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2006
■ BY JEFF ECKERT
ADVANCED TECHNOLOGY
NANOGENERATORS
TURN MOTION INTO
ELECTRICITY
energy from the slightest activity.
To study the effect, the
researchers grew arrays of zinc-oxide
nanowires, then
used an atomic-force microscope
tip to deflect
individual wires.
According to Zhong
Lin Wang, a regents
professor in the
School of Materials
Science and
Engineering, as a
wire was contacted
and deflected by
the tip, stretching
on one side of
the structure and
compression on
the other side
created a charge
separation — positive on the
stretched side and
negative on the
compressed side —
due to the piezoelectric effect. The
charges were
preserved in the
nanowire because
a Schottky barrier
was formed between the AFM tip and
the nanowire. The coupling between
semiconducting and piezoelectric
properties resulted in the charging
and discharging process when the tip
scanned across the nanowire.
The top portion of the illustration
shows an array of the nanowires, and
the middle image depicts a schematic
of how an AFM tip was used to
bend them to produce current. The
bottom image depicts output voltages
produced by the array.
According to the researchers,
motions from body movement, the
stretching of muscles, and even the
ILLUS TRATION BY Z. L. WANG.
flow of liquids should be able to
generate electrical charges in the
wires, making them useful for
implantable medical devices, sensors,
portable electronics, and a variety of
other applications.
SINGLE-MOLECULE
DIODE COULD
REVOLUTIONIZE
ELECTRONICS
PHOTO COURTESY OF TRENT SCHINDLER,
NATIONAL SCIENCE FOUNDATION.
■ This single-molecule diode could
eventually replace conventional devices
and allow electronic devices to be
shrunk to very tiny sizes.
■ Tiny nanowires create electricity that
may power implantable medical and
other devices.
Researchers at the Georgia Institute
of Technology ( www.gatech.edu)
have come up with some tiny
nanowires that generate electricity
when they vibrate. Just like the quartz
crystal in a watch, the zinc-oxide
nanowires are piezoelectric, so
bending causes them to produce an
electrical charge. Only 20 to 40
billionths of a meter in diameter, each
fiber works with millions of others to
form a nanogenerator capable of
producing significant amounts of
Using the power of modern
computing and some innovative
theoretical tools, an international team
of researchers has come up with a single-molecule diode and figured out
how it works. Created by a research
team at the University of Chicago
( www.uchicago.edu), the diode is
merely a few tens of atoms in size and
1,000 times smaller than its
conventional counterparts. Recently,
theorists from the University of South
Florida ( www.usf.edu) and the
Russian Academy of Sciences (visit
www.intertec.co.at/itc2/partners/RA
S/ Default.htm for English-language
information) have explained the
principles that make the device work.
The researchers showed that electron energy levels in a molecule are
efficient channels for transferring electrons from one electrode to another.
Because the molecule in the diode is
8
June 2006
