Crystal Plane Dependent Growth of Aligned Single-Walled Carbon Nanotubes on Sapphire

On single-crystal substrates, such as sapphire (α-Al2O3) and quartz (SiO2), single-walled carbon nanotubes (SWNTs) align along specific crystallographic axes of the crystal, indicating that the SWNT growth is influenced by the crystal surface. Here, we show that not only the orientation, but also the diameter and chirality of SWNTs are affected by the crystal plane of the sapphire substrate. The aligned SWNTs grown on the A- and R-planes of sapphire have narrower diameter distributions than randomly oriented tubes produced on the C-plane sapphire and amorphous SiO2. Photoluminescence measurements reveal a striking difference between the aligned SWNTs: near-zigzag tubes are observed on the A-plane and near-armchair tubes on the R-plane. This study shows the route for the diameter and chirality control of SWNTs by surface atomic arrangements of a single-crystal substrate

Orthogonal Growth of Horizontally Aligned Single-Walled Carbon Nanotube Arrays

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

Unidirectional Growth of Single-Walled Carbon Nanotubes

Unidirectional Growth of Single-Walled Carbon Nanotube

Visualization of Horizontally-Aligned Single-Walled Carbon Nanotube Growth with ¹³C/¹²C Isotopes

Horizontally aligned growth of single-walled carbon nanotubes (SWNTs) on single-crystal surfaces has attracted great interest in terms of nanoelectronic applications, but their growth mechanism is not fully understood. We report on the 13C/12C isotope-labeled growth of SWNTs on a sapphire surface to visualize their growth process. Switching carbon feedstock from 13CH4 to 12CH4 during SWNT growth induces a gradient distribution of the carbon isotopes along the tube axis. From the Raman mapping analysis, we succeeded to observe the gradual change in the isotope distribution of individual SWNTs. The results indicate the base-growth mode for the horizontally aligned SWNTs, which suggests that nanotube−sapphire interaction is essential to alignment. This method offers a unique technique to analyze the nanotube growth mechanism and kinetics