Experimental and gas phase modeling of nanocrystalline diamond films grown on titanium alloys for biomedical applications

For biomedical applications, it is highly desirable to be able to deposit smooth adherent diamond films on various complex-shaped substrates using the hot filament chemical vapor deposition technique (HFCVD). The properties of these films are affected profoundly by process parameters such as filament temperature, gas composition, and pressure. In this study, we present an insight into the gas phase chemistry involved in HFCVD of smooth nanocrystalline diamond films using Ar/CH₄/H₂ precursor mixtures. Experimental results on the growth, surface morphology, and crystalline structure are also presented. It is evident that the addition of a noble gas such as argon has a considerable effect on the gas surface chemistry. Notably at high concentrations of inert gas dilution (>90 vol.% argon) there are significant changes in diamond crystallinity ranging from polycrystalline through microcrystalline, and at argon concentrations >98 vol.%, nanocrystalline facets are observed. Modeling of the gas phase chemistry showed that the relative concentrations of CH₃ and C₂H alter significantly in this region, and these in turn influence surface morphology and crystallinity of the deposited films.