Length-Selective Chemical Assembly of Vertically Aligned Carbon Nanotubes

Many potential applications of carbon nanotubes (CNTs), ranging from electronics and optoelectronics to biology and medicine, require length-controlled and well-aligned CNTs on surfaces. In this work, the length selectivity behavior of wet-dispersed CNTs on gold functionalized surfaces is investigated, providing new mechanistic insights into the length-selective process that occurs upon chemical assembly. A combination of experimental evidence derived from atomic force microscopy and plane and cross-sectional transmission electron microscopy implies a length-selective deposition of CNTs on the functionalized gold surface. All the solutions containing either a high distribution of longer or shorter CNTs lead to the selective formation of vertically aligned carbon nanotubes with average lengths of 10.6 ± 3.1 nm. It is postulated that such length-selective phenomenon is not only driven by diffusion mechanisms but also is governed by the interactions between the CNTs and the chemically functionalized surfaces. The orientation of the initial attached nanotubes, which act as nucleation sites in the CNT assembly process, is proposed to dictate the CNT length distribution on the surface and be dependent on the packing and ordering of the molecules on the functionalized surface.