Patterned forest-assembly of single-wall carbon nanotubes on gold using a non-thiol functionalization technique

Abstract

An approach for non-thiol functionalization of single-wall carbon nanotubes (SWNTs) on gold was demonstrated via an Fe³⁺-assisted self-assembly technique. Upon immersion of gold into a pH 2.2 aqueous FeCl₃ solution, FeCl₃ oxidized the gold surface, due to the aqua regia effect, resulting in the formation of films of FeO(OH)–FeOCl crystallites. Subsequent immersion into a SWNT dimethylformamide (DMF) dispersion led to needle-like forest assemblies of SWNTs based on metal-assisted chelation and electrostatic interactions. Two approaches for surface patterning of these SWNT forests were investigated based on shadow-mask evaporation and conventional photolithographic lift-off to localize FeO(OH)–FeOCl/Au composite pads on Si substrates. The strong adhesion of Fe³⁺ ions onto silica surfaces can be partially overcome by repeated washes in aqueous HCl solution (pH < 4), and completely overcome by photoresist-assisted protection which prevents unwanted Fe³⁺ ions from complexing with the unexposed silica surfaces. Such patterned Fe³⁺-functionalized Au structures provided the basis for the site-specific forest-assembly of SWNTs as characterized by atomic force microscopy (AFM) and resonance Raman spectroscopy.