The "Small Frontier" – Exploring the Atomic Landscape

Imagine beaches with rolling surf – the terrain of a tiny tropical island. Now picture a whole string of such islands, not on the Pacific, but on the tip of your finger.

According to physicist and IBM fellow Don Eigler this "small frontier" not only exists, but is "hugely important" to our future computing capabilities.

By small, Eigler means really small. Far from the realm of grass skirts and Bahama Mamas, he explores the smallest landscape possible - one formed from "nature's building blocks," atoms and their electrons.

Too Small to See

Just seeing this tiny world proves a feat. To "see" something, you need to bounce waves off it, but not just any wave will work. The smaller the object, the smaller the wave you need to see it. Though light waves are the right size for things we look at everyday, they are about a thousand times too big to see atoms.

To see Eigler's world, scientists need waves smaller than atoms – electron waves.

Figure 1. Electron waves on a metal surface.  Image Courtesy of National Center of Competence in Research (NCCR) on Nanoscale Science, Switzerland.

Figure 1. Electron waves on a metal surface. Image Courtesy of National Center of Competence in Research (NCCR) on Nanoscale Science, Switzerland.

As pleasing as it may feel to picture atoms as baby solar systems, with electron planets orbiting proton suns, physicists now use a model where electrons exist as fuzzy clouds with both particle and wave properties.

The "Atomoscope," Eigler's custom-designed microscope, sees atoms using these electron waves. The microscope consists of a metal tip mounted on a robotic arm. The arm moves across a sample, measuring (with a beam of electrons) its distance from the atoms under observation. As the arm moves up and down to maintain a constant distance – feeling its way through the dark – an attached computer records its motions and plots the atomic landscape.

Island Activities

So once you can see it, what do you do on a deserted nano-island? Eigler's answer: build things.

By bringing the tip of his microscope just close enough to touch (and temporarily bond with) an atom, Eigler can "slide" atoms along to form deliberate designs. In 1989, he formed his first such design, the three letters, I-B-M, from 35 xenon atoms.

In response to doubts from the audience, Eigler stressed the importance of such tiny patterns: "Just think if we couldn't create structures of our own design – we wouldn't have tables, or the chairs you are sitting in."

Though Eigler is not in the furniture business, he also hopes to employ his work for practical purposes - namely transforming the modern computer.

Quantum Computing and Mirages on the Pond

"In the computer business, what's important is moving information from one place to another," says Eigler. With atoms in the right configurations, he believes he can do just this.

In one early technique, Eigler set atoms in a row, "where they don't want to be," and then placed one too many atoms at the head of the line. This started a chain reaction of atoms pushing and shoving. As one atom moved the next, it sent information along the row, much like children playing whisper down the lane.

"It's a process very similar to setting off a row of dominos," says Eigler.

But now Eigler focuses on another method , what he believes may lead to new advances in quantum computing.

Imagine a calm pond. You throw a stone into the water and ripples travel out towards the shores. They reflect and travel back towards the pond's center. In some places the waves build off their reflections, making higher waves. In other places the waves and their reflections fight one another, leaving nothing.

Eigler studies these wave interactions, not by casting stones into water, but atoms into a pool of electrons. His ponds, "electron corrals," consist of a series of xenon atoms formed into ellipses. Inside the ellipses, he places one additional atom in a key location. The building and canceling of the resulting electron ripples creates a large wave, comparable in size to the atom itself, on the other side of the corral. These large waves, called "quantum mirages," allow information to flow across the corral.

The Real Nano MP3 Player?

Eigler has linked these corrals to form nano-versions of circuits found in today's computers, but admitted that these circuits are "not very realistic right now." Though a thousand times smaller than their present-day counterparts, they work about a million times more slowly.

At the same time, he reassured that as an explorer on the newest and tiniest "terra incognita" there is still much more to do:

"This is only the first shot."

- Joseph Calamia

JYI has received funding support from several sources, including the Burroughs Wellcome Fund, the National Science Foundation, and Duke University.
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