Weaving electronics into any
material
Researchers have used two abundant raw
materials to create
fibres of pure crystalline silicon which could be used to
add
electronics, including microchips and solar cells, to almost any fabric
Scientists have known how to draw thin fibres
from bulk materials
for decades.
But a new approach to that old meth od,
developed by researchers at
Massa chusetts Institute of Technology, could lead
to a whole new
way of making highquality fibre-based electronic devices.
The idea grew out of a long-term research effort
to develop
multifunctional fibres that incorporate different materials into a
single long functional strand.
Until now, those long strands could only be
created by arranging the
materials in a large block or cylinder called a
preform, which is then
heated and stretched to create a thin fibre that is
drastically
smaller in diameter, but retains the same composition.
Now, for the first time, fibres created through
this method
can have a composition that's completely different from that of
the
starting materials an advance that senior author Yoel Fink
refers to as a
kind of “alchemy,“ turning inexpensive and abundant
materials into high-value
ones. The new findings are described in
a paper in the journal Nature
Communications co-authored by
Chong Hou, and six others at MIT and in
Singapore.
The fibres are made from aluminium metal and
silica glass, abundant
low cost materials, which are commonly used to make
windows
and window frames. The aluminium metal and silica glass react
chemically as they are heated and drawn, producing a fibre with a core of pure,
crystalline silicon the raw material of computer chips and solar cells and
a coating of silica.
The initial discovery was a complete surprise:
In experiments
designed to test the possibility of incorporating metal wires
inside
fibres, Hou tried a variety of metals, including silver, copper,
and
aluminium and in the latter case, the result was not what
they expected.
“When I looked at the fibre, instead of a shiny
metallic core,
I observed a dark substance; I really didn't know what
happened,“
says Hou, who is the lead author of the paper. Upon analysis,
the
researchers found that the core had turned to silicon in fact,
very pure,
crystalline silicon.
“My initial reaction might have been to discard
the sample altogether,“
Fink says, after seeing that the experiment “failed“ to
produce
the expected result. But instead, Hou began to examine the specimen
and
apply rigorous analysis, soon realising that the mundane result he expected was
replaced by a surprising one which is how this discovery came about.
It turned out that the chemical reaction in the
fibre was a well-known
one: At the high temperatures used for drawing the
fibre, about 2,200
degrees Celsius, the pure aluminium core reacted with the
silica,
a form of silicon oxide. The reaction left behind pure silicon,
concentrated
in the core of the fibre, and aluminium oxide, which deposited a
very
thin layer of aluminium between the core and the silica cladding.
Now, Hou says, “We can use this to get
electrical devices, like solar cells
or transistors, or any silicon-based
semiconductor devices, that could be
built inside the fibre.“ Many teams have
tried to create such devices
within fibres, he says, but so far all of the
methods tried have required
starting with expensive, high-purity silicon.
“Now we can use an inexpensive metal,“ Hou says.
“It gives us
a new approach to generating a silicon-core fibre.“
Fink adds that this is “a new way of thinking
about fibres, and it could
be a way of getting fibres to do a lot more than
they ever have.“ As
mobile devices continue to grow into an everlarger segment
of the electronics business, for example, this technology could open up new possibilities for electronics including solar cells and microchips to be incorporated into fibres and woven into clothing or accessories.
MM24FEB15
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