How to Bend a Crystal ? Try a Little Light

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Piezoelectric crystals have proved useful in industrial and consumer applications because of a special characteristic: they can be bent by electricity. (Conversely, they can also generate electricity when bent.)

But to be so useful, piezoelectric crystals must still be wired so the electricity can flow to or from them.

How great would it be, then, to have a crystal that could work ?wirelessly? ? bending when exposed to light, for example? Seiya Kobatake of Osaka City University in Japan and colleagues have developed such a crystal that can reversibly change its shape when exposed to alternating ultraviolet and visible light. Their work is descri Naturere.

Materials that can be deformed by photoirradiation are not unknown, but generally consist of polymer films and gels and are rather slow-acting. The new research used diarylethene chromophores, ringed molecules that switch from an open-ring version, or isomer, to a closed-ring isomer when irradiated with ultraviolet light, and back to an open-ring isomer when exposed to visible light. Those changes alter the shape of crystals made up of these molecules, from a square to more of a diamond.

This quality was put to use in a crystal rod attached to a substrate at one end. When exposed to ultraviolet light from one side, the side near the light changed shape, causing the rod to bend in 25-millionths of a second.

The force generated was powerful enough to shoot a gold particle that was much heavier than the crystal a distance of 30 micrometers.

The researchers say the materials may someday be used to make microscopic actuators that would need no wired source of power.

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