Synthesis of Colloidal Tungsten Diselenide (WSe2) Nanocrystals by Hot Injection Method

Following the discovery of graphene, a vibrant research area on two-dimensional (2D) transition metal chalcogenides (TMDs) layered materials has emerged in recent years due to their exciting and diverse properties.1-4 The existing approaches to make TMDs are mainly exfoliation, substrate growth and colloidal synthesis. Among them, colloidal wet-chemistry methods are particularly promising as the as-synthesized colloidal dispersions are directly fit for solution-based processing, opening a gateway for a straightforward and cost-efficient introduction into various technology platforms. However, compared to the other two preparation schemes, colloidal synthesis is relatively underdeveloped with only a few examples being known.2-4 In this contribution, we describe the preparation of WSe2 nanocrystals using a hot injection colloidal synthesis in the presence of a capping ligand as the solvent. We find that the choice of capping ligands influences the shape of the nanocrystals to great extent. Nano-flowers were obtained in the presence of oleic acid as capping ligand, whereas, nanosheets were obtained in the presence of oleylamine. Moreover, modification of the reaction temperature allowed to control the size of the nanocrystals. A thorough investigation of the reaction yield by means of quantitative XRF analysis enabled us to rationalize the reaction process. This synthesis strategy might provide a versatile approach to synthesize a wide range of TMDs such as WS2 and MoSe2. [1] Novoselov, K. S., Geim, A. K., Morozov, S. V., Jiang, D., Zhang, Y., Dubonos, S. V., ... & Firsov, A. A. (2004). Electric field effect in atomically thin carbon films. Science, 306(5696), 666-669. [2] Mahler, B., Hoepfner, V., Liao, K., & Ozin, G. A. (2014). Colloidal synthesis of 1T-WS2 and 2H-WS2 nanosheets: applications for photocatalytic hydrogen evolution. Journal of the American Chemical Society, 136(40), 14121-14127. [3] Jung, W., Lee, S., Yoo, D., Jeong, S., Miro, P., Kuc, A., ... & Cheon, J. (2015). Colloidal synthesis of single-layer MSe2 (M= Mo, W) nanosheets via anisotropic solution-phase growth approach. Journal of the American Chemical Society, 137(23), 7266-7269. [4] Jin, H., Ahn, M., Jeong, S., Han, J. H., Yoo, D., Son, D. H., & Cheon, J. (2016). Colloidal single-layer quantum dots with lateral confinement effects on 2D exciton. Journal of the American Chemical Society, 138(40), 13253-13259.