Hot filament chemical vapour deposition processing of titanate nanotube coatings

Abstract

In the present paper, we report on the processing of titanate nanotubes using the hotfilament chemical vapour deposition (HF-CVD) method to synthesize titania–carbonnanotube–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 coatingsat different temperatures in vacuum as well as in different concentrations of hydrogen(H2) andmethane (CH4) gas mixtures. The evolutions of the surface and precipitation for variousphases have been monitored using different characterization techniques.It is observed that titanate nanotubes start disintegrating aboveTs∼500 °C, and exhibit different types of phase precipitation depending upon the temperature andgas ambient. Under appropriate conditions, the presence of activated hydrogen and carbonradicals leads to the formation of novel architectures of mixtures of nanophases such ascarbide, nonstoichiometric titania, carbon nanotubes, and titania decorated carbonnanowires. The results are discussed in terms of reduction in the thermal reaction barrierdue to the presence of atomic hydrogen, and the formation of energetic sites duringdisintegration of titania nanotubes to facilitate nucleation of nanotube and nanowirestructures.