Enzymatically Synthesized Conducting Polyaniline Nanocomposites: A Solid‐State NMR Study

Abstract

The chiral conducting polyaniline (PANI) nanocomposites [polyacrylic acid/polyaniline/(?) camphorsulphonic acid (CSA)] were synthesized using enzyme, horseradish peroxidase (HRP) in the aqueous buffer solution at pH 4.3. It appears that the enzyme HRP apart being a biocatalyst, plays an important role during the polymerization, which allows PANI to prefer a specific helical conformation whether the induced chirality in the monomer‐CSA complex is either by (+)CSA or (?)CSA. In this paper, we report, the structural characterization of these nanocomposites by solid‐state ¹³C cross‐polarization with magic angle spinning (CP/MAS) NMR techniques. The structural features of PANI in the conducting form of nanocomposite (as‐synthesized) are similar to that of enzymatically and chemically synthesized PANI. Preliminary data also suggest that some portion of nanocomposite samples are not completely doped. Dedoping of as‐synthesized PANI nanocomposite with aqueous NH₄OH shows the spectral features that of the emeraldine base form. Solid‐state ¹³C NMR data suggest that it is possible to detach PAA and CSA from PANI in the nanocomposite material.     

Magnetization reversal dynamics in Co nanowires with competing magnetic anisotropies

We present the magnetization reversal dynamics of Co nanowires with competing magnetic anisotropies. The aspect ratio (R) of the nanowires is varied between 2.5 and 60, and we observe a cross-over of the directions of the magnetic easy and hard axes at R=6.8. Micromagnetic simulations qualitatively reproduce the observed cross-over and give detailed insight into the reversal mechanisms associated with the cross-over. The reversal mechanism for a field applied along the long axis of the nanowire exhibits a quasi-coherent rotation mode and a corkscrew-like mode, respectively, above and below the cross-over, with the formation of a Bloch domain near the cross-over region. For a field applied along the short axis, the reversal occurs by nucleation and propagation of reversed domains from the two ends of the nanowires for very high values of the aspect ratio down to the cross-over region, but it transforms into quasi-coherent rotation mode for smaller aspect ratios (below the cross-over region).     

Ultrafine Fe-Co nanowires: Fabrication and heat treatment influence on the structure and magnetic properties

Ultrafine nanowires of Fe-Co with a diameter around 15 nm have been fabricated by electrodeposition method using anodic porous alumina as a template. The alloy nanowires were in the form of arrays and consisting of polycrystalline structures. They showed obvious shape anisotropy parallel to the axis of nanowires and the perpendicular coercivity (Hc_⊥) was found to be 2576.8 Oe which is higher than any coercivity value reported in the literature. The effects of critical factors such as heat treatment and temperature of annealing on the structure and magnetic properties of the ultrafine nanowire arrays were studied and discussed.     

Structural evolution of self‐assisted GaAs nanowires grown on Si(111)

GaAs nanowires are grown on Si(111) by self‐assisted molecular beam epitaxy, and the ratio between wurtzite and zinc‐blende phases is determined as function of nanowire length using asymmetric X‐ray diffraction. We show that under the applied growth conditions, nanowires grow in both phases during the initial stage of growth, whereas the zinc‐blende content increases with growth time and dominates in long nanowires. Compared to the zinc‐blende units, the vertical lattice parameter of the wurtzite segments is 0.7% larger, as measured by the positions of respective diffraction peaks. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic structure of twinned ZnS nanowire

The electronic properties of twinned ZnS nanowires （NWs） with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal （2H） stacking inside the cubic （3C） stacking has no effect on the electronic properties of thin ZnS NWs.     

Novel photoluminescence properties of InAlO3（ZnO）m superlattice nanowires

One-dimension InAlO 3 (ZnO) m superlattice nanowires were successfully synthesized via chemical vapor deposition.Transmission electron microscopy measurements reveal that the nanowires have a periodic layered structure along the 0001 direction.The photoluminescence properties of InAlO 3 (ZnO) m superlattice nanowires are studied for the first time.The near-band-edge emissions exhibit an obvious red shift due to the formation of the localized tail states.The two peaks centered at 3.348 eV and 3.299 eV indicate a lever phenomenon at the low-temperature region.A new luminescence mechanism is proposed,combined with the special energy band structure of InAlO 3 (ZnO) m.     

One-dimensional iron oxides nanostructures

Iron oxides,including α-Fe2O3,γ-Fe2O3,Fe3O4,etc.are one of the most widely investigated materials for their fundamental properties and potential applications.One-dimensional(1-D) iron oxides nanostructures are the focus of recent research activities because of their wide applications in magnetic refrigeration,information storage,electronics,catalysts,Li-ion battery,pigment,gas sensors,etc.This review covers the recent progress in the synthesis,properties and applications of 1-D iron oxides nanostructures.Th...     

段化(A/B)m复合纳米线阵列的矫顽力机理

基于球链模型的对称扇形转动机理，考虑了段间的界面交换耦合作用，对利用电化学沉积方法制备的段化复合磁性纳米线六角阵列的磁滞回线进行了系统的研究，提出了矫顽力随复合段数m的变化规律.指出在这种段化复合纳米线阵列中，段间的交换耦合作用对磁化反转起着重要的影响. 关键词： 球链模型 复合纳米线 矫顽力 交换耦合     

Radial heterostructure and interface effects on thermoelectric transport properties of Bi/Sn and Bi/Sb core/shell nanowires

The thermoelectric transport properties of Bi/Sn and Bi/Sb core/shell (C/S) nanowires grown by the method of on-film formation of nanowires were systematically investigated. The electrical conductivity and Seebeck coefficient of nanowires with different diameters were measured as a function of the temperature. The contribution of Sn and Sb shells to the total transport in the C/S nanowires was determined using analytical fitting based on the parallel combination of the conductive system model. The carrier-interface boundary scattering at the C/S interface was quantitatively evaluated as the sheet resistance. In addition, the effect of hole doping on the transport properties was also observed in the Bi/Sn C/S nanowires.