Showing papers on "Diamond published in 1983"

Electron microscopic observation of diamond particles grown from the vapour phase

Abstract: Diamond particles prepared by chemical vapour deposition from a mixture of methane and hydrogen gases have been examined by electron microscopy. The particles were crystalline with a cubic structure. The typical habit was cubo-octahedron and twinned crystals, i.e. spinel-law twins and multiply-twinned particles, were also observed. Four cage compounds, i.e. bicyclo[2.2.2] octane, tetracyclo[4.4.0.13,9.14,8] dodecane, hexacyclo[5.5.1.12,6.18,12.03,11.05,9]pentadecaneand dodecahedrane are proposed for embryos of twinned crystals.

Will diamond transform under megabar pressures

Abstract: It is predicted that among the fcc, bcc, hcp, simple cubic, and $\ensuremath{\beta}$-tin phases, diamond will first transform to the simple cubic phase under a hydrostatic pressure of 23 Mbar. The absence of $p$ electrons in the core causes remarkably strong $s{p}^{3}$ bonding in diamond. This stabilizes diamond against the other five phases under high pressures. The study is carried out using ab initio pseudopotential theory within the local-density-functional formalism.

Luminescence decay time of the 1.945 eV centre in type Ib diamond

Abstract: The luminescence decay time of the 1.945 eV centre has been determined as 13+or-0.5 ns for natural type Ib diamonds. For synthetic diamonds the value is slightly lower, probably because of competitive non-radiative recombination in these relatively impure crystals. The similarity of the decay time to that for the H3 centre further supports the model proposed for the vacancy-enhanced aggregation of nitrogen in diamond. No temperature dependence of the 1.945 eV decay time has been detected in the range 77-700K, and this result is not inconsistent with the energy level scheme used to interpret ESR data for the 1.945 eV centre.

Process for making diamond and cubic boron nitride compacts

Abstract: The high pressure/high temperature (HP/HT) process for making diamond or CBN compacts has been modified by placing partitions within the crystal mass before HP/HT processing. With reference to FIG. 3, within the shield metal sleeve 11 and shield metal cup 14 are placed pliable metal shapes 20 in a honeycomb pattern. The abrasive crystals within the tubes 18 and outside the tubes 26 is sintered, and a compact containing the tubes embedded therein results. This compact can be acid leached to give a plurality of small compacts which need little if any additional shaping. The partitions can also be left intact as chip arresters.

Diamond-like film and process for producing same

Abstract: An amorphous, carbonaceous, diamond-like film and a process for producing the same is disclosed. The film has an extremely low hydrogen content and an extremely low stress, is resistant to both acids and alkalis, and adheres tenaciously to many types of substrates including glasses, plastics, metals, and semiconductors. The process for producing this film is a hybrid process using radio frequency plasma decomposition of an alkane and a pair of spaced carbon electrodes.

Abrasive product and method for manufacturing

Abstract: An abrasive body is provided which has high strength and an ability to withstand high temperatures making it suitable as a tool insert for dressing tools and surface set drill bits. The body comprises a mass of diamond particles present in an amount of 80 to 90 percent by volume of the body and a second phase present in an amount of 10 to 20 percent by volume of the body, the mass of diamond particles containing substantial diamond-to-diamond bonding to form a coherent skeletal mass and the second phase containing nickel and silicon, the nickel being in the form of nickel and/or nickel silicide and the silicon being in the form of silicon, silicon carbide and/or nickel silicide. The abrasive bodies are made under conditions of elevated temperature and pressure suitable for diamond compact manufacture.

Hard diamondlike carbon films deposited by ionized deposition of methane gas

Abstract: Very hard diamondlike carbon films have been prepared with the aid of an ionized deposition technique. The growth mechanism of films deposited in the presence of methane gas is discussed. The properties of these carbon films are as follows: The concentration of hydrogen atoms contained in the films is almost negligible. Micro‐Vickers hardness changes depended largely on the deposition conditions, but some of the values obtained were larger than that of sapphire. The 111, 220, and 311 reflections can be observed clearly in the electron diffraction patterns. Moreover the crystal structure obtained from these rings is very close to that of diamond.

Effective p‐type doping of diamond by boron ion implantation

Abstract: Highly conducting p‐type diamond layers have been obtained by high‐dose boron implantation followed by annealing (1400 °C) and subsequent removal of the graphite‐like layer that is formed as a result of the heat treatment. Conductivity and Hall measurements showed transport features typical of heavily doped semiconductors. The fact that identical carbon implantations have yielded no measurable conductivity is taken as evidence that the highly conductive p‐type layer obtained by boron implantation is indeed due to effective doping.

Randomly-oriented polycrystalline silicon carbide coatings for abrasive grains

Abstract: Disclosed is a composite abrasive particle comprising a core abrasive crystal and a silicon carbide coating inherently bonded to substantially all of the exterior surfaces of said core crystal, said silicon carbide coating characterized by silicon carbide crystals having a random orientation substantially independent of the structure of the core crystal, the outer surface of the coating being conformationally irregular Aggregates of the composite abrasive particles are interconnected by a matrix of silicon carbide which has an open structure Preferred core abrasive crystals are diamond or cubic boron nitride The composite abrasive particles preferably are made by infiltrating core crystals coated with non-diamond carbonaceous material with fluid silicon to produce a mass of core crystals bonded together by silicon carbide and elemental silicon, leaching substantially all of the silicon from the bonded mass with a silicon leaching agent, sub-dividing the resulting leached mass, and recovering the composite abrasive particles

Sweep through process for making polycrystalline compacts

Abstract: The high pressure/high temperature catalyst sweep through process for making diamond and cubic boron nitride compacts has been improved by adding an intermediate metal or metal alloy. The added metal (whether alone or contained in an alloy) has a melting point below that of the catalyst (e.g. cobalt), is miscible with the catalyst, and preferably sweeps through the mass of abrasive crystals first. This modification has reduced flaw formation in such compacts.

Multiple layer polycrystalline diamond compact

Abstract: A polycrystalline diamond and metal element for use as a cutting element for drilling holes or similar uses. The cutting element comprises a polycrystalline diamond center portion and at least one metal side portion. The metal side portion is made from a soft metal having a Young's Modulus less than approximately 45×10 6 psi and is selected from a group comprising cobalt, nickel, iron, copper, silver, gold, platinum, palladium and alloys of these metals and intermetallic compounds containing these metals. Since the metal portion is sufficiently yielding the internal stresses formed in the polycrystalline diamond/metal bond during cooling and subsequent attachment to a tool body are signficantly reduced. The reduction the stress in the polycrystalline diamond/metal bond reduces fracturing in the diamond or metal and delamination of the polycrystalline diamond/metal interface during attachment to the tool and during use.

Self-consistent-field investigation of location and hyperfine interaction of muonium in diamond

Abstract: With use of an unrestricted Hartree-Fock self-consistent-field cluster approach, the potential experienced by a muon in diamond has been investigated. The results strongly indicate that normal muonium is localized in the tetrahedral interstitial space. By using the calculated spin density and averaging it explicitly over the vibrational motion of the muon a quantitative explanation is obtained for the observed reduction of the hyperfine field as compared to free muonium.

Dissociation of Dislocations in Diamond

Abstract: Weak-beam electron microscopy has been applied to study the dissociation of dislocations in a type II a diamond. Dislocations with Burgers vector ½[110] on (111) glide planes have been found to be dissociated into two Shockley partials, with separations between 2.5 and 4.3 nm, and extended nodes and dissociated dipoles have also been observed. The stacking fault energy has been determined from the mean and distribution of the separ­ations of the partials to be 279 ± 41 mJ m -2 . The behaviour of dislocations in diamond appears to be similar to that of dislocations in Ge and Si.

Helium as a probe of the (111) surface of diamond

Abstract: Recent experimental results have stimulated this investigation of the potential of interaction, V(r), between a He atom and the (111) surface of diamond. The potential has been computed with various assumptions concerning the presence and configuration of hydrogen adatoms on the surface. Good agreement with He scattering measurements is obtained in the case of a (1 x 1) overlayer with each carbon atom terminated by a single hydrogen adatom of which the C-H bond length is 1.09 A.

Measuring the electrical resistance of metals to 40 GPa in the diamond‐anvil cell

Abstract: A four‐probe technique is described for measuring the electrical resistance of metals in a diamond‐anvil cell at pressures up to 40 GPa. The pressure range for electrical resistance measurements was extended by developing insulating gaskets that provide the necessary support for the diamonds and the electrical leads at the diamond edges. The various gasket materials and construction methods that were tested fall into two categories: (1) gaskets made entirely of insulating materials, and (2) gaskets made of metal coated with insulating materials. Gaskets developed in each category were used successfully in making resistance measurements up to 40 GPa. The most reliable gaskets were composites of sheet mica and MgO powder. This report describes the testing and development of the gaskets and presents electrical resistance data obtained for iron and beryllium to 40 GPa.

Hall-coefficient factor and inverse valence-band parameters of holes in natural diamond

Abstract: In strict analogy with the case of silicon, the Hall-coefficient factor of holes in natural diamond is found to be systematically less than unity in the range of temperature $100lTl1000$ K investigated here. A microscopic interpretation is shown to provide information on the reliability of a different set of inverse valence-band parameters which can be found currently in the literature. Agreement between theory and experiment confirms the values $|A|=3.61$, $|B|=0.18$, and $|C|=3.76$ deduced from pseudopotential band-structure calculations.

Apatite inclusions in natural diamond coat

Abstract: Electron microscopic techniques have been applied to investigate the composition and structure of the non-diamond particles, of submicrometre dimensions, that profusely populate the coat of natural coated diamonds Energy dispersive X-ray spectroscopic analysis (EDS) has shown phosphorus to be commonly present in this included matter, and in the case of some individual crystallites calcium and phosphorus have been the only elements detected with atomic number greater than 11 (the minimum atomic number detectable in the experiments) The latter inclusions exhibit hexagonal prismatic facets and their electron diffraction pattern corresponds to the apatite structure Approximate lattice parameter values found were c/a=073 with a=95 A

Defects production and interaction in ion-implanted diamond

Abstract: Point defects production and interaction are studied by luminescence technique under various conditions of implantation and annealing. New data are presented on the structure and transformation of nitrogen defect complexes. The luminescence due to centres containing implanted atoms of hydrogen, helium, neon and some metals is observed for the first time. The importance of interstitial configurations in ion-implanted diamond is emphasized.

Diamond sintered body and treatment thereof

Abstract: PURPOSE: To improve remarkably the heat resistance of a composite material formed by joining the layer of a sintered body consisting of the binding phase of diamond and a ferrous metal to a sintered hard alloy base material when said material is used for a tool, etc. by removing the binding phase in the surface layer part of said body. CONSTITUTION: A composite sintered body in which a disc-shaped diamond sintered body 1 obtd. under ultrahigh pressure is joined to a sintered hard alloy base material 2 is manufactured. The sintered body 1 contains 90vol% diamond particles having, for example, 5μ average grain size and consists of the balance Co binding phase. The composite sintered body is placed in such a way that the surface of the body 1 contacts with the sponge of a plastic contg. diluted hydrochloric acid soln. and is rested for a required time while a prescribed DC voltage is impressed between the base material 2 and the electrode placed under the sponge. The binding metal Co phase in the certain region 1' from the surface of the body 1 is thus mostly electrolytically removed. The heat resistance of the composite sintered diamond as a tool is thus improved without deteriorating the strength thereof. COPYRIGHT: (C)1984,JPO&Japio

High voltage optoelectronic switching in diamond

Abstract: Subnanosecond photoconductive switching has been observed in ultraviolet illuminated type IIa diamonds. Switching efficiencies up to 50% were attainable in coaxially mounted samples for direct current bias voltage as high as 8 kV at room temperature.