Showing papers on "Diamond published in 2002"

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

High carrier mobility in single-crystal plasma-deposited diamond.

Abstract: Room-temperature drift mobilities of 4500 square centimeters per volt second for electrons and 3800 square centimeters per volt second for holes have been measured in high-purity single-crystal diamond grown using a chemical vapor deposition process. The low-field drift mobility values were determined by using the time-of-flight technique on thick, intrinsic, freestanding diamond plates and were verified by current-voltage measurements on p-i junction diodes. The improvement of the electronic properties of single-crystal diamond and the reproducibility of those properties are encouraging for research on, and development of, high-performance diamond electronics.

DNA-modified nanocrystalline diamond thin-films as stable, biologically active substrates.

Abstract: Diamond, because of its electrical and chemical properties, may be a suitable material for integrated sensing and signal processing. But methods to control chemical or biological modifications on diamond surfaces have not been established. Here, we show that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes. We used a photochemical modification scheme to chemically modify clean, H-terminated nanocrystalline diamond surfaces grown on silicon substrates, producing a homogeneous layer of amine groups that serve as sites for DNA attachment. After linking DNA to the amine groups, hybridization reactions with fluorescently tagged complementary and non-complementary oligonucleotides showed no detectable non-specific adsorption, with extremely good selectivity between matched and mismatched sequences. Comparison of DNA-modified ultra-nanocrystalline diamond films with other commonly used surfaces for biological modification, such as gold, silicon, glass and glassy carbon, showed that diamond is unique in its ability to achieve very high stability and sensitivity while also being compatible with microelectronics processing technologies. These results suggest that diamond thin-films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.

Estimation of the isotope effect on the lattice thermal conductivity of group IV and group III-V semiconductors

Abstract: The isotope effect on the lattice thermal conductivity for group IV and group III-V semiconductors is calculated using the Debye-Callaway model modified to include both transverse and longitudinal phonon modes explicitly. The frequency and temperature dependences of the normal and umklapp phonon-scattering rates are kept the same for all compounds. The model requires as adjustable parameters only the longitudinal and transverse phonon Gr\"uneisen constants and the effective sample diameter. The model can quantitatively account for the observed isotope effect in diamond and germanium but not in silicon. The magnitude of the isotope effect is predicted for silicon carbide, boron nitride, and gallium nitride. In the case of boron nitride the predicted increase in the room-temperature thermal conductivity with isotopic enrichment is in excess of 100%. Finally, a more general method of estimating normal phonon-scattering rate coefficients for other types of solids is presented.

Thermal conductivity of multiwalled carbon nanotubes

Abstract: Thermal conductivity of multiwalled carbon nanotubes (CNT's) prepared using a microwave plasma chemical vapor deposition system is investigated using a pulsed photothermal reflectance technique. We find that the average thermal conductivity of carbon nanotube films, with the film thickness from 10 to 50 \ensuremath{\mu}m, is around 15 W/m K at room temperature and independent of the tube length. Taking a small volume filling fraction of CNT's into account, the effective nanotube thermal conductivity could be $2\ifmmode\times\else\texttimes\fi{}{10}^{2}\mathrm{W}/\mathrm{m}\mathrm{}\mathrm{K},$ which is smaller than the thermal conductivity of diamond and in-plane graphite by a factor of 9 and 7.5, respectively.

Thermogravimetric Analysis of the Oxidation of Multiwalled Carbon Nanotubes: Evidence for the Role of Defect Sites in Carbon Nanotube Chemistry

Abstract: Thermogravimetric analysis (TGA) has demonstrated that multiwalled nanotubes (MWNTs) annealed at 2200 to 2800 °C are more air stable than as-produced MWNTs, diamond, graphite, and annealed diamond. The annealed MWNTs are similar in stability to annealed graphite. Defect sites along the walls and at the ends of the raw MWNTs facilitate the thermal oxidative destruction of the nanotubes. Thermal annealing removes these defects, thereby providing MWNTs with enhanced air stability.

X-ray absorption near-edge structure calculations with the pseudopotentials: Application to the K edge in diamond and α -quartz

Abstract: We present a reciprocal-space pseudopotential scheme for calculating x-ray absorption near-edge structure (XANES) spectra. The scheme incorporates a recursive method to compute absorption cross section as a continued fraction. The continued fraction formulation of absorption is advantageous in that it permits the treatment of core-hole interaction through large supercells (hundreds of atoms). The method is compared with recently developed Bethe-Salpeter approach. The method is applied to the carbon K edge in diamond and to the silicon and oxygen K edges in $\ensuremath{\alpha}$-quartz for which polarized XANES spectra were measured. Core-hole effects are investigated by varying the size of the supercell, thus leading to information similar to that obtained from cluster size analysis usually performed within multiple scattering calculations.

Polycrystalline diamond partially depleted of catalyzing material

Abstract: The present invention provides a superhard polycrystalline diamond or diamond-like element with greatly improved resistance to thermal degradation without loss of impact strength. Collectively called PCD elements, these elements are formed with a binder-catalyzing material in a high-temperature, high-pressure process. The PCD element has a plurality of partially bonded diamond or diamond-like crystals forming at least one continuous diamond matrix, and the interstices among the diamond crystals forming at least one continuous interstitial matrix containing a catalyzing material. The element has a working surface and a body, 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. This translates to higher wear resistance in cutting applications, higher heat transfer capacity in heat sink applications, and has advantages in numerous other applications including hollow dies, indentors, tool mandrels, and wear elements.

Photochemical Functionalization of Diamond Films

Abstract: We report a new scheme for attachment of functionalized organic molecules to polycrystalline diamond films. In this scheme, ultraviolet light is used to cause a local reaction between a hydrogen-terminated diamond surface and organic molecules present as a thin overlayer liquid film. Comparison of functionalized alkenes and alkanes shows that alkenes attach more efficiently. By attaching organic molecules with suitable protecting groups and then deprotecting after attachment to the surface, it is possible to prepare diamond surfaces terminated with carboxylic acid groups or with primary amine groups. These functional groups may serve as an attractive starting point for further chemical modification of diamond surfaces.

Boron suboxide: As hard as cubic boron nitride

Abstract: The Vickers hardness of boron suboxide single crystals was measured using a diamond indentation method. Under a loading force of 0.98 N, our test gave an average Vickers hardness of 45 GPa. The average fracture toughness was measured as 4.5 MPa m1/2. We also measured the hardness of the cubic boron nitride and sapphire single crystals for comparison. The average measured hardness for boron suboxide was found to be very close to that of cubic boron nitride under the same loading force. Our results suggest that the boron suboxide could be a new superhard material for industrial applications, surpassed in hardness only by diamond and cubic boron nitride.

Very high growth rate chemical vapor deposition of single-crystal diamond

Abstract: Diamond possesses extraordinary material properties, a result that has given rise to a broad range of scientific and technological applications. This study reports the successful production of high-quality single-crystal diamond with microwave plasma chemical vapor deposition (MPCVD) techniques. The diamond single crystals have smooth, transparent surfaces and other characteristics identical to that of high-pressure, high-temperature synthetic diamond. In addition, the crystals can be produced at growth rates from 50 to 150 μm/h, which is up to 2 orders of magnitude higher than standard processes for making polycrystalline MPCVD diamond. This high-quality single-crystal MPCVD diamond may find numerous applications in electronic devices as high-strength windows and in a new generation of high-pressure instruments requiring large single-crystal anvils.

Superhard B–C–N materials synthesized in nanostructured bulks

Abstract: We report here the high-pressure synthesis of well-sintered millimeter-sized bulks of superhard BC2N and BC4N materials in the form of a nanocrystalline composite with diamond-like amorphous carbon grain boundaries. The nanostructured superhard B–C–N material bulks were synthesized under high P–T conditions from amorphous phases of the ball-milled molar mixtures. The synthetic B–C–N samples were characterized by synchrotron x-ray diffraction, high-resolution transmission electron microscope, electron energy-loss spectra, and indentation hardness measurements. These new high-pressure phases of B–C–N compound have extreme hardnesses, second only to diamond. Comparative studies of the high P–T synthetic products of BC2N, BC4N, and segregated phases of diamond + cBN composite confirm the existence of the single B–C–N ternary phases.

Nanomechanical Resonant Structures in Nanocrystalline Diamond

Abstract: We report the fabrication and the operation of nanomechanical resonant structures in nanocrystalline diamond. For this purpose, continuous diamond films as thin as 80 nm were grown using microwave plasma enhanced chemical vapor deposition. The lateral dimensions of the fabricated structures were as small as 50 nm and the measured mechanical resonant frequencies were up to 640 MHz. The mechanical quality factors were in the range of 2500–3000 at room temperature. The elastic properties of these films obtained via the resonant measurements indicate a Young’s modulus close to that of single-crystal diamond.

Single spin states in a defect center resolved by optical spectroscopy

Abstract: Individual paramagnetic defect centers in diamond nanocrystals have been investigated by low-temperature high-resolution optical spectroscopy. Narrow fluorescence excitation spectral lines have been found, indicating transitions between individual spin sublevels. Spectral diffusion is explained by cross relaxation among spin sublevels and by the presence of excited electrons in the conduction band of diamond. The relaxation times are in the millisecond range. The system may be useful for quantum information processing with individual electron spins.

Molecular-scale tribology of amorphous carbon coatings: effects of film thickness, adhesion, and long-range interactions.

Abstract: Classical molecular dynamics simulations have been conducted to investigate the atomic-scale friction and wear when hydrogen-terminated diamond (111) counterfaces are in sliding contact with diamond (111) surfaces coated with amorphous, hydrogen-free carbon films Two films, with approximately the same ratio of sp(3)-to-sp(2) carbon, but different thicknesses, have been examined Both systems give a similar average friction in the load range examined Above a critical load, a series of tribochemical reactions occur resulting in a significant restructuring of the film This restructuring is analogous to the "run-in" observed in macroscopic friction experiments and reduces the friction The contribution of adhesion between the probe (counterface) and the sample to friction was examined by varying the saturation of the counterface Decreasing the degree of counterface saturation, by reducing the hydrogen termination, increases the friction Finally, the contribution of long-range interactions to friction was examined by using two potential energy functions that differ only in their long-range forces to examine friction in the same system

Morphology and electronic structure in nitrogen-doped ultrananocrystalline diamond

Abstract: Ultrananocrystalline diamond (UNCD) thin films consist of 2–5 nm grains of pure sp3-bonded carbon and ∼0.5-nm-wide grain boundaries with a disordered mixture of sp2- and sp3-bonded carbon. UNCD exhibits many interesting materials properties that are a direct consequence of its nanoscale morphology. In this work, we report the changes in morphology induced in UNCD by the addition of nitrogen gas to the Ar/CH4 microwave plasma, as studied using high-resolution transmission electron microscopy and nanoprobe-based electron energy-loss spectroscopy. Both the grain size and grain-boundary widths increase with the addition of N2, but the overall bonding structure in both regions remains mostly unchanged. These results are used to explain the variation of materials properties of nitrogen-incorporated UNCD films.

The mechanism of diamond nucleation from energetic species.

Abstract: A model for diamond nucleation by energetic species (for example, bias-enhanced nucleation) is proposed. It involves spontaneous bulk nucleation of a diamond embryo cluster in a dense, amorphous carbon hydrogenated matrix; stabilization of the cluster by favorable boundary conditions of nucleation sites and hydrogen termination; and ion bombardment-induced growth through a preferential displacement mechanism. The model is substantiated by density functional tight-binding molecular dynamics simulations and an experimental study of the structure of bias-enhanced and ion beam-nucleated films. The model is also applicable to the nucleation of other materials by energetic species, such as cubic boron nitride.

Electrochemistry of Diamond: A Review

Abstract: Because of its extraordinary chemical stability, diamond is a perspective electrode material to be used in electrochemistry and electrochemical engineering. In this review-article, the results of basic studies in the synthetic-diamond electrochemistry are summarized: the electrochemical kinetics, photoelectrochemistry, electrochemical impedance spectroscopy. Relations between the semiconductor nature and crystal structure of diamond and its electrochemical behavior are revealed. Prospects for using diamond electrodes in the electroanalysis, electrosynthesis, and environmentally-oriented industry are outlined.

Nanorobotic Manipulation of Microspheres for On‐Chip Diamond Architectures

Abstract: Diamond-like structures with micrometer-size periodicity have been fabricated by means of nanorobotic manipulation of microspheres (see cover). The technique enables the preparation of macroporous lattices, and opens the way to controllable formation of a wide variety of microstructures and thus provides a new route to the study of novel lattices with photonic properties. The Figure shows a "diamond" lattice made of 0.9 μm silica spheres.

Femtosecond ablation of ultrahard materials

Abstract: Several ultrahard materials and coatings of definite interest for tribological applications were tested with respect to their response when irradiated with fs laser pulses. Results on cemented tungsten carbide and on titanium carbonitride are reported for the first time and compared with outcomes of investigations on diamond and titanium nitride. The experiments were carried out in air, in a regime of 5–8 J/cm2 fluences, using the beam of a commercial Ti:sapphire laser. The changes induced in the surface morphology were analysed with a Nomarski optical microscope, and with SEM and AFM techniques. From the experimental data and from the calculated incident energy density distributions, the damage and ablation threshold values were determined. As expected, the diamond showed the highest threshold, while the cemented tungsten carbide exhibited typical values for metallic surfaces. The ablation rates determined (under the above-mentioned experimental conditions) were in the range 0.1–0.2 μm per pulse for all the materials investigated.

Photonic properties of bicontinuous cubic microphases

Abstract: Band structures of three dimensionally periodic bi- and tricontinuous cubic structures have been calculated using the plane-wave method for solving Maxwell's equations. In particular, we consider the single primitive, single diamond, single gyroid, double primitive, double gyroid, and double diamond level surface families as examples of such structures found in self-organizing systems. We also provide design guidelines for creating three-dimensional photonic crystals with a complete photonic band gap from block copolymer systems and other self-organizing systems.

Morphological investigation of the microstructure, dimensions, and fractal geometry of diesel particulates

Abstract: Strong support from Dr. Sidney Diamond at the US DOE-OHVT is greatly appreciated. The authors also thank Dr. Russell Cook of Argonne’s Electron Microscopy Center for his valuable advice on microscopy.

Nanostructured ceramics for biomedical implants.

Abstract: Recent progress in the synthesis, characterization, and biological compatibility of nanostructured ceramics for biomedical implants is reviewed. A major goal is to develop ceramic coating technology that can reduce the friction and wear in mating total joint replacement components, thus contributing to their significantly improved function and longer life span. Particular attention is focused on the enhancement of mechanical properties such as hardness, toughness, and friction coefficient and on the bioactivity as they pertain to the nanostructure of the material. The development of three nanostructured implant coatings is discussed: diamond, hydroxyapatite, and functionally graded metalloceramics based on the Cr-Ti-N ternary system. Nanostructured diamond produced by chemical vapor deposition (CVD) techniques and composed of nano-size diamond grains have particular promise because of the combination of ultrahigh hardness, improved toughness over conventional microcrystalline diamond, low friction, and good adhesion to titanium alloys. Nanostructured processing applied to hydroxyapatite coatings is used to achieve the desired mechanical characteristics and enhanced surface reactivity and has been found to increase osteoblast adhesion, proliferation, and mineralization. Finally, nanostructured metalloceramic coatings provide continuous variation from a nanocrystalline metallic bond at the interface to the hard ceramic bond on the surface and have the ability to overcome adhesion problems associated with ceramic hard coatings on metallic substrates.

Electrochemical oxidation of chlorophenols at a boron-doped diamond electrode and their determination by high-performance liquid chromatography with amperometric detection.

Abstract: Anodically pretreated diamond electrodes have been used for the detection of chlorophenols (CPs) in environmental water samples after high-performance liquid chromatographic (HPLC) separation. The anodization of as-deposited boron-doped polycrystalline diamond thin-film electrodes has enabled the stable determination of phenols over a wide concentration range. Prior to the HPLC analysis, a comparative study with ordinary glassy carbon, as-deposited diamond, and anodized diamond was made to examine the oxidative behavior of phenols by cyclic voltammety and flow injection analysis with amperometric detection. At anodized diamond electrodes, reproducible, well-defined cyclic voltammograms were obtained even at high CP concentration (5 mM), due to a low proclivity for adsorption of the oxidation products on the surface. In addition, after prolonged use, the partially deactivated diamond could be reactivated on line by applying a highly anodic potential (2.64 V vs SCE) for 4 min, which enabled the destruction ...