties which depend on lattice distortion, including the jahn-teller effect, and formation energies. The ratios of the atomic displacements under uniform external stresses for the perfect lattice and for the lattice with a vacancy are also determined.

Point defect calculations in diamond-type crystals by the extended Huckel method 1: General theory and the vacancy problem

Abstract: The applicability of the extended Huckel method for the calculation of the electronic properties of point defects in diamond-type crystals is discussed A detailed study of the isolated vacancy in both the diamond and silicon lattice shows that the results obtained depend upon the size of the cluster chosen and the approximations made at the boundary of the system Clusters with up to 47 host lattice atoms are considered A cluster of 41 atoms, which includes all atoms directly bonded to the second neighbours from the point defect, is considered to be the most suitable system On the basis of a comparison of ab initio and extended Huckel calculations for small molecules, it is argued that studies involving distortions are beyond the validity of the simple method used here At best, the results from extended Huckel studies for point defects in diamond type crystal should be considered to be semiquantitative

Wear resistant diamond coating and method of application

Abstract: A process for producing an extremely hard and wear resistant coating on a basis metal comprising the electro-deposition of fine grained diamonds and diamond particles in a metal matrix upon said basis metal. The coating comprises a uniform electrolytic deposit of a metal matrix having embedded therein diamonds and diamond particles ranging between 0.01 micron to 30 microns in size.

Lattice distortion near vacancies in diamond and silicon .1.

Abstract: A dynamical relaxation procedure, coupled with a valence force potential, has been used to calculate the distortion around point defects in a diamond-type crystal. The method has been applied to the vacancy in diamond and silicon. The response of the lattice to symmetrized forces on the nearest neighbours to the vacancy was calculated. The results can be used in estimates of point defect properties which depend on lattice distortion, including the jahn-teller effect, and formation energies. The ratios of the atomic displacements under uniform external stresses for the perfect lattice and for the lattice with a vacancy are also determined.

Method for Finishing Composite Restorative Materials

Abstract: An instrument, designed to finish the surface of composite restorative materials, was made by bonding 1μ to 5μ diamond particles to flexible paper disks. The surface finish produced by this instrument was superior to that obtained by fine cuttlefish disks and inferior to surfaces obtained by the hardening of the material in contact with polished glass. Results are presented with use of scanning electron photomicrographs.

Microstructural Study of Diamonds Synthesized under Conditions of High Temperature and Moderate Explosive Shock Pressure

Abstract: Diamond explosively synthesized from metal/graphite mixtures in shock configurations resulting in high temperatures, moderately high pressures, and relatively long holding times at pressure were investigated by electron microscopy and electron diffraction. Particles up to 5‐μ diameter consist of a matrix of 10–40 A, variously oriented crystallites which contain clusters of randomly oriented 100–1600‐A crystallites. Particles larger than 4–5 μ are densely fused aggregates of such composite units.

Anharmonic interactions in diamond‐type crystals

Abstract: The potential energy of diamond, Si, and Ge crystals has been expanded in a double power series of the infinitesimal strain parameters and phonon coordinates. Third and fourth order expansion coefficients have been fitted to give reasonable agreement with the Gruneisen parameters of the individual modes of vibration, the mean Gruneisen parameters and thermal expansion coefficients, the third order elastic constants and the temperature dependence of the elastic constants. Calculations have been made for the mass operators of normal mode spropagating in the [100] and [111] directions. The relative renormalization of the low energy TA modes in Ge and Si is of the order of 10% while it is one order of magnitude less for phonons of the other branches. Die Kopplungskoeffizienten dritter und vierter Ordnung einer Entwicklung des Kristall-potentials von Diamant, Si und Ge in eine Doppelreihe nach Dehnungsparametern und Ionenauslenkungen wurden aus Gruneisenparametern einzelner Phononen, mittleren Gruneisenparametern, thermischen Ausdehnungskoeffizienten, elastischen Konstanten dritter Ordnung und der Temperaturabhangigkeit der elastischen Konstanten bestimmt. Die Massenoperatoren von Phononen in der [100]- und [111]-Richtung wurden berechnet. Es zeigt sich, das bei Ge und Si die relative frequenzabhangige Renormierung der harmonisch berechneten transversal akustischen Zweige bis zu 10% betragt, wahrend sie fur andere Zweige eine Grosenordnung schwacher ist.

Diamond-nondiamond carbon polycrystalline composites

Abstract: Diamond-nondiamond carbon polycrystalline composites particularly useful as abrasives are made by sintering diamond particles at temperatures above about 1440*K but at pressures below which diamond is stable or metastable with respect to its conversion to graphite.

Temperature Dependence of the Long-Wavelength Optical Phonons in Diamond

Abstract: Temperature effects on long wavelength photon frequency and linewidth in diamond, using Raman scattering techniques

X-ray study of neutron irradiated diamonds

Abstract: The diffuse X-ray maxima exhibited by single crystal diamonds, which had undergone a density decrease of about 6% on fast neutron irradiation, lay closer to the Bragg positions of the irradiated crystals than those of the unirradiated crystals. Annealing resulted in shift of both the diffuse maxima and the Bragg positions. Diamonds in which the macroscopic density decrease on irradiation was less than about 12% recovered towards the original single crystal form on annealing. However, diamonds in which the density decrease on irradiation was more than about 12% reverted towards a semi-amorphous state, the density of which was about half that of unirradiated diamond, on annealing at temperatures below that required to produce significant graphitization in unirradiated diamond. Type I X-ray behaviour was observed after annealing diamonds which had undergone density decreases on irradiation of up to 9%.

Process for epitaxial growth of diamonds

Abstract: A method for growing diamonds in the form of diamond dust, industrial grade diamonds and the like, by epitaxy comprising the steps of providing a diamond seed crystal, contacting said diamond seed crystal with a hydrocarbon having from one to about five carbon atoms in an environment consisting of at least 95 percent hydrogen gas by volume and about no more than 5 percent of the said hydrocarbon by volume, maintaining the temperature of the reaction environment in the range of from about 1,100 DEG C. to about 1,700 DEG C., and reacting the said diamond seed crystal with the said hydrocarbon and the hydrogen gas in the presence of a catalyst being a member selected from the group consisting of platinum and paladium, thereby causing said hydrocarbon to form diamond carbon and deposit it on the surface of said diamond seed crystal while simultaneously causing less stable forms of carbon also formed from said hydrocarbon to react with the hydrogen gas in the presence of the catalyst and the temperature conditions to form additional quantities of hydrocarbon, said process continuing until the desired diamond growth has been achieved.

Radiation-induced defects in diamond.

Abstract: A critical review of radiation damage in diamond is presented, focusing on important specific centres rather than attempting a review of the whole field. The proposed models for these centres are examined and often found wanting. Phenomena observed in ion bombardment of diamond is discussed and found to probably be due to amorphous or graphite surface layers. Throughout a number of suggestions of important experiments are given.

Diamond genesis — A synthesis of opposing views

Abstract: Estimates of the pressure and temperature in the region of kimberlite magma generation are compatible with the formation of diamond in its own thermodynamic stability field as deduced from high pressure experimental synthesis of diamond. However, if diamond growth is allowed only within its stability field, preservation during ascent of kimberlite magma and many properties of diamond distribution in kimberlite pipes as well as some of the geochemical properties of diamond are very difficult to explain. Metastable diamond growth in the laboratory is well established and its occurrence in natural systems is proposed. A theory of genesis with synthesis of diamond seed nucleii in kimberlite magma at depth in the mantle and with continued metastable growth during ascent and in kimberlite magma pools at the base of the crust is proposed. Eruption of kimberlite pipes to the surface terminates diamond growth.

Method for preparing diamonds for use with grinding wheels

Abstract: A grinding element having a grinding section comprising diamond particles individually embedded in a resin binding medium with improved performance characteristics is provided, along with a method of making same. The improved characteristics are obtained by utilizing a metal coating on the diamond particles in the grinding section, which metal coating has a thickness of between 0.5 and 25 microns, preferably 5 to 20 microns, to impart to the section superior grinding properties to those which can be obtained with a like section wherein the diamond particles are not so coated.