Effects Of Edge Passivation On The Electronic Structure,Magnetism,and Electron Transport In Armchair MoS₂ Nanoribbons

As a kind of graphene-like material,molybdenum disulfide nanoribbon(MoS2NR)has attracted considerable attention due to its unique physical and electrical properties.In this paper,by using the density functional theory(DFT)calculations and non-equilibrium Green’s function(NEGF)technique,we study the electronic structure,magnetism,and electron transport in edge-passivated armchair molybdenum disulfide nanoribbon(AMoS2NR).In this paper,we first introduce the structure,basic properties and experiment preparation of MoS2 and electronic and physical properties of AMoS2NR.Then we give a brief introduction of the main theoretical methods used in this paper,including density functional theory and transport theory,and the ATK software.Finally,we describe and summarize the work done during my study.The main contents are as follows:(1)We study the effects of hydrogen atoms or hydroxyl groups edge passivation on the transport properties of AMoS2NR.AMoS2NR is a semiconductor material,and it can exhibit metal properties with appropriate hydrogen atoms or hydroxyl groups edge-passivation.In this paper,we chose metal structures with large conductance as electrodes to study the transport properties of MoS2 nanoribbons under different edge passivation.In the homogeneous H-edge-passivated system(H-H-H),it has a triangular current-voltage curve exhibiting a characteristic of single energy band systems.A strong negative differential resistance(NDR)effect occurs in the low bias region with the peak-to-valley ratio of NDR up to 71.When hydroxyl groups are used,the system(OH-OH-OH)also exhibits negative differential resistance effect in the low-bias region and another triangular current-voltage curve appears in the high bias region.Since our previous study showed that passivation of an edge Mo atom by a hydroxyl group in AMoS2NR can introduce magnetism in an adjacent bare Mo atom,we also consider the non-uniform system OH-O-OH,in which there is one unit cell without edge passivation.Similarly,a negative differential resistance effect is observed in the system.Different from systems H-H-H and OH-OH-OH,the spin up and down currents of the OH-0-OH system are no longer degenerate,and spin splitting occurs.Furthermore,in the heterogeneous system H-0-OH,the spin splitting can be enhanced and the peak-to-valley ratio of negative differential resistance effect is greater than that of the OH-0-OH system.(2)We study the electronic structure,total energy and the different distribution of magnetism of AMoS2NR induced by the hydroxyl group edge-passivation.It is shown that the variation of passivation concentration can switch the nanoribbon between non-magnetic and magnetic semiconductors.In the magnetic case,the magnetism is mainly concentrated on an adjacent bare molybdenum atom rather than the passivated molybdenum atom.In order to reveal the physical mechanism behind this phenomenon,we increase the distance dO between the hydroxyl group and the nanoribbon gradually,and simulate the corresponding property change of the nanoribbon.As dO increases,the stability of the nanoribbon decreases and the passivated molybdenum atom follows with the hydroxyl group.The magnetic moment of the adjacent molybdenum atom decreases continuously and that of the passivated molybdenum atom increases.When the hydroxyl group is about 1.62A away from its equilibrium position,the passivated atom shifts 1.0 A and reaches the maximum deviation.Its magnetic moment maximizes and the adjacent molybdenum becomes almost non-magnetic.Subsequently,the passivated atom jump to its equilibrium position and exchange magnetism with the oxygen atom,and the structure becomes stable again.In this case,the nanoribbon separates from the magnetic hydroxyl group and gradually converts into a non-magnetic bare nanoribbon.Finally,we calculate the dO dependence of the total energy difference between systems before and after the structural optimization.Energetic analysis of magnetism transfer among the adjacent molybdenum atom,the passivated molybdenum atom,and the oxygen atom follows.