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Silicon devices respond to infrared light
A new system developed by
researchers at five institutions, in-
cluding Massachusetts Institute
of Technology, Cambridge, cre-
ates detectors that are responsive
to a broad range of infrared light.
Silicon normally lets most in-
frared light pass through. The
new system works at room tem-
perature and provides a broad in-
frared response, say researchers.
It incorporates atoms of gold into
the surface of silicon’s crystal
structure in a way that maintains
the material’s original structure. It
also has the advantage of using
silicon, a common semiconductor
that is relatively low cost, easy to
process, and abundant. The approach works by implanting gold into the top hundred
nanometers of silicon and then using a laser to melt the surface for a few nanoseconds.
The silicon atoms recrystallize into a near-perfect lattice, and the gold atoms do not have
time to escape before getting trapped in the lattice. For more information: Tonio Buonas-
sisi, 617/324-5130, , .
Increasing domestic plastic production
Low U.S. natural gas prices are helping increase domestic plastic production after a de-
cline from the 2008 recession. Because many U.S. plastic manufacturers use natural gas as
their primary fuel source and natural gas-sourced liquids as a feedstock, continued low
prices for those resources could boost raw plastic exports, given higher foreign energy
prices. During the economic downturn in 2008 and 2009, U.S. production of plastic prod-
ucts declined further than raw plastic production and has been slower to recover. Demand
for raw plastic from other parts of the world, such as China, remained strong, keeping U.S.
plastic resin production from falling further and enabling it to recover faster. Given the in-
expensive and versatile nature of polyethylene and polypropylene plastics, demand for
these materials has grown rapidly since the late 1990s, both domestically and abroad.
Self-healing battery electrode
Researchers made the first battery electrode that heals itself, opening a new and poten-
tially commercially viable path for making the next generation of lithium ion batteries for
electric cars, cell phones, and other devices. The secret is a stretchy polymer that coats the
electrode, binds it together, and spontaneously heals tiny cracks that develop during bat-
tery operation, according to the team from Stanford University and DOE’s SLAC National
Accelerator Laboratory, both in California.
Chao Wang, a researcher at Stanford, developed the self-healing polymer in the lab
of Zhenan Bao, whose group has been working on flexible electronic skin for use in
robots, sensors, prosthetic limbs, and other applications. For the battery project, he
added tiny nanoparticles of carbon to the polymer so it would conduct electricity.
“We found that silicon electrodes lasted 10 times longer when coated with the self-
healing polymer, which repaired any cracks within just a few hours,” explains Bao.
The electrodes worked for about 100 charge-discharge cycles without significantly
losing their energy storage capacity. For more information: Zhenan Bao, 650/723-2419,
, .
ADVANCED MATERIALS & PROCESSES • MARCH 2014 12
ENERGY TRENDS
briefs
Researchers at Kansas State
University,Manhattan,
demonstrated that a composite
paper—made of interleaved
molybdenum disulfide and
graphene nanosheets—can be
both an active material to
efficiently store sodium atoms and
a flexible current collector. The
newly developed composite paper
can be used as a negative
electrode in sodium-ion batteries.
Synthesis of large quantities of
single or few-layer-thick 2D
materials is crucial to
understanding the commercial
potential of materials such as
transition metal dichalcogenides
and graphene. .
Researchers at the University of
Cambridge, UK, developed a new
method to probe silicon batteries
and determined what causes
silicon expansion, which degrades
battery performance, to take place.
Using nanoscale wires made of
silicon and nuclear magnetic
resonance techniques, a robust
model system able to
accommodate the expansion of the
silicon over multiple cycles was
developed and integrated with
short-range probing techniques,
which reveal what is happening
inside the battery at the atomic
level. .
Researchers at the University of
Liverpool, UK, are investigating
the use of ultraviolet light to create
thin films that can be used on
solar panels. Funding from the
Engineering and Physical Sciences
Research Council (EPSRC) will
enable the scientists to develop
new methods for atomic layer
deposition using light rather than
heat to create the layers. The
project will replace the use of heat
from below with light from above
in order to create the reaction. This
is significantly more energy
efficient and will allow industry to
use atomic layer deposition in
many more applications that
require larger surfaces to be
covered. .
A laser beam is used in the lab to test the gold-
hyperdoped sample of silicon to confirm its infrared-
sensitive properties. Courtesy of the researchers.