“We illustrated how 2D materials can be reassembled into new types of 3D networks with unique physical properties. Practically, we have shown that our materials have very strong and unusual nonlinear optical properties – they efficiently convert light from one color into another.”Ventsislav Valev
A team from the University of Bath in the UK have demonstrated modified energy landscapes at the intersection of 2D materials. By nanoengineering a number of defects in 2D materials that induce intra-bandgap energy levels, these characteristics establish nanomeshes with enhanced optical and electronic properties as useful for the next generation of ultrathin devices in energy, communications, imaging and quantum computing.
2D materials such as graphene and transition metal dichalcogenides, including tungsten disulfide (WS2), are made up of layers of single atoms, with electrons able to move in two dimensions while their motion in the third dimension is restricted. Most applications using 2D materials involve sheets that are lying flat, but they are so thin that, on being illuminated, light only interacts with them for a small thickness, limiting their usefulness. To increase the interaction length with light, studies have been investigating ways to stack and fold 2D materials into “thicker” complex 3D shapes.
As reported in Laser & Photonics Reviews [Murphy et al. Laser Photonics Rev. (2021) DOI: 10.1002/lpor.202100117], the researchers here designed an approach to making intricate 3D networks of 2D sheets of WS2 that retain their 2D characteristics, offering a strongly modified energy landscape compared to the flat-lying WS2 sheets. This 3D arrangement, called a “nanomesh”, is a webbed network of randomly distributed and densely packed stacks.
The WS2 sheets have finite dimensions with irregular edges, with the sheets intersecting and fusing together, and even twist on top of each other and lean against each other, which alters the energy landscape of the materials and brings new physical properties. This energy landscape is evidence that assembling 2D materials into a 3D arrangement goes beyond making 2D materials “thicker” to produce completely new materials.
As team leader Ventsislav Valev told Materials Today, “We illustrated how 2D materials can be reassembled into new types of 3D networks with unique physical properties. Practically, we have shown that our materials have very strong and unusual nonlinear optical properties – they efficiently convert light from one color into another.” The materials are also more broadband than other 2D materials, allowing for a broader spectrum of colors that can be converted into other colors.
The nanomesh is relatively easy to make, and as the material grows on silicon and is therefore compatible with quantum optical technologies, it could be deposited on Si waveguides and used to process optical signals for innovative light-based computing chips. The team now hope to demonstrate how efficiently the material can convert light of one color into another, and are looking to apply their approach to other types of 2D materials.
Stacked 2D nanosheets with enhanced optical and electronic properties