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Ab Initio Investigation of Atomistic Insights into the Nanoflake Formation of Transition-Metal Dichalcogenides: The Examples of MoS₂, MoSe₂, and MoTe₂

Caturello, Naidel A. M. S., Besse, Rafael, Da Silva, Augusto C. H., Guedes-Sobrinho, Diego, Lima, Matheus P., Da Silva, Juarez L. F.
Journal of physical chemistry 2018 v.122 no.47 pp. 27059-27069
algorithms, density functional theory, energy, molybdenum disulfide, physical chemistry, physicochemical properties, selenium, sulfur, tellurium, tree growth
An atom-level understanding of the evolution of the physical and chemical properties of transition-metal dichalcogenide (TMD) nanoflakes is a key step to improve our knowledge of two-dimensional (2D) TMD materials, which can help in the designing of new 2D materials. Here, we report a density functional theory (DFT) study of the evolution of the structural, energetic, and electronic properties of (MoQ₂)ₙ nanoflakes, where Q = S, Se, and Te and n = 1–16. All optimized DFT configurations for each system (10n) were generated by an in-house implementation of the tree-growth scheme combined with the modified Euclidean similarity distance algorithm, which reduces a large set configurations (10n million) to 10n trial structures. We found that the energetic favored configurations change between two sorts of clusters: frameworks elongated in one dimension with tetrahedral and square pyramidal coordination of Mo atoms, which is followed by 2D nanoflakes with tetrahedral, square pyramidal, and distorted octahedral coordination environments of Mo atoms. Both structure types maintain the same Q-terminated edge configuration, a crucial factor for the increased stability of those nanoflakes in relation to stoichiometric 2H monolayer cuts. The structural properties of the lowest energy configurations evolve smoothly as a function of the nanoflake sizes. We found that more intense effects of charge transfer in the edges are an important factor for the stabilization of the 2D nanoflakes. The smaller charge transfer for larger Q radius leads to the increase of n, which stabilizes the 2D nanoflakes, namely, n = 6, 8, and 9 for MoS₂, MoSe₂, and MoTe₂, respectively.