Study On Electronic-and Magnetic Properties Of One-dimensional Systems From Graphene And Graphene-like Nanomaterials

A new research climax of two-dimensional(2D)materials has been triggered since graphene was successfully prepared in 2004.Due to the excellent physical properties,graphene was considered to be the most likely candidate to replace silicon materials.However,2D graphene is a semi-metal with zero-band gap.In order to open its band gap,functionalizing graphene is necessary.At the same time,the discovery of graphene.also encourages more and more researchers to prepare and study new two-dimensional materials.In this thesis,by using the first-principles methods based on the density functional theory,the physical properties of functionalized graphene nanoribbons and one-dimensional graphene-like nanomaterials(such as arsenic nanotubes and Fe3GeTe2 nanoribbons)are studied.It is expected to provide a reference for the electronic applications of new nanomaterials.Firstly,we introduce the discovery of 2D nanomaterials such as graphene,including research background,the present situation,the main research methods and the basic theory.Subsequently,we theoretically propose the functionalization of armchair graphene nanoribbons by low-concentration metal(M)atom(M=Ti,Ni,Sn,or Hg)doping and investigate the structural stability and electronic behaviors of these doped systems in depth.With metal doping,the ribbons present rich and flexibly tunable bandgaps,depending on the metal atom and doping position.And the carrier mobility is calculated based on the deformation potential theory,which shows that the metal doping can effectively control the carrier mobility,and a large carrier polarity can also be clearly observed.Furthermore,the metal doping can significantly enhance the device properties of the ribbon as compared with those of the pristine ribbon,such as creating a large negative differential resistance phenomenonWe also propose to adjust the magneto-electronic properties of armchair arsenic nanotubes doped by transition metal(TM)atoms(TM=Co,Y,Rh,Ni,Mo,Ru).With metal doping,the ribbons present rich and flexibly tunable bandgaps,depending on the metal atoms But no all transition metal atoms can induce magnetism in arsenic nanotubes.And the magneto-electronic properties of the hybridized tubes can be further regulated by stress and applying external electric field.Both methods can realize the transition from half-semiconductor to semi-metal,bipolar magnetic semiconductor,magnetic metal and non-magnetic metal for tubes.In addition,the carrier mobility calculated based on the deformation potential theory indicates that different transition metal atoms doping can effectively adjust the carrier mobility of the hybridized tubes.Finally,we study the the structural stability and magneto-electronic properties of Fe3GeTe2 nanoribbons.The calculated formation energy as well as molecular dynamics simulations indicate that the nanoribbons in geometric structure are very stable,and the calculated magnetic energy suggests their magnetism stability is very high.NR(5)and NR(7)can achieve 100%spin polarization at the Fermi level.When n?12,the spin polarization of nanoribbons with a symmetric structure about the ribbon axis-line is much higher than the asymmetric structure,and after the increase of width to a certain value,the spin polarization change remains in a small range.In addition,the calculation of the tensile effect demonstrates that the strain can flexibly adjust the magnetic moment and spin polarization.This findings show that such nanomerials have great potential applications for developing flexibly tuned room-temperature magnetic devices in the future.