Diamond nucleation by carbon fibers on unscratched substrate by hot-filament chemical vapor deposition
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In order to overcome the difficulty of nucleation of diamond particles on unscratched substrates by the chemical vapor deposition (CVD) method, carbon fibers are introduced on unscratched substrates as a nucleation site of diamond particles. With assistance of carbon fibers, diamond particles can be synthesized on unscratched silicon substrate from a gas mixture of methane and hydrogen by the hot-filament CVD method. From SEM observations, nucleation of diamond particles has been confirmed on fibers at the beginning of deposition. Fine particles have formed initially on the rugged surface of fibers, and then they grow up to be diamond particles. Detailed SEM observations reveal nucleation has occurred on irregular surfaces such as boundaries on carbon fibers. We propose that nucleation of diamond particles can be controlled by arranging carbon fibers on the substrate without applying any mechanical pretreatment.
It has been reported that diamond particles are nucleated on various materials, and different kinds of intermediate layers are formed between substrates and diamond particles.^ In our previous paper,5 we reported that hydrogenated amorphous carbon (a-C:H) layers were formed between diamond particles and silicon substrate by the hot-filament chemical vapor deposition (HFCVD) method, and the change in the surface morphology of the amorphous layer during diamond deposition was observed by atomic force microscopy (AFM). Furthermore, we have studied the influence of the surface morphology and the bonding state of carbon atoms in a-C: H films on nucleation of diamond particles and found that diamond nucleation is affected by surface morphology rather than the bonding state of carbon atoms.6 Usually, substrates are abraded with diamond powders to enhance the nucleation of diamond particles. However, mechanical treatment onto the substrate will inevitably cause damage to the surface. It is desirable to avoid mechanical treatment like polishing with diamond powders. Dubray et al. have shown that the presence of the a-C: H layers enables diamond to grow without any polishing treatment on silicon and SiAlON substrates.1 Drory et al. have examined the feasibility of fiberreinforced diamond matrix composites using SiC fibers and deposited diamond particles onto the fibers which are lightly abraded with diamond powders using plasmaenhanced CVD. 7 Diamond nucleation has been observed underneath the graphite fibers and along lines replicating graphite fibers on unscratched silicon substrate.8 It is concluded that the presence of the fiber affects the local gas phase nearby the fiber, and is merely a source of local carbon J. Mater. Res., Vol. 9, No. 7, Jul 1994
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contamination to the substrate surface. Although studies of diamond nucleation using carbon and other fibers have been performed, the nucleation process of diamond particles on fibers is not completely elucidated. In the present paper, carbon fibers are placed on unscratched substrates to nucleate diamond par
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