While only the monolayer MoS 2 exhibits a direct band gap of 1.9 eV, few-layered MoS 2 structures in addition to monolayer MoS 2 also render a faster electron-hole recombination process attributed to quantum confinement effects as compared to bulk MoS 2 crystals 5. When bulk MoS 2 is thinned to monolayer, the VBM shifts from Γ to K, and the CBM shifts from Σ min to K, which results in an intriguing indirect-to-direct transition of band gap energies for monolayer MoS 2. This band structure corresponds to a valence band maximum (VBM) at Γ and the conduction band minimum (CBM) at Σ min 4. Bulk MoS 2 is characterized by an indirect band gap with an energy of 1.29 eV using absorption and photoluminescence (PL) spectroscopy measurements. Two-dimensional (2D) transition metal dichalcogenide (TMD) structures, with their unique electronic structure, show significant promise for applications in field effect transistors 1, optoelectronic device 2, photo transistors and photo detectors 3. The vertical displacements of the atoms and the dimensions of the Moiré islands predicted using the MD simulation are in excellent agreement with that observed experimentally. The nucleation of these islands is observed to happen at tensile strains of ~ 2% and at compressive strains of ~2.5%. The Moiré islands are observed to nucleate at the corners or edges of the few-layered structure and propagate inwards under both tensile and compressive strains. MD simulations suggest that the strain relaxation of CVD-grown triangular terraced structures is observed in the vertical displacement of the atoms across the layers that results in the formation of Moiré patterns. In this study, the strain response of CVD-grown few-layered MoS 2 terraced structures is investigated at the atomic scales using classic molecular dynamics (MD) simulations. The strain response of such few-layer terraced structures is therefore likely to be different from exfoliated few-layered structures with similar dimensions without any terraces. The top layers are relatively smaller in size than the bottom layers, resulting in the formation of edges/steps across adjacent layers. Finally, the present computations can introduce P-MoS 2 crystal as a new thermoelectric material with unique and extraordinary properties.The chemical vapor deposition (CVD)-grown two-dimensional molybdenum disulfide (MoS 2) structures comprise of flakes of few layers with different dimensions. A low thermal conductivity at room temperature along with an extremely high power factor at 1000 K exhibited by P-MoS 2 suggests P-MoS 2 crystal as a potential thermoelectric material. The thickness dependence of thermoelectric properties in 1T-, 2H-, and 3R-MoS 2 crystals is substantiated. From the two newly reported crystals (P-MoS 2 and FCC-MoS 2), P-MoS 2 exhibits exclusive thermoelectric properties (within 300-1000 K) such as high electrical conductivity, Seebeck coefficient, and low thermal conductivity. According to spectroscopic studies, two typical E 1 2g and A 1g Raman peaks are indicators of in-plane and out-of-plane vibrational modes of S atoms. The variation of the bandgap and density of states (DOS) in all structures represents crystals comprising both semiconductors (2H-and 3R-MoS 2 crystals) and metals (1T-, P-MoS 2, and FCC-MoS 2). While all crystals of MoS 2 were explored by undertaking several methods, the DFT method corrected for dispersion interaction (DFT-D2) confirmed the production of the cell parameters closer to the experimental. We present the results of computational-theoretical studies on the structural, vibrational thermoelectric, and thermodynamic properties of five crystal structures, known and newly developed, of MoS 2 based on first-principles density functional theory (DFT). Therefore, these materials with privileged applications have urged theoretical and experimental investigation for understanding and development of new crystals for particular applications. Nontoxicity and economic production have turned some of the molybdenum disulfide (MoS 2) polytypes into very interesting thermoelectric materials.
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