Showing papers on "Diamond published in 1984"

Modeling studies of amorphous carbon

Abstract: Three structural models of amorphous carbon with differing percentages of threefold- and fourfold-coordinated atoms were constructed and analyzed, along with a purely four-coordinated amorphous Ge model which was scaled to diamond bond lengths. The radial distribution function and interference function, $F(k)$, of the model containing 14% four-coordinated atoms were in best agreement with the experimental results of Boiko et al., although the functions containing 48% four-coordinated atoms were in best agreement with the results of Kakinoki et al. The unavoidable planar nature of the entirely three-coordinated model caused its $F(k)$ to be in poor agreement with experiment. Raman and vibrational density-of-states (DOS) spectra were also calculated for the models. The presence of disorder in the three-coordinated model produced a downward shift in frequency of the principal Raman peak and DOS band edge from the position seen in graphite. With the addition of four-coordinated atoms, there was a gradual transition from graphitelike spectra to diamondlike spectra, rather than spectra with a mixture of distinct features typical of graphite and diamond. In addition, there was a further downward shift in frequency of the main Raman peak and in that of the "disorder peak" seen in microcrystalline and amorphous carbon. The spectra of the model containing 14% four-coordinated carbon was in best agreement with recent Raman scattering experiments. These results suggest a structure for amorphous carbon consisting of three-coordinated planar regions with occasional four-coordinated atoms allowing changes in orientation of the planes. The positions of the peaks in the spectra suggest that the proportion of four-coordinated atoms is not likely to exceed 10%.

Total energies of diamond (111) surface reconstructions by a linear combination of atomic orbitals method

Abstract: An ab initio linear combination of atomic orbitals approach to local-density theory, capable of handling complex structural geometries, is presented. It incorporates a self-consistent treatment of interatomic charge transfer, which allows an accurate calculation of total energies. The method is applied to study a variety of possible 1 x 1 and reconstructed 2 x 1 models of the diamond (111) surface. Among the many models suggested, only the Pandey ..pi..-bonded chain model has a lower energy than that of the 1 x 1 surface. A minimum-energy structure is obtained for this model after extensive consideration of relaxations. No dimerization of the surface chain is found to occur.

Structural theory of graphite and graphitic silicon

Abstract: The graphitic phases of C and Si are studied with the use of the pseudopotential local-density-functional approach. For graphite, good agreement with experiment is obtained for the in-plane lattice constant, interlayer spacing, isotropic bulk modulus, and graphite-diamond structural energy difference. Graphitic Si has relatively weak bonding and its formation is unlikely since its energy is 0.71 eV/atom higher than the diamond phase and a large negative pressure of -69 kbar is required.

Si-III (BC-8) crystal phase of Si and C: Structural properties, phase stabilities, and phase transitions

Abstract: With use of the pseudopotential local-density-functional approach, the lattice constant, the $x$ parameter for atomic coordinates, and the phonon frequency of the mode ${\ensuremath{\Gamma}}_{1}^{+}$ are calculated for the Si-III (BC-8) crystal phases of Si and Ci. The results agree well with available experimental data for the BC-8 phases of Si. From the total-energy curves of the diamond and the BC-8 phases of Si, we find that the BC-8 phase of Si is not stable at ambient pressure or at high pressure. The diamond---BC-8 (I-III) transition of Si will not occur quasistatically. Comparing the diamond, the BC-8, and the simple-cubic phases of C, we find that diamond will first transform to the BC-8 phase at 12 Mbar and then to the simple-cubic phase at 27 Mbar under quasistatic conditions.

Preparation and structure of carbon film deposited by a mass‐separated C+ ion beam

Abstract: Carbon films were deposited using mass‐separated C+ ions of 300 and 600 eV. The films have diamond‐like characteristics such as transparency in the visible spectral region with wavelengths longer than about 650 nm and in the infrared, and high electrical resistivity. Transmission electron diffraction analysis shows that the film is amorphous and does not contain graphitically bonded carbon atoms. Kα x‐ray emission spectrum of the carbon in the film agrees well with that of diamond. In the x‐ray photoemission spectrum of the film, no characteristic energy loss due to π plasmon was observed. The atomic density of the film calculated from the energy loss due to the plasma oscillation of valence electrons is 1.7×1023 atoms/cm3, which is in good agreement with that of diamond. These results indicate that the film deposited using C+ ion beam consists of tetrahedraly bonded carbon atoms.

Sintered polycrystalline diamond compact construction with integral heat sink

Abstract: A sintered polycrystalline diamond compact having an integral metallic heat sink bonded to and covering at least the outer diamond surface is used to increase compact life when the compact is used for material removal without a fluid coolant.

Characterization of the treated surfaces of silicon alloyed pyrolytic carbon and SiC

Abstract: The treated surfaces of artificial heart valves made of silicon alloyed pyrolytic carbon were compared to similarly treated SiC using x‐ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The materials were exposed to water, isopropanol, and acetone cleaning, diamond and alumina polishing, and sterilization. Three chemical states of carbon, three states of silicon, and low concentrations of polishing contaminants were identified and related to surface treatment. Characterization of the heart valve surfaces will assist in determining appropriate manufacturing processes required for assuring blood compatibility of the devices.

Cathodoluminescence and polarization studies from individual dislocations in diamond

Abstract: A cathodoluminescence detector attached to a transmission electron microscope has been used to record visible optical-emission spectra from individual dislocations of known type in type IIb diamond over a range of temperatures. The polarization of the emission has also been determined from individual dislocations and this information correlated with the type and degree of dissociation of the dislocations. It was found that the dislocation emission at 435 nm was polarized along the dislocation line (independent of the Burgers vector) and had maximum intensity at 170 K. The emission spectrum was independent of dislocation type, and showed a broad (0·416 eV f.w.h.m.) band. All luminescent dislocations were dissociated, and one non-luminescent dislocation was found which was undissociated within the resolution of the weak-beam technique (∼ 15 A). Non-luminescent dissociated dislocations were also found. Curved dislocations were less luminescent than straight ones. A one-dimensional donor-acceptor mod...

Crystal structure of diamondlike carbon films prepared by ionized deposition from methane gas

Abstract: Diamondlike carbon films have been prepared by ionized deposition from methane gas. The film structures were examined by transmission electron microscopy, electron diffraction, and electron spectroscopy for chemical analysis techniques. It was found that the structure of the carbon films could be classified into three types: (i) amorphous, (ii) graphite, and (iii) cubic. These types depended mainly on the deposition conditions. Usually crystalline carbon films were diamond mixed with graphite showing an average grain size of several hundred angstroms. Very hard films were composed of diamond crystallites distributed in amorphous matrix.

Synthesis of Diamond in Its Thermodynamic Metastability Region

Abstract: Heterogeneous and homogeneous processes in the formation of diamond at low pressures, where diamond is a metastable modification of carbon, are discussed. Data on the kinetics of the growth of diamond from hydrocarbons under conditions which give codeposition with graphite are reported, together with data on the influence of hydrogen on this process and on the resulting fractionation of the stable carbon isotopes. Chemical and plasma-chemical methods of preparing diamond and diamond-like layers are discussed, as well as methods based on the use of atomic and ionic beams. The most recent theoretical and experimental results on the homogeneous formation of diamond in the gas phase are presented. The bibliography includes 73 references.

One-phonon infrared absorption in diamond

Abstract: The defect-induced one-phonon infrared absorption in natural diamond can be divided into a number of overlapping components. The computational method of extracting the spectral shapes of these contributions is described. The A and B components are associated with nitrogen defects. The A defect is a pair of substitutional nitrogen atoms and the B defect is currently considered to be an agglomerate containing four nitrogen atoms. The C spectrum is associated with the singly substituted nitrogen atom and is characteristic of synthetic diamonds. The D spectrum has been observed only in diamonds which also contain B defects, and for this reason is also considered to be a defect which contains nitrogen. Some studies have been carried out on the thermal stability of the A, B and D defects during heat treatment in the range 2100-2800 degrees C under a pressure of 9.5 GPa. A possible nitrogen aggregation sequence is suggested to describe the observations.

Interstitial muons and hydrogen in diamond and silicon

Abstract: The authors have calculated self-consistent total-energy surface for hydrogen present interstitially as H+, H0 and H2 in crystalline silicon and diamond. The dissimilarities of the two materials are more evident than their similarities, for they show molecular hydrogen to be the stable form in silicon, and atomic hydrogen to be the stable form in diamond in the absence of impurities. The energy surfaces for H0 and H+ are complex, with minima too small to trap the atoms when zero-point energy is taken into account. They discuss their results in relation to other theories and to the normal and anomalous muonium ( mu +e-) experiments.

Interstitial-sphere linear muffin-tin orbital structural calculations for C and Si

Abstract: It is demonstrated that the linear muffin-tin orbital (LMTO) method used with interstitial spheres can provide accurate structural energy differences involving the open-packed diamond and simple-cubic (sc) structures. The total-energy differences calculated between these two structures in this manner, and between these and more conventionally LMTO calculated fcc, hcp, and bcc structures, are seen to be in excellent agreement with the highly accurate results of Yin and Cohen for both carbon and silicon. The agreement persists over a wide range of volume, including the prediction of a high-pressure diamond to sc transition in carbon, in the absence of intermediate phases.

Etching of diamond with argon and oxygen ion beams

Abstract: The angular dependences of the sputter yield of (100) single crystal diamond under argon and oxygen ion beams were investigated. For argon ion beams a large increase in the sputter yield was observed as the angle of incidence was increased from the normal, with a maximum occurring at approximately 60 deg from the normal. The magnitude of the increase and the angle at which the maximum was observed were dependent on the ion energy and species. The shape of the yield versus angle of incidence curve indicated the presence of a highly damaged surface layer. Large deviations from this curve were observed where ion incidence was along channeling directions. Studies with oxygen ion beams showed almost no angular dependence for 500 eV ions while at an energy of 1000 eV the angular dependence was similar to that for argon ions. At normal incidence the yield for 500 eV oxygen ions was seven times larger than that for 500 eV argon ions. For 1000 eV oxygen and argon ions the corresponding ratio is only 2.5. Implications for mechanisms of inert and reactive ion etching are discussed. Application of the data to ion beam shaping of diamond tips for ultrahigh pressure research is discussed.

Shock compression and flash heating of graphite/metal mixtures at temperatures up to 3200 K and pressures up to 25 GPa

Abstract: Different aspects of phase‐transition processes in carbon in dynamic conditions were studied. Samples of graphite/metal mixtures have been recovered and analyzed after exposure to the combined action of high temperature and pressure pulses generated by a unique flash‐heating hemispherical implosion system. Transmission electron microscopy together with x‐ray and electron diffraction examinations proved the existence of diamond, different forms of graphite, and carbynes in the samples. A mechanism of formation of diamond is proposed which relies on a solid‐vapor‐liquid‐solid (SVLS) sequence of phase transformations. The experimental results were found to be in reasonable agreement with the proposed SVLS model. A tetragonally crystallized diamondlike carbon phase ( p‐diamond) was identified in the course of the work as well as a new linear carbon polymorph (Carbon‐XIV).

Electronic excitations in semiconductors. II. Application of the theory to diamond

Abstract: A previously developed theory for calculating electronic excitations in semiconductors is applied to diamond. The starting point is a self-consistent-field calculation within a given basis set of Gaussian-type orbitals. From that the fully correlated electronic wave function and correlation energy are calculated. The reduction of the direct energy gap and the widths of valence and conduction bands due to correlations are studied and compared with experiments. The results can be understood in terms of simple physical pictures. The largest correlation energy contribution results from the polarization cloud of the excited electron and hole pair, but changes in the ground-state correlations due to the presence of the excited electron are also of importance. Intra-atomic correlations such as relaxation effects are only estimated from molecular calculations. A detailed comparison with other methods is made, in particular with the local approximation to the density-functional formalism.

Persistent spectral hole burning of colour centres in diamond

Abstract: Four zero-phonon lines of defect centres in diamond (GR1 (741 nm), N-V (637 nm), H4 (496 nm) and N3 (415 nm)) have been shown to exhibit persistent spectral hole burning. The phenomenon appears to be a rather general one in diamond and should prove very powerful for elucidation of the nature of defect centres. As an example, preliminary results for the N-V centre suggest a previously undetected splitting of the excited state.

Diamond heatsink assemblies

Abstract: A diamond heatsink assembly for small electronic components such as microwave or millimetric wave devices comprises a frusto-conical shaped diamond held on a support by a clamping member with a part-conical hole through it. One or both of the support and the clamping member are made of a high thermal conductivity metal such as gold, silver, copper or aluminum. The clamping member may be secured to the support by soldering, friction welding, a screw thread or any other suitably tight clamping method. The diamond, the support and the clamping member may be metallized to reduce electrical skin resistance. The arrangement is an improvement on diamond heatsinks in which a diamond is simply bonded to the support by soldering or brazing and heatsinks in which the diamond is pressed into the surface of the support.

Preparation of sp3-Rich Amorphous Carbon Film by Hydrogen Gas Reactive RF-Sputtering of Graphite, and Its Properties

Abstract: An a-C:H film was prepared for the first time by H2 gas reactive rf-sputtering of a graphite target onto low temperature (room temperature ~150°C) substrate. This film has a uniform amorphous structure and an H-atom ratio of 0.8 H/C; its electrical resistivity was 106~1012 Ωcm. Vickers' hardness number of the film was 1000~2000. IR, Raman and ESCA spectra showed that the bonding between the neighbouring C-atoms was for the most part by sp3 bond, and that sp2 bond was rare. Approximately 200 A of diamond grains were observed by TEM in annealed film at 1000°C, and verified by electron diffraction pattern.

Diamond abrasive products

Abstract: A diamond abrasive body which comprises a coherent, skeletal diamond mass constituting at least 70 percent by volume of the body and a glass phase comprising up to 30 percent by volume of the body uniformly dispersed throughout the diamond mass. The glass phase has a melting point in the range 800° to 1400° C. The abrasive body has good thermal stability and strength making it suitable for use as an insert for tools such as dressing tools and surface set drill bits. The abrasive body is produced by infiltrating molten glass into a coherent skeletal diamond mass. The glass phase is preferably transformed to a ceramic form by heat treatment of the infiltrated diamond mass.

Diamond eclogite and graphite eclogite xenoliths from Orapa, Botswana

Abstract: Twenty four diamond eclogites, four with both diamond and graphite and twenty graphite eclogites are described. All of the diamond-bearing rocks and most of the graphite eclogites contain minor amounts of Na 2 O in their garnet and K 2 O in their clinopyroxene and are classed as Group I eclogites (after MacGregor and Carter, 1970). Four graphite-bearing rocks are classed as Group II eclogites. The diamond eclogites tend to contain relatively magnesian garnets and to give higher estimated temperatures of equilibration than the Group I graphite eclogites. A relatively deep origin is postulated for the diamond eclogites. The Group II graphite eclogites are geochemically distinct from those of Group I. They give relatively low estimated temperatures of equilibration and appear to be derived from shallower depths. There is no reason to link the Group II eclogites to diamond-forming processes. Geochemical evidence suggests that many of the diamond-bearing eclogites are not directly related to the eclogitic inclusions in diamond and the silicates intergrown with diamond aggregates which have been studied from the Orapa kimberlite. Some fundamental differences between the xenolith diamonds and those from the kimberlite substantiate that the former are not dominant in the Orapa Mine diamond population. This is notwithstanding that the eclogitic paragenesis predominates amongst the Orapa diamonds and that the xenoliths studied are many thousands of times richer in diamonds than the kimberlite.

Stress analysis of a beveled diamond anvil

Abstract: A finite element stress analysis has been performed on a brilliant cut high‐pressure diamond anvil. The analysis includes the presence of a metal gasket. A perfectly cohesive interface is assumed to exist between the diamond and metal. Different configurations of the anvil face were studied. The stress distribution resulting from various beveled angles has been analyzed. It has been found that for a flat anvil, with a center normal pressure of about 210 kbar, an octahedral shearing stress of about 90 kbar is present near the center and monotonically increases radially to about 208 kbar along the outer edge. When the anvil surface is beveled, the octahedral shearing stress at the outer corner decreases significantly. The optimum beveled angle necessary to minimize these stresses seems to lie in the neighborhood of 15°. The assumptions made and other stress considerations are discussed.

Experiments at high temperature and pressure : laser heating through the diamond cell

Abstract: CW laser heating through a diamond anvil cell by means of a focused Nd:YAG laser has resulted in the achievement of temperatures in the 1500-5000 K range for pressures of 10-100 GPa. Temperatures are determined radiometrically, with an accuracy of about 200 K, and temperature variation across the laser-heated spot is derived by means of spatial filtering with a slit that can be scanned. Melting temperatures are thus determined either on the basis of observed temperature at the liquid-solid interface or on that of the peak temperature at which glass is first produced with increasing laser power.

Synthetic diamond heat sink

Abstract: A synthetic diamond heat sink which can be easily shaped and which ensures a consistently high thermal conductivity in which the diamond is a Type Ib diamond containing 5 to 100 ppm nitrogen. The synthetic diamond crystal has a shape approaching that of a hexahedron with a high proportion of (100) planes and is synthesized by heating a carbon source, a solvent and a diamond seed crystal in the stability region of diamond at a high pressure. The temperature gradient between the carbon source and the seed crystal is adjusted to cause diamond growth on the seed crystal. The solvent employed is selected from the group of cobalt, nickel, iron, chromium and manganese. The diamond crystal is caused to grow as the temperature of the solvent is gradually decreased at a rate of 0.15 to 10°C per hour so that the temperature of the area where growth occurs on the seed crystal is held constant within a range the lower limit of which is a temperature 20°C higher than the melting point of the solvent and carbon source system and the upper limit of which is a temperature 40°C higher than the lower limit.