Nanotechnology: stable metal nanowires with diameters of single atoms inside carbon nanotubes

Wires with atomic dimensions are interesting materials for nanoscopic electronic components in future. Such fine wires have completely new electronic properties. Apart from the fact that metalllic nanowires are not that easy to produce, the main problem is their high chemical reactivity: they oxidise easily in air and are not stable. Japanese research scientists headed by R. Kitaura and H. Shinohara have now developed a new method that is simple and produces stable nanowires at the same time: they deposit the metal atoms inside carbon nanotubes. The scientists report in the magazine Angewandte Chemie that metal wires consisting of atoms strung together individually are created, which are protected so well by their casing that they remain stable in the long term too.

The manufacturing process consists simply of heating carbon nanotubes and a metal powder in a vacuum. It works for all metals that switch to the gas phase at relatively low temperatures, such as Europium, Samarium, Ytterbium and Strontium. The metal atoms fill the cavity inside the carbon nanotubes almost completely. With Europium and carbon nanotubes that have an internal diameter of about 0.76 nm, the research scientists succeeded in obtaining wires that consist of only one single chain of strung-together atoms. This first truly one-dimensional nanowire was still stable even after a month in air.

By using carbon nanotubes with different internal diameters, it was possible to produce ultrathin wires with different diameters, e.g. from two or four atomic chains. There were considerable differences in the electronic and magnetic properties of the atomic wires compared with the macroscopic Europium crystal.

The nanowires are an ideal model for studying one-dimensional phenomena. The research scientists now intend to investigate the properties of the wires with respect to their suitability as "cabling" for nanoelectronic components.

Source: Hisanori Shinohara et al.: High-Yield Synthesis of Ultrathin Metal Nanowires in Carbon Nanotubes; Angewandte Chemie 2009, 121, No. 44