Objective
Investigate charge carrier transports through the heterointerfaces made by stacking the van der Waals (vdW) layered materials at different “twist” angles. The final objective is to search for the “right” angle where the designed device has the optimized performance and/or new phenomena occur.
Background
Layered materials, such as graphite and transition-metal dichalcogenides (TMDs), usually exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction. This allows exfoliation into individual, atomically thin layers. One can stack the layers of different materials together to form a so-called vdW heterostructure. Owing to the strong interlayer coupling and weak screening effects, the vdW heterostructures are the excellent platforms for exploring new phenomena of interfacial charge transfers. Crucially, these interfacial interactions strongly depend on the twist angle where the two component layers are stacked together. For example, semimetal graphenes could be an insulator or superconductor when they are stacked at a “magic” twist angle of 1.1 deg.
Contents
In the project you will do mechanical exfoliation of atomically thin TMDs (MoS2, MoSe2, WSe2, WS2, and so on) from their bulk form, then stack them at different angles to make the van der Waals heterostructures.
Structural, optical properties of the fabricated heterostructures will be investigated by atomic force microscopy (AFM), scanning/transmission electron microscopy (SEM/TEM), Raman and photoluminiscence spectroscopy. While electrical properties will be examined by making devices with electrical contacts for transport measurements.
Reference
1. J. C. W. Song & N. M. Gabor, Nat. Nano. 13, 986.
2. A. Nimbalkar & H. Kim, Nano-Micro Lett. 12, 126.