IN THE movie Superman, the Man of Steel discovers why he was
jettisoned from the doomed planet Krypton by watching a video message
stored on a transparent crystal. Now, more than 20 years on, Japanese
scientists are working on a revolutionary new semiconductor that might
one day be turned into just this kind of gadget.
Computer displays made of the material will have all the image
processing and memory circuits invisibly buried in the screen itself,
making them cheaper and less power hungry than today's displays.
A team led by Yuji Matsumoto of the Tokyo Institute of Technology
(Titech) in Yokohama were looking for a material that was both a
semiconductor and a permanent magnet, or "ferromagnet". They
succeeded--and were amazed to find that the material is transparent as
well.
Best of all, the
new material
works at room
temperature. "This
is a very
important step,"
says Hideo Ohno,
a semiconductor
physicist at
Tohoku University
in Sendai. "If it
didn't work at
room temperature
it would be no
good for use in
everyday
applications."
Ohno and his
colleagues have
created a
ferromagnetic
semiconductor of
their own by
mixing manganese
into gallium
arsenide. But their
material is
opaque, and only works at a frigid 110 kelvin.
To produce magnetic semiconductors that can stand the heat, the Titech
team with colleagues from the National Institute for Research in
Inorganic Materials in Tsukuba turned to a technique called combinatorial
chemistry. They carried out thousands of tiny chemical reactions
simultaneously in a vacuum, each with slightly different ingredients. They
then screened the products of the different reactions en masse to see
which had the best properties.
Matsumoto and his colleagues will soon report in Science that one of the
reactions produced a thin film of titanium dioxide doped with just under 8
per cent cobalt. This transparent material turned out to be both
semiconducting and permanently magnetic at room temperature. Using
magnetic microscopy the researchers found areas in the material where
electron spins line up spontaneously to produce magnetism.
The Titech researchers say they don't know why the cobalt has this
effect. "We need to accumulate more data," says team member Hideomi
Koinuma.
Ohno says the discovery is important in the emerging field of
"spintronics", in which engineers hope to harness both the
charge-carrying aspects of electrons and their spin, which is the root of
magnetism. Because the material is magnetic parts of it could store data
in much the same way as a computer hard drive. And as a
semiconductor, other parts could process information like the transistors
in a microchip.
Ohno says the material will most likely be turned into flat-panel displays
which have all their processing and storage circuits invisibly built-in.
"Currently, transistors in laptop displays absorb a quarter of the
brightness of the backlight. Transparent transistors could solve this."
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