Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

mercredi 15 septembre 2004

For the first time, a team of physicists of the National Institute of Standards and Technology (NIST) has controlled "the movement of a single atom back and forth between neighboring locations on a crystal." This will allow to build nanoscale devices atom by atom. Not happy enough with this technological breakthrough, the NIST team also discovered that the atoms were 'noisy' when moving on the crystal surface. They converted the electronic signals emitted by the atoms into audio ones and they were quite surprised to hear something similar to a 'hip-hop' musician's rhythmic 'scratching'. The audio files also helped the team to know in real time that atoms have moved into desired positions. Read more...

Here are some general details about the experiments.

Several research groups already are using specialized microscopes to build simple structures by moving atoms one at a time. The NIST advance makes it easier to reliably position atoms in very specific locations. "What we did to the atom is something like lubricating a ball bearing so that less force is required to move it," says Joseph Stroscio, a member of the NIST team.
Such basic nanoscale construction tools will be essential for computer-controlled assembly of more complex atomic-scale structures and devices. These devices will operate using quantum physics principles that only occur at the atomic scale, or may be the ultimate miniaturization of a conventional device, such as an "atomic switch" where the motion of a single atom can turn electrical signals on and off.

And now, here is more technical information.

The research involved using a custom-built, cryogenic scanning tunneling microscope (STM) to move a cobalt atom around on a bed of copper atoms that are closely packed in a lattice pattern.
NIST scientists discovered that the cobalt atom responds to both the STM tip and the copper surface, and that the atom "hops" back and forth between nearby bonding sites instead of gliding smoothly. With slight increases in the current flowing through the tip to the atom, the researchers were able to make the cobalt atom heat up and vibrate and weaken the cobalt-copper bonds. This induced the cobalt atom to hop between the two types of lattice sites, with the rate of transfer controlled by the amount of current flowing.
NIST logo made with cobalt atoms Here is a 40-nanometer-wide NIST logo made with cobalt atoms on a copper surface. "The ripples in the background are made by electrons, which create a fluid-like layer at the copper surface. Each atom on the surface acts like a pebble dropped in a pond." (Credit: Joseph Stroscio and Robert Celotta, NIST)
Gaia Spacecraft And this is a scanning tunneling microscope (STM) topographic image of a single atom of cobalt this copper surface shown in a light shaded view. Each side is about 5 nanometers wide. (Credit: Joseph Stroscio and Robert Celotta, NIST)
The NIST researchers also found that they could use the STM tip to reshape the energy environment around the cobalt atom. This allows control over the amount of time the cobalt atom spends in one of the lattice sites. Using this technique the researchers found they can even trap the cobalt atom in a lattice site that the atom normally avoids. Sounds of the "protesting" atom give rise to the "hip hop" scratching sound.

Here is a direct link to an audio file of the hip-hop atoms (Real Player necessary, 2 minutes and 40 seconds).

The new results are among the earliest to be published based on work performed at NISTís Nanoscale Physics Facility, where scientists are using a computer-controlled STM to autonomously manipulate and control individual atoms, with the intent to build useful devices and nanostructures.

The research work has been published by the magazine Science in its September 9 issue. Here is a link to the abstract of the paper named "Controlling the Dynamics of a Single Atom in Lateral Atom Manipulation." The above image of the single atom of cobalt comes from supporting online material to this article.

Sources: National Institute of Standards and Technology (NIST) news release, via EurekAlert!, September 14, 2004; Science, September 9, 2004; and other NIST pages

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