Co(x)Ni(1-x) alloy nanowires with varying Co content (0 ≤ x ≤ 0.95), having a diameter of 130 nm and length of around 20 μm, are synthesized by template-assisted electrodeposition into the nanopores of SiO(2) conformal coated hard-anodic aluminum oxide membranes. The magneto-structural properties of both single isolated nanowires and hexagonally ordered nanowire arrays of Co-Ni alloys are systematically studied by means of magneto-optical Kerr effect magnetometry and vibrating sample magnetometry, respectively, allowing us to compare different alloy compositions and to distinguish between the magnetostatic and magnetocrystalline contributions to the effective magnetic anisotropy for each system. The excellent tunable soft magnetic properties and magnetic bistability exhibited by low Co content Co-Ni nanowires indicate that they might become the material of choice for the development of nanostructured magnetic systems and devices as an alternative to Fe-Ni alloy based systems, being chemically more robust. Furthermore, Co contents higher than 51 at.% allow us to modify the magnetic behavior of Co-rich nanowires by developing well controlled magnetocrystalline anisotropy, which is desirable for data storage applications.
Inverse opals are most widely used as photonic crystals for ultraviolet, optical, and infrared applications. [1] These highly interconnected porous structures are also attractive for applications such as sensors, fuel cells, filters, and catalysts. [2] At the same time, engineers are aiming for lightweight structures with optimized mechanical strength, often inspired by nature's cellular materials with foam-like structures such as sponges, [3] trabecular bone, [4] or plant parenchyma. [5] The resultant optimized strut-based structures have shown high stiffness-and compressive strength-to-weight ratios, [6][7][8][9] but can suffer from strut buckling and a lack of mass production techniques. Here, we show that mechanical metamaterials based on ceramic inverse opaline structures with densities in the range of 330-910 kg m À3 are not only suitable as photonic crystals but also show better stiffness-and compressive strength-to-weight ratios compared to microfabricated optimized strut-based structures, [6][7][8][9] but lower than carbon nanoframes fabricated by interference lithography. [10] Pure silica inverse opal structures and silica inverse opals whose pores have been internally coated by a thin TiO 2 layer have been fabricated and their structural and mechanical behavior was investigated. Our experimental results, supported by numerical simulations, show that these arch-shaped porous structures outperform both strut-based and honeycomb structures due to their nearly isotropic mechanical response.The silica inverse opal films presented here are fabricated by vertical co-assembly based on the procedure described by Hatton et al. [11] Monodisperse colloidal polystyrene (PS) spheres were mixed in a water-based suspension containing tetraethylorthosilicate (TEOS) solution and vertically assembled on soda-lime silica glass. The resulting FCC opaline structure was calcined at 500°C for 30 min to burn out the PS template leaving an inverse-FCC opaline structure of nanoporous amorphous silica in which the adjacent pores are interconnected by %170 nm diameter holes (Figure 1a). Some samples were subsequently coated with an amorphous layer of TiO 2 by atomic layer deposition (ALD). After full crystallization to anatase, the layer thickness was %28 nm (Figure 1b). The specular reflection in Figure 1c shows the characteristic reflection peaks, which can be tuned by both the pore diameter and/or the TiO 2 coating.The effective density of the silica inverse opals was estimated by four independent methods: gravimetric, pycnometric, and two opticals. All four methods yield a comparable density of 330 kg m À3 AE 10%. The effective density of the TiO 2 ALD-coated silica inverse opals was estimated gravimetrically and optically to be 910 kg m À3 AE 10%. Detailed information can be found in the Supporting Information.Some examples of mechanical properties of opaline structures can be found in the literature. These works investigated polymer, [12,13] metal, [14] and ceramic-based [14][15][16] opals. Toivola et al. [15] investigated s...
The magneto-optical properties of Au-Co(x)Fe(3 - x)O(4) core-shell nanowires embedded in porous alumina membranes are studied. The structures were obtained by depositing Co(x)Fe(3 - x)O(4) on the pore walls of alumina membranes by atomic layer deposition and filling the resulting nanotube with gold by electrodeposition. The effect of plasmon resonance excitation on the magneto-optical activity is clearly observed as a modification of the spectral line shape of the Kerr rotation signal.
A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons.
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.
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