IBM Scientists have built and operated the world's smallest working computer circuits using an innovative new approach in which individual molecules move across an atomic surface like toppling dominoes.
The new "molecule cascade" technique enabled the IBM scientists to make working digital-logic elements some 260,000 times smaller than those used in today's most advanced semiconductor chips.
The circuits were made by creating a precise pattern of carbon monoxide molecules on a copper surface. Moving a single molecule initiates a cascade of molecule motions, just as toppling a single domino can cause a large pattern to fall in sequence. The scientists then designed and created tiny structures that demonstrated the fundamental digital-logic OR and AND functions, data storage and retrieval, and the "wiring" necessary to connect them into functioning computing circuitry.
The most complex circuit they built -- a 12 x 17-nanometer three-input sorter -- is so small that 190 billion could fit atop a standard pencil-top eraser 7mm (about 1/4-inch) in diameter. A nanometer is a billionth of a meter; the length of five to 10 atoms in a line.
"This is a milestone in the quest for nanometer-scale computer circuitry," said Andreas Heinrich, a physicist at IBM's Almaden Research Center in San Jose, Calif., and one of the lead authors of the research article published in today's online edition of Science Magazine, Science Express. "The molecule cascade is not only a novel way to do computation, but it is also the first time all of the components necessary for nanoscale computation have been constructed, connected and then made to compute. It is way smaller than any operating circuits made to date."
"Molecule cascades show how we are learning to harness the properties of very small structures," added IBM Fellow Don Eigler. "I was amazed at how rapidly we progressed from initial discovery to design and operation of functional circuitry."
IBM's molecule cascade works because carbon monoxide molecules can be arranged on a copper surface in an energetically metastable configuration that can be triggered to cascade into a lower energy configuration, just as with toppling dominoes. The metastability is due to the weak repulsion between carbon monoxide molecules placed only one lattice spacing apart.
This molecule cascade and the quantum mirage that Eigler and colleagues discovered two years ago are intriguing examples of novel nanoscale science and information-processing approaches that also yield new insights in the properties and interactions of atoms, molecules and surfaces.
Heinrich, Eigler and colleagues Christopher Lutz and Jay Gupta are continuing their exploratory research to find additional nanometer-scale computing systems based on the cascade mechanism.
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