Influences of organometallic polymer-derived catalyst dispersion on SWNT growth

Catalyst formation kinetics of a ferrocene-containing homopolymer, polyferrocenylethylmethylsilane (PFEMS), is investigated as it relates to the catalysis of single walled carbon nanotubes (SWNTs) through a chemical vapor deposition (CVD) process. The formation and efficiency of the PFEMS-based iron catalyst is compared with that of the corresponding polystyrene (PS)-b-PFEMS diblock copolymer. The PFEMS homopolymer contains 23 wt % iron, while PS-b-PFEMS, with a 25 vol % PFEMS content, is only 6% iron. Despite its lower iron content, spin-cast PS-b-PFEMS films on SiO₂/Si substrates produce more active iron sites than spin-cast PFEMS films during CVD growth of SWNTs. This is related to the self-assembly of the block copolymer, where PFEMS domains are well dispersed in the PS matrix, which degrades at a CVD temperature of 920°C to leave catalytically active elemental iron behind. On the contrary, the pure PFEMS films contain a high percentage of iron and silicon, which tend to transform into ceramic-coated iron at this high temperature, thus rendering the iron inactive towards SWNT growth.