Growth of diamond thin film on tool materials from a gas phase

Abstract

In the present paper, diamond films have been synthesized on tungsten carbide, sintered diamond and high pressure diamond by hot filament chemical vapour deposition method from the mixture gas of methane and hydrogen, and growth features of diamond were studied.     

On compressibility of osmium metal

On the basis of the high-pressure diamond anvil cell experiments on Os metal, Cynn et al. [Phys. Rev. Lett. 88, 135701-1 (2002)] have reported that this metal has lower compressibility than diamond. In the present work we have reanalysed the experimental data of Cynn et al. We find that the bulk moduli of Os and diamond are close to each other, implying that Os metal is as incompressible as diamond, but not more so. Our first principles total energy calculations using the full potential linearised augmented plane wave method on Os and diamond also suggest the same results.     

Melting behaviors of carbon underhigh pressures

Abstract

The melting behaviors of graphite and diamond were investigated at pressures up to 25 GPa using flash-heating method. By rapid heating, the metastable graphite was melted in the diamond stable P-T field, competing with its conversion to diamond in the rate of reaction. For the diamond the pressure dependence of inserted energy required to reach the molten state suggested that the melting temperature of diamond increases with pressure.     

The structure of diamond nanoclusters

A model describing the structure of diamond nanoclusters produced by explosive shocks is proposed. The model is based on experimental data obtained from x-ray diffraction and small-angle x-ray scattering. This model considers the diamond nanocluster as a crystalline diamond core coated by a carbon shell having a fractal structure. The shell structure depends both on the cooling kinetics of the detonation products and on the method used to extract from them the diamond fraction. Fiz. Tverd. Tela (St. Petersburg) 41, 740–743 (April 1999)     

Reactions and stresses in polycrystalline diamond-metal and diamond-carbide compacts

Abstract

The kind of bonding phase has a significant influence on the microstructure and mechanical properties of diamond compacts. Microstructural studies of diamond with 5% wt. Ti and 5%wt. Tic (and also 30%wt. Tic) were carried out with a Transmission Electron Microscope. The TEM microstructural observations show differences between the metal and metal carbide bonding phase in diamond compacts. The mismatch of thermal expansion coefficients between diamond and the bonding metal or the compound induces significant internal stresses and may generate micro-cracks in polycrystalline diamond compacts. Twins and dislocations are the important details of microstructures in diamond crystals after HPHT sintering. They can appear as a result of residual stress relaxation. Results of measurements of residual stresses on a diamond compact surface by means of the “sin²ψ X-ray diffraction method are reported.     

Determination of the thermal conductivity of polycrystalline diamond films by means of the photoacoustic effect

A new method of determining the heat-conducting properties of diamond films is proposed, based on the photoacoustic effect. This method is used to study diamond polycrystalline films grown on silicon by chemical vapor deposition in a microwave discharge plasma. The thermal conductivity obtained was approximately half that for single-crystal diamond. Zh. Tekh. Fiz. 69, 97–101 (April 1999)     

Novel techniques for the prepartion of synthetic diamond

Abstract

The objectives of this work are two fold: (1) to study the effect of using oxygen-acetylene flame grown synthetic diamond as seed crystals for the high pressure-high temperature conversion of graphite into diamond and (2) to demonstrate the ability to produce small crystallites of diamond by a simple, electron beam evaporation technique. In each case, the production of diamond from graphite was confirmed.     

The laboratory confirmed natural crystallization of diamond from carbonized organic compounds

Abstract

In the paper the conception of the natural diamond growth as a result of the organic compounds reaction in the presence of noncompensated spin was checked. They might have played the essential role in the nucleation of diamond crystals. In the experiments, the partly carbonized phenolformal-dehyde resin instead of graphite was used as a carbon source. The final result of the process of the diamond growth depended on the temperature of resin carbonization as well as on the temperature and pressure of synthesis. The 3,8 GPa pressure, which is less than needed for graphite to diamond transformation in the classic industrial process, was sufficient to produce transparent and colourles diamond crystal of the size up to 0,7 mm.     

Peculiarities of phase transitions when synthesizing diamond in high pressure apparatus of various types

Abstract

The influence of P, T-parmeters and duration of heat when synthesizing diamond in high pressure apparatus both of recessed anvil-type and cylindrical type (belt-type) on properties of diamond powders was studied. The dependence of pressure in reaction cells on temperature of force elements of apparatus in initial state and on efficiency of high pressure production in a reaction cell before heating was shown.     

Photoacoustic spectroscopy of diamond powders and polycrystalline films

Photoacoustic spectroscopy is used to study optical absorption in diamond powders and polycrystalline films. The photoacoustic spectra of diamond powders with crystallite sizes in the range from ∼100 μm to 4 nm and diamond films grown by chemical vapor deposition (CVD) had a number of general characteristic features corresponding to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (∼5.4 eV) and to absorption in the visible and infrared by crystal-structure defects and the presence of non-diamond carbon. For samples of thin (∼10 μm) diamond films on silicon, the photoacoustic spectra revealed peculiarities associated with absorption in the silicon substrate of light transmitted by the diamond film. The shape of the spectral dependence of the amplitude of the photoacoustic signal in the ultraviolet indicates considerable scattering of light specularly reflected from the randomly distributed faces of the diamond crystallites both in the polycrystalline films and in the powders. The dependence of the shape of the photoacoustic spectra on the light modulation frequency allows one to estimate the thermal conductivity of the diamond films, which turns out to be significantly lower than the thermal conductivity of single-crystal diamond. Fiz. Tverd. Tela (St. Petersburg) 39, 1787–1791 (October 1997)     

Chess 2001 users' meeting

Diamonds attract enormous interest as gemstones. This rather frivolous “application” is based on their optical properties and contributes about 95 percent of the turnover in the diamond industry. Another area of application, which may now be seen as a crude application, is a diamond-tipped tool for the abrasive and cutting industries. These applications exploit the hardness and wear resistance of diamond, and dominate the demand for synthetic diamond production. These applications do not place the most stringent requirements on the quality of diamond. As has become clear at this workshop, a crucial new role for diamond in an ultra-high technology area is emerging. Diamond devices at synchrotrons require near– theoretical values of perfection of the diamond lattice. This material is vital to the continued increase in beam performance as well as the expansion of the suite of measurement techniques of modern synchrotrons.

An international workshop on “diamond single crystals for 3rd and 4th generation X-ray sources” was held in Grenoble, France, on May 24–25, 2004.     

Phase Diagrams and Synthesis of Diamond

For reasons of phase equilibria, the lowest temperatures T min , above which at high pressures the diamond crystallization from melt solutions is allowable in terms of thermodynamics, have been found for a number of metal-carbon systems. In the Ta-C and Nb-C systems, the diamond synthesis is possible at temperatures below T min , while to synthesize diamond in the Mg-Zn-C system, the temperatures much higher than T min , are required because of the necessity to overcome the kinetic difficulties.     

The formation of a diamond layer on a carbide substrate during diamond interaction with Si,WC and Co

Abstract

A diamond layer was formed on a carbide substrate in an irregular temperature field at high pressures (HP). A gradient scheme of HP cell set-up has been developed, which provides for a simultaneous impregnation of opposite planes of a diamond layer by components that differ in melting temperature. The cell temperature field has been calculated and physico-mechanical properties of the obtained composite material have been studied.     

Influence of the nucleation behaviour on the synthesis of diamond

Abstract

Using a solid state nucleation model the influence of different carbon types on the nucleation number of diamond has been studied, keeping constant the synthesis parameters p, T, t. The carbon types used have been investigated concerning their mechanical, electrical and chemical properties; the graphite content and the lattice perfection of the graphite are also determined. As a experimental result the nucleation number shows a significant dependence on the carbon type used, particularly on the amount of crystalline graphite.

The results show the possibility to influence certain steps of the diamond synthesis process.     

Development of superhard materials,sintered diamond and cubic boron nitride

Abstract

Recent advances on the preparation technique of sintered diamond and cubic boron nitride containing small amount of sintering additives having superior thermal and mechanical properties is reviewed. Sintered diamond of lower metallic content (1–5 vol%) shows high hardness (100–150 GPa) and high electrical resistivity (10⁸ ohm-cm) at room temperature. Reaction sintered cubic boron nitride contained 1–3 mole % of magnesium boron nitride shows high thermal conductivity. (7 watt/cm K at RT)     

Bulk diamond formation from graphite in the presence of C-O-H fluid under high pressure

Abstract

C-O-H fluids have been successfully applied as catalysts for bulk diamond formation under high pressure. New insight into C-O-H fluids extends the understanding of the origin of natural diamond, which is presently of interest in materials and geological sciences. This review presents current literature data concerning the synthesis and characterization of bulk diamond formation assisted by C-O-H fluids at high pressure and high temperature. Based on a general survey of this subject, the pressure-temperature regime for diamonds formed in these fluids was established and the mechanism of conversion from graphite to diamond is discussed. Finally, a few questions are put forward that may be useful for the continued development of this research area.     

Ab initio modelling of band states in doped diamond

Presented in this study is an analysis of the electronic properties of doped diamond calculated using the Vienna ab initio simulation package, employing density functional theory within the generalized-gradient approximation. The dopants studied here have been inserted substitutionally into a 64-atom diamond supercell and include the single-electron acceptors boron and aluminium, the single-electron donors nitrogen and phosphorus and the double-electron donors oxygen and sulphur. Co-doping of diamond with sulphur and boron has also been briefly examined. The doped supercells have been relaxed, followed by calculation of electronic properties from the electronic density of states such as the indirect bandgap E _g, the valence bandwidth and an examination of the acceptor and donor states in the bandgap. It is anticipated that this study will provide a useful comparison of the third- and fourth-row donors and acceptors in diamond.     

Influence of Synthesis and Composition conditions on Strength Characteristics of Synthetic Carbonado-Type Diamonds

Polycrystalline diamonds carbonado were synthesized under pressure 6.0-12.0 GPa. Ni-Cr-Mo alloy and pure Ni were used as the catalysts. The strength was tested by static compression technique according to GOST 9206-80. Diamond powders APK 4 with the grit size 500/400 and 400/315 were made by crushing of the bulk polycrystalline samples and this diamond powders were under investigation. Influences of the synthesis pressure and the chemical treatment on strength of diamond carbonado were studied.     

A New Class of Low Compressibility Materials: Clathrates of Silicon and Related Materials

We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.     

Materials for high temperature diamond anvil cells

Abstract

We review the chemical and mechanical behaviour of diamond and other materials of use in diamond anvil cells intended to operate at high temperature. Operation at up to 600?C presents no special problems, whereas high-pressure studies at higher temperatures require cells constructed from unusual materials and controlled-atmosphere operation. Methods of P and T determination are also discussed.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for HighPressure Crystallography’. Daresbury Laboratory 20-21 July 1991