Nanomesh takes 2D materials into the next dimension

In 1884, Edwin Abbott wrote the novel Flatland: A Romance in Many Dimensions as a satire of Victorian hierarchy. He imagined a world that existed in only two dimensions, where the beings are 2D geometric figures. The physics of such a world are somewhat akin to that of modern 2D materials such as graphene and the transition metal dichalcogenides, which include tungsten disulfide (WS₂), tungsten diselenide (WSe₂), molybdenum disulfide (MoS₂) and molybdenum diselenide (MoSe₂).

In modern 2D materials, which consist of single-atom layers, electrons can move in two dimensions but their motion in the third dimension is restricted. Due to this 'squeeze', 2D materials have enhanced optical and electronic properties that show great promise as next-generation, ultrathin devices in the fields of energy, communications, imaging and quantum computing, among others.

Typically, for all these applications, the 2D materials are envisioned in flat-lying arrangements. Unfortunately, however, the strength of these materials is also their greatest weakness – they are extremely thin. This means that when they are illuminated, light can only interact with them over a tiny thickness, which limits their usefulness. To overcome this shortcoming, researchers are starting to look for new ways to fold 2D materials into complex 3D shapes.

In our 3D universe, 2D materials can be arranged on top of each other. To extend the Flatland metaphor, this arrangement would represent parallel worlds inhabited by people who are destined never to meet.

Now, scientists from the Department of Physics at the University of Bath in the UK have found a way to arrange 2D sheets of WS₂ (previously created in their lab) into a 3D configuration with an energy landscape that is strongly modified when compared to that of the flat-laying WS₂ sheets. This particular 3D arrangement is known as a 'nanomesh' – a webbed network of densely packed, randomly distributed stacks, containing twisted and/or fused WS₂ sheets – and is described in paper in Laser & Photonics Reviews.

In Flatland, modifications of this kind would allow people to step into each other's worlds. "We didn't set out to distress the inhabitants of Flatland," said Ventsislav Valev, who led the research, "But because of the many defects that we nanoengineered in the 2D materials, these hypothetical inhabitants would find their world quite strange indeed.

"First, our WS₂ sheets have finite dimensions with irregular edges, so their world would have a strangely shaped end. Also, some of the sulphur atoms have been replaced by oxygen, which would feel just wrong to any inhabitant. Most importantly, our sheets intersect and fuse together, and even twist on top of each other, which modifies the energy landscape of the materials. For the Flatlanders, such an effect would look like the laws of the universe had suddenly changed across their entire landscape."

"The modified energy landscape is a key point for our study," explained Adelina Ilie, who developed the new material together with her former PhD student and post-doc Zichen Liu. "It is proof that assembling 2D materials into a 3D arrangement does not just result in 'thicker' 2D materials – it produces entirely new materials. Our nanomesh is technologically simple to produce, and it offers tunable material properties to meet the demands of future applications."

"The nanomesh has very strong nonlinear optical properties – it efficiently converts one laser color into another over a broad palette of colours," added Valev. "Our next goal is to use it on Si waveguides for developing quantum optical communications."

"In order to reveal the modified energy landscape, we devised new characterization methods and I look forward to applying these to other materials," said PhD student Alexander Murphy, who was also involved in the research. "Who knows what else we could discover?"

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