J. Hone, Department of Mechanical Engineering, Columbia University, New York NY 10027 USA
Two-dimensional materials such as graphene can achieve spectacular performance but are highly sensitive to disorder from the environment. We have developed techniques to controllably ‘stack’ graphene on insulating hexagonal boron nitride, which dramatically reduces disorder and increases electronic mobility, which in turn leads to superior performance in FETs and emergence of new low-T physics. In addition, these heterostructures can display novel behavior due to the presence of ‘superlattice’ potentials arising from the graphene-BN stacking. We have recently extended these techniques to create fully encapsulated devices whose performance approaches the ideal behavior of graphene. At room temperature, the electronic mean free path is near one µm, and the mobility ranges from 30,000 to over 100,000 cm2/Vs. At low temperature, fully ballistic transport is seen in devices as large as 15 µm, and phenomena such as magnetic focusing can be observed. BN-encapsulated bilayer graphene shows a well-developed fractional quantum Hall spectrum that can be tuned by an applied displacement field. These devices show high performance in a range of practical applications such as photonic devices and sensors. These techniques can be used to create heterostructures of other 2D materials such as MoS2 and WSe2, which also show improved performance.