Size-Dependent Structural, Energetic, and Spectroscopic Properties of MoS3 Polymorphs

In spite of the interest of a-MoS3 based nanomaterials, the amorphous nature of the MoS3 phase makes it challenging to control and understand its chemical reactivity. In particular, the type of the structural building unit such as Mo-3 triangular vs Mo chain is still debated, while the ambivalent interpretation of the nature of sulfur species (S-2(-), S-2(2-)) and Mo-Mo bonds leads to ambiguous interpretations of spectroscopic data and reactivity. By density functional theory (DFT), we simulate the energetic, structural, and spectroscopic features of relevant zero-dimensional 0D-, 1D-, and 2D-MoS 3 triangular, chain-like polymorphs, including unprecedented ones (ring, wave, and helix) and revisit the interpretation of EXAFS, IR-RAMAN, and XPS experimental data. We analyze how Mo(k)S(3k )clusters of a few k atoms may grow up to infinite (periodic replica) MoS3 polymorphs. The evolution of the growth energy and the computed IR spectra within the density functional perturbation theory level suggest the coexistence of various polymorphs in the MoS3 phase as a function of sizes. Molecular dynamics simulations reveal how the small triangular MokS3k oligomers may transform into condensed MoS3 patches resembling embryos of the 2D 1T'-MoS2 phase. Finally, we discuss some plausible transformation pathways from one polymorph to another.