 The naphthalocyanine molecule in the “on” and the “off” states. (Photo: IBM) |
August 31, 2007 — IBM has announced two major scientific achievements, detailed in two articles by the journal Science, that advance the futuristic concept of using molecules as electronic components.
The first reports major progress in probing magnetic anisotropy in individual atoms, a fundamental measurement that determines an atom’s ability to store information. Previously, nobody had been able to measure the magnetic anisotropy of a single atom, says IBM. And with further work it may be possible to build structures consisting of small clusters of atoms, or even individual atoms, that could reliably store magnetic information. The breakthrough could lead to new kinds of structures and devices so small they could be applied to entire new fields and disciplines beyond traditional computing.
The second article describes the first single-molecule switch that, IBM says, “can operate flawlessly without disrupting the molecule’s outer frame — a significant step toward building computing elements at the molecular scale that are vastly smaller, faster, and use less energy than today’s computer chips and memory devices.” In addition to switching within a single molecule, the researchers demonstrated that atoms inside one molecule can be used to switch atoms in an adjacent molecule, representing a rudimentary logic element. This is made possible partly because the molecular framework is not disturbed.
In the paper titled “Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network,” the researchers used IBM’s special scanning tunneling microscope (STM) to manipulate individual iron atoms and arranged them with atomic precision on a specially prepared copper surface. They then determined the orientation and strength of the magnetic anisotropy of the individual iron atoms.
“One of the major challenges for the IT industry today is shrinking the bit size used for data storage to the smallest possible features, while increasing the capacity,” said Gian-Luca Bona, manager of science and technology at the IBM Almaden Research Center in San Jose, California. “We are working at the ultimate edge of what is possible — and we are now one step closer to figuring out how to store data at the atomic level. Understanding the specific magnetic properties of atoms is the cornerstone of progressing toward new, more efficient ways to store data.”
In the paper titled “Current-Induced Hydrogen Tautomerization and Conductance Switching of Naphthalocyanine Molecules,” IBM researchers describe the ability to switch a single molecule “on” and “off,” a basic element of computer logic, using two hydrogen atoms within a naphthalocyanine organic molecule. Previously, researchers at IBM and elsewhere have demonstrated switching within single molecules, but the molecules would change their shape when switching, making them unsuitable for building logic gates for computer chips or memory elements.
The switching within the molecule used by the IBM researchers is well-defined, highly-localized, reversible, intrinsic to the molecule, and does not involve changes in the molecular frame. Therefore, this molecule could be used as a building block for more complex molecular devices that serve as logic elements. As the shape of the molecule does not change during switching, single switches can be coupled in a controlled way. The switching process should also work with molecules embedded in more complex structures.
Molecular switches could one day lead to computer chips with speeds as fast as today’s fastest supercomputers. Development of conventional silicon-based CMOS chips is approaching its physical limits, and the IT industry is exploring new, truly disruptive technologies to achieve further increases in computer performance. Modular molecular logic is a possible candidate. The next step for the research team is to build a series of these molecules into a circuit, then figure out how to network those together into a molecular chip.