Single-step CVD growth of high-density carbon nanotube forests on metallic Ti coatings through catalyst engineering

We demonstrate the direct growth of carbon nanotube (CNT) forests on metallic titanium (Ti) coatings by single-step chemical vapor deposition. This was achieved by catalyst engineering, which involves a novel design of Fe/Ti/Fe nanostructure sputtering coated on SiO2/Si wafers. The Fe sublayer, an additional catalyst added to the conventional catalyst/support design, plays a key role in the growth of well aligned and highly dense CNT forests. Depth profile analysis of substrates by secondary ion mass spectroscopy shows that the Fe sublayer is thermally unstable at the Ti/SiO2 interface under the growth conditions. Catalyst diffusion back to the surface from the Fe sublayer is much more significant than down towards the SiO2/Si substrate from the surface Fe layer. This makes it possible to minimize the thickness of surface catalyst layer, and ensures the growth of well aligned and high-density CNT forests on Ti coatings. The filling factor of nanotubes on the substrate after liquid-induced compaction can be dramatically increased up to 57%, leading to an estimation of the areal density of around 1012 cm−2.