Ozonation of single-walled carbon nanotubes and their assemblies on rigid self-assembled monolayers

Ozonation of single-walled carbon nanotubes (O-3-SWNTs) produces oxygenated functional groups, e.g., carboxylic acid, ester, and quinone moieties, which can be removed from the SWNT surface by heating at 600-800 degreesC. The annealed SWNTs appear to be pristine. The electrical resistance of the O-3-SWNTs depends on the degree of oxidation and is about 202000 times higher than that of pristine SWNTs, owing to the deformation of the pi-conjugation structure along the tube. The O-3-SWNTs are easily dispersed in dimethylformamide (DMF) and show enhanced solubility in other polar solvents such as water and ethanol. The O-3-SWNT suspensions consist of individual and shortened tubes due to the separation of nanotube bundles and the shortening that results from oxidation. Toward fabrication of SWNT-based molecular electronic devices, two methods have been used to assemble the O-3-SWNTs on functionalized self-assembled monolayers (SAMs) of conjugated oligo(phenylene ethynylene)s. The first, termed "chemical assembly", is based on a condensation reaction between the carboxylic acid functionalities of O-3-SWNTs and the amine functionalities of SAMs to form amides. The results show that O-3-SWNTs coat the amino-terminated SAM with a high degree of surface coverage. The second method is based on physical adsorption via layer-by-layer (LBL) deposition with bridging of metal cations, i.e., Fe3+ on carboxylate-terminated SAMs or Cu2+ on thiol-terminated SAMs. The oxidatively shortened O-3-SWNTs are shown to be perpendicular to the surface with random adsorption of longer tubes. The patterned nanotube assemblies may be useful in hybridized electronic devices, where device functions can be modified by the orientation and stacking of SWNTs and the properties of the SAM.