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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Saturday, September 01, 2007

Single-Atom Data Storage & Single-Molecule Logic Switch: Nano Breakthroughs by IBM Physicists

Last week, IBM announced development of a technique that could allow data to be stored in bits containing as little as a single atom. The technique developed by physicists at IBM involves using a scanning tunnelling microscope to place an iron or manganese atom at a specific location on the surface of a non-magnetic thin film -- where interactions between the atom and the surrounding film cause its magnetic moment to point in a certain direction.

Although still far from making their way into products, these breakthroughs will enable scientists at IBM and elsewhere to continue driving the field of nanotechnology. Among other things, this could lead to devices that have storage densities a thousand times greater than today’s best computer disk drives [That 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]. It would pave the way for the exploration of building structures and devices out of ultra-tiny, atomic-scale components which might be used as future computer chips, storage devices, sensors and for applications nobody has imagined yet.

In the paper entitled “Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network,” published in Science, IBM physicists describe major progress in probing the magnetic anisotropy in individual atoms. 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 and this fundamental measurement has important technological consequences because it determines whether or not a magnet can maintain a specific orientation to represent either a “0” or “1” state, the basis for data storage in computers. Previously, nobody had been able to measure the magnetic anisotropy of a single atom.

In a second paper entitled “Current-Induced Hydrogen Tautomerization and Conductance Switching of Naphthalocyanine Molecules,” IBM 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.

The concept of using molecules as electronic components is still in its infancy. Previously, researchers from various laboratories had demonstrated switching within single molecules, but the molecules, because of their complex 3D structures, would change their shape when switching, making them unsuitable for building logic gates for computer chips or memory elements. The researchers have also demonstrated that atoms inside one molecule can be used to switch atoms in an adjacent molecule, representing a rudimentary logic element. Therefore, such molecules could be used as building blocks for more complex molecular devices that serve as logic elements.

References
"Large Magnetic Anisotropy of a Single Atomic Spin Embedded in a Surface Molecular Network" Cyrus F. Hirjibehedin, Chiung-Yuan Lin, Alexander F. Otte, Markus Ternes, Christopher P. Lutz, Barbara A. Jones, and Andreas J. Heinrich,
Science (31 August 2007) p1199-1203. Abstract
&
"Current-Induced Hydrogen Tautomerization and Conductance Switching of Naphthalocyanine Molecules"
Peter Liljeroth, Jascha Repp, and Gerhard Meyer,

Science (31 August 2007) p1203-1206. Abstract

[We thank IBM Media Relations for materials used in this posting]

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