Submicron Patterning of Iron Nanoparticle Monolayers for Carbon Nanotube Growth

We describe a method to reliably pattern monolayers of iron nanoparticle (FeNP) colloids into submicron features for growth of single-walled carbon nanotubes (SWNTs) by chemical vapor deposition. Our process results in very clean patterns that are readily imaged by atomic force microscopy, which has allowed the observation of nanoparticle size evolution before and after high-temperature nanotube growth. For our growth conditions, SWNTs grew only from nanoparticles smaller than ∼5 nm high. At the high growth temperature of 850 °C, nanoparticle sintering was clearly evident and had important effects on nanotube yield from the FeNP catalyst. The nanoparticle sintering and growth are drastically accelerated by brief reduction in H2, resulting in nanoparticles that were too large to catalyze SWNT growth. The results suggest that if ultimate control over SWNT diameters is to be achieved from patterned nanoparticle catalysts, it will be critical to control nanoparticle aggregation and sintering during SNWT growth.