Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photoemission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers.
A “passivation first, metallization second” technique is developed for fabricating edge contacts to a multi‐layer MoS2 sample encapsulated under an Al2O3 thin film. The in‐time sealing of the newly exfoliated MoS2 under a dielectric ensures a complete isolation from the environment. CF4 plasma is used to open trenches in the passivation layer and to expose the atoms at the edges of MoS2. Edge contacts are next made to h‐BN/MoS2/h‐BN 3‐level heterostructures, earlier assembled through a solvent‐free 2D material transfer procedure. Both types of MoS2‐based heterostructures are further fabricated into back‐gated FETs and show n‐type doping behavior. In particular, trends of field‐effect mobility with respect to a varying drain voltage are analyzed based on the ID–VDS data measured from each device. The result verifies the effect of Schottky barrier on channel conduction, which is, only at the presence of a highly transparent contact interface, the field‐effect mobility can manifest the intrinsic material property by staying constant against the changes in drain voltage. The wide applicability of the processing sequence makes edge contacts an appealing option to future nanoelectronics on 2D heterostructures.
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