Investigation On Layer Transiton Metal Dichalcogenides And Nanoribbons By First Principles

In this paper, we have studied the properties of low-dimension transition metal dichalcogenides MX2(M=Mo, W and X=S, Se) by means of first-principles calculations. According to our results, it is concluded that the band gap of WX2 nanoribbons can be effectively modulated by strain and bilayer MoS2 can transform from semiconductor to conductor when applied a critical strain. Additionally, we have investigated the electronic behaviors and analyzed the physical mechanism. Moreover, we also have investigated Fe/MoS2/Fe three-layer heterostructures and found that the value of magnetic anisotropy energy (MAE) could be effectively tuned via injecting charge. Details and some creative points are summarized as below:1. From the calculationresults of WX2 nanoribbons, we find that the band gap can be tuned with considerable range. In particular,WSe2 is more sensitive to the applied tensile, which means that it is easier to be tuned by strain in WX2 systems.2. Our first principles calculation results show that the band gap of bilayer MoS2 can be modulated by tensile strength. The gap significantly decreased when applying tensile field on the structure. In particular, the band gap is quenched as the tensile strain reaches to a specific value, resulting in semiconductor-metal (S-M) transition.3. Monolayer MoS2 becomes aferromagnetic material when Fe atoms are adsorbed on its surface. Through our DFT calculations, we find that its magnetic properties mainly originate from the strong coupling between the Fe-3d and Mo-4d orbits, resulting in charge redistribution between majority and minority spins, which lead to emerged occupied minority spins states of Mo.4. The calculated MAE value changes from positive to negative as the charge injection reaches to a specific value, which means that the direction of easy-axis of the Fe/MoS2/Fe system transforms from in-plane to out-of plane. However, when amount of charge is injected into the system of Fe/MoSe2/Fe and Fe/MoTe2/Fe, the sign of MAE is unchanged, meanwhile, the absolute value increases as the amount of injected charge increases. From further analyze, we find that the variation of easy-axis is due to the shift of Fe-dxy orbits with charge injection.