THE EFFECTS OF METHANE CONCENTRATION IN HYDROGEN ON THE MICROSTRUCTURE AND PROPERTIES OF DIAMOND FILMS GROWN BY HOT-FILAMENT CHEMICAL VAPOR-DEPOSITION

Diamond films, ranging in thickness from 5 to 20-mu-m, were grown on Si(100) and polycrystalline Si3N4 substrates using hot-filament chemical vapour deposition. The concentration of methane in flowing hydrogen was varied over the range 0.15-1.0 vol.% at a constant flow rate of 100 standard cubic centimeters per minute. Photoluminescence and Raman spectroscopies indicated the presence of an electron bonding character ranging from predominantly sp2 to exclusively sp3 bonding, with sp3 character being favored by more dilute concentrations. An accompanying change in growth morphology from highly faceted, polyhedral crystallites showing significant {111} texture to a less well defined, finer-grained spherical morphology was observed for increasing methane concentrations. Ultralow-load indentation measurements on polished diamond surfaces led to the establishment of an inverse relation between hardness and methane concentration, with hardnesses ranging from 110 to 180 GPa. Further evidence of the outstanding quality of the film deposited using the most dilute mixture of methane in hydrogen is offered by an indentation load-deflection curve which exhibits substantially reduced hysteresis, indicating essentially elastic deformation.