Carbon monoxide makes the world's smallest circuit.

by Courtesy of IBM Almaden Research Center

THE TRICKLE-DOWN COMPUTER CIRCUIT IBM scientists have created the world’s smallest computer circuit using 545 carbon monoxide (CO) molecules arranged on a grid of copper atoms. The circuit runs in an ultrahigh vacuum at 4 to 10 Kelvins. Here’s how it works: A single input destabilizes a trio of CO molecules (1). The combined repulsive force of two CO molecules pushes the middle molecule onto the next grid space, where a new unstable trio forms (2). The hopping motion repeats itself, creating an information-routing domino effect. Toppled and untoppled CO cascades represent binary 1 and binary 0, respectively (3).

In the never-ending quest for smaller electronics, IBM has produced a computer circuit so small that 200 billion could fit comfortably on your thumbnail. The world’s most petite molecular circuit touts digital-logic elements about 260,000 times tinier than those used in today’s most advanced silicon circuitry — and uses 100,000 times less energy. “This is a milestone in the quest for nanometer-scale computer circuitry,” claims physicist Andreas Heinrich of IBM’s Almaden Research Center in San Jose, California. “It’s the first time all of the components necessary for molecular computation have been constructed, connected, and then made to compute.”

At their most basic, computer circuits calculate complex instructions using thousands of logic gates — components that alter incoming data based on the rules of logic. Heinrich and colleagues created several linked logic gates by arranging intersecting patterns of some 500 carbon monoxide molecules on a flat copper sheet. A nudged molecule kicks off a cascade of tumbling molecules — similar to a row of falling dominoes — and each cascade transmits a bit of information. “It’s beautiful, beautiful laboratory work,” lauds James Tour, a nanoresearch chemist at Rice University.

But don’t expect CO molecules to revolutionize the desktop computer: It’s an aesthetic, rather than a practical, beauty. A single operation takes the nanomachine several hours to complete and the program can’t be reset. Each molecule must be artfully prodded back into position with a scanning tunneling microscope before calculations can be repeated. Says Tour, “It’s not a practical system. But that does not detract from the beauty of the science.”