"Understanding how atom manipulation works will allow us to extend these manipulation techniques so that we can build large-scale working nanodevices, atom by atom," Joseph Stroscio told nanotechweb.org. "This work also has potential applications toward the development of an atomic switch, where the motion of a single atom can turn electrical signals on and off."
Stroscio and colleague Robert Celotta moved the cobalt atom with the tip of the STM. The atom "jumped" between the neighbouring face-centred cubic (fcc) and hexagonal close-packed (hcp) sites on the Cu (111) surface.
"The atom motion is not smooth as the tip tries to move the atom, but consists of a series of hops between the binding sites of the surface," explained Stroscio. "We show this very nicely in a new type of image we call a manipulated atom image, which we obtain by dragging the atom across the surface as it is trapped under the scanning tip."
It's energetically favourable for the cobalt atom to sit at fcc sites in the copper surface, rather than hcp sites. As the atom moved between different types of binding site, the researchers also noticed noise in the tunnel current measurements. By translating this electrical noise into an audio signal, the scientists were able to hear when the atom had moved.
"We use the tunnel current in an audio system for a real-time feedback to tell us if the atom is moving or not," said Stroscio.
The team found that they could "lubricate" the motion of the atom by increasing the current flowing through the tip.
"We have shown that it is not just the chemical forces that determine the atom motion but we can also heat the atom up locally by vibrationally exciting it via inelastic electron scattering from the tunnelling electrons," said Stroscio. "This allows the atom to come closer to the top of its potential well and move more easily to the next site."
"It turns out that this is a way to obtain an 'ideal' two-state fluctuating system, which is fundamental in 1/f noise studies," said Stroscio. "Studying this switching process allowed us to determine the heating mechanism involved. In addition we found that we could control the switching by varying the strength of the interaction between the probe tip and the adatom by adjusting the distance between them. This allowed us to obtain a quantitative measure of the interaction strength."
Now the researchers say they have two main goals - understanding and optimizing atom-manipulation techniques, and developing ways to "build large-scale real working nanodevices using autonomous atom-assembly techniques".
The team reported their work in Sciencexpress.