Showing papers on "Diamond published in 1982"

Vapor Deposition of Diamond Particles from Methane

Abstract: Microcrystalline diamond has been formed on silicon or molybdenum substrates by vapor deposition from a geseous mixture of methane and hydrogen. Cubo-octahedral or multiply-twinned crystals were obtained. The structure of the deposits was identified by electron diffraction and Raman scattering.

Growth of diamond particles from methane-hydrogen gas

Abstract: Microcrystals of diamond were grown on non-diamond substrates including silicon, molybdenum and silica, as well as on diamond by chemical vapour deposition. Deposition was carried out by passing a mixture of hydrocarbon and hydrogen gases through a heated reaction chamber in which a hot tungsten filament was held near the substrates. The deposit was identified by reflection electron diffraction and Raman spectroscopy. The effects of experimental conditions on the growth features were studied.

High-pressure research in geophysics

Abstract: Session I Instrumentation and Pressure Calibration.- Triple-Stage High Pressure Apparatus Using Sintered Diamond Anvils.- A Wedge-Type Cubic Anvil High Pressure Apparatus and Its Application to Material Synthesis Research.- Pressure Measurement at High Temperature in X-Ray Diffraction Studies: Gold as a Primary Standard.- Application of a Diamond-Cell to High-Temperature and High-Pressure Experiments.- Rapid High-Pressure Structural Information from Energy Dispersive Analyses of Diffracted Synchrotron Radiation.- Improvements in Energy Dispersive X-Ray Diffraction with Conical Slit and Diamond Cell.- Rapid X-Ray Measurements to 100 GPa Range and Static Compression of ?-Fe2O3.- Session II Elasticity, Attenuation and Rheology of the Crust and Upper Mantle.- The Elasticity of Periclase to 3 GPa and Some Geophysical Implications.- Pressure Dependence of Elastic Moduli of Forsterite by Brillouin Scattering in the Diamond Cell.- The Effect of Crystal Structure and Composition on Elastic Properties of Silicates.- Brillouin Measurements of n-H2 and n-D2 in the Pressure Range 0.5 to 20 GPa at Room Temperature.- Pressure Dependence of Q in Selected Rocks.- Diffusion Coefficients of Ions in Alkali Halides Determined by a Low-Frequency Impedance Measurement.- Dynamic Recrystallization and High-Temperature Rheology of Olivine.- Session III Mechanical Properties and Melting of the Crust and Upper Mantle.- Fracture and Deformation of Silicate Rocks at High Pressures in a Cubic Press.- Brittle Bahavior of Rocks at High Pressure.- Interfacial Energies in the Olivine-Basalt System.- Experimental Determination of Near-Equilibrium Textures in Partially Molten Silicates at High Pressure.- Reduced Volatiles in the System C-O-H: Implications to Mantle Melting, Fluid Formation and Diamond Genesis.- Fluid-Magma Interaction at High Pressure-Temperature Conditions.- Melting of Various Silicates at Elevated Pressures.- Session IV Geophysics and Geochemistry of the Mantle.- Anharmonicity in the Equation of State at High Temperature for Some Geophysically Important Solids.- Shear Velocity in the Mantle Transition Zone.- Chemical Composition and Evolution of the Mantle.- Iron Magnesium Fractionation Model for the Earth.- Session V High-Pressure Phase Transformations and Crystal Chemistry.- High-Pressure Phase Transformations in Rutile Structured Dioxides.- High-Pressure Phase Transformations of the Dioxides: Implications for Structures of SiO2 at High Pressure.- The Kinetics of Martensitic Olivine ?-Spinel Transition and Its Dependence on Material and Experimental Parameters.- Experimental Investigation on the Mechanism of Olivine?Spinel Transformation: Growth of Single Crystal Spinel from Single Crystal Olivine in Ni2SiO4.- Crystal Structure Studies on Spinel-Related Phases, Spinelloids: Implications to Olivine-Spinel Phase Transformation and Systematics.- Stability Relations of Silicate Spinels, Ilmenites, Perovskites.- Disproportionation of Fe2SiO4 at High Pressure.- Size and Compressibility of Ions at High Pressure.- Session VI Thermochemistry and Crystal Growth.- Thermochemical Properties of Synthetic High-Pressure Compounds Relevant to the Earth's Mantle.- Calorimetric Studies of Crystalline and Glassy High Pressure Phases.- Effect of Coordination Change on Thermodynamic Properties.- Study of Synthetic Minerals of the Orthopyroxene-Pyrope System by Analytical Transmission Electron Microscopy.- Molecular Dynamic Calculations Applied to Silicate Systems: Molten and Vitreous MgSiO3 and Mg2SiO4 under Low and High Pressures.- Growth of Large Diamond Crystals.- Growth and Properties of Olivine Single Crystals by the Floating-Zone Method.- Session VII Shock Wave Experiments.- Anomalous Compression Mechanism of Fused Silica.- Behavior of Single-Crystal Forsterite under Dynamic Compression.- Temperature Induced by Sock Waves in Minerals: Application to Geophysics.- Shock-Induced Spin-Pairing Transition in Fe2O3 Due to the Pressure Effect on the Crystal Field.- The Equation of State for Iron and the Earth's Core.- Author Index.

The Kinetics of the Aggregation of Nitrogen Atoms in Diamond

Abstract: Most natural diamonds contain nitrogen as the main impurity. In some rare diamonds (termed type lb) the nitrogen is mainly present as single substitutional atoms. However, the large majority of diamonds (termed type Ia) contain the nitrogen atoms in various forms of aggregate. The different types of aggregate are the A centre (two nitrogen atoms), the N3 centre (three nitrogen atoms) and the B centre (a larger number of nitrogen atoms). These defects give characteristic absorption spectra in the infrared except for the N3 centre which gives a characteristic absorption in the visible region. In this type of diamond there are usually platelets present in the cube planes and these defects can be examined by transmission electron microscopy and infrared absorption techniques. The paper reports work in which synthetic diamonds containing a high concentration of single nitrogen atoms have been heated in a temperature range of 1500 to 2500°C under various pressures. These heat treatments have resulted in the formation of all the types of aggregate that are found in natural type la diamonds. Also some natural diamonds have been heated up to 2700°C under pressure and the ratio of the concentration of the A centres to that of the B centres has been changed. Information has been obtained on the kinetics of the aggregation process. This information has been used to give an approximate estimate of the length of time that natural diamonds spent in the Upper Mantle prior to being ejected to the surface of the Earth. It is suggested that the type I a diamonds spent between about 200 and 2000 Ma in the Upper Mantle at temperatures of between 1000 and 1400°C. Type l b diamonds either spent a comparable time in the Upper Mantle at about 800°C or a considerably shorter period if they encountered temperatures in the same range as the type la diamonds.

New dimerized-chain model for the reconstruction of the diamond (111)-(2 × 1) surface

Abstract: Of the relaxed, graphitic, buckled, and $\ensuremath{\pi}$-bonded-chain-type models for the diamond (111)-(2 \ifmmode\times\else\texttimes\fi{} 1) surface, only the chain model appears to account for the measured surface-band dispersion. The interaction of dangling orbitals which determines the dispersion is large in the chain model because only in this model are the dangling bonds located on nearest-neighbor atoms. The data also suggest a dimerization of the chains.

Bipolar transistor action in ion implanted diamond

Abstract: Using a natural type IIb diamond, which is p‐type semiconducting, as a substrate material, and implanting this diamond with carbon ions to induce n‐type regions, diode and bipolar transistor action could be obtained. Owing to the geometrical positions of the collector, base, and emitter, which in this case were lateral to the surface, very low current gain was obtained. However, the results indicate that an improvement in the geometry will probably lead to a diamond transistor of high gain.

Method for synthesizing diamond

Abstract: A method for synthesizing diamond wherein hydrogen gas which has passed through a micro-wave non-electrode discharge and mixed with hydrocarbon gas, or a mixture gas consisting of hydrocarbon and hydrogen after its passing through a micro-wave non-electrode discharge, is introduced onto the surface of a substrate heated to a temperature of from 300° to 1300° C. to decompose hydrocarbon in its energetically activated state for the diamond deposition.

Direct Verification of Hydrogen Termination of the Semiconducting Diamond (111) Surface

Abstract: Low‐energy, high‐resolution electron energy loss spectroscopy has been used to identify the vibrational modes of hydrogen on the semiconducting diamond surface providing the first direct evidence that the (111) 1×1 surface is terminated by hydrogen. The vibrational loss spectrum from the ’’as‐polished’’ surface shows two major losses near 160 meV (CH3 deformation), a major loss at 360 meV (CH3 stretch), and two minor losses at 520 and 720 meV (combinations and overtones). All of these losses disappear from the spectrum after heating the sample to ∠1000 °C (which has been established by other experiments to be sufficient to reconstruct the surface to 2×2/2×1). The loss spectrum for the reconstructed surface is indicative of a two‐dimensional metallic state of the dangling‐bond surface states for clean diamond. Exposure of this reconstructed surface to atomic hydrogen results in a loss spectrum which is essentially identical to that for the as‐polished surface. Further verification that the loss spectrum re...

Effect of electronic structure of the diamond surface on the strength of the diamond-metal interface

Abstract: Recent electron spectroscopic investigations have shown that the diamond surface undergoes a transformation in its electronic structure by a vacuum anneal at ∠900 °C. The polished surface has no electronic states in the band gap, whereas the annealed surface has both occupied and unoccupied states in the band gap. In addition, the annealed surface exhibits some electrical conductivity. The effect of this transformation on the strength of the diamond–metal interface is investigated by measuring the static friction force of an atomically clean metal sphere on a diamond flat in ultrahigh vacuum. The friction force is due to interfacial bonding. It is found that low friction (weak bonding) is associated with the diamond surface devoid of gap states whereas high friction (strong bonding) is associated with the diamond surface with gap states. Exposure of the annealed surface to excited hydrogen also leads to weak bonding. The interfacial bond will be discussed in terms of interaction of the metal conduction band electrons with the band gap states on the diamond surface. Effects of surface electrical conductivity on the interfacial bond will also be considered.

Method for producing a diamond sintered compact

Abstract: The invention relates to a diamond sintered compact wherein diamond crystal particles are uniformly oriented in a particular direction and the method for producing the same, and has for an object to provide a diamond sintered compact having a high thermal conductivity particularly suitable for heat sink for use in the field of electronics. According to the invention, graphite is used as carbonaceous raw material, diamond crystal particles having such elongated shape that the ratio of the length of the long axis to that of the short axis is more than 2 being synthesized in such state that the greater part of the crystal particles have their long axes uniformly oriented in a particular direction, the crystal particles being sintered in the direction of the long axes thereof so that transformation of the graphite into diamond and sintering thereof may be accomplished synchronously. The invention has for an object to obtain a diamond sintered compact suitable for the aforesaid use by degassing reaction system raw material plugged into an air permeable container by heating it in vacuum in order to intercept gaseous components causing a decrease of thermal conductivity at the time of synthesizing diamond from carbonaceous material and a catalytic metal and sintering thereof, subsequently the air permeable part of the said container being sealed by means of soldering material preliminarily placed in contact with the said container.

Photoemission and photon‐stimulated ion desorption studies of diamond(111): Hydrogen

Abstract: The interaction of hydrogen with the diamond (111) surface is examined using our new results in photoemission spectroscopy (PES) and photon‐stimulated ion desorption (PSID) yield at photon energies near the carbon K edge. Also discussed in the light of our new results are previous studies using PES and low energy electron diffraction (LEED). PSID verifies that the mechanically polished 1×1 surface is hydrogen terminated and finds that the reconstructed surface is hydrogen free. Atomic hydrogen is found to be reactive with the reconstructed surface, while molecular hydrogen is relatively inert. Exposure of the reconstructed surface to atomic hydrogen results in chemisorption of hydrogen and removal of the intrinsic surface state emission in and near the band gap region.

Diamond for a tool and a process for the production of the same

Abstract: An improved diamond compact of the present invention comprises 20 to 85% by volume of diamond grains with a grain size of at least 3 μm and the balance of a binder consisting of 20 to 95% by volume of ultra-fine diamond grains with a grain size of at most 1 μm, at least one member with a grain size of at most 1 μm, selected from the group consisting of carbides, carbonitrides, nitrides, borides of Group 4a, 5a and 6a elements of Periodic Table, solid solutions thereof and mixed crystals thereof and at least one member selected from the group consisting of iron group metals.

Optical Polishing Of Metals

Abstract: A polishing model and a fixed charge lap model are presented. Optical polishing data is presented for 11 metals partially supporting the above.

Detection of nitrogen at {100} platelets in diamond

Abstract: Platelets in type Ia diamond were first directly observed with transmission electron microscopy by Evans and Phaal1 in 1962. Considerable controversy still exists over their structure and chemical composition. One of the earliest models of the platelet structure was that proposed by Lang2 in which nitrogen, the major impurity in type Ia diamonds, is segregated into plate-like structures, only two atoms thick, lying on the cube planes. Later evidence seemed to favour interstitial carbon as the major component of the platelets3–5, although more recent evidence from the production of platelets in synthetic diamond6 again points to nitrogen as forming an important constituent. High resolution electron microscopy also supports this view7,8. Here we report for the first time the direct observation of nitrogen at platelets using the technique of electron energy loss spectroscopy (EELS).

The structure and mechanism of formation of platelets in natural type Ia diamond

Abstract: Observations have been made on medium- and large-sized platelets in a natural type Ia diamond. Attempts have been made to detect any regularity in the structure of the platelets by means of electron diffraction, but none was found. The displacement associated with the platelets has been determined to be extrinsic, normal to the plane of the platelet and of magnitude 0.4 . This value has led to the proposal of a model for the platelet structure in which the platelet consists of an interstitial layer of carbon atoms pentagonally bonded to the surrounding diamond matrix. The way in which the detailed bonding may be varied, while complete tetrahedral bonding is maintained, can lead to irregular structures consistent with the diffraction evidence. Possible mechanisms for producing interstitial carbon atoms are considered and the role of nitrogen in this context and in providing possible nuclei for platelet growth is discussed.

Method and means for converting graphite to diamond

Abstract: A host liquid, such as a liquid metal, which is "seeded" with small bubbles of an inert gas, is maintained in a sealed chamber at an ambient temperature of about 100° K. above the melting point of the host liquid, and at a static pressure ranging from 1 to 100 bars. A substance (for example carbon) which is capable of being allotropically transformed from a first form thereof (for example graphite) to a second form (for example diamond), is placed in the host liquid, which is then subjected to a time-varying acoustical pressure applied, for example, by a plurality of solid acoustical horns, which cause at least certain of the bubbles of inert gas to expand and then suddenly to collapse in a cavitation zone located substantially centrally of the chamber. By maintaining the host liquid at a pressure and temperature sufficient to cause the Hugonoit curve of the liquid to intersect a predetermined area of the phase diagram of the substance, the shock waves produced by the collapsing bubbles can be caused to envelop particles of graphite and to instantaneously transform them into diamond particles. The host liquid can be selected from a group consisting of aluminum, tin, gallium, thallium and indium, and alloys thereof; and the substance to be transformed may be selected from the group consisting of carbon, boron nitride and zinc sulphide.

Sintering behaviour of the diamond-cobalt system at high temperature and pressure

Abstract: A powder mixture of diamond—8.9 vol % Co was consolidatedin situ on a WC-10 wt % Co base at temperatures of 1300 to 1500° C under a pressure of 5.8 GPa. The sintered body obtained at 1300° C, which is below the diamond—cobalt eutectic point, was not hard, and the surface of the diamond particle was partially graphitized. On the other hand, the sintered body obtained at 1400 to 1500° C was fairly hard. A strong correlation was also observed between hardness and the cobalt content found in the sintered body. The cobalt content in the harder sintered body was clearly lower compared with that of the softer one. The surface graphitization of the diamond particles is necessary to the transfer of cobalt during the sintering of diamond. In sintering the diamond-cobalt system, the sinterability of diamond was closely related to the feasibility of transformation from diamond to graphite.

A systematic study of positron lifetimes in semiconductors

Abstract: Positron lifetimes for the ten semiconductors Si, Ge, alpha -Sn, GaP, GaAs, GaSb, InP, InAs, InSb, and CdTe as well as for diamond and SiC have been measured. The bulk-annihilation rates range from 8.7 ns-1 for diamond to 3.44 ns-1 for CdTe and agree well with theoretical calculations. The effect of doping of GaAs was investigated with four different concentrations of Si and of Cd and Cr. In contrast to Si, significant doping effects are present in GaAs.

Electron correlations in the ground state of diamond

Abstract: The correlated ground-state wave function and energy of diamond are calculated. The calculations are done in order to demonstrate that electron correlations in solids can be treated with the same accuracy as in small systems. This is achieved by applying a recently developed Local Approach to the correlation problem. The approach requires a SCF calculation as a starting point. We present such a calculation for diamond by applying a method due to Stoll and Preuss which uses localization potentials. The correlation energy is analysed in terms of inter- and intraatomic correlation energy contributions. The results are used to calculate the binding energy of diamond.

Diamond sintered compact wherein crystal particles are uniformly orientated in the particular direction and the method for producing the same

Abstract: The invention relates to a diamond sintered compact wherein diamond crystal particles are uniformly orientated in a particular direction and the method for producing the same, and has for an object to provide a diamond sintered compact having a high thermal conductivity particularly suitable for heat sink for use in the field of electronics. According to the invention, graphite is used as carbonaceous raw material, diamond crystal particles having such elongated shape that the ratio of the length of the long axis to that of the short axis is more than 2 being synthesized in such state that the greater part of the crystal particles have their long axes uniformly oriented in a particular direction, the crystal particles being sintered in the direction of the long axes thereof so that transformation of the graphite into diamond and sintering thereof may be accomplished synchronously. The invention has for an object to obtain a diamond sintered compact suitable for the aforesaid use by degassing reaction system raw material plugged into an air permeable container by heating it in vacuum in order to intercept gaseous components causing a decrease of thermal conductivity at the time of synthesizing diamond from carbonaceous material and a catalytic metal and sintering thereof, subsequently the air permeable part of the said container being sealed by means of soldering material preliminarily placed in contact with the said container.

Transformation of the diamond (110) surface

Abstract: The diamond surface undergoes a transformation in its electronic structure by a vacuum anneal at approximately 900 C. This transformation is characterized by the appearance of a feature in the band gap region of the energy loss spectrum. The kinetics of the transformation on the (110) surface is studied by observing the growth of this feature with time and temperature. The transformation is found to be consistent with first-order kinetics with an activation energy of 4.8 eV. It is also found that the band gap feature could be removed by exposure of the transformed surface to excited hydrogen. The results are consistent with the polished diamond (110) surface being covered with hydrogen which removes the band gap states and can be thermally desorbed at approximately 900 C.

Residual Stresses in Hot‐Pressed Si3N4 Grooved by Single‐Point Grinding

Abstract: Hot-pressed silicon nitride plates were grooved by single diamond points with varying degrees of flatness mounted on a wheel rotating at varying speeds. The plates were divided into bars and the remaining strengths were measured. The depths of damage were measured and used to calculate the theoretical strengths. For sharp diamonds and in some cases for diamonds with flat tips, the measured strengths were less than the theoretical strengths. The differences between the measured strengths and the theoretical strengths are attributed to the presence of residual loads acting to wedge open the cracks.

Method for producing diamond compact

Abstract: A method for producing compact of diamond particles, comprising: providing a mass of diamond particles and a metallic material capable of dissolving carbon, as infiltrant, with a substantially identical cross section, placing said diamond and infiltrant metal close to but separated with each other with an intervening layer of high melting metal, as barrier, which has a cross section of 85 to 97% relative to that of the diamond and infiltrant metal, and subjecting the whole to an elevated pressure and temperature condition within the diamond stability region of carbon phase diagram, thus allowing a regulated amount of fused infiltrant metal to flow in among the mass of diamond to join adjacent particles with each other, and recovering a compact of thus joined diamond particles.