van der Waals interaction controls orientations of single-walled carbon nanotubes on quartz during growth

Single-walled carbon nanotubes (SWNTs) possess extraordinary electrical and mechanical properties, with many possible applications in electronics and materials science. Dense, horizonally aligned arrays of linearly configured SWNTs represent perhaps the most attractive and scalable way to implement this class of nanomaterial in practical systems. Recent work shows that templated growth of tubes on certain crystalline substrates (e.g. quartz) yields arrays with the necessary levels of perfection, as demonstrated by the formation of devices and full systems on quartz. To study the alignment (orientation preference) of SWNTs on quartz substrate, we established a mechanics model for the van der Waals interaction between SWNTs and quartz substrate. This model, together with experiments, have shown that the van der Waals interaction between SWNTs and quartz substrate can account for nearly all aspects of alignment of SWNTs on quartz with X, Y, Z, and ST cuts, as well as quartz with disordered surface layers. It is shown that larger SWNTs have worse alignment than smaller ones. The crystalline quality of the quartz surface is paramount to the alignment, while small features of surface relief or general surface roughness are relatively unimportant. These findings provide important insights into methods for guided growth of SWNTs, and possibly other classes of nanomaterials, for applications in electronics, sensing, photodetection, light emission, and other areas. 
This work appeared in Nano Letters: Alignment Controlled Growth of Single-Walled Carbon Nanotubes on Quartz Substrates