Effects Of Edge Passivation On The Electric And Magnetic Properties Of 2D-material Nanoribbons

In two-dimensional(2D)materials electrons can move freely only in two dimensions.2D materials are widely used in catalysis,energy storage,biomedicine and other fields due to their excellent mechanical,electric,and magnetic properties.They can be elemental crystals such as graphene,black phosphorene,and borophene,or compounds like molybdenum disulfide.In this thesis,we study systematically the effects of edge modification on the magnetism and the spin transport in zigzag borophene nanoribbons employing the density functional theory combined with the non-equilibrium Green's function(NEGF-DFT)method.In addition,we study also the effect of edge modification on the electronic structure and the magnetic properties of armchair molybdenum disulfide nanoribbonsFirstly we overview the physical properties and the preparation methods of 2D borophene and molybdenum disulfide followed by the electric and magnetic properties of their corresponding nanoribbons.Secondly,we introduce the main theoretical tools used in this paper-the density functional theory,and the non-equilibrium Green's function method,and the ATK software package used in simulation calculation.Finally,we describe in detail the main results in Chapter 3 and Chapter 4,outlined as follows(1)The electronic structures,the magnetisms,and the current-voltage characteristics of pristine ZBNRs and those edge passivated by H and N atoms are studied.There are five typical passivation configurations:only one edge is passivated by H(H-n-ZBNRs)or N(N-n-ZBNRs)atoms,both edges are passivated by H(HH-n-ZBNRs)or N(NN-n-ZBNRs)atoms,and one edge is passivated by H atoms while the other by N atoms(HN-n-ZBNRs).Hydrogenation can suppress very well the magnetism on edge in agreement with previous results.In contrast,passivation of N atoms can enhance the magnetism significantly.In addition,N atoms on edge introduce energy band gaps by coupling states of different bands to form band anticrossing.Half metal can appear when one spin band gap is located at the Fermi level in NN-4-ZBNR and N-6-ZBNR.As a result,strong spin polarization may be realized in large range of voltage bias.Finally,passivated of N atom can lead to spin negative differential resistance in ZBNRs(2)We study the electronic structures and magnetic properties of armchair MoS2 nanoribbons of width n=5 edge passivated by hydrogen atoms of various densities.Pristine armchair MoS2 nanoribbons are non-magnetic semiconductors,and edge passivation by H atoms can significantly manipulate the magnetic and electronic properties of the system.Under low passivation concentration,the passivated edge Mo atoms become magnetized with a magnetic moment around 1?B.If more than one atom is passivated in each primitive cell,even-odd effect of the passivation number is predicted in the conductivity of nanoribbons.Overall,a vanishing tendency of magnetism is observed with the increase of the passivation concentration.