Researchers Investigate Healing of Nanotube Defects

A collaborative study by researchers from Hong Kong Polytechnic, Rice University and Tsinghua University shows that it is possible to build single layered carbon nanotubes measuring 1 m in length. This is significant to researchers who are constantly trying to build advanced materials that could change the landscape of power distribution systems.

Self-healing of nanotubes

Defects in nanotube formation typically consist of structures with too few or too many atoms. These topological defects appear as pentagons or heptagons of carbon atoms as opposed to the desired structure of hexagons. These defects alter the electrical and physical properties of nanotubes. The researchers found that a combination of optimum conditions, specifically temperature, heals the defect by directing stray atoms to form the desired hexagon structure. The energy required for the healing was analyzed using density functional theory. The presence of defects was found to be less than one-ten billionth under desirable conditions.

Nanotubes are synthesized in furnaces by adding carbon atoms at the rate of millions per minute to a catalyst such as iron, nickel and cobalt. Due to the rapid rate of addition, mistakes tend to happen in structure formation. Having too few or too many atoms would affect the way other atoms arrange themselves in the chain, thereby turning the nanotube into a cone (pentagon defects) or horn (heptagon defects). Also, the defects cannot be healed if they become a part of the nanotube wall. Calculations showed the researchers that defects occur in pentagon-heptagon pairs and never in isolation. This means that a quick fix can be facilitated by simply moving an atom from the heptagon to the pentagon. The researchers found iron to be the best catalyst for healing and established that a temperature of 930 kelvins was the optimum temperature to facilitate natural healing. They also demonstrated through simulation that a perfect nanotube could be achieved via slower growth rate of about 1 µm/sat 700 kelvins.



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