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 gives rise to a range of physical phenomena and distinctive properties, such as good conductivity, high strength or heat resistance, making 2D materials of interest both within fundamental research and applications.
鈥淚n a film that鈥檚 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,鈥� says Johanna Ros茅n, professor in Materials physics at Link枚ping University.
Three-step process
The largest family of 2D materials is called MXenes. MXenes are created from a three-dimensional 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 Link枚ping researchers have introduced a theoretical method for predicting other three-dimensional 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. In the first step, they developed a theoretical model to predict which parent materials would be suitable. Using large-scale calculations at the National Supercomputer Centre, the researchers were able to identify 119 promising 3D materials from a database and a selection consisting of 66,643 materials.
From theory to lab
The next step was to try to create the material in the lab.
鈥淥ut 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,鈥� says 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.
But to confirm success in the lab, verification is necessary 鈥� step three. The researchers used the scanning transmission electron microscope Arwen at Link枚ping University. It can examine materials and their structures down at the atomic level. In Arwen it is also possible to investigate which atoms a material is made up of using spectroscopy.
鈥淲e 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鈥檚 amazing that the theory could be put into practice, thereby expanding the concept of chemical exfoliation to more materials families than MXenes,鈥� says Jonas Bj枚rk, associate professor at the division of Materials design.
Endless applications
The researchers鈥� discovery means that many more 2D materials with unique properties are within reach. These, in turn, can lay the foundation for a plethora of technological applications. The next step for the researchers is to explore more potential precursor materials and scale up the experiments. Johanna Ros茅n believes that future applications are almost endless.
鈥淚n 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鈥檚 about scaling up the synthesis and doing it in a sustainable way,鈥� says Johanna Ros茅n.
The study was funded by the Knut and Alice Wallenberg Foundation, the Wallenberg Initiative Materials Science for Sustainability (WISE), the G枚ran Gustafsson Foundation for Research in Natural Sciences and Medicine, the Swedish Foundation for Strategic Research, the European Union, the Swedish Research Council and the Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials, AFM, at Link枚ping University.
Article: ; Jonas Bj枚rk, Jie Zhou, Per O. 脜. Persson and Johanna Rosen; Science 2024. Published online 15 March 2024. DOI: 10.1126/science.adj6556
