Research roundup

15 October 2003

DOE to fund co-generation effort
The campus’s Energy and Resources Group (ERG) will receive $300,000 from the U.S. Department of Energy over the next one-and-a-half years to assist businesses and homeowners in installing heating systems that use the waste heat from electricity generation. The funding is Berkeley’s share of $1.5 million allocated by DOE to five regional U.S. projects to encourage conversion to combined heat and power (CHP), also known as co-generation.

“Combined heat and power is a step toward greater energy efficiency that we know works and that we can move toward today, as we investigate other solutions that might or might not pan out in the future,” said Timothy Lipman, executive director of the Center for Interdisciplinary Distributed Energy Research (CIDER), a joint collaboration between Berkeley and Lawrence Berkeley National Laboratory. “CHP focuses on end-user efficiency, which is a big part of the solution to reducing energy use and greenhouse gases.”

Berkeley has had a co-generation plant for many years, operated by outside contractors to supply both steam heat and enough electrical power to feed the campus. The planned UC Merced campus also will have a significant CHP component, Lipman said, and he hopes that Berkeley will consider CHP as part of a new green-building program mandated by the UC Board of Regents in July.
—Robert Sanders

Satellite explores secrets of solar explosions
A team of researchers used NASA’s orbiting Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), built and operated by UC Berkeley, to take pictures of a large solar flare on July 23, 2002. This was the first flare large enough to allow images to be made from high-energy gamma-ray emissions.

Berkeley’s RHESSI satellite was launched in February 2002 to obtain X-ray and gamma-ray pictures of solar flares in an attempt to understand these huge explosions. Its first gamma-ray image, from July 23, 2002, showed scientists they don’t know as much as they thought they did about the production of high-energy X-rays and gamma rays from flares.

Scientists had assumed that gamma rays, produced by ionized particles slamming into denser gas on the sun, originate in the same place as X-rays, which are produced in a similar way by high-speed electrons. Both should issue from the feet of the glowing loops that arc hundreds of thousands of miles across the face of the sun and accelerate ions and electrons to very high speeds before they crash into surrounding gas.

The observations showed, however, that gamma rays come from a spot far from the source of X-rays, separated by about the diameter of the Earth. Apparently, the sun’s magnetic processes are able to separate the electrons from the ions, sorting them either by mass or electric charge, as they blast them to almost the speed of light. The gamma rays seem to be coming from the feet of the large magnetic field loops, while the X-rays come from the feet of the small magnetic loops nested inside the larger ones.

Solar flares are among the largest explosions in the solar system, releasing as much energy as a billion one-megaton nuclear bombs. Arising in the solar atmosphere — a gas of electrically charged particles composed of negatively charged electrons and positively charged ions — they are often closely associated with fast coronal mass ejections (CMEs), which propel energetic particles into space. These particles impinge on the Earth’s magnetic field, igniting the auroras and generating magnetic storms that can interfere with radio communications and satellites.
— Robert Sanders

Changes in crystal structure of nanometer-sized particles
Scientists who shrink materials down to the nanometer scale have found weird and puzzling behaviors that have fired their imaginations and promised unforeseen applications. Now campus scientists have found another unusual effect that could have both good and bad implications for semiconductor devices once they’ve been shrunk to the nanometer scale.

In a paper appearing in a recent issue of Nature, a team of Berkeley physicists, chemists, and mineralogists reported on the unusual behavior of a semiconducting material, zinc sulphide (ZnS), when reduced to pieces only three nanometers across — clumps containing only 700 or so atoms. They found that when the surface of a ZnS nanoparticle gets wet, its entire crystal structure rearranges to become more ordered, closer to the structure of a bulk piece of solid ZnS.

“People had noticed that nanoparticles often had unexpected crystal structures and guessed it might be due to surface effects,” said post-doctoral physicist Benjamin Gilbert of the Department of Earth and Planetary Science. “This is a clear-cut demonstration that surface effects are important in nanoparticles.”

Gilbert and co-author Hengzhong Zhang, a research scientist and physical chemist, suggested that many types of nanoparticles may be as sensitive to water as ZnS. “We think that, for some systems of small nanoparticles maybe two to three nanometers across, this kind of structural transition may be common,” Zhang said.

“There’s a good and bad side to this,” Gilbert added. “If we can control the structure of a nanoparticle through its surface, we can expect to produce a range of structures depending on what molecule is bound to the surface. But this also produces unexpected effects that researchers may not want.”
— Robert Sanders