provides more bang
Technology Research News
In old spy novels, secret agents ate their
instructions. Researchers in California have come up with a computer chip
material that takes Agent Ethan Hunt's self-destructing directives for
impossible missions to a new level. The technology will eventually allow
computer chips to self-destruct.
This is possible because scientists at the University of California at
San Diego zeroed in on a quirky quality of crystalline porous silicon:
when scratched with a diamond or exposed to an electric spark, it explodes.
The explosion works somewhat like a child's cap gun, "except that you
can program the chip to explode electronically, and you can't do that
with your cap gun," said Michael J. Sailor, a professor of chemistry and
biochemistry at the University of California at San Diego.
When the hammer of the gun strikes the cap's gunpowder, a mixture of potassium
nitrate, sulfur, and charcoal, it explodes. What the researchers have
made is essentially a silicon version of gunpowder that explodes when
it is charged with electrons.
The explosion is "packaged, transportable and self-contained," said Sailor.
It is also clean burning with few residual impurities, he said.
These properties make it useful in a range of applications in addition
to self-destructing computer
chips. The explosive properties could be controlled to provide propulsion
for microdevices and combustion sources for labs-on-a-chip, Sailor said.
For instance, it could be used to ascertain if the air is toxic, he said.
"Put a small amount of drinking water on a wire and dip it into a flame.
The color of the flame is often characteristic of the metal ions present
in the water. The classic example is sodium, which burns with a very yellow
flame. Potassium is purple. Lead is blue."
Since the explosion can be controlled remotely, it would also be possible
to program a chip to self-destruct, said Sailor. Email correspondence
and credit card numbers are generally stored on the hard drive of a computer.
"We canít touch that with our invention," he said. However, often key
information can be on part of a single chip.
"Not all the information necessary to guide a smart bomb or the trigger
for a nuclear weapon is contained in the software; rather it is hardwired
into the circuitry of that computer chip," Sailor said. "If someone were
to capture the weapon and take the chip apart they may be able to figure
out how to defeat the targeting or safety interlocks. These are examples
in which you want to not only disable the chip but completely obliterate
The researchers made the silicon explosives by doping silicon wafers with
gadolinium nitrate, rather than the usual potassium nitrate. Each layer
of the prepared silicon film is about 25 microns thick and 1.2 cm in diameter,
or about the size of a dime.
When an electrical current hits, the porous silicon explodes. The researchers
measured the strength of the explosion by analyzing the light it emitted
with a spectrometer. The strength of intensity of the explosions can be
controlled by varying the mix of materials, according to the researchers.
This work is an important step towards practical applications for porous
silicon, said Dmitri Kovalev, a senior scientific employee at the physics
department of the Technical University of Munich. "It is novel since this
silicon-based explosive can work at room temperature and can be ignited
under [strict] control," he said. It is useful because "it can be efficiently
exploded in negligible amounts," he added.
The explosion is more powerful and more efficient than charcoal-based
explosions because the grains of porous silicon are much smaller than
carbon and are networked. This type of material mixes with oxygen and
explodes very quickly, Kovalev said.
Additionally, "it is a planar explosive: lateral sizes are an order of
magnitude larger than the depth of the layer. Therefore during the explosion
the momentum is always transferred [perpendicular] to the surface [which
gives it] high propulsion properties," Kovalev said.
The material could also be used as a primer for secondary explosives or
as a propellant for orientating satellites in space, he said. Kovalev's
group has made a similar explosive system by doping the material with
a different oxidizer.
The San Diego researchers are aiming to integrate the material with real
circuits, Sailor said.
Sailorís research colleagues were Fredrik V. Mikulec and Joseph D. Kirtland.
They published the research in the January 4, 2002 issue of the journal
Advanced Materials. The research was funded by the Defense Advanced Research
Projects Agency (DARPA).
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Explosive Nanocrystalline
Porous Silicon and Its Use in Atomic Emission Spectroscopy," Advanced
Materials, January 4, 2002.
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