Naoki Ishigami

Crystal plane dependent growth of aligned single-walled carbon nanotubes on sapphire.

On single-crystal substrates, such as sapphire (alpha-Al 2O 3) and quartz (SiO 2), 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 SiO 2. 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.

Competition and cooperation between lattice-oriented growth and step-templated growth of aligned carbon nanotubes on sapphire

The authors study the growth mechanism of single-walled carbon nanotubes (SWNTs) horizontally aligned on A-plane single crystal sapphire (112¯0) by making the controlled step/terrace structure. SWNT growth direction was sensitive to the surface geometry of the sapphire, and there was competition between two growth modes, lattice-oriented growth and step-templated growth. On the substrate with single-atomic steps, SWNTs aligned parallel to the [11¯00] direction as dominated by the lattice-oriented growth mode, while SWNTs aligned along the step edges when the double-atomic or higher steps were formed. Our findings have potential for the fabrication of designed architecture of SWNTs by combining these two growth modes.

Unidirectional growth of single-walled carbon nanotubes.

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.

Horizontally-Aligned Single-Walled Carbon Nanotubes on Sapphire: Growth Mechanism and Characterization

In this paper, the authors reported the recent progress on the growth and characterization of aligned single-walled carbon nanotubes (SWNTs) on sapphire substrate. They introduced the position-and direction-controlled growth of SWNTs on a sapphire substrate and showed the highly-aligned SWNTs grown from the Fe-based wet catalyst patterned with the aid of an electron beam lithography technique. The catalyst patterning was found to give much better alignment than those grown on the homogeneously deposited catalyst. This is because the non-patterned area of the sapphire is kept clean without the catalyst contamination. To monitor the growth period chemical vapor deposition (CVD) is used with the combination of Raman mapping measurements.