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simple, chemical way to attach electrical contacts to
molecular-scale electronic components has been developed
by researchers at the National Institute of Standards
and Technology (NIST). The recently patented* method
attaches a layer of copper on the ends of delicate molecular
components to avoid damage to the components that commonly
occurs with conventional techniques. Molecular
electronics--designing carbon-based molecules to act
as wires, diodes, transistors and other microelectronic
devices--is one of the most dynamic frontiers in nanotechnology.
An area equal to the cross-section of a typical human
hair might hold about a thousand semiconductor transistors
at the current state of art, but up to 13 million
molecular transistors.
A
key challenge in molecular electronics is making electrical
contacts to the fragile molecules, chemical chains
that are easily damaged. Currently, this is most often
done by vaporizing a metal onto the molecules that
stand like blades of grass on a metal substrate. The
vaporized metal atoms are supposed to settle on the
tops of the molecules but they also often eat away
at the delicate structures, or fall through gaps in
the "turf" and short out the device. Yields
of working devices are typically only a few percent.
NIST
researchers designed a technique in which the molecules
are synthesized with an additional chemical group
attached to the top of the molecule. The chip is immersed
in a solution including copper ions, which preferentially
bind to the added group, forming a strong, chemically
bonded contact that also protects the underlying molecule
during further metallic vapor deposition steps. Tests
at NIST have demonstrated that the technique works
well on surfaces patterned with microcontact printing,
producing clean, sharply defined edges, important
for the fabrication of practical devices.
*See U.S. patent, no. 6,828,581 available here: http://patapsco.nist.gov/TS/220/sharedpatent/pdf/6828581.pdf.
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