Substrate characteristics beneath self-aligned carbon-nanotube forests

The catalyst has been examined before and after heating as well as after forest removal. This has revealed the importance of FeO and an additional role for a SiO2 buffer layer in the production of higher-quality faster-growing carbon-nanotube (CNT) forests. Our results, together with the literature, show that oxidation during heating (even when an inert gas is used) breaks up the Fe layer into small Fe2O3 islands. A suitable SiO2 buffer layer (either deposited or formed during the process) acts to inhibit Fe2O3 reduction past FeO, even in the presence of hydrogen from catalytic breakdown of the hydrocarbon during CNT growth. It is suggested that FeO is a more active catalyst than Fe and is more strongly bound to the surface. The interaction appears crucial for faster-growing, self-aligned forests and also for avoiding tip growth, disoriented layers, and included metal particles, which would be toxic in biomedical applications. (C) 2008 American Institute of Physics.