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Manchester scientists uncover new interaction in two-dimensional materials

10 Mar 2016

Self-rotating graphene observed for the first time brings unique designer materials one step closer.

moire pattern in graphene
moire pattern in graphene

 Researchers at the University had asked the question – could self-rotation incur in heterostructures, when different crystals are stacked together such as graphene on boron nitride? It was found that   perfect stacking between graphene and boron nitride did indeed exist. Furthermore, if the layers in the heterostructure were disturbed – the crystals would self-rotate back to the ideal configuration, this effect had been seen at a nanoscale but had yet to be observed on larger scales until now, as published in Nature Communications.

This scientific discovery is important for better understanding the fundamentals of how 2D materials interact with each other and how these interactions can be provide another degree of control to fine tune the materials with tailored properties.

Graphene was the world’s first two-dimensional material, isolated in 2004 at The University of Manchester, since then a whole family of other 2D materials have been discovered.

Using graphene and other new materials, scientists can layer these materials in a precisely chosen sequence known as heterostructures, to produce high-performance structures for novel applications. For example layering graphene with hexagonal boron nitride or transition metal dichalcogenides can result in new types of transistors, solar cells or light emitting diodes.

The interaction between the individual layers is governed by the van der Waals forces. It is those forces, which ensures specific stacking between the layers in layered crystals. When perfect stacking is lost, for example due to a rotational fault, the layers are restored to perfect stacking- known as self-rotation.

Sir Kostya Novoselov who led the team of researchers said “This work will pave the way for a new direction in physics and technology in van der Waals heterostructures. 2D crystals assembled together can exhibit dynamic properties which will be able to produce precision nanomechanics.”

Colin Woods added: “The self-alignment mechanism will allow more controllable fabrication of ever complex van der Waals heterostructures”

The relationship between the two materials has also exhibited interesting phenomena such as a moiré pattern- which due to the mismatch and rotation between the layers produces a geometric pattern similar to a kaleidoscope, and Hofstader’s elusive butterfly, a structure of energy levels in the shape of a butterfly due to the complex behaviour of electrons in a magnetic field.

Although at this time, the interaction has only been observed between these two materials, this now opens up discussion on the relationship between other 2D materials and how the interactions between these materials can be used to maximise the potential of heterostructures.

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