Research scientists from Linköping University (LiU) in Sweden say they have created the first two-dimensional single-atom layer of gold using a technique perfected by Japanese smiths over 100 years ago. Dubbed “goldene” in reference to the popular single-atom carbon material graphene that essentially kicked off the 2D materials revolution, the breakthrough material could possess a large number of exotic properties like those found in other single-atom 2D materials.
The researchers behind the first-ever accomplishment also say they believe goldene could also offer several immediate applications. These include new methods for harvesting energy, catalysis for hydrogen generation, carbon conversion, water purification, or even the manufacture of customized chemicals.
Material Challenges Preventing the Creation of a Single-Atom Layer of Gold
In their published study outlining their achievement, the LiU researchers explain how previous attempts to create single-atom layer gold have failed. The most common issue, they explain, is the fact that individual gold atoms tend to clump together, resulting in a 3D glob of gold instead of a smooth 2D sheet. Nonetheless, researchers have still tried to create 2D gold sheets due to the unique properties and myriad potential applications that 2D materials, especially metals, offer.
“If you make a material extremely thin, something extraordinary happens – as with graphene,” explained Shun Kashiwaya, a researcher at the Materials Design Division at LiU. “The same thing happens with gold.”
Surprisingly, Lars Hultman, a professor of thin film physics at LiU, admits that the research team didn’t actually set out to create a single-atom layer of gold. Instead, they stumbled upon the material during another experiment.
“We had created the base material with completely different applications in mind,” Hultman explained. “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.”
To the researchers’ surprise, they didn’t end up with gold-plated titanium silicon carbide. Instead, their base material underwent a chemical process known as “intercalation,” where one material in a layered structure is replaced by another.
“When we exposed the component to high temperature, the silicon layer was replaced by gold inside the base material,” said Hultman.
In effect, the researchers had turned their titanium silicon carbide into titanium gold carbide. Of course, researchers already had this material available to them. However, the team’s fabrication process triggered the idea of using titanium gold carbide to create a single-atom layer of gold.
Single-Atom Layer of Gold Is Best Made In the Dark
Armed with their process of creating titanium gold carbide and a goal of using it to create 2D gold, the LiU team looked for ways to “etch out” the other materials until only the layer of gold atoms remained. They hoped the solution lay in an over 100-year-old technique used by Japanese smiths to etch metals for things like art and knife making, called Murakami’s reagent. While the process immediately showed promise, the researchers said that finding the exact formula involved a lot of trial and error.
“I tried different concentrations of Murakami’s reagent and different time spans for etching,” said Kashiways. “One day, one week, one month, several months.” After various levels of success, the materials scientist quickly determined that the lower the concentration of the etching agent and the longer the etching process, the closer they got to their ultimate goal.
“But it still wasn’t enough,” Kashiwaya explained.
The team soon figured out that the process was more successful if it was done in the dark. That’s because light hitting Murakami’s reagent can produce cyanide, which dissolves gold. When trying to create a 2D gold sheet, having it dissolve is clearly an unwanted result.
Fortunately, and as hoped, the change proved successful. The dark environment prevented the dissolution of the gold, and as the etched titanium gold carbide slowly dissolved away, the desired single-atom layer of gold was left behind. To stabilize the 2D gold and prevent it from rolling up, the team also added a single molecule layer of a surfactant.
“The (resulting) goldene sheets are in a solution, a bit like cornflakes in milk,” said Kashiwaya of his team’s single-atom layer of gold. “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.”
Potential Applications Include Energy Harvesting and Water Purification
Up next, the LiU researchers say they are hoping to look into using their process to create 2D sheets from other noble metals. In the meantime, they are also celebrating their first-ever creation of 2D gold sheets, which they believe could not only dramatically reduce the amount of gold needed in current material configurations but could also offer a wide range of commercial and industrial applications.
The research team explains, “Future applications could include carbon dioxide conversion, hydrogen-generating catalysis, selective production of value-added chemicals, hydrogen production, water purification, communication, and much more.”
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.