Heterostructure of Tungsten/Molybdenymn Diselenide Prepared by Colloidal Synthesis

초록

Fabrication of two-dimensional (2D) heterostructure of transition metal dichalcogenides (TMDs) promises a range of opportunities to broaden the physical properties of 2D semicondcutor materials. Especially, the lateral heterostructures where two different atomic monolayers are connected in-plane could exhibit tunable optoelectronic properties. The formation of TMDs lateral heterojunction has been demonstated recently via chemical vapor deposition (CVD) method. Nevertheless, it is desirable to synthesize such 2D heterostructures in large scale with tailored morphology. Here we report the colloidal synthesis of stable heterostructure of molybdenum / tungsten diselenide (WSe2/MoSe2) by controlling the delivery of precursors during the crystal growth. 2D heterostructures are grown via a two-step process: (1) we introduce W precursor (W(CO)6, 1 mmol) into 5 mL of oleic acid and heat to 350 oC under Ar condition. Then, Se precursor (Ph2Se2, 2 mmol) dissolved in 2 mL of oleic acid is slowly injected and heated for 4 hr to continue the growth of WSe2 nanosheets, then naturally cooled down to room temperature. (2) Mo precursor (Mo(CO)6, 1mmol) dissolved in oleic acid is sebsequently injected into the solution and heated to 370 oC, followed by the injection of 2 mmol of Se precursor in oleic acid, and MoSe2 growth is continued for 2 hrs. We confirm the growth morphology of the heterostructure is strongly dependent on the temperature ramping rate and the Se precursor injection. The effect of the reaction medium other than oleic acid on the heterostructure morphology ? vertical vs lateral will be discussed. We also propose a simple mechanism showing the favorable nucleation sites for the heterostructure formation via interaction between precursors and oleic acid. Our results suggest new methods to create TMDs heterostructures and highlight the importance of ligand chemistry governing the colloidal synthesis of semiconducting TMDs structures.