The Baltimore Sun from Baltimore, Maryland • Page 7

The Sun Monday, July 15, 1996 Page 7a '4 Why smaller is better atom 1TTT 1 1 or King atom III 'l i il ft f-'lll 'i Performance: Scientists are developing molecular computer memories with greater capacity and materials of higher strength. By Frank D. Roylance BUN STAFF I Is, "i 'I if! The IBUs are placed at key points on branching molecules called dendritic polymers, all precisely constructed in the consortium's laboratories. The IBUs are like knots on a vast and Intricate net that is just one molecule thick. In a computer memory, the polymer lattice might be mounted on a spinning disc, and its IBUs could be read, written upon and erased by the tip of an STM.

A functioning, nano-scale electronic memory is probably five to 10 years away, Dalton said. Scientists still need to figure out how far apart the individual iron molecules need to be to insulate them from each other. That's critical to prevent "cross-talk" an exchange of electrons that would trash data. They also need a way to anchor the lattice and a technology for precisely maneuvering the STM probe. Up the Pacific Coast, at the Lawrence Livermore lab, materials scientist Barbee is laying down mists of metal in thousands of alternating layers barely 25 atoms thick.

The process creates high-performance metal alloys, joining chemical elements that can't be combined by conventional metallurgy because their crystal structures won't link up. "We are at the limits of mi-crostructure engineering," he said. "We're doing nano-science and nano-engineering." These "microlayers" are put down in a process called "sputtering." In a vacuum chamber, he said, "we bombard the surface of a solid like copper with the inert gas argon." The argon atoms hit the copper atoms with so much energy that they heat up to 5.5 million degrees Celsius and evaporate. They quickly condense again on nearby surfaces in layers a few dozens of atoms thick, "in much the same way that one produces dew in the morning," he said. Repeated thousands of times with alternating metals, the process creates many-layered sheets of an entirely new alloy.

"We have made things with 250,000 layers of materials with a total thickness of 125 microns, a little more than a human hair," Barbee said. His lab has put more than 75 of the 92 naturally occurring elements into microlayer materials, and some have begun to appear in new products. The materials have great commercial potential because of their remarkable properties: Strength: "Some of these microlayer materials have been pushed to 70 percent of their theoretical strength limits," Barbee said. Typical strengths in normal metals are 3 percent to 5 percent of those limits. One copper-nickel microlayer material has a tensile strength a resistance to being torn apart of 270,000 pounds per square inch 65 percent of its theoretical limit.

Hardness: By itself, chromium is 2 percent the hardness of a diamond, while platinum is 1 percent. Platinum-chromium microlayers, however, have a hardness that is 25 percent that of a diamond. "It's a very hard, corrosion-resistant ma- UNIVERSITY OF SOUTHERN CALIFORNIA Teamwork: George A. Olah (left) and Larry R. Dalton are leading a team working to create a computer memory device the size of bacteria.

dollars each year in fuel costs alone. Data storage: New microlayer coatings for computer disk drives would greatly increase their sensitivity and capacity. The best commercially available drives can now store a half-gigabyte (500 million bytes) of data per square inch. New coatings could push that to 10 gigabytes (10 billion). teriaL," Barbee said.

Heat tolerance: Microlayer materials on gas turbine blades could immensely improve cooling, boosting jet engine performance and durability while reducing engine weight. Engine-maker Pratt Whitney, a partner on the project, predicts that the U.S. commercial jet fleet could save a quarter-billion miBMilMi mm, ta Warn mm wm $mmi 0 Soree Enter to win one of six 5 -minute Shopping Sprees and get up to $5,000 of RadioShack merchandise-FREE Enter at RadioShack by August 7 See details below SOMEWHERE IN THE descent through the realm of the extremely small, you cross a line from engineering into chemistry. You leave behind silicon circuits and tiny machines that are merely microscopic, and begin to move among atoms and molecules. That's where Larry R.

Dalton and Troy W. Barbee Jr. work. Barbee is a materials scientist at the Lawrence Livermore National Laboratory near San Francisco, where he is creating new, high-performance alloys, atom by atom. Dalton, a professor of chemistry and electrical engineering at the University of Southern California, co-directs a team that is assembling individual molecules into working computer memory devices as small as bacteria.

He and USC chemist and 1994 Nobel laureate Dr. George A. Olah are leading a multi-university consortium of scientists working under a $6.7 million Defense Department grant. If successful, their work could lead to computers packing a thousand times more data in their disk drives than they do today, or providing miniature memories for devices now too small to hold them. A home computer with a gigabyte (a billion bytes) of memory could be transformed into one with a trillion bytes (a terabyte).

The technology could make other devices more portable and open hundreds of new applications to computerization. "The more you can store per unit of space, the greater flexibility you have In manufacturing devices," Dalton said. The demand for huge capacities in small spaces is increasing rapidly. NASA, for example, wants to build smaller spacecraft. It also receives torrents of data from space that needs to be stored and retrieved.

Law enforcement agencies need rapid access to criminal information data banks, including digital fingerprint files. Scientists, corporations, air traffic controllers and ernment agencies need help with their voluminous files. But scientists like Dalton are also driven by the sheer challenge of building things in what he calls the "netherworld" between the dimensions where things are manufactured today and the realm of the atom. "Can I do it? Can I build something that hasn't been done before? That's the intellectual curiosity that drives research," he said. "There isnt a scientist in the field that isn't highly motivated by that." Twenty years ago, he said, "any reasonable scientist would have said we were crazy.

It would have been impossible." Such tiny dimensions are almost unfathomable. Engineers who build objects such as computer chips typically work in scales measured in microns millionths of a meter. Dalton's work is measured in nanometers billionthsofameter. If that's hard to grasp, try this: Pull a hair from your head and look at it. That hair is probably about 100 microns thick.

That's 100,000 nanometers. A single virus might measure 100 nanometers. A line of three or four silicon atoms is a structure that's already one nanometer long. Nano-fabrication became feasible only after the development of the scanning tunneling microscope (STM) by IBM researchers in 1981. The microscopes familiar to biology students use light to illuminate a specimen.

But light cant illuminate the nano-world. Its wavelengths are too wide to reveal the details. The STM works more like an old-fashioned phonograph. It "sees" by systematically moving a probe a needle Just a few atoms thick across the surface of an object. It records tiny changes In the needle's electrical charge as it passes just above individual atoms.

Those electrical signals are measured and reassembled by computer, then enlarged into a video image of the atomic terrain beneath the probe. Scientists found that what they could see with the STM probe, they could also manipulate. In a 1989 publicity stunt, IBM researchers piled 35 individual xenon atoms into a nano-scale IBM signboard. At USC, Cornell, the California Institute of Technology and the University of North Carolina, Dalton and his colleagues are using an STM probe to add and subtract electrons on iron-based molecules. That switches their chemical state, changing them to represent ones or zeros the fundamental alphabet of digital memory.

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