Showing papers on "Diamond published in 2001"

Synthesis and Design of Superhard Materials

Abstract: ▪ Abstract The synthesis of the two currently used superhard materials, diamond and cubic boron nitride, is briefly described with indications of the factors influencing the quality of the crystals obtained. The physics of hardness is discussed and the importance of covalent bonding and fixed atomic positions in the crystal structure, which determine high hardness values, is outlined. The materials investigated to date are described and new potentially superhard materials are presented. No material that is thermodynamically stable under ambient conditions and composed of light (small) atoms will have a hardness greater than that of diamond. Materials with hardness values similar to that of cubic boron nitride (cBN) can be obtained. However, increasing the capabilities of the high-pressure devices could lead to the production of better quality cBN compacts without binders.

Optical properties of diamond

Abstract: 1 Refraction.- 2 Reflection and Transmission.- 3 Vibronic Absorption.- 4 Scattering.- 5 Optical Electronic Transitions.- 6 Coloration of Diamond.- 7 Physical Classification of Diamond.- 8 Interaction with Energetic Light Beams.- 9 Thermostimulated Luminescence and Tunnel Luminescence.- 10 Photoconductivity.- 11 Related Data.- Appendix: Abbreviations, Definitions and Methods.- References.

Ultraviolet Emission From a Diamond Pn Junction

Abstract: We report the realization of an ultraviolet light–emitting diode with the use of a diamond pn junction. The pn junction was formed from a boron-doped p-type diamond layer and phosphorus-doped n-type diamond layer grown epitaxially on the {111} surface of single crystalline diamond. The pn junction exhibited good diode characteristics, and at forward bias of about 20 volts strong ultraviolet light emission at 235 nanometers was observed and was attributed to free exciton recombination.

The role of hydrogen in tribological properties of diamond-like carbon films☆

Abstract: Extensive research on diamond and diamondlike carbon (DLC) films in our laboratory has further confirmed that hydrogen plays an important role in the tribological properties of these films. Specifically, model experiments in inert gas environments revealed a very close relationship between the hydrogen-to-carbon (H/C) ratios of source gases and the friction and wear coefficients of the resultant DLC films. The friction coefficient of films grown in source gases with very high H/C ratios (e.g. 10) was superlow (0.003), whereas that of hydrogen-free DLC films (with essentially zero H/C ratio) was very high (0.65). The friction coefficients of films grown in source gases with intermediate H/C ratios were between 0.003 and 0.65. Experiments also revealed that the frictional properties of these films were very sensitive to test environments. Specifically, when tested in open air, the friction coefficient of hydrogen-free DLC dropped to 0.25, whereas that of highly-hydrogenated DLC increased to 0.06. Fundamental knowledge combined with surface analytical and tribological studies have led to the conclusion that the type and extent of chemical interactions between carbon–carbon, carbon–hydrogen, and carbon–adsorbate atoms at the sliding-contact interfaces determine the friction and wear properties of DLC films.

Synthesis of superhard cubic BC2N

Abstract: Cubic BC2N was synthesized from graphite-like BC2N at pressures above 18 GPa and temperatures higher than 2200 K. The lattice parameter of c-BC2N at ambient conditions is 3.642(2) A, which is larger by 1.48% than would be expected based on ideal mixing between diamond and cubic boron nitride. The bulk modulus of c-BC2N is 282 GPa which is one of the highest bulk moduli known for any solid, and is exceeded only by the bulk moduli of diamond and c-BN. The hardness of c-BC2N is higher than that of c-BN single crystals which indicates that the synthesized phase is only slightly less hard than diamond.

Synthesis and characterization of highly-conducting nitrogen-doped ultrananocrystalline diamond films

Abstract: Ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma-enhanced chemical-vapor-deposition method using a CH4(1%)/Ar gas mixture and 1%–20% nitrogen gas added. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω−1 cm−1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films.

Nonclassical radiation from diamond nanocrystals

Abstract: The quantum properties of the fluorescence light emitted by diamond nanocrystals containing a single nitrogen-vacancy (NV) colored center are investigated. We have observed photon antibunching with very low background light. This system is therefore a very good candidate for the production of single photon on demand. In addition, we have measured a larger NV center lifetime in nanocrystals than in the bulk, in good agreement with a simple quantum electrodynamical model.

High volume density polycrystalline diamond with working surfaces depleted of catalyzing material

Abstract: Disclosed is a polycrystalline diamond or diamond-like element with greatly improved wear resistance without loss of impact strength. These elements are formed with a binder-catalyzing material in a high-temperature, high-pressure (HTHP) process. The PCD element has a body with a plurality of bonded diamond or diamond-like crystals forming a continuous diamond matrix that has a diamond volume density greater than 85%. Interstices among the diamond crystals form a continuous interstitial matrix containing a catalyzing material. The diamond matrix table is formed and integrally bonded with a metallic substrate containing the catalyzing material during the HTHP process. The diamond matrix body has a working surface, where a portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material. Typically, less than about 70% of the body of the diamond matrix table is free of the catalyzing material.

Materials Science - The hardest known oxide

Abstract: A material as hard as diamond or cubic boron nitride has yet to be identified1,2,3,4,5,6, but here we report the discovery of a cotunnite-structured titanium oxide which represents the hardest oxide known. This is a new polymorph of titanium dioxide, where titanium is nine-coordinated to oxygen in the cotunnite (PbCl2) structure. The phase is synthesized at pressures above 60 gigapascals (GPa) and temperatures above 1,000 K and is one of the least compressible and hardest polycrystalline materials to be described.

Tight-binding molecular-dynamics simulation of impurities in ultrananocrystalline diamond grain boundaries

Abstract: Ultrananocrystalline diamond (UNCD) films grown from hydrogen-poor plasmas have grain sizes of 3-10 nm, resulting in a large number of grain boundaries. We repon on density-functional-based tight-binding molecular-dynamics calculations of high-energy high-angle twist (100) grain boundaries in diamond as a model for the UNCD grain boundaries. About one-half of the carbons in the grain boundary are threefold coordinated and are responsible for states introduced into the band gap. Simulations were also performed for N, Si, and H impurities in (100) twist grain boundaries where substitution energies, optimized geometries, and electronic structures were calculated. Substitution energies were found to be substantially lower for the grain boundaries compared to the bulk diamond crystal. Nitrogen increases the number of threefold-coordinated carbons while hydrogen saturates dangling bonds. The electronic structure of UNCD is characterized by a large number of states in the band gap attributed to the bonding disorder and impurities in the grain boundaries.

DNA‐Directed Assembly of Gold Nanowires on Complementary Surfaces

Abstract: branes. The tubes are well ordered but somewhat tilted due to their relatively low mechanical strength compared with cylinders. The Raman spectra of the tubes have shown two broad peaks centered on 1345 and 1565 cm ‐1 , indicating that the tubes consist mainly of DLC. All the nanotubes have a uniform outer diameter of about 300 nm. The wall thickness of the tubes is very small, which can be controlled by optimizing the growth conditions. The tube length was about 7 lm, as in the case of cylinders. All the tubes have uniform height and are found to be hollow inside. Such nanotube arrays are probably useful for field emitters as well as for depositing metal catalysts or enzymes in the tubes, which in turn may be useful for new technologies. Other applications presumably include their use as porous electrodes in electrochemistry, as conductive diamond is known to exhibit outstanding electrochemical properties such as low background current, wide electrochemical potential window and high resistance to deactivation. [19] The present technique is a simple one for producing highly ordered diamond nanocylinders and nanotubes in high yield. The dimensions of these nanofibers are easily controllable by varying the pore dimensions of the alumina membrane. This technique enables others to adopt it easily and study the physical properties of these arrays for various applications in fieldemission displays, photonic bandgap materials, composite materials, and electrochemistry.

Laser heated diamond cell system at the Advanced Photon Source for in situ x-ray measurements at high pressure and temperature

Abstract: We describe a laser heated diamond anvil cell system at the GeoSoilEnviroCARS sector at the Advanced Photon Source. The system can be used for in situ x-ray measurements at simultaneously ultrahigh pressures (to >150 GPa) and ultrahigh temperatures (to >4000 K). Design goals of the laser heating system include generation of a large heating volume compared to the x-ray beam size, minimization of the sample temperature gradients both radially and axially in the diamond anvil cell, and maximization of heating stability. The system is based on double-sided laser heating technique and consists of two Nd:YLF lasers with one operating in TEM00 mode and the other in TEM01* mode, optics to heat the sample from both sides, and two spectroradiometric systems for temperature measurements on both sides. When combined with an x-ray microbeam (3–10 μm) technique, a temperature variation of less than 50 K can be achieved within an x-ray sampled region for longer than 10 min. The system has been used to obtain in situ str...

Polycrystalline diamond cutters with working surfaces having varied wear resistance while maintaining impact strength

Abstract: Disclosed is a polycrystalline diamond or diamond-like element with greatly improved wear resistance without loss of impact strength. These elements are formed with a binder-catalyzing material in a high-temperature, high-pressure (HTHP) process. The PCD element has a body with a plurality of bonded diamond or diamond-like crystals forming a continuous diamond matrix that has a diamond volume density greater than 85%. Interstices among the diamond crystals form a continuous interstitial matrix containing a catalyzing material. The diamond matrix table is formed and integrally bonded with a metallic substrate containing the catalyzing material during the HTHP process. The diamond matrix body has a working surface, where a first portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and a second portion of the interstitial matrix in the body adjacent to the working surface contains the catalyzing material. The first portion of the interstitial matrix and the second portion of the interstitial matrix have substantially the same impact strength.

Conversion of silicon carbide to crystalline diamond-structured carbon at ambient pressure

Abstract: Synthetic diamond is formed commercially using high-pressure1, chemical-vapour-deposition2 and shock-wave3 processes, but these approaches have serious limitations owing to low production volumes and high costs. Recently suggested alternative methods of diamond growth include plasma activation4, high pressures5, exotic precursors6,7 or explosive mixtures8, but they suffer from very low yield and are intrinsically limited to small volumes or thin films. Here we report the synthesis of nano- and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 °C. The presence of hydrogen in the gas mixture leads to a stable conversion of silicon carbide to diamond-structured carbon with an average crystallite size ranging from 5 to 10 nanometres. The linear reaction kinetics allows transformation to any depth, so that the whole silicon carbide sample can be converted to carbon. Nanocrystalline coatings of diamond-structured carbon produced by this route show promising mechanical properties, with hardness values in excess of 50 GPa and Young's moduli up to 800 GPa. Our approach should be applicable to large-scale production of crystalline diamond-structured carbon.

Electron field emission for ultrananocrystalline diamond films

Abstract: Ultrananocrystalline diamond (UNCD) films 0.1–2.4 μm thick were conformally deposited on sharp single Si microtip emitters, using microwave CH4–Ar plasma-enhanced chemical vapor deposition in combination with a dielectrophoretic seeding process. Field-emission studies exhibited stable, extremely high (60–100 μA/tip) emission current, with little variation in threshold fields as a function of film thickness or Si tip radius. The electron emission properties of high aspect ratio Si microtips, coated with diamond using the hot filament chemical vapor deposition (HFCVD) process were found to be very different from those of the UNCD-coated tips. For the HFCVD process, there is a strong dependence of the emission threshold on both the diamond coating thickness and Si tip radius. Quantum photoyield measurements of the UNCD films revealed that these films have an enhanced density of states within the bulk diamond band gap that is correlated with a reduction in the threshold field for electron emission. In additio...

Diamond coatings on reactor wall and method of manufacturing thereof

Abstract: A corrosion resistant component of semiconductor processing equipment such as a plasma chamber includes a diamond containing surface and process for manufacture thereof.

Microstructure of ultrananocrystalline diamond films grown by microwave Ar–CH4 plasma chemical vapor deposition with or without added H2

Abstract: Ultrananocrystalline diamond (UNCD) films, grown using microwave plasma-enhanced chemical vapor deposition with gas mixtures of Ar–1%CH4 or Ar–1%CH4–5%H2, have been examined with transmission electron microscopy (TEM). The films consist of equiaxed nanograins (2–10 nm in diameter) and elongated twinned dendritic grains. The area occupied by dendritic grains increases with the addition of H2. High resolution electron microscopy shows no evidence of an amorphous phase at grain boundaries, which are typically one or two atomic layer thick (0.2–0.4 nm). Cross-section TEM reveals a noncolumnar structure of the films. The initial nucleation of diamond occurs directly on the Si substrate when H2 is present in the plasma. For the case of UNCD growth from a plasma without addition of H2, the initial nucleation occurs on an amorphous carbon layer about 10–15 nm thick directly grown on the Si substrate. This result indicates that hydrogen plays a critical role in determining the nucleation interface between the UNCD...

Diamond colour centres as a nanoscopic light source for scanning near-field optical microscopy.

Abstract: Recently it was shown that a single molecule at cryogenic temperatures could be used as a local light source for illumination of a sample in the near field. Conventional light-emitting systems such as dye molecules and semiconductor quantum dots could also be used for this purpose, but they suffer from lack of photostability. However, colour centres in diamond have been found to be remarkably stable against bleaching and blinking effects. Here we present the first SNOM images taken with nanoscopic diamond crystals as a light source.

Analysis on high-speed face-milling of 7075-T6 aluminum using carbide and diamond cutters

Abstract: This research is concerned with the analytical and experimental study on the high-speed face milling of 7075-T6 aluminum alloys with a single insert fly-cutter. The results are analyzed in terms of cutting forces, chip morphology, and surface integrity of the workpiece machined with carbide and diamond inserts. It is shown that a high cutting speed leads to a high chip flow angle, very low thrust forces and a high shear angle, while producing a thinner chip. Chip morphology studies indicate that shear localization can occur at higher feeds even for 7075-T6, which is known to produce continuous chips. The resultant compressive residual stresses are shown for the variation of cutting parameters and cutting tool material. The analysis of the high-speed cutting process mechanics is presented, based on the calculation results using extended oblique machining theory and finite element simulation.

Codoping method for the fabrication of low-resistivity wide band-gap semiconductors in p-type GaN, p-type AlN and n-type diamond: prediction versus experiment

Abstract: We review our new valence control method of a co-doping for the fabrication of low-resistivity p-type GaN, p-type AlN and n-type diamond. The co-doping method is proposed based upon ab initio electronic structure calculation in order to solve the uni-polarity and the compensation problems in the wide band-gap semiconductors. In the co-doping method, we dope both the acceptors and donors at the same time by forming the meta-stable acceptor-donor-acceptor complexes for the p-type or donor-acceptor-donor complexes for the n-type under thermal non-equilibrium crystal growth conditions. We propose the following co-doping method to fabricate the low-resistivity wide band-gap semiconductors; p-type GaN: [Si + 2 Mg (or Be)], [H + 2 Mg (or Be)], [O + 2 Mg (or Be)], p-type AlN: [O + 2 C] and n-type diamond: [B + 2 N], [H + S], [H + 2 P]. We compare our prediction of the co-doping method with the recent successful experiments to fabricate the low-resistivity p-type GaN, p-type AlN and n-type diamond. We show that the co-doping method is the efficient and universal doping method by which to avoid carrier compensation with an increase of the solubility of the dopant, to increase the activation rate by decreasing the ionization energy of acceptors and donors, and to increase the mobility of the carrier.

Electrolyte-Solution-Gate FETs Using Diamond Surface for Biocompatible Ion Sensors

Abstract: Diamond field effect transistors have operated in electrolyte solution for the first time Since the hydrogen-terminated diamond surfaces are stable enough for the use as an electrochemical electrode, the diamond surface channels are exposed to the electrolyte in the transistor structure A perfect pinch-off and saturated current-voltage characteristics have been obtained for bias voltages within the potential window The threshold voltages are almost constant in electrolytes with different pH values of 7-13, indicating pH insensitiveness of the hydrogen-terminated diamond surface Based on this pH insensitive surface, ion selective regions can be fabricated to form transistor-based biosensors