Template-Assisted Fabrication of Ferromagnetic Nanomaterials

Abstract Template assisted deposition was used to produce various nanomaterials including simple nanowires, nanorods, multi-segmented metal nanowires, core-shell nanowires, alloy and polymer wires and tubes. Anodized aluminum oxide (AAO) membranes were used as templates for the growth of the various structures using an electrochemical deposition method and also by wetting the porous templates. In the electrochemical deposition method, the pore size of the templates affects the rate of synthesis and the structures of the nanomaterials while in the wetting method, the viscosity and reaction time in the polymer solution influence the structures of the nanomaterials. A conventional two-step anodization procedure was used to synthesize thick AAO templates with porous hexagonal channels at a constant applied voltage and temperature. A maximum thickness of over 180 µm oxide layer could be fabricated using mild anodization at 60 V and 80 V. Compared to conventional mild anodization, these conditions facilitated faster growth of oxide layers with regular pore arrangement. Polyethylene glycol (PEG) containing ferromagnetic nanowires were synthesized using template assisted electrochemical deposition method. During the synthesis, simultaneous deposition of polymer and metal ions resulted nanowires coated with a uniform layer of PEG without interfering with the structure and magnetic properties of the nanowires. PEG-coated Ni nanowires were embedded in polyethylene diacrylate (PEGDA) matrix after the removal of the AAO templates. Comparison of results with and without a magnetic field during embedding showed that the presence of magnetic field supported embedding of nanowire arrays in polymer. Influence of using AAO templates with several pore diameters for the synthesis of bimetallic nanowires were studied by growing Ni-Fe and Ni-Co bi-metallic nanowires. At a constant applied current by using templates with a pore diameters of 60 nm alloy formed while with a pore diameter of 130 nm core-shell nanowires formed. Polyvinylidene fluoride (PVDF) films and nanotubes were synthesized using a solution recrystallization method that favored the formation of piezoelectric β phase thin films. Variation in the concentration of polymer in the mixture solution allowed synthesis of different types of structures such as PVDF composites, nanorods and nanocrystals with tunable morphologies. Keywords: One-dimensional structures, electrodeposition, porous alumina, ferromagnetic nanostructures, magnetic core-shell nanowires, alloys, polymer composite, stimuli-active, PEGDA, azobenzene, and PVDF