gold is converted into a semiconductor using chemistry

Over the centuries, goldsmiths have strived to give gold more graceful forms. Finally, thanks to the use of modern chemistry, it was possible to create a material consisting of a single atomic layer, which cannot be made even thinner.

The study, published in the journal Nature Synthesis, introduced this new two-dimensional material, called “gold”, in keeping with established names in the field of materials science. This material has unique properties that are different from the three-dimensional form of gold.

“Once the material becomes extremely thin, something amazing happens, similar to graphene,” explains materials scientist Shun Kashiwaya from Linköping University in Sweden. “This also applies to gold. Gold is normally a metal, but if it is just one atom thick, it takes on semiconductor properties.”

Transforming gold into a two-dimensional form is challenging due to its tendency to stick together. Previous attempts have resulted in either thin sheets of a few atoms or a monolayer trapped between other materials, making it impossible to extract.

Kashiwaya and his colleagues weren’t looking to create monolayer gold, but stumbled upon the process by accident.

“We created a basic material with completely different purposes,” says materials physicist Lars Hultman of Linköping University. “We started by using an electrically conductive ceramic called titanium-silicon carbide, where the silicon is present in thin layers. We then added a layer of gold to make electrical contact. However, when we exposed the component to high temperature, the silicon layer was replaced by gold within the base material.” .

Everything went well, but, as in previous attempts, progress stopped at the stage of monolayer formation. For several years, the team’s gold monolayer remained inaccessible to extraction due to problems with the surrounding layers of titanium and carbon.

This is where a technique based on the use of an etching solution known as Murakami’s reagent came to the rescue.

Murakami’s reagent is a mixture of chemicals used in metalworking to etch carbon and color steel, creating patterns similar to those seen on some Japanese knives.

The researchers experimented with different concentrations of the mixture and time frames of the etching process to remove the titanium and carbon surrounding the gold. The longer the process, the better the result, but for this it was necessary to fulfill several more conditions.

The etching process with Murakami’s reagent produces a byproduct, potassium ferrocyanide. When exposed to light, this compound releases cyanide, which dissolves the gold, so the entire etching process had to be carried out in complete darkness.

Finally, to prevent the thin gold layer from curling and sticking together, a surfactant was added to maintain its integrity.

Analysis showed that these efforts were able to create a stable gold monolayer, consistent with theoretical models.

Gold generally conducts electricity well. However, when it takes the form of a two-dimensional sheet, its atoms take on additional properties, making it a semiconductor with conductive characteristics between a conductor and an insulator.

These properties can be useful in various fields such as water purification, communications and chemical production, opening new prospects for the use of this material.