Controlling the electronic and optical properties of two-dimensional crystal heterostructures

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Two-dimensional (2D) crystals such as graphene or transition metal dichalcogenides (TMD) are promising materials for the development of future devices because of their unique physical properties. So far, extensive investigations have been done on the individual, atomically thin, 2D layers. Recently, experimental works on the combination of different 2D structures in form of vertically stacked, van der Waals bonded heterostructures (HS) are reported and proof-of-principle devices, such as transistors, diodes, photodiodes, solar cells, were demonstrated. Heterostructures are formed by the interaction between individual 2D structures and the potential function of a device explores these interlayer interactions. So far there is only little understanding about how such 2D layers interact, what properties are modified by the interactions and how one can obtain precise control over these properties. With this proposed project we want to combine experimental and theoretical methods to investigate the electronic, optical, structural and vibrational properties of 2D HS. We will explore a variety of different 2D HS by considering multiple combinations within the set of semiconducing TMDs. The central objectives are to (1) develop fabrication methods that allow for the controlled production of high-quality, 2D HS with well-defined, reproducible properties and characterize their electronic and optical properties, (2) develop a platform for the theoretical study of TMD-based 2D-HS, (3) understand how the electronic structure and optical properties of the HS are related to the properties of the individual monolayers and what new effects arise in HS, and (4) control the electronic structure and optical properties of HS using an informed choice of material combination, interlayer misorientation angle and number of layers