Preferential forest assembly of single-wall carbon nanotubes on low-energy electron-beam patterned nafion films

With the aid of low-energy (500 eV) electron-beam direct writing, patterns of perpendicularly aligned single-wall carbon nanotube (SWNT) forests were realized on Nafion modified substrates via Fe3+-assisted self-assembly. Infrared spectroscopy (IR), atomic force microscopy (AFM) profilometry, and contact angle measurements indicated that a low-energy electron beam cleaved the hydrophilic side chains (-SO3H and C-O-C) of Nafion to low-molecular-weight byproducts that sublimed in the ultrahigh vacuum (UHV) environment exposing the hydrophobic Nafion backbone. Auger mapping and AFM affirmed that the exposed hydrophobic domains absorbed considerably fewer Fe3+ ions upon exposure to pH 2.2 aqueous FeCl3 solution, which yielded considerably less FeO(OH)/FeOCl precipitates (FeO(OH) in majority) upon washing with lightly basic DMF solution containing trace amounts of adsorbed moisture. Such differential deposition of FeO(OH)/FeOCl precipitates provided the basis for the patterned site-specific self-assembly of SWNT forests as demonstrated by AFM and resonance Raman spectroscopy.