By Stephen Beech via SWNS
The thinnest bands of gold – just a single atom layer thick – have been created using a century-old technique.
The ground-breaking material has been dubbed ‘goldene’ by Swedish scientists.
They say the process has given the precious metal “new properties” that can make it suitable for use in applications such as carbon dioxide conversion, hydrogen production and even water purification – while the amount of gold used can be much reduced.
Researchers have been trying to make single-atom-thick sheets of gold for several years but failed because of the metal’s tendency to lump together.
But a team at Sweden’s Linköping University has now succeeded thanks to a 100-year-old method first used by Japanese smiths.
Dr. Shun Kashiwaya, an Assistant Professor in the Materials Design Division at Linköping University, said: “If you make a material extremely thin, something extraordinary happens – as with graphene.
“The same thing happens with gold.
“As you know, gold is usually a metal, but if a single-atom-layer thick, the gold can become a semiconductor instead,”
To create goldene, the researchers used a three-dimensional base material where gold is embedded between layers of titanium and carbon.
However, coming up with goldene still proved to be a challenge.
Professor Lars Hultman says part of the progress is due to serendipity.
“We had created the base material with completely different applications in mind,” he said.
“We started with an electrically conductive ceramics called titanium silicon carbide, where silicon is in thin layers.
“Then the idea was to coat the material with gold to make a contact.
“But when we exposed the component to high temperature, the silicon layer was replaced by gold inside the base material.”
Hultman explained that the phenomenon is called “intercalation” – and what the researchers had discovered was titanium gold carbide.
For several years, the Swedish team has had titanium gold carbide without knowing how the gold can be exfoliated or “panned” out.
Hultman found a method, by chance, that has been used in Japanese forging art for over a hundred years.
It is called Murakami’s reagent, which etches away carbon residue and changes the colour of steel, for example in knife making.
However, it was not possible to use the exact same recipe as the smiths did.
Dr. Kashiwaya had to look at modifications.
He said: “I tried different concentrations of Murakami’s reagent and different time spans for etching.
“One day, one week, one month, several months. What we noticed was that the lower the concentration and the longer the etching process, the better. But it still wasn’t enough.”
He says the etching must also be conducted in the dark as cyanide develops in the reaction when it is struck by light, and it dissolves gold.
The last step was to get the gold sheets stable. To prevent the exposed two-dimensional sheets from curling up, a surfactant was added.
Dr. Kashiwaya said: “The goldene sheets are in a solution, a bit like cornflakes in milk.
“Using a type of “sieve”, we can collect the gold and examine it using an electron microscope to confirm that we have succeeded. Which we have.”
He says the new properties of goldene, described in the journal Nature Synthesis, are due to the fact that the gold has two free bonds when two-dimensional.
The Swedish team now plan to investigate whether it is possible to do the same with other noble metals and identify additional future uses.
