Livermore - April 3, 2000 - Now thanks to Lawrence Livermore National Laboratory's high-pressure physics technologies that monitor the well-being of nuclear weapons, we can explain some mysteries of materials at the center of our planet and understand the formation of our universe better. And in the near future we may see diamond-encapsulated micro-circuits and semiconductors -- or "smart cookware" that controls its own temperature.
Both solid and gaseous materials behave quite differently when under extreme pressures: The kinds at the center of the Earth, within a star like the Sun, or during the energy-yield of a nuclear weapon. Oxygen, for example, transforms to a shiny metal under ultra-high pressure.
The Department of Energy's stockpile stewardship program will someday simulate the operation of a nuclear weapon with supercomputers. So scientists must learn how weapon materials behave under extreme pressures.
Absent underground tests that produce a nuclear yield, other high-pressure physics experiments must provide this answer. Remarkable results have been achieved by the Lab's Jagannadham "Jagan" Akella and Sam Weir using diamond anvil cell technology. They collaborated with Professor Yogesh Vohra and research associate Aaron Catledge at the University of Alabama.
Diamonds are strong, hard, good electrical insulators, great heat conductors and they permit radiation-like diagnostic x-rays to pass unhampered through their crystalline structure. Diamonds also can withstand ultra-high pressures.
Polished by a laser-guided process until perfectly flat, then fabricated into a diamond anvil, these precious stones provide the foundation for technology to measure electrically the effects of ultra-high-pressure on material samples ranging from hydrogen to berkelium.
But diamonds are relatively small. So an initial challenge is to make the samples size very small. Even more challenging is adapting instrumentation to investigate samples narrower than the width of a human hair, placed on a surface smaller than a pin-head, and squeezed under a pressure several million times the Earth's normal atmosphere. Sometimes the compression reaches the 3.6 million atmospheres estimated at the Earth's center.
A technology for chemical vapor deposition of epitaxial diamond crystals allows fabrication on diamonds of miniature printed circuits that can withstand tremendous pressure, yet yield accurate results.
"At these extreme pressures, shear stresses would deform any known metal. So epitaxial diamond encapsulation is crucial to ensure that the instrument probes survive an experiment," Weir said.
The diamond deposition is coupled with Livermore's advanced 3D laser pantography system that deposits a precise pattern of lines on non-flat surfaces. Akella believes this combination paves the way for the creation of diamond microcircuits, and eventually semiconductors that could be used in specialized applications such as spacecraft, where strength, radiation and super heat-conductivity are required.
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