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New look for molecular photodiodes - helical peptides

New look for molecular photodiodes - helical peptides - Physics Forum

New look for molecular photodiodes - helical peptides - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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Old 06-25-2004, 12:06 PM
Bubba Do Wah Ditty
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Default New look for molecular photodiodes - helical peptides



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New look for molecular photodiodes
24 June 2004

Scientists in Japan have made a new type of molecular photodiode, whose
current switches direction depending on the wavelength of the light used to
excite it. Designed by Shunsaku Kimura and colleagues at Kyoto University,
the device consists of two helical peptide molecules, whose dipole moments
point in opposite directions. Their technique could be used to make a wide
variety of molecular electronics devices on the nanoscale (S Yasutomi et al.
2004 Science 304 1944).

helical peptides

Molecular electronics has made steady progress in recent years and
components made from single molecules could overcome the limits of
conventional, silicon-based microelectronics. However, many challenges still
need to be overcome before molecular electronic devices can become a
reality, including the fact that it is difficult to integrate them into
ordered structures.

The photodiode fabricated by Kimura and colleagues consists of two types of
helical peptide -- long protein chains -- each of which has a different
light-absorbing end-group, or chromophore. The two peptides, which are about
1 nanometre across, were anchored on a gold substrate. Such molecules are
good candidates for molecular devices because they can form highly ordered
self-assembled monolayers.

The Kyoto team found that when one of the chromophores was excited with
light of a certain wavelength it generated an anodic photocurrent. However,
when the other chromphore was excited -- with light of a different
wavelength -- the current flowed in the opposite direction, towards the
cathode. The reason for this behaviour is that each helical peptide has a
large intrinsic dipole moment that accelerates electron transfer in the same
direction in which its dipole moment is pointing. Since the two peptides
have dipole moments that point in opposite directions, the current is sent
in opposite directions (see figure).

"The large dipole moment of helical peptides means they could be used as
modulators in many types of electronic device made on the nanoscale," Kimura
told PhysicsWeb. "They could thus be useful starting materials for the
coming age of molecular electronics." The team now hopes to make a molecular
transistor using such peptides.

Author
Belle Dumé is Science Writer at PhysicsWeb

--
Bubba Do Wah Ditty,

"One of the great things about books is sometimes there are some fantastic
pictures."

Bushisms, 2000



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