Artificial 2D materials
Artificial 2D materials, image: The University of Manchester
A research team from the National Graphene Institute at the University of Manchester has developed a new method to synthesize 2D materials that are considered impossible or at least unreachable with today's technologies.
Graphene was the world's first two-dimensional material that later opened the doors to the isolation of other two-dimensional materials.
Graphene and other 2D materials usually have a 3D counterpart called a “bulk analog”. For example, graphene is a single layer of carbon atoms derived from graphite.
Recently, there is a growing interest in the production of synthetic 2D materials which do not have a layered bulk analog. Researchers have begun to look at 2D materials that do not have an 3D counterpart.
Traditionally, 2D materials are isolated through a process called mechanical exfoliation - absorbing the bulk material and exfoliating the layers from one another until a single layer is reached.
In contrast to these layered crystals, materials without layered structures are held together by covalent bonds between the atomic planes that do not allow mechanical exfoliation.
As published in Nano Letters, the team of the University has been able to chemically transform layers of existing layered materials into a new covalent two-dimensional material. For example, mechanically exfoliated 2D indium selenide (InSe) is converted into atomically thin indium fluoride (InF3), which has an uncoated structure and is therefore impossible to obtain by exfoliation, by a fluorination process.
"We believe our work represents a significant advance in materials science and represents a clear milestone in the development of artificial 2D materials."
Professor Rahul Nair
In fact, the proposed chemical conversion strategy of 2D material is nothing but chemical stitching of atomic layers from existing 2D materials.
The resulting new 2D indium fluoride is a semiconductor that has high optical transparency over the visible and infrared spectral range and could possibly be used as 2D glass.
Professor Rahul Nair of the National Graphene Institute and Department of Chemical Engineering and Analytical Science, who led the team, said, “The chemical modification of materials has proven to be a powerful tool for creating new materials with desirable and often unusual properties. More work is needed to understand the chemical transformation of 2D materials at the atomic level, including the effects of relative orientation and synergy between the individual atomic layers on their chemical reactivity. We believe that our work represents a significant advance in materials science and represents a clear milestone in the development of artificial 2D materials. "
Vishnu Sreepal, who led the experiments and is the lead author of this paper, said, “Our work clearly shows the possibility of making artificial 2D covalent materials. The process is controllable, easy to perform and very effective. By precisely controlling the thickness of the starting 2D layers, the thickness of the new 2D covalent materials can be controlled with atomic accuracy. The new covalent 2D material can also be doped with dopants in a controlled manner.
"We also demonstrate the scalability of our approach by chemically converting large, thin InSe films into InF3 films". In addition, the team sees the possibility of extending this chemical conversion to van der Waals heterostructures in order to obtain artificial hetero-covalent solids.
By layering atoms in a precisely chosen order, the so-called heterostructures, designer materials can be created with certain properties that do not occur naturally and have certain properties. Researchers assemble these new materials in application-relevant sequences, similar to the stacking of Lego bricks. By demonstrating the possibility of covalent 2D solids, the researchers now have more “Legos” on their playground to develop new materials with tailor-made properties.
The work was carried out in collaboration with the University of Antwerp, Belgium, the University of Nottingham, the National Academy of Sciences of Ukraine and the Izmir Institute of Technology, Turkey.
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