(8c) Mechanism of Growth of Vertically-Oriented Single-Walled Carbon Nanotubes on Surface: Topologically Confinement Induced Synchronized Alignment and Growth
Growth mechanism of Vertical Alignment of Single-walled carbon nanotubes on Si wafer is investigated by combination of information probed with polarized X-ray, secondary electron and laser. Angle-resolved x-ray absorption near edge structure (XANES) study was performed on vertically aligned single-walled carbon nanotubes (or V-SWNT) which was produced by unique atmospheric or pressurized CVD method developed in our group. Deviation of fitted C-C π* and σ* transition peaks from experimental data at low angles indicates existence of random orientation of SWNT bundles on the top of forest sample. A time evolved process of growth of V-SWNT on silicon substrate was examined by scanning electron microscopy (SEM) and resonant Raman spectroscopy. An introduction period in the beginning of V-SWNT growth is clear, during which a thin layer of randomly oriented single-walled carbon nanotubes (or Crust) is formed. Both studies lead to crucial role of formation of crust which guides and aligns uniform growth of SWNT bundles perpendicular to substrate. Furthermore, several examples of different forms of SWNTs grown on surface, including flat and rough surface, are given to demonstrate effect of crust structure on the topology of SWNTs.