Manipulation Of Electronic Properties Via Transition-Metal Doping In Black Phosphene Nanoribbons

As the characteristic size of transistors in digital integrated circuits is further reduced to less than 10 nm,Moore's law,which has led the development of semiconductor technology for more than half a century,is gradually declining in the development of traditional silicon-based electronic devices due to the quantum confinement.Scientists and engineers have been looking for approaches to constructing new electronic devices in the fields of nanoelectronics and spintronics,including the introduction of novel nanomaterials and alternative electronic degree of freedom(spin).Specifically,developing new electronic devices based on low-dimensional materials has been attracting extensive interest.Outstanding device performances originated from novel electronic characteristics of those materials have been not only predicted theoretically but slao observed in experiments.Among them,black phosphorene,a novel two-dimensional(2D)semiconductor material has shown huge advantages in the development of 2D-material devices because its bandgap can be modulated by its number of stacked atomic layers.In this thesis,we study the geometry structures and electronic properties of monolayer armchair black phosphene nanoribbons(APNRs)passivated by transition metal atoms V,Cr,and Mn on both sides employing the density functional theory combined with the non-equilibrium Green's function method.We propose a possible spin diodes junction based on the heterostructure of black phosphene nanoribbons passivated by Cr and Mn atoms.The thesis is composed of four chapters.In Chapter one we firstly present briefly the properties,the fabrication,and the applications of three typical 2D materials,graphene,molybdenum disulfide and hexagonal boron nitride;secondly outline the spintronics and its development,focusing on the spintronics in 2D materials;and finally introduce the novel type of 2D semiconductor material,phosphorene including its crystal structure,basic properties,preparation methods and applications.In Chapter two we describe mainly the first-principles simulation method we used and its theoretical basis,including the density functional theory and the non-equilibrium Green's function method.In Chapter three we present our main results.We firstly studied the geometry structure and electronic properties of armchair black phosphorus nanoribbons of different widths,passivated by V,Cr,and Mn atoms on both edges.The simulations show that V,Cr,and Mn atoms can all be stably adsorbed at the hollow edge cites of the nanoribbons with binding energies around 4 eV,which is close to the binding energy of adsorption of hydrogen atoms on edges.Meanwhile,the electronic properties of the nanoribbons can be significantly changed by the spin-polarized edge states introduced by the 3d orbitals of transition metals,and can be further adjusted by an external electric field.Interestingly,in nanoribbons passivated by edge Mn atoms(Mn-APNRs),the band structures exhibit half-semiconductor properties in their ferromagnetic states whtere the energy gaps of the opposite spins differ greatly.Under an external transverse electric field,the conduction bands move as a result of the Stark effect and Mn-APNRs can become metallic instead.Finally,we propose that the Mn/Cr-APNR heterojunctions can be used to produce spin-dependent diodes,with strong rectification effect only on electronic current of one spin.