Samples of materials that have been made into fibers in the lab of MIT’s Yoel Fink. The initial material is made into a ‘preform,’ in the lower portion, which is then heated and drawn out like taffy into a fiber from the top, preserving the arrangement of materials within the structure. Photo: Greg Hren/RLE |
Researchers
at MIT have succeeded in making a fine thread that functions as a diode. This
feat—made possible by a new approach to a type of fiber manufacturing known as
fiber drawing—could open up possibilities for fabricating a wide variety of
electronic and photonic devices within composite fibers, using a variety of
materials.
Fiber-drawing
techniques are used to produce the optical fibers behind much of today’s
broadband communications, but these techniques have been limited to materials
that can partially melt and stretch like taffy at the temperatures being used
for drawing the fibers. The new work demonstrates a way of synthesizing new
materials during the fiber-making process, including materials whose melting
points are far higher than the temperatures used to process the fibers. The
simple proof-of-concept demonstration carried out by the MIT researchers could
open the door to a wide array of sophisticated devices based on composite
fibers, they say.
The
findings, part of a doctoral research project in materials science by Nicholas
Orf, have
been published in the journal Proceedings
of the National Academy of Sciences. The work was carried out in Yoel
Fink’s research group.
All
previous work on fiber-drawing ended up with the same materials that were there
to begin with, just in a different shape, Orf says, adding: “In this method,
new materials are formed during the drawing process.”
Fiber
drawing involves preparing a “preform” of materials, such as a large glass rod
resembling an oversized model of the fiber to be produced. This preform is
heated until it reaches a taffy-like consistency and then pulled into a thin
fiber. The materials comprising the preform remain unchanged as its dimensions
are drastically reduced.
In
the current research, the preform contained selenium, sulfur, zinc, and tin,
arranged within a coating of polymer material. The drawing process, carried out
at a temperature of just 260 degrees Celsius (500 degrees Fahrenheit), combined
these materials to form fibers containing zinc selenide, even though that
compound has a melting point of 1,530 degrees Celsius (2,786 degrees
Fahrenheit).
The
resulting fiber was a simple but functional diode. Diodes have never been
created by this method before.
Nicholas Orf, a postdoctoral researcher at MIT who was lead author of a paper describing the synthesis of materials inside a fiber. He is holding samples of fibers produced in the lab. Photo: Melanie Gonick |
“This
shows that many more kinds of materials can be incorporated into fibers than
ever before,” Orf says. Because the physical arrangements placed in the preform
are preserved in the drawn fiber, it should ultimately be possible to
incorporate more complex electronic circuits within the structure of the fiber
itself.
Such
fibers might find uses as sensors for light, temperature, or other
environmental conditions, Orf says. Or the fibers could then be woven, such as
to make a solar-cell fabric, he says.
Fink
says his research group has been working for more than a decade on expanding
the kinds of materials and structures that can be incorporated into fibers. He
says that despite the rapid progress made in the last few decades in various
forms of electronics, “there has been little progress in advancing the overall
functionality and sophistication of fibers and fabrics … one of the earliest
forms of human expression.”
The
group’s research, he says, has stemmed from the basic question, “How
sophisticated can a fiber be?” Over the years they have incorporated more and
more materials, structures and functions into fibers. But one of the biggest
limitations has been the set of materials that could be incorporated into the
fibers; this new work has greatly expanded that list. The work shows that it is
possible, Fink says, “to use the fiber draw as a way to synthesize new
materials. It’s the first time this has been demonstrated anywhere.”
Zinc
selenide, the specific compound formed in this drawing process, is an important
material for both its electronic and its optical properties, Orf says. Such
fibers might have uses in new photonic circuits, which use light beams to
perform functions similar to those carried out by flowing electrons in
electronic circuits.
While
this experiment produced 15 individual diode devices in the fiber, each
separate from the others, Fink says that through continuing research, “We think
you could probably do hundreds” and even interconnect them to form electronic
circuits.