A new age of 2.5D materials
Summary
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. Commonly used building blocks for 2.5D materials include graphene, hexagonal boron nitride (hBN) (a compound used in cosmetics and aeronautics), and transition metal dichalcogenides (TMDCs) (a nanosheet semiconductor). Using the CVD method, researchers selectively synthesised a bilayer of graphene, the simplest form of a 2.5D material, using a copper-nickel foil with relatively high nickel concentration as a catalyst. Similarly, another group in the UK and the US found that a layer of graphene and hBN results in the quantum Hall effect, a conduction phenomenon involving a magnetic field that produces a difference of potential. New robotic assembly techniques have also made it possible to build more complex vertical structures, including a stacked heterostructure consisting of 29 alternating layers of graphene and hBN, for example.