Graphoepitaxial effect in the guided growth of SWNT arrays on quartz

Researchers have demonstrated that the alignment of single-walled carbon nanotubes (SWNTs) on the surface of the single crystal substrate is due to guided growth along either step edges (graphoepitaxial) or certain directions in the atomic lattice (epitaxial), with only one of the two alignment modes predominating in different research systems. For the SWNTs grown on a quartz surface, the growth of a perfectly aligned array and other shapes were induced by the epitaxial effect. Here we report the finding that water vapor introduced during the catalyst annealing process can change the alignment mode of the SWNTs on the quartz surface by modifying the surface status of both the catalyst and the substrate. Zigzag shaped nanotube arrays can be obtained by enabling both alignment modes simultaneously through adjusting the water vapor concentration, changing the oxidation state of the metal catalyst and/or modifying the morphology of the substrate surface. These findings provide important insights into the mechanism of guided growth of complex nanotube shapes, for potential applications including electronics, photodetection, sensing, and in other devices.