High quality diamond growth

FIGURE 11 Synthesized high-quality diamond crystals, showing their typical growth faces. 

H. Shiomi, K. Tanabe, Y. Nishibayashi, and N. Fujimori, Epitaxial growth of high quality diamond film by the microwave plasma-assisted chemical-vapor-deposition method, Jpn. J. Appl Pl s., 29(l) 34-40 (1990)... 

The possible success of a synthesis route using nongraphitic carbon would seem to depend upon the suppression of graphite nucleation and purity factors, since growth of high quality diamond requires low levels of impurities. This is more difficult to achieve in a carbon which has not been graphitized. 

In addition to C onions, C atoms condense into various kinds of chemically bonded forms, and they are known to have excellent physical properties depending on the bonding nature. This means that research and applications not only in the materials science but also in other scientific fields are expected. At JAERI, the optimum growth conditions have been successfully obtained for the preparation of high-quality Cgo, diamondlike carbon, and nanocrystalline diamond by means of ion-beam-assisted deposition [80-82]. The susceptibility of Ni/Cgo thin films to thermal treatment, the formation of nanocrystalline diamond and nanotubes due to codeposition of Co and Ceo, and the surface modification of glassy... 

Another candidate for a useful material from very high pressure synthesis is the gem material, jadeite (NaAlSi206). The natural material of Imperial quality can cost as much as 2000 per carat. Jadeite can be synthesized at about 30 kb and above in equipment similar to that used for diamond growth, and it has been made into pieces of jewelry. Since jadeite is used as a poly-crystalline aggregate, synthesis is essentially hot pressing and sintering, much simpler than if single crystals were needed. However, it does not appear to be a commercial product in competition with the natural supply. 

It has been reported that the carbon concentration in the gas phase should also be controlled during deposition in order to achieve step-flow growth. When the carbon concentration in the gas phase exceeds the ability of the surface steps to incorporate the carbon atoms, abnormal nucleation occurs on the surface terraces, and this results in non-epitaxial growth [12]. For a (100) diamond substrate, non-epitaxial growth can be seen as a pyramidal hillock, which consists of (ill) facets [9,12]. In order to obtain homoepitaxial BDD thin films of high quality, the carbon concentration in the gas phase should be low, however, low carbon concentration also leads to a low growth rate. Therefore, the carbon concentration should be optimized and controlled [13]. 

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