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A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 5
1 8 NANOTECHNOLOGY
WOODEN SEMICONDUCTOR
CHIPS ARE BIODEGRADABLE
In an effort to alleviate the environ-
mental burden of electronic devices, a
teamof University of Wisconsin-Madison
researchers collaborated with research-
ers in the Madison-based U.S. Depart-
ment of Agriculture Forest Products
Laboratory (FPL) to develop a surprising
solution: A semiconductor chip made
almost entirely of wood. The research
team, led by UW-Madison electrical and
computer engineering professor Zhen-
qiang “Jack” Ma, demonstrated the
feasibility of replacing the substrate, or
support layer, of a computer chip with
cellulose nanofibril, a flexible, biode-
gradable material made of wood. “The
majority of material in a chip is sup-
port. We only use less than a couple of
micrometers for everything else,” says
Ma. “Now the chips are so safe you can
put them in the forest and fungus will
degrade them. They become as safe as
fertilizer.” .
NANOSPIRALS COMBAT
COUNTERFEITING
Take gold spirals about the size of
a dime and shrink them down about six
million times. The result is the world’s
smallest continuous spirals—nanospi-
rals—with unique optical properties
that are almost impossible to coun-
terfeit when added to identity cards,
currency, and other valuable objects.
Students and faculty at Vanderbilt
University, Nashville, Tenn., fabricat-
ed these tiny Archimedes’ spirals and
then used ultrafast lasers to character-
ize their optical properties. The spirals
have solid arms and are much smaller
than traditional ones: A square array
with 100 nanospirals on a side is less
than a hundredth of a millimeter wide.
When these spirals are shrunk to sizes
smaller than the wavelength of visi-
ble light, they develop unusual optical
properties. For example, when they are
illuminated with infrared laser light,
they emit visible blue light. A number
of crystals produce this effect, called
frequency doubling or harmonic gener-
ation, to various degrees. The strongest
frequency doubler previously known is
the synthetic crystal beta barium bo-
rate, but the nanospirals produce four
times more blue light per unit volume.
The combination of the unique char-
acteristics of their frequency doubling
and response to polarized light gives
the spirals a unique, customizable sig-
nature that would be extremely difficult
to counterfeit, according to research-
ers. .
A cellulose nanofibril computer
chip rests on a leaf.
REALIZING THE FULL
POTENTIAL OF NANOFIBERS
Researchers at Massachusetts In-
stitute of Technology, Cambridge, de-
veloped a new technique for producing
nanofibers that increases the rate of
production fourfold while reducing en-
ergy consumption by more than 90%,
enabling inexpensive, efficient nanofi-
ber production.
“We demonstrated a systemat-
ic way to produce nanofibers through
electrospinning that surpasses the
state of the art,” says Luis Fernando
Velásquez-García, a principal research
scientist at MIT. “But the way that it’s
done opens a very interesting possibil-
ity. Our group and many other groups
are working to push 3D printing fur-
ther, to make it possible to print com-
ponents that transduce, that actuate,
that exchange energy between differ-
ent domains, like solar to electrical or
mechanical. We have something that
naturally fits into that picture. We have
an array of emitters that can be thought
of as a dot-matrix printer, where you
would be able to individually control
each emitter to print deposits of nano-
fibers.” For more information: Luis Fer-
nando Velásquez-García, 617.253.0573,
, .
Scanning electron microscope image of
a single gold nanospiral. Courtesy of Ha-
glund Laboratory, Vanderbilt University.
A scanning electron micrograph of the
newmicrofiber emitters, showing arrays
of rectangular columns etched into their
sides.