Inorganic tubes get smaller than ever.

Researchers have created the smallest stable, freestanding nanotubes yet. The molybdenum disulfide tubes, each less than 1 nanometer (nm) in diameter, could eventually become components of novel materials, electronic devices, and batteries, say the scientists.

Previous experiments have produced tubes of carbon just 0.4 nm wide, but those structures were created in the confined spaces of zeolite crystals or larger carbon nanotubes (SN: 12/16/00, p. 398). The new, inorganic tubes form in bundles from which the researchers can remove individual tubes, says Dragan Mihailovic of the Jozef Stefan Institute in Ljubljana, Slovenia, whose team reports the structures in the April 20 SCIENCE.

The researchers, from the Jozef Stefan Institute and the Ecole Polytechnique Federale de Lausanne in Switzerland, grew the tubes by heating molybdenum disulfide powder with iodine and a catalyst, carbon-60, for about 3 weeks. The researchers then washed away the carbon. They found that about 15 percent of the original material had become molybdenum disulfide nanotubes, held together by iodine.

These structures, which can be hundreds of micrometers long, are stable at high temperatures, resist friction, and can be separated mechanically, says Mihailovic. The tubes' uniform width gives them an edge over carbon nanotubes in possible applications, he adds, since carbon nanotubes are hard to grow with consistent diameters.