Preferential Forest-assembly of Single-Wall Carbon Nanotubes on Low-energy Electron-beam Patterned Nafion Films

TL;DR

This study demonstrates a method to pattern aligned single-wall carbon nanotube forests on Nafion substrates using low-energy electron-beam modification, which alters surface chemistry to control nanotube assembly.

Contribution

It introduces a novel electron-beam patterning technique that selectively modifies Nafion to enable site-specific self-assembly of SWNT forests.

Findings

Electron-beam cleaves Nafion's hydrophilic groups, exposing hydrophobic regions.

Patterned Fe3+ absorption leads to localized FeO(OH)/FeOCl precipitate formation.

SWNT forests are successfully assembled on patterned Nafion surfaces.

Abstract

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 low-energy electron-beam cleaved the hydrophilic side chains (-SO3H and C-O-C) of Nafion to low molecular byproducts that sublimed in the ultra-high vacuum (UHV) environment exposing the hydrophobic Nafion backbone. Auger mapping and AFM microscopy affirmed that the exposed hydrophobic domains absorbed considerably less Fe3+ ions upon exposure to pH 2.2 aqueous FeCl3 solution, which yield 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.