Hot filament chemical vapour deposition processing of titanate nanotube coatings

In the present paper, we report on the processing of titanate nanotubes using the hot filament chemical vapour deposition (HF-CVD) method to synthesize titania-carbon nanotube-wire composites. The titanate nanotubes are prepared using a chemical route, and then deposited on silicon using an electrodeposition method. The HF-CVD is used to process these coatings at different temperatures in vacuum as well as in different concentrations of hydrogen (H₂) and methane (CH₄) gas mixtures. The evolutions of the surface and precipitation for various phases have been monitored using different characterization techniques. It is observed that titanate nanotubes start disintegrating above T_s∼500 °C, and exhibit different types of phase precipitation depending upon the temperature and gas ambient. Under appropriate conditions, the presence of activated hydrogen and carbon radicals leads to the formation of novel architectures of mixtures of nanophases such as carbide, nonstoichiometric titania, carbon nanotubes, and titania decorated carbon nanowires. The results are discussed in terms of reduction in the thermal reaction barrier due to the presence of atomic hydrogen, and the formation of energetic sites during disintegration of titania nanotubes to facilitate nucleation of nanotube and nanowire structures.