Ni Nanowire Arrays Research Articles

Morphology and Magnetic Properties of Ni Nanowires in Thin Film Anodic Alumina Templates

The features of the morphology and magnetic properties of Ni nanowire arrays have been studied. Aluminum oxide matrices are used as a template for electrolytic deposition of nanowires. The matrices are obtained by anodizing the aluminum films with a thickness of 2 μm that are formed on glass substrates by high frequency ion sputtering. Electrochemical deposition of the metal is carried out using direct and alternating currents. Morphology and microstructure studies show that the nanowire arrays are polycrystalline and have a branched dendritic structure due to the morphological features of aluminum oxide matrices. A relationship between the magnetization reversal patterns and the modes of electrodeposition of Ni nanowire arrays is established. The process of magnetization reversal of an array of this kind of structures is simulated.

Uniaxial Magnetization and Electrocatalytic Performance for Hydrogen Evolution on Electrodeposited Ni Nanowire Array Electrodes with Ultra-High Aspect Ratio.

Ni nanowire array electrodes with an extremely large surface area were made through an electrochemical reduction process utilizing an anodized alumina template with a pore length of 320 µm, pore diameter of 100 nm, and pore aspect ratio of 3200. The electrodeposited Ni nanowire arrays were preferentially oriented in the (111) plane regardless of the deposition potential and exhibited uniaxial magnetic anisotropy with easy magnetization in the axial direction. With respect to the magnetic properties, the squareness and coercivity of the electrodeposited Ni nanowire arrays improved up to 0.8 and 550 Oe, respectively. It was also confirmed that the magnetization reversal was suppressed by increasing the aspect ratio and the hard magnetic performance was improved. The electrocatalytic performance for hydrogen evolution on the electrodeposited Ni nanowire arrays was also investigated and the hydrogen overvoltage was reduced down to ~0.1 V, which was almost 0.2 V lower than that on the electrodeposited Ni films. Additionally, the current density for hydrogen evolution at -1.0 V and -1.5 V vs. Ag/AgCl increased up to approximately -580 A/m2 and -891 A/m2, respectively, due to the extremely large surface area of the electrodeposited Ni nanowire arrays.

Optical analysis of aligned Ni nanowire arrays with different degree of oxidation for terahertz polarizer application

The optical properties of aligned nickel nanowire arrays (NiNWAs) with different degrees of oxidation for terahertz (THz) polarizer applications have been investigated by using THz time-domain spectroscopy. In frequency-domain spectra, the full width at half maxima of transmitted peaks was broadened and the peak positions have a blue shift with increasing oxidation levels, besides the enhancement in peak intensity. It is indicated that the oxidation of Ni nanowires (NWs) has a significant influence on the interaction between Ni NWs and THz wave. The transmittance of the aligned NiNWAs increases with annealing temperature increasing. Conversely, the degree of polarization and extinction ratio (ER) decreases. A corresponding relationship between the change of ER and degree of oxidation is summarized by means of thermogravimetric analysis. The change of ER for the annealing sample with the degree of oxidation of 0.507% is 27.32%, which induced the polarization properties of aligned NiNWAs to be sensitive to the oxidation of Ni NWs. These findings can provide new positive features in the development of future polarization-based device applications for THz electronics and photonics.

Triple‐Asymmetric Flexible Strain Sensor Based on High‐aligned Ni Nanowire Arrays with Opposite Resistance Responding for Multidimensional Motions Detection

AbstractHerein, a triple‐asymmetric flexible strain sensor by using the single‐layered high‐aligned Ni‐nanowire arrays is proposed for the applications of monitoring multidimensional motions of human joints. The triple‐asymmetric structures consist of a spatially ordering distribution of Ni nanowires (NWs) and double position asymmetric distributions of the Ni NWs in width and thickness direction of sensor. Because Ni NWs are isolated from each other, the resistance change of the sensor is by tunneling effect. The resistance values of the proposed sensor decrease with the increasing of stretching strain, which is different from that of the common flexible strain sensors, and the maximum absolute valve of gauge factor is 35. Furthermore, the proposed sensor has a good bending sensitivity, ranging from 90° to −90°, and minimum resolution angle of 5° in out‐plane bending. Benefiting from the asymmetric structures and tunneling effect, the complex movements of human joints (such as up‐down bending, left‐right swing, and rotating of wrist) are successfully detected. The practical applicability in real‐time monitoring and the processes of handwriting are also shown. Therefore, this proposed sensor is believed to have great potential in future development of micro‐motion monitoring, wearable electronics, and artificial intelligence.

FORC-investigation of magnetic properties of Ni nanowire arrays synthesized using Al2O3 templates with different order of pores

FORC-investigation of magnetic properties of Ni nanowire arrays synthesized using Al2O3 templates with different order of pores

Single Diameter Modulation Effects on Ni Nanowire Array Magnetization Reversal.

Geometrically modulated magnetic nanowires are a simple yet efficient strategy to modify the magnetic domain wall propagation since a simple diameter modulation can achieve its pinning during the nanowire magnetization reversal. However, in dense systems of parallel nanowires, the stray fields arising at the diameter interface can interfere with the domain wall propagation in the neighboring nanowires. Therefore, the magnetic behavior of diameter-modulated nanowire arrays can be quite complex and depending on both short and long-range interaction fields, as well as the nanowire geometric dimensions. We applied the first-order reversal curve (FORC) method to bi-segmented Ni nanowire arrays varying the wide segment (45–65 nm diameter, 2.5–10.0 μm length). The FORC results indicate a magnetic behavior modification depending on its length/diameter aspect ratio. The distributions either exhibit a strong extension along the coercivity axis or a main distribution finishing by a fork feature, whereas the extension greatly reduces in amplitude. With the help of micromagnetic simulations, we propose that a low aspect ratio stabilizes pinned domain walls at the diameter modulation during the magnetization reversal. In this case, long-range axial interaction fields nucleate a domain wall at the nanowire extremities, while short-range ones could induce a nucleation at the diameter interface. However, regardless of the wide segment aspect ratio, the magnetization reversal is governed by the local radial stray fields of the modulation near null magnetization. Our findings demonstrate the capacity of distinguishing between complex magnetic behaviors involving convoluted interaction fields.

Magnetic Properties of the Densely Packed Ultra-Long Ni Nanowires Encapsulated in Alumina Membrane.

High-quality and compact arrays of Ni nanowires with a high ratio (up to 700) were obtained by DC electrochemical deposition into porous anodic alumina membranes with a distance between pores equal to 105 nm. The nanowire arrays were examined using scanning electron microscopy, X-ray diffraction analysis and vibration magnetometry at 300 K and 4.2 K. Microscopic and X-ray diffraction results showed that Ni nanowires are homogeneous, with smooth walls and mostly single-crystalline materials with a 220-oriented growth direction. The magnetic properties of the samples (coercivity and squareness) depend more on the length of the nanowires and the packing factor (the volume fraction of the nanowires in the membrane). It is shown that the dipolar interaction changes the demagnetizing field during a reversal magnetization of the Ni nanowires, and the general effective field of magnetostatic uniaxial shape anisotropy. The effect of magnetostatic interaction between ultra-long nanowires (with an aspect ratio of >500) in samples with a packing factor of ≥37% leads to a reversal magnetization state, in which a “curling”-type model of nanowire behavior is realized.

Electrodeposition of Ni nanowire arrays and their magnetic properties

Electrodeposition of Ni nanowire arrays and their magnetic properties

Ferromagnetic resonance study on the influence of the electrolytic bath acidity on the magnetic anisotropy of Ni nanowires

In this work, a ferromagnetic resonance study on the influence of the electrolytic bath acidity on the magnetic anisotropy and hardness parameter of arrays of 50 nm diameter Ni nanowires in porous alumina membranes, is reported. Fine tuning the effective magnetic anisotropy of the arrays has been achieved by progressively changing the nanowires microstructure from polycrystalline textured to single-crystalline as the electrolyte acidity is reduced. The micro-structural analysis carried out by X-ray diffraction and high resolution transmission electron microscopy has revealed that a preferred crystal texture is not a sufficient condition for the enhancement of the magnetic anisotropy. Instead, a correlation between the increase of crystallite size and quality, and the increase of both the magnetic anisotropy and hardness parameter has been shown. Ferromagnetic resonance and alternating gradient magnetometry experiments have shown that no additional magnetic contributions take place in Ni NWs grown from highly acidic electrolytes (pH 1.6), whereas a significant additional anisotropy contribution progressively appears as the electrolyte acidity is reduced (pH 5.0). Besides the careful adjustment of electrodeposition conditions, achieving a very long length for the nanowires is also a key requirement to have a precise control on the effective magnetic anisotropy energy, which can be fine tuned in the wide range from 64-167 kJ·m−3 as a result of an energy enhancement of magnetoelastic origin. Ferromagnetic resonance measurements have demonstrated that nanocomposites based on arrays of nanowires made of low cost and abundant elements like Ni exhibit hardness parameters in the range 0.47–0.75 within the semihard region, where those with κ>0.5 are suitable for permanent magnet applications. These features make arrays of low diameter Ni nanowires very appealing for their use in the development of agile microwave and spintronic devices.

Control of the asymmetric growth of nanowire arrays with gradient profiles.

A novel electrochemical methodology for the growth of arrays of Ni and Co nanowires (NWs) with linear and non-linear varying micro-height gradient profiles (μHGPs), has been developed. The growth mechanism of these microstructures consists of a three-dimensional growth originating from the allowed electrical contact between the electrolyte and the edges of the cathode at the bottom side of porous alumina membranes. It has been shown that the morphology of these microstructures strongly depends on electrodeposition parameters like the cation material and concentration and the reduction potential. At constant reduction potentials, linear Ni μHGPs with trapezoid-like geometry are obtained, whereas deviations from this simple morphology are observed for Co μHGPs. In this regime, the μHGPs average inclination angle decreases for more negative reduction potential values, leading as a result to more laterally extended microstructures. Besides, more complex morphologies have been obtained by varying the reduction potential using a simple power function of time. Using this strategy allows us to accelerate or decelerate the reduction potential in order to change the μHGPs morphology, so to obtain convex- or concave-like profiles. This methodology is a novel and reliable strategy to synthesize μHGPs into porous alumina membranes with controlled and well-defined morphologies. Furthermore, the synthesized low dimensional asymmetrically loaded nanowired substrates with μHGPs are interesting for their application in micro-antennas for localized electromagnetic radiation, magnetic stray field gradients in microfluidic systems, non-reciprocal microwave absorption, and super-capacitive devices for which a very large surface area and controlled morphology are key requirements.

The influence of the synthesis conditions on the magnetic behaviour of the densely packed arrays of Ni nanowires in porous anodic alumina membranes.

The densely packed arrays of Ni nanowires of 70 nm diameter and 6–12 μm length were obtained via electrodeposition into porous alumina membranes (PAAMs) of 55–75 μm thickness. The morphology, microstructure and magnetic properties between the room and liquid-helium temperature of Ni nanowires in PAAMs have been investigated using scanning electron microscopy, X-ray diffraction and vibrating sample magnetometry. The crystal structure of the Ni nanowires is fcc with (220) preferred orientation. The magnetic characteristics of the Ni nanowires in PAAMs were compared with the same characteristics of bulk Ni and with other researchers' data. The effect of the porous alumina membrane and the Ni nanowires synthesis conditions on the magnetic characteristics of Ni nanowire arrays has been studied. The coercivity reached more than 750 kOe and the squareness ratio up to 0.65 under the proposed optimal synthesis conditions for Ni nanowires. Magnetic parameters of the densely packed arrays of Ni nanowires allow using them in magnetic recording media, hard disk drives, storage systems and sensors. In addition, such structures are of considerable interest for basic research on nanomagnetism which is significantly different from the magnetic properties of bulk and thin films materials.

Mechanically tunable broadband terahertz modulator based on high-aligned Ni nanowire arrays* *Project supported by the National Natural Science Foundation of China (Grant No. 62075245) and Xinjiang Uygur Autonomous Region University Scientific Research Foundation (Grant No. XJEDU2018I021).

We present a mechanically tunable broadband terahertz (THz) modulator based on the high-aligned Ni nanowire (NW) arrays. The modulator is a sandwich structure consisting of two polydimethylsiloxane layers and a central layer of high-aligned Ni NW arrays. Our experimental measurements reveal the transmittance of THz wave can be effectively modulated by mechanical stretching. The NW density in arrays increases with the strain increasing, which induced an enhancement in the absorption of THz wave. When the strain increases from 0 to 6.5%, a linear relationship is observed for the variation of modulation depth (MD) of THz wave regarding the strain, and the modulated range is from 0 to 85% in a frequency range from 0.3 THz to 1.8 THz. Moreover, the detectable MD is about 15% regarding the 1 % strain change resolution. This flexible Ni NW-based modulator can be promised many applications, such as remote strain sensing, and wearable devices.

Ordered Mesoporous Ni-P Amorphous Alloy Nanowire Arrays: High-Efficiency Catalyst for Production of Polyol from Sugar.

Mesoporous metals have shown significant potential for use in catalysis; however, controllably synthesizing highly ordered mesoporous amorphous alloys is a serious challenge. In this paper, a synthesis strategy was developed for generating ordered amorphous alloy nanowire arrays from mesoporous Ni-P by combining mesoporous silica templating with electroless plating. Mesoporous silica is externally grafted with -CH3 and internally covered with -NH2 acting as an efficient template, ensuring the formation of Ni-P nanowires inside the pore channels and endowing the final product with an ordered mesoporous array structure. The resulting ordered mesoporous Ni-P amorphous alloy nanowire arrays were subjected to a liquid-phase sugar hydrogenation to polyols and exhibited a highly superior catalytic performance (97% glucose conversion and 94% maltose conversion) within 4 h at 4 MPa hydrogen pressure and 373 K relative to those reference catalysts, including conventionally prepared Ni-P amorphous alloy nanoparticles (87% glucose conversion and 86% maltose conversion), ordered mesoporous Ni nanowire arrays (90% glucose conversion and 87% maltose conversion), and the commercial Raney Ni catalyst (76% glucose conversion and 66% maltose conversion). According to a comparative study, the enhanced catalytic efficiencies can be ascribed to the integration of amorphous alloy properties and mesoporous material characteristics. The composition- and morphology-controllable synthesis presented here might supply a general synthetic methodology for rationally designing ordered mesoporous amorphous alloys for a broader range of applications.

Co–Ni nanowires supported on porous alumina as an electrocatalyst for the hydrogen evolution reaction

Water electrolysis is a promising way to produce hydrogen fuel, but many electrocatalytic systems require electrodes made of noble metals such as platinum. There is a demand for high-efficiency, low-cost materials to replace these noble metals. Herein, porous anodic alumina (AAO) templates are prepared by direct current (DC) constant voltage anodization and the step-down method. Cobalt, nickel and Co–Ni alloy nanowires are then prepared by alternating current (AC) electrodeposition. This nanoarray system can be employed in fuel cells to minimize the use of precious metals and reduce the cost of the cathodes. The pores of the AAO template are uniform with a size range from 35 to 75 nm. Using cyclic voltammetry (CV) and linear sweep voltammetry (LSV), the Co–Ni nanowire array prepared on AAO by this method is shown to have a low overpotential for hydrogen evolution and excellent stability.

High extinction ratio terahertz broadband polarizer based on the aligned Ni nanowire arrays.

We present a broadband terahertz (THz) polarizer based on the stacks of aligned Ni nanowire (NW) arrays. We demonstrated that the polarizer has an extinction ratio of 58.8 dB and an average extinction ratio of 46.6 dB throughout a frequency range of 0.3-2.3 THz. Compared to carbon-nanotube and metallic wire-grid polarizers, our Ni-NW polarizers with rapid, reliable, low-cost fabrication processes are ideal candidates for emerging THz technologies.

Magnetostatic dipolar anisotropy energy and anisotropy constants in arrays of ferromagnetic nanowires as a function of their radius and interwall distance

Magnetostatic dipolar anisotropy energy and the total dipolar anisotropy constant, , in periodic arrays of ferromagnetic nanowires have been calculated as a function of the nanowire radius, the interwall distance of the nanowires in the arrays and the geometry of the array (square or hexagonal), by using a realistic atomistic model and the Ewald method. The simulated nanowires have a radius size up to 175 Å that corresponds to 31 500 atoms, and the simulated nanowire arrays have interwall distances between 35 and 3000 Å. The dependence of total magnetostatic dipolar anisotropy constant on the nanowire radius, their interwall distance and the type of array symmetry has been analyzed. The total dipolar anisotropy constant, which is the sum of the intrananowire dipolar anisotropy constant, , due to the dipolar interactions inside an isolated nanowire and the main responsible of the shape anisotropy, and of the internanowire dipolar anisotropy constant, , due to the magnetostatic dipolar interactions among nanowires in the array, have been calculated and compared with the magnetocrystalline anisotropy constant for three nanowire compositions and their crystalline structures. The simulations of the nanowire arrays with large interwall distances have been used to calculate the intrananowire anisotropy constant, , and to analyze the competition between the intrananowire, internanowire and magnetocrystalline anisotropies. According to some magnetic theories, the ratio equals to the areal filling fraction of a nanowire array. Present calculations indicate that the equation for the areal filling fraction matches perfectly for any interwall distance and radius of Ni and Co nanowire arrays. This first equation is used to write a general equation that relates the radius and interwall distance of nanowire arrays with the intrananowire, internanowire and magnetocrystalline anisotropies. This general equation allows to design the geometry of nanowire arrays with the desired orientation of the easy magnetization axis.

Integrative Ni@Pd‐Ni Alloy Nanowire Array Electrocatalysts Boost Hydrazine Oxidation Kinetics

AbstractOwing to the oxophilic property of Ni catalysts and their sluggish kinetics toward the hydrazine oxidation reaction (HzOR), an ultra‐low amount of Pd is incorporated with Ni to form integrative Ni@Pd−Ni alloy nanowire array electrocatalysts by using templated electrodeposition and subsequent galvanic replacement. The morphology, crystalline structure, and composition of the as‐prepared catalysts are characterized by using FESEM, TEM, XRD, XPS, and ICP. The electrochemical evaluation shows that the onset potential of the Ni@Pd−Ni alloy nanowire arrays for HzOR is −0.99 V vs. Ag/AgCl, which is significantly lowered by 800 mV than that for the Ni nanowire arrays. Two possible factors contribute to the robust HzOR kinetics: 1) the metallization of Ni by the PdHx; 2) the heterogeneous catalytic pathway on the Pd−Ni alloy. Furthermore, the innovative structure also endows Ni@Pd−Ni alloy nanowire arrays with considerable durability, indicating it as a promising anode electrocatalyst for HzOR‐assisted hydrogen production and simultaneous hydrazine‐containing sewage treatment.

Template-assisted fabrication of Ni nanowire arrays for high efficient oxygen evolution reaction

Architecture construction of electrode is one key factor for hydrogen generation from electrochemical water splitting. To enhance the efficiency of oxygen evolution reaction (OER) at high current density, the architecture construction must be designed skillfully to prevent the surface blanketed by gas bubbles. In this work, we developed a three-level hierarchical surface with cluster-like nickel (Ni) nanowire array. The contact angle measurement indicates the surface having excellent hydrophilicity. The OER performance characterization reveals that after the surface is loaded with NiFe-based catalyst the Ni nanowire array electrode can deliver 500 mA cm−2 at an overpotential of 297 mV in 1 M KOH solution and can survive for over 24 h under 500 mA cm−2 operation. All the results demonstrate that the cluster-like nanowire array is beneficial for the spatial pathway separation for electrolyte supply and gas bubbles departure and the enhancement of OER efficiency.

NiFe/(Ni,Fe)3S2 Core/Shell Nanowire Arrays as Outstanding Catalysts for Electrolytic Water Splitting at High Current Densities

AbstractNiFe/(Ni,Fe)3S2 core/shell nanowire arrays, fabricated with an anodic aluminum oxide membrane templated electrodeposition followed by sulfur ion exchange, are developed as an outstanding catalyst for electrolytic water splitting. Ni nanowire arrays achieve low overpotentials of 112 and 347 mV for the hydrogen evolution reaction at current densities of 10 and 400 mA cm−2, respectively, whereas ultralow overpotentials of 224 and 305 mV for the oxygen evolution reaction at current densities of 10 and 400 mA cm−2, respectively, are achieved by NiFe/(Ni,Fe)3S2 core/shell nanowire arrays. The pairing of the Ni nanowire array electrode as the cathode and the NiFe/(Ni,Fe)3S2 core/shell nanowire array electrode as the anode, delivers current densities of 10 and 400 mA cm−2 at ultralow cell voltages of 1.56 and 1.9 V, respectively, for the overall water splitting. The stability of the electrodes is also excellent, exhibiting only minor chronoamperometric decay after 24 h continuous operation at 400 mA cm−2. The nanowire array‐based electrodes, offering extended reaction surface areas and 1D guided charge transport and mass transfer, prove to be a promising new catalyst architecture design for electrocatalytic processes.

Stepwise magnetization reversal of geometrically tuned in diameter Ni and FeCo bi-segmented nanowire arrays

Magnetization reversal processes of hexagonal dense arrays of bi-segmented Ni and Fe50Co50 nanowires consisting of two well defined diameters (45 and 80 nm) have been studied. The nanowires were grown inside of tailored pores of anodic alumina templates by combined anodization, atomic layer deposition (ALD) and electrodeposition techniques. The experiments have allowed to identify their two-step magnetization reversal process ascribed to the respective segments of different diameter. This is concluded from the differential susceptibility observed in the hysteresis loops, contrary to those for nanowires with homogeneous diameter. These results are also confirmed by the first-order reversal curve (FORC) distribution diagrams, where an elongation parallel to the interaction axis around two coercive field values is obtained, which is correlated to the difference in diameter of the two segments. This well-defined two-step magnetization reversal process through the nanowire diameter design is thought to be very useful for the advanced control of the remagnetization in arrays of magnetic multidomain systems.