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Scientists at the US National Institute of Standards and Technology (NIST) have developed a new device that will measure the motion of small particles covering distances almost unimaginably small, shorter than the diameter of a hydrogen atom, or less than one-millionth the width of a human hair.
According to NIST’s press release, It’s relatively easy to measure small movements of large objects but much more difficult when the moving parts are on the scale of nanometers, or billionths of a meter. The ability to accurately measure tiny displacements of microscopic bodies has applications in sensing trace amounts of hazardous biological or chemical agents, perfecting the movement of miniature robots and accurately deploying airbags.
NIST physicists Brian Roxworthy and Vladimir Aksyuk researched and measured subatomic-scale motion in a gold nanoparticle. They did this by engineering a small air gap, about 15 nanometers in width, between the particle and a gold sheet. This gap is so small that laser light cannot penetrate it.
The light energized the surface causing groups of electrons to travel along the boundary between the gold surface and the air. The researchers exploited the light’s wavelength, the distance between successive peaks of the light wave. With the right choice of wavelength. the laser light causes a particular frequency to go back and forth along the gap. As the nanoparticle moves, it changes the width of the gap.
To use this motion-sensing technique in a practical device, Aksyuk and Roxworthy embedded the gold nanoparticle in a microscopic-scale mechanical structure made of silicon. Even when they’re not set in motion, such devices never sit perfectly still, but vibrate at high frequency, jostled by the random motion of their molecules at room temperature. Even though the amplitude of the vibration was tiny moving subatomic distances it was easy to detect with the new plasmonic technique. Similar, though typically larger, mechanical structures are commonly used for both scientific measurements and practical sensors; for example, detecting motion and orientation in cars and smartphones.
The NIST scientists hope their new way of measuring motion at the nanoscale will help to further miniaturize and improve the performance of many such micromechanical systems.
“This architecture paves the way for advances in nanomechanical sensing,” the researchers write. “We can detect tiny motion more locally and precisely with these plasmonic resonators than any other way of doing it,” said Aksyuk.