Showing papers on "Diamond published in 1978"

Electron spin resonance in the study of diamond

Abstract: The role of electron spin resonance in the study of both natural and synthetic diamond is reviewed. A brief survey of the physical significance of the constants in the spin Hamiltonian, as well as experimental technique, is given. The various nitrogen centres are discussed treating exchange-interaction, Jahn-Teller and relaxation effects associated with these centres. The spin Hamiltonian parameters of these centres are tabled and the results are discussed within the framework of the defect molecule approach. In conclusion, the correlation between optical effects and the ESR measurements in the case of four defect centres are discussed in some detail as this seems to be a powerful method of testing the various models suggested for the observed defects.

Effect of uniaxial stress on the zone-center optical phonon of diamond

Abstract: The effect of uniaxial stress along [001] and [111] on the zone-center optical phonon of diamond has been studied, and the corresponding deformation potentials determined. The results are interpreted in terms of a valence-field-force model. A fit to the theory of our experimental results and the measured variation of the elastic constants under hydrostatic stress, a total of six data with three adjustable parameters, allows all the third-order elastic constants to be determined.

High-pressure physics: sustained static generation of 1.36 to 1.72 megabars.

Abstract: The pressure in experiments with the diamond-window pressure cell exceeded 1.7 megabars (at 25°C). This is the highest sustained pressure ever generated under static conditions where the pressure in the sample itself was measured. At 1.72 megabars, macroscopic flow of one of the diamond pressure faces was observed.

Silicon carbide and silicon bonded polycrystalline diamond body and method of making it

Abstract: A mass of diamond crystals contacting a mass of elemental silicon are confined within a pressure-transmitting medium. The resulting charge assembly is subjected to a pressure of at least 25 kilobars causing application of isostatic pressure to the contacting masses which dimensionally stabilizes them and increases the density of the mass of diamond crystals. The resulting pressure-maintained charge assembly is heated to a temperature sufficient to melt the silicon and at which no significant graphitization of the diamond occurs whereby the silicon is infiltrated through the interstices between the diamond crystals producing, upon cooling, an adherently bonded integral body.

Composite compact components fabricated with high temperature brazing filler metal and method for making same

Abstract: A component comprised of a composite compact, preferably diamond, and a substrate bonded to the compact. A preferred embodiment of the component is a cutter for a drill bit. The compact is comprised of a layer of bonded diamond or boron nitride particles and a base layer of cemented carbide bonded, preferably under high temperatures and pressures, to the particulate layer. The particulate layer is degradable by exposure to temperatures above a predetermined temperature. The substrate is bonded to the base layer of the compact with a filler metal which, to form a bond, requires the exposure of the surfaces to be bonded to a temperature substantially greater than the degradation temperature of the particulate layer. The component is fabricated by heating the base layer, filler metal and substrate to a temperature in excess of the degradation temperature while maintaining the temperature of the particulate layer below the degradation temperature via a heat sink.

Conductivity and mobility edges in disordered systems. II. Further calculations for the square and diamond lattices

Abstract: For pt.I see ibid., vol.8, p.4150 (1975). Further calculations for the Anderson model (1972) of a disordered lattice and square lattice are described. For the diamond lattice the critical value of disorder needed to destroy extended states is found to be W/V=8, which is considerably less than earlier calculations gave. There is however a wide range for which states seem to be intermediate between extended and exponentially localised states. Calculations of the conductance for much larger samples of a square lattice than were previously studied show that states identified as extended have a conductance that gets less as the sample gets larger, so that some doubt is cast on earlier conclusions about the minimum metallic conductance in two dimensions. Studies of the parameter A= integral mod Psi alpha mod 4/( mod integral Psi alpha mod 2)2 for the square and diamond lattices are reported. This seems to decrease smoothly to zero as the mobility edge is approached, but, since it approaches zero as (Ec-E)delta with delta apparently less than unity, interaction effects should lead to a vanishing density of states at the mobility edge and to the coexistence of itinerant electrons and unpaired localised electrons when the Fermi energy is just above the mobility edge.

Clean surface reactions between diamond and steel

Abstract: THE rate of wear of diamond grinding on machining steel is known to be extremely high. For example, the wear rate of a diamond turning mild steel is 104 times greater than when turning brass of comparable hardness1. Several discussions of this wear conclude that it is due principally to the high local flash temperatures generated during machining and to the catalytic properties of the steel. Static experiments show that diamond graphitises at temperatures above 1,800K in vacuo, or above 1,100K in the presence of iron, and other experiments that flash temperatures of this order may be generated by machining. Hence, there is now general agreement that the wear proceeds by the graphitisation of the diamond; the surface layer of graphite being continually removed either by the abrasion of the steel or by solution in the steel2–7. However, little information is available on the actual conditions prevailing at the interface during machining. Therefore, we have studied the mechanism of wear more closely by making quantitative measurements of the wear rates of round-nosed diamond tools turning billets of mild steel under well defined conditions.

Plastic deformation of diamond at room temperature

Abstract: POLISHED (101) surfaces of type IIB diamonds have been indented with a Knoop indenter at room temperature. The diamonds were thinned from the opposite side by ion-beam bombardment and the resulting deformation observed and analysed using transmission electron microscopy. For the two orientations of indentation examined so far, it has been found that shear events (probably shear cracks) and dislocations comprise the major part of the deformation. Diamond is usually considered to be a brittle material, easy fracture (cleavage) occurring on {111} planes. Although plastic deformation and dislocation generation (also on {111} planes) have been demonstrated in diamond at 1,800 °C (ref. 1) there has been continuing interest as to whether any plastic flow at all occurs at normal temperatures2. Several means of deciding this question have been tried3–7, but the results are mostly inconclusive. We have indented diamond specimens with a Knoop indentor8 and observed the resulting deformation directly using transmission electron microscopy. We report here preliminary results for indentations whose long axes are close to [ 01] and [010] directions in the (101) surface.

Growth of synthetic diamonds

Abstract: A method of growing a diamond crystal which comprises bombarding the diamond with a flux of carbon ions of sufficient energy to penetrate the diamond crystal and cause crystal growth which is at least predominantly internal, the temperature of the crystal being at least 400° C. and less than the graphitisation temperature, such that the diamond crystal structure is maintained during growth.

Ion implantation into diamond

Abstract: The data on the possibilities of controlling of the properties of diamond by ion implantation are presented and analyzed.

Partial dissociation of nitrogen aggregates in diamond by high temperature-high pressure treatments

Abstract: Type I(a) diamonds contain high concentrations of nitrogen, almost all of which is in an aggregated form. The two main aggregates are recognized by characteristic absorption features in the infrared region of the spectrum. These are called A and B features; usually a peak designated B' is also present. When such diamonds were heated at 1960 degrees C and above under a stabilizing pressure of 85 kbar (8.5 GPa) the nitrogen aggregates partially dissociated, producing single substitutional atoms which were identified by electron paramagnetic resonance (e.p.r.) measurements. Experiments with selected diamonds, showing wide variations in their characteristic infrared absorption, determined the relative stability of the A and B centres. Optical measurements led to the determination of a general relation between the strengths of the A, B and B' features. The experimental observations suggest a scheme for the occurrence of type I(a) diamonds containing nitrogen atoms which have aggregated into A centres; type I(b) diamonds can also be included in this scheme.

Polycrystalline diamond and/or cubic boron nitride body and process for making said body

Abstract: A shaped confined mass of diamond and/or cubic boron nitride crystals coated with elemental non-diamond carbon, under a partial vacuum, is infiltrated by fluid silicon producing a like-shaped product wherein the crystals are bonded together by a medium comprised of silicon carbide and elemental silicon.

Relaxation about the vacancy in diamond

Abstract: The relaxation about a vacancy in diamond results from modifications in the local chemical bonding. Further relaxation occurs to lower the electronic degeneracy through the Jahn-Teller effect. Both effects are considered by using a semi-empirical molecular-orbital cluster-model of the vacancy to calculate the relaxation of the lattice about it. An 1E ground state of the neutral vacancy is found with a Jahn-Teller energy of 460 meV coupled to tetragonal modes. The negative vacancy is found to have an 4A2 ground state. Both give rise to substantial, totally symmetric, inwards relaxation.

Dielectric breakdown threshold, two-photon absorption, and other optical damage mechanisms in diamond

Abstract: The breakdown threshold and two-photon absorption coefficient are measured in diamond with picosecond pulses at 1.06 and 0.53 μm. The rms breakdown threshold at 1.06 μm is 21.5 MV/cm. The two-photon absorption coefficient at 0.53 μm is less than 2.6 \times 10^{-4} cm/MW.

The structure and motion of the self-interstitial in diamond

Abstract: We have made self-consistent semi-empirical molecular orbital calculations for various possible self-interstitial geometries in diamond, both with and without lattice distortion. Total energies are obtained, not merely the sum of one-electron eigenvalues. The results show that the (100) split interstitial has the lowest formation energy, not the cubic, hexagonal or bond-centred forms favour previously. The nature of the interstitial does not support the local heating model of enhanced diffusion in the presence of recombination or ionisation. A Bourgoin-Corbett mechanism involving negative hexagonal and neutral split interstitials is possible, but the apparent stability of the negative hexagonal interstitial may be an artefact of the calculation. We suggest a local excitation model is appropriate in fourfold-coordinated semiconductors.

The decay time of N3 luminescence in natural diamond

Abstract: Measurements are reported of the decay time of photoluminescence from the N3 centre: an impurity centre commonly found in natural diamond. The intrinsic decay time at low temperature is found to be 41 ± 1 ns. The decay time is specimen dependent, decreasing with increasing concentrations of pairs of substitutional nitrogen atoms in the diamonds. The data are consistent with an electric dipole, electric-quadrupole coupling of the N3 centres to the nitrogen pairs. In addition, the decay time is reduced by raising the specimen temperature, especially above 450 K. These results are consistent with internal conversion occurring into another excited electronic state of the N3 centre. The properties required for this state agree with deductions from other optical and electron paramagnetic resonance (e. p. r.) data. The radiative lifetime of the N3 luminescence transition is estimated at 150 ns, in agreement with previous luminescence efficiency measurements.

Method of producing a sintered diamond compact

Abstract: A sintered compact for use in a cutting tool and a method of producing the same are disclosed. The compact comprises 95 to 20 volume % of diamond finer than one micron in size and the balance binder also finer than one micron selected from the group of WC, (MoW)C, WC base cemented carbide and (MoW)C base cemented carbide. The method comprises pulverizing a diamond powder by using cemented carbide balls and a pot having a cemented carbide lining, mixing the diamond powder with a powder abraded from the balls and pot to produce a powder mix finer than one micron containing 95 to 20 volume % of diamond, heat-treating the powder mix in vacuum so as to degas, and hot-pressing the powder mix under high pressure at high temperature within the stable range of diamond.

Self-consistent pseudopotential calculations for Ge and diamond (111) surfaces

Abstract: The self-consistent pseudopotential method with a slab geometry is applied to electronicstructure calculations of the Ge and diamond (111) surfaces. A nonlocal pseudopotential is derived and found to produce an energy band structure of bulk diamond in good agreement with other calculations and experiments. This potential is then used for the diamond surface calculations. The calculations are restricted to unrelaxed unreconstructed surfaces. Various surface states are identified and discussed.

Process for producing a composite of polycrystalline diamond and/or cubic boron nitride body and substrate phases

Abstract: A shaped confined structure composed of a mass of diamond and/or cubic boron nitride crystals coated with elemental non-diamond carbon in contact with a carbonaceous substrate is infiltrated by fluid silicon producing a like-shaped composite of a polycrystalline body phase integrally bonded to a substrate supporting phase.

Thermal conductivity of natural diamond between 320 and 450 K

Abstract: Thermal-conductivity experiments with linear heat flow and radiation thermometry were done on one hundred selected natural diamonds. The results were found to correlate with the infrared absorptions and thus with the nitrogen impurity concentrations. A few results for synthetic diamonds are also reported.

Epitaxial synthesis of diamond by carbon-ion deposition at low energy

Abstract: THIN epitaxial layers have been grown in vacuum by the controlled deposition of low-energy carbon ions on to heated single crystal diamond substrates by a process described here. Reproducible crystalline growth, up to 10 µm in thickness and up to several mm2 in area, has been observed on both natural stones and polished diamond plaques1. Three competing forms of ion-deposited carbon have also been characterised.

Migration of nitrogen in electron-irradiated type Ib diamond

Abstract: The 1.945 eV optical centre is produced in type Ib diamond by radiation damage and annealing at approximately 800 degrees C. The author reports that H3 (2.463 eV) centres, characteristic of irradiated and annealed type Ia diamond, have been created by heating an irradiated type Ib diamond to temperatures where nitrogen aggregation occurs. This observation strongly supports the models recently proposed for the H3 and 1.945 eV centres. The rate of nitrogen aggregation appears to be considerably faster than that reported previously for unirradiated samples.

Diamond-Metal Interfaces and the Theory of Schottky Barriers

Abstract: A self-consistent pseudopotential calculation of the diamond-metal interface is used to examine interface states and empirical correlation for the dependence of the Schottkybarrier height and interface index, $S$, on ionicity. The properties of diamond are crucial because of its large gap and zero ionicity. Predictions based on experimental extrapolations give $S\ensuremath{\approx}0$. Our calculations give $S=0.4$ and a barrier height of 2.2 eV; the latter is in good agreement with experiment.

Process for preparing a polycrystalline diamond body

Abstract: A cavity of predetermined size is formed in a compressed pressure transmitting powder medium, a mass of diamond crystals in contact with a mass of elemental silicon are disposed within the cavity and additional pressure transmitting powder is placed over the cavity and its contents producing a powder-enveloped cavity. Pressure is applied to the powder medium resulting in substantially isostatic pressure being applied to the cavity therein and its contents sufficient to dimensionally stabilize the cavity and its contents. The resulting shaped substantially isostatic system of powder-enveloped diamond and silicon is hot-pressed to liquefy and infiltrate the silicon through the interstices between the diamond crystals producing, upon cooling, an adherently bonded integral body.

Impregnated diamond drill bit

Abstract: An impregnated diamond drill bit having a crown containing a plurality of diamond particles The crown is formed from a fused powdered metallic matrix that includes titanium carbide and a nickel-manganese alloy The diamond particles are dispersed within the metallic matrix which is then fused so as to hold the diamond particles in place Although the mixture including the nickel-manganese solid solutions has a lower degree of hardness than that of prior impregnated diamond drill bits, the use of the nickel-manganese alloy improves the retention ability of the metallic matrix for securing the diamonds within the crown A steel shank is attached to the crown

Diamond targets for producing high intensity soft x-rays and a method of exposing x-ray resists

Abstract: The present invention relates to diamond targets for carbon K x-ray generators and to a method for exposing x-ray sensitive resists to carbon K x-rays using an x-ray generator with a diamond target. It has been discovered that diamond targets, preferably of Type IIb diamond, will dissipate considerably more power and thus produce higher intensity x-rays than graphite targets despite diamond's lower limiting temperature. Such x-rays allow one to expose an x-ray resist through a mask in only 67 seconds and achieve a resolution of 0.2μ.

Fresnel diffraction at {100} platelets in diamond: An attempt at defect structure analysis by high-resolution (3 Å) phase-contrast microscopy

Abstract: High-resolution (0·3 nm) images of platelets in diamond have been obtained using ultra-high resolution pole-pieces with spherical aberration coefficient C s = 0·7 mm. A through-focal series of images of a (100) defect, viewed edge-on in the [001] zone, shows phase contract which may be interpreted, using the projected-charge-density approximation, as arising from a thin lamella 2 ± 1 atomic layers thick having charge density, as seen by electrons, only slightly less dense than diamond. Image matching, using full-scale N-beam dynamical theory and the method of periodic continuation (MacLagan, Bursill and Spargo 1977) was undertaken using a number of structural models designed to probe the width and charge density of the patelets. The calculation included the effects of beam divergence, crystal tilt and phase changes caused by spherical aberration and objective lens defocus. Models included the nitrogen platelet proposed by Lang (1964), interstitial carbon (also with hydrogen to complete tetrahedra...