Multisegmented Nanowires Research Articles

Unusual behavior of the magnetization reversal in soft/hard multisegmented nanowires

The magnetization reversal mechanisms in soft/hard multisegmented nanowires have been investigated using numerical simulations. In most of the studied systems the magnetization reversal process starts at the ends. However in short soft/hard/soft nanowires, the magnetization reversal process starts at the center of the wire, generating an unusual behavior of the coercivity as a function of the length.

Magnetic behaviour of multisegmented FeCoCu/Cu electrodeposited nanowires

Understanding the magnetic behaviour of multisegmented nanowires (NWs) is a major key for the application of such structures in future devices. In this work, magnetic/non-magnetic arrays of FeCoCu/Cu multilayered NWs electrodeposited in nanoporous alumina templates are studied. Contrarily to most reports on multilayered NWs, the magnetic layer thickness was kept constant (30 nm) and only the non-magnetic layer thickness was changed (0 to 80 nm). This allowed us to tune the interwire and intrawire interactions between the magnetic layers in the NW array creating a three-dimensional (3D) magnetic system without the need to change the template characteristics. Magnetic hysteresis loops, measured with the applied field parallel and perpendicular to the NWs’ long axis, showed the effect of the non-magnetic Cu layer on the overall magnetic properties of the NW arrays. In particular, introducing Cu layers along the magnetic NW axis creates domain wall nucleation sites that facilitate the magnetization reversal of the wires, as seen by the decrease in the parallel coercivity and the reduction of the perpendicular saturation field. By further increasing the Cu layer thickness, the interactions between the magnetic segments, both along the NW axis and of neighbouring NWs, decrease, thus rising again the parallel coercivity and the perpendicular saturation field. This work shows how one can easily tune the parallel and perpendicular magnetic properties of a 3D magnetic layer system by adjusting the non-magnetic layer thickness.

Ni-Co Alloy and Multisegmented Ni/Co Nanowire Arrays Modulated in Composition: Structural Characterization and Magnetic Properties

Design of novel multisegmented magnetic nanowires can pave the way for the next generation of data storage media and logical devices, magnonic crystals, or in magneto-plasmonics, among other energy conversion, recovery, and storage technological applications. In this work, we present a detailed study on the synthesis, morphology, structural, and magnetic properties of Ni, Co, and Ni-Co alloy and multisegmented Ni/Co nanowires modulated in composition, which were grown by template-assisted electrodeposition employing nanoporous anodic aluminum oxide as patterned templates. X-ray diffraction, and scanning and high-resolution transmission electron microscopies allowed for the structural, morphological, and compositional investigations of a few micrometers long and approximately 40 nm in diameter of pure Ni and Co single elements, together with multisegmented Ni/Co and alloyed Ni-Co nanowires. The vibrating sample magnetometry technique enabled us to extract the main characteristic magnetic parameters for these samples, thereby evaluating their different anisotropic magnetic behaviors and discuss them based on their morphological and structural features. These novel functional magnetic nanomaterials can serve as potential candidates for multibit magnetic systems in ultra-high-density magnetic data storage applications.

Co/Au multisegmented nanowires: a 3D array of magnetostatically coupled nanopillars

Arrays of multisegmented Co/Au nanowires with designed segment lengths and diameters have been prepared by electrodeposition into aluminum oxide templates. The high quality of the Co/Au interface and the crystallographic structure of Co segments have determined by high-resolution transmission electron microscopy. Magnetic hysteresis loop measurements show larger coercivity and squareness of multisegmented nanowires as compared to single segment Co nanowires. The complementary micromagnetic simulations are in good agreement with the experimental results, confirming that the magnetic behavior is defined mainly by magnetostatic coupling between different segments. The proposed structure constitutes an innovative route towards a 3D array of synchronized magnetic nano-oscillators with large potential in nanoelectronics.

Synthesis and magnetism of modulated FeCo-based nanowires

FeCo based nanowire arrays have been proposed for different applications as high-density magnetic storage or sprintronics. Depending on the application different magnetic properties are required and the electrochemical techniques are low-cost routes to tailor them, by tuning the nanowires composition and geometry. In this work two different types of nanowires are studied: multisegmented nanowires and nanowires with modulated diameter. The magnetic properties of multisegmented [FeCoCu(y)/Cu(x)]10 nanowire arrays have been studied considering different Cu layer thicknesses (x) and FeCoCu segment lengths (y). The obtained results show that the hard magnetic properties of these nanowire arrays present a higher coercivity and remanence comparing to the continuous nanowires, for thicker Cu layers and shorter FeCoCu segments. On the other hand, for the nanowires with modulated diameter it has been stated that the magnetization reversal process takes place by a vortex domain wall and with the tailored modulations along the nanowire it is possible to induce the domain wall pinning. This opens the possibility of controlling the domain wall motion along magnetic nanowires.

Magnetically Propelled Fish-Like Nanoswimmers.

The swimming locomotion of fish involves a complex interplay between a deformable body and induced flow in the surrounding fluid. While innovative robotic devices, inspired by physicomechanical designs evolved in fish, have been created for underwater propulsion of large swimmers, scaling such powerful locomotion into micro-/nanoscale propulsion remains challenging. Here, a magnetically propelled fish-like artificial nanoswimmer is demonstrated that emulates the body and caudal fin propulsion swimming mechanism displayed by fish. To mimic the deformable fish body for periodic shape changes, template-electrosynthesized multisegment nanowire swimmers are used to construct the artificial nanofishes (diameter 200 nm; length 4.8 μm). The resulting nanofish consists a gold segment as the head, two nickel segments as the body, and one gold segment as the caudal fin, with three flexible porous silver hinges linking each segment. Under an oscillating magnetic field, the propulsive nickel elements bend the body and caudal fin periodically to generate travelling-wave motions with speeds exceeding 30 μm s-1 . The propulsion dynamics is studied theoretically using the immersed boundary method. Such body-deformable nanofishes exhibit a high swimming efficiency and can serve as promising biomimetic nanorobotic devices for nanoscale biomedical applications.

Magnetotransport Measurements of Domain Wall Propagation in Individual Multisegmented Cylindrical Nanowires

Magnetotransport measurements were performed on multisegmented Co/Ni nanowires (NWs) fabricated by template-assisted electrodeposition. Individual NWs were isolated and electrodes patterned to study their magnetization reversal process. The magnetoresistance reversal curve of the multisegmented NW exhibits a step in the switching field. Micromagnetic simulations of the magnetization reversal process are in agreement with the experimental findings and attribute the step at the switching field to the pinning of a domain wall at the interface of the Co/Ni NW.

Geometry-Dependent Magnetic Properties of Ising-Type Multisegment Nanowires

An effective-field theory (EFT) with correlations has been used to investigate magnetic hysteresis properties and soft/hard magnetic behaviors of an Ising-type multisegment nanowire (IMN) with ferromagnetic/non-magnetic segment structure. The effects of the geometrical parameters on the magnetic hysteresis properties are studied in detail. Morphological dependence of the segmented nanowire is presented via segment thickness ( l), wire thickness ( d), and aspect ratio (AR) obtained from the exchange interactions. The coercive field ( HC) and squareness ( Mr/ MS) of the IMN are also derived from hysteresis loops as a function of geometrical parameters. We find that the geometry has a significant effect on the magnetic characteristics of the nanowire. Comparisons between the observed theoretical results and some experimental works of nanowire arrays with hysteresis behaviors are made, and a very good agreement is obtained.

Modeling the collective magnetic behavior of highly-packed arrays of multi-segmented nanowires

A powerful model to evaluate the collective magnetic response of large arrays of segmented nanowires comprising two magnetic segments of dissimilar coercivity separated by a non-magnetic spacer is introduced. The model captures the essential aspects of the underlying physics in these systems while being at the same time computationally tractable for relatively large arrays. The minimum lateral and vertical distances rendering densely packed weakly-interacting nanowires and segments are calculated for optimizing their performance in applications like magnetic sensors or recording media. The obtained results are appealing for the design of multifunctional miniaturized devices actuated by external magnetic fields, whose successful implementation relies on achieving a delicate balance between two opposing technological demands: the need for an ultra-high density of nanowires per unit area and the minimization of inter-wire and inter-segment dipolar interactions.

Solvent Vapor Growth of Axial Heterostructure Nanowires with Multiple Alternating Segments of Silicon and Germanium.

Herein, we report the formation of multisegment Si-Ge axial heterostructure nanowires in a wet chemical synthetic approach. These nanowires are grown by the liquid injection of the respective silicon and germanium precursors into the vapor phase of an organic solvent in which a tin-coated stainless steel substrate is placed. The Si-Ge transition is obtained by sequential injection with the more difficult Ge-Si transition enabled by inclusion of a quench sequence in the reaction. This approach allows for alternating between pure Si and pure Ge segments along the entire nanowire length with good control of the respective segment dimensions. The multisegment heterostructure nanowires presented are Ge-Si, Si-Ge-Si, Ge-Si-Ge, Si-Ge-Si-Ge, and Si-Ge-Si-Ge-Si-Ge. The interfacial abruptness of the Ge to Si interface is also determined through the use of aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy.

Magnetic reversal modes in multisegmented nanowire arrays with long aspect ratio

A detailed numerical analysis of the magnetization reversal processes in multisegmented nanowire arrays was developed. The nanowires have a long aspect ratio and are formed by magnetic and non-magnetic sections alternately arranged in such a way that the array resembles magnetic layers separated by non-magnetic layers. Attention has been focused on the influence of magnetostatic interaction in the magnetic pattern formation of these magnetic nanostructures. Results from a magnetic correlation function among layers show that three different reversal modes can be detected depending on the number and distance between the magnetic segments. As a consequence of the different reversal modes, a non-monotonic behavior of the annihilation field in function of the distance between the layers is evidenced. Thus, these results are important for the production of magnetic devices with multisegmented nanowire arrays.

Multisegmented FeCo/Cu nanowires: electrosynthesis, characterization, and magnetic control of biomolecule desorption.

In this paper, we report on the synthesis of FeCo/Cu multisegmented nanowires by means of pulse electrodeposition in nanoporous anodic aluminum oxide arrays supported on silicon chips. By adjustment of the electrodeposition conditions, such as the pulse scheme and the electrolyte, alternating segments of Cu and ferromagnetic FeCo alloy can be fabricated. The segments can be built with a wide range of lengths (15-150 nm) and exhibit a close-to-pure composition (Cu or FeCo alloy) as suggested by energy-dispersive X-ray mapping results. The morphology and the crystallographic structure of different nanowire configurations have been assessed thoroughly, concluding that Fe, Co, and Cu form solid solution. Magnetic characterization using vibrating sample magnetometry and magnetic force microscopy reveals that by introduction of nonmagnetic Cu segments within the nanowire architecture, the magnetic easy axis can be modified and the reduced remanence can be tuned to the desired values. The experimental results are in agreement with the provided simulations. Furthermore, the influence of nanowire magnetic architecture on the magnetically triggered protein desorption is evaluated for three types of nanowires: Cu, FeCo, and multisegmented FeCo15nm/Cu15nm. The application of an external magnetic field can be used to enhance the release of proteins on demand. For fully magnetic FeCo nanowires the applied oscillating field increased protein release by 83%, whereas this was found to be 45% for multisegmented FeCo15nm/Cu15nm nanowires. Our work suggests that a combination of arrays of nanowires with different magnetic configurations could be used to generate complex substance concentration gradients or control delivery of multiple drugs and macromolecules.

Synthesis of Nanoscale Heterostructures Comprised of Metal Nanowires, Carbon Nanotubes, and Metal Nanoparticles: Investigation of Their Structure and Electrochemical Properties

One‐dimensional nanoscale heterostructures comprised of multisegment gold‐nickel nanowires, carbon nanotube, and nickel nanoparticles were fabricated in a unique approach combining top‐down and bottom‐up assembly methods. Porous alumina template was utilized for sequential electrodeposition of gold and nickel nanowire segments. This was followed by chemical vapor deposition growth of carbon nanotubes on multisegment gold‐nickel nanowires, where nickel segment also acted as a carbon nanotube growth catalyst. The aligned arrays of these gold‐nickel‐carbon nanotube heterostructures were released from porous alumina template and then subjected to wet‐chemical process to be decorated with nickel/nickel oxide core/shell nanoparticles. X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were utilized for morphology, interface, defect, and structure characterization. The electrochemical performance of these heterostructures was studied using cyclic voltammetry method and the specific capacitance of various heterostructures was estimated and compared.

A soft/hard magnetic nanostructure based on multisegmented CoNi nanowires.

In this paper we have introduced a new soft/hard nanostructure based on multisegmented CoNi nanowire arrays having diameters of around 110 nm and made of five segments with nominal compositions of Co, Co66Ni33, Co50Ni50, Co33Ni66 and Ni, each of which has a length of 800 nm, so that the total length of the multisegmented nanowire is 4 μm. These arrays have been synthesized by means of potentiostatic electrodeposition into the pores of hard-anodic alumina templates. The morphology, chemical composition and microstructure of the multisegmented CoNi nanowires were determined by high-resolution scanning electron microscopy, energy dispersive X-ray microanalysis, and powder X-ray diffraction method, respectively. The room temperature magnetic behavior of the multisegmented nanowire arrays is also studied and compared with CoNi nanowire arrays with homogeneous composition (non-segmented nanowires), synthesized in the same templates and having the same dimensions as the segmented ones. These nanostructures could be used to control the movement of magnetic domain walls. In this way, these nanostructures can be an alternative to store information or even perform logic functions.

Fabrication and Characterization of Single-segmented CoNiP and Multi-segment CoNiP/Au Nanowires

This paper represents the fabrication of CoNiP single segment and CoNiP/Au multisegment nanowires. We have fabricated these nanowires by electrodeposition method into polycarbonate templates with a nominal pore diameter about 100 nm. The hystersis loops were measured with the applied magnetic field parallel and perpendicular to the wire axis using a vibrating sample magnetometry (VSM). The structure morphology was observed by Scanning Electron Miroscopy (SEM) and the element composition of CoNiP/Au multisegment nanowires were analyzed by EDS. The results show that these nanowires are very uniform with the diameter of 100 nm. The observed coercivity (HC) and squareness (Mr/Ms) of CoNiP single nanowires are larger than the CoNiP/Au multisegment nanowires.

Glucose biosensor based on multisegment nanowires exhibiting reversible magnetic control

We describe the amperometric detection of glucose using oriented nanowires with magnetic switching of the bioelectrochemical process. The fabrication process of the nanowires was prepared through controlled nucleation and growth during a stepwise electrochemical deposition, and it was characterized using scanning electron microscopy. Cyclic voltammetry and amperometry were used to study the magnetoswitchable property; this control was accomplished by changing the surface orientation of nanowires. Under the optimal condition, the amperometric response was also linear up to a glucose concentration of 0.1–16.0mmolL−1 with a sensitivity of 81μAmM−1. The detection limit was estimated for 4.8×10−8molL−1, defined from a signal/noise ratio of 3. It also exhibits good reproducibility and high selectivity with insignificant interference from ascorbic acid, acetoaminophen, and uric acid. The resulting biosensor was applied to detect the blood sugar in human serum samples without any pretreatment, and the results were comparatively in agreement with the clinical assay.

Template‐assisted Co–Ni alloys and multisegmented nanowires with tuned magnetic anisotropy (Phys. Status Solidi A 5∕2014)

Nanostructured magnetic materials synthesized through electrochemical methods by employing nanoporous anodic aluminum oxide membranes as patterned templates have recently attracted a huge attention. In their work reported on pp. 1041–1047, García et al. synthesized Co100-xNix (15 ≤ x ≤ 61) alloy nanowires of about 180 nm in diameter and 14 μm in length, as well as multisegmented Co54Ni46/Co85Ni15 nanowires with an approximate length of 300 nm per each segment, by means of electrochemical deposition into the pores of hard-anodic alumina membranes. The composition and crystalline structure of Co-Ni alloy segments and nanowires were properly adjusted by varying the electrodeposition potential. The magnetic properties of the alloyed nanowire arrays were correlated with their microstructural features. Co-richer nanowires show a hard magnetic phase due to the stronger influence of the high magnetocrystalline anisotropy of the majority hcp phase, whilst the Co-poorer ones exhibit a softer magnetic phase (fcc) and their magnetic behaviour is mainly determined by shape anisotropy. The comparison between the alloyed nanowires with different cobalt contents sheds light into the magnetization processes determining the overall magnetic behaviour of the multisegmented nanowire arrays.

Engineering Nonlinear Electrical Behavior with Asymmetric Multisegmented Polymer–Metal Nanowires

In this paper, we report on novel hybrid nanowires as prototypical building blocks for nanocomponents. Multisegmented hybrid nanowires (HNWs) made of metallic and conjugated polymer (CP) segments were elaborated and the impact of metal/polymer interfaces on the rectifying behavior was determined. Using HNWs integrated into micromachined devices, the relationship between electronic properties and original structure is revealed. By combining transmission electron microscopy (TEM) directly on the symmetric and asymmetric HNWs structures studied by current–voltage (I–V) spectroscopy, we show that rectifying I–V characteristics are observed only for asymmetric HNWs. Moreover, it is shown that the rectification ratio can be improved up to 3 orders of magnitude by a proper selection of the HNW composition. While the rectifying behavior is observed in HNWs after oxidative or acid doping, the charge transport mechanism in as-synthesized HNWs is bulk-limited and independent from their structure. Both symmetric and asymmetric HNWs exhibit Ohmic and nonlinear I–V curves above and below TNL ≈ 120 K, respectively. These electrical behaviors are consistent with a progressive transition from an Ohmic to a non-Ohmic variable-range-hopping (VRH) mechanism. We discuss the origin of these nonlinearities, comparing the two- and four-probe measurements on single HNWs, and we propose a simple model based on dual back-to-back Schottky diodes to explain qualitatively the rectifying properties.

Template‐assisted Co–Ni alloys and multisegmented nanowires with tuned magnetic anisotropy

Homogeneous Co85Ni15 and Co54Ni46 alloys, together multisegmented Co85Ni15/Co54Ni46 magnetic nanowire arrays have been synthesized by means of potentiostatic and pulsed potentiostatic electrodeposition techniques, respectively, into the pores of hard‐anodic alumina templates. Morphological, compositional and structural characterization indicate that the composition of Co–Ni alloy segments and nanowires can be properly adjusted by varying the electrochemical deposition potential, leading to different crystalline structures (fcc or hcp) depending on the Co–Ni alloy composition. The magnetic properties of homogeneous and multisegmented Co–Ni alloy nanowire arrays, obtained from hysteresis loops and switching field distribution calculations, are correlated with their crystalline structure and effective magnetic anisotropy, to shed light on the magnetization processes that determine the magnetic behaviour of the nanowire arrays. Part (a) shows a schematic drawing of freestanding multisegmented Co85Ni15/Co54Ni46 nanowires. Part (b) displays the magnetic hysteresis loops of multisegmented nanowire arrays measured along the parallel and perpendicular directions with respect to the nanowires long axis.

Capillary Force-Driven, Large-Area Alignment of Multi-segmented Nanowires

We report the large-area alignment of multi-segmented nanowires in nanoscale trenches facilitated by capillary forces. Electrochemically synthesized nanowires between 120 and 250 nm in length are aligned and then etched selectively to remove one segment, resulting in arrays of nanowires with precisely controlled gaps varying between 2 and 30 nm. Crucial to this alignment process is the dispersibility of the nanowires in solution which is achieved by chemically modifying them with hexadecyltrimethylammonium bromide. We found that, even without the formation of an ordered crystalline phase at the droplet edges, the nanowires can be aligned in high yield. To illustrate the versatility of this approach as a nanofabrication technique, the aligned nanowires were used for the fabrication of arrays of gapped graphene nanoribbons and SERS substrates.