The researchers at Linkoping University in Sweden have successfully developed a free-standing thin sheet of gold, known as goldene in April 2024. Goldene is the first free-standing 2D metallic material, overcoming the challenge of metal atoms tendency to cluster into nanoparticles instead of forming nanosheets. Its thickness is just one atom layer. It is for the first time that such a sheet of gold has been produced. It is a significant achievement in material science, as it transforms gold from its traditional metallic form into a semiconductor when reduced to this ultra-thin state. The discovery opens up numerous potential applications, including carbon dioxide conversion, hydrogen production, and water purification.
With the development of goldene, the gold metal now becomes a part of a select group of elements, like carbon and phosphorous, that can be transformed into 2D sheets. Making 2D sheets using non-metallic elements, like graphene that is based on carbon, is much easier. It is comparatively more difficult to develop 2D sheets using iron, gold and other such metals.
Some important features of goldene are as follows:
- Its size is one-atom thick, i.e., around 100 nanometres. It is 400 times finer than the finest gold leaf available in the market. (1 nanometre is equal to a billionth of a metre.)
- It is a free-standing 2D sheet.
- Its properties differ from those of 3D form of gold (i.e., standard gold), similar to graphene that has different properties than that of carbon.
- Gold in the form of goldene is extremely thin. It, thus, gets transformed into a semi-conductor. As scientists can tune its conductivity, it becomes very useful.
Process of Developing Goldene
In 2004, the scientists developed graphene, i.e., an atom-sized material prepared using carbon. Thenceforth, hundreds of 2D materials have been made by the scientists.
However, scientists faced much difficulty in creating atom-sized metallic sheets, i.e., a single-atom thick 2D gold sheet. This was due to the fact that gold forms clusters, which result in the formation of nanoparticles. Besides, when gold sheets were developed earlier, they remained squashed in between other materials. Now, researchers at the Linkoping University in Sweden have employed an age-old method, called Murakami technique, traditionally adopted by Japanese smiths, to create gold sheets.
Using Murakami Technique Firstly, an atomic monolayer of silicon was placed in between the couple of layers of titanium carbide. This sandwich was then coated with gold. Soon, the gold atoms spread all around the material and occupy the place of silicon atoms. Now, the gold atoms were trapped in the form of a monolayer. Afterwards, the layers of titanium carbide were removed, which led to an atom-sized layer of gold that was free-standing. This technique was used to create high-quality knives and katanas with the help of Murakami’s reagent, a type of chemical.
Challenges Faced by Scientists while Making Goldene
Hultman, a materials physicist at Linkoping University, and his colleagues found it to be very difficult to transform gold into 2D configuration, as it tends to become clustered. In initial attempts, they obtained a thin sheet whose thickness was several atoms. In the following attempts, they obtained a monolayer of gold placed between or on another material. This could not be detached.
In the later attempts, scientists used titanium silicon carbide, which is an electrical conductive ceramic. Inside it, the silicon was present in thin layers. Then, gold was deposited all over the material. Upon placing this component in high temperature, gold replaced the silicon within the base material.
As a result, titanium gold carbide, a 3D material, was developed by the scientists. This structure encompassed 2D sheets of gold. The structure remained like this for many years, as there was no method to pull out gossamer gold layers. Afterwards, the scientists learnt about an etching solution and used it to remove the surrounding layers of titanium and carbon. As a result, goldene was obtained.
When the scientists were freeing goldene, it got turned into a scroll by curling up itself, the moment it got freed. In order to prevent the curling up, the scientists had to modify the etching solution by mixing a surfactant to it. Now, instead of curling up, the sheets began to float in the solution. These tiny sheets resembled cornflakes in milk. Scientists then gathered the gold with the help of a certain sieve and analysed it with an electron microscope.
Potential Applications of Goldene
Goldene has many potential applications. It has become feasible to carry out various processes, ranging from catalysis to electrolysis, using less gold. With the development of goldene, the world of nanotechnology has taken the shape of reality and has not remained merely a realm of possibility. Goldene has led to the creation of new opportunities in different fields. Apart from satisfying scientific curiosity, goldene, a major breakthrough in the scientific field, has the potential of revolutionising the electronics industry.
Being a super thin and super light material, goldene is a promising catalyst that is far more practicable compared to the thicker 3D gold. As a few gold atoms are required to carry out a particular function, goldene has become an economically feasible option. This implies that a lot of gold is used in electronics owing to its electrical conductivity. But now, for the same purpose, lesser amounts can be sufficient. Besides, similar to 2D materials already developed, goldene, too, possesses certain specific properties. This is because there are only six neighbouring atoms for each gold atom in 2D materials; while in 3D crystals, there are 12 neighbouring atoms for each atom.
Some of the potential applications for which goldene can be used are as follows:
- Hydrogen-generating catalysis
- Selective production of value-added chemicals
- Carbon dioxide conversion into ethanol, methane, and other such fuels
- Hydrogen production through water
- Water purification
- Sensing
- Catalysis, and many more
Conclusion
Being just one-atom thick, goldene is a flimsy and the thinnest gold leaf in the world. It has the capability of capturing light in different ways, which makes it apt for catalysis, sensing, and other such applications. It opens up a multitude of interesting opportunities in varied fields for the upcoming generations. It exemplifies human ingenuity and shows the power of scientific exploration. A materials scientist at Linkoping University and co-author, Shun Kashiwaya, said that if scientists applied the technique of creating goldene to other noble metals as well, it would enhance their knowledge of 2D materials and their possible usage in future applications. For instance, a team of scientists at Linkoping University has already started conducting experiments on metals like iridium and platinum to produce their 2D sheets. Besides, they would use aluminas as the base to produce a single layer of silver. This indicates that there could be grand potential even in the tiniest of things.
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