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INDUSTRY, TECHNOLOGY, PRODUCTS AND INNOVATION

A new age of 2.5D materials: important

development for high performance

rechargeable batteries

cientists are exploring new include graphene, hexagonal boron nitride (hBN) (a compound used in cosmetics
ways to artificially stack two- and aeronautics), and transition metal dichalcogenides (TMDCs) (a nanosheet semi-
Sdimensional (2D) materials, conductor).
introducing so-called 2.5D materials Using the CVD method, researchers selectively synthesised a bi-layer of graphene,
with unique physical properties. the simplest form of a 2.5D material, using a copper-nickel foil with relatively
By stacking layers of different 2D high nickel concentration as a catalyst. Nickel makes carbon highly soluble, giving
materials, it is now possible to create researchers more control over the number of graphene layers. When an electrical
2.5D materials with unique physical field was applied vertically across the bi-layer of graphene, it opened a band gap,
properties that can be used in solar meaning that its conductivity can be turned on and off. This is a phenomenon that
cells, quantum devices and devices is not observed in mono layer graphene because it has no band gap and stays on all
with very low energy consumption. the time. By tilting the stacking angle one degree, scientists found that the material
“The 2.5D concept symbolises became super-conducting.
freedom from the composition, Similarly, another group in the UK and the US found that a layer of graphene
materials, angles and space typically and hBN results in the quantum Hall effect, a conduction phenomenon involving a
used in 2D materials research,” magnetic field that produces a difference of potential. Others showed that stacking
explains nanomaterials scientist TMDCs traps excitons– electrons paired with their associated holes in a bound state ¬
Hiroki Ago of Kyushu University in in the overlapping lattice patterns. This can lead to applications in information storage
Japan. 2D materials, like graphene, devices. New robotic assembly techniques have also made it possible to build more
consist of a single layer of atoms complex vertical structures, including a stacked hetero-structure consisting of 29
and are used in applications such alternating layers of graphene and hBN, for example.
as flexible touch panels, integrated
circuits and sensors. Recently, new Research paper: https://www.tandfonline.com/doi/full/10.1080/14686996.2022.2062576
methods have been introduced to
make it possible to artificially stack
2D materials vertically, in-plane or
at twisted angles, regardless of their
compositions and structures. This is
thanks to the ability to control the
van der Waals forces: weak electric
interactions between atoms and
molecules, similar to a microfiber
cloth’s attraction of dust. It is
also now possible to integrate 2D
materials with other dimensional
materials such as ions, nanotubes
and bulk crystals.
A common method for fabricating
2.5D materials is chemical vapour
deposition (CVD), which deposits a
layer, one atom or molecule at a time,
onto a solid surface. Commonly used
building blocks for 2.5D materials

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