Growth Aspects of Iron-Filled Carbon Nanotubes Obtained by Catalytic Chemical Vapor Deposition of Ferrocene

The thermal decomposition of ferrocene combined with an Fe-catalyst nanostructuring on an oxidized Si
substrate is investigated in the temperature range of 1015-1200 K. The optimal growth conditions for aligned
and homogeneous Fe-filled carbon nanotubes are found at 1100 K. From the nanostructures the corresponding
growth rates are determined, and the activation energy of carbon diffusion is calculated to be ∼0.4-0.5
eV/atom. Further, the Fe particle size on the substrate after pretreatment in different gas atmospheres is studied
and compared with the nanotube dimensions. With these data the diffusion coefficient of carbon in the catalyst
particle amounts to 0.5-1.5 × 10-9 m2/s. Such values prove the formation of liquid catalyst particles during
the nanotube growth. Mo¨ssbauer spectroscopy was utilized to analyze and quantify the different Fe phases.
In conclusion we propose a simple base-growth model from the experimental results.