Researchers at the National Institute of Technology and Standards (NIST) have introduced a novel device that estimates the movement of super small particles traversing distances almost unthinkably small and shorter than the diameter of a hydrogen atom or less than a single millionth the width of a human hair. Not just they can handheld device sense the overall atomic scale movement of its small parts with unexpected precision, but the scientists have devised a technique to bulk produce the exceedingly sensitive measuring tool.
It is quite convenient to estimated small movements of big objects but much more intricate when the moving components are on the scale of nanometers or billionths of a meter. The potential to precisely estimate small displacements of microscopic bodies has application in sensing the trace amounts of hazardous biological or chemical agents, rectifying the movement of miniature robots, precisely deploying airbags and identifying exceedingly weak sound waves moving through sleek films.
The scientists estimated subatomic – scale movement in a gold nanoparticle. They performed this by engineering a tiny air gap, about 15 nanometers long in the width and between the gold particles and a gold layer. The gap is so tiny that the laser light cannot penetrate deep into it.
But, the light energized surface plasmons – the absolute, wave – like motion of groups confined to move along the boundary between the air and gold surface. The scientists used the wavelength of light, the distance between successive peaks of the light wave. With the precise choice of wavelength, or equivalently, its frequency, the laser light tends plasmons of a specific frequency to oscillate back and forth, or resonate along the gap, similar to the reverberations of a plucked guitar string.
In the course of time, as the nanoparticle moves, it alters the width of the gap and similar to tuning a guitar string, alters the frequency at which the overall plasmons resonate. The interaction between plasmons and laser light is crucial for sensing small displacements from nanoscale particles. Light cannot conveniently identify the motion or location of an object tinier than the wavelength of the laser, but transforming the light to plasmons combats this limitation. As the plasmons are confined to the small gap, they are more sensitive than the light is for sensing the movement of tiny objects such as the gold nanoparticle.
The volume of laser light reflected back from the total plasmon device discloses the width of a gap and the movement of nanoparticle. Suppose, for instance, that the gap alters, due to the movement of the nanoparticle in such a way that the natural frequency or resonance of the plasmons more closely matches the total frequency of laser light.
“Such architecture paves the way for advances in nanomechanical sensing,” says the scientists. “We can identify small movement more locally and accurately with such plasmonic resonators that any other method of doing it,” says Aksyuk.
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