Pristine and Hybrid Nickel Nanowires: Template-, Magnetic Field-, and Surfactant-Free Wet Chemical Synthesis and Raman Studies

Anisotropic nanostructures of metals are extensively studied due to their sizeand shapedependent properties and interesting growth mechanisms. Usually materials based on noble metals are investigated in this context, although anisotropic nanostructures of other transition metals are also prepared. Spherical as well as anisotropic magnetic nanoparticles are of great interest due to potential applications like magnetic data storage, magnetic fluids, and biomedical purposes, etc. Nickel nanowires (NWs), rods, tubes, flowers, and triangles were synthesized by different groups. Among these anisotropic structures, NWs are studied extensively, presumably due to the ease of synthesis. Catalytic activity of Ni NWs is utilized for the conversion of methane to synthesis gas. Even though Ni NWs have been used for various applications in biology, including cell and protein separation, the biocompatibility and cytotoxicity of Ni nanoparticles is still under investigation. Magnetic properties of the Ni NWs have been extensively investigated by many groups.They are expected to be useful in high-density magnetic data storage. Advances in synthetic methods provide numerous possibilities for obtaining novel functional materials with highly controlled morphology and composition, useful for practical applications. Two-component triblock magnetic nanorods composed of Au and Ni were synthesized by templated methods and used for efficient separation of protein mixtures. Spherical nanoparticles and NWs of alloys like Ni/Fe, Co/Ni and Ni/ γ-Fe2O3 23 were prepared by template-assisted methods. Bimetallic core-shell nanorods like Ni@Co were prepared by template-assisted methods. Uniform Cu@Ni nanorods of well-defined composition were synthesized by a surfactantassisted one-pot wet-chemical method. Hybrid metal-semiconductor nanomaterials are expected to show novel electronic properties. Te and ZnO nanostructures are widely studied systems due to their interesting physical and chemical properties. Tellurium is a p-type semiconductor that exhibits good nonlinear optical response, photoconductivity, piezoelectricity, and thermoelectric properties. ZnO is a direct wide band gap semiconductor and its nanocrystals find applications in optoelectronic devices and solar cells. Ni NWs have been synthesized mainly by well-known template-assisted electrodeposition onto porous membranes. Wet chemical syntheses of Ni NWs in solvents like water, aqueous ethanol, ethylene glycol, and benzyl alcohol have been reported. A serious limitation of these wet-chemical methods is the need to control several parameters like concentration of reagents, pH, surfactants, or external magnetic field to get NWs in good yield. Furthermore, use of surfactants and other chemicals decreases the purity of the material, which is necessary for several practical applications. Here, we demonstrate the synthesis of Ni NWs in high yield by a simple wet-chemical method without the assistance of any templates, surfactants, and