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Various structures of two-dimensional (2D) WSe2 were controllably grown in a chemical vapor deposition (CVD) system. Using salt as the co-solvent and surfactant, we were able to grow monolayer single-crystalline WSe2 flakes with lateral size of up to 215 μm and monolayer polycrystalline WSe2 with lateral size of a few millimeters on amorphous SiO2 substrates. Optical microscopy, atomic force microscopy, Raman spectra, photoluminescence spectra and X-ray photoelectron spectra measurements disclosed high quality of as-grown 2D WSe2. Moreover, multilayer WSe2 flakes with spiral dislocations and uniform size were also achieved. Our study demonstrates that the salt-assisted CVD technique can be applied for the controllable synthesis of 2D transition metal dichalcogenides with various structures and morphologies, paving the way for developing novel catalysts and electronic devices. [ABSTRACT FROM AUTHOR]