Atomic line-up surprises scientists

Some of the patterns made by lead atoms

By BBC News Online science editor Dr David Whitehouse

US scientists have for the first time observed in detail how groups of atoms can self-assemble into patterns and structures.

The process is due to the effect of tiny forces between the atoms and is not completely understood. It leads to the formation of dots and stripes made of ordered atoms.

The next step is to watch the process happening under different conditions to deduce what parameters influence the atomic behaviour.

Eventually, the scientists hope that they will be able to persuade atoms to assemble useful structures, such as advanced electronic and photonic components for computers.

Unexpected behaviour

The researchers, from the US government Sandia National Labs in New Mexico, saw that when atoms of lead were deposited on a copper sheet they formed themselves into lead dots. While that may not seem surprising, they found that when more lead atoms were added the atoms arranged themselves into stripes.

Watching with the aid of a low-energy electron microscope, the scientists commented that the atoms seemed to be "organised" as one researcher put it. Following the spillage of lead atoms on to the copper, the atoms seemed to be moving according to a "master plan".

The effect has long been predicted by theory. The interplay of competing attractive and repulsive inter-atomic forces could, according to some, lead to the spontaneous formation of patterns.

But not all scientists have expected atoms to actually behave this way. Many suspected that because the predicted behaviour was so peculiar, the theory had to be wrong.

'New physics'

"Such theories were treated with a great deal of scepticism," said Dr Norm Bartlet of the Sandia National Laboratory. According to Sandia's Dr Richard Plass, many scientists have been puzzled by the atoms' behaviour.

"Ten thousand moving atoms should go anywhere, he said. "Nobody really expected an assembly would arise."

Now the researchers believe they have shown that atoms do arrange themselves spontaneously into what could be useful patterns.

"This work - which to our knowledge is the first unambiguous observation of the expected sequence of domain patterns - helps understand the new physics that manifests itself at these small scales," said researcher Dr Gary Kellogg.

Future computers

"New materials with highly specialised properties necessary to meet consumer needs can be fabricated only by tailoring the structure of the material on the nanometre scale.

"This work provides insight into how nature does this, and how humans can do the same," he added.

The hope is that by observing atoms in the act of self-assembly, combined with an influence on some of the factors that control the process, scientists could gain an understanding that would enable them to persuade atoms to assemble useful structures.

One possibility is the construction of a photonic lattice - a network of silicon rods that channels light - that could be the basis for tomorrow's advanced computers.