Showing papers on "Diamond published in 1995"
TL;DR: In this paper, the phonon dispersion relations of diamond and graphite are calculated using an ab initio force constant method via a self-consistent supercell approach in the local density approximation in terms of the Hellmann-Feynman forces induced by the displacement of a single atom in the supercell.
Abstract: The phonon dispersion relations of diamond and graphite are calculated using an ab initio force constant method. The force constants are calculated via a self-consistent supercell approach in the local-density approximation in terms of the Hellmann-Feynman forces induced by the displacement of a single atom in the supercell. For diamond our ab initio results are in very good agreement with the neutron inelastic scattering and Raman data. For graphite we find good agreement with the neutron data for the low-energy modes as well as with the reflections electron energy loss spectroscopy (REELS) and optical data at higher energies. Significant differences to the predictions of semi-empirical models appear.
609 citations
01 Jan 1995
TL;DR: In this paper, the authors discuss the properties of the bulk diamond surface and the free carrier dynamics of the diamond surface, and propose a method to measure the thermal conductivity of the surface.
Abstract: 1: Electronic and Vibrational Properties of Bulk Diamond C.Y. Fong, B.M. Klein. 2: Diamond Surface B. Pate. 3: Growth of CVD Diamond for Electronic Applications L.S. Plano. 4: Doped Diamonds K. Okano. 5: Defects in Diamond W. Zhu. 6: Free Carrier Dynamics in Diamond S. Han, L.S. Pan, D.R. Kania. 7: Thermal Conductivity of Diamond J.E. Graebner. 8: Electrical Contacts to Diamond T. Tachibana, J. Glass. 9: Electronic Device Processing M.A. Plano. 10: Passive Diamond Electronic Devices D.L. Freifus. 11: Active Diamond Electronic Devices S. Grot. Appendix: Table A1. Properties of Semiconductors at 293 K. Index.
378 citations
TL;DR: In this article, diamond and SiC were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in Orgued (CI) and LL3.1 chondrites.
366 citations
TL;DR: In this paper, two kinds of amorphous carbon (a-C) thin film samples were synthesized, one by magnetron sputtering, the other by filtered cathodic arc deposition.
359 citations
TL;DR: A simple preparation of Cd17S4(SCH2CH2OH)26 clusters in aqueous solution leads to the formation of colorless blocky crystals that resemble the self-similarities known from fractal geometry.
Abstract: A simple preparation of Cd17S4(SCH2CH2OH)26 clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient (∼84,000 per molar per centimeter).
316 citations
TL;DR: In this paper, the lowest reported field, < 0.2 V εμm−1, was characterized as a function of surface treatment of diamond field emitters, Cs treated, air stable, and carbonized polymer.
Abstract: This letter reports, diamond field emitters, Cs treated, air stable, that emit electrons at the lowest reported field, <0.2 V μm−1. Field emission from B‐, Li‐, P‐, and N‐doped diamonds and carbonized polymer was characterized as a function of surface treatment. A treated with an O2 plasma, coated with Cs, heated, and exposed to O2 exhibited increased emission for all samples except for B‐doped diamond. The best emission was obtained from N‐doped diamond samples, followed by carbonized polymer, the Li‐doped, and polycrystalline P‐doped diamond. Li‐ and N‐doped samples treated with Cs were stable in laboratory air for several days. This stability of the surface‐activated diamond is believed to be due to the formation of a diamond–O–Cs salt. If the sample is treated with a H2 plasma instead of an O2 plasma, the Cs‐enhanced emission degrades with heat and exposure to O2. Subbands formed by Li and N impurities are believed to be responsible for this enhanced emission. The surface treatment on N‐doped diamond ...
297 citations
Abstract: Diamond samples with varying defect densities have been synthesized by chemical vapor deposition, and their field emission characteristics have been investigated. Vacuum electron field emission measurements indicate that the threshold electric field required to generate sufficient emission current densities for flat panel display applications (≳10 mA/cm2) can be significantly reduced when the diamond is grown so as to contain a substantial number of structural defects. The defective diamond has a Raman spectrum with a broadened peak at 1332 cm−1 with a full width at half maximum (FWHM) of 7–11 cm−1. We establish a strong correlation between the field required for emission and the FWHM of the diamond peak. The threshold fields are typically less than 50 V/μm and can reach as low as 30 V/μm for diamond with a FWHM greater than 8.5 cm−1. It is believed that the defects create additional energy bands within the band gap of diamond and thus contribute electrons for emission at low electric fields.
287 citations
TL;DR: In this paper, a new approach to deciphering the origin of diamond is presented, involving the collation of all primary genetic information collected from large single crystals, and it is concluded that diamond monocrystals of both eclogitic and peridotitic parageneses took place during early igneous events within the mantle.
275 citations
TL;DR: The critical dose for graphitization of diamond as a result of ion implantation induced damage (boron and arsenic) and subsequent thermal annealing was determined by combining secondary ion mass spectroscopy measurements, chemical etching of the graphitized layer, and TRIM simulations as mentioned in this paper.
Abstract: The critical dose for graphitization of diamond as a result of ion implantation induced damage (boron and arsenic) and subsequent thermal annealing is determined by combining secondary ion mass spectroscopy measurements, chemical etching of the graphitized layer, and TRIM simulations. Li ions are implanted as a deep marker to accurately determine the position of the graphite/diamond interface. The damage density threshold, beyond which graphitization occurs upon annealing, is found to be 1022 vacancies/cm3. This value is checked against published data and is shown to be of general nature, independent of ion species or implantation energy.
270 citations
TL;DR: The results indicate that CVD diamond is as biocompatible as titanium (Ti) and 316 stainless steel (SS), and there appears to be less cellular adhesion and activation on the surface of CVD diamonds surfaces compared to Ti and SS.
TL;DR: The physical origin and quantitative nature of the dimer reconstructions are investigated systematically, and it is shown by analyzing chemical trends why Si(001) is the most subtle case for an unequivocal surface structure determination.
Abstract: Ab initio calculations of structural and electronic properties of the C(001)-(2 \ifmmode\times\else\texttimes\fi{} 1) diamond surface are reported and discussed in direct comparison with Si(001) and Ge(001). Our results strongly favor a symmetric dimer reconstruction of C(001)-(2 \ifmmode\times\else\texttimes\fi{} 1) as opposed to an asymmetric dimer reconstruction of Si and Ge (001). The physical origin and quantitative nature of the dimer reconstructions are investigated systematically, and it is shown by analyzing chemical trends why Si(001) is the most subtle case for an unequivocal surface structure determination.
TL;DR: In this article, the authors measured Raman spectra of diamond with nanometer size, called cluster diamond, and found that sp2 and sp3 clusters have been observed at around 1600 and 1322 cm−1, respectively, suggesting that the cluster diamond slightly contains the sp2 cluster.
Abstract: We have measured Raman spectra of diamond with nanometer size, called cluster diamond. The Raman bands assigned to sp2 and sp3 clusters have been observed at around 1600 and 1322 cm−1, respectively. This result suggests that the cluster diamond slightly contains the sp2 cluster. The Raman band assigned to sp3 cluster is found to shift by −10 cm−1, compared with that of bulk crystal and to be asymmetric with some tailing toward lower Raman frequency. The observed Raman spectrum agrees well with that calculated by a phonon confinement model. The crystallite size of the cluster diamond estimated from the phonon confinement model agrees approximately with that estimated from x‐ray measurement. Raman spectroscopy gives some information about the crystallite size of diamond particles with nanometer size.
TL;DR: In this article, the authors investigated the stability of diamond-like carbon (DLC) films at elevated temperature and high humidity using Raman spectroscopy and thermal desorption analysis.
TL;DR: In this paper, two approaches have been adopted in attempting to determine the strength of the one-phonon infrared absorption by the B nitrogen aggregate in diamond, which is complicated because diamonds in which the B aggregate is the only point defect also contain extended defects that may or may not involve nitrogen.
Abstract: Two approaches have been adopted in attempting to determine the strength of the one-phonon infrared absorption by the B nitrogen aggregate in diamond. On the one hand, we have heat treated purely type IaA specimens with known infrared absorption strengths (and thus also known nitrogen concentrations) to bring about partial aggregation of the A centres to B centres, monitoring changes in the strengths of the A, and resultant B, one-phonon components by decomposition of the ensuing infrared spectra. Secondly, we have made direct chemical assays of nitrogen in diamonds that show dominant B absorption features. This approach is complicated because diamonds in which the B aggregate is the only point defect also contain extended defects that may or may not involve nitrogen. These defects may or may not, in turn, contribute to absorption in the one-phonon region. Nevertheless, the nitrogen concentrations have been measured for two distinct groups of diamonds that both uncritically might at first glance ...
TL;DR: In this article, a theoretical analysis of the SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation, and it was shown that a SiO/sub 2/ZnO/diamond/Si structure with a high phase velocity of 8,000-9,000 m/s and a large electro-mechanical coupling coefficient of up to 4%.
Abstract: Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus can provide much advantage for fabrication of high frequency SAW devices when it is combined with a piezoelectric thin film. Basic SAW properties of layered structures consisting of a piezoelectric material layer, a diamond layer and a substrate were examined by theoretical calculation. Rayleigh mode SAW's with large SAW velocities up to 12,000 m/s and large electro-mechanical coupling coefficients from 1 to 11% were found to propagate in ZnO/diamond/Si, LiNbO/sub 3//diamond/Si and LiTaO/sub 3//diamond/Si structures. It was also found that a SiO/sub 2//ZnO/diamond/Si structure can realize a zero temperature coefficient of frequency with a high phase velocity of 8,000-9,000 m/s and a large electro-mechanical coupling coefficient of up to 4%. >
TL;DR: In this article, a tri-layer diamond/tungsten carbide and tungsten buffer layer was used to enhance the adhesion of steel with high compressive stress, σ ≈ 7 GPa.
Patent•
16 Jun 1995
TL;DR: In this paper, a preform cutting element for a drag-type rotary drill bit includes a facing table of polycrystalline diamond bonded to a less hard substrate, such as cemented tungsten carbide.
Abstract: A preform cutting element for a drag-type rotary drill bit includes a facing table of polycrystalline diamond bonded to a less hard substrate, such as cemented tungsten carbide. The element is formed by first forming a solid substrate, and then applying an electron beam, laser, or other intense heating source to adjacent areas of the front surface of the substrate to melt the surface and form an array of holes or holes therein. A layer of polycrystalline diamond particles is applied to the substrate so that such particles fill the holes or holes, and the diamond layer and substrate are then subjected to pressure and temperature in a high pressure, high temperature press to bond the superhard layer to the substrate. The engagement of parts of the diamond table in the holes or holes in the substrate provides a mechanical interlock to improve the strength of the bond between the table and substrate.
TL;DR: In this article, the role of defects in the electron emission from undoped or p-type doped diamond and indicate that the improved emission characteristics of as-implanted diamond is due to the defects created by the ion implantation process.
Abstract: Diamond films and islands grown by chemical vapor deposition were implanted with boron, sodium, and carbon ions at doses of 1014–1015/cm2. This structural modification at the subsurface resulted in a significant reduction of the electric field required for electron emission. The threshold field for producing a current density of 10 mA/cm2 can be as low as 42 V/μm for the as‐implanted diamond compared to 164 V/μm for the high quality p‐type diamond. When the ion‐implanted samples were annealed at high temperatures in order to anneal out the implantation‐induced defects, the low‐field electron emission capability of diamond disappeared. These results further confirm our earlier findings about the role of defects in the electron emission from undoped or p‐type doped diamond and indicate that the improved emission characteristics of as‐implanted diamond is due to the defects created by the ion implantation process.
TL;DR: In this article, cyclic voltammetry and ac impedance analysis were used to measure the background current response and capacitance of interfaces formed at as grown (untreated) boron-doped polycrystalline diamond thin-film electrodes in contact with aqueous electrolytes.
Abstract: Cyclic voltammetry and ac impedance analysis were used to measure the background current response and capacitance of interfaces formed at as grown (untreated) boron-doped polycrystalline diamond thin-film electrodes in contact with aqueous electrolytes. The diamond films (∼1 cm 2 , 15 μm thick ; carrier concentration, ∼10 17 cm -3 ) were grown on conducting Si substrates by plasma-enhanced chemical vapor deposition. Cyclic voltammetry was also used to determine the charge transfer reactions of several redox analytes at as grown and chemically wet etched diamond thin-film electrodes and to study the effect of surface pretreatment, including Fe(CN) 6 3-/4- , IrCl 6 2-/3- , Ru(NH 3 ) 6 3+/2+ , dopamine, 4-methylcatechol, MV 2+/+/0 , and ferrocene. The electrochemical response exhibited by the films is explained using two models : (i) traditional electron transfer at a p-type semiconductor-electrolyte interface and (ii) electron transfer at a composite electrode composed of nondiamond carbon impurities contained within a diamond matrix such that k° nondiamond >> k° diamond.
TL;DR: The ion-beam-induced transformation of insulating diamond to a conducting form of carbon is explored by performing measurements of the electrical conductivity, and remarkable similarities between the conductivity induced in diamond and fused quartz implanted with C ions under identical conditions are reported.
Abstract: The ion-beam-induced transformation of insulating diamond to a conducting form of carbon is explored by performing measurements of the electrical conductivity of diamond subject to ion damage. A wide range of implantation temperatures (150--690 K) with both Xe (320 keV) and C (100 keV) ions are employed. The dose dependence of the conductivity, R(D), is found to scale with the nuclear energy deposited in the irradiated volume, thus demonstrating that it is the density of collisionally induced defects that governs the electrical conductivity. The data are analyzed in terms of a model that proposes that the passage of an ion through the solid leaves in its wake conducting spheres of varying radii. The average radius of these spheres is found to decrease from about 2.05 nm for irradiation at 150 K with 320-keV Xe ions to zero for implantation at about 815 K. At critical doses ${\mathit{D}}_{\mathit{c}}$, which depend on the implantation temperature and the ion species, these spheres overlap to form a continuous conductive pathway through the irradiated diamond. In some cases this transition is sharp enough to be well accounted for by a simple percolation theory. Below ${\mathit{D}}_{\mathit{c}}$, R(D) displays complicated nonmonotonic behavior, which is explained as being due to the competition of the contribution of different types of defects to the observed electrical conductivity. Remarkable similarities between the conductivity induced in diamond and fused quartz implanted with C ions under identical conditions are reported.
TL;DR: In this paper, the authors reviewed the tribological properties of carbon-like carbon (DLC), diamond and more novel carbonaceous coatings and discussed their tribological performance in light of their adhesion, residual stress and hardness.
TL;DR: This work has simulated the conversion of carbon from graphite to diamond under high pressure and found that the transformation path proceeds through sliding of graphite planes into an unusual orthorhombic stacking, from which an abrupt collapse and buckling of the planes leads to both cubic and hexagonal forms of diamond in comparable proportions.
Abstract: Using constant-pressure ab initio molecular dynamics we have simulated the conversion of carbon from graphite to diamond under high pressure. We found that the transformation path proceeds through sliding of graphite planes into an unusual orthorhombic stacking, from which an abrupt collapse and buckling of the planes leads to both cubic and hexagonal forms of diamond in comparable proportions. The mutual orientation of the initial and final phases is in agreement with that of shock-wave experiments.
TL;DR: In this paper, the position of the local paleogeotherm can be derived from garnet concentrates, and the depth of origin of each garnet grain is determined by referral of its T n i to the derived geotherm.
TL;DR: In this article, a force field derived from ab initio quantum mechanics has been used to predict the hardness of C_3N_4 ceramic films, and the predicted structure for α-C-3N-4 is in good agreement with transmission electron diffraction (TED) studies.
TL;DR: In this paper, a model of the formation of a p-type surface conductive layer on deposited diamond films is proposed, and the experimental results concerning the change in electrical resistance at the surface of diamond films can be explained using the proposed model.
Abstract: A model of the formation of a p-type surface conductive layer on deposited diamond films is proposed. According to the model, the ionization of acid in water produces oxonium ion ( H3O+) which reacts with hydrogen on diamond films and causes the creation of holes in diamond films. The model also explains the disappearance of the p-type surface conductive layer by the action of alkaline substances. The experimental results concerning the change in electrical resistance at the surface of diamond films can be explained using the proposed model.
TL;DR: In this paper, a lattice-matched structural template was proposed to seed the growth of carbon nitride crystallites, and the resulting coatings are smooth, fully crystalline, with nanoindentation hardness in the range of 45-55 GPa.
Abstract: Crystalline carbon nitride/TiN composite coatings have been deposited using a dual‐cathode magnetron sputtering system onto polished silicon and M2 steel substrates held at room temperature. We propose that TiN provides a lattice‐matched structural template to seed the growth of carbon nitride crystallites. The resulting coatings are smooth, fully crystalline, with nanoindentation hardness in the range of 45–55 GPa. This hardness is in the low‐end range of diamond films. Suggestions for better seeding materials to further improve the hardness are proposed.
TL;DR: In this paper, the authors employed the Raman spectroscopy to investigate the nature and sources of stress and the type and distribution of impurities and defects in thin diamond films grown on silicon substrates.
Abstract: Photoluminescence (PL) and Raman spectroscopy were employed to investigate the nature and sources of stress and the type and distribution of impurities and defects in thin diamond films grown on silicon substrates. The types of impurities and defects which were detected in the diamond films are the nitrogen, silicon, and the sp2‐type bonding of the graphitic phase. Our Raman analyses indicate that the diamond films exhibit a net compressive stress. After compensating for the thermal interfacial stress and for the stress due to grain boundaries it was found that the residual internal stress is compressive in nature. From Raman line‐shape analysis it was determined that the internal stress is due to the various impurities and defects present in the film. Moreover, the stress magnitude exhibits a strong correlation with the graphitic phase implying that the sp2 bonding produces a dominant compressive stress field. The PL analytical line‐shape investigation of the nitrogen band at 2.154 eV indicates that the ...
TL;DR: In this article, the Wooten-Weaire method was used to generate a model of amorphous diamond with four-fold coordination everywhere, where four-membered rings are allowed.
Abstract: We computer generate a model of amorphous diamond using the Wooten-Weaire method, with fourfold coordination everywhere. We investigate two models: one where four-membered rings are allowed and the other where the four-membered rings are forbidden; each model consisting of 4096 atoms. Starting from the perfect diamond crystalline structure, we first randomize the structure by introducing disorder through random bond switches at a sufficiently high temperature. Subsequently, the temperature is reduced in stages, and the topological and geometrical relaxation of the structure takes place using the Keating potential. After a long annealing process, a random network of comparatively low energy is obtained. We calculate the pair distribution function, mean bond angle, rms angular deviation, rms bond length, rms bond-length deviation, and ring statistics for the final relaxed structures. We minimize the total strain energy by adjusting the density of the sample. We compare our results with similar computer-generated models for amorphous silicon, and with experimental measurement of the structure factor for (predominantly tetrahedral) amorphous carbon.