Engineering preferential adsorption of single-walled carbon nanotubes on functionalized ST-cut surfaces of quartz

Horizontal alignment during synthesis of single-walled carbon nanotubes has been found experimentally along certain directions of well-defined quartz surfaces. The reasons for such alignment are here examined using first-principles computational analysis, as a function of structure and chemistry of the specific exposed facet, presence and location of OH and H functional groups, and degree of hydration of the surface. It is found that selective functionalization of low-coordinated surface sites may cause exposure of low-coordinated Si atoms that bond strongly to nanotube walls. On the other hand, saturation of low-coordinated oxygen also favors carbon nanotube adhesion to the substrate. As found previously on bare silica surfaces, a chirality preference is confirmed on functionalized surfaces toward zigzag over armchair nanotubes. Magnetization effects on the surface originated by the presence of adsorbed functional groups are found to enhance adsorption of arm-chair nanotubes compared to that on clean surfaces. On the basis of the findings, it is suggested that surfaces may be engineered to favor horizontal adsorption of specific chiralities along preferential directions.