ARCHIVE :: OCTOBER 2002 :: COVER STORY

Atomic Sage
Charles Lieber and His Nanotechnology Research Promise an Era of Microscopic Machines

By David P. Hamilton
Staff Reporter of The Wall Street Journal

Adecade from now, if the silicon computer chip has been replaced by newer, even smaller computing technology, Charles Lieber and his vials of nanowires may well have played a big role.

Name: Charles Lieber Age: 43 Occupation: Nanotechnologist Affiliation: Harvard University "My students are working day and night, and I'm working like crazy- I've never worked so hard in my life."

Dr. Lieber's Harvard University laboratory is one of several around the world focused on manipulating matter at its most basic dimensions-atoms and molecules-to create working electronic devices. The field has been dubbed "nanoelectronics" because atoms themselves are typically only a few nanometers, or billionths of a meter, in diameter.

Much of Dr. Lieber's work so far has focused on ways to create computing circuits out of tiny wire-like structures he calls nanowires, some only a few atoms thick. But the 43-year-old chemist and his research team also are exploring other applications of the technology, including minute sensors that can detect signs of cancer much earlier than existing tests.

"It's really an amazing time, and things are really working well," says the boyish Dr. Lieber. "My students are working day and night, and I'm working like crazy-I've never worked so hard in my life."

Nanoelectronics itself is only the leading edge of a broader effort known as nanotechnology, a catchall term for efforts to manipulate matter at the most fundamental level possible. Some visionaries suggest that nanotechnology could become the next major industrial revolution. While today's applications are limited to areas such as new industrial coatings, enthusiasts figure that nanotechnology could one day lead to tiny molecule-sized machines and novel manufacturing methods in which objects essentially assemble themselves. Critics argue that it is far too early to make such grandiose claims and predict a coming wave of "nanohype" that will end in disappointment.

Bottom-Up

Conceptually, at least, the nanotechnological notion of manipulating material structure and behavior at the atomic level is vastly different from today's most advanced techniques for dealing with the tiny, such as the processes that stamp computer-chip circuitry into silicon. Chip processing is a "top-down" technique, using stencil masks and high-tech tools to essentially spray-paint or sandblast fine circuit patterns on a silicon surface.

By contrast, nanotechnologists focus on "bottom-up" methods involving advanced chemistry that induce atoms and molecules to assemble themselves into functional structures, such as current-carrying "nanowires." Atomic-level computer circuits, for instance, might "grow" themselves under the influence of carefully prepared chemical solutions and controlled environmental conditions.

In Dr. Lieber's basement laboratory, which now employs roughly 25 researchers, graduate student Mark Gudiksen shows off the system the group now uses to grow nanowires. At one end of a glass tube rests a silicon surface dotted with gold particles that serve as catalysts, which help to stimulate the chemical reaction. At the other lies a small pellet of semiconductor material. Blasting the pellet with a laser releases atomic vapors that travel down the tube and recombine on the gold particles, leading to a crazy pincushion of nanowires that grow out every which way from the particles. The nanowires are easily washed from the surface in a simple chemical reaction, then stored in a liquid suspension in small vials. The nanowires, of course, are invisible to the naked eye.

Successfully growing the nanowires was a big step, but it mainly opened the door for much more ambitious research. By altering the reactants as the nanowires are growing, the team can make wires whose composition varies along their lengths. Such nanowires can themselves function as basic electronic components such as diodes and transistors; more recently, former Lieber lab researcher Xianfeng Duan figured out how to make them glow in any color. So such nanowires could conceivably be used as LEDs, the long-lasting, low-powered lights used everywhere from glowing sneakers to traffic lights.

Quantum Leaps

Dr. Lieber's group has also made great strides in laying down grids of crossed nanowires, in which every junction can theoretically function as a transistor-the basic switch used to direct the calculations in computer chips. Such grids don't have to be made on silicon, the material used in most chips these days. He envisions a day when it will be possible to fabricate nanowire circuits on plastic or any other material.

Just last year, Dr. Lieber's team succeeded in wiring up such arrays into simple but working computer circuits. Now, the team is hard at work refining its techniques and designing new components for a basic, programmable nanowire-based computer-a goal Dr. Lieber thinks might be achievable in just a few years.

Such nanowire-based computing could lead to incredibly dense memory chips-a few hundred gigabytes of storage on a chip the size of your thumbnail. The technology might make possible tiny, superfast computers that could be laid out on a small square of plastic, and could theoretically also enable a potentially powerful form of calculation known as quantum computing.

That said, even Dr. Lieber isn't willing to bet that nanowires will end up outgunning existing computer-chip technology. For starters, the chip industry has decades of experience and billions of research dollars aimed at surmounting seemingly insuperable physical obstacles, one reason it has been able to cut chip sizes in half every 18 months or so.

More than that, though, Dr. Lieber thinks nanowires and other nanotechnologies are likely to have their greatest impact in unexpected ways. For instance, another group in his lab recently demonstrated a nanowire-based sensor so sensitive that it can detect single molecules of a given substance. Using such a sensor, the team demonstrated the ability to detect a protein known as the prostate-specific antigen, a fairly reliable marker for prostate cancer, with nearly 10 times greater sensitivity than existing tests.

"If we limit ourselves to the idea that these [nanowires] are just for molecular electronics, I think that's just too limiting," Dr. Lieber says. "We have a remarkable wealth of things in hand to play with."