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HERE’S another one for the list of miraculous things you can do with carbon nanotubes: blow gas over them and you can generate electricity.

Ajay Sood of the Indian Institute of Science in Bangalore and colleagues reported last year that pushing water through carbon nanotubes generates electricity (New ÐÓ°ÉÔ­´´, 25 January 2003, p 15). Now they have discovered that gas has a similar effect. For instance, argon flowing at 11 metres per second over single-walled carbon nanotubes inclined at an optimal angle of 45 degrees generated 5.6 microvolts across the ends of the nanotubes. Oxygen and nitrogen flowing past other materials such as copper and some semiconductors also generated voltages (Physical Review Letters, vol 93, p 86601).

When the gas strikes the base of the inclined surface, it is momentarily halted. As it tries to flow up the slope a pressure gradient is set up, which in turn causes the temperature of the gas to change as it moves. That is when something called the Seebeck effect — in which a temperature gradient across a solid generates a voltage — kicks in, and a voltage appears across the sample.

Even human breath blown at an inclined sample of carbon nanotubes produced a measurable result of several microvolts.