How to switch from a tip to base growth mechanism in carbon nanotube growth by catalytic chemical vapour deposition

The catalytic growth of carbon nanotubes is performed at 580 °C with iron catalyst using a hot-wall CVD technique. It is shown that the growth mode can be switched from ‘tip’ to ‘base’ growth mode by an insertion of plasma pre-treatment of catalyst at room temperature before growth. To understand this phenomenon, the oxidation state of catalyst is compared using XPS before and after the pre-treatment. Growth mechanisms induced by different oxidation states of catalyst are proposed to explain the switching of the growth mode. A thermodynamic calculation shows the relation between induced growth mode and resulting CNT diameter.