Showing papers on "Diamond published in 2005"

Bright Fluorescent Nanodiamonds: No Photobleaching and Low Cytotoxicity

Abstract: Diamond nanocrystals emit bright fluorescence at 600−800 nm after irradiation by a 3 MeV proton beam (5 × 1015 ions/cm2) and annealing at 800 °C (2 h) in vacuum. The irradiation/annealing process yields high concentrations of nitrogen-vacancy defect centers (∼107 centers/μm3), making possible visualization of the individual 100 nm diamond crystallites using a fluorescence microscope. The fluorescent nanodiamonds (FND) show no sign of photobleaching and can be taken up by mammalian cells with minimal cytotoxicity. The nanomaterial can have far-reaching biological applications.

Characterization methods of carbon nanotubes : a review.

Abstract: Carbon nanotubes due to their specific atomic structure have interesting chemical and physical properties according to those of graphite and diamond. This review covers the characterization methods of carbon nanotubes which are most employed today. The structure of carbon nanotubes is first briefly summarized followed by a description of the characterization methods such as STM, TEM, neutron diffraction, X-ray diffraction, X-ray photoelectron spectroscopy, infrared and Raman spectroscopy. The most interesting features are indexed for each technique.

Calculations of electron inelastic mean free paths

Abstract: We report calculations of electron inelastic mean free paths (IMFPs) for 50–2000 eV electrons in 14 elemental solids (Li, Be, diamond, graphite, Na, K, Sc, Ge, In, Sn, Cs, Gd, Tb, and Dy) and for one solid (Al) using better optical data than in our previous work. The new IMFPs have also been used to test our TPP-2M equation for estimating IMFPs in these materials. We found surprisingly large root-mean-square (RMS) deviations (39.3–71.8%) between IMFPs calculated from TPP-2M and those calculated here from optical data for diamond, graphite and cesium; previously we had found an average RMS deviation of 10.2% for a group of 27 elemental solids. An analysis showed that the large deviations occurred for relatively small computed values of the parameter β in the TPP-2M equation (β ∼ 0.01 for diamond and graphite) and also for relatively large values of β (β ∼ 0.25 for Cs). Although such extreme values of β are unlikely to be encountered for many other materials, the present results indicate an additional limitation in the reliability of the TPP-2M equation. We also show that the parameter Nv in the TPP-2M equation should be computed for the rare-earth elements from the number of valence electrons and the six 5p electrons. Copyright © 2004 John Wiley & Sons, Ltd.

Collapse : how societies choose to fail or survive

Abstract: Jared Diamond investigates the fate of past human societies, and the lessons for our own future.

Designing Superhard Materials

Abstract: In their Perspective, [ Kaner et al. ][1] describe recent efforts to make a material that matches or exceeds the hardness of diamond. Such a material must contain highly directional, short, and strong bonds. Hardness may also be increased by introducing a nanometer-scale structure that hinders the migration of dislocations. Despite all the scientific efforts to find a material that surpasses it, diamond remains the hardest known material. And hardness is not enough: To replace diamond in practical applications, a new superhard material must also match its other properties, such as chemical inertness. [1]: http://www.sciencemag.org/cgi/content/full/308/5726/1268

Osmium diboride, an ultra-incompressible, hard material.

Abstract: The need for wear- and scratch-resistant materials drives the quest for new superhard materials. In this work, we apply two design parameters to identify ultra-incompressible, superhard materials-high valence electron density and high bond covalency. Our first example of such a material is OsB2. The bulk modulus of OsB2 was measured using in situ high-pressure X-ray diffraction and was determined to be in the range of 365-395 GPa. While this value is slightly less than that of the bulk modulus of diamond, due to the anisotropic crystal structure of OsB2, the axis compressibility in the orthorhombic c-direction is less than the axis compressibility found in diamond. OsB2 also scratches the surface of a sapphire window, indicating that the hardness of OsB2 exceeds 2000 kg/mm2.

Stable Isotopes and the Origin of Diamond

Abstract: Most diamonds form in a relatively narrow depth interval of Earth's subcontinental mantle between 150 and 250 km From carbon isotope analyses of diamond obtained in the 1970s, it was first proposed that eclogitic diamonds form from crustal carbon recycled into the mantle by subduction and that the more abundant peridotitic diamonds formed from mantle carbon More recent stable isotope studies using nitrogen, oxygen, and sulfur, as well as carbon, combined with studies of mineral inclusions within diamonds, have strengthened arguments supporting and opposing the early proposal The conflicting evidence is reconciled if mantle carbon is introduced via fluid into mantle eclogites and peridotites, some of which represent subducted oceanic crust

Self-assembly of patchy particles into diamond structures through molecular mimicry.

Abstract: Fabrication of diamond structures by self-assembly is a fundamental challenge in making three-dimensional photonic crystals. We simulate a system of model hard particles with attractive patches and show that they can self-assemble into a diamond structure from an initially disordered state. We quantify the extent to which the formation of the diamond structure can be facilitated by “seeding” the system with small diamond crystallites or by introducing a rotation interaction to mimic a carbon−carbon antibonding interaction. Our results suggest patchy particles may serve as colloidal “atoms” and “molecules” for the bottom-up self-assembly of three-dimensional crystals.

Generation of single colour centers by focussed nitrogen implantation

Abstract: Single defect centers in diamond have been generated via nitrogen implantation. The defects have been investigated by single defect center fluorescence microscopy. Optical and EPR spectra unambiguously show that the produced defect is the nitrogen-vacancy colour center. An analysis of the nitrogen flux together with a determination of the number of nitrogen-vacancy centers yields that on average two 2 MeV nitrogen atoms need to be implanted per defect center.

Experimental observation of the 1/3 magnetization plateau in the diamond-chain compound Cu3(CO3)2(OH)2.

Abstract: The magnetic susceptibility, high field magnetization, and specific heat measurements of Cu3(CO3)2(OH)2, which is a model substance for the frustrating diamond spin chain model, have been performed using single crystals. Two broad peaks are observed at around 20 and 5 K in both magnetic susceptibility and specific heat results. The magnetization curve has a clear plateau at one third of the saturation magnetization. The experimental results are examined in terms of theoretical expectations based on exact diagonalization and density matrix renormalization group methods. An origin of magnetic anisotropy is also discussed.

Origin of the metallic properties of heavily boron-doped superconducting diamond

Abstract: The recent discovery that heavily boron-doped diamond is a superconductor with a transition temperature of 7.4 K raises the prospect of superconducting devices with the unique properties of diamond. A study of the electronic structure responsible for superconductivity in heavily boron-doped diamond supports the idea that superconductivity is phonon-mediated, and provides information on the electronic structure that must be retained in order to harness this effect in practical devices. The physical properties of lightly doped semiconductors are well described by electronic band-structure calculations and impurity energy levels1. Such properties form the basis of present-day semiconductor technology. If the doping concentration n exceeds a critical value nc, the system passes through an insulator-to-metal transition and exhibits metallic behaviour; this is widely accepted to occur as a consequence of the impurity levels merging to form energy bands2. However, the electronic structure of semiconductors doped beyond nc have not been explored in detail. Therefore, the recent observation of superconductivity emerging near the insulator-to-metal transition3 in heavily boron-doped diamond4,5 has stimulated a discussion on the fundamental origin of the metallic states responsible for the superconductivity. Two approaches have been adopted for describing this metallic state: the introduction of charge carriers into either the impurity bands6 or the intrinsic diamond bands7,8,9. Here we show experimentally that the doping-dependent occupied electronic structures are consistent with the diamond bands, indicating that holes in the diamond bands play an essential part in determining the metallic nature of the heavily boron-doped diamond superconductor. This supports the diamond band approach and related predictions, including the possibility of achieving dopant-induced superconductivity in silicon and germanium7. It should also provide a foundation for the possible development of diamond-based devices10.

Self-assembly of patchy particles into diamond structures through molecular mimicry

Abstract: Fabrication of diamond structures by self-assembly is a fundamental challenge in making three-dimensional photonic crystals. We simulate a system of model hard particles with attractive patches and show that they can self-assemble into a diamond structure from an initially disordered state. We quantify the extent to which the formation of the diamond structure can be facilitated by "seeding" the system with small diamond crystallites or by introducing a rotation interaction to mimic a carbon-carbon antibonding interaction. Our results suggest patchy particles may serve as colloidal "atoms" and "molecules" for the bottom-up self-assembly of three-dimensional crystals.

Pyramidal lattice truss structures with hollow trusses

Abstract: A method for fabricating pyramidal lattice structures with hollow metallic trusses has been explored. A periodic diamond hole pattern sheet consisting of 304L stainless steel hollow tubes was made by an alternating collinear lay-up process followed by vacuum brazing. The array was then folded at the nodes to create a periodic pyramidal cellular metal lattice and was then bonded to face sheets by a second vacuum brazing process. The out-of-plane compression properties of this hollow truss lattice structure have been investigated and compared to a similar lattice made with the solid trusses. In both cases, the peak strength is found to be governed by inelastic truss buckling. The compressive strength of a hollow lattice with a relative density of 2.8% was approximately twice that of a solid pyramidal lattice of similar relative density. The increased strength resulted from an increase in the buckling resistance of hollow trusses because of their higher radius of gyration.

Ion-Beam-Assisted Lift-Off Technique for Three-Dimensional Micromachining of Freestanding Single-Crystal Diamond

Abstract: Diamond is a very attractive material for micromachining: it has high mechanical hardness, high Young’s modulus, a low coefficient of friction, high thermal conductivity, and a low thermal expansion coefficient. It is chemically inert and biocompatible. Optically, it is transparent over the widest range of the electromagnetic spectrum (from 220 nm to the far infrared), has a high refractive index, and exhibits a vast inventory of luminescent centers (> 500 electronic, > 150 vibrational), many of which are related to impurities or defects in the crystalline structure. [1] Some of these can therefore be controlled and engineered. Of particular interest is the nitrogen vacancy (NV – ) center that possesses very promising quantum properties. [2]

Charge-carrier properties in synthetic single-crystal diamond measured with the transient-current technique

Abstract: For optimal operation of chemical-vapor deposition (CVD) diamonds as charged particle detectors it is important to have a detailed understanding of the charge-carrier transport mechanism. This includes the determination of electron and hole drift velocities as a function of electric field, charge carrier lifetimes, as well as effective concentration of space charge in the detector bulk. We use the transient-current technique, which allows a direct determination of these parameters in a single measurement, to investigate the charge-carrier properties in a sample of single-crystal CVD diamond. The method is based on the injection of charge using an α source close to the surface and measuring the induced current in the detector electrodes as a function of time.

Carbon phase diagram from ab initio molecular dynamics.

Abstract: We compute the free energy of solid and liquid diamond from first-principles electronic structure theory using efficient thermodynamic integration techniques. Our calculated melting curve is in excellent agreement with the experimental estimate of the graphite-diamond-liquid triple point and is consistent with shock wave experiments. We predict the phase diagram of diamond at pressures and temperatures that are difficult to access experimentally. We confirm early speculations on the presence of a reentrant point in the diamond melting line but find no evidence for a first order liquid-liquid phase transition near the reentrant point.

Thermodynamics of metastable phase nucleation at the nanoscale

Abstract: Chemical and physical routes under conditions of moderate not extreme temperatures and pressures are generally used to synthesize nanocrystals and nanostructures with metastable phases. However, the corresponding bulk materials with the same metastable structures are prepared under conditions of high temperatures or high pressures. The size effect of nanocrystals and nanostructures may be responsible for the formation of these metastable phases at the nanometer size. To date, there has not been a clear and detailed understanding of the effects causing the formation of the metastable structures from the viewpoint of thermodynamics. There is no a clear insight into which chemical and physical origins leading to the tendency of the metastable phases emerging at the nanoscale. We have proposed universal thermodynamic approach on nanoscale to elucidate the formation of the metastable phases taking place in the microphase growth. In this review, we first introduce the fundamental concepts and methods of the thermodynamic approach on nanoscale (so-called nanothermodynamics). Note that our nanothermodynamics, by taking into account the size-dependence of the surface tension of nanocrystals, differs from the thermodynamics of small systems proposed by Hill [T.L. Hill, J. Chem. Phys. 36 (1962) 3182; T.L. Hill, Proc. Natl. Acad. Sci. U.S.A. 93 (1996) 14328; T.L. Hill, R.V. Chamberlin, Proc. Natl. Acad. Sci. U.S.A. 95 (1998) 12779; T.L. Hill, J. Chem. Phys. 34 (1961) 1974; T.L. Hill, J. Chem. Phys. 35 (1961) 303; T.L. Hill, Nano Lett. 1 (2001) 273; T.L. Hill, R.V. Chamberlin, Nano Lett. 2 (2002) 609; T.L. Hill, Nano Lett. 1 (2001) 159]. Our thermodynamic theory emphasizes the size effect of the surface tension of nanocrystals on the stable and metastable equilibrium states during the microphase growth. Then, taking the syntheses of diamond and cubic boron nitride (c-BN) nanocrystals as examples, we summarize the applications of the nanothermodynamics to elucidate the nucleation of diamond and related materials nanocrystals in various moderate environments. Firstly, we studied diamond nucleation upon chemical vapor deposition (CVD), and found out that the capillary effect of the nanosized curvature of diamond critical nuclei could drive the metastable phase region of the nucleation of CVD diamond into a new stable phase region in the carbon thermodynamic equilibrium diagram. Consequently, the diamond nucleation is preferable to the graphite phase formation in the competing growth of diamond and graphite upon CVD. Similarly, c-BN nucleation upon CVD has been investigated. Secondly, we investigated the c-BN nucleation taking place in the high-pressure and high-temperature supercritical-fluids systems under conditions of the low-threshold-pressures (<3.0 GPa) and low-temperatures (<1500 K), and predicted the threshold pressure of the formation of c-BN in the high-pressure and high-temperature supercritical-fluids system. Thirdly, to gain a clear insight into the diamond nucleation upon the hydrothermal synthesis and the reduction of carbide (HSRC), we have performed the thermodynamic approach on nanoscale, in which the diamond nucleation is preferable to the graphite phase formation in the competing growth between diamond and graphite upon HSRC. We theoretically predicted that the pressure of 400 MPa should be the threshold pressure for the diamond synthesis by HSRC in the metastable phase region of diamond in the carbon phase diagram. More importantly, these theoretical results above are consistent with the experimental data. Additionally, the developed nanothermodynamics was used to study the theory of nucleation and growth of diamond nanowires inside nanotubes. Accordingly, the thermodynamic

n-type doping of (001)-oriented single-crystalline diamond by phosphorus

Abstract: n-type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350cm2∕Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.

Transformation of nanodiamond into carbon onions: A comparative study by high-resolution transmission electron microscopy, electron energy-loss spectroscopy, x-ray diffraction, small-angle x-ray scattering, and ultraviolet Raman spectroscopy

Abstract: The structural properties of both nanodiamond particles synthesized by detonation and the products of their transformation into carbon onions via vacuum annealing at 1000 and 1500°C have been studied using high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy, x-ray diffraction (XRD), small-angle x-ray scattering (SAXS), and Raman spectroscopy. The advantages of UV Raman spectroscopy over visible Raman spectroscopy for the analysis of these carbon nanomaterials are demonstrated. It was found that the synthesized nanodiamond particles have a composite core-shell structure comprising an ordered diamond core covered by a disordered (amorphous) outer shell formed by the mixed sp2∕sp3 bonding of carbon atoms. The observed structure of the nanodiamond particles are comparable with the structure of the bucky diamond clusters comprising a diamond core and a reconstructed surface which stabilizes the cluster at the average diameter of ∼30A, as predicted recently from theoretic...

Corundum, diamond, and PtS metal-organic frameworks with a difference: self-assembly of a unique pair of 3-connecting D2d-symmetric 3,3',5,5'-tetrakis(4-pyridyl)bimesityl.

Abstract: There is an upsurge of interest in the synthesis of coordination polymers in contemporary supramolecular chemistry, as coordination polymerization may lead to materials with controllable functions such as porosity, sensing, nonlinear optical (NLO) activity, and chirality. Crystal engineering based on predesigned organic linkers and metal centers (building blocks) with specific coordination geometries is an important approach in the preparation of coordination materials with desired functions. Based on the knowledge of the structures of the ligands and the coordination geometries of a variety of metal centers, diverse 2D and 3D nets—several of which are analogous to structures of inorganic materials—have been engineered in the field of metal–organic frameworks (MOFs). Thus, the syntheses of 3connected nets corresponding to the topologies of SrSi2/(10,3)-a, ThSi2/(10,3)-b, [4] (12,3), (3,4)-connected nets with the topologies of boracite, Cu15Si4, [7] (5,4), [8] and (3,6)connected nets corresponding to the topologies of rutile and pyrite have been accomplished. Insofar as the 4connected nets are concerned, the syntheses of MOFs with unusual topologies and with topologies corresponding to those of diamond, NbO, quartz, and PtS have been reported. Similarly, the (4,8)and 6-connected metal– organic frameworks with fluorite and cubic topologies, respectively, have been designed and synthesized. In view of the success of such building-block approaches to realize metal–organic frameworks with specific topologies, the multidentate ligands with novel structural features offer the possibility to construct new and unique coordination poly-

Diamond-bonded bodies and compacts with improved thermal stability and mechanical strength

Abstract: Thermally stable diamond-bonded compacts include a diamond-bonded body having a thermally stable region extending a distance below a diamond-bonded body surface. The thermally stable region comprises a matrix first phase of bonded together diamond crystals, and a second phase interposed within the matrix phase. At least some population of the second phase comprises a reaction product formed between an infiltrant material and the diamond crystals at high pressure/high temperature conditions. The diamond bonded body further includes a polycrystalline diamond region that extends a depth from the thermally stable region and has a microstructure comprising a polycrystalline diamond matrix phase and a catalyst material disposed within interstitial regions of the matrix phase. The compact includes a substrate attached to the diamond-bonded body.

Implantation of labelled single nitrogen vacancy centers in diamond using 15N

Abstract: Nitrogen-vacancy (NV-) color centers in diamond were created by implantation of 7 keV 15N (I = 1/2) ions into type IIa diamond. Optically detected magnetic resonance was employed to measure the hyperfine coupling of the NV- centers. The hyperfine spectrum from 15NV- arising from implanted 15N can be distinguished from 14NV- centers created by native 14N (I = 1) sites. Analysis indicates 1 in 40 implanted 15N atoms give rise to an optically observable 15NV- center. This report ultimately demonstrates a mechanism by which the yield of NV- center formation by nitrogen implantation can be measured.

Thermally stable diamond bonded materials and compacts

Abstract: Thermally stable diamond bonded materials and compacts include a diamond body having a thermally stable region and a PCD region, and a substrate integrally joined to the body. The thermally stable region has a microstructure comprising a plurality of diamond grains bonded together by a reaction with a reactant material. The PCD region extends from the thermally stable region and has a microstructure of bonded together diamond grains and a metal solvent catalyst disposed interstitially between the bonded diamond grains. The compact is formed by subjecting the diamond grains, reactant material, and metal solvent catalyst to a first temperature and pressure condition to form the thermally stable region, and then to a second higher temperature condition to both form the PCD region and bond the body to a desired substrate.

Polycrystalline diamond materials having improved abrasion resistance, thermal stability and impact resistance

Abstract: PCD materials comprise a diamond body having bonded diamond crystals and interstitial regions disposed among the crystals. The diamond body is formed from diamond grains and a catalyst material at high pressure/high temperature conditions. The diamond grains have an average particle size of about 0.03 mm or greater. At least a portion of the diamond body has a high diamond volume content of greater than about 93 percent by volume. The entire diamond body can comprise high volume content diamond or a region of the diamond body can comprise the high volume content diamond. The diamond body includes a working surface, a first region substantially free of the catalyst material, and a second region that includes the catalyst material. At least a portion of the first region extends from the working surface to depth of from about 0.01 to about 0.1 mm.

Electrochemical impedance sensing of DNA hybridization on conducting polymer film-modified diamond.

Abstract: The impedimetric sensing of DNA hybridization on polyaniline/polyacrylate (PANI/PAA)-modified boron-doped diamond (BDD) electrode has been investigated. An ultrathin film of PANI−PAA copolymer was electropolymerized onto the diamond surfaces to provide carboxylic groups for tethering to DNA sensing probes. The electrochemical impedance and the intrinsic electroactivity of the polymer-diamond interface were analyzed after the hybridization reaction with target and non-target DNA. The impedance measurement shows changes in the impedance modulus as well as electron-transfer resistance at the stage of probe DNA immobilization (single-strand), as well as after hybridization with target DNA (double-strand). DNA hybridization increases the capacitance of the polymer−DNA layer and reduces the overall impedance of the DNA−polymer−diamond stack significantly. The polymer-modified BDD electrode shows no detectable nonspecific adsorption, with good selectivity between the complementary DNA targets and the one-base mi...