The Research On Diamond Films Deposited By Hot Filament Chemical Vapor Deposition

Diamond films have aroused many scientists' interests for its remarkable properties in mechanics, thermology, optics, electrics and acoustics. So far, the investigation of CVD diamond films has been the highspot of the materials, physics and chemistry. The research on diamond films were made in self-designed hot filament chemical vapor deposition of high-power (10 kilowatts) and low-power (1 kilowatt) respectively.In this paper, another filament was introduced into the conventional HFCVD systems to construct double filaments configuration, and a few assisted-growth methods were formed by connecting between filament and substrate. Their different growth rate and mechanism powered by direct current or radio frequency discharge were compared and analyzed. It is shown that growth rate was improved obviously on the condition that plasma generated between two hot filaments without substrate bias. So a growth model of active complex is brought forward to illustrate the phenomena.Meanwhile, the adhesive properties of diamond deposited on both silicon nitride ceramics and cemented carbide substrates were studied. Adhesive strength of the former is stronger than that of the later owing to their different bonding types by Indentation Test. Prior to diamond deposition, acid etching or in-situ decarburization pretreatments of cemented carbide substrate were made, and Indentation Test were performed to evaluate adhesive strength between diamond films to the substrate. It is found that adhesion by in-situ decarburization is nearly two times stronger than that of by acid etching, and the reasons of their different cohesion are discussed in detail.In addition, the optimize parameter for the deposition of large area diamond thick films in the high-power HFCVD systems were obtained, especial for the life of hot filament and the uniform substrate temperature. To resolve the contamination of a filament, an innovative idea that Ta filament should cover a layer of thin W films is proposed, and it is successfully realized with the current of 750 Ampere. The lattice relaxation in the CVD diamond thick films were detected by the X-ray diffraction attachments. It is associated with self-annealing of diamond thick films in the process of long time deposition. The wearing discrepancy of diamond coated cuttings and diamond thick films brazed cuttings is well illustrated by means of lattice relaxation.