Single-Atom Data Storage And Single-Molecule Switching – New Pathways Of Nanotechnology
Two major scientific achievements in the field of nanotechnology could one day lead to new kinds of devices and structures built from a few atoms or molecules.
Schematic three-dimensional image of a molecular “logic gate” of two naphthalocyanine molecules, which are probed by the tip of the low-temperature scanning tunneling microscope. (Credit: IBM)
Although still far from making their way into products, these breakthroughs will enable scientists to continue driving the field of nanotechnology, the exploration of building structures and devices out of ultra-tiny, atomic-scale components. Such devices might be used as future computer chips, storage devices, sensors and for applications nobody has imagined yet.
In the first report, scientists describe major progress in probing a property called magnetic anisotropy in individual atoms. This fundamental measurement has important technological consequences because it determines an atom’s ability to store information. Previously, nobody had been able to measure the magnetic anisotropy of a single atom.
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. Such a storage capability would enable nearly 30,000 feature length movies or the entire contents of YouTube – millions of videos estimated to be more than 1,000 trillion bits of data – to fit in a device the size of an iPod. Perhaps more importantly, the breakthrough could lead to new kinds of structures and devices that are so small they could be applied to entire new fields and disciplines beyond traditional computing.
In the second report, researchers unveiled the first single-molecule switch that 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 also 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.
The Science of The Small: Understanding the Magnetic Properties of Atoms
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.
Anisotropy is an important property for data storage because it determines whether or not a magnet can maintain a specific orientation. This in turn allows the magnet to represent either a “1” or “0,” which is the basis for storing data in computers.
“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.”
Lilliputian Scale Devices: Single Molecule Logic Switching
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.
Switches inside computer chips act like a light switch to turn the flow of electrons on and off and, when put together, make up the logic gates, which in turn make up electrical circuits. Having ever smaller switches allows the circuits to be shrunk to ever smaller sizes, making it possible to pack more circuits into a processor and boosting speed and performance.
These molecular switches could one day lead to computer chips with speeds as fast as today’s fastest supercomputers, but much smaller in size; with some speculating even building computer chips so small they could be the size of a speck of dust or fit on the tip of a needle.
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, though still several years from reality. 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.
The concept of using molecules as electronic components is still in its infancy. Only a few examples of individual molecules serving as switches or memory elements have been demonstrated to date. Most of these molecules are complex, three-dimensional structures and change their shape when switching. Placing them on a surface while maintaining their function is extremely difficult, making them unsuitable as building blocks for computer logic.
The used switching within the molecule 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.
Science 31 August 2007:Vol. 317. no. 5842, pp. 1199 – 1203 DOI: 10.1126/science.1146110
Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network
Cyrus F. Hirjibehedin,1 Chiung-Yuan Lin,1,2 Alexander F. Otte,1,3 Markus Ternes,1,4 Christopher P. Lutz,1 Barbara A. Jones,1 Andreas J. Heinrich1
Magnetic anisotropy allows magnets to maintain their direction of magnetization over time. Using a scanning tunneling microscope to observe spin excitations, we determined the orientation and strength of the anisotropies of individual iron and manganese atoms on a thin layer of copper nitride. The relative intensities of the inelastic tunneling processes are consistent with dipolar interactions, as seen for inelastic neutron scattering. First-principles calculations indicate that the magnetic atoms become incorporated into a polar covalent surface molecular network in the copper nitride. These structures, which provide atom-by-atom accessibility via local probes, have the potential for engineering anisotropies large enough to produce stable magnetization at low temperatures for a single atomic spin.
1 IBM Research Division, Almaden Research Center, San Jose, CA 95120, USA.
2 Center for Probing the Nanoscale, Stanford University, Stanford, CA 94309, USA.
3 Kamerlingh Onnes Laboratorium, Universiteit Leiden, 2300 RA Leiden, Netherlands.
4 Institut de Physique des Nanostructures, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
Science 31 August 2007: Vol. 317. no. 5842, pp. 1203 – 1206 DOI: 10.1126/science.1144366
Current-Induced Hydrogen Tautomerization and Conductance Switching of Naphthalocyanine Molecules
Peter Liljeroth,1* Jascha Repp,1,2 Gerhard Meyer1
The bistability in the position of the two hydrogen atoms in the inner cavity of single free-base naphthalocyanine molecules constitutes a two-level system that was manipulated and probed by low-temperature scanning tunneling microscopy. When adsorbed on an ultrathin insulating film, the molecules can be switched in a controlled fashion between the two states by excitation induced by the inelastic tunneling current. The tautomerization reaction can be probed by resonant tunneling through the molecule and is expressed as considerable changes in the conductivity of the molecule. We also demonstrated a coupling of the switching process so that the charge injection in one molecule induced tautomerization in an adjacent molecule.
1 IBM Zurich Research Laboratory, 8803 Rüschlikon, Switzerland.
2 Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany.