Li Fa-Shen

Fabrication and optical properties of platinum nanowire arrays on anodic aluminium oxide templates

Arrays of Pt nanowires, fabricated by electrodepositing Pt metal into nanoporous anodic aluminium oxide (AAO) templates, exhibit a preferable optical absorption band in the ultraviolet-visible (UV-VIS) spectra and present a blueshift as the wire aspect ratio increases or its radius decreases. This type of optical property of Pt nanowire/porous alumina composites has been theoretically explored using Maxwell-Garnett (MG) effective medium theory. The MG theory, however, is only applicable to nanowires with an infinitesimally small radius relative to the wavelength of an incident light. The nanowire radius is controlled by the pore radius of the host alumina, which depends on anodizing conditions such as the selected electrolyte, anodizing time, temperature and voltage. The nanowire aspect ratios depend on the amount of Pt deposited into the nanopores of AAO films. The optical absorption properties of the arrays of Pt nanowires with diameters of 24, 55 and 90 nm have been investigated by the UV-VIS spectra, which show that the extinction maximum (λmax ) shifts to shorter wavelength side as the wire aspect ratio increases or its radius decreases. The results are qualitatively consistent with those calculated based on the MG theory.

Microwave Magnetic Permeability of Fe3O4 Nanoparticles

Well-dispersed Fe3O4 nanoparticles are synthesized via an oxidization method with NaNO2 as oxidant. The microwave magnetic properties of the composites are studied with different volume fractions of Fe3O4 nanoparticles. It is found that a lower volume fraction corresponds to a higher magnetic resonance frequency. This could be ascribed to the enhancement of exchange interaction with a weakened dipolar interaction when the volume fraction decreases.

Structure and 57Fe conversion electron Mössbauer spectroscopy study of Mn-Zn ferrite nanocrystal thin films by electroless plating in aqueous solution

Mn1−xZnxFe2O4 thin films with various Zn contents and of different thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90°C without heat treatment. The Mn-Zn ferrite films have a single spinel phase structure and well-crystallized columnar grains growing perpendicularly to the substrates. The results of conversion electron 57Fe Mössbauer spectroscopy (CEMS) indicate that the cation distribution of Mn1−xZnxFe2O4 ferrite nanocrystal thin films fabricated by electroless plating is different from the bulk materials’ and a great quantity of Fe3+ ions are still present on A sites for x>0.5. When the Zn content of the films increases, Fe3+ ions in the films transfer from A sites to B sites and the hyperfine magnetic field reduces, suggesting that Zn2+ has strong chemical affinity towards the A sites. On the other side, with the increase of the thickness of the films, Fe3+ ions, at B sites in the spinel structure, increase and the array of magnetic moments no longer lies in the thin film plane completely. At x = 0.5, Hc and Ms of Mn1−xZnxFe2O4 thin films show a minimum of 3.7 kA/m and a maximum of 419.6 kA/m, respectively.

Fabrication and Mössbauer Study of FeCo Alloy Nanotube Array

Arrays of FeCo nanotubes are fabricated in the pores of porous anodic aluminium oxide templates. Transmission electron microscopic result shows that the nanotubes are regular and uniform. Magnetic hysteresis loops measured at room temperature are different from those of nanowires with the same composition, which are caused by the unique shape of nanotubes. The Mossbauer spectra show that the hyperfine field is smaller than that of the bulks and increases with decrease of measuring temperature. However, the areas of the doublets appeared in Mossbauer spectra decrease with decrease of measuring temperature.

Mechanical Properties of Single-Walled (5,5) Carbon Nanotubes with Vacancy Defects

First-principles simulation is used to investigate the structural and mechanical properties of vacancy defective single-walled (5,5) carbon nanotubes. The relations of the defect concentration, distribution and characteristic of defects to Youngs modulus of nanotubes are quantitatively studied. It is found that each dangling-bond structure (per supercell) decreases Youngs modulus of nanotube by 6.1% for symmetrical distribution cases. However the concentrative vacancy structure with saturated atoms has less influence on carbon nanotubes. It is suggested that the mechanical properties of carbon nanotubes depend strongly upon the structure and relative position of vacancies in a certain defect concentration.

STRUCTURE AND M?SSBAUER STUDY OF NANOCRYSTALLINE Ni-Zn FERRITE

Ni1-xZnxFe2O4 (0.0≤x≤1.0) nanoparticles have been prepared by the polyvinyl alcohol (PVA) sol-gel method. The lattice parameter of Ni-Zn ferrite nanoparticles is larger than that of the bulk material. The variation of saturation magnetization (Ms) as a function of x has been studied. The Mossbauer spectra of the samples at room temperature showed the presence of ultrafine particles, exhibiting superparamagnetic relaxation. At higher annealing temperature, the portion of the ferromagnetic ultrafine particles increased.