Theoretical Study Of Transition Metal Disulfides And The Heterostructures

With the rise of the graphene, other two-dimensional materials have been gradually concerned and investigated. In recent years, two-dimensional transition metal dichalcogenides（TMDs） has attracted great interests, such as molybdenum disulfide（MoS₂）, vanadium disulfide（VS₂）.MoS₂, a kind of graphene-like structure material, has attracted great attentions due to its unique properties and potential applications in electronics and sensors fields. In this paper, we have systematically studied the adsorption of the non-polar gases（CO₂ and CH₄） on monolayer MoS₂（with and without defects） based on the first-principles calculations combined with grand canonical Monte Carlo（GCMC） simulations. Compared with the popular gas sorbents（metal organic frameworks and carbon-based materials）, the MoS₂ monolayer has additional advantages, including large surface to volume ratio and tunable properties. The perfect MoS₂ shows little or no adsorption for CO₂ and CH₄ molecules, but the MoS₂ with S vacancy exhibits an excellent adsorption ability for CO₂ and CH₄ gases（with the adsorption energy of 40-60 kJ?mol-1）. GCMC simulation results show that MoS₂ with a single S vacancy could achieve the capacity of 42.1 wt% for CO₂ and 37.6 wt% for CH₄ under the pressure of 80 bar at room temperature, respectively. The results given in this paper indicate that monolayer MoS₂ can be used as a highly efficient absorbent for non-polar gases and gas sensors by tuning the defect concentration.Two dimensional（2D） monolayer VS₂, is a kind of TMDs material with magnetic property. In this paper, we have studied the structures and the magnetic properties of the heterostructure consisted of VS₂ and fluorinated graphene by the first principles calculation. By modulating the coverage of fluorinated graphene, the magnetic properties of the heterostructure can be controlled. With the changing of the fluorinate coverage, that is, changing the magnetic moment of the fluorinated graphene, the overall magnetic moments of the heterostructure increase compared to the isolated VS₂ monolayer. Through the analysis of the electronic properties and the spin density distributions, we can clarify the interaction mechanism between the layers and the magnetism properties. According to the spin density distributions, the main magnetic moment is attributed from the V atoms. Our results show that the TMDs heterostructures have the potential application in the spintronic devices.Two dimensional（2D） monolayer MoSe₂, is a kind of TMDs material with semiconductive property. Here we investigated the electronic, magnetic and optical properties of the perfect MoSe₂ monolayer and the MoSe₂ monolayer with Se defects（VSe, DVSe, Vdi-Se） occupied by the halogen atoms（X=F, Cl, Br, I） based on the first principles calculation. It is found that the occupancy of Se point defects by the halogen atoms does not destroy the original semiconductor property. And it is also an efficient way to introduce p-type doping, which is a main reason for the experimental photoluminescence（PL） enhancement. The Se vacancies can induce impurities states and decrease the bandgap and optical absorption for the MoSe₂ monolayers. However, when the Se vacancies are repaired by halogen atoms, the defective energy level moves to the CBM and the band gap becomes larger.At the same time, the halogen atoms can induce a local magnetic moment. Our results provide valuable theoretical insights for MoSe₂ and the other TMDs of the application in the spintronics and the photoelctronic devices.