Image: JOHN CUMINGS/University of California, Berkeley

The minuscule size of carbon nanotubes¿hollow cylinders measuring a few billionths of a meter wide¿can boggle the mind. Now picture the straws nestled inside one another like Matryoshka dolls, with the inner set of tubes sliding in and out a billion times a second. In fact, according to a report published in the January 28th edition of Physical Review Letters, scientists could conceivably fashion just such a gigahertz oscillator¿one that could aid in the creation of nanomechanical devices.

Previous work by John Cumings and Alex Zettl of the University of California, Berkeley, had shown that prying open one end of such a multiwalled nanotube transformed it into a telescoping tube: the inner tubes slid in and out of the surrounding straws with very little friction (see image). In the new study, Qing Jiang of the University of California, Riverside and Quanshui Zheng of Tsinghua University in Beijing modeled the sliding action of a tube with two open ends. Their calculations show that if the inner core were pulled out of such a tube, it would not only retract back into the center of the tube, but it would also continue right out the other end. Nearly negligible friction between the tubes would enable a breakneck gigahertz oscillation frequency, the investigators report. And shorter tubes could move at even greater speeds.

Jiang suggests that the tubes may one day make their way into fiberoptic systems as ultrafast optical filters. Before that can happen, however, researchers will have to figure out exactly how to excite the oscillator and how to couple it with the rest of the nanoscopic device. "The actual implementation of this coupling," the authors conclude, "represents another challenge in development."