Molecular billiards

24 February 2008
Posted by Chris Smith.

 Scientists have revolutionised the study of chemical surfaces by coming up with a way to push individual atoms around like a miniature billiard game. Markus Ternes from IBM's Almaden Research Center in San Jose used a technique called atomic force microscopy to move atoms of cobalt over platinum or copper surfaces and at the same time measured the friction between the atoms and the surface. The technique makes use of a tiny quartz probe shaped like a miniature tuning fork. One prong is fixed whilst the other vibrates 20,000 times per second but over a very small distance. When the sharp tip of the probe is brought close to an atom of interest the electrical interaction between them alters the vibration frequency of the probe by a characteristic amount, allowing the atom to be identified. But team have also found that the atom can be moved by dragging the probe across it, and by measuring how much force needs to be applied, the friction between the atom and the surface it's sitting on can also be calculated. By measuring the behaviour of atoms sliding over a surface in a range of directions the team are able to generate "energy landscapes" which resemble the atomic equivalent of an egg-box with low-energy wells where the atoms prefers to sit on the surface; these areas represent the spaces between the atoms making up the surface. Intriguingly, a cobalt atom sitting on a player of platinum requires more than 12 times the force to move it compared with the same atom sitting on copper. The discovery of this technique, which is highly reminiscent of IBM's famous 1990 experiment in which they wrote their company initials in atoms of xenon, will help scientists to much better understand how atoms and molecules interact and spread out on surfaces. Ternes and his colleagues point out that the breakthough is a big step forward in our drive to assemble nanoscale devices because it will provide a much more powerful and quantitative way to understand how atomic and molecular structures interact.

AFM Diagram The Atomic Force Microscope
The oscillating tip interacts with an atom pulling it along. Which affects the speed the tip is vibrating. The machine itself
The tuning fork The head of the machine
The tiny scanning head. A close up of the quartz tuning fork, The little white bump on the fork is the tip which does the scanning

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