A Single Hydrogen Molecule Vibrates Macro Object


Inside a quartz crystal tuning fork. Credit: Image by Chribbe76/Wikimedia Commons

Physicists have demonstrated that a hydrogen molecule dancing between two possible positions can induce regular vibration of a nearby cantilever, creating a miniature tuning fork made up of quartz.

The scientists published their findings in the journal Science. A single molecule has never been shown to be able to move something on a macroscopic scale, states Jose Ignacio Pascual, at the CIC nanoGUNE Consolider research center in San Sebastián, Spain, and lead author of the paper.

If the molecule were the size of a person, it could be like moving something the size of Mount Everest, Pascual continues. The resonances between the hydrogen molecule’s own vibrations and the tuning fork’s natural vibration rate convert the randomness of the molecule’s position into regular oscillations in the cantilever, harvesting energy from noise.

This is akin to what is happening inside quartz watches. The team affixed the quartz beam to the end of an atomic force microscope, a scanning probe with a sensor tip akin to a tiny phonograph needle that also doubles as an electrode to deliver current into the hydrogen molecule. The hydrogen molecule’s current-induced fluctuation between states attracted and repelled the tip of the microscope, driving the cantilever up and down. The cantilever’s own motion could in turn influence the fluctuations of the hydrogen molecule, depending on the proximity of the atomic force microscope tip. The feedback between the two systems could be tuned to the resonances that drive the cantilever to large-amplitude vibrations.

This is an example of stochastic resonance, and it is one way of coupling something that is periodic with something that is noisy. The researchers note that it could be useful in building nanoscale motors driven by single molecules or other tiny objects, whose haphazard fluctuations could be harnessed to produce coordinated motion.

Reference: “Driving a Macroscopic Oscillator with the Stochastic Motion of a Hydrogen Molecule” by Christian Lotze, Martina Corso, Katharina J. Franke, Felix von Oppen and Jose Ignacio Pascual, 9 November 2012, Science.
DOI: 10.1126/science.1227621

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