EFFECTS OF SUBSTRATE PRETREATMENTS ON DIAMOND SYNTHESIS FOR SI3N4 BASED CERAMICS

Diamond synthesis for Si3N4 ceramics after various substrate pretreatm ents has been carried out by the microwave-plasma enhanced chemical va por deposition (CVD) method using a mixture of methane and hydrogen ga ses. Four types of pretreatments for various substrates were performed as follows: scratching with diamond powder (I), applying O-2-C2H2, co mbustion flames (II), polishing with alumina (III), and platinum vapor deposition (IV). The products deposited on the substrate were examine d with micro-Raman spectroscopy, scanning electron microscopy (SEM) an d an X-ray diffractometer (XRD). It was found that the application of O-2-C2H2 flames as a pretreatment of the substrate in diamond synthesi s was suitable, because a higher density of diamond nucleation could b e obtained, and a film-like diamond could be formed on the surface in a shorter time than without applying them. The diamond could be synthe sized on the surface for all four types of substrate pretreatments per formed in the present study. The effects of the substrate pretreatment s on the surface morphology of grown diamond were that a film-like dia mond for (I) or (II), a particle-like diamond for (III) and a particle and/or a film-like diamond for (IV) were formed on the surface. The s urface morphology of grown diamond depended very much on the substrate temperature under deposition. (C) 1998 Elsevier Science S.A.