Stable silver wire measures just one atom wide

An international research team has developed a stable silver wire that is just one atom wide, in a major step towards the goal of shrinking electronic devices to the molecular scale. Their breakthrough has been published in the journal Nature Communications.

For the past two decades, researchers wanting to develop nanodevices have rarely been successful in creating long atomic wires assembling into a coherently oriented array. In addition, such wires have been unstable in anything outside of a vacuum.

The research team from Fudan University, Japan’s National Institute for Materials Science and the Queensland University of Technology (QUT) found they had surprising success when they did not try to create a wire, atom by atom, within a vacuum. Instead, the researchers put nanoparticles of silver onto the outside of tiny nanorods that have channels inside.

“When we do this in a vacuum, or in some inert atmosphere as people usually do, nothing happens,” said QUT’s Professor Dmitri Golberg, a material scientist and physicist with more than 30 years of experience in working with nanomaterials.

“But we did it in air. The atoms from silver particles diffused very fast and they diffused inside the channels.”

Prof Golberg said the expected result on an experiment like this would be that the silver would react with the oxygen in the air and form silver oxide. “Instead, the atoms go inside the channels to accommodate themselves and make these small strings,” he said.

“It wasn’t intentional, it wasn’t planned to make wires.”

Prof Golberg said the process was like water drops going through a sieve; the result was that wires, as thin as just one atom, formed inside the channels in a self-organisation process, with up to 200 strings in each channel. The researchers then attached the nanowires to electrodes and ran a current through the wire, expecting it to behave like a metal in that current should increase as voltage was increased.

“But at some temperature, the material became an insulator. This is not common for silver and is called metal insulator transition,” Prof Golberg said.

“This is quite an interesting transition in physics.

“And this is a major point, because it means the silver wire could be used as a thermal switch. Depending on the temperature, you change the properties of the material by changing the temperature.”

In the work towards building nanodevices the wire is considered quite long, although it only measures around one-fiftieth of the width of a human hair. According to Prof Goldberg, “It’s still pretty small but for me it’s quite long. In the electron microscope, it’s very big.”

Image caption: Professor Dmitri Golberg.

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