Working atom by atom Performance: Scientists are developing molecular computer memories with greater capacity and materials of higher strength.

July 15, 1996|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

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, 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 1,000 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 and needs new ways to store and quickly retrieve it.

Law enforcement agencies need rapid access to criminal information data banks, including digital fingerprint files. Scientists, corporations, air traffic controllers and government agencies such as the Social Security Administration have similar needs.

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 isn't 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 -- billionths of a meter.

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 can't 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 quickly found that what they could see with the STM probe, they could also manipulate, atom by atom. 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 1s or zeros -- the fundamental alphabet of digital memory. The molecules then become "information-bearing units," or IBUs.

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.

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