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.
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.
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.
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