A single hydrogen molecule just might be a real-life little engine that could, according to a new study. It would be hard to imagine an engine much tinier.

Physicists in Germany and Spain have demonstrated that a hydrogen molecule dancing between two possible positions can induce regular vibration of a nearby cantilever—essentially a miniature tuning fork made of quartz.

The molecule's effect is no small feat, given the tiny size of a hydrogen molecule (H₂) in relation to the cantilever. "A single molecule, actually the smallest molecule we have, is capable of exciting the motion of something that is macroscopic," says physicist Jose Ignacio Pascual, now at the CIC nanoGUNE Consolider research center in San Sebastián, Spain, who led the research while working at the Free University of Berlin. "If the molecule is a person, like me, the cantilever would be something like Mount Everest." Pascual and his Berlin colleagues reported their experimental results in the November 9 issue of Science.

Although the hydrogen molecule switches position at random times, resonances between the hydrogen molecule's own vibrations and the tuning fork's natural vibration rate convert that randomness into regular oscillations in the cantilever, essentially harvesting energy from noise. (This is no perpetual-motion machine, however—the physicists applied an electric current to spur the hydrogen molecule's fluctuations.)

The type of cantilever in the new demonstration is well known for its orderly oscillations. "It's actually the same tuning fork that you have in your quartz watch," Pascual says. He and his colleagues 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 its two states alternately attracted and repelled the tip of the microscope, driving the cantilever up and down. But the researchers found that the cantilever's motion could in turn influence the fluctuations of the hydrogen molecule, which depends on the proximity of the atomic force microscope tip. The feedback between the two systems—molecule and tuning fork—can be tuned to resonances that drive the cantilever to surprisingly large-amplitude vibrations.

The new leveraging of molecular motion exemplifies a phenomenon called stochastic resonance, which bridges the worlds of the random and of the orderly. A stochastic resonance is "one way of coupling something that is periodic with something that is noisy," Pascual says. "In this case it turns out that the coupling is very effective." Such resonances, he adds, 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.

14 Comments

1. 1. Mythusmage 08:23 PM 11/9/12

   The goal now becomes to move the larger object in a way that does meaningful work.

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2. 2. Exiled Star 08:37 PM 11/9/12

   That is staggeringly awesome.

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3. 3. metamorphmuses 10:24 PM 11/9/12

   I'd be very interested to know what the mechanical efficiency of the system is: how much electrical energy was put in to produce how much mechanical energy (work)?

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4. 4. MartyMosti in reply to metamorphmuses 01:06 PM 11/10/12

   This is pretty interesting news. I wish they would have included the energy ratio. It could be revolutionary news.

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5. 5. alan6302 08:10 PM 11/10/12

   the goal is efficient levitation.

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6. 6. Mythusmage in reply to alan6302 08:53 PM 11/10/12

   First you read, then you comment.

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7. 7. jtdwyer 10:42 PM 11/10/12

   The molecular "engine" requires both the cantilever ('tuning fork') and atomic force microscope to operate. I'll withhold my wild enthusiasm until the can produce a nanoscale cantilever and, especially, nanoscale atomic force microscopes (power supply device).

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8. 8. robert schmidt in reply to jtdwyer 02:29 AM 11/11/12

   right JT because the steps along the way are meaningless.
   

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9. 9. jtdwyer in reply to jtdwyer 02:51 AM 11/11/12

   Because there's no indication that a nonoscale power source that can discretely pass an electrical current through a single molecule (like a atomic force microscope) can be produced. A nonoscale motor that required an atomic force microscope power source would be of very limited utility.

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10. 10. justyntoo 04:09 PM 11/11/12

    thank telsa for this .

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11. 11. jtdwyer in reply to jtdwyer 05:21 PM 11/11/12

    My use of the term "nonoscale" was an unintended typo, but then perhaps that's the more appropriate descriptive term.

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12. 12. Flying Fish in reply to jtdwyer 07:13 PM 11/11/12

    What about electroplating a nano electrode? Not enough alignment precision? Then why not etch away an electrode gap with electron beam lithography or add an electrode tip with a scanning tunneling microscope? Neither of these methods would be practical for mass production but I bet they would work if you just wanted to show a working device without the AFM.

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13. 13. jtdwyer in reply to Flying Fish 08:30 PM 11/11/12

    I suspect the issue would be the generation and delivery of sufficient current to produce the oscillations. I don't find that information in the freely available abstract:
    http://dx.doi.org/10.1126/science.1227621

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14. 14. alan6302 in reply to Mythusmage 06:40 AM 11/12/12

    manipulating a surface may create lift

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