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The research concerns making diamond plates of mono crystalline quality with an area of 1 to 2 cm. The quality of the plates must be high, so that they can be used for optical components by the optical industry and for substrate by the electronic industry. A method, called the 'Mosaic' process, has been developed for producing large-area, single-crystal, diamond plates. It starts by carefully orienting and closely packing a set of diamond seed crystals. This assembly, or mosaic, is then overgrown by chemical vapour deposition (CVD) with a single-crystal diamond layer. The success of the 'Mosaic' process was shown for three different CVD techniques, namely the hot filament method (HF-CVD), microwave plasma assisted CVD (MPACVD) and the acetylene-oxygen combustion flame. The largest mosaic structure successfully grown up to now consists of seven crystals and has a surface area slightly in excess of 1 cm. Although several technical problems still have to be solved, there seem to exist no fundamental reasons which could hamper the further enlargement of the surface area.
In order to realize the 'Mosaic' process, know-how had to be developed about the diamond characteristics of the growth environment. The MPACVD system was studied by optical emission spectroscopy (OES) and laser spectroscopy while the combustion flame was studied by laser induced fluorescence (LIF). The molecular density distributions of different species and their rotational temperatures have been determined. These results provide essential input data for the optimization and validation of modelling calculations, necessary to unravel the chemistry and dynamics of the dominant precursors, which in-turn are indispensable for the optimization and up-scaling of the deposition processes.
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