Hexahedral nanocementites catalysing the growth of carbon nanohelices
by J.H. Xia, X. Jiang, C.L. Jia, and C.Dong
The formation mechanism of carbon nanohelices grown on iron needles by microwave plasma assisted chemical vapour deposition was studied by means of transmission electron microscopy and scanning electron microscopy.
The catalyst assisting the helix formation was identified to be the single crystalline cementite Fe3C particle at the tip of each carbon nanohelix. The Fe3C particles show the general morphology of a hexahedron with six different crystallographic planes as the surface planes.
The different catalytic effect of different crystallographic surface planes produces an anisotropic growth on the front surface of the carbon nanostructure, which results in a rotation of the cementite particles. The rotating particles atalyse the growth of the carbon nanostructure in a helical way.
Further reading: Applied Physics Letters 92 (2008) 063121.