Fe Nanowires Research Articles

In-depth profile analysis of filled alumina and titania nanostructured templates by radiofrequency glow discharge coupled to optical emission spectrometry

The development of highly ordered and self-assembled magnetic nanostructures such as arrays of Fe or Ni nanowires and their alloys is arousing increasing interest due to the peculiar magnetic properties of such materials at the nanoscale. These nanostructures can be fabricated using nanoporous anodic alumina membranes or self-assembled nanotubular titanium dioxide as templates. The chemical characterization of the nanostructured layers is of great importance to assist the optimization of the filling procedure or to determine their manufacturing quality. Radiofrequency glow discharge (RF-GD) coupled to optical emission spectrometry (OES) is a powerful tool for the direct analysis of either conducting or insulating materials and to carry out depth profile analysis of thin layers by multi-matrix calibration procedures. Thus, the capability of RF-GD-OES is investigated here for the in-depth quantitative analysis of self-aligned titania nanotubes and self-ordered nanoporous alumina filled with arrays of metallic and magnetic nanowires obtained using the template-assisted filling method. The samples analysed in this work consisted of arrays of Ni nanowires with different lengths (from 1.2 up to 5 microm) and multilayer nanowires of alternating layers with different thicknesses (of 1-2 microm) of Ni and Au, or Au and FeNi alloy, deposited inside the alumina and titania membranes. Results, compared with other techniques such as scanning electron microscopy and energy-dispersive X-ray spectroscopy, show that the RF-GD-OES surface analysis technique proves to be adequate and promising for this challenging application.

Cytotoxicity and cellular uptake of iron nanowires

The toxicity of nanostructured materials and nanoparticles are very important considerations for many nanotechnology applications. Iron nanowires (NWs), as useful magnetic nanomaterials, may be good candidates for several biomedical applications. Here Fe NWs with an average diameter of about 50 nm were prepared by electrodeposition within the nanopores of anodic aluminum oxide (AAO) templates, and characterized by using scanning electron microcopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The cytotoxicity of the Fe NWs was studied at cell level. Specifically, the influence of concentration and size on the cytotoxicity of Fe NWs to HeLa cells was evaluated by MTT assay combined with direct morphology observations by TEM and phase contrast microscopy. The results clearly showed that the presence of Fe NWs had no significant effect on the cell proliferation and cell viability, even the HeLa cells exposed to Fe NWs at the high concentration of 10 000 per cell for 72 h still showed high cell viability of about 80%. From phase contrast microscopy, confocal laser scanning microscopy (CLSM) and TEM observations, it was found that Fe NWs were indeed internalized by HeLa cells. The cellular uptake process and results of Fe NWs demonstrated that as-prepared Fe NWs had not only a good biocompatibility but also a very low cytotoxicity.

The influence of crystallinity enhancement on the magnetic properties of ac electrodeposited Fe nanowires

Fe nanowire arrays with different degrees of crystallinity were fabricated by ac electrodeposition into anodic aluminium oxide templates. A (110) preferential crystal orientation was observed for all the samples. An extensive investigation of X-ray patterns revealed that the variation of the magnetic properties is a direct consequence of the crystallinity degree of Fe nanowires. The results indicate that the degree of crystallinity varies with electrolyte acidity, waveform and frequency of the ac electrodeposition voltage. Regardless of the waveform and electrolyte acidity, higher deposition frequency induces higher coercivity. The effect of waveform and pH value on the magnetic properties is seen to be more pronounced in the low deposition frequency. Improving the ac electrodeposition conditions increased the coercivity and squareness from almost 1010 Oe and 0.49 to 1810 Oe and 0.99, respectively. It was seen that annealing improved the crystallinity, thereby increasing the coercivity and squareness.

Transformation pathways in the solid-solid phase transitions of iron nanowires

Using molecular dynamics simulations, we study the solid-solid phase transitions induced by strain in Fe nanowires. These show an intricate dependence on the crystallographic orientation of the wire. ⟨001⟩ oriented nanowires exhibit a bcc→fcc transition and preferably follow the Nishiyama–Wassermann path. In ⟨011⟩ and ⟨111⟩ oriented nanowires the transformation is bcc→hcp and proceeds according to the Burgers path. Additionally we show that it is possible to obtain multiple phase transitions accompanied with reorientations.

Structural, electronic and magnetic properties of Fe nanowires encapsulated in boron nitride nanotubes

The structural, electronic and magnetic properties of Fe nanowire encapsulated in zigzag ( n,0) BNNTs (8≤ n≤15) have been investigated systematically using the first-principles PAW potential within DFT under GGA. Among the eight Fe@( n,0) systems, only the Fe@(8,0) system is formed endothermically, the other larger systems are formed exothermically. Therefore it is expected that thicker Fe nanowires would be pulled spontaneously into larger BNNTs by forces amounting to a fraction of a nanonewton. The high spin polarization and magnetic moments of the Fe@( n,0) systems coming solely from the Fe nanowire imply the Fe@( n,0) systems can be applied to the circuits that demand preferential transport of electrons with a specific spin, in particular for Fe@(12,0) and Fe@(13,0) systems.

Structure and magnetism of self-assembled Fe nanowires on a faceted Cu(332) surface: the influence of oxygen-induced reconstruction

We present a study on the structural and magnetic properties of Fe nanowires as grown on an oxidized-reconstructed Cu(332) surface. A template surface consisting of alternate parallel stripes of Cu(111) terraces and (110) oxidized facets, with a periodicity of 4 nm, was used to grow iron wires, by the selective affinity of iron to the oxygen adsorption sites. Atomic resolution scanning tunnelling microscopy shows that Fe grows preferentially on the (110) facets, forming well-ordered Fe nanowires in the submonolayer regime. The (111) terraces are not affected by the iron deposition. Magneto-optical Kerr effect and x-ray magnetic circular dichroism reveal a long-range magnetic ordering of the wires with an out-of-plane magnetic easy axis at an early stage of the Fe growth. For coverages higher than 2–3 atomic layers, the magnetization switches to in-plane, but is perpendicular to the stripes.

Comparison of Electronic and Magnetic Properties of Fe, Co, and Ni Nanowires Encapsulated in Boron Nitride Nanotubes

The electronic and magnetic properties of the three types of ferromagnetic nanowires (FN4’s), Fe4, Co4, and Ni4, encapsulated in boron nitride nanotubes (BNNTs) have been investigated systematically using the first-principles projector-augmented wave potential within the density functional theory under the generalized gradient approximation. We find that all three types of the FN4 encapsulated into the narrower (6,6) BNNT are endothermic, whereas if they are encapsulated into the broader (8,8) BNNT, they are exothermic. Both the spin polarization and the magnetic moment of the FN4@(8,8) systems are larger than those of the FN4@(6,6) systems due to weaker restriction of the broader (8,8) BNNT, but those of these two combined systems are smaller than those of the corresponding freestanding FN4. The spin polarization of the Co4@(8,8) system is larger than that of either the Fe4@(8,8) system or the Ni4@(8,8) system, which means that the Co4@(8,8) system can be used as a spin valve in spin-dependent transport ...

Tunable magnetic properties of arrays of Fe(1 1 0) nanowires grown on kinetically grooved W(1 1 0) self-organized templates

We report a detailed magnetic study of a new type of self-organized nanowires discussed briefly previously [B. Borca et al., Appl. Phys. Lett. 90 (2007) 142507]. The templates, prepared on sapphire wafers in a kinetically limited regime, consist of uniaxially grooved W(1 1 0) surfaces, with a lateral period here tuned to 15 nm. Fe deposition leads to the formation of (1 1 0) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coefficients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50 to 200 K.

Formation of oxide nanotubes via oxidation of Fe, Cu and Ni nanowires and their structural stability: Difference in formation and shrinkage behavior of interior pores

Changes in the morphology of Fe, Cu and Ni nanowires with a diameter of 55 nm during oxidation at 423–923 K were studied by transmission electron microscopy. Oxide nanotubes with a cylindrical interior pore of uniform diameter were formed after the oxidation of Fe and Cu nanowires in air at 573 and 423 K, respectively, while the Ni nanowires became bamboo-like nanowires of NiO with separate interior voids after oxidation at 673–773 K. Oxide nanotubes of Fe and Cu and the bamboo structures of NiO showed a tendency to shrink into solid oxide nanowires after annealing at higher temperatures in air. In the shrinking process of Fe 3O 4 nanotubes, however, an array of additional nanovoids was observed along the inner wall of the nanotubes, suggesting the formation of a duplex porous nanostructure. This can be explained by the recombination of vacancies diffusing outward from the inner cylindrical pore.

Magnetism of 3d-Transition Metal (Fe, Co, and Ni) Nanowires on w-BN (0001)

We study the magnetic properties of monoatomic Fe, Co, and Ni nanowires on wurtzite boron nitride (w-BN)(0001) using state-of-the-art first-principles calculations. Our results show that the most stable phase is the ferromagnetic Co(Fe) metal-atom chain adsorbed on the w-BN(0001) surface terminated by N layers. The monoatomic Co and Ni chains on the w-BN (0001) surface terminated by N layers are found to be excellent half-metallic ferromagnets with large half-metallic gaps (up to 0.65 eV). The monoatomic Co and Fe nanowires on B-terminated w-BN (0001) and Fe nanowires on N-terminated w-BN (0001) present large but not complete spin polarization. We found that the large magnetic anisotropy energy (MAE) of ferromagnetic atoms is caused by a magnetic Coulomb interaction between the ferromagnetic atoms and N and B atoms. In this case, the large spin−orbit coupling of the ferromagnetic atoms and the hybridization between the ferromagnetic atoms d-, N p-, and B p-like states are crucial. The w-BN (0001) surface ...

Solid–solid phase transitions in Fe nanowires induced by axial strain

By means of classical molecular-dynamics simulations we investigate the solid–solid phasetransition from a bcc to a close-packed crystal structure in cylindrical iron nanowires,induced by axial strain. The interatomic potential employed has been shown to be capableof describing the martensite–austenite phase transition in iron. We study thestress versus strain curves for different temperatures and show that for a range oftemperatures it is possible to induce a solid–solid phase transition by axial strain beforethe elasticity is lost; these transition temperatures are below the bulk transitiontemperature. The two phases have different (non-linear) elastic behavior: thebcc phase softens, while the close-packed phase stiffens with temperature. Wealso consider the reversibility of the transformation in the elastic regimes, andthe role of the strain rate on the critical strain necessary for phase transition.

Spin-orbit interaction of charge carriers with impurities in aligned Ge0.99Me0.01 (Me = Mn, Cr, Co, Fe) nanowires

Aligned Ge0.99Me0.01 (Me = Mn, Cr, Co, Fe) nanowires have been investigated by electron spin resonance (ESR). Resonance lines corresponding to a magnetically ordered subsystem of localized spins (clusters of Ge alloys with transition metals) and an asymmetric Dysonian line, corresponding to the ESR of charge carriers in Ge, are identified in the ESR spectra. A systematic decrease in the effective g factor of the asymmetric Dysonian line with enhancement of spin-orbit interaction is found in the series of transition-metal ions Mn2+, Cr2+, Fe3+, and Co2+, which were used to dope Ge nanowires.

Magnetic properties of Ni–Fe nanowire arrays: effect of template material and deposition conditions

The objective of this work is to study the magnetic properties of arrays of Ni–Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that the application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of the Ni–Fe nanowires. The samples with magnetic field perpendicular to the template plane during deposition exhibit strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in the Ni–Fe nanowires deposited in polycarbonate templates. In the case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squareness ratio decrease, saturation field increases. Such magnetic behaviour (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires and perpendicular shape anisotropy in individual nanowires.

Biological and Magnetic Contrast Evaluation of Shape-Selective Mn–Fe Nanowires

One-dimensional composite Mn-Fe oxide nanostructures of different sizes (nanoneedles, nanorods, and nanowires) were prepared by a linker-induced organization of manganese-doped iron oxide nanoparticles. The nanostructures were obtained by the treatment of MnFe(2)O(4) nanoparticles in the presence of cystamine. The average lengths of nanoneedle, nanorod, and nanowire are approximately 400, 800, and 1000 nm, respectively. High-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) spectroscopy, and inductively coupled plasma-optical emission spectroscopy (ICP-OES) were employed to characterize the morphologies and the elemental contents of the nanostructures. As an example of their potential applications, these nanostructures were explored as the cell-labeling agents for magnetic resonance imaging (MRI). The magnetic contrast properties of the nanostructures were characterized by a 1.5 T (Tesla) whole body MR system. 10 microg/mL of the nanostructures caused substantial negative contrast. After in vitro incubation, the nanostructures could be effectively incorporated into the cells of a monocyte/macrophage cell line (RAW264.7). These cells' viability and proliferation potential were not affected when the labeling concentration was less than 50 microg/mL.

Fabrication and magnetic properties of metallic nanowires via AAO templates

Metallic (Ni, Co, Cu and Fe) nanowires were fabricated by electrodeposition into anodic aluminum oxide (AAO) template. In this work, we have studied the effect of the electrode potential on the microstructure and magnetic properties of nanowires. Transmission electron microscopy (TEM) results showed that the metal nanowires were single-crystal. Cu and Ni nanowires had the same orientation along the [2 2 0] direction, while Co had a preferred orientation along the [1 0 0] direction. Fe nanowires had a preferred orientation along the [2 0 0] direction. The growth mechanisms are probably due to the competition growth of the adjacent grains and the confinement of growth in the nano-sized hole of the AAO template. Results showed that single crystal or highly textured nanowires had better magnetic properties compared with that of polycrystal nanowires in terms of coercivity and squareness.

On the structural and mechanical properties of Fe-filled carbon nanotubes—a computersimulation approach

The structural and mechanical properties of single-and multi-walled carbon nanotubesfilled with iron nanowires are studied using a recent parameterization of the modifiedembedded atom model. We have analyzed the effect of different crystal structures of iron(bcc and fcc) inside carbon nanotubes of different topographies. We have computed strainenergy versus strain curves for pure systems: Fe nanowires, carbon and Fe-filled carbonnanotubes. A noticeable difference is found when these monatomic systems are joined toform iron-capped nanowires and where multi-layers of graphite are added to the nanotubes.

Electrochemical Preparation of Magnetic Nanowires

Electrochemistry is a method, which can be used for creation of nanomaterials. This method has big advantage such as no restriction for shape and size of the sample and do not need to involve expensive equipment for the sample preparation. In the paper the preparation of Fe nanowires as well as Co and Ni are presented. The diameter and length of obtained nanowires can be tuned by properties of the template porous material and time of deposition, respectively. The quality of the nanowires depends also from deposition mode (AC - alternating current or DC - constant current) and pH of the solution. The anodization conducted in oxalic acid allows us to obtain anodic alumina oxide (AAO) with the smallest pore diameter of about 40 nm. Usage of phosphoric acid results in largest pores with diameter around 120 nm. The deposited material inside the pores has diameter of the templates. The length can be as large as the thickness of the oxide and reach up to around 1 μm. The wires shows magnetization direction along main axis. The morphology of wires were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The magnetic characterization of the structures was done by magnetic force microscopy (MFM) and Mössbauer spectroscopy.

A simple method for fabricating single-crystalline Fe nanowires

This work reports a simple and environmental friendly approach for the fabrication of Fe nanowires under normal pressure and low temperature in the absence of any inorganic or organic templates, substrate, surfactant, external field or magnetic field. This approach involved the production of Fe(OH) 3/NaCl by mechanically milling a mixture of Fe(OH) 3 and NaCl, and the reduction of Fe(OH) 3/NaCl to Fe nanowires. The as-prepared product (Fe/NaCl) and the Fe nanowires obtained by dissolving the NaCl from Fe/NaCl were characterized using transmission electron microscopy, X-ray diffraction and vibrating sample magnetometer. The results showed that the Fe nanowires are about 10–100 nm in diameter and 8–16 μm in length and their saturation magnetization ( M s) and coercivity ( H c) values are 145 emu/g and 206 Oe, respectively.

A magnetic force microscopy study of the magnetic reversal of a single Fe nanowire

The magnetization reversal properties of a single 60 nm diameter Fe nanowire wereinvestigated with an in-field magnetic force microscope (MFM). MFM images wereobserved in a successively decreasing applied field, at various angles between the appliedfield and the nanowire axis. The results show that the magnetization undergoes a sharpreversal at various angles. When the applied field deviates from the nanowire axis, beforecomplete magnetization reversal, a coherent rotation of magnetic moments inside thenanowire and a stable vortex state at the end of the nanowire are exhibited. Theangle dependence of the switching field can be closely described by a curlingmodel, despite the fact the magnetization reversal process is not identical to thismodel.

Study of Biosensors Based on Fe Nanowires

AbstractAnodic aluminum oxide (AAO) template was prepared by using anodizing voltage step-decreasing method after two-step oxide method. Based on AAO template, Fe nanowires arrays were electrochemically deposited. Fe nanowires were coated by chitosan. Fe nanowires/chitosan was synthesized by glutaraldehyde as cross-linking reagent. By crosslinking α-human chorionic gonadotropin (α-HCG), biological probes with Fe nanowires/chitosan/antibody were prepared. An easy operating, easy taking and rapid reacting magnetic detecting system was developed after optimizing the geometry parameters of detect coil. Different concentration samples with 1, 2 and 5 g(Fe)/L were detected. The results show that the sensitivity of system is 0.2 g(Fe)/L and can be improve better.