Molecular-resolved imaging of conductive polymer self-organization at single-walled carbon nanotube interfaces

Molecular-resolved real-space images of self-assembled structures of the conductive polymer regioregular poly(3- hexylthiophene) (rrP3HT) on single-walled carbon nanotubes (SWNT) were obtained using scanning tunneling microscopy (STM). The STM images revealed that the adsorbed polymer typically formed a 10 nm thick coating on SWNT's. This is in agreement with transmission electron microscopy (TEM) results for drop-cast composite films that provided strong evidence that SWNTs were isolated in a polymer matrix and coated with rrP3HT multilayers. A 10 nm thick deposit corresponds to a coating of ~25 layers of polymer on SWNT, assuming that π-π interactions between rrP3HT layers determine deposition and that the underlying SWNT directs the polymer self-assembly process. STM measurements of adsorbed monolayers and multilayers of rrP3HT on SWNT surfaces were compared to rrP3HT monolayer and multilayer deposition on highly ordered pyrolytic graphite (HOPG) surfaces. The average inter-lamellar distances of adsorbed polymer was greater for both rrP3HT monolayer and multilayer films adsorbed onto the curved surfaces of SWNTs than on the flat surfaces of HOPG samples. Analysis of STM images yielded the interchain spacings of adsorbed macromolecules, d cc = 1.55 - 1.68 ± 0.02 nm. The polymer was observed to wrap around some SWNTs at an angle with respect to the SWNT long-axis, which indicated that the rrP3HT self-assembly is hierarchical. The conductive polymer's deposition appears to occur with epitaxy and is directed by the underlying SWNT chiral structure.