Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

10j 1 Introduction
Figure 1.8 (a) Schematic illustration of vapor–liquid–solid
nanowire growth mechanism including three stages: (I) alloying,
(II) nucleation, and (III) axial growth. The three stages are
projected onto the conventional Au–Ge binary phase diagram
(b) to show the compositional and phase evolution during the
nanowire growth process. Reproduced with permission from [49].
Copyright Ó (2001) The American Chemical Society.
the substrate. It differs distinctly from PVD techniques that involve no chemical
reactions during deposition. CVD has found widespread industrial applications
for the deposition of thin films and coatings due to its simplicity, flexibility, and low
cost. Moreover, CVD has the ability to produce high purity ceramic, metallic and
semiconducting films at high deposition rates. CVD is a versatile and cost-effective
technique for CNTsynthesis because it enables the use of a feedstock of hydrocarbons
in solid, liquid or gas phase and a variety of substrates, and permits the growth of
nanotubes in the forms of powder, thin film or thick coating, randomly oriented or
aligned tubes. The process involves the decomposition of hydrocarbon gases over
supported metal catalysts at temperatures much lower than the arc discharge and
laser ablation. The type of CNTs produced in CVD depends on the synthesis
temperatures employed. MWNTs are generally synthesized at lower temperatures