Metal chalcogenides that can be isolated as 2D semiconducting layers form a diverse family of materials with unique properties. Integrating these materials with other materials and controlling their properties is important for a wide range of potential applications, and can be achieved using a set of strategies for chemical modification that has been pursued in our laboratory. This talk will highlight our recent work on covalent chemical functionalization, structural and geometric conversion, and self-assembly of organic van der Waals heterostructures. In the first strategy, semiconducting MoS2 is covalently functionalized using aryl diazonium salts that form out-of-plane bonds on the basal plane. Detailed imaging studies of the reaction under a range of parameters combined with density functional theory calculations show that the functionalization initiates at point defects but then propagates in a chain-like morphology across the MoS2 surface. The reaction is also shown to be well-described by Freundlich and Temkin isotherm models, and to have pseudo-second-order kinetics. The diazonium salts can also be modified to enable tethering of proteins to the MoS2 surface. The same reaction scheme is also extended across the metal chalcogenides family including MoSe2, WS2, WSe2, Bi2S3, and Sb2S3. In the second strategy, MoO3 and WO3 nanoscrolls are formed by transformation from 2D MoS2 and WS2 nanosheets, respectively, via atmospheric plasma treatment. The combination of different radicals in the plasma simultaneously oxidize the layered disulfides and initiate delamination from the substrate, so that the strain of the altered crystal structure is relieved by rolling into nanoscroll geometries. In the final strategy, we form a self-assembled monolayer of fullerene molecules on WSe2, and use atomic resolution scanning tunneling microscopy to show that the molecules exhibit a 2x2 rotational superstructure due to the interplay of molecule-molecule, molecule-substrate, van der Waals, and Coulomb interactions. The system forms a charge redistribution network with long-range ordering.

Strategies for chemical modification of semiconducting 2D metal chalcogenides: Functionalization, transformation, and self-assembly

2019 Fall National Meeting

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