Surface morphology, nano-indentation and TEM analysis of tantalum carbide-graphite composite film synthesized by hot-filament chemical vapor deposition

Hot-filament chemical vapor deposition was used to deposit tantalum carbide-graphite composite films on etched silicon. Thermal evaporation from heated tantalum wires provided tantalum while carbon was obtained from methane diluted with hydrogen. Resulting films were characterized and analyzed by field emission scanning electron microscope, high-resolution transmission electron microscopy and nano-indentation. The results indicate that surface morphology of coatings and their hardness are greatly influenced by the process parameters. The grain distribution obtained is more homogenous at moderate pressure rather than at lower or higher pressures. Average grain size at 60 Torr is 30 nm, while at low pressure it is 15 nm and at high pressure nano-scale grains coalesced and formed cauliflower structure and secondary nucleation. With increase in methane concentration grains coalesce and become coarse. The films grown at 100 Torr and higher methane concentration show higher porosity but better growth rate compared to others. Elemental composition analysis and nano-indentation results reveal that higher the graphite content lower is the hardness.