Unidirectional growth of single-walled carbon nanotubes (SWNTs) was achieved using the patterned Co-Mo salt catalyst on the r-plane sapphire substrate. This is in marked contrast with the SWNTs grown on an a-plane sapphire and ST-cut quartz, on which the SWNTs grew bidirectionally. This new growth mode is not dependent on the gas flow and attributed to the asymmetric surface atomic arrangement of the sapphire surface.
Direction-controlled growth of horizontally aligned single-walled carbon nanotubes (SWNTs) on r-plane sapphire substrates and their alignment mechanisms are demonstrated. On a flat r-plane substrate, anisotropic nanotube−substrate interaction is known to align SWNTs parallel to the [11̅01̅] direction of the sapphire. We find that the introduction of a slight miscut (−1° inclined to the [11̅01̅] direction) on the substrate changed the SWNT growth direction by 90°, aligning perpendicular to the [11̅01̅] direction. This dramatic change of the growth direction is explained by the contribution of newly proposed one-dimensional surface atomic rows and/or atomic steps appeared on the r-plane. Annealing the substrate in hydrogen atmosphere prior to SWNT growth recovers the original nanotube growth direction, while annealing in air deteriorates the alignment. The direct growth of an orthogonally aligned SWNT array is achieved through optimized surface treatment. Site-selective directional control of aligned SWNTs is also demonstrated by applying hydrogen annealing to the miscut substrate whose surface is partially covered with SiO2. Our study gives insights into the alignment mechanism on single crystal substrates and offers a new means to assemble SWNTs for advanced integrated structures.
Bending of horizontally aligned single-walled carbon nanotubes (SWNTs) was achieved on surface engineered single-crystal sapphire (α-Al2O3). The SWNTs grown on the r-plane sapphire are aligned along the specific crystallographic [11̅01̅] direction due to the lattice-oriented growth, and we created artificial step structures perpendicular to this SWNT growth direction. These steps changed the nanotube growth direction from the [11̅01̅] to the step direction with the bending angle of nearly 90°. Effects of the bending structure on electron transport property were studied. Our approach to combine the lattice-oriented growth with the step-templated growth will offer a new route toward the growth of two-dimensionally controlled SWNT architectures for future nanoelectronics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.