For example, the strains in top layers of the multilayered MoS 2 structures may be relaxed through nucleating ripples 24, 25, 26 or sliding between the layers 27. These band gap transitions are observed to be consistent with the PL and absorption spectrum measurements that demonstrate strong blueshifts in E g of 2D MoS 2 under the presence of uniaxial strain 6, 7.Īn interesting aspect of the strain response of few-layered 2D structures is that the weak van de Waals (vdW) interactions between substrate and 2D structures can render variations in the strain response of the 2D structures. Several transitions for the indirect band gap are also observed for various strains for the bilayer MoS 2 systems 19. These studies suggest a transition from a direct band gap to an indirect band gap for monolayer MoS 2 at ~ 2% tensile strains and a semiconductor to metallic transition at ~10% biaxial strain 18. A significant number of theoretical studies have also been carried out to understand the variations in the electronic band structures of 2D MoS 2 structures 18, 19, 20, 21, 22, 23. Similar reductions in band gap energies have been reported for trilayer MoS 2 16, as well as under strain conditions normal to the layers 17. For example, PL and absorption spectroscopies measurements reveal that the band gap (E g) of a monolayer or bilayer MoS 2 sample decreases significantly upon a moderate in-plane uniaxial extension that is applied by bending the substrate 6, 7, 9. As a result, several experimental studies have investigated the strain response of 2D MoS 2 structures. Moreover, the electronic properties of 2D MoS 2 structure are remarkably reconstructed under the external strain 6, 7, 8, 9, 10, 11, which opens up the opportunity to tailor the performance of these materials for device application 12, 13, 14, 15. 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. The chemical vapor deposition (CVD)-grown two-dimensional molybdenum disulfide (MoS 2) structures comprise of flakes of few layers with different dimensions.
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