NUCLEATION AND GROWTH OF DIAMOND FILMS ON NI-CEMENTED TUNGSTEN CARBIDE .2. EFFECTS OF DEPOSITION CONDITIONS

Diamond films were deposited by hot-filament chemical vapor deposition (HFCVD) on substrates made of WC sintered with 6 wt% of Ni. The as-gr ound substrates were scratched with diamond powder (S samples) or scra tched and wet-etched (SE samples), Diamond synthesis was carried out a t substrate temperatures ranging between 600 degrees and 1050 degrees C, and using 1.0% or 2.0% CH4 in H-2. The diamond nucleation density, as measured by scanning electron microscopy (SEM) and automatic image analysis (AIA), did not significantly change in the 600 degrees-900 de grees C temperature range, while at substrate temperatures higher than 900 degrees C a steep decrease of the density of nuclei was observed and attributed to the thermal annealing of nucleation sites. The activ ation energy of the growth process was measured and found to be 21 +/- 2 kcal/mol, Neither nucleation density nor growth rate were affected by an increase of CH4 concentration in the feed gas, while a lack of c rystallinity was observed at the higher methane concentration, Raman a nalysis showed that phase purity of the films was affected mainly by t he substrate temperature: the lower the temperature, the better the fi lm quality. The presence of Ni on the substrate surface did not induce the preferential formation of non-diamond carbon phases, as confirmed by comparing the Raman spectra obtained from both S and SE substrates , As a comparison, continuous films were deposited on scratched WC-5 w t% Co substrates under the same experimental conditions. The results i ndicated that the use of Ni as a binder is preferable to Co.