The world's thinnest gold leaf, called "gold", is only 1 atom thick

Scientists have created the thinnest in the world gold a sheet that is only one atom thick.

The new material, called “gold,” could have important applications in carbon dioxide conversion and hydrogen generation, the researchers said.

To make the gold, the team used a 100-year-old technique used by Japanese smiths to isolate single layers of the precious metal. They reported their work in the journal Natural synthesis on April 16.

Researchers are particularly interested in two-dimensional materials because of their unusual optical, electronic and catalytic properties. The extremely large surface area of these substances relative to their volume means that they behave very differently from chemically identical bulk solids, and many examples of 2D materials have been reported since the discovery of graphene in 2004.

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However, most of these materials are made from non-metals or mixed compounds, and creating single-atom sheets of pure metals is much more challenging.

Structural layer golden.

Goldene sheets are only one atom thick. (Image: Shun Kashiwaya)

“Metals don’t like to be alone” Michael Jung, a solid-state chemist at the University at Albany, told Live Science in an email. “Because the bonding in metals is delocalized, they will easily bond together and agglomerate. Preparing a single layer is a big feat because you’re fighting against the metal’s desire to bond not only to itself but also to other sheets.”

Previous attempts have encountered this problem. Several teams have created a single layer of gold atoms embedded in a a supporting solid such as silicon carbide coated with graphene — “as a sort of ‘sandwich’ structure using graphene as the pseudo-bread and gold as the meat,” Yeung said. But extracting the gold from these complex layered solids proved problematic, with the gold atoms coagulating into nanoparticles as soon as the support was removed.

Avoid Kashiwayaassistant professor in the Department of Physics, Chemistry and Biology at Linkӧping University in Sweden, and his colleagues turned this approach on its head to successfully isolate gold sheets for the first time.

They started by creating a layered structure of titanium, silicon and carbon, which they then coated with a surface layer of gold. Over the course of 12 hours, gold particles diffuse into the material, replacing the silicon layer with gold and creating a gold leaf embedded in the solid. However, instead of trying to remove the gold layer, the team carefully etched away the entire surrounding solid, leaving the gold leaf untouched.

Deconstructed diagram of atomic sheets made to create the gold material.

Goldene is prepared by first exchanging silicon atoms in a layered structure with gold. The surrounding solid is then etched away to leave single gold sheets. (Image: Shun Kashiwaya)

They figured out the technique when they co-authored the study Lars Hultman, a professor in the Department of Physics, Chemistry and Biology at Linkӧping University, was researching chemical etchants. Hultman discovered a 100-year-old method used by Japanese blacksmiths to etch carbide residue into steel, Kashiwaya told Live Science. Called Murakami’s reagent, or alkaline potassium ferricyanide, the solution etches the surrounding titanium carbide support without affecting the gold leaf.

To refine the method, the team experimented with different reaction conditions and etching solution concentrations. Most importantly, they found that adding cysteine as a surfactant, or a chemical that lowers the surface tension of a liquid, stabilizes the isolated sheets and prevents the gold atoms from clustering and combining into nanoparticles.

Free-standing gold sheets are up to 100 nanometers long and hundreds of times thinner than regular gold leaf.

Kashiwaya and Hultman believe that because of goldene’s increased chemical reactivity, it may have important applications in reactions for converting carbon dioxide into fuels such as ethanol and methane and water into hydrogen. They are currently working on improving the synthetic method.

“We aim to explore the basic physical and chemical properties of gold gold and further develop the synthetic process to increase gold leaf area and yield,” said Kashivaya. “We also envision applying this approach to fabricate other elemental 2D materials (metals) beyond gold.”

Yeung is particularly interested in the preparation of new 2D materials made possible by this method. “The ability to selectively etch what is normally stable means that a bunch of new materials can be made,” he said.

The next step could be to create a single layer of silver using aluminum as a base, Yeung said.

The world’s thinnest gold leaf, called “gold”, is only 1 atom thick

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