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Making Micromachines On The Cheap

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Making Micromachines on the Cheap

STARTING MORE THAN 10 YEARS AGO, electrical and mechanical engineers joined forces to craft minuscule gears, switches, and power supplies for next-generation electronic devices. Micromachines have now arrived in the form of air-bag sensors and other tiny gizmos. But prices have remained high because the devices are often made in costly semiconductor cleanrooms.

Adam Cohen, an engineer at the University of Southern California's Information Sciences Institute, has a different production approach that could drastically reduce costs. Dubbed Efab, for electrochemical fabrication, the process relies on a technique known as rapid prototyping, in which engineers build up devices layer by layer, rather than precision-machining them from silicon.

The most common devices currently produced by rapid prototyping are plastic components a few centimeters in diameter. Cohen hopes to do much better. His team has already built tiny chains consisting of up to 12 metal layers. Soon, the team plans to stack up thousands of layers to make sophisticated 3-D components that are far smaller than the width of a human hair. These could be constructed directly on top of other semiconductors. Efab, according to Cohen, could reduce the cost of some microcomponents by a factor of 100.EDITED BY NEIL GROSSReturn to top

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Your Lawn Is Killing the Planet

THERE'S NOTHING LIKE THE SWEET SMELL OF FRESHLY MOWN GRASS. But the chemicals that cause the pleasant fragrance in certain combinations do a lot of harm to the atmosphere. What's more, the emissions grow stronger as cut grass withers, according to the Cooperative Institute for Research in Environmental Sciences in Boulder, Colo.

The troublesome gases, called volatile organic compounds (VOCs), consist mostly of carbon, hydrogen, oxygen, or nitrogen. They contribute to greenhouse-effect warming and react in sunlight with nitrogen oxides to form photochemical smog. In a lab experiment that simulated typical outside conditions, stems of white clover and fescue grass were cut and evaluated for VOC content by means of mass spectrometry. The researchers found that emissions of certain VOCs spiked immediately after cutting, while others continued at a high rate for the next two days, until the stems dried out.

Uncut grass, like trees and other plants, also give off VOCs. But cutting makes it worse. During the summer, in a city the size of Los Angeles, mowing accounts for up to 10% of the VOCs entering the atmosphere, researchers say. EDITED BY NEIL GROSSReturn to top

It Weighs Nothing, but This Gel's No Lightweight

AEROGELS ARE MADE BY TAKING A GEL OF SILICA AND DRYING IT to form a solid material only three times heavier than air. This exotic stuff, invented in the 1930s, has been used for insulation on the Mars Rover, among other applications. But the incredibly lightweight material would be far more versatile if scientists could easily tailor its properties to conduct electricity or perform other useful tasks.

Now, scientists at the Naval Research Laboratory in Washington have discovered a way to make a wide variety of custom aerogels. A team led by Debra R. Rolison and Celia Merzbacher has developed a method of adding other substances, such as minuscule particles of carbon or gold, to the silica just before it begins to gel. By a mechanism that is still under study, the added particles end up "glued" into the gel and are dispersed throughout the material when it is dried into aerogel.

That opens up many possibilities. In the Apr. 23 issue of Science, Rolison reported that she had created a sensor by coating gold particles with an organic dye that instantly changes color when acid wafts through the many pores in the aerogel. She also has made aerogels with carbon and platinum particles, in which the added elements can act as catalysts for chemical reactions. And she envisions putting in the right combination of electric pathways and catalytic materials to fashion the guts of more efficient fuel cells for pollution-free energy. With the new method of gluing materials into aerogels, "the only restriction of their versatility is how clever you are," she says.EDITED BY NEIL GROSSReturn to top

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