Group tweaks semiconductor properties using nanoscale twist

Researchers at The University of Manchester have demonstrated how the properties of a material made from layers of atomically thin semiconductors can be precisely altered by rotating the position of adjacent crystals.

Since the isolation of graphene in 2004, researchers have identified a multitude of 2D materials, each with specific properties and by stacking these thin crystals together, have created a number of artificial materials known as heterostructures.

A number of studies have demonstrated that it’s possible to further refine the properties of these heterostructures by adjusting the rotation – or twist angle – of adjacent crystals, but until now, these studies have been limited to graphene and hexagonal boron nitride.

A new study carried out by researchers at the University of Manchester’s National Graphene, has shown how that technique can also be used to tweak the properties of a class of atomically thin semiconductors known as transition metal dichalcogenides.

In a report published in the journal Nature Nanotechnology, the team describes that for small twist angles atomic lattices of transition metal adjust locally to form perfectly stacked bilayer islands, separated by grain boundaries which accumulates the resulting strain.

Using atomic resolution transmission electron microscopy (TEM) they have demonstrated that stacking the two monolayers nearly parallel to each other (twist angle close to 0o) and anti-parallel (twist angle close to 180o) produces strikingly different periodic domain patterns.

According the team, the study shows how  the “twist” degree of freedom in heterostructure design can be used to precisely  pattern material properties, potentially allowing the creation of new exciting quantum systems, such as controllable periodic arrays of quantum dots and single photon emitters.

Dr Roman Gorbachev, who led the team said: “The twist will have ground-breaking impact on the field of 2D materials, and our work is an important milestone on this path.”