Chip provides more bang

By Chhavi Sachdev, 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 it."

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).

Timeline:  Now
Funding:  Government
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.


February 20, 2002

Page One

DNA map IDs diseases

Real birds change virtual evolution

Material turns infrared to green

Nanotube chips draw near

Chip provides more bang


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