Formation Of Single-Wall Carbon Nanotubes Forrest Assemblies On Metal Surfaces
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Formation Of Single-Wall Carbon Nanotubes Forrest Assemblies On Metal Surfaces Debjit Chattopadhyay, Izabela Galeska and Fotios Papadimitrakopoulos* Nanomaterials Optoelectronics Laboratory, Department of Chemistry, Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136. ABSTRACT Learning how to purify and manipulate single wall carbon nanotubes (SWNTs) presents a unique challenge in material science. The processing-related difficulties of these long nanofibers stem from their high aspect ratio, rigidity and the profound hydrophobic attractions along their tubular walls. Shortening them into discrete segments, with lengths from tens to hundreds of nanometers, presents a viable methodology to alleviate the shape-induced intractability. In addition, the metal-assisted self-organization of these nanosized objects into nano-forest geometries with dense perpendicular surface grafting, demonstrates that such nanosized objects hold significant promise for the development of nanoscale devices. This paper will present an extensive characterization of the topological characteristics of these assemblies, along with their surface coverage, growth characteristics and height fluctuation on iron hydroxide substrates. INTRODUCTION The growth of dense arrays of single-wall carbon nanotubes (SWNTs), aligned normal onto various substrates has been envisioned to enhance performance of various technologically important devices such as sensors,1-3field emitters,4,5and organic light emitting diodes.6-8 High temperature catalytic decomposition of hydrocarbon precursors on metal functionalized substrates have yielded such geometries, however, only multi-wall nanotubes (NTs) have been realized thus far.5,9 Drawing NTs suspension through a 0.2-µm-pore ceramic filter, while immobilizing the other end on a Teflon substrate, also produced vertically aligned geometries.10 Shortening SWNTs in an oxidizing environment,11 followed by chemical modifications of the carboxyl end-groups12, presents an alternative method to align the NTs perpendicular to the substrate. Short and long (tens of nm for the shortened SWNTs (s-SWNTs) to a few microns for pristine SWNTs and 1.3-1.4 nm in diameter) SWNTs have exhibited considerable affinity for amine functionalized substrates, although they tend to orient parallel to the substrate.13-15 Thiolfunctionalization of s-SWNTs resulted in better alignment on gold substrates, nonetheless, this system was plagued by low surface coverage and long adsorption times.12 In this paper, we present a methodology that yields dense s-SWNTs forest arrays onto an iron hydroxide surfaces, which can be produced on a variety of flexible substrates.16 Such metallorganic-assisted self-assembly process can be readily realized in non-aqueous media (i.e. DMF, THF, etc.), and also permits the growth of successive stacks of s-SWNTs, one on top of each other, in a layer-by-layer (LBL) assembly format. On the basis of this methodology, dense arrays of s-SWNTs-forest have been utilized in sharp
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