First-principles Study Of Graphene-like Molybdenum Disulfide

In this thesis, using the first-principles method within the framework of densityfunctional theory, we have studied structures, electronic energy band properties andmagnetic behavior of molybdenum disulfide sheet (2H-MoS2, monolayer and bilayer) withthe adsorption of3d transition metal adatom (TM) Fe to its surface and interlayer, andbilayer MoS2with various3d TM atoms (Cr, Mn, Fe, Co and Ni) doped in its interlayer,aiming to provide a theoretical basis for potential spintronic applications. At the same time,we also explore the band structure changes of monolayer MoS2on top of1-5layers ofhBN substrate (MoS2/n-h-BN heterostructures). The results show that different numberlayers of h-BN can provide different lattice strain in single-layer MoS2so as to realize theeffective control of band structure.Firstly, functionalization of MoS2sheet (monolayer and bilayer) by the adsorption oftransition metal Fe adatom to its surface and interlayer has been investigatedcomputationally by using the first-principles method within the framework of densityfunctional theory. We find that the systems with absorption of Fe adatoms on the surfacesof both monolayer and bilayer MoS2sheets are still semiconductors without spinpolarization at the Fermi level. However, for the system with absorption of Fe adatom inthe interlayer of bilayer MoS2sheet, its electronic structure exhibits half-metal behavior,with100%spin polarization at the Femi level. Furthermore, on the basis of the first work,we continue to explore the structural, electronic band structure and magnetic properteiesof bi-layer MoS2with various3d TM atoms (Cr, Mn, Fe, Co and Ni) doped in itsinterlayer. We find that local moments of the doping TM atoms are smaller than themagnetic moments of their free states and the Ni dopant shows zero magnetic moment.The spin polarization is found to be100%at the Fermi level for Cr and Fe or at theHOMO level for Mn and Co, which ensures a selective passage of the preferred spin. Ourresults suggest that bilayer MoS2sheets with Cr, Mn, Fe and Co atoms interlayer dopingare excellent candidates for spintronic devices.In addition, we have carried out first-principles study within the framework ofdensity functional theory and theoretical analysis to explore the structural and electronicenergy band properties of MoS2/n-h-BN heterostructures consisting of monolayer MoS2on top of h-BN substrates with one to five layers. We find that the MoS2/n-h-BNheterostructures show indirect band-gap features with both of CBM (in the K point) andVBM (in the Γ point) localized on the monolayer MoS2. We find that the band-gaps of MoS2/n-h-BN heterostructures decrease with increasing number of h-BN layers, which isproposed to be resulted from the different strain distributions in MoS2due to the varietiesof lattice mismatch rates between MoS2and h-BN layers. Our results suggest that theMoS2/n-h-BN heterostructure could serve as a prototypical example for band structureengineering of two-dimensional (2D) crystals with atomic layer precision.