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Showing papers on "Diamond published in 1996"


PatentDOI
19 Dec 1996-Science
TL;DR: A cubic form of C3N4 with a zero-pressure bulk modulus exceeding that of diamond is described in this paper, and a process for preparing such product which comprises combining carbon and nitrogen at a pressure of 120,000 to 800,000 atmosphere and a temperature of 1000-3000 °C is described.
Abstract: A cubic form of C3N4 with a zero-pressure bulk modulus exceeding that of diamond Also a process for preparing such product which comprises combining carbon and nitrogen at a pressure of 120,000 to 800,000 atmosphere and a temperature of 1000-3000 °C Carbon particles may be immersed in liquid nitrogen and the mixture heated by a laser beam followed by quenching

1,016 citations


Journal ArticleDOI
01 Aug 1996-Nature
TL;DR: In this article, it was shown that carbon onion cores can be transformed to diamond by electron irradiation of graphitic carbon materials, and that the carbon onions act as nanoscopic pressure cells for diamond formation.
Abstract: SPHERICAL particles of carbon consisting of concentric graphite-like shells ('carbon onions') can be formed by electron irradiation of graphitic carbon materials1,2. Here we report that, when such particles are heated to ∼700 °C and irradiated with electrons, their cores can be transformed to diamond. Under these conditions the spacing between layers in the carbon onions decreases from 0.31 in the outer shells (slightly less than the 0.34-nm layer spacing of graphite) to about 0.22 nm in the core, indicating considerable compression towards the particle centres. We find that this compression allows diamond to nucleate—in effect the carbon onions act as nanoscopic pressure cells for diamond formation.

620 citations


Journal ArticleDOI
01 Jan 1996-Carbon
TL;DR: In recent years, important advances in the understanding of the pressure-temperature phase and transformation diagram for carbon have occurred as a result of developments in both experimental and theoretical techniques as discussed by the authors.

580 citations


Journal ArticleDOI
09 May 1996-Nature
TL;DR: In this article, high concentrations of nitrogen can be incorporated into diamond films by using urea as the gaseous nitrogen source, and such heavily doped films shown very low-threshold electron emission, which augurs well for cold-cathode technology.
Abstract: BECAUSE diamond surfaces terminated with hydrogen have a negative electron affinity1–4 (the conduction band minimum lies below the vacuum level), they are expected to emit electrons spontaneously. This has led to attempts to develop 'cold cathodes'—miniaturized vacuum diodes that might have applications in microelectronics and flat-panel displays. In previous studies of electron emission from diamond grown by chemical vapour deposition5–9 (CVD), the threshold voltages for emission were more than an order of magnitude too large for use in battery-driven cold cathodes. Although low-threshold emission from caesium-coated, nitrogen-doped high-pressure synthetic diamond was reported recently10, ultimately diamond thin films grown by chemical vapour deposition (CVD) look to be the most promising material for cold-cathode applications. But to obtain low-threshold emission, it is necessary to introduce high concentrations of donor dopants such as nitrogen—something that is difficult for CVD diamond. Here we report that high concentrations of nitrogen can be incorporated into diamond films by using urea as the gaseous nitrogen source, and that such heavily doped films shown very-low-threshold electron emission, which augurs well for cold-cathode technology.

513 citations


Journal ArticleDOI
TL;DR: The first application of hydrogen-terminated surfaces as electron devices is presented in this article for the metal-semiconductor field effect transistor (MSE transistor), where the surface states of (1 1 1) and (0 0 1) were discussed.

462 citations


Journal ArticleDOI
TL;DR: In this article, the evolution of hydrogen and oxygen was studied on diamond electrodes containing approximately 1021 boron atom/cm3, and the extent of surface oxidation increased with sp2 content.
Abstract: The evolution of hydrogen and oxygen was studied on diamond electrodes containing approximately 1021 boron atom/cm3. Voltammetry showed a wide potential window [−1.25 to +2.3 V vs. standard hydrogen electrode (SHE)] without significant water decomposition. This window was much narrower for poor quality diamond films with appreciable sp2 content. A redox couple observed at +1.7 V indicates oxidation of the diamond surface prior to oxygen evolution. The extent of surface oxidation increased with sp2 content. Anodic polarization made the diamond surface hydrophilic; x‐ray photoelectron spectroscopy showed an increase in oxygen coverage and the presence of carbon‐oxygen bonds. The estimated capacitance of the interface ranged from 0.05 μF/cm2 for high quality diamond to 5 μF/cm2 for low quality diamond. Preliminary measurements of the exchange current densities for oxygen and hydrogen evolution indicated slow kinetics compared to metals or highly oriented pyrolytic graphite.

373 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the structure of amorphous carbon (ta-C) can be simulated using ab initio quantum mechanics with high elasticity and low friction coefficients.
Abstract: Electron configurations close to the tetrahedral hybridization are found in pure amorphous carbon at a concentration which depends on preparation conditions. Tetrahedral bonding at levels of approximately 80% is found in amorphous carbons formed from beams of carbon ions with energies in a `window' between 20 eV and approximately 500 eV. Suitable techniques for its formation include cathodic arc deposition, ion beam deposition and laser ablation. Similar material appears to be formed by pressure treatment of fullerene precursors and by displacement damage in diamond. Highly tetrahedral forms of amorphous carbon (ta-C) show electronic, optical and mechanical properties which approach those of diamond and are quite different from amorphous carbons with low content. Useful techniques for determining the content include electron energy loss spectroscopy, electron and neutron diffraction and Raman spectroscopy. Considerable progress has been made in the understanding of this material by simulating its structure in the computer with a range of techniques from empirical potentials to ab initio quantum mechanics. The structure shows departures from an idealized glassy state of diamond which would have a random tetrahedral network structure as used to describe amorphous silicon and germanium. A surprising feature of the structure simulated using ab initio methods is the presence of small rings containing three or four carbon atoms. The electronic and optical properties are strongly influenced by the residual of carbon. Applications to electronic devices are at an early stage with the demonstration of photoconductivity and some simple junction devices. Applications as a wear resistant coating are promising, since the theoretically predicted high values of elastic constants, comparable to but less than those of diamond, are achieved experimentally, together with low friction coefficients.

367 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between the cutting edge radius and the minimum cutting thickness was analyzed, and the effect of cutting edge sharpness on the machined surface integrity was investigated.

331 citations



Journal ArticleDOI
TL;DR: In this paper, a hypothesis is proposed that ascribes chemical wear of diamond tools to the presence of unpaired d electrons in the sample being machined, which is used to explain a range of results for metals, alloys, and other materials including “electroless” nickel.
Abstract: A hypothesis is proposed that ascribes chemical wear of diamond tools to the presence of unpaired d electrons in the sample being machined. This hypothesis is used to explain a range of results for metals, alloys, and other materials including “electroless” nickel. The hypothesis is further tested by experiments presented here on the machining of a range of high purity elements. The implications for diamond turnability of other materials are discussed.

298 citations


Book ChapterDOI
01 Jan 1996
TL;DR: In this paper, the internal structure of fullerenes is analyzed and it is shown that the structure and properties of these solids are strongly dependent on the structure of the constituent fullerene molecules.
Abstract: This chapter illustrates the internal structure of the molecules. Many independent experiments show that the crystalline materials formed from fullerenes are molecular solids. Therefore the structure and properties of these solids are strongly dependent on the structure and properties of the constituent fullerene molecules. The 60 carbon atoms in C 60 are now known to be located at the vertices of a truncated icosahedron where all carbon sites are equivalent. This is consistent with the observation of a single sharp line in the nuclear magnetic resonance (NMR) spectrum. Since the bonding requirements of all the valence electrons in C 60 are satisfied, it is expected that C 60 has filled molecular levels. Because of the closed-shell properties of C 60 (and also other fullerenes), the nominal sp2 bonding between adjacent carbon atoms occurs on a curved surface, in contrast to the case of graphite where the sp 2 trigonal bonds are truly planar. This curvature of the trigonal bonds in C 60 leads to some admixture of sp 3 bonding, characteristic of tetrahedrally bonded diamond, but absent in graphite.

Journal ArticleDOI
TL;DR: In this paper, the fabrication of gated diamond field-emission cathodes is described and a theory of their operation is discussed, and the cathodes are made using commercial diamond grit with the addition of Ni and Cs salts to enhance emission.
Abstract: The fabrication of gated diamond field‐emission cathodes is described and a theory of their operation is discussed. These cathodes are made using commercial diamond grit with the addition of Ni and Cs salts to enhance emission. The resulting structure resembles a field‐emission Spindt cathode with the internal metal cone replaced by a ∼100 nm layer of diamond grit. Emission from these cathodes occurs at the lowest reported gate voltage of any field emission device and is unaffected by operation at pressures of over 100 Pa of N2. Operation in oxygen and H2S at pressures of 6×10−4 Pa degrades emission, but the cathodes recover once the ambient pressure is reduced to below 1×10−4 Pa. The emission current noise is 2.5% rms over an 8 h period and 1% rms over 3 ms. These cathodes suffer from high gate current that varies from 0.2 to 1000 times the emitted current. The high gate current is known to be process dependent and not inherent to the cathodes. The emission performance is explained by the stable negative electron affinity of diamond, which allows for injection of electrons from diamond into vacuum with little to no electric field, 0–1 V μm−1. Cathode operation is limited by the injection of electrons into the diamond at the back metal–diamond interface, which depends upon the doping of the diamond and the roughness of that interface.

Journal ArticleDOI
TL;DR: In this paper, the authors review the present understanding of diamond-like carbon growth mechanisms and discuss the correlation between the deposition parameters (e.g., species energy, substrate temperature, substrate material, angle of incidence, deposition rate and environment) and the film properties (density, surface morphology, sp 3 /sp 2 ratio) studied using a host of experimental methods.

Journal ArticleDOI
TL;DR: Ab initio cluster methods are used to investigate vacancy-impurity complexes in diamond and assign the 1.682 eV, twelve-line optical band to a vacancy-Si complex which has a very unusual, possibly unusual, structure.
Abstract: Ab initio cluster methods are used to investigate vacancy-impurity complexes in diamond. We assign the 1.682 eV, twelve-line optical band to a vacancy-Si complex which has a very unusual, possibly unique structure with a Si atom at the center of a split vacancy. The method also successfully accounts for the 1.945, 2.156, and 2.985 eV optical transitions in trigonal vacancy-N defects and estimates of radiative lifetimes are given.

Journal ArticleDOI
01 Dec 1996-Wear
TL;DR: In this article, the authors compared the abrasion resistance of nanostructured WCCo composites, synthesized by a novel spray conversion method, compared with that of conventional materials.

Journal ArticleDOI
TL;DR: In this article, the microstructures of presolar diamond crystallites were compared to those of (terrestrial) synthesized nano-diamonds using high-resolution transmission electron microscopy.

Journal ArticleDOI
TL;DR: The new crystal structure information system DIAMOND is presented and is a powerful tool for establishing structural relationships and for evaluating crystallographic data.
Abstract: The new crystal structure information system DIAMOND is presented. It handles all kinds of crystallographic databases on PCs including SHELX files and Chemical Information Files (CIF’s). DIAMOND, because of its graphics capability, is a powerful tool for establishing structural relationships and for evaluating crystallographic data.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated carrier transport in a highconductivity layer formed in the surface region of asdeposited homoepitaxial diamond films prepared by chemical vapor deposition.
Abstract: Using Hall effect measurements, we have investigated carrier transport in a high‐conductivity layer formed in the surface region of as‐deposited homoepitaxial diamond films prepared by chemical vapor deposition. The results of undoped and B‐doped films were compared to those obtained from an oxidized B‐doped film. It is found that (1) the carrier (hole) density per unit area of both as‐deposited films is 4–5 orders of magnitude larger than that of the oxidized B‐doped film at 297 K and is nearly constant in the temperature range of 150–400 K, while that of the oxidized B‐doped film shows a strong temperature dependence with an activation energy of 0.38 eV, and (2) the Hall mobility of both as‐deposited films is 1–2 orders of magnitude smaller than that of the oxidized B‐doped film at 297 K and increases with increasing temperature, while that of the oxidized B‐doped film decreases. These results and the secondary ion mass spectroscopy analysis suggest that the high‐conductivity layer formed in the as‐depo...

Journal ArticleDOI
S. Vepřek1, M. Haussmann1, S. Reiprich1, Li Shizhi1, J. Dian1 
TL;DR: In this paper, a theoretical concept for the design of novel, nanocrystalline and thermodynamically stable materials with hardness of ≥50 GPa (about 5000 kg mm−2), elastic modulus of ≥500 GPa and a high stability against oxidation in air up to 800°C is described together with its experimental verification on several systems nc-MexN/a-Si3N4 (Me  Ti, W, V).
Abstract: A theoretical concept for the design of novel, nanocrystalline and thermodynamically stable materials with hardness of ≥50 GPa (about 5000 kg mm−2), elastic modulus of ≥500 GPa and a high stability against oxidation in air up to 800°C is described together with its experimental verification on several systems nc-MexN/a-Si3N4 (Me  Ti, W, V). The concept is based on avoiding the formation and multiplication of dislocations in the nanocrystalline phase, and blocking the crack propagation in a 0.3–0.5 nm thin amorphous tissue. The theoretical principles of the design of such materials and the thermodynamic criteria for the segregation of the nc- and a-phases, which is necessary for the preparation of such materials, are discussed. Several micron thick films of such materials have been prepared by plasma CVD at a rate of 0.6–1 nm s−1 from the corresponding metal halides, hydrogen, nitrogen and silane at deposition temperatures of ≤550°C. A low content of chlorine of ≤0.3 at.% assures their stability against corrosion in air. Upon microindentation up to a load of ≥100 mN the films show a remarkably high elastic recovery of about 80%. Unlike diamond, c-BN, and C3N4 these materials are thermodynamically stable and relatively easy to prepare.

Journal ArticleDOI
TL;DR: In this article, a relative Raman scattering cross-section has been determined for diamond and non-diamond carbon spectra excited by argon ion 514.5 nm radiation.

Patent
29 Jul 1996
TL;DR: Hardfacing to protect wear surfaces of drill bits and other downhole tools having coated diamond particles (44) dispersed within and bonded to a metallic matrix deposit was proposed in this paper.
Abstract: Hardfacing to protect wear surfaces of drill bits and other downhole tools having coated diamond particles (44) dispersed within and bonded to a metallic matrix deposit (20). The coating (42) on the diamond particles (44) may be formed from materials and alloys such as particles of tungsten carbide, and tungsten carbide/cobalt and cermets such as metal carbides and metal nitrides. The coated diamond particles (40) are preferably sintered and have a generally spherical shape. The coated diamond particles (40) are pre-mixed with selected materials such that welding and cooling will form both a metallurgical bond and a mechanical bond within the solidified metallic matrix deposit (20). A welding rod (70) is prepared by placing a mixture of coated diamond particles (40), hard particles such as tungsten carbide/cobalt (30), and loose filler material (74) into a steel tube (72). A substrate (24) is hardfaced by progressively melting the welding rod into a selected surface of the substrate (24) and allowing the melted material to solidify, forming the desired hardfacing with coated diamond particles (40) dispersed therein on the substrate surface (22).

Journal ArticleDOI
TL;DR: In this paper, a polycrystalline diamond film was grown by microwave assisted chemical vapor deposition from methane/hydrogen gas mixtures, and the addition of small amounts of nitrogen with concentrations below 50 ppm to the process gas was found to drastically increase the deposition rate depending on the microwave power.
Abstract: Polycrystalline diamond films have been grown by microwave assisted chemical vapor deposition from methane/hydrogen gas mixtures. The addition of small amounts of nitrogen with concentrations below 50 ppm to the process gas was found to drastically increase the deposition rate depending on the microwave power. At 4.2 kW microwave power a five times higher growth rate compared to nitrogen‐free depositions was achieved. The optical transmission and thermal conductivity have been measured. The incorporation of small amounts of nitrogen does not degrade the infrared transmission of the samples; the thermal conductivity measured at room temperature decreased only slightly from 20.5 to 18 W/(cm K).

Journal ArticleDOI
TL;DR: In this paper, the authors compared the field emission of boron and nitrogen-doped diamond and showed that the latter is more conductive than the former, and that a roughened interface substantially reduces the potential in the diamond and increases emission.
Abstract: Field emission of electrons from boron‐ and nitrogen‐doped diamond is compared. Emission from boron‐doped diamond requires vacuum electric fields of 20–50 V μm−1, while nitrogen‐doped, type Ib diamond requires fields of 0–1 V μm−1. Since boron‐doped diamond is very conductive, very little voltage drop occurs in the diamond during emission. Nitrogen‐doped diamond is insulating, so during emission a potential of 1–10 kV appears in the diamond. This potential is a function of the back contact metal‐diamond interface. A roughened interface substantially reduces the potential in the diamond and increases emission. The electrons are often emitted from the nitrogen‐doped diamond as beamlets. These beamlets leave the surface of the diamond at angles up to 45° from the substrate normal. Although the vacuum field is small, these electrons have energies of several kV. It is unknown whether the electrons are accelerated to these energies in the bulk of the diamond, or at high electric fields near the emitting surface.

Journal ArticleDOI
TL;DR: In this article, a series of high-pressure (P ), temperature (T ) experiments on synthetic and natural type Ib diamond were conducted to unravel the sector dependency of the aggregation rate in the starting materials.

Journal ArticleDOI
TL;DR: In this paper, near-edge x-ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type.
Abstract: Near‐edge x‐ray absorption fine structure (NEXAFS) measurements were performed on a variety of carbon materials, covering a range of hybrid bonding character from pure sp3 type to pure sp2 type. Diamond, chemical vapor deposited (CVD) diamond films of varying quality. Diamond‐like carbon (DLC) films, and graphite were examined with this technique and these measurements were compared with Raman spectroscopy results and scanning electron microscopy images of carbon film morphology. For the mixed sp2 and sp3 bonded DLC materials, NEXAFS does not suffer from the large Raman cross‐section difference between sp2 and sp3 type bonds, thus allowing unambiguous characterization of carbon thin films with a broader range of sp2/sp3 bonding ratios than possible with Raman spectroscopy alone. This capability was used to determine the transition point where the sequential‐CVD carbon film growth technique produces predominately sp3 or sp2 bonded material.

Journal ArticleDOI
TL;DR: A series of boron-doped polycrystalline diamond films grown by hot-filament-assisted chemical vapor deposition was studied with transmission electron microscopy (TEM), secondary-electron microscopy, Raman spectroscopy, Hall effect and currentvoltage measurements.

Journal ArticleDOI
TL;DR: In this article, spatially resolved electron field emission measurements from a nanocrystalline diamond film grown by plasmaenhanced chemical transport deposition have been obtained using a scanning probe apparatus with micrometer resolution.
Abstract: Spatially resolved electron field emission measurements from a nanocrystalline diamond film grown by plasma‐enhanced chemical transport deposition have been obtained using a scanning probe apparatus with micrometer resolution. Macroscopic regions with a high emission site density, and turn‐on fields below 3 V/μm, comprised approximately 1/2 of the total sample area. The emitting and the nonemitting regions of the specimen are differentiated distinctly by Raman spectra and subtly by morphologies. Both areas are largely sp3‐bonded, but only the nonemitting regions exhibit a sharp line at 1332 cm−1, a well‐known signature of diamond in larger crystallites.

Journal ArticleDOI
TL;DR: In this paper, the electron field emission properties of the (111)1×1:H surface of natural semiconducting diamond have been examined with simultaneous field emission and photoemission measurements.
Abstract: The electron field emission properties of the (111)1×1:H surface of natural semiconducting (p‐type) diamond have been examined with simultaneous field emission and photoemission measurements. We find that the origin of the field emission is due to the electron tunneling from the valence band and show that the shape of the field emission energy distributions can be described by the theory of semiconductor field emission. Analysis of our results demonstrate that the combination of field emission and photoemission is a powerful technique for the study of the electron emission properties of materials.

Journal ArticleDOI
TL;DR: In this paper, the transition from reversible behavior, with a wide range of outer sphere redox couples with potentials positive of about -0.5 V vs. SCE, to extremely slow kinetics, with systems such as the halogen/halide couples, requires placing all the above properties in context.
Abstract: Boron-doped diamond electrodes have many possibilities for electroanalytical and electrosynthetic application because of their stability and range. However, their combination of semiconductive origin, nearly metallic resistive characteristics when heavily doped, and surface inertness make the understanding of electron transfer at these materials complex. The transition from reversible behavior, with a wide range of outer sphere redox couples with potentials positive of about -0.5 V vs. SCE, to extremely slow kinetics, with systems such as the halogen/halide couples, requires placing all the above properties in context. Experimental data pertaining to these issues and speculation concerning the controlling factors are discussed.

Journal ArticleDOI
TL;DR: In this article, a syngenetic multiphase inclusion assemblage was found in a natural diamond from the Finsch kimberlite pipe of South Africa, where a euhedral rhombohedron-shaped magnesite (MgCO3) crystal co-exists with several idiomorphic olivine [(Mg1.86Fe0.14)SiO4] grains (d ∼ 80 μm).