Reactions Between Carbon Species and Tube Caps Affect Carbon Nanotube Growth and Electronic Properties

Single-walled carbon nanotubes (SWCNTs) are versatile nanomaterials made of rolled-up honeycomb-like sheets of carbon atoms. Depending on the direction and degree of twisting of these sheets, nanotubes can behave as metals or semiconductors, which is a potential boon for the development of ultrasmall electromagnetic devices. However, the exact mechanism that controls this twisting, known as chirality, has so far eluded materials scientists.

Now, using quantum calculations, a team led by Man-Fai Ng and Shuo-Wang Yang from the A*STAR Institute of High Performance Computing in Singapore has revealed the role of single carbon atoms and carbon–carbon (C2) dimer molecules in the ‘growth’ mechanism of chiral SWCNTs.

During the synthesis of SWCNTs, nanotubes are often capped by hemispherical arrays of pentagonal and hexagonal carbon rings. As nanotube caps have an important role in determining chirality, Yang and his team undertook a systematic approach to determine how the ‘armchair’ and ‘near-armchair’ types of caps evolve during SWCNT growth upon interacting with single carbon atoms and C2 dimers without catalysts.

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