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Researchers create 'goldene.' Will it be as useful as graphene?

By Anders Torneholm, Linkoping University

For the first time, scientists have managed to create sheets of gold only a single-atom-layer thick. The material has been termed "goldene." According to researchers from Linkoping University, Sweden, this creation has uncovered new properties of gold, making it suitable for use in applications such as carbon dioxide conversion, hydrogen production, and production of value-added chemicals.

Lars Hultman, professor of thin film physics at Linkoping's Department of physics, chemistry, and biology (IFM), examines goldene during its creation. [Credit: Olov Planthaber]

 

 

Scientists have long tried to make single-atom-thick sheets of gold but failed because of the metal's tendency to lump together. However, the Linkoping researchers succeeded thanks to a 100-year-old method used by Japanese metal smiths.

"If you make a material extremely thin, something extraordinary happens -- as with graphene, the same thing happens with gold. Gold is usually a metal, but at a single-atom-layer thick, the gold can become a semiconductor instead," says Shun Kashiwaya, researcher at the Materials Design Division at Linkoping.

A paper about goldene's creation was published in Nature Synthesis in April.

3D base material
To create goldene, the researchers used a three-dimensional base material where gold is embedded between layers of titanium and carbon. However, creating the goldene proved to be a challenge. According to Lars Hultman, professor of thin film physics at Linkoping, part of the progress was due to serendipity.

"We had created the base material with completely different applications in mind. We started with an electrically conductive ceramic 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," says Hultman.

This phenomenon is called intercalation, and what the researchers had discovered was titanium gold carbide. For several years, the researchers have had titanium gold carbide without knowing how the gold could be exfoliated -- or panned out, so to speak.

Japanese forging art
By chance, Hultman found a method that has been used in Japanese forging art for over a century. It is called Murakami's reagent, which etches away carbon residue and changes the color of steel in knife-making, for example. However, it was not possible to use the exact same recipe as the Japanese metal smiths did. The researchers had to look at modifications.

"I tried different concentrations of Murakami's reagent and different time spans for etching," Kashiwaya says. "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."

The etching must also be carried out in the dark, because 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. In this case, a long molecule that separates and stabilizes the sheets, i.e. what's called a "tenside."

"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," says Kashiwaya.

Many possible applications
Will goldene prove as useful and surprising as the "wonder material" graphene (made of carbon), which exhibits ultra-high tensile strength, hardness, electrical conductivity, elasticity, and thermal conductivity? Now scientists have a chance to find out.

The new properties of goldene are due to the fact that the gold has two free bonds when it is two-dimensional. Thanks to this makeup, future applications could include carbon dioxide conversion, hydrogen-generating catalysis, selective production of value-added chemicals, hydrogen production, water purification, communication, and much more.

Moreover, the amount of gold used in applications today may be able to be reduced markedly. Other properties of goldene are yet to be discovered. The next step for the Linkoping researchers is to investigate whether it is possible to do the same with other noble metals and identify additional future applications.

Published April 2024

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