Two-dimensional (2-D) materials such as graphene have unique electronic, magnetic, optical, and mechanical properties that promise to drive innovation in areas from electronics to energy to materials to medicine. Columbia University researchers report a major advance that may revolutionize the field, a “twistronic” device whose characteristics can be varied by simply varying the angle between two different 2-D layers placed on top of one another.
In a paper published online today in Science, the team demonstrates a novel device structure that not only gives them unprecedented control over the angular orientation in twisted-layer devices, but also allows them to vary this angle in situ, so that the effects of twist angle on electronic, optical, and mechanical properties can be studied in a single device.
Led by Cory Dean (physics, Columbia University) and James Hone (mechanical engineering, Columbia Engineering), the team built upon techniques that they previously pioneered to mechanically layer graphene and other 2-D materials, one on top of another, to form new structures. “This mechanical assembly process allows us to mix and match different crystals to construct entirely new materials, often with properties fundamentally different from the constituent layers,” says Hone, leader of Columbia’s Materials Research Science and Engineering Center (MRSEC), which investigates the properties of these heterostructures. “With hundreds of 2-D materials available, the design possibilities are enormous.”
Recent studies have shown that rotational alignment between the layers plays a critically important role in determining the new properties that arise when materials are combined. For example, when conducting graphene is placed on top of insulating boron nitride with the crystal lattices perfectly aligned, graphene develops a band gap. At non-zero angles, the band gap disappears and intrinsic graphene properties are recovered. Just this past March, researchers at MIT reported the groundbreaking discovery that two stacked layers of graphene can exhibit exotic properties including superconductivity when the twist angle between them is set to 1.1 degrees, referred to as the “magic angle.”
thumbnail courtesy of phys.org