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Anodic alumina membranes with modulated pore diameters serve as template for the preparation of magnetic nanowires. Filling the pores with Ni by electrodeposition delivers wires replicating the variation in modulation in pore diameter from 80 to 160 nm. Such structures are of interest for the observation and control of magnetic domain wall motion. Single-object characterization utilizing the magneto-optical Kerr effect magnetometry evidences a strong correlation between geometric parameters and magnetic properties. Ensemble magnetization measurements with a superconducting quantum interference device show the effect of dipolar interactions. Analytical models can reproduce the lowering of coercivity due to the presence of enhanced stray fields within the array. Magnetic force microscopy at individual wires indicates the presence of a strong stray field in the vicinity of the diameter change. The preparation technique demonstrates a mass production method of nano-objects with designed geometric irregularities, which could be used to control the motions of magnetic domain walls. [ABSTRACT FROM AUTHOR]

With only two matched processing steps, the fabrication of thick nanoporous alumina membranes with mono-oriented, perfect hexagonal packing of pores, and precise control of all structural parameters over large areas is demonstrated. The cylindrical pores are uniform in shape and widely tunable in their dimensions and spatial distribution, with aspect ratios as high as 500. In brief, electropolished aluminum is first patterned using three-beam interference lithography in a single step and then anodized in a hard regime. The periodic concavities in the aluminum surface guide the pore nucleation, and the self-ordering phenomenon guarantees the maintenance of the predefined arrangement throughout the entire layer. In contrast to other methods, the interpore distance can be easily adjusted, the porous layer is not limited in thickness, no prefabricated stamps are involved, and the periodic pattern can be easily reproduced without risk of degradation. The approach overcomes the time, cost, and scale limitations of other existing processes. These membranes are well-suited for the templated fabrication of perfectly ordered arrays of highly uniform 1D nanostructures. Thus, the application fields of these functional membranes are diverse: magneto-optical and opto-electronic devices, photonic crystals, solar cells, fuel cells, and chemical and biochemical sensing systems, to name a few. [ABSTRACT FROM AUTHOR]

A new method for the formation of coaxial TiO2–Ag nanowires is presented, in which TiO2 nanotubes were formed by the templated electrochemically induced sol–gel method, followed by thermal annealing. The as-formed TiO2 nanotubes have been successfully filled with a Ag core using a subsequent electrodeposition step. Coaxial nanowires have a very suitable architecture for photocatalysis, solar cells or batteries due to the high contact area between the two different phases, the large outer surface area exposed to the reactant, and short electron diffusion paths. The coaxial nanowires showed a higher efficiency than empty TiO2 nanotubes and TiO2 nanotubes with attached Ag nanoparticles in photocatalytic water splitting. Coaxial TiO2–Ag nanowires formed H2 at a rate of ∼1.23 × 10−3± 0.3 × 10−3 mol g−1 h−1 without deactivation for at least 6 h. [ABSTRACT FROM AUTHOR]

Nanotubes of TiO2 (anatase) and their ordered arrays are emerging, promising candidates as efficient host materials in many applications such as photovoltaic cells, batteries, sensors and catalysts/catalytic supports, but the interplay between these structures and their transport properties has been reported only rarely. Monodisperse, stoichiometric TiO2 nanotubes with smooth morphology and controlled wall thickness were fabricated by template-directed low-temperature atomic layer deposition (ALD), followed by annealing at elevated temperatures. We present a study on the wall thickness-dependent crystallization behaviors due to physical and/or self-confinement, as well as on the corresponding electrical properties. Over certain wall thicknesses, unexpectedly, our TiO2 nanotubes were found to be a new type of mesoporous wide gap semiconductor in which they possess similar porosity, but in terms of conductivity differ from previously known mesoporous photoanodes (i.e., anodized surfaces of Ti films and sintered films consisting of TiO2 nanoparticles). These results were ascribed to the large, elongated anatase domains (by a factor of up to 15–40 wall thicknesses) that developed via boosted crystal growth on porous alumina templates (physical confinement) as well as to the highly curved tubular shape (self-confinement). Indeed, nanotube arrays with walls thicker than 10 nm exhibited an enhancement in conductivity, by more than three orders of magnitude, compared to sintered, mesoporous TiO2 (anatase) particles, approaching the bulk value. The nearly single-crystalline TiO2 nanotubes presented here should allow for a good model system to study TiO2-based surface chemistry and have potential for many applications in photovoltaic and/or catalytic systems. [ABSTRACT FROM AUTHOR]

Reversal modes and magnetostatic interactions of multilayered Fe3O4/ZrO2/Fe3O4 nanotubes consisting of a ferromagnetic internal tube, an intermediate non-magnetic spacer and an external magnetic shell are investigated as a function of their geometric parameters and compared with those produced inside the pores of anodic alumina membranes by atomic layer deposition. Based on a continuum approach we obtained analytical expressions that underline the first experimental results and support their interpretation that the system of multilayer tubes behaves as the reversal of two isolated systems. It is observed that the magnetostatic interaction between both phases depends on the magnetic configurations in each phase and also on the geometrical parameters considered. These structures have potential applications in novel spintronics devices, ultra-small magnetic media and other nano-devices. [ABSTRACT FROM AUTHOR]