Carbon nanotubes and nanostructures grown at below 400°C

In this paper, we report clear evidence for the growth of carbon nanotubes and nanostructures at low substrate temperatures, using direct-current plasma-enhanced chemical vapour deposition. The catalyst particles are mounted on a titanium layer which acts as a thermal barrier, and allows for a larger temperature gradient between the Ni catalyst surface and the substrate. A simple thermodynamic simulation shows that the temperature differential between the substrate growth surface and the growth electrode is determined by the thickness of the titanium layer. This facilitates the growth of nanotubes, as opposed to nanofibres with herring-bone or amorphous structures. The growth properties are discussed as a function of the bias voltage and hydrocarbon concentration. The heating during growth provided solely by the plasma is below 400°C and is dependent on the process conditions and the electrode configuration in the growth chamber. These conditions need to be taken into account when comparing processes across different growth methods and instruments. The novel approach based on the use of a thermal barrier ensures the synthesis of carbon nanotubes at room temperature substrate conditions, which can be attained with a suitable cooling scheme.