Study On Electric, Magnetic And Transport Properties Of MoS₂Nanoribbons

Molybdenum disulfide (MoS2), a typical inorganic transition-metal dichalcogenide, in its monolayer form has received lots of attention due to its significant applications in nanoelectronic devices. Compared with zero band-gap pristine graphene, monolayer MoS2is a semiconductor with a direct band gap of1.8eV, which give it some advantages of application in transistor over graphene, such as large ON-OFF current ratio, large transconductance and excellent short channel behavior with low-power dissipation. Along with the research of two-dimensional MoS2, studies extend to one-dimensional MoS2, especially MoS2nanoribbons. Recently, MoS2nanoribbons have been achieved by different methods and their properties and potential applications have been an active field of theoretical studies. In this thesis, we focuses on the electronic, magnetic and transport properties of MoS2nanoribbons based on the first-principle calculations, as well as the doped MoS2nanoribbons. Our studies are as follow:(1) Based on density functional theory in combination with nonequilibrium Green’s function methods we investigate electronic transport properties of MoS2nanoribbion heterostructures which consist of edge hydrogen-passivated and non-passivated zigzag MoS2nanoribbons (ZMoS2NR-H/ZMoS2NR). Our calculations show that the heterostructures have half-metallic behaviors which are independent of the nanoribbon widths. The opening of spin channels of the heterostructures depend on the matching of particular electronic orbitals in the Mo-dominated edges of ZMoS2NR-H and ZMoS2NR. Perfect spin filter effects appear at small bias voltages, and large negative differential resistance and rectifying effects are also observed in the heterostructures.(2) We investigate transport properties of zigzag MoS2nanoribbons with parallel and antiparallel spin configurations. The results show that the parallel configuration has conventional metallic properties while the antiparallel configuration presents semiconductor properties. Consequently, the conduction calculations predict that the zigzag MoS2nanoribbons exhibit giant magnetoresistance effect with value over four orders of magnitude at room temperature by applying local mangetic fields to alter the configuration from the parallel to antiparallel spin junction. We clarify that the orbital mismatching near the Fermi level between spin up and spin down is a key factor which prevent the current and generate this large magnetoresistance. Our results indicate that the giant magnetoresistance effect in zigzag MoS2nanoribbons remain robust to the change of the ribbon widths and lengths. In addition, the ZMoS2NR in the antiparallel configuration shows dual spin filter effect.(3) We investigate the stability, electronic and magnetic properties of armchair MoS2nanoribbons (AMoS2NR) with Re dopant substituting Mo atom.The results indicate that the doping results in the converting of the ground state of the AMoS2NR from nonmagnetic to ferromagnetic or antiferromagnetic state. And the properties of the doped AMoS2NR are strongly dependent on the doping sites. The most energetically favorite doping sites are the edges of the nanoribbon in comparison with the inner sites. The ground state of the edge-doped AMoS2NR converts to antiferromagnetic state.The ground state of the AMoS2NR converts to ferromagnetic state with Re substituting the inner Mo atoms and the doped nanoribbon shows half metal behavior and keeps its strong stability. Our calculations prove that the properties of the Re-doped nanoribbons are independent on the widths of the ribbons.