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
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.
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