Fluorine atoms used to cut nanotubes. (Nanotubes).

Since they were first made in 1991, microscopic tubes of carbon atoms have become the focus of research aimed at developing future nanoscale electronics, machines, and drug-delivery systems. To realize such dreams, some scientists are adding groups of atoms to the carbon nanotubes' exteriors that enable the tubes to dissolve in water, join together chemically, or otherwise interact with various materials.

One of those techniques has yielded an unexpected result that could improve the nanotubes for some uses, reports Zhenning Gu of Rice University in Houston. After adding fluorine atoms to the nanotubes' surfaces, Gu and her colleagues found that heating the 1-micrometer-long tubes to high temperatures drove off the fluorine and cut the cylinders into short pieces. Most of these segments were less than five percent the length of the original tube.

These pieces have been sorted by size in a centrifuge, says Rice's John Margrave. Such short tubes might be useful as uniform, rigid parts in new electronics or as reinforcing filler in composite materials for structures ranging from rockets to tennis rackets.

For several years, the research team has been using fluorination as a chemical step toward creating designer nanotubes. The fluorine atoms bond only weakly to the carbon nanotubes, permitting the scientists to replace them in a second step with other atoms or molecular fragments that could give the nanotubes specific properties.

But when Gu and her colleagues instead simply heated their fluorinated nanotubes to 800 [degrees] C, the fluorine atoms left and the tube broke into shorter segments, which were visible with atomic force microscopy.

By chemically modifying these rigid segments, the researchers might be able to create a set of tiny tubes that will automatically assemble into specific three-dimensional nanoscale architectures. --J.G.