Photo molecules flip current

Many research teams are working to make electronic components from molecules. Such small electronics would be faster and more powerful than today's versions.

Researchers from Kyoto University in Japan have constructed a photodiode that consists of a mix of slightly different peptide molecules anchored to a gold surface. Photodiodes produce electricity when they are stimulated by light; they can detect and generate electricity from light.

The work shows that one or a few peptide molecules can function as a photodiode. Each molecule is 1 to 1.5 nanometers in diameter. A nanometer is one millionth of a millimeter.

The researchers caused the two types of peptides to self-assemble on a gold surface to make the minuscule photodiode. The peptides contain different types of chromophores, or molecular complexes that respond to light, and the two types of peptides have different dipole moment directions. Dipole moments are the strength and separation between a molecule's oppositely charged ends. Dipole moment directions depend on the orientation of the positively and negatively charged ends.

When the peptides are exposed to certain wavelengths of light, their ability to conduct electricity is changed, and each type of peptide responds to a particular wavelength of light differently. Each type of molecule in the researchers device can be controlled independently to change the current flowing through it; this attribute can be used to reverse the direction of the current.

It will be one or two decades before the molecular photodiode can be used in practical devices, according to the researchers. The work appeared in the June 25, 2004 issue of Science.