Nanotechnologists edge towards their Holy Grail of controlled fabrication.

Discovery of bundles of carbon nanotubes that all spiral with the same angle of twist could help researchers to confront the major challenge of nanoelectronics by guiding development of controlled production methods, according to Jean-François Colomer and his team at Laboratoire de Physique du Solide in Brussels.

Electron microscopy revealed the identical helicity of the bundles of double-walled carbon nanotubes (DWNTs), which marked the first time such a feature had been observed, says Colomer.

DWNTs, which comprise two concentric cylindrical grapheme layers, are significant because they bridge the gap between single and multi-walled tubes, he notes. They allow researchers to investigate interactions between the inner and outer layers, he adds.

Identical inner and outer layers support the idea that bundles of tubes can grow by what is know as a 'collective growth' mechanism. It is hard to imagine, argues Colomer, that identical DWNTs grow individually from different catalyst nanoparticles of different shapes and sizes, and then congregate in perfectly arranged bundles. It is far more likely, he suggests, that all the tubes grow together from a single catalyst particle.

Such a 'collective growth' mechanism raises interesting questions and possibilities, comments Professor C. N. R. Rao, chairman of the chemistry and physics of materials unit at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore. 'The observation of well-crystallised double-walled nanotube bundles is noteworthy and constitutes an important addition to the arsenal of novel one-dimensional nano objects,' says Rao.

Helen Fletcher