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July 21st, 2008

Nanotube 'springboard' weighs bouncing atoms

Abstract:
A tiny springboard constructed from a carbon nanotube can weigh individual atoms as they fall onto its surface. The device could replace high-resolution mass spectrometers, which tend to destroy the samples they weigh.

Resonators, materials that naturally oscillate strongly at certain frequencies, help to enhance the sound of many musical instruments.

But physicists also take advantage of resonators to calculate tiny masses. When extra mass lands on the surface of a resonator, it alters the frequency of the resonator, which gives physicists a means to calculate the extra mass.

Existing mass sensors of this kind, however, are constructed from relatively dense materials, such as quartz.

When atoms, which generally have a mass under a zeptogram (a trillionth of a billionth of a gram) land on the quartz, they are too small to make any impression on its vibration frequency. To weigh individual atoms, physicists need a resonator of a much lower density.
Hollow tubes

Kenneth Jensen, Kwanpyo Kim and Alex Zettl at the University of California in Berkeley have discovered that carbon nanotubes are perfect for the task.

Because nanotubes are hollow, they have a mass four orders of magnitude lower than specially built micromachined resonators. That brings their mass into the attogram range (a billionth of a billionth of a gram), and means they respond to single atoms.

Source:
technology.newscientist.com

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