NIST's JILA Apparatus Measures Fast Nanoscale Motions
April 17, 2007 // Published as a news service by IHS
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A new nanoscale apparatus - a tiny gold beam that has its 40 million vibrations per second measured by hopping electrons - offers the potential for a 500-fold increase in the speed of scanning tunneling microscopes (STM), perhaps paving the way for scientists to watch atoms vibrate in high definition in real time.
The new device, developed at JILA - a joint venture of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder - measures the wiggling of the beam, or rather the space between it and an electrically conducting point just a single atom wide, based on the speed of electrons tunneling across the gap.
The work is the first use of an "atomic point contact" to sense a nanomechanical device oscillating at its resonant frequency - where it naturally vibrates like a tuning fork.
Although the technique, described in Physical Review Letters, is not necessarily as precise as more complex and much colder methods of measuring fast motions of ultra-small devices, researchers said it incorporates several innovative attributes.
These include the ability to minimize unwanted random electronic noise, as well as to measure the random shaking of the beam caused by back-action or recoil (similar to what happens when a gun is fired).
This level of sensitivity is possible because the atomic point contact acts as an amplifier for these otherwise imperceptible factors, and the gold beam is tiny and floppy enough - just 100 nanometers (nm) thick, and 5.6 micrometers (m) long by 220 nm wide - to respond to single electrons.
The new method involves bringing the sharp point within 1 nm of the gold beam. A current is applied through the point across the gap, until an increase in resistance indicates that electrons are tunneling across the gap (a phenomenon observed only at atomic dimensions). The size of the gap is then monitored based on variations in the current.
The beam's undulations were measured with significantly greater precision than a typical STM result. That's because the oscillations are measured using microwave electronics, which are much faster than the audio frequency technology typically used with STMs, thus enabling greater precision. Scientists said the microwave measurement technique could potentially be applied to STMs.
Source: National Institute of Standards and Technology (NIST).