Electronic And Magnetic Properties Of Triangular Graphene Nanofiakes Embedded In Fluorographene

In this thesis, structural stabilities, electronic and magnetic properties of triangulargraphene nanoflakes (GNFs) embedded in fluorinated graphene are systematicallyinvestigated using first-principles density functional theory (DFT) calculations. The mainresults and conclusions are summarized as follows:(1) Geometries relaxation of two types of triangular GNFs embedded in fluorinatedgraphene was carried out by us. In order to evaluate the thermodynamic stability of thetriangular GNFs embedded in fluorinated graphene, we also calculated the formationenergies. And the results showed that the formation energies of both embedded ATGNFsand ZTGNFs decrease with the increasing sizes, so the larger nanoflakes the more stable.On the other hand, the embedded ATGNFs have lower formation energies than theZTGNFs, so the former is energetically more favorable than the latter.(2) The electronic properties of the triangular graphene nanoflakes (GNFs) embeddedin fluorinated graphene are systematically investigated using first-principles calculations.First, we focus on the electronic structures of these nanoflakes based on thenon-spin-polarized calculations. The calculations showed that the various–sized ATGNFsembedded in fluorinated graphene are semiconducting with band gap values decreasingmonotonously with the increasing NAC; Local localized bands around Fermi level appearfor embedded ZTGNFs induce instability against spin polarization. Thus the spinpolarization were taken into account in the case of embedded ZTGNFs, highly localizeddispersionless metallic bands split into multiple branches with two spin states (spin-up andspin-down) near EF, creating a band gap at Fermi level, and the variation in band gap ofZTGNFs embedded in fluorinated graphene is not monotonous, the band gap valuereaches the maximum at NZZ=3.(3) We discussed the magnetism of triangular GNFs embedded in fluorinated graphene in detail. The results from our calculations show that the embedded ATGNFs arenonmagnetic, and both the total magnetic moments and the local magnetic moments areexactly equal to zero. The embedded zigzag triangular GNFs are magnetic with aferrimagnetic ground state and the magnetic moment scales linear with the size of thetriangular GNF. The partially filling pzorbital of the C atoms at the interfaces drivesspontaneous spin-polarization, resulting in finite magnetic moments and the spin densityresides mainly at the C atoms at the borders of the embedded graphene and decaysgradually to the central regions. With the increase in nanoflakes size, the energydifferences between spin-polarized and spin-unpolarized states increase monotonouslyindicating that the magnetism in lager triangular nanoislands should render more stability.