Ni Nanowire Arrays Research Articles

Orientation Growth and Magnetic Properties of Electrochemical Deposited Nickel Nanowire Arrays

Highly ordered ferromagnetic metal nanowire arrays with preferred growth direction show potential applications in electronic and spintronic devices. In this work, by employing a porous anodic aluminum oxide template-assisted electrodeposition method, we successfully prepared Ni nanowire arrays. Importantly, the growth direction of Ni nanowire arrays can be controlled by varying the current densities. The crystalline and growth orientation of Ni nanowire arrays show effects on magnetic properties. Single-crystallinity Ni nanowires with [110] orientation show the best magnetic properties, including coercivity and squareness, along the parallel direction of the nanowire axis. The current preparation strategy can be used to obtain other nanowire arrays (such as metal, alloy, and semiconductor) with controlled growth direction in confined space, and is therefore of broad interest for different applications.

Magnetization reversal switching in nanocylinders using dynamic techniques

The high aspect ratio Ni nanocylinders (nanowires and nanotubes) were fabricated by means of potentiostatic electrochemical deposition in porous anodic alumina templates with pore diameter of 200 nm and a thickness of 60 µm. The growth of nanocylinders was found to depend upon deposition parameters. The structural, morphological and magnetic analysis revealed the face-centred cubic texture, uniformity and magnetic properties of nanowires and nanotubes respectively. The dynamic properties of one-dimensional uniform arrays of Ni nanowires (NWs) and nanotubes (NTs) were studied by ferromagnetic resonance technique at various frequencies ranging from 6 to 25 GHz. In particular, we identify the onset of magnetization reversal from the angular variation studies of resonance fields [Hr(θH)] and FMR linewidths [ΔHr(θH)]. Parameters such as gyromagnetic ratio (γ), damping constant (α) and effective field (Heff) were derived from theoretical fits to Hr and ΔHr data. We found that Hr and ΔHr both depend sensitively on the angle between the magnetization direction and wire-axis. For a NT geometry, the fitting of ΔHr(θH) data divulges that the magnetization reversal mechanism dominant by coherent rotation and thereafter beyond transition angle (∼80°) curling mode contributes. In case of nanowires, the curling reversal mode is the dominant magnetization reversal process.

Vertically Aligned Ni Nanowires as a Platform for Kinetically Limited Water-Splitting Electrocatalysis

Electrochemical templating through porous membranes is applied to form arrays of micrometer long Ni nanowires (NWs). Detailed structural and electrochemical characterization, including electrochemical impedance spectroscopy (EIS), was conducted to assess the electrocatalytic properties of these Ni NW arrays for the O2 evolution reaction (OER) in 1 M KOH. Detailed structural analysis showed that Ni NWs have a diameter of ca. 350 nm and a mean 80 nm average distance between the NW center. For the longest NWs (20 μm long), the ratio between the pore opening and pore length is 0.4%. From detailed HR-TEM and EELS analysis providing information on the chemical state of atoms from quantitative analysis of the signals, Ni NWs are composed of a Ni metallic core surrounded by a Ni(OH)2 layer that thickens from 10 to 20 nm after extensive electrochemical tests. Three different methods, namely, SEM geometry measurements, the α-Ni(OH)2 charge method, and the capacitance method, were used to assess how the current varies with the NW length. The three different methods are all in agreement, and the current increases with length (or mass) precisely and only because of the surface area effect. The most surprising result is that the OER process occurs with exactly the same intrinsic catalytic activity at the bottom of these deep pores, and gas is evolved without any significant effects of electrolyte resistance, mass transport of dissolved oxygen, or bubble occlusion of the pores. Accordingly, vertically aligned 1D NWs can be used as an effective platform that mitigates the negative effects of gas evolution. Increasing the intrinsic activity by incorporating more active materials will further improve this type of electrode.

The effect of magnetic nickel nanowires structural parameterson the electrodeposition efficiency

In this work, magnetic Ni nanowire arrays were ac-pulse electrodeposited into the anodic aluminum oxide (AAO) template fabricated by the common two-step anodization technique. The barrier layers at the bottom of the pores were exponentially thinned in a non-equilibrium anodization process to 8, 12, 16 and 20 V. These were fabricated using the constant of 15 mA deposition current, 48 mS off-time between pulses, 10, 20 substrate temperatures, and 30°C electrolyte temperature. The effects of thinning voltage and substrate temperature on the electrodeposition efficiency and the magnetic quality of the Ni nanowires were investigated by a Vibrating sample magnetometer (VSM) and a scanning electron microscope (SEM). In this paper, we realized that the bed temperature of 10°C, by increasing the thickness of the barrier layer, reduced deposition efficiency and the temperature was 20 degrees backfired.

Oxygen-Incorporated NiMoP2 Nanowire Arrays for Enhanced Hydrogen Evolution Activity in Alkaline Solution

Catalytic water splitting for commercial hydrogen production demands efficient and robust earth-abundant catalysts. However, sluggish kinetics of water dissociation in alkaline electrolyte impedes the formation of reactive intermediates by discharge of water. Here, oxygen-incorporated NiMoP2 nanowire arrays are engineered on Ni foam substrate (denoted as O-NiMoP2/Ni) by controllable partial phosphorization of metal oxide precursors to boost HER activity under alkaline environment. The incorporation of oxygen can significantly modify the electronic structure of NiMoP2 and optimize both HER Gibbs free-energy change (ΔGH*) and water adsorption energy change (ΔGH2O*). Results demonstrate that the O-NiMoP2/Ni nanowire arrays require quite low HER overpotentials of 31 and 134 mV to drive the geometrical catalytic current densities of 10 and 100 mA cm–2, respectively. The activity and stability in 1 M KOH are also superior to those of the state-of-the-art transition-metal phosphides (TMPs).

Two-Step Magnetization Reversal FORC Fingerprint of Coupled Bi-Segmented Ni/Co Magnetic Nanowire Arrays.

First Order Reversal Curve (FORC) analysis has been established as an appropriate method to investigate the magnetic interactions among complex ferromagnetic nanostructures. In this work, the magnetization reversal mechanism of bi-segmented nanowires composed by long Co and Ni segments contacted at one side was investigated, as a model system to identify and understand the FORC fingerprint of a two-step magnetization reversal process. The resulting hysteresis loop of the bi-segmented nanowire array exhibits a completely different magnetic behavior than the one expected for the magnetization reversal process corresponding to each respective Co and Ni nanowire arrays, individually. Based on the FORC analysis, two possible magnetization reversal processes can be distinguished as a consequence of the ferromagnetic coupling at the interface between the Ni and Co segments. Depending on the relative difference between the magnetization switching fields of each segment, the softer magnetic phase induces the switching of the harder one through the injection and propagation of a magnetic domain wall when both switching fields are comparable. On the other hand, if the switching fields values differ enough, the antiparallel magnetic configuration of nanowires is also possible but energetically unfavorable, thus resulting in an unstable magnetic configuration. Making use of the different temperature dependence of the magnetic properties for each nanowire segment with different composition, one of the two types of magnetization reversal is favored, as demonstrated by FORC analyses.

Temperature dependence of the effective anisotropy in Ni nanowire arrays

Magnetic hysteresis in Ni nanowire arrays grown by electrodeposition inside the pores of anodic alumina templates is studied as a function of temperature in the range between 5 K and 300 K. Nanowires with different diameters, aspect ratios, inter-wire distance in the array and surface condition (smooth and rough) are synthesized. These microstructure parameters are linked to the different free magnetic energy contributions determining coercivity and the controlling magnetization reversal mechanisms. Coercivity increases with temperature in arrays of nanowires with rough surfaces and small diameters ─33 nm and 65 nm─ when measured without removing the alumina template and/or the Al substrate. For thicker wires ─200 nm in diameter and relatively smooth surfaces─ measured without the Al substrate, coercivity decreases as temperature rises. These temperature dependences of magnetic hysteresis are described in terms of an effective magnetic anisotropy Ka, resulting from the interplay of magnetocrystalline, magnetoelastic and shape anisotropies, together with the magnetostatic interaction energy density between nanowires in the array. The experimentally determined coercive fields are compared with results of micromagnetic calculations, performed considering the magnetization reversal mode acting in each studied array and microstructure parameters. A method is proposed to roughly estimate the value of Ka experimentally, from the hysteresis loops measured at different temperatures. These measured values are in agreement with theoretical calculations. The observed temperature dependence of coercivity does not arise from an intrinsic property of pure Ni but from the nanowires surface roughness and the way the array is measured, with or without the alumina template and/or the aluminum support.

Carbon- and Binder-Free Core-Shell Nanowire Arrays for Efficient Ethanol Electro-Oxidation in Alkaline Medium.

To achieve high electrochemical surface area (ECSA) and avoid carbon support and binder in the anode catalyst of direct ethanol fuel cell, herein, we design freestanding core-shell nickel@palladium-nickel nanowire arrays (Ni@Pd-Ni NAs) without carbon support and binder for high-efficiency ethanol electro-oxidation. Bare Ni nanowire arrays (Ni NAs) are first prepared using the facile template-assistant electrodeposition method. Subsequently, the Ni@Pd-Ni NAs are formed using one-step solution-based alloying reaction. The optimized Ni@Pd-Ni NA electrode with a high ECSA of 64.4 m2 g-1Pd exhibits excellent electrochemical performance (peak current density: 622 A g-1Pd) and cycling stability for ethanol electro-oxidation. The facilely obtained yet high-efficiency core-shell Ni@Pd-Ni NA electrode is a promising electrocatalyst, which can be utilized for oxygen reduction reaction, urea, hydrazine hydrate, and hydrogen peroxide electro-oxidation, not limited to the ethanol electro-oxidation.

Study on the Stability of CoxM3-xO4 (M = Ni, Mn and Ce) Nanowire Array Electrodes for Electrochemical Oxygen Evolution at Large Current Densities

Non-precious cobalt-based oxide nanoarrays with a doping of other metal ions have been reported as promising electrocatalysts for the oxygen evolution reaction (OER) of electrochemical water splitting. However, the influence of doped metal ions on their catalytic characteristic and inactivation mechanism for the OER at large current densities (> 500 mA cm−2) are rarely studied. Here, carbon fiber paper (CFP) possesses three-dimensional (3D) macroporous structure, excellent electrical performance and high stability, which is employed as the substrate material. Homogeneous CoxNi3-xO4, CoxMn3-xO4 and CoxCe3-xO4 nanowire arrays grown on CFP (CoNiO-NWs/CFP, CoMnO-NWs/CFP and CoCeO-NWs/CFP, respectively) are successfully fabricated by using the facile methods of hydrothermal synthesis and thermal decomposition. The CoNiO-NWs/CFP electrode at a current density of 1000 mA cm−2 achieve high OER stability of approximately 130 h, which is higher than that of clean Co3O4 nanowire array, CoMnO-NWs/CFP and CoCeO-NWs/CFP electrodes. The incorporation of the Ni in the spinel Co3O4 nanowires improves its electrocatalytic activity and long-term stability at large current densities. In contrast, the doping of the Mn and Ce to spinel Co3O4 nanowires has the opposite effect. This research shows that the inactivation mechanism of nanoarray electrodes for the OER of large current densities differs from traditional metal-oxide electrodes.

Tunable terahertz transmission properties of aligned Ni-nanowire arrays.

Aligned Ni nanowire (NW) arrays were investigated for terahertz (THz) wave modulation. By adjusting the NW density and order of the NW arrays, the resonant frequency and intensity of the THz waves can be effectively tuned. The tuning range of the resonant frequency is about 0.29 THz, and a transmittance of less than 40% in the frequency region from 0.5 to 2 THz is achieved by changing the NW density. Although the order of the NW arrays has no influence on the resonant frequency, the transmittance can be tuned about 21%. The ability to tune the intensity and resonant frequency effectively and the ease of fabrication of the Ni-NW arrays make them the potential candidates for THz tunable filters, intensity modulators, and spatial light modulators.

Facile fabrication of gold coated nickel nanoarrays and its excellent catalytic performance towards sodium borohydride electro-oxidation

Novel Au@Ni nanoarrays electrode is facilely obtained by firstly template-assisted electro-deposition of Ni nanowire arrays (NAs), followed by galvanostatic deposition of Au catalysts onto the Ni NAs without any conductive agents and binders. The Au@Ni NAs electrode shows a rough surface and fringe with the diameter of ∼90nm, which assures a high utilization of Au catalysts and provides a large specific surface area. The elemental distribution of Ni mainly exists in the inner layer of a single Au@Ni nanowire with the diameter ∼56nm, while the elemental distribution of Au catalysts merely appears in the outer layer to form the unique core-shell nanowire structure. The Au@Ni NAs electrode reveals excellent electrochemical property and desirable stability for catalyzing NaBH4 electro-oxidation in basic solutions. The Au@Ni NAs electrode in the 2.00M NaOH and 0.24M NaBH4 solution demonstrates an oxidation current density of 2.35Amg−1 at −0.5V (vs. Ag/AgCl), which is much higher than that of the noble metal catalysts previously reported, indicating that this material may be hopefully used as anodic catalysts for applying in fuel cells.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures.

Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 108 J cm-3 and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world's largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 × 1019 W cm-2, we demonstrate energy penetration depths of several micrometers, leading to UHED plasmas of that size. Relativistic three-dimensional particle-in-cell simulations, validated by these measurements, predict that irradiation of nanostructures at intensities of >1 × 1022 W cm-2 will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 × 1010 J cm-3, equivalent to a pressure of 0.35 Tbar.

Identifying weakly-interacting single domain states in Ni nanowire arrays by FORC

The control and understanding of magnetization reversal mechanisms and magnetostatic interactions in nanomagnet arrays is a critical point that has to be overcome in order to reach industrial applications. However, usual magnetic characterization techniques can only provide information on the overall array behaviour and are not able to discriminate relevant local properties. In this work, we show that the first-order reversal curve (FORC) method is a unique tool to identify weakly-interacting uniaxial single domain (SD) particles in systems with complex mixed magnetic states. We compare the FORC diagrams of two sets of Ni nanowire (NW) arrays electrodeposited in hexagonally ordered nanoporous alumina templates: A) with a uniform length distribution (interacting SD particles), and B) with a non-uniform length distribution. For non-uniform length distributions, regions of isolated NWs occur in the array, creating a complex mixture of strongly and weakly-interacting SD particles. These weakly-interacting NWs are here identified by a characteristic ridge along the coercive field axis of the FORC diagram. Micromagnetic simulations confirmed the presence of this weakly-interacting magnetic behaviour in the array with non-uniform length distributions. Combining FORC results with micromagnetic simulations, we show that the magnetization reversal of interacting wires occurs by the nucleation of transverse domain walls at the NWs' ends, while isolated wires nucleate vortex domain walls. This work thus highlights the importance of the FORC method for the accurate identification and understanding of local magnetic behaviours in nanomagnet arrays.

Vapor-Phase Polymerized Poly(3,4-Ethylenedioxythiophene) on a Nickel Nanowire Array Film: Aqueous Symmetrical Pseudocapacitors with Superior Performance.

Three-dimensional (3D) nanometal scaffolds have gained considerable attention recently because of their promising application in high-performance supercapacitors compared with plain metal foils. Here, a highly oriented nickel (Ni) nanowire array (NNA) film was prepared via a simple magnetic-field-driven aqueous solution deposition process and then used as the electrode scaffold for the vapor-phase polymerization of 3,4-ethylenedioxythiophene (EDOT). Benefiting from the unique 3D open porous structure of the NNA that provided a highly conductive and oriented backbone for facile electron transfer and fast ion diffusion, the as-obtained poly(3,4-ethylenedioxythiophene) (PEDOT) exhibited an ultra-long cycle life (95.7% retention of specific capacitance after 20 000 charge/discharge cycles at 5 A/g) and superior capacitive performance. Furthermore, two electrodes were fabricated into an aqueous symmetric supercapacitor, which delivered a high energy density (30.38 Wh/kg at 529.49 W/kg) and superior long-term cycle ability (13.8% loss of capacity after 20 000 cycles). Based on these results, the vapor-phase polymerization of EDOT on metal nanowire array current collectors has great potential for use in supercapacitors with enhanced performance.

Density Detection of Aligned Nanowire Arrays Using Terahertz Time-Domain Spectroscopy.

A rapid technique is necessary to quantitatively detect the density of nanowire (NW) and nanotube arrays in one-dimensional devices which have been identified as useful building blocks for nanoelectronics, optoelectronics, biomedical devices, etc. Terahertz (THz) time-domain spectroscopy was employed in this research to detect the density of aligned Ni NW arrays. The transmitted amplitude of THz peaks and optical thickness of NW arrays was found to be the effective parameters to analyze the density change of NW arrays. Owing to the low multiple scattering and high order of Ni NW arrays, a linear relationship was observed for the transmitted amplitude and optical thickness regarding NW density, respectively. Therefore, THz technique may be used as a promising tool to characterize the density of one-dimensional structures in the large-scale integrated nanodevice fabrication.

An Ultralong, Highly Oriented Nickel-Nanowire-Array Electrode Scaffold for High-Performance Compressible Pseudocapacitors.

Ultralong, highly oriented Ni nanowire arrays are used as the electrode scaffold to support metal-oxide- and conductive-polymer-based electrode materials with a high mass loading; the as-obtained asymmetric supercapacitor can be compressed by fourfold and exhibits superior energy and power densities with ultrahigh cycle stability.

Magnetic Anisotropy in Bicomponent Self-Assembled Ni and Ni-Pd Nanowires Studied by Magnetic Resonance Spectroscopy

Self-ordered arrays of Ni, Ni(50)Pd(50), and Ni(78)Pd(22) nanowires were synthesized by simultaneous electrochemical deposition of Ni and Pd components into porous templates of anodic aluminum oxide using alternating current. This paper is focused on the interplay of structure and chemical composition of Ni and Ni–Pd bicomponent nanowires arrays and the peculiarities of its magnetic anisotropy.

Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures

Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures were investigated in this study. The periodic and quasi-periodic structures were designed based on Fibonacci sequence and golden ratio. Ni nanowires arrays were electrodeposited in anodic aluminum oxide (AAO) templates with patterned Cu electrodes, and then the AAO templates were attached to the coplanar waveguide lines fabricated on quartz substrate for measurement. The S21 of both periodic and quasi-periodic structure-patterned Ni nanowire arrays showed an extra absorption peak besides the absorption peak due to the ferromagnetic resonance of Ni nanowires. The frequency of the absorption peak caused by the patterned structure could be higher than 40 GHz when the length and arrangement of the structural units were modified. In addition, the frequency of the absorption peak due to the quasi-periodic structure was calculated based on a simple analytical model, and the calculated value was consistent with the measured one. The experimental data showed that it could be a feasible approach to tune the performance of microwave devices by patterning ferromagnetic nanowires.

Magnetic anisotropy and one-dimensionality finite-size scaling law in polycrystalline Ni nanowire arrays

Ordered Ni nanowire arrays were successfully fabricated by electrochemical deposition method based on the anodized aluminum oxide (AAO) templates. It was found that the diameter of nanowire can be well controlled by the pore size of AAO template. The nanowire arrays with 50nm in diameter were characterized by X-ray diffraction, electron microscopy, and physical properties measurement system. The results indicate that the polycrystalline Ni nanowire arrays exhibit obvious magnetic anisotropy, and the easy magnetization direction is oriented along the nanowire axial direction. By measuring the temperature dependence of magnetization, the Curie temperatures of nanowires with different sizes were obtained. The Curie temperature of one-dimensionality (1D) nanowire arrays is found to decrease with decreasing diameter and follow a finite-size scaling theory with λ=0.926 and ξ0=17.35Å. The fitting exponent of 1D nanowire arrays is close to the nanoparticles (zero-dimensionality, 0D) result and two-dimensionality (2D) nano-films result.

Co-Ni alloy nanowires prepared by anodic aluminum oxide template via electrochemical deposition.

The alloy nanowires are more prospective magnetic and shape memory materials. Fabrication of binary or more alloy nanowires using electrochemical deposition process is generally challenging due to the different synthesis conditions of individual elements. In the present work, binary NiCo alloy nanowire arrays have been fabricated by electrochemical deposition using anodic aluminum oxide template medium technique. The optimum conditions (temperature, voltage and time) for synthesis of NiCo alloy nanowire array were achieved based on the ideal experimental conditions of single Ni and Co nanowire arrays. The synthesized NiCo alloy nanowire arrays were characterized by X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectrometer. The amorphous NiCo alloy nanowires were crystallized by annealing of 800 degrees C for 1 hour in argon atmosphere. The controlled composition of electrolyte provided to achieve a uniformly distributed chemical composition of Ni and Co (49.26:50.74) in nanowires.