Scanning Tunneling Microscope
Fact sheet
Overview
One of the most tantalizing frontiers in computers is engineering circuits on the nanometer scale, the millionth of a millimeter measure on a par with individual atoms. Scientists at IBM's Zurich Research Laboratory pioneered this field when they invented a device called the scanning tunnelling microscope, or STM, that could image some types of individual atoms on electrically conducting surfaces. For this, the inventors won a Nobel Prize. A few years later, scientists at IBM's Almaden Research Center in California used an STM to move and precisely position individual atoms for the first time.
How it works
Nanocosmos
Computer designers have long sought the benefits of building computers with the tiniest features possible -- eventually even down to a few atoms or molecules. IBM researchers are moving ever closer to that world with pioneering work using a scanning tunnelling microscope, or STM.
The STM can be used not only for imaging surfaces with atomic resolutions, but also for positioning atoms and molecules on such surfaces. In an STM Gallery, Don Eigler, an IBM Fellow, displays examples of his work -- images of various atoms arranged on different surfaces in both artful and scientifically illuminating patterns. Among other achievements, Eigler's team has shown how to visualize quantum behavior on a metal surface and also how individual magnetic atoms can disrupt a material's superconductivity over short distances.
Sticky Wickets
While Eigler works at exceedingly low temperatures so he can make particularly precise scientific measurements, scientists at IBM's Zurich Research Laboratory have succeeded in positioning a certain type of molecule at room temperature -- an environment where many atoms and molecules will just not stay put.
The challenge was to find a molecule that was slippery enough to be pushed around by the STM tip, but sticky enough to remain in place after the tip was withdrawn. The chemical bonds within the molecule also had to resist being broken or altered as the molecule is pushed. The Zurich researchers focused on an organic molecule having a total of 173 atoms, including at its core a stable ring of atoms known as a porphyrin. Computer simulation revealed that when pushed by the STM tip, this molecule "walks" in uncorrelated steps and exhibits exactly the desired degree of stickiness.
The Zurich researchers have used this technique to build an abacus with individual molecules as beads with a diameter of less than one nanometer, one millionth of a millimeter. Using the STM, they form stable rows of ten molecules along steps just one atom high on a copper surface. These steps act as "rails", similar to the earliest form of the abacus, which had grooves instead of rods to keep the beads in line. Individual molecules were then approached by the STM tip and pushed back and forth in a precisely controlled way to count from 0 to 10.
Future applications
IBM's nanoscale research is already yielding scientific insights into the behavior of very small structures, which will help computer designers as they shrink the features on integrated circuits. In the future, developments by IBM researchers using STM technology may eventually pave the way for circuits made from atomic or molecular components. Such circuits could be hundreds of times small than today's electronic circuits, allowing designers to put even more processing power onto chips. That, in turn, could lead to smaller, faster, lower-power and even more portable computers.
For Researchers
Links to related topics
Surface Understanding at the Smallest Level
IBM STM Image Gallery
STM Projects at IBM Research
Scanning Tunneling Microscopy
Zurich Scientists Position Individual Molecules at Room Temperature
STM studies of metal and semiconductor surfaces
Alternative storage mechanisms
Measuring Miniscule Forces
Putting the Squeeze on Buckyballs
IBM CyberDigest Articles
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