Diamond seed crystals

The growth of diamond on diamond seed crystals from low pressure low temperature decomposition of acetylene in the presence of mercury vapor was reported by von Bolton as early as 1911, but the claim went unnoticed for nearly half a century. Systematic studies of the vapor synthesis of diamond began in 1950 s. ... 

J. C. Angus, H. A. Will, and W. S. Stanko, Growth of diamond seed crystals by vapor deposition, J. Appl Phys., 39 2915-2922 (1968)... 

For some time, mixtures of H2 and natural gas have been used for chemical vapor deposition (CVD) growth of diamond-like carbon (DEC) films. It is now possible to use this technique to grow diamond seed crystals to produce clear, perfect colorless diamonds. Diamonds grown by the high-pressure methods are invariably doped and thus colored. One company, Apollo, has used the CVD technique to grow 1-ct diamonds. 

Figure 3. SEM micrographs of (a) aggregate after 12 h hydrothermal treatment of nanocrystalline diamond at 740°C and 300 MPa, (b) plate-like erystals on the surface of a diamond seed crystal after 150h hydrothermal treatment of graphite and diamond single crystals at 800°C and 300 MPa, (c) liquid-phase hydrothermal homoepitaxy of diamond on diamond seed at 170 MPa and 400°C in a specially prepared water solution. Reproduced from [15] with permission from A. Szymanski.

DJ Poferl, NG Gardner, JC Angus. Growth of boron-doped diamond seed crystals by vapor deposition. J Appl Phys 44 1428, 1972. 

The two stones B and C show hitherto unknown features [18], as follows. There is a core portion with a square outline in cross-section and cuboid form in three dimensions, and all dislocation bundles with Burgers vector <100> generate from the surface of the core portion (Fig. 9.19). This implies that the core portion was formed somewhere else it was then trapped in a different environmental phase and acted as a seed under the new conditions, after which the major part of the crystal was formed. This was the first piece of evidence to prove the presence of seed crystals in the growth of natural diamond. 

The cubic form resembles diamond in its crystal structure and is almost as hard. The theoretical density is 3.48 g/mL. It is colodess and a good electrical insulator when pure traces of impurities add color and make it semiconducting, eg, a few ppm of Be make it blue and />-type whereas small amounts of S, Si, or CN favor yellow, -type crystals. It is possible to makep—n junctions by growing -type material on j -type seed crystals (12). If this is done carefully in an alkaline-earth nitride bath using a temperature difference technique, as with large diamond crystals (see Diamond, SYNTHETIC), the resulting diodes are several mm in size and emit blue light when forward-biased (13,14). 

From the table above, it appears that aluminium oxide is extremely hard. That is why the material has to be processed with diamond. The compression, bending and tensile strengths of metals are dependent on the heat treatment. The modulus of elasticity of aluminium oxide is almost double that of stainless steel this means that twice the strength is needed for the same elastic deformation. Single crystals of aluminium oxide have been successfully used as implant material. They are made by adding the oxide powder to the surface of a seed crystal which is slowly withdrawn from an electric arc flame or oxygen/... 

The substrate materials are metals (W, Mo, Ti), silicon (e.g. mirror-polished wafers used in the production of semiconductor devices), glassy carbon, graphite [15], etc., depending on manufacturer or user preferences. Diamond nanocrystals are used as seed-crystals on the substrate surface to enhance the nucleation and make the film growth more uniform. The silicon substrate can be then etched off, and a freestanding diamond film is thus produced. 

Carsten Jacobsen (Novo Nordisk) presented results on protein crystallization in preclarified, concentrated fermentation broths. In particular, the impact of filtration rate on the formation of favorable large diamond versus rod shapes was examined. By adding seed crystals just above the solubility curve, where no nucleation occurred, the authors were able to produce 30% larger crystals as compared to an unseeded crystallization. Although there was minimal recovery and characterization data, this technique may prove very beneficial for dealing with difficult feed streams. While the work presented in this talk was done at the laboratory scale, scale-up experiments will be required to confirm the suitability of this approach for industrial process applications. 

The growth of diamond in metal-carbon systems under superhigh pressures has been observed on a substrate (seed crystals of synthetic diamond) in the form of single crystallites, as discrete linear series of crystals, or in groups of... 

Successful hydrothermal diamond synthesis was carried out in autoclaves filled with a specially prepared carbon enriched water solution , the composition of which was not disclosed [15,45,46]. The carbon precursor should be fine-grained diamond, vitreous carbon or emulsion of crude oil and water [29]. The presence of free radical catalysts was mentioned and paragenetic crystallization of quartz needles and diamond indicate the presence of silicon [45]. The synthesis was described as a sol/gel colloidal process working in the range 200-600°C and 100-200 MPa. Healing and joining of diamond crystals was reported. After 21 days at 400°C and 170 MPa, thin colorless films of polycrystalline diamond were obtained on (111) surfaces of seed crystals (Fig. 3c). With a reported size of 15-40 pm, these are the largest diamond crystals from hydrothermal experiments. 

Figure 5. Raman spectra of carbon on a-SiC crystals, A = 632.8 nm, after 4 h hydrothermal treatment at 600°C and 200 MPa (a) homogeneous carbon film, (b) diamond particle at seed crystal edge, (c) example of an inhomogeneous carbon film after 4h hydrothermal treatment at 700°C and 200 MPa.

Small amounts of well crystallized diamond were found after hydrothermal treatment of P-SiC powder at 700-750°C in the presence of diamond seed [55]. After removing silica and nondiamond carbon, small (<3pm) carbon particles of predominantly octahedral shape, thus being probably diamond, were found. They were attached to the surfaces of the single crystal seed but could be removed by intense ultrasonic treatment. Tetrahedral hillocks of etch pits appeared on the seed diamond surfaces. The hillocks always showed a faceted structure and sometimes common orientation, as expected for homoepitaxial diamond growth. 

DIAMOND POWDER CARBON HEATER SOLVENT-CATALYST-GROWING CRYSTAL SEED CRYSTAL... 

Figure 16. Dependence of critical growth rate of diamond crystals on 100 faces of seed crystals, on...

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