AB Binary Nanotubes Modified Filling And First-principles Study Of Doping

Nanomaterials like nanotubes have the larger specific surface area, a lot of physical and chemical processes, such as surface diffusion, adsorption, oxidation, catalysis, corrosion and so on, are related to the surface. The modifications of doping on Inside and outside surface of the nanotubes can effectively expand their applications. In this study, Therefore, Using first-principles method, we pay special attention on the geometry structure, electronic, magnetic and optical properties of the transition metal filled, adsorbed and substitution doped A-B binary nanotubes. The important conclusions are shown as follows:(1) The structural, electronic and magnetic properties of single-wall (8,8) GeC, BN and SiN nanotubes filled with bcc Fen nanowires (n=5,9, and13)(denoted as Fen@(8,8)AB) have been investigated systematically using the first-principles PAW method. We find that the initial shapes of both wires and tubes are retained in the composite systems where the coulomb interaction is dominated between Fe nanowires and outer nanotubes, while those are badly distorted in the composite systems where the chemical bonding is dominated between Fe nanowires and outer nanotubes. The calculated binding energy of the Fen@(8,8)AB systems show that the forming progress of the considered composite is exothermic. Furthermore, the stability of the Fen nanowires is enhanced in the composite systems where the coulomb interaction is dominated between Fe nanowires and outer nanotubes. Concerning the conductivity of Fe5@(8,8)AB, compared with the corresponding free-standing Fe5nanowires, both Fe5@(8,8)GeC and Fes@(8,8)BN systems hold the same or higher conductivity, and Fe5@(8,8)SiN system holds lower conductivity. Additionally, the higher spin polarization at Fermi energy for the Fes@(8,8)AB composite systems is preserved, especially for the Fes@(8,8)GeC and Fes@(8,8)BN. Therefore, these composite systems can be used in the applications for the nanometer microelectronics circuit connection and spin injection, and thus the multi-functional materials occur.(2) The structural, electronic and magnetic properties of HCP Fe nanowire filled in (m,0) BN and (n,0) C nanotubes have been investigated using the first-principles PAW method. Among Fe@(m,0)BN (8≤m≤15) systems, only the Fe@(8,0)BN system is formed endothermically, the other larger systems are formed exothermically, while among Fe@(n,0)C (8≤n≤14) systems, only the Fe@(8,0)C system is also formed endothermically. Furthermore, the formation energy of the most stable Fe@(13,0)BN is smaller than that of the most stable Fe@(12,0)C, indicating BN nanotubes may be more appropriate to protect HCP ferromagnetic nanowires compared with C nanotubes. It is found that the all composite systems hold high spin polarization at Fermi energy with the exception of the Fe@(8,0)BN system. Hence, such nanocables have potential application in the spin inject and spin transport. The magnetic analysis shows that the BN nanotubes have potential advantage in shielding the magnetic moment of the inner metal nanowires. More important, the BN and C nanotubes can be protected Fe nanowires from oxidation and demagnetization, and thus these nanowires could be existed in the conventional environment for long time.(3) Adsorption configurations for ten kinds of3d transition metal M atoms adsorbed on the zigzag (8,0) BN nanotube at five different initial sites have been investigated using the first-principles PAW potential. The most stable adsorption sites are different for different M atoms. Partially filled3d metals V, Cr and Mn can bind strongly with zigzag (8,0) BN nanotube (Eb>4.0eV), and Sc, Ti, Co and Ni can be chemically adsorbed on the (8,0) BN nanotube (1.0eV<Eb<2.0eV). The binding between the Fe or Cu atom and the BN nanotube is only marginal (Eb<0.5eV). One unusual case is Zn. Its zero binding energy independent of the adsorption sites implies it can only physically adsorbed on the BN nanotube mainly stemmed from the van de Waals interaction. For V-, Mn-and Fe-adsorbed (8,0) BN nanotube, only one type of electrons (either spin up or spin down) passes through the Fermi level implies these adsorbed systems are all half-metals, suggest that these systems could be used in the field of spintronics devices for producing nearly100%spin polarized currents. The more stable possess magnetic and semiconducting characters, hence a promising diluted magnetic semiconductor.(4) The electronic structure, magnetic and optical properties of3d transition metal M (M=V, Cr, Mn and Fe) doped (5,5) boron nitride nanotube (B19MN20) are investigated by using the first-principles PAW potential. It is found that B19VN20and B19MnN20systems have half-metallic character. Similar to Cr-adsorbed (8,0) BN nanotube, the B19CrN20system also possess magnetic and semiconducting character that may be undependent or less dependent on the chirality of the BN nanotubes for low concentration Cr substitutional doped BN nanotubes. The analyses of optical dielectric functions show that in the ε"(ω) spectrum, the absorption edge of the pristine (5,5) BNNT is shifted towards the low energy after introducing M impurities, i.e., there is a significant redshifted phenomenon, and hence the light absorption range is increased. Remarkably, the ε"(ω) spectrum of B19CrN20system exhibits a new main peak at about0.3eV (infrared region), implying the absorption of infrared light is strongly enhanced, and thus may be utilized in the fields that are associated with the infrared technology, such as infrared detector, infrared maser and so on.(5) Attributing to the influence of curvature, the band gaps of the defect-free, Cd substitutional and O deficient ZnO nanotubes are decreased, as compared with the corresponding sheets. Moreover, for both ZnO sheets and ZnO nanotubes, the band gap of the substitutional Cd case is smaller than that of the defect-free case, by contraries, O vacancy case is larger. In particular, the Zn vacancy could introduce magnetism in both ZnO sheet and ZnO nanotubes. Curvature-induced drifting of the conduction bands towards the Femi level allows the red-shift of absorption edge, resulting in the absorption in visible region for both perfect and defective ZnO nanotubes. Meanwhile, the required energy is decreased when the electrons at valence-band maximum are excited to the adjacent conduction band at Γ-point, and the corresponding absorption peak shifts towards visible region. Different from the ZnO nanotubes with Cd impurity and Zn vacancy, at Γ-point the electronic excitation from valence-band maximum to adjacent conduction band may become easier in the case of O vacancy. This contributes strongly to the optical absorption in visible region. The results we obtain may be an inspiration for the design of new generation of materials with improved solar radiation absorption.(6) A systematic density functional theoretical study of the suggested single walled LiF nanotubes in armchair (n,n) and zigzag (n,0)(2<n<11) configurations is presented. Both zigzag and armchair LiF nanotubes can exist stably due to their large binding energies which are slightly smaller than the bulk LiF. Furthermore, the insulating character is observed for them, hence potential application in nanooptics and material storage. Given single transition metal M atom adsorbed stable (8,0) LiF nanotube, it is found that M atom almost locates on the top site of the nearest F atom, regardless of the initial sites. Dramatically, the half-metallic character is obtained for V-, Cr-and Mn-adsorbed (8,0) LiF nanotubes. Thus, these adsorbed systems are expected to be used in the field of quasi-one-dimensional spintronics devices.