Preparation And Magnetic Properties Of Core-shell Nanowires And Nanotubes

In recent years, core-shell nanowires and nanotubes have attracted extensive interestin nanomaterial science, chemistry, electronics and many other fields because of theirunique structures and excellent properties. However, these two nanostructuressynthesis by controllable way over the geometrical and morphological characteristicsstill remain huge challenges due to their relatively complex structures, thus preventinga further study on their properties. In this work, a novel method, employed withchemical etching, electrochemical deposition and electrolysis, was proposed tofabricate Cu/Ni core-shell nanowires and Ni nanotubes in polycarbonate (PC)ion-track templates. Firstly, PC membranes were irradiated by heavy ions inaccelerator. Then they were etched in NaOH solution to obtain cylindrical nanopores.And then Cu nanowire arrays were deposited in the pores by electrochemicaldeposition. Secondly, the template with embedded Cu nanowires was immersed oncemore in NaOH solution to create an annular nanochannel around each Cu nanowire.Afterwards, Ni was subsequently deposited into the annular nanochannels to formCu/Ni core-shell nanowires. Finally, in order to prepare Ni nanotubes, the Cu corenanowires were selectively electrolyzed from Cu/Ni nanowires.Using this method, Cu/Ni core-shell nanowires with an inner Cu core diameter of60nm and Ni shell thickness varying from10to80nm, and Ni nanotubes with an inner diameter of100nm and different wall thicknesses from10to110nm weresuccessfully fabricated, respectively. The morphologies and structures of nanowiresand nanotubes were characterized by scanning electron microscopy (SEM),transmission electron microscopy (TEM). The results verified that this method forcontrolled fabrication of the Cu/Ni core-shell nanowires and Ni nanotubes waseffective. The results observed by X-ray diffraction (XRD) and selected-area electrondiffraction (SAED) patterns of the Cu/Ni core-shell nanowires and Ni nanotubesindicated that the nanostructures prepared in the experiments were polycrystallinestructures. The elemental composition of Cu/Ni core-shell structure and purity of Ninanotubes were confirmed by EDX.To find out the influence of Ni shell thickness/wall thickness on the magneticproperties of Cu/Ni core-shell nanowires and Ni nanotubes, hysteresis curves of thesetwo structures were measured with magnetic field applied parallel and perpendicularto the wires’ and tubes’ axes. The results reveal that Cu/Ni core-shell nanowires and Ninanotubes possess clearly magnetic anisotropy due to their shape anisotropies, and theeasy axes of magnetization was found to be parallel to the axes of wires/tubes. Regularchange of hysteresis loops for different thicknesses of Ni shell can be obviouslyobserved when magnetic field applied parallel to the wires’ and tubes’ axes. Withincreasing Ni shell thickness, the squareness and coercivity values became smaller dueto the shape anisotropy and the formation of multi-domain structure. In addition,Cu-Ni core-shell nanowires with thinner Ni shell exhibited strong diamagneticcharacter, whereas ferromagnetic behavior was obviously measured for thicker Nishell.