Scientists get ball rolling on stacks of 2D materials

Layered transition metal dichalcogenides (TMDCs) – materials composed of metal nanolayers sandwiched between two layers of chalcogens such as sulfur or selenium – have become extremely attractive to the research community due to their ability to exfoliate into single two-dimensional (2D) layers. Similar to graphene, these 2D layers not only retain some of the unique properties of the bulk material, but also demonstrate direct-gap semiconducting behavior, excellent electrocatalytic activity and unique quantum phenomena such as charge density waves (CDW).

But generating complex, multi-element TMDCs, which are essential for the future development of new generations of quantum, electronic and energy conversion materials, has proved difficult.

"It is relatively simple to make a binary material from one type of metal and one type of chalcogen," said Viktor Balema, a senior scientist at Ames Laboratory. "Once you try to add more metals or chalcogens to the reactants, combining them into a uniform structure becomes challenging. It was even believed that alloying of two or more different binary TMDCs in one single-phase material is absolutely impossible."

To overcome this obstacle, postdoctoral research associate Ihor Hlova tried using ball-milling and subsequent reactive fusion to combine such TMDCs as molybdenum disulfide (MoS₂), tungsten diselenide (WSe₂), tungsten disulfide (WS₂), tantalum disulfide (TaS₂) and niobium diselenide (NbSe₂). Ball-milling is a mechanochemical process capable of exfoliating layered materials into single- or few-layer-nanosheets and then restoring their multi-layered arrangements by restacking.

"Very likely, we have just opened doors to the entirely new class of finely tunable, quantum matter."Vitalij Pecharsky, Ames Laboratory

"Mechanical processing treats binary TMDCs like shuffling together two separate decks of cards," explained Balema. "They are reordered to form 3D-heterostructured architectures – an unprecedented phenomenon first observed in our work."

Heating the resulting 3D heterostructures brings them to the edge of their stability, by reordering atoms within and between their layers. This results in single-phase solids that can, in turn, be exfoliated or peeled into 2D single layers similar to graphene, but with their own unique tunable properties. The scientists report this work in a paper in Chemical Communications.

"Preliminary examination of properties of only a few, earlier unavailable, compounds proves as exciting as synthetic results are," said Vitalij Pecharsky, a senior scientist at Ames Laboratory and a professor of materials science and engineering at Iowa State University. "Very likely, we have just opened doors to the entirely new class of finely tunable, quantum matter."

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