For the first time, scientists have succeeded in creating sheets of gold that are only one atomic layer thick. The material has been named gold. According to the researchers from Linköping University, the gold acquires new properties that can make it suitable for, among other things, carbon dioxide conversion, hydrogen production and the production of valuable chemicals. The results are published in the journal Nature Synthesis.
Scientists have long tried to make sheets of gold one atomic layer thick but have failed because of the metal’s tendency to clump together. But now researchers from Linköping University have succeeded thanks to a centuries-old recipe used by Japanese blacksmiths.
– If you make a material extremely thin, something extraordinary happens – like with graphene. The same thing happens with gold. Normally, gold is a metal as you know, but if it becomes an atomic layer thick, the gold can become a semiconductor instead, says Shun Kashiwaya, researcher at the Department of Materials Design at Linköping University.
Started with conductive ceramics
To create the gold, the Linköping researchers started from a three-dimensional basic material in which the gold is embedded between layers of titanium and carbon. But the road to gold has not been smooth sailing. According to Lars Hultman, professor of thin-film physics at Linköping University, part of the progress is down to luck.
– We had created the basic material with completely different applications in mind. We started with electrically conductive ceramics called titanium silicon carbide, where silicon is in thin layers. Then the idea was to coat the ceramics with gold to create a contact. But when we exposed the material to high temperatures, the silicon layer was replaced by gold inside the base material, says Lars Hultman.
The phenomenon is called intercalation and what the researchers had then discovered was titanium gold carbide. For several years, researchers have had titanium gold carbide without knowing how the gold can be “washed out”.
Japanese blacksmithing art
As if by chance, Lars Hultman found a method that has been used in Japanese blacksmithing for over a hundred years. It is called Murakami’s reagent, which etches away carbon residues and changes the color of steel in, for example, knife manufacturing. But it was not possible to use the exact same recipe as those blacksmiths did. Shun Kashawaya had to test himself:
– I tried different concentrations of the Murakami reagent and different time spans for the etching. A day, a week, a month, several months. What we noticed was that the lower the concentration and the longer the etching time, the better. But it still wasn’t enough, he says.
The etching must also be done in the dark as cyanide is developed in the reaction when it is hit by light and it dissolves the gold. The last step was to make 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, a so-called surfactant.
– The sheet with the gold is in a solution, a bit like cornflakes in milk. With the help of a type of “net”, we can collect the gold and examine it in an electron microscope to confirm that we have succeeded. Which we have, says Shun Kashawaya.
Many applications
The new properties of gold are due to the fact that the gold gets two free bonds when it lies in two dimensions. Thanks to it, future applications may include carbon dioxide conversion, production of valuable chemicals, catalysis to produce hydrogen, water purification, communication and much more. In addition, the amount of gold used in applications today can be greatly reduced.
The next step for the LiU researchers is to investigate whether it is possible to do the same with other precious metals and to identify more future applications.
The research was funded by the Swedish Research Council, the Government’s strategic research area in materials science AFM at Linköping University, Knut and Alice Wallenberg Foundation, Åforsk Foundation, Olle Enqvist Foundation, Carl Trygger Foundation, Göran Gustafsson Foundation, MIRAI 2.0, Swedish National Infrastructure for Computing (SNIC) and National Academic Infrastructure for Supercomputing in Sweden (NAISS).
(Source: Linköping University)
