'Magic' chemical gives 2D materials the edge

Ultrathin 2D materials such as graphene promise a revolution in nanoscience and technology. Researchers at Chalmers University of Technology in Sweden have now made an important advance in this field. In a paper in Nature Communications, they present a novel method for controlling the edges of 2D materials using a 'magic' chemical.

"Our method makes it possible to control the edges – atom by atom – in a way that is both easy and scalable, using only mild heating together with abundant, environmentally friendly chemicals, such as hydrogen peroxide," says Battulga Munkhbat, a postdoctoral researcher in the Department of Physics at Chalmers University of Technology, and first author of the paper.

Materials as thin as just a single atomic layer are known as 2D materials, with graphene being the most famous example. Future developments within the field could benefit from studying one particular characteristic inherent to such materials – their edges. Controlling the edges is a challenging scientific problem because they are very different in comparison with the main body of a 2D material. For example, a specific type of edge found in 2D materials known as transition metal dichalcogenides (TMDs) can have magnetic and catalytic properties.

Typical TMDs have edges that can exist in two distinct variants, known as zigzag or armchair. These alternatives are so different that their physical and chemical properties are totally distinct. For example, calculations predict that zigzag edges are metallic and ferromagnetic, whereas armchair edges are semiconducting and non-magnetic.

Similar to these remarkable variations in physical properties, the chemical properties of zigzag and armchair edges can also be very different. This means certain chemicals might be able to 'dissolve' armchair edges, while leaving zigzag ones unaffected. Now, Munkhbat and his colleagues have found just such a 'magic' chemical – in the form of ordinary hydrogen peroxide.

At first, the researchers were totally surprised by their new results.

"It was not only that one type of edge was dominant over the others, but also that the resulting edges were extremely sharp – nearly atomically sharp," says Munkhbat. "This indicates that the 'magic' chemical operates in a so-called self-limiting manner, removing unwanted material atom-by-atom, eventually resulting in edges at the atomically sharp limit. The resulting patterns followed the crystallographic orientation of the original TMD material, producing beautiful, atomically sharp hexagonal nanostructures."

The new method, which combines standard top-down lithographic methods with a new anisotropic wet etching process, therefore makes it possible to create perfect edges in 2D materials.

"This method opens up new and unprecedented possibilities for van der Waals materials (layered 2D materials). We can now combine edge physics with 2D physics in one single material. It is an extremely fascinating development," says Timur Shegai, associate professor in the Department of Physics at Chalmers and the lead researcher.

These and other related 2D materials often attract significant research attention, as they enable crucial advances within nanoscience and technology, with potential applications ranging from quantum electronics to new types of nano-devices. These hopes are manifested in the Graphene Flagship, Europe's biggest ever research initiative, which is coordinated by Chalmers University of Technology.

To make the new technology available to research laboratories and high-tech companies, the researchers have founded a start-up company that offers high quality atomically sharp TMD materials. The researchers also plan to develop further applications for these atomically sharp materials.

This story is adapted from material from Chalmers University of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.