New opportunities for 2D material

Cut: Johanna Rosén, professor at Linköping University. Photo: Anna Nilsen

Materials that are only a few atoms thick exhibit unique properties that make them appealing for energy storage, catalysis and water purification.

Researchers at Linköping University in Sweden have developed a method that enables the synthesis of hundreds of new 2D materials. The study was published in the journal Science.

Since the discovery of graphene, the field of research in extremely thin materials, so-called 2D materials, has increased exponentially. The reason is that 2D materials have a large surface area in relation to their volume or weight. This means the materials have properties such as good conductivity, high strength or heat resistance, which makes the 2D materials of interest in research and applications.

“In a film that’s only a millimetre thin, there can be millions of layers of the material. Between the layers there can be a lot of chemical reactions and thanks to this, 2D materials can be used for energy storage or for generating fuels, for example,” said Johanna Rosén, professor in materials physics at Linköping University.

The largest family of 2D materials is called MXenes. MXenes are created from a 3D parent material called a MAX phase. It consists of three different elements: M is a transition metal, A is an (A-group) element, and X is carbon or nitrogen. By removing the A element with acids (exfoliation), a two-dimensional material is created. Until now, MXenes has been the only material family created in this way.

The Linköping researchers have introduced a theoretical method for predicting other 3D materials that may be suitable for conversion into 2D materials. They have also proved that the theoretical model is consistent with reality.

To succeed, the researchers used a three-step process. They first developed a theoretical model to predict which parent materials would be suitable. Using large-scale calculations at the National Supercomputer Centre, the researchers identified 119 promising 3D materials from a database and a selection consisting of more than 66,000 materials.

The next step was to try to create the material in the lab.

“Out of 119 possible materials, we studied which ones had the chemical stability required and which materials were the best candidates. First, we had to synthesise the 3D material, which was a challenge in itself. Finally, we had a high-quality sample where we could exfoliate and etch away a specific atom layers using hydrofluoric acid,” said Jie Zhou, assistant professor at the Department of Physics, Chemistry and Biology.

The researchers removed yttrium (Y) from the parent material YRu2Si2, which resulted in the formation of two-dimensional Ru2SixOy.

To confirm success in the lab, verification is necessary: the third step. The researchers used the scanning transmission electron microscope Arwen at Linköping University. It can examine materials and their structures at the atomic level. Arwen also makes it possible to investigate which atoms a material is made up of using spectroscopy.

“We were able to confirm that our theoretical model worked well, and that the resulting material consisted of the correct atoms. After exfoliation, images of the material resembled the pages of a book. It’s amazing that the theory could be put into practice, thereby expanding the concept of chemical exfoliation to more materials families than MXenes,” said Jonas Björk, associate professor at the division of Materials design.

The researchers’ discovery means that many more 2D materials with unique properties are within reach. These, in turn, can lay the foundation for many technological applications. The next step for the researchers is to explore more potential precursor materials and scale up the experiments. Rosén believes that future applications are almost endless.

“In general, 2D materials have shown great potential for an enormous number of applications. You can imagine capturing carbon dioxide or purifying water, for example. Now it’s about scaling up the synthesis and doing it in a sustainable way,” said Rosén.

Jim Cornall is editor of Deeptech Digest and publisher at Ayr Coastal Media. He is an award-winning writer, editor, photographer, broadcaster, designer and author. Contact Jim here.