"We discovered that very long 1D linear carbon chains consisting of more than 100 carbon atoms could be inserted into multiwalled carbon nanotubes to form a new 1D carbon allotrope - carbon nanowires," Yoshinori Ando of Meijo University told nanotechweb.org. "These carbon nanowires are composed of both sp2 and sp bondings, although carbon allotropes are usually based on one of the three types of carbon bonding: sp3 (diamond), sp2 (graphite, fullerenes and nanotubes) and sp bonding (carbon chain and carbyne)."

Ando and colleagues grew the nanowires by dc arc discharge evaporation of pure carbon electrodes in hydrogen gas - the nanowires formed in the cathode deposits. High-resolution transmission electron microscopy and Raman scattering studies indicated that the carbon nanowires were made up of a multiwalled carbon nanotube, containing sp2 bonding, with a 1D linear carbon chain (with sp bonding) inside its innermost 0.7 nm diameter tube.

"Carbon nanowires have possible uses as nose tips for space shuttles, materials for ultrastrong fibres, friction-free rotational nanobearings, probes, emitters, and even highly coherent point sources of monochromatic electron beams," added Ando. "Moreover, if carbon chains can be inserted into single-walled carbon nanotubes to form the smallest possible carbon nanowires, it will lead to the achievement of the smallest metal-metal junction, metal-semiconducting junction and diodes in nanoelectronics."

Now, the researchers are working on the mass-production of carbon nanowires, and are trying to insert carbon chains into single-walled carbon nanotubes.

The scientists reported their work in Physical Review Letters.