Showing papers on "Diamond published in 1970"

Impurity conduction in synthetic semiconducting diamond

Abstract: Electrical conductivity and Hall effect measurements have been made on a series of synthetic p-type semiconducting diamonds in the temperature range 80 to 450K. The dominant conductivity mechanism at low temperatures is shown to be impurity conduction, and effects have been isolated due both to impurity-band conduction and to hopping transport between neutral and ionized acceptor centres. The activation energies associated with the latter processes are much lower than the acceptor ionization energy, and the variation with temperature of the onset of impurity conduction as a function of the neutral acceptor concentration accounts for the wide range of activation energies reported for synthetic diamonds by previous authors.

Aggregation of nitrogen in diamond.

Abstract: THIS note is an attempt to make quantitative the view1 that it is erroneous that the impurity nitrogen in diamonds is mostly located in the platelets of diamonds.

Sintered diamond: a synthetic carbonado.

Abstract: Diamond powder is rapidly sintered into molded shapes at a pressure of about 65 kilobars and a temperature of 2500 degrees Kelvin. Other conditions of pressure and temperature are also suitable. The product compares favorably with natural carbonado in its properties.

Reaction vessel for high pressure apparatus

Abstract: AN IMPROVED REACTION VESSEL CONSTRUCTION FOR THE COMPACTION OF A MASS OF DENSE, STRONG PARTICLES E.G. DIAMOND IS DISCLOSED. THIS IMPROVED CONSTRUCTION EMBODIES A MECHANICALLY UNSTABLE STRUCTURAL SYSTEM TO PREVENT THE FORMATION OF PRESSURE-SUPPORTING GEOMETRIES WITHIN OR ENCIRCLING THE MASS.

The stylus or scratch method for thin film adhesion measurement: some observations and comments

Abstract: The effect of applying a rounded stylus to thin metallic films on glass substrates has been investigated using diamond and steel styli with tip radii of approximately 25 μm and loadings of up to 230 g. The films were vacuum-deposited indium, tin, lead, gold, copper, aluminium, nickel, chromium and molybdenum of various thicknesses up to 32 μm. Scanning electron microscope and optical interference microscope observations showed that the process of scratch formation was generally very complex and varied with the film material, indicating that it is not possible to deduce absolute values of adhesion forces using a simple general theoretical model. The method can, however, be used with caution for qualitative comparisons under certain restricted conditions.

Temperature Coefficient of the Refractive Index of Diamond- and Zinc-Blende-Type Semiconductors

Abstract: We have calculated the temperature coefficient of the long-wavelength refractive index of several group-IV and III-V semiconductors, using the Penn model for the electronic contribution to the dielectric constant. The isotropic band gap of this model is identified with the band gap at the $X$ point of the Brillouin zone, which can be simply expressed in terms of pseudopotential coefficients. The explicit temperature dependence of this gap is calculated by applying to these pseudopotential coefficients the appropriate Debye-Waller factors. The thermal expansion effect is obtained in the manner suggested recently by Van Vechten. Good agreement between the calculated and the observed temperature dependence of the long-wavelength refractive index is found.

Plastic deformation and anisotropy in the hardness of diamond.

Abstract: A NUMBER of methods may be used to determine the hardness of solids. The most reproducible and most widely used for crystalline solids are those in which the size of an indentation is measured after the surface of the specimen has been subjected to deformation by an indenter under a known normal load. Ideally, the indenter material should be considerably harder than the specimen in order to avoid inaccuracies due to deformation of the indenter tip, but this implies that the hardness of diamond cannot be measured, for it is the hardest indenter material available. A limited amount of data concerning the hardness of diamond, using the static indentation technique, has nevertheless been published. More than thirty years ago the Knoop indenter was developed and used to measure the hardness of a wide range of ductile and brittle materials. This indenter produces an indentation in the form of a parallelogram with one diagonal at least seven times longer than the shorter diagonal. In that early work, the hardness of diamond was quoted as 8,000–8,500 kg mm−2 (ref. 1). No details were given concerning the normal load used, the type of deformation associated with the indentation or the crystallographic relationships between the indenter and the indented diamond surface. It was reported subsequently that the hardness of a (001) diamond surface, again using the Knoop indenter and a normal load of 500 g, was 6,000–6,500 kg mm−2. Apparently, anisotropy in the hardness could not be detected at that time2. Bernhardt3 gave a limiting value of 10,000 kg mm−2 on the (111) surface. He used a conventional square based pyramidal indenter and a normal load of 200 g. Kruschov and Berkovich4, using an indenter in the form of a three sided pyramid with an angle of 65° between its geometrical axis and the side faces, derived a hardness of 10,060 kg mm−2 from one indentation also on a (111) plane and with a load of 200 g. On the basis of a very limited number of indentations, therefore, it seems that the hardness of diamond lies between 6,000 and 10,400 kg mm−2 with no evidence of anisotropy. On the other hand, studies of abrasion on diamond surfaces have established marked anisotropy in wear resistance. These observations have been used to suggest that the directions of high and low wear resistance represent the hard and soft directions respectively on a given diamond surface. For example, it has been proposed5 that, on the (001) plane of diamond, the hard directions are 〈110〉 and the soft directions are 〈100〉. It is now clear that directions of high wear resistance, on a given crystal plane, are not necessarily the hard directions6.

Epitaxial Synthesis of Diamond in the Metastable Region

Abstract: Recent trends in the preparation of synthetic diamonds, relying on the influence of surface forces exerted by the diamond seed crystal on the carbon deposition processes, are discussed. Epitaxial synthesis can occur from carbon-containing gases or from molten metals. Foreign publications and patents are discussed as well as the work of Soviet scientists. The preparation and properties of filamentary and of isometric diamond crystals, prepared at low pressures for the first time, are also discussed. 22 references.

Support for electrical components and method of making the same

Abstract: A heat conducting support on which an electrical component can be mounted so as to conduct heat generated by the component away from the component. The support includes a substrate of good heat conducting material and a diamond body embedded in the substrate with a surface of the diamond body being flush with a surface of the substrate. A metal film extends over the surface of the substrate and the diamond body and is strongly adhered to the substrate. An electrical component can be mounted on and secured to the metal film over the diamond body. The support is formed by placing the diamond body on the surface of a plate of the material of the substrate and coating the surface of the plate around the diamond body with additional material of the substrate. The coating contacts the peripheral edge of the diamond body to secure the diamond body to the substrate and extends to the surface of the diamond body. A metal film can then be deposited on the surface of the diamond body and the coating.

A study of grinding damage in magnesium oxide single crystals

Abstract: The sub-surface and surface damage produced by alumina and diamond grinding wheels has been studied as a function of material removal rate. Sub-surface damage is characterised in all cases by a discrete, dense layer of dislocations adjacent to the machined surface. The depth of the layer increases with material removal rate. The nature of the surface damage depends on the mechanism of material removal. As long as the cutting points are unloaded and the residue can escape the material is removed in a brittle manner. This is always the case for the diamond wheel and occurs for low rates of material removal with the alumina wheel. When the cutting surface is loaded with residue, the tool-workpiece interface temperature becomes so high that the material is removed by plastic flow. The finished surface is burnished. Unfortunately as the burnished surface cools down thermal quenching produces a network of surface cracks.

Thermal Expansion of Garnets Included in Diamond

Abstract: The lattice parameters of two garnet inclusions in diamonds have been measured by X rays as functions of temperature, with the inclusions first in situ and then freed from their hosts. The included garnets have smaller lattice parameters than the free garnets and must therefore be under pressure. From an equation of state for garnet calculated from thermoelastic data, the pressures in situ are found to vary from 2 to 15 kbar for one garnet (D1) and from 2 to 7 kbar for the other (D2) as the temperature is increased. A model is proposed which assumes that, under uniform isotropic stress and temperature, diamond forms around garnets and behaves purely elastically thereafter. The model is used to calculate theoretical values for the difference in lattice parameters of free and included garnet; it gives the external pressure that removes shear stress in the host at each temperature, a curve that should pass through the temperature and the pressure of formation of the host. For diamond D1, whose behavior agreed with the model, this curve crosses the thermodynamic diamond-graphite equilibrium line at about 500°C; because some nonelastic processes may have occurred, the curve is proposed merely as a lower bound to pressures of formation of the diamond. The method cannot be applied to D2: below 400°C the thermal expansion of the included garnet was greater than that predicted by the model, and the curve obtained from the high-temperature data lies wholly in the region where graphite is stable. It is concluded that in D2 pressure has probably been released by a nonelastic mechanism during some stage of the diamond's history.

Diamond tool and method of making the same

Abstract: A grinding and cutting tool comprised of diamond particles bonded to a support base member by the process of vapor deposition to form a metal lattice matrix chemically bonded to a surface of the diamond particles and metallurgically bonded to the support base member and the diamonds bonded to each other by inosculation, the reactions greatly enhancing the strength of the bonds. A novel method of vapor deposition, controlled by electrical charges and by said means to impart kinetic energy to the ions of the vapor of sufficient velocity to cause penetration of said ions into the molecular structure of the support base causing a metallurgical reaction and into the molecular structure of the diamond surfaces causing a chemical reaction. In addition, by inducing a secondary electrical field, divergence of said ions can be controlled to cause said ions to be deposited in a predetermined pattern.

Interpretation of Diamond and Graphite Compressibility Data Using Molecular Force Constants

Abstract: The diamond and in‐plane graphite compressibility data of Lynch and Drickamer are analyzed in terms of simple bond‐compression and bond‐compression, buckling, and puckering models, respectively, using carbon–carbon stretching and out‐of‐plane displacement force constants from molecular studies. To the highest experimental pressures of over 300 kbar it is found that the quotient of potential energy of bond compression and macroscopic work of compression, for the same values of the lattice parameter ratio (a/a0), remains essentially constant for diamond at 0.7 indicating that bond compression is the dominant mechanism for storing energy of compression. Similar quotients for graphite at corresponding values of (a/a0) vary from 1.4 at the lowest pressures to 0.6 at the highest for the in‐plane bond compression, from 100–4 for the out‐of‐plane buckling, and from 300–13 for the out‐of‐plane puckering with the last two modes assuming a fixed C–C in‐plane bond distance. It is suggested that in graphite bond compression is the primary mechanism for absorbing intraplanar energy of compression with out‐of‐plane buckling and puckering much less important until quite high pressures are reached, in contrast to earlier views. This would seem to lead to a partial understanding of the difficulties present in synthesizing diamond from graphite.

An investigation of the shape and dimensions of some diamond styli

Abstract: An appraisal is given of the qualities of diamond styli which are used for surface texture measurement. Some of the difficulties encountered in normal optical and electron optical methods of assessment are discussed, and a possible solution which involves a two-stage replica process is described.

The polarization of luminescence associated with the 4150 and 5032 Å centres in diamond

Abstract: The polarization of luminescence of the 2.989 eV (4150 A) and 2.464 eV (5032 A) centres in diamond as a function of the energy of excitation is compared with the excitation spectra of these centres. The results are interpreted in terms of two electric dipole transitions in both types of centre. The 2.989 eV and 3.602 eV absorption lines are shown to be associated with a defect of trigonal symmetry, while the 2.464 eV and 3.368 eV absorption lines are associated with a defect of monoclinic I symmetry.

The microscopic dielectric function in silicon and diamond

Abstract: The microscopic dielectric function epsilon (q) of diamond and silicon was calculated using a pseudopotential scheme. Sufficient plane waves were included to obtain energy convergence to within 0.1 eV. Four valence, seven conduction bands, and 11520 points were used in the sampling of the Brillouin zone. Good agreement with experiment was obtained for the static limit epsilon (0). The effect of the higher conduction bands was investigated and it was shown that it cannot be neglected. The calculated values of epsilon (q) for q>or=q (Fermi) are smaller than those predicted from the simple Penn model. The covalent 222 contribution to the valence charge density in Si was calculated as 0.219 electrons/atom, in agreement with the experimental value 0.22.

The symmetry properties of the ND1 absorption centre in electron- irradiated diamond

Abstract: The ND1 centre is produced in natural and synthetic diamond by primary radiation damage, but only occurs in strength when substantial concentrations of nitrogen are present in the lattice. The optical absorption associated with this centre consists of a sharp no-phonon line at 3.149 ev (80 degrees K) and phonon-assisted structure at higher energies centred at about 3.4 ev. Uniaxial stress measurements on the no-phonon line have been interpreted in terms of an A to T transition at a centre of Td symmetry, and from this and other evidence of the ND1 centre has been tentatively identified with an interstitial nitrogen atom.

Novel diamond powder dispersions and process for obtaining same

Abstract: THIS APPLICATION IS DIRECTED TO DISPERSIONS OF SYNTHETIC SHOCK-FORMED DIAMOND POWDER AND TO THE METHOD OF OBTAINING SAME BY SUBJECTING A MIXTURE OF SYNTHETIC SHOCKFORMED DIAMOND POWDER IN A LIQUID DISPERSION MEDIUM TO SHEAR STRESSES. THE PREFERRED DISPERSIONS ARE STABLE FOR AT LEAST 24 HOURS. THE DIAMOND POWDER USED IS CHARACTERIZED BY AN AVERAGE PARTICLE DIAMETER RANGE OF FROM ABOUT 7X10**-4 TO ABOUT 1X10**-2 MICRONS AND A SURFACE AREA OF BETWEEN ABOUT 40 AND ABOUT 400 SQUARE METERS PER GRAM.

Mössbauer Study of 57Co Implanted in Diamond

Abstract: A Mossbauer source of 57Co in diamond has been produced by implanting 57Co with an isotope separator directly into a diamond single crystal. The Mossbauer spectra taken at 80 and 300°K and in the [100] and [110] orientations displays two peaks of equal intensity. These two peaks can be interpreted as quadrupole splitting caused by the displacement of the iron interstitial from its site of tetrahedral symmetry.

Resinoid pocketed cutoff and grinding wheel and method of making same

Abstract: A cutoff or grinding wheel having a rotatable support, preferably in the form of a disk with a thickness of up to 1 mm, formed with a multiplicity of openings along the disk periphery. Diamond particles, with or without other abrasive, are incorporated in a resinous binder and are bonded thereby in the openings of the wheel. Diamond particles have a particle size up to 40 microns and the binder is resinified by prolonged heating.

A re‐evaluation of bonding features in diamond and silicon

Abstract: Published X-ray powder measurements on diamond and three different sets of published X-ray data on silicon have been re-analysed for bonding features using full-matrix least-squares refinement combined with a statistical analysis of the results obtained In all cases a highly significant improvement in the fit between observed and calculated structure factors was obtained by introducing a tetrahedral distortion of the spherical `prepared' charge distribution, but subsequent introduction of a fourth-order cubic distortion proved to be highly significant only for the diamond data and one set of the silicon data Hartree–Fock calculations gave a better fit to the diamond measurements than calculations based on Hartree–Fock–Slater wavefunctions The necessity for placing restrictions on the form of the radial functions associated with the non-spherical distortions, the large estimated standard deviations of the distortion parameters and the dependence of the parameter values on the set of basis wavefunctions chosen to describe the spherical `prepared' charge distribution indicate the need for exercising caution in analysing the experimental measurements for bonding features

Ion Milling of Magnetic Oxide Platelets for the Removal of Surface and Near‐Surface Imperfections and Defects

Abstract: Magnetic oxide platelets, useful for memory and logic circuits, are presently prepared by diamond abrasive polishing techniques. Processed platelets, however, usually contain thin damage layers and microscopic scratches resulting in increased domain wall coercivity. Platelets less than 1 mil in thickness and of desirable flatness are difficult to prepare using these techniques. Ion milling has been successfully used to rapidly remove abrasive and polishing induced defects and at the same time produce flat surfaces of much less than 1 mil in thickness. The measured removal rate was 0.5 μ/h/side; however 500‐μ/h/side rates are attainable. Final platelets are scratch free, flat, and highly reflecting, having lower domain wall coercivity than diamond polished plates. No change in mobility was observed following ion milling. The process is adaptable to large areas and a wide variety of related applications.

Method and means of making diamond heat sinks and heat sinks obtained by this method

Abstract: A method of making diamond heat sinks for mounting small powerdissipating devices, such as semi-conductor devices and solidstate lasers, in which diamonds of the type II A are selected having a level or rising light transmission curve for infrared rays in the wave length range of 7 to 8 micrometer wave length. The selected diamonds are sawn into slices which are polished on both their sawn parallel faces and which are then cut in two directions normal to each other to obtain block-shaped diamond heat sink bodies of a weight in the range of 0.0005 to 0.02 carat. In sawing the diamond slices a saw guide comb is used for guiding the saw blade along straight paths.

Producing diamonds synthetically

Abstract: TE INVENTION RELATES TO METHODS OF PRODUCING DIAMOND SYNTHETICALLY WITH THE USE OF SEED CYRSTALS. ACCORDING TO THE INVENTION, THE METHOD OF SYNTHESIZING DIAMOND CONSISTS IN CONTACTING DIAMOND SEED CRYSTALS WITH AN ORGANOMETAL COMPOUND CONTAINING AT LEAST ONE EASILY BROKEN METAL CARBON BOND, AND IS CARRIED OUT AT A TEMPERATURE SELECTED FROM THE RANGE OF 300 TO 1800* K. AND AT THE RESULTING PARTIAL PRESSURE OF SAID ORGANOMETAL COMPOUND.