Preparation of Horizontal Single-Walled Carbon Nanotubes Arrays

The synthesis of SWNTs has achieved great success with the development of synthetic methodologies. From the viewpoint of exploiting the exceptional electrical properties of single-walled carbon nanotubes (SWNTs) in advanced applications, one of the most difficult challenges is how to assemble the SWNTs with high degrees of alignment and purity in electronic conducting (mainly semiconducting) behavior into functional nanodevices. Numerous approaches have been developed to reach this goal, which could be divided into two categories. One is direct preparation of SWNT arrays on the substrate, and the other is self-assembly of pre-sorted SWNTs from solution. The former one obtains SWNT arrays via chemical vapor deposition (CVD) growth, with the sorting realized by either selective growth or post-growth treatment; the latter one assembles SWNT into arrays from solution, with the sorting process occurring before the aligning process in most cases. This review will highlight both in situ and post-synthetic approaches for preparing samples of aligned arrays of SWNTs with well-defined electronic properties-including the working mechanism for directional growth of SWNTs, growth/sorting methods like catalyst engineering, cloning/cap engineering, in situ etching, and ex situ selective removal/etching for surface-grown SWNT sample, and assembling technologies from SWNT solution such as dielectrophoresis, adsorption on lithographically patterned and/or chemically functionalized substrates, Langmuir-Blodgett and Langmuir-Schaefer techniques, and evaporation-driven self-assembly-and research efforts towards direct growth of arrays of complex SWNT structures.