Physics Tip Sheet #48 - June 24, 2005

Contact: James Riordon
riordon@aps.org
301-209-3238
American Physical Society

Highlights in this issue:

Programming organic transistors with light; the unusual origin of peacock brown; and rotating nanowires.

1) Programming organic transistors with light

V. Podzorov and M. E. Gershenson
Physical Review Letters
Forthcoming article

Researchers at Rutgers University in Piscataway, New Jersey have shown that they can change the threshold voltage of organic transistors by exposing them to visible light, making it possible to essentially "reprogram" the transistor. By illuminating a single-crystal organic transistor with visible light and applying a gate voltage at the same time, they can controllably vary the threshold voltage over a wide range. Furthermore, they found that they can do this reversibly many times without deteriorating the characteristics of the transistor. The effect could find many uses in the developing field of organic electronics, for example in developing novel light-recordable smart media and sensors, the authors suggest.

2) The Unusual Origin of Peacock Brown

Y. Li et al.
Physical Review E
Forthcoming article

Many animals' colors originate from photonic crystals, which reflect specific colors of light as a result of their nanoscopic structures, rather than from pigments, which derive their colors from their chemical composition. The brown in peacocks' tails is a particularly unusual type of photonic crystal coloration, according to research soon to appear in the journal Physical Review E.

Brown is a mixture of light of different colors. Generally, photonic crystals in animal coloring produce pure colors, such as blue, green, yellow or violet. Nevertheless, researchers at Fudan University in Shanghai have found that the brown in peacocks' feathers is indeed due to microscopic structure. The researchers' experiments and analysis show that peacocks' brown microstructures are a good deal more complex than most natural photonic crystals.

Mimicking the photonic crystals in peacock tail feathers could lead to new ways to manipulate light in cutting edge optical instruments. In addition, the discovery points the way to new paints and coatings that are not susceptible to the chemical changes that can degrade pigments over time.

3) NanoSpinners

D. L. Fan et al.
Physical Review Letters
Forthcoming articles

A new method for controlling the rotation of nanowires will likely lead to tiny mixers, motors, and other microscopic devices. Researchers at Johns Hopkins University made videos of their spinning nanowires, which are only about 5 millionths of a meter long (ten times smaller than the diameter of a human hair). Some of the videos are available at the links below.

The researchers used electrodes to create rotating electric fields that spun the wires suspended in water. In some case the wires were attached to a substrate, creating minuscule fixed motors. In other cases, the wires were unattached and simply spun freely in the water.

The researchers spun gold, platinum, nickel, and carbon wires at precisely controlled rates up to 1800 revolutions per minute. They predict that higher rotation rates are possible, but could not be adequately measured with their experimental equipment. According to the researchers, the technology will help manipulate micrometer scale objects, aid in the study of microorganisms, and lead to a host of micro electromechanical (MEMS) machines.

Watch a video of nanowire motor attached to a substrate (27M).

Watch a video of spinning, free nanowire (5M).

QuickTime is required to view videos. Get QuickTime.

Journal articles are available to journalists on request.

For media assistance with these or other physics stories, contact:

James Riordon
Head of Media Relations
American Physical Society
Ph: +1 301 209 3238
Fax: +1 301 209 3264
Email: riordon@aps.org