Showing papers on "Diamond published in 1989"

Prediction of new low compressibility solids.

Abstract: An empirical model and an ab initio calculation of the bulk moduli for covalent solids are used to suggest possible new hard materials. The empirical model indicates that hypothetical covalent solids formed between carbon and nitrogen are good candidates for extreme hardness. A prototype system is chosen and a first principles pseudopotential total energy calculation on the system is performed. The results are consistent with the empirical model and show that materials like the prototype can have bulk moduli comparable to or greater than diamond. It may be possible to synthesize such materials in the laboratory.

Characterization of diamond films by Raman spectroscopy

Abstract: As the technology for diamond film preparation by plasma-assisted CVD and related procedures has advanced, Raman spectroscopy has emerged as one of the principal characterization tools for diamond materials. Cubic diamond has a single Raman-active first order phonon mode at the center of the Brillouin zone. The presence of sharp Raman lines allows cubic diamond to be recognized against a background of graphitic carbon and also to characterize the graphitic carbon. Small shifts in the band wavenumber have been related to the stress state of deposited films. The effect is most noticeable in diamond films deposited on hard substrates such as alumina or carbides. The Raman line width varies with mode of preparation of the diamond and has been related to degree of structural order. The Raman spectrum of hexagonal diamond (lonsdaleite) is distinct from that of the cubic diamond and allows it to be recognized.

Diamond—Ceramic Coating of the Future

Abstract: On etudie le depot chimique en phase vapeur et la croissance cristalline de revetement de diamant

Optimum semiconductors for high-power electronics

Abstract: Elemental and compound semiconductors, including wide-bandgap semiconductors, are critically examined for high-power electronic applications in terms of several parameters. On the basis of an analysis applicable to a wide range of semiconducting materials and by using the available measured physical parameters, it is shown that wide-bandgap semiconductors such as SiC and diamond could offer significant advantages compared to either silicon or group III-V compound semiconductors for these applications. The analysis uses peak electric field strength at avalanche breakdown as a critical material parameter for evaluating the quality of a semiconducting material for high-power electronics. Theoretical calculations show improvement by orders of magnitude in the on-resistance, twentyfold improvement in the maximum frequency of operation, and potential for successful operation at temperatures beyond 600 degrees C for diamond high-power devices. New figures of merit for power-handling capability that emphasize electrical and thermal conductivities of the material are derived and are applied to various semiconducting materials. It is shown that an improvement in power-handling capabilities of semiconductor devices by three orders of magnitude is feasible by replacing silicon with silicon carbide; improvement in power-handling capability by six orders of magnitude is projected for diamond-based devices. >

Resistivity of chemical vapor deposited diamond films

Abstract: Diamond films grown by plasma chemical vapor deposition techniques display a fairly low resistivity (∼106 Ω cm). Heat treating the films causes an increase in the resistivity by up to six orders of magnitude. The low resistivity of the as‐grown films is postulated to be due to hydrogen passivation of traps in the films. Annealing causes dehydrogenation resulting in the electrical activation of deep traps with an attendant increase in the resistivity. This mechanism has been confirmed by an observed reduction of the resistivity of the heat‐treated films when they are subjected to a plasma hydrogen treatment.

Cutting elements for rotary drill bits

Abstract: A preform cutting element for a rotary drill bit includes a layer of polycrystalline diamond material, the rear face of which is bonded to the front face of a backing layer of less hard material, such as tungsten carbide. The rear face of the backing layer is substantially greater in area than the rear face of the diamond layer. A method of manufacturing such cutting elements comprises forming an intermediate structure comprising polycrystalline diamond material bonded between two outer layers of tungsten carbide, and then cutting the intermediate structure to provide two pieces, each of the pieces including part of the diamond material and at least a major part of a respective one of the two outer layers.

Hydrogen passivation of electrically active defects in diamond

Abstract: Subjecting natural diamond single crystals to the action of atomic hydrogen in a hydrogen plasma is shown to result in the passivation of interband states in the crystal resulting in a marked reduction in the resistivity to about 105 Ω cm from the expected high resistivity of∼1016 Ω cm. When the hydrogenated crystals are heat treated in a neutral ambient, the hydrogen can be expelled from the crystals, restoring the high resistivity. The behavior of natural diamond crystals, with respect to the effects of hydrogen, is shown to be similar to the behavior of diamond thin films synthesized by plasma‐enhanced chemical vapor deposition techniques.

Resonant Raman scattering of amorphous carbon and polycrystalline diamond films.

Abstract: Resonant Raman scattering has been used to study amorphous carbon and polycrystalline diamond films. The incident photon energies were varied over the range 2.2--4.8 eV. In hydrogenated amorphous carbon films containing both ${\mathrm{sp}}^{3}$- and ${\mathrm{sp}}^{2}$-bonded carbon, a high-frequency shift is observed for the main Raman peak with increasing photon energies up to 3.5 eV. This shift is interpreted in terms of scattering from \ensuremath{\pi}-bonded carbon clusters which is resonantly enhanced for photon energies approaching the \ensuremath{\pi}-${\ensuremath{\pi}}^{\mathrm{*}}$ resonance of ${\mathrm{sp}}^{2}$-bonded carbon. In polycrystalline diamond films excitation with photon energies \ensuremath{\ge}3.0 eV enhances the Raman signal from the ${\mathrm{sp}}^{3}$-bonded diamond phase relative to the scattering by ${\mathrm{sp}}^{2}$-bonded carbon and with respect to the underlying broadband luminescence. The Raman band arising from scattering by ${\mathrm{sp}}^{2}$-bonded carbon shows a high-frequency shift with increasing photon energy for energies \ensuremath{\ge}3.0 eV. Possible models for the structure of this ${\mathrm{sp}}^{2}$-bonded carbon phase are discussed on the basis of the present Raman data.

On the role of oxygen and hydrogen in diamond-forming discharges

Abstract: Plasma emission actinometry has been used to study the mechanism by which small additions of oxygen (∼0.5%) enhance the rate of diamond deposition in a dilute (4%) CH4/H2 discharge at high temperature (900–1300 K). Increasing amounts of CH4 in the feed depress [H], while increasing the O2 concentration, up to ∼5%, produces a fivefold increase in atomic hydrogen in the discharge zone. Invoking a mechanism where diamond growth competes with the formation of an amorphous/graphitic inhibiting layer, these results and earlier studies suggest that oxygen (1) increases [H] which selectively etches amorphous/graphitic carbon, (2) accelerates reaction of this layer with molecular hydrogen, and (3) may itself act as a selective etchant of nondiamond carbon. As a result, the number of active diamond growth sites is increased and enhanced growth rates are observed. We also have grown diamond by alternating a CH4/He discharge with a H2/O2/He discharge and results are consistent with this mechanism. Instantaneous growt...

Characterization of diamond thin films: Diamond phase identification, surface morphology, and defect structures

Abstract: Thin carbon films grown from a low pressure methane-hydrogen gas mixture by microwave plasma enhanced CVD have been examined by Auger electron spectroscopy, secondary ion mass spectrometry, electron and x-ray diffraction, electron energy loss spectroscopy, and electron microscopy. They were determined to be similar to natural diamond in terms of composition, structure, and bonding. The surface morphology of the diamond films was a function of position on the sample surface and the methane concentration in the feedgas. Well-faceted diamond crystals were observed near the center of the sample whereas a less faceted, cauliflower texture was observed near the edge of the sample, presumably due to variations in temperature across the surface of the sample. Regarding methane concentration effects, threefold {111} faceted diamond crystals were predominant on a film grown at 0.3% CH4 in H2 while fourfold {100} facets were observed on films grown in 1.0% and 2.0% CH4 in H2. Transmission electron microscopy of the diamond films has shown that the majority of diamond crystals have a very high defect density comprised of {111} twins, {111} stacking faults, and dislocations. In addition, cross-sectional TEM has revealed a 50 A epitaxial layer of β3–SiC at the diamond-silicon interface of a film grown with 0.3% CH4 in H2 while no such layer was observed on a diamond film grown in 2.0% CH4 in H2.

Pressure-temperature phase diagram of elemental carbon

Abstract: Carbon atoms form very strong bonds to each other yielding solid crystalline materials like graphite and diamond. Because of the high bonding energies, the vaporization and melting temperatures are very high. Different kinds of atom-to-atom bonding make many solid forms possible, ranging from pure graphite to pure diamond, as well as many types of molecules in liquid or gaseous carbon. Rigorous conditions of high temperature, high pressure, or both, are required to change a given elemental phase of carbon to another. Currently the vapor-pressure line of graphite, the P, T equilibrium line between graphite and diamond, and the graphite/diamond/liquid triple point are fairly well established. The triple point (or points) for graphite (or carbynes)/vapor/liquid remain controversial. At pressures less than 0.1 GPa liquid carbon seems to be a poor electric conductor while at higher pressures it is a good one. Current experimental and theoretical evidence indicate that diamond is stable against collapse to metallic forms (unlike Si and Ge) up to pressures over 350 GPa, and possibly as high as 2300 GPa. The latest static and shock compression experiments on diamond indicate that it melts to a conducting liquid at about 5000 K at pressures of 15 to 30 GPa, but does not melt at about 6000 K at 125 GPa. This suggests that the melting temperature of diamond increases with pressure, and that at the melting temperature liquid carbon is slightly less dense than diamond.

Composite polycrystalline diamond compact with improved impact resistance

Abstract: A compact blank for use in operations that require very high impact strength and abrasion resistance is disclosed. The compact comprises a substrate formed of tungsten carbide or other hard material with a diamond or cubic boron nitride layer bonded to the substrate. The interface between the layers is defined by topography with irregularities having non-planar side walls such that the concentration of substrate material continuously and gradually decreases at deeper penetrations into the diamond layer.

Hydrogen atom detection in the filament‐assisted diamond deposition environment

Abstract: The resonance‐enchanced multiphoton ionization (REMPI) technique was employed for detection of gas phase atomic hydrogen in the filament‐asisted diamond growth environment. The H atom REMPI signal varied significantly with the reactant CH4/H2 fraction as well as with the filament temperature. We interpret these observations as evidence for the surface role of atomic hydrogen in the diamond growth mechanism. The spatial resolution of the REMPI technique allowed us to confirm that hydrogen atom transport in the deposition region occurs by diffusion.

Diamond metal composite cutter and method for making same

Abstract: A superhard material-metal composite product comprises a plurality of metal coated superhard particles (diamond or cubic boron nitride), and a binder alloy forming a cementing matrix which binds the coated superhard particles into a coherent mass. The binder alloy has a melting point below about 1300° C. and is capable of wetting the metal coating on the superhard particles. The superhard material-metal composite product is formed by assembling the coated particles and the binder alloy in a graphite mold, and then hot pressing at temperatures and pressures well below the temperatures and pressures of the diamond forming region. The superhard component comprises about 40% to 75% by volume of the composite product. The superhard material-metal composite product is of intermediate quality and is particularly useful in earth boring bits for drilling soft rock formations having abrasive rock stringers therein.

Characterization of crystalline quality of diamond films by Raman spectroscopy

Abstract: We have measured Raman spectra of diamond films prepared by a hot‐filament method and found that diamond layers on Si substrates are under compressive strain. The degree of the strain is found to increase with increasing nondiamond component in the diamond films. It is shown that Raman spectroscopy is a powerful method to estimate the crystalline quality, especially the strain in the diamond films.

The role of hydrogen in vapor deposition of diamond

Abstract: The effect of hydrogen addition on growth of diamond films under the conditions of chemical vapor deposition was investigated computationally. A detailed chemical kinetic mechanism was composed to describe the evolution of reaction species in pyrolysis of hydrogen‐ and argon‐diluted methane mixtures with imposed temperature profiles, simulating the gas‐phase conditions of diamond film growth in an idealized hot‐filament reactor. The reaction mechanism was comprised of two basic parts: decomposition of methane, and formation and growth of polycyclic aromatic hydrocarbons; it contained a total of 120 elementary reactions and 45 chemical species. The reaction rate coefficients included temperature and pressure dependencies. The computations were performed for a variety of initial conditions, elucidating the effects of critical parameters on the product composition in the regime of diamond deposition. Analysis of the computational results indicated that the key role of the hydrogen addition in the diamond deposition process is to suppress the formation of aromatic species by H2 in the gas phase and thereby to prevent the formation and growth of nondiamond, graphitic phases on the deposition surface.

In situ characterization of diamond nucleation and growth

Abstract: Filament‐assisted chemical vapor deposition (CVD) diamond film growth on Si(100) was studied using x‐ray photoelectron spectroscopy (XPS) to examine the sample at selected intervals during the nucleation and growth processes. The sample was transferred under vacuum from the growth chamber to the attached XPS analysis chamber without exposure to air. Before growth XPS showed that the Si sample is covered by a layer of SiO2 and carbonaceous residue; however, after 15 min of growth both of these substances are removed and replaced by a distinct SiC layer [Si(2p)=100.3 eV and C(1s)=282.7 eV].

Homogeneous nucleation of diamond powder in the gas phase

Abstract: Homogeneous nucleation of diamond powder is reported. The experiments were performed in a low‐pressure microwave‐plasma reactor. The deposits were collected downstream of the reaction zone and subjected to wet oxidation to remove nondiamond carbons. The residues were analyzed by optical and electron microscopy, electron diffraction, and Raman spectroscopy. A variety of hydrocarbons diluted in argon, hydrogen, or oxygen gas mixtures were tested. In most cases only nondiamond materials, like graphite and carbyne, were obtained. Homogeneous nucleation of diamond was clearly observed in dichloromethane‐ and trichloroethylene‐oxygen mixtures. The particles formed had crystalline shapes, mostly hexagonal. The largest particles were about 0.2 μm, although most of the particles were on the order of 50 nm in diameter. The powder was identified to be a mixture of polytypes of diamond.

Single-Point Diamond Machining of Glasses

Abstract: A machine tool of very high stiffness has been constructed and used for single-point diamond grooving of blanks of soda-lime glass and optical glassy quartz. Results show that below a critical depth of cut predicted in order of magnitude by a fracture mechanics analysis, material is removed by the action of plastic flow, leaving crack-free surfaces. Subsequent observations by scanning electron microscopy indicate that a crucial part in the detachment of ribbons of swarf is played by the operation of residual stresses after the passage of the tool, particularly in the case of the amorphous ceramic.

Method of toughening diamond coated tools

Abstract: of the Disclosure Method of toughening the structure of a diamond or diamond-like coated tool, by the steps of: (a) depositing, by low pressure CVD, a plurality of layers of separated diamond or diamond-like particles onto a nondiamond or nondiamond-like tool substrate (i.e., SiAlON, Si3N4, SiC, Si, Ti, Co cemented WC, TiC, Ni-Mo cemented TiCN), the substrate being selected to facilitate diamond or diamond-like deposition and to retain its strength-related properties after such CVD; and (b) interposing a mechanically adherent, planarized binding material (i.e. transition metals, silicon, boron) between and on said layers of particles and across the separated particles of each particle layer, said binding material being substantially devoid of diamond graphitizing or dissolution agents. A barrier layer is deposited onto said tool substrate prior to step (a) to prevent the egress of chemicals capable of graphitizing diamond or diamond-like particles. The total thickness of the coating structure is about 50-125 microns.

Electrical Characteristics of Metal Contacts to Boron-Doped Diamond Epitaxial Film

Abstract: Current-voltage characteristics have been obtained for various metal contacts formed on boron-doped diamond epitaxial film prepared on synthesized Ib diamond by the microwave plasma-assisted chemical vapor deposition method. Ti contacts and W contacts have exhibited good ohmic and Schottky properties, respectively. For the first time, we have fabricated Schottky diodes on boron-doped diamond epitaxial films using these contacts and investigated their properties.

Method for producing polycrystalline compact tool blanks with flat carbide support/diamond or CBN interfaces

Abstract: The present invention relates to a method for making a supported PCD or CBN compact comprising placing in an enclosure a cup assembly having a mass of diamond or CBN particles having a surface and the mass of cemented metal carbide having a surface, and optionally a catalyst for diamond (or optionally, CBN) recrystallization, said surfaces being in adjacency to form an interface. The enclosure then is subjected to a high pressure/high temperature process which results in diamond or CBN compacts preferably characterized by diamond-to-diamond or CBN-to-CBN bonding joined to a cemented carbide support at their respective surfaces. The supported compacts are recovered from the enclosures and cup assemblies and finished. The finished supported compacts in the enclosure exhibit non-planar bonded interface resulting in PCD or CBN compacts of substantially non-uniform thickness. The improvement in process of the present invention comprises said carbide mass surface being the mirror image of the finished PCD or CBN non-planar interface for making a finished supported compact of substantially uniform diamond or CBN compact thickness. Preferably, at least two compacts are produced in the process and the catalyst for diamond recyrstallization is provided from the cemented metal carbide mass,

Diamond films and method of growing diamond films on nondiamond substrates

Abstract: A method of forming a polycrystalline film, such as a diamond, on a foreign substrate involves preparing the substrate before film deposition to define discrete nucleation sites. The substrate is prepared for film deposition by forming a pattern of irregularities in the surface thereof. The irregularities, typically craters, are arranged in a predetermined pattern which corresponds to that desired for the location of film crystals. The craters preferrably are of uniform, predetermined dimensions (in the sub-micron and micron size range) and are uniformly spaced apart by a predetermined distance. The craters may be formed by a number of techniques, including focused ion beam milling, laser vaporization, and chemical or plasma etching using a patterned photoresist. Once the substrate has been prepared the film may be deposited by a number of known techniques. Films prepared by this method are characterized by a regular surface pattern of crystals which may be arranged in virtually any desired pattern. Diamond film materials made by this technique may be used in many electrical, optical, thermal and other applications.

Diamond and diamondlike films: Deposition processes and properties

Abstract: Considerable interest has been aroused in the synthesis of diamond films due to their potential applications in microelectronics and optoelectronics. Although synthesis of diamond films by a variety of chemical and plasma assisted chemical as well as physical vapor deposition techniques has been reported, the practical applications of these coatings are still very few. The basic reason limiting the applications of these coatings is the inability to deposit films with smooth surface morphology and desired optical and electrical properties at acceptable deposition rates. Published work on diamond films is reviewed to highlight the above issues.

Effects of oxygen on diamond growth

Abstract: In situ mass spectral measurements of gas composition at the substrate surface were made during filament‐assisted diamond growth. The input gases were various mixtures of CH4, O2, and H2 chosen in order to discern the effects of oxygen addition on diamond formation and growth. The gas phase chemistry was modeled as a one‐dimensional flow reactor, and the measured and calculated species mole fractions were in good agreement. The model was then used to estimate mole fractions of several atomic and radical species which could not be measured. We find that addition of O2 has only a small effect on the radical mole fractions. However, O2 can reduce the effective initial hydrocarbon mole fraction, which is important because higher quality diamond is grown at a lower initial hydrocarbon mole fraction. Most important, perhaps is that O2 addition leads to the formation of sufficient gas phase OH to remove nondiamond (pyrolytic) carbon from the film. Thus, O2 addition allows diamond films to be grown under composition and temperature conditions which otherwise would produce largely nondiamond carbon.

Flame structure and diamond growth mechanism of acetylene torch

Abstract: To understand the diamond growth mechanism in C2H2/O2 flame, we carried out gas analyses for various mixture ratios (R=C2H2/O2) with laser-induced fluorescence and mass spectrometric techniques. These measurements show that CO and H2 are the dominant gases in the feather, and that C2H2 and C-containing radicals (e.g., C2H, CR, Cn, n=1-3) are minor species. Their concentrations are found to be consistent with the equilibrium values estimated by the adiabatic calculation. The feather is formed by the inter-diffusion and reactions between these C-radicals and O-radicals (e.g., O and OH), which are produced in the intermediate zone by the oxidation with O2 supplied through the secondary flame. It is also found that R-dependences of the diamond growth rate is in good agreement with those of CH and C2 concentrations in the feather.

Emerging Technology of Diamond Thin Films

Abstract: Hardness and resistance to wear are often distinct advantages for materials used in industry, and the archetypal substance displaying these properties is diamond. But diamonds, at least in the size that many industrial uses demand, often are prohibitively costly—or totally unavailable. Now, however, advances in materials science are showing the way to put a coating of diamond on many other, less exotic materials, thereby imparting to them the beneficial properties—electronic and optical properties as well as hardness—that only diamond has. The beauty and hardness of diamond—and its rarity, especially in sizes larger than a centimeter—have made it an object of fascination for nearly as long as recorded history. Natural industrial diamond is a byproduct of the exploration for gemstones, and, since the early part of this century, its supply has been stagnant or uncertain, and far too low to match the growing demand for this material from the polishing, cutting, and drilling industries. This shortage ...

Defect-induced stabilization of diamond films

Abstract: THE growth of diamond thin films by low-pressure vapour deposi-tion should find technological applications in such diverse fields as hard coatings for cutting tools, lens coatings, heat sinks and electronics1–4. Under such growth conditions diamond should be unstable relative to graphite, yet diamond is formed in practice. Present approaches to describing the growth of diamond explain this paradox by means of a variety of surface kinetic reactions that are controlled by concentrations of adsorbed hydrogen and hydrocarbon radicals5–8. Here we propose a simpler explanation, that high vacancy concentrations are present near the growth face of the diamond film. The formation energy of vacancies in diamond is lower than in graphite, so that large vacancy concentrations (1–8%) can raise the formation energy of graphite above diamond, permitting nucleation and stable growth of diamond. This quasi-thermodynamic model is fundamentally different from the kinetic models for diamond film growth, and predicts that the growth of films with low defect concentrations will be difficult.

Negative thermal expansion of diamond and zinc-blende semiconductors.

Abstract: Experimentally it is well known that diamond and zinc-blende semiconductors show an ``unusual'' (i.e., negative) thermal expansion at about 100 K. We performed density-functional-theory calculations of thermodynamic potentials (i.e., total energies and entropies) for perfect crystals, to study the temperature dependence of the lattice parameter. The origin of the negative expansion effect is traced back to the entropy contribution of the Gibbs free energy.