Size-Dependent Orientation Growth of Large-Area Ordered Ni Nanowire Arrays

Additive printing of pure nanocrystalline nickel thin films using room environment electroplating

Given its high temperature stability, oxidation-, corrosion- and wear-resistance, and ferromagnetic properties, Nickel (Ni) is one of the most technologically important metals. This article reports that pure and nanocrystalline (Ni) films with excellent mechanical and magnetic properties can be additively printed at room environment without any high-temperature post-processing. The printing process is based on a nozzle-based electrochemical deposition from the classical Watt's bath. The printed Ni film showed a preferred (220) and (111) texture based on x-ray diffraction spectra. The printed Ni film had close to bulk electrical conductivity; its indentation elastic modulus and hardness was measured to be 203 ± 6.7 GPa and 6.27 ± 0.34 GPa, respectively. Magnetoresistance, magnetic hysteresis loop, and magnetic domain imaging showed promising results of the printed Ni for functional applications.

Multi-Segmented Nanowires: A High Tech Bright Future

In the last couple of decades, there has been a lot of progress in the synthesis methods of nano-structural materials, but still the field has a large number of puzzles to solve. Metal nanowires (NWs) and their alloys represent a sub category of the 1-D nano-materials and there is a large effort to study the microstructural, physical and chemical properties to use them for further industrial applications. Due to technical limitations of single component NWs, the hetero-structured materials gained attention recently. Among them, multi-segmented NWs are more diverse in applications, consisting of two or more segments that can perform multiple function at a time, which confer their unique properties. Recent advancement in characterization techniques has opened up new opportunities for understanding the physical properties of multi-segmented structures of 1-D nanomaterials. Since the multi-segmented NWs needs a reliable response from an external filed, numerous studies have been done on the synthesis of multi-segmented NWs to precisely control the physical properties of multi-segmented NWs. This paper highlights the electrochemical synthesis and physical properties of multi-segmented NWs, with a focus on the mechanical and magnetic properties by explaining the shape, microstructure, and composition of NWs.

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.

Synthesis of ultrathin Ni nanosheets for semihydrogenation of phenylacetylene to styrene under mild conditions

The synthesis of ultrathin metal nanosheets (NSs) attracts broad scientific and technological interest, and it still remains a challenge for non-noble metals like nickel due to their intrinsic cubic symmetry and high surface energy. Herein, we report a NiO intermediated solvothermal method towards the synthesis of ultrathin Ni NSs (thickness < 3 nm) using N,N-dimethylformamide as the solvent and n-butylamine as the shape controlling reagent. The growth of the ultrathin Ni NSs follows an intermediate mechanism which was proved by the results obtained by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectra (XAS) and X-ray photoelectron spectroscopy (XPS). Under solvothermal conditions, the nickel acetylacetonate precursor was first reduced to a NiO NS intermediate, then reduction occurred and NiO NSs were reduced to Ni NSs. The synthesized ultrathin Ni NSs predominately in a metallic state showed high selectivity (88.0-92.0%) towards styrene (ST) in the phenylacetylene (PA) semihydrogenation reaction under mild conditions (323 K, 1 atm of hydrogen) in a broad PA conversion range (2.0-98.0%). The low coverage of oxygen atoms on the Ni NS surface is proposed to account for the high ST selectivity, as indicated by density functional theory (DFT) calculations.

Noble-metal Ag nanoparticle chains: annealing Ag/Bi superlattice nanowires in vacuum

One-dimensional noble-metal Ag nanoparticle chains have been prepared by electrodepositing Ag/Bi superlattice nanowires in a porous anodic alumina oxide (AAO) template and following an annealing process in vacuum. It is found that Bi, as a sacrificial metal, can be removed completely after annealing at 450 °C with a vacuum degree of 10(-5) Torr. The regulation of particle size, shape and interparticle spacing of Ag NP chains has been realized by adjusting the segment length of the Ag/Bi superlattice nanowires and the annealing condition. With an extension of the annealing time, it is observed that Ag particles display the transform trend from ellipsoid to sphere. Our findings could inspire further investigation on the design and fabrication of metal nanoparticle chains.

Stereo-epitaxial growth of single-crystal Ni nanowires and nanoplates from aligned seed crystals

Epitaxially grown anisotropic Ni nanostructures are promising building blocks for the development of miniaturized and stereo-integrated data storage kits because they can store multiple magnetic domain walls (DWs). Here, we report stereo-epitaxially grown single-crystalline Ni nanowires (NWs) and nanoplates, and their magnetic properties. Vertical and inclined Ni NWs were grown at the center and edge regions of c-cut sapphire substrates, respectively. Vertical Ni nanoplates were grown on r-cut sapphire substrates. The morphology and growth direction of Ni nanostructures can be steered by seed crystals. Cubic Ni seeds grow into vertical Ni NWs, tetrahedral Ni seeds grow into inclined Ni NWs, and triangular Ni seeds grow into vertical Ni nanoplates. The shapes of the Ni seeds are determined by the interfacial energy between the bottom plane of the seeds and the substrates. The as-synthesized Ni NWs and nanoplates have blocking temperature values greater than 300 K at 500 Oe, verifying that these Ni nanostructures can form large magnetic DWs with high magnetic anisotropy properties. We anticipate that epitaxially grown Ni NWs and nanoplates will be used in various types of 3-dimensional magnetic devices.

Large magnetic anisotropy enhancement in size controlled Ni nanowires electrodeposited into nanoporous alumina templates

A large enhancement of the magnetic anisotropy of Ni nanowires (NWs) embedded in anodic aluminium oxide porous membranes is obtained as a result of an induced magnetoelastic (ME) anisotropy contribution. This unusual large anisotropy enhancement depends on the diameter of the NWs and exceeds the magnetostatic (MS) contribution. As a consequence, it leads to effective magnetic anisotropy energies as large as 1.4 × 10(6) erg cm(-3), which are of the same order of magnitude and comparable to the MS energies of harder magnetic materials like Co NWs. Specifically, from ferromagnetic resonance experiments, the magnetic anisotropy of the NWs has been observed to increase as its diameter is decreased, leading to values that are about four times larger than the corresponding value when only the MS anisotropy is present. Our results are consistent with the recently proposed growth mechanism of Ni NWs that proceeds via a poly-crystalline stage at the bottom followed by a single-crystalline stage with texture [110] parallel to the axis of the NWs. A strong correlation between reducing the diameter of the NWs with the decrease of the length of the poly-crystalline segment and the enhancement of the effective magnetic anisotropy has been shown. Magnetization curves obtained from alternating gradient magnetometry experiments show that the average ME anisotropy results from the competition between the magnetic anisotropies of both crystalline segments of the NWs. Understanding the influence of size and confinement effects on the magnetic properties of nanocomposites is of prime interest for the development of novel and agile devices.

Cyanide-free preparation of gold nanowires: controlled crystallinity, crystallographic orientation and enhanced field emission

Gold nanowires with controlled crystallinity and preferred crystallographic orientations have been fabricated in ion track-etched templates using a cyanide-free bath.

Optical properties of Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays

: In this study, Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays are fabricated using standard techniques such as electrochemical deposition of metals into porous anodic alumina oxide templates having pore diameters of about 50 nm. We perform optical measurements on these nanowire array structures. Optical reflectance (OR) of the as-prepared samples is recorded using an imaging spectrometer in the wavelength range from 400 to 2,000 nm (i.e., from visible to near-infrared bandwidth). The measurements are carried out at temperatures set to be 4.2, 70, 150, and 200 K and at room temperature. We find that the intensity of the OR spectrum for nanowire arrays depends strongly on the temperature. The strongest OR can be observed at about T = 200 K for all samples in visible regime. The OR spectra for these samples show different features in the visible and near-infrared bandwidths. We discuss the physical mechanisms responsible for these interesting experimental findings. This study is relevant to the application of metal nanowire arrays as optical and optoelectronic devices.

Controlled crystallinity and crystallographic orientation of Cu nanowires fabricated in ion-track templates

The hallmark of materials science is the ability to tailor the structures of a given material to provide a desired response. In this work, the structures involving crystallinity and crystallographic orientation of Cu nanowires electrochemically fabricated in ion-track templates have been investigated as a function of fabrication condition. Both single crystalline and polycrystalline nanowires were obtained by adjusting applied voltages and temperatures of electrochemical deposition. The anti-Hall-Petch effect was experimentally evidenced in the polycrystalline nanowires. The dominant crystallographic orientations of wires along [111], [100], or [110] directions were obtained by selecting electrochemical deposition conditions, i.e., H(2)SO(4) concentration in electrolyte, applied voltage, and electrodeposition temperature.

Effect of crystallographic texture on magnetic characteristics of cobalt nanowires

Cobalt nanowires with controlled diameters have been synthesized using electrochemical deposition in etched ion-track polycarbonate membranes. Structural characterization of these nanowires with diameter 70, 90, 120 nm and length 30 μm was performed by scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction techniques. The as-prepared wires show uniform diameter along the whole length and X-ray diffraction analysis reveals that [002] texture of these wires become more pronounced as diameter is reduced. Magnetic characterization of the nanowires shows a clear difference of squareness and coercivity between parallel and perpendicular orientations of the wires with respect to the applied field direction. In case of parallel applied field, the coercivity has been found to be decreasing with increasing diameter of the wires while in perpendicular case; the coercivity observes lower values for larger diameter. The results are explained by taking into account the magnetocrystalline and shape anisotropies with respect to the applied field and domain transformation mechanism when single domain limit is surpassed.

The control of the growth orientations of electrodeposited single-crystal nanowire arrays: a case study for hexagonal CdS

The controllable growth of highly aligned and ordered semiconductor nanowire arrays is crucial for their potential applications in nanodevices. In the present study, both the growth orientation and the microstructure of hexagonal CdS nanowire arrays electrodeposited in a porous alumina template with 40 nm diameter pores have been controlled by simply tuning the deposition current density. An extremely low current density of 0.05 mA cm(-2) is favorable for the growth of single-crystal CdS nanowires along the normal direction of the intrinsic low-surface-energy (103) face. This can be understood well by a modified critical dimension model given in the present work.

Structural study on Ni nanowires in an anodic alumina membrane by using in situ heating extended x-ray absorption fine structure and x-ray diffraction techniques

Polycrystalline Ni nanowires have been prepared by electrochemical deposition in an anodic alumina membrane template with a nanopore size of about 60 nm. In situ heating extended x-ray absorption fine structure and x-ray diffraction techniques are used to probe the atomic structures. The nanowires are identified as being mixtures of nanocrystallites and amorphous phase. The nanocrystallites have the same thermal expansion coefficient, of 1.7 × 10(-5) K(-1), as Ni bulk; however, the amorphous phase has a much larger thermal expansion coefficient of 3.5 × 10(-5) K(-1). Details of the Ni nanowire structures are discussed in this paper.

Preferred growth orientation of metallic fcc nanowires under direct and alternating electrodeposition conditions

Gold and copper nanowires were generated through electrochemical deposition into nanoporous polymeric templates. Depending on the growth conditions, such wires exhibited a distinct textured structure as evidenced by x-ray diffraction. The preferred growth orientation is explained by applying the broken-bond model in combination with surface-energy anisotropy and energy minimization. During the growth process, the aspect ratio of the cylindrical nanowire and thus the area of the mantle surface and its contribution to the total surface energy increase. Under direct current deposition conditions, [Formula: see text] textured metallic fcc nanowires represent the configuration of lowest surface energy at aspect ratios above 1. Under alternating current deposition conditions, {110} nanowire base surfaces vanish due to their high surface energy, leading to successive development of a [Formula: see text] texture as the configuration of lowest energy at aspect ratios above 5.

Effective Deposition Potential Induced Size-Dependent Orientation Growth of Bi−Sb Alloy Nanowire Arrays

The influence of effective deposition potential on the orientation and diameter of Bi(1-x)Sbx alloy nanowire arrays by pulsed electrodeposition technique was reported. X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy analysis show that the orientation of the Bi(1-x)Sbx nanowires can be turned from the [110] to the [202] direction by increasing the effective deposition potential, and the nanowires fully fill in the pores of the AAM in the lower potential region, while in the higher potential region the nanowires partly fill the pores of the AAM. The origin of those phenomena and the growth mechanism of the nanowire are discussed together with composition analysis.