Theoretical Research On The Electronic Properties And Quantum Control Behavior Of New Two-dimensional Materials

In resent years,two-dimensional(2D)materials,due to novel physical and chem-ical properties,have attracted the research interest of scholars from condensed matter physics,materials,chemistry,energy and engineering.At present,some 2D materials have been successfully applied into the practical application.For example,graphene has been successfully used in flexible display screen,super capacitor,integratecd cir-cuit,sensor and hydrogen storage material.More and more 2D materials have been prepared and characterized by researchers.At the same time,it has been found that the functionalization of 2D materials can be realized by means of the atomic doping,structure defects,stress-strain,boundary effect and so on.In this work,based on the first-principles calculations method,we systematically investigated the adsorption be-haviors and adsorption properties of lanthanide,actinide and transition metal atoms on the surface of 2D materials.We focused on the study of the adsorption stabili-ty,magnetism and diffusion behavior for uranium/plutonium atoms on the surface of graphene.We also predicted that the charge doping can regulate the stability of 2D zirconium diselenide(ZrSe2)under stress and that the boundary effect can regulate the physical properties of ZrSe2 nanoribbons.Firstly,the adsorption properties of transition metals,lanthanides and actinides on the surface of new two-dimensional materials were studied.We predicted that most of the 3d TMs adsorbed on MX monolayer will spontaneously adsorb on the top of the intrinsic valleys of MX monolayer forming atomic chains.The magnetic properties of the adsorption systems can be well maintained under both uniaxial and biaxial strain conditions from 2.5%compression strain to 2.5%tensile strain,which indicates that these system possess good stability.For most of 3d TM atoms,the adsorption energies are in the range of 1.54?4.86 eV,which are very sizable.Large adsorption energy and high magnotio moment indic ate that these adsorption systems are be used in the design and application of spintronics and magnetic storage devices.In addition,we also stuclied the adsorption behavior of 3d/4d/5d transition metal atoms on single layer hexangular boron nitride(SLBN)thin films and lanthanide(Ln)atoms on the defect of graphene.It is clear that TMs can strongly adsorbed on SLBN and defect can enhance the adsorption energies of Ln on graphene.Most of TMs on SLBN and a.ll Ln on defect of graphene can keep the larger magnetic moments.Secondly,we focused on the study of the diffusion behavior and adsorption prop-erties of uranium(U)and plutonium(Pu)atoms on graphene and single layered hexan-gular boron nitride.By calculating the diffusion ban'ier of U and Pu atoms on graphene and single layer hexangular boron nitride along the pathes between the two most sta-ble sites,respectively.It can be found that U and Pu atoms can only exist stably on graphene at room temperature.The energy of the diffusion barrier of U atom is as high as 454 meV,which is much higher than that of Pu atom on graphene(79 meV).On the one hand,U and Pu atoms can be adsorbed on the surface of graphene stably,on the other hand,graphene has a characteristic of large surface area per unit mass.Then,graphene is a good material for enriching U and Pu atoms.We also studied the stability of the adsorption system under different coverage ratlos of U atoms.When the coverage ratio is 2/3,the system is the most stable and the uranium film structure sim-ilar to the ?-u structure with a single atomic thickness can be formed on the surface of graphene.This means that graphene is likely to be used to grow high-quality uranium monocrystalline films.In addition,similar to the adsorption behavior of lanthanide atoms on graphene,we found that structural defects can also significantly enhance the adsorption energy of U and Pu atoms on graphene and single layer layered boron nitride.In this case,the adsorption energy of U and Pu atoms are more than twice as high as that on perfect graphene and single layered hexangular boron nitride.Finally,we predicted that charge doping can inhibit the softening of phonon modes in two-dimensional ZrSe2 materials.Single layered ZrSe2 is a semiconductor material with band gap in the visible infrared light range.The thermodynamic stability of materials is estimated by phonon speetrum.Through VASP+PHONOPY calculation.we confirmed that the phonon mode softens under the biaxial tensile strain of 6.32%.When electrons or holes are doped to the strained system,the softening of phonon mode disappears.The ideal strength of monolayer ZrSe2 has also been enhanced.Thus,charge doping can avoid the instability caused by lattice mismatch or external stress in the actual device preparation process.Moreover,we studied the properties of one-dimensional ZrSe2 nanoribbons.Single layered ZrSe2 film is a semieonduetor with an indirect hand gap.Zigzag and armchair nanoribbons can be obtained by shearing along diffeient directions similar to graphene nanorilbbons.It was found that all zigzag ZrSe2 nanoribbons are semiconductors with direct band gap,and the size of band gap(0,51?1.12 eV)falls within the visible infrared light range.However,the band gaps of armchair ZrSe2 nanoribbons are largely dependent on ribbon widths.For ribbon width N>3 with integer N,the armchair ZrSe2 nanoribbons are semiconductors with indirect band gap.For N?3,the band gap of armchair ZrSe2 nanoribbons is direct.The size of band gaps(0.6?1.25 eV)for armchair nanoribbons have also fallen in the range of visible infrared light.In addition,the ZrSe2 nanoribbons keep the semiconducting behaviors and the band gap characteristics,irrespective of their widths and thickness.The novel properties make the ZrSe2 nanoribbons to apply for future nanoelectronic device.