Mahdi Ghorbani-Asl

• The electronic industry is rapidly approaching the limit of silicon-based technology. As a consequence, the development of new technology to replace silicon has become a very important topic in electronic and materials science. Layered transition-metal chalcogenides (TMCs), denoted as TX2 (T=Mo, Nb, W and X=Se, S, Te), have shown spectacular physical properties which make them intriguing candidates as a material for nanoelectronics. We present the development of a flexible and generic method which can be used to calculate coherent electron transport based on the density functional based tight-binding (DFTB) method in combination with the non-equilibrium Green’s function (NEGF) technique and Landauer-Büttiker formula. We have concentrated our efforts to understand the effect of intrinsic defects and mechanical deformations in electronic and transport properties of TX2 monolayers (MLs). We show that MoS2 MLs present spontaneous rippling which significantly alter their electronic properties e.g. band gap and electron conductivity. It is found that structural defects in MoS2 ML form scattering centers which can induce anisotropy in the electron conductivity. The results show that tensile strain modifies the direct band gap into an indirect one, and substantial strain even induces a semiconductor-metal transition without bond breaking. Furthermore, Raman signals of MLs depend linearly on the strain. In contrast to global deformations, the nanoindentation does not change significantly the electronic properties of the macroscopic MoS2 MLs. Our results show that noble TMCs demonstrate intriguing characteristics as they are subject to mechanical deformations and quantum confinement effects. As a result, the bilayers show metallic characteristics in contrast to semiconducting monolayers. We believe that the knowledge obtained from this thesis can provide new perspectives for the application of TMCs in future nanoelectronic devices.