Chiral‐selective etching effects on carbon nanotube growth at edge carbon atoms

Abstract

Chemical vapor deposition (CVD) utilizing metal cluster nanoparticle catalysts is commonly used to synthesize carbon nanotubes (CNT), with oxygen-containing species such as water or alcohol included in the feedstock for enhanced yield. However, the etching effect of these additives on the growth mechanism has rarely been investigated, despite evidence suggesting that etching potentially affects the chirality distribution of product CNTs. We used quantum chemical methods to study how water-based etchant radicals (OH and H) may enhance the chiral selectivity during CVD growth using CNT cap models. Chemical reactivities of the caps with the etchant radicals were evaluated using density functional theory (DFT). It was found that the reactivities on the cap edges correlate with the chirality of the caps. These results suggest that proper selection of etchant species can provide opportunities for selective chirality control of the product CNTs.

Scalable growth of single-walled carbon nanotubes with a highly uniform structure

“…Kimura et al recently calculated the reaction energy of an OH radical (ΔE OH ) for different chiralities and proposed that there is a selective removal of low chiral angle tubes in the presence of OH due to a high ΔE OH . 31 This prevents the growth of nanotubes in a wide distribution of chiral angles and makes the distribution narrow at high chiral angles. Similarly, the addition of water selectively removed the small diameter (less than 1 nm) SWCNTs as shown in diameter distribution (Fig.…”

Contrasting H-Etching to OH-Etching in Plasma-Assisted Nucleation of Carbon Nanotubes

“…The dual role of hydrogen has already been explored in several previous studies, both experimental − and computational , and is reasonably well understood. Hydrogen can enhance or prevent the CNT growth regarding its concentration in the system .…”

“…16 As a result, the net growth kinetics of the CNTs can be understood as a balance between growth and removal processes. 14−17 The dual role of hydrogen has already been explored in several previous studies, both experimental 18−20 and computational 17,21 and is reasonably well understood. Hydrogen can enhance or prevent the CNT growth regarding its concentration in the system.…”

“…In the same vein as with the H 2 species, a number of studies have shown the usage OH or O species as a way to selectively grow semiconducting CNTs. ,− Most often, the added water vapor in a CVD setup decomposes to form OH radicals. But also species such as isopropyl alcohol and carbon monoxide have proven to give similar results. , These oxygen-containing species are shown to mostly etch semiconducting nanotubes during the growth stage.…”

Universal map of gas-dependent kinetic selectivity in carbon nanotube growth

“…So far, we have discussed the carbon supply/removal for catalysts. One might wonder if the susceptivity to carbon removal is determined by chirality (n, m) [40], but that is excluded by the widely distributed γ e /γ C (0.15-0.68) within the (12,8) nanotubes (Fig. S11).…”