Strain Engineering of Two-Dimensional (2D) Materials at the Atomic Scales

Since the discovery of graphene, there has been a fast-growing interest in fabricating ultrathin 2-dimensional (2D) films and nano flakes out of materials with layered structures. Among all these materials, transition metal dichalcogenides (TMDs) such as MoS2, WSe2, HfS2 and ReS2, are semiconductors that show significant promise for use in electronics, optoelectronics, and catalytic applications. These materials comprise of covalent interactions between the atoms within the layer and van der Waals (vdW) interactions between the layers. Recent experiments have demonstrated that strain engineering is an effective method to tune the electronic, magnetic and optical properties of these 2D materials for their optimal performance. Strain engineering of 2D materials entails a thorough understanding of the deformation behavior, which is hard to capture experimentally. However, the recent advancements in computational methods at the atomic scales are well-suited to probe the effects of strains on the electronic properties as well as the mechanical response of 2D materials. The chemical vapor deposition (CVD) grown 2D materials comprise of flakes of several layers wherein the top layers are relatively narrower than the bottom layers. The strain response of such multi-layered structures is likely to be different as compared to their thin film counterpart. As a result, the investigation of the strain response of monolayer and CVD-grown few layered 2D materials at the atomic scales is performed in this thesis