Researchers Discover Properties of New Two-Dimensional Material

Thanks to a team of Danish and Italian researchers, a new two-dimensional (2D) material has become a reality.

Guided by physicists at Aarhus University, the study succeeded in the first experimental realization and structural examination of single-layer vanadium disulfide (VS2). It has been reported in the July 24th issue of journal 2D Materials.

VS2 belongs to a diverse group of compounds referred to as transition metal dichalcogenides (TMDs). A number of these can adopt a layered crystal structure from which atomically thin crystalline sheets can be isolated. The electronic properties of the single-atomic-layer crystals can vary in significant ways from those of the layered bulk crystals.

Lead author Dr Charlotte Sanders of Aarhus University elucidated the significance of the new findings: "Theoretical studies suggest that single-layer VS2 might exhibit very interesting physics, including magnetism and strong correlations. It might also host charge density wave states, as does bulk VS2. However, making VS2 is difficult and the single layer has not been successfully made before now.

"In fact, magnetism in single-layer materials has only recently been observed, and is still quite rare. So, the possibility that this material might be magnetic is exciting."

In order to create a single layer of VS2, the scientists evaporated vanadium onto a clean gold surface at room temperature. Next, they heated the sample in the presence of sulfur-containing molecules that react with the vanadium to yield the VS2. The team computed the properties of the samples using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy.

Notably, a new and unpredicted vanadium sulfide compound was also discovered by the team. Many of the 2D materials can, in theory (although not essentially in practice), be derived from bulk layered crystals. However, there is no 3D material that has a similar crystal structure and stoichiometry to those of the new compound, which is created when single-layer VS2 is exhausted of sulfur by heating.

In consideration of the probable magnetic properties of related vanadium compounds, the new material could be another candidate for 2D magnetism.

The new material's electronic structure, along with possible charge density wave phases and magnetic ordering, remain to be explored, and an interesting open question is how its properties differ from those of stoichiometric single-layer VS2.

Dr Charlotte Sanders, Lead Author


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