Multisegmented Nanowires Research Articles

Site-selective core/shell deposition of tin on multi-segment nanowires for magnetic assembly and soldered interconnection

The field of nanotechnology continues to grow with the ongoing discovery and characterization of novel nanomaterials with unconventional size-dependent properties; however, the ability to apply modern manufacturing strategies for practical device design of these nanoscale structures is significantly limited by their small size. Although interconnection has been previously demonstrated between nanoscale components, such approaches often require the use of expensive oxidation-resistant noble metal materials and time-consuming or untargeted strategies for welded interconnection such as laser ablation or plasmonic resonance across randomly oriented component networks. In this work, a three-segment gold–nickel–gold nanowire structure is synthesized using templated electrodeposition and modified via monolayer-directed aqueous chemical reduction of tin solder selectively on the gold segments. This core/shell nanowire structure is capable of directed magnetic assembly tip-to-tip and along substrate pads in network orientation. Upon infrared heating in a flux vapor atmosphere, the solder payload melts and establishes robust and highly conductive wire–wire joints. The targeted solder deposition strategy has been applied to various other multi-segment gold/nickel nanowire configurations and other metallic systems to demonstrate the capability of the approach. This core/shell technique of pre-loading magnetically active nanowires with solder material simplifies the associated challenges of size-dependent component orientation in the manufacture of nanoscale electronic devices.

Fast nanoscale imaging of strain in a multi-segment heterostructured nanowire with 2D Bragg ptychography.

Developing semiconductor devices requires a fast and reliable source of strain information with high spatial resolution and strain sensitivity. This work investigates the strain in an axially heterostructured 180 nm-diameter GaInP nanowire with InP segments of varying lengths down to 9 nm, simultaneously probing both materials. Scanning X-ray diffraction (XRD) is compared with Bragg projection ptychography (BPP), a fast single-projection method. BPP offers a sufficient spatial resolution to reveal fine details within the largest segments, unlike scanning XRD. The spatial resolution affects the quantitative accuracy of the strain maps, where BPP shows much-improved agreement with an elastic 3D finite element model compared with scanning XRD. The sensitivity of BPP to small deviations from the Bragg condition is systematically investigated. The experimental confirmation of the model suggests that the large lattice mismatch of 1.52% is accommodated without defects.

Electrodeposition of Multi-Segment Nanowires and Site-Selective Solder Deposition for Magnetic Assembly and Nanoscale Joining

Electronic device packaging involves complex wiring assemblies for transport of electrical and thermal energy, enabling increasingly sophisticated circuit designs in an industry favoring aggressive device miniaturization. Nanoscale miniaturization of the wire morphology has become increasingly sophisticated in recent years with regards to synthesis; however, the ability to arrange and manufacture these small-scale materials to fully exploit their novel properties has been quickly outpaced. The purpose of this investigation is the establishment of a synthesis technique for a core/shell nanowire structure with tunable compositional templating via electrodeposition which can pass through this bottleneck via directed matrix assembly. A gold-nickel-gold nanowire structure was utilized as the core, synthesized via electrochemical deposition into an anodic aluminum oxide (AAO) template; the nickel segment was chosen to act as a magnetic vehicle for directed assembly, while the bordering gold tips were coated with a solder shell. Gold-selective deposition of this tin solder shell was achieved by establishing a chemisorbed nickel-protective monolayer via immersion in azelaic acid solution. Next, the protected nanowires were dispersed in an aqueous reaction vessel with excess sodium borohydride reducing agent. Controlled addition of tin sulfate and sodium dodecyl sulfate solution to the vessel resulted in the formation of tin seeds which deposited along the gold tips of the nanowires, growing into a “dumbbell” shape nanowire with tin deposited on both gold tips. Composition and confirmation of the solder deposition was performed with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopic (EDS) analysis. Crystal structure of the core/shell nanowires was performed with x-ray diffraction (XRD) to identify intermetallic formation between the tin and gold. The core/shell nanowires were arranged magnetically across a conductive interdigitated electrode and melted by an infrared-driven reflow procedure under flux atmosphere, establishing ohmic contact tip-to-tip between nanowires and in wire-to-pad morphologies. This work establishes an effective and scalable method for site-specific nanowire functionalization while simultaneously addressing miniaturization-associated assembly issues in its desired applications.

Multi-segmented nanowires for vortex magnetic domain wall racetrack memory

A vortex domain wall’s (VW) magnetic racetrack memory’s high performance depends on VW structural stability, high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. Thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. This junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction (l) and vertically (d) in the y-direction. The VW structure became stable by manipulating magnetic properties, such as magnetic saturation (M s) and magnetic anisotropy energy (K u). In this case, increasing the values of M s ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires, which contributes to maintenance of the storage memory’s lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. Moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions (l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW (J d) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the M s and K u, can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires (multi-segmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density (J d) for moving the VW from one state to another was highly influenced by the offset area geometry (l and d) and the material’s magnetic properties, such as the M s and K u.

Current-induced zero-field domain wall depinning in cylindrical nanowires

Multi-segmented cylindrical nanowires have properties that make them attractive for high-density, high-speed logic and memory applications. Investigations of the current-induced domain wall motion in cylindrical nanowires have, so far, typically been conducted with a background magnetic field. However, if performed at zero external field, they would be much more viable for their use in prospective electronic devices. Here, we present an all-magneto electrical method to consistently pin domain walls in multi-segmented nanowires and induce their de-pinning using current pulses. The experiments were conducted with compositionally modulated three-segmented nickel/cobalt/nickel and two-segmented cobalt/nickel nanowires of 190 and 150 nm diameter, respectively, where the soft/hard magnetic texture has been fairly studied. We find that for the 3 segmented nanowire, the domain wall can be de-pinned independent of the polarity of the pulse, while for the 2 segmented nanowire the domain wall de-pins only for one polarity. Applying current pulses of 1 × 1012 A/m2, we use a pulse width of 22 ns to estimate a lower boundary for the domain wall speed of 634.54 m/s in cobalt. We study the resistive heating effect from the DC measurement current to find a temperature increase of no more than 2 °C after more than 20 h of tests.

Bilayered soft/hard magnetic nanowires as in-line writing heads

Multi-segmented cylindrical nanowires (NWs) are the most promising systems for 3D racetrack memory devices, where information is stored as in-line magnetic domains. However, reading and writing information is still a challenge, as external reading/writing heads have to be implemented near the tracks. The writing component should be made of a bilayered soft/hard coupled magnetic system, so that information could be easily written by external magnetic fields. Here, we demonstrate the feasibility of using a Ni90Cu10/Fe20Co80 segmented NW as the writing element, in which magnetic information is written by applying external magnetic fields. Using low-cost template-assisted electrodeposition methods, single, bi- and multi-segmented NW hexagonal arrays of NiCu and FeCo/Au were fabricated. A throughout magnetic characterization using magnetic hysteresis loops, ferromagnetic resonance and first-order reversal curves (FORCs) revealed that the soft segment (NiCu) induced the reversal of the hard segment (FeCo) in a two-step process, reducing its coercive and effective anisotropy fields when coupled. Finally, micromagnetic simulations certified the experimental observations of a multi-step reversal process. This work demonstrates the important role of interface interactions for the future implementation of an in-line writing component in a 3D racetrack memory device, enhancing their potential applicability.

Distinguishing Local Demagnetization Contribution to the Magnetization Process in Multisegmented Nanowires.

Cylindrical magnetic nanowires are promising materials that have the potential to be used in a wide range of applications. The versatility of these nanostructures is based on the tunability of their magnetic properties, which is achieved by appropriately selecting their composition and morphology. In addition, stochastic behavior has attracted attention in the development of neuromorphic devices relying on probabilistic magnetization switching. Here, we present a study of the magnetization reversal process in multisegmented CoNi/Cu nanowires. Nonstandard 2D magnetic maps, recorded under an in-plane magnetic field, produce datasets that correlate with magnetoresistance measurements and micromagnetic simulations. From this process, the contribution of the individual segments to the demagnetization process can be distinguished. The results show that the magnetization reversal in these nanowires does not occur through a single Barkhausen jump, but rather by multistep switching, as individual CoNi segments in the NW undergo a magnetization reversal. The existence of vortex states is confirmed by their footprint in the magnetoresistance and 2D MFM maps. In addition, the stochasticity of the magnetization reversal is analysed. On the one hand, we observe different switching fields among the segments due to a slight variation in geometrical parameters or magnetic anisotropy. On the other hand, the stochasticity is observed in a series of repetitions of the magnetization reversal processes for the same NW under the same conditions.

Unveiling the Origin of Multidomain Structures in Compositionally Modulated Cylindrical Magnetic Nanowires.

CoNi/Ni multisegmented cylindrical nanowires were synthesized via an electrochemical route. The wires are 140 nm in diameter, with 1000 nm long Ni segments and CoNi segments between 600 and 1400 nm in length. The magnetic configuration was imaged by XMCD-PEEM in the demagnetized state and at remanence after magnetizing axially and perpendicularly. Ni segments, with cubic crystal symmetry, show an axial magnetic configuration with a small curling component at the surface. In turn, CoNi segments, with hexagonal crystal symmetry and a strong magnetocrystalline anisotropy perpendicular to the nanowires, show a single vortex state in the shorter segments and multivortex or multitransverse magnetic configurations in medium and long segments, respectively. A detailed study by micromagnetic simulations reveals that the magnetic configuration is determined mainly by the coupling between soft Ni and harder CoNi segments. For short CoNi segments, Ni segments are magnetostatically coupled and the chirality of the single vortex formed in CoNi remains the same as that of the curling in neighboring Ni segments. For longer CoNi segments, the remanent state is either the multivortex or multitransverse state depending on whether the previously applied field was parallel or perpendicular to the magnetocrystalline axis. The results point out the relevance of the cylindrical geometry to promote the occurrence of complex magneto-chiral effects and provide key information for the design of cylindrical magnetic nanowires for multiple applications.

Fe/Mn multilayer nanowires as dual mode T1 -T2 magnetic resonance imaging contrast agents.

To overcome the negative contrast limitations, and to improve the sensitivity of the magnetic resonance signals, the mesoporous silica coated Fe/Mn multilayered nanowires (NWs) were used as a T1 -T2 dual-mode contrast agents (CAs). The single component Fe and Mn NWs, and Fe/Mn multilayer NWs were synthesized by electrodeposition in the homemade anodic aluminum oxide (AAO) templates with the aperture of about 30 nm. The structural characterization and morphology of single component and multisegmented NWs was done by X-ray diffraction and transmission electron microscopy. The elemental composition of Fe/Mn multilayerd NWs was confirmed by energy-dispersive X-ray and energy-dispersive spectrometer. Vibrating sample magnetometer was used to test the magnetic properties, and 1.5 T magnetic resonance imaging (MRI) scanner was used to measure the relaxation efficiency. Importantly, the MRI study indicated that the Fe/Mn multilayer NWs showed a significant T1 -T2 imaging effect, and have longitudinal relaxivity (r1 ) value, that is, 1.25 ± 0.0329 × 10-4 μM-1 s-1 and transverse relaxivity (r2 ), that is, 5.13 ± 0.123 × 10-4 μM-1 s-1 , which was two times of r1 value (0.654 ± 0.00899 × 10-4 μM-1 s-1 ) of Mn NWs, and r2 value (2.96 ± 0.0415 × 10-4 μM-1 s-1 ) of Fe NWs. Hence, Fe/Mn multilayer NWs have potential to be used as T1 -T2 dual-mode CAs.

Infrared (IR) irradiation induced surface and morphology changes in Sn-based multi-segmented metallic nanowires

In this research, infrared (IR) irradiation has been used as a new heating method for the melting and joining of tin (Sn)-based multi-segmented metallic nanowires. Sn-based nanowires were synthesized by using an electrodeposition method in nanoporous polycarbonate templates. Both Sn nanowires and Sn-based multi-segmented nanowires, which have a barrier layer in the middle and two Sn segments on both ends, were fabricated, and their surface and morphology changes were investigated by IR heating and melting method. The melting behavior and morphology changes were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The morphology changes of Sn nanowires and Sn segments on multi-segmented nanowires were observed when optimized parameters were applied, including flux, heating time, peak melting temperature, and substrate. Vapor phase reflow has been realized for these Sn-based nanowires with the assistance of a flux. Finally, the joining and soldering of multi-segmented nanowires has been successfully achieved, which will enable nanowire integration and device fabrication.

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.

Effect of Segment length on domain wall pinning in multisegmented Co/Ni nanowires for 3D memory applications

Abstract The interfaces between different materials in multisegmented nanowires act as pinning centers for domain walls, making these nanowires attractive materials for 3D memory devices. Here, the switching events which accompany a domain wall pinning and depinning in two-segmented Co/Ni nanowires with 80 nm in diameter have been simulated for various segment lengths, using the MAGPAR package within the Virtual Micromagnetics environment. Different switching mechanisms of the magnetization were found for nanowires with different segment lengths, contributing to different values of the pinning and depinnning fields. Domain wall pinning is caused by the stray field from the Co segment; therefore, the position of the pinned domain wall depends on the cobalt segment’s length: in case of the smaller segment lengths, the domain wall is pinned at the interface itself, whereas in case of 700 nm segments a 150 nm displacement of the pinned domain wall from the interface is found, consistent with experimental reports. Domain wall pinning is manifested as a plateau in the magnetization curve. In case of nanowires with shorter segments, another plateau is observed that is related to the creation of a magnetic vortex structure. These findings are crucial towards determining the minimum segment length to achieve a higher bit density that displays optimal pinning and depinning fields.

Contactless Electrical and Structural Characterization of Semiconductor Nanowires with Axially Modulated Doping Profiles.

Efficient characterization of semiconductor nanowires having complex dopant profiles or heterostructures is critical to fully understand these materials and the devices built from them. Existing electrical characterization techniques are slow and laborious, particularly for multisegment nanowires, and impede the statistical understanding of highly variable samples. Here, it is shown that electro-orientation spectroscopy (EOS)-a high-throughput, noncontact method for statistically characterizing the electrical properties of entire nanowire ensembles-can determine the conductivity and dimensions of two distinct segments in individual Si nanowires with axially encoded dopant profiles. This analysis combines experimental measurements and computational simulations to determine the electrical conductivity of the nominally undoped segment of two-segment Si nanowires, as well as the ratio of the segment lengths. The efficacy of this approach is demonstrated by comparing results generated by EOS with conventional four-point-probe measurements. This work provides new insights into the control and variability of semiconductor nanowires for electronic applications and is a critical first step toward the high-throughput interrogation of complete nanowire-based devices.

Ising-tipi çok segmentli nanoyapıda kompozisyon ve sıcaklık bağımlılıkları

In the present study , an Ising-type multisegment nanowire (IMN) with ferromagnetic / non-magnetic segment structure is investigated by means of the effective-field theory (EFT) with correlations. The effects of the composition (p) and temperature (T) on the magnetic hysteresis properties are investigated in detail. The coercive field (H C ) and squareness ( M r /M S ) of the IMN is also derived from hysteresis loops as a function of p and T. In this system, it was found that the p and T have a significant effect on the magnetic behavior. When the obtained theoretical results compare with some experimental works of nanowire in view of hysteresis behaviors, a very good agreement between them is observed.

Study on magnetic properties of NiFe/Cu multisegmented nanowire arrays with different Cu thicknesses via FORC analysis: coercivity, interaction, magnetic reversibility

Two sets of the large hexagonally ordered arrays of Ni30Fe70/Cu multisegmented nanowires (NWs) with different non-ferromagnetic (NFM) thicknesses of 4 and 12 nm were grown by ac pulse electrodeposition method into anodic aluminum oxide templates with a pore diameter of 40 nm and 100 nm inter-pore distance. The shape anisotropy of the single domain (SD) FM segments was varied from symmetrical-shaped (aspect ratio ~ 1) to rod-shaped (aspect ratio > 1). X-ray diffraction result showed a change in the crystalline phase from NiFe BCC (110) to Cu FCC (111) with increasing the NFM thickness. First-Order Reversal Curve (FORC) method was used to study magnetizing and demagnetizing interactions among the SD segments of the multisegmented NW arrays. The study mainly has been focused on the clarification of the effect of NFM thickness on magnetostatic interactions in the presence of high reversibility, which was estimated to be more than 50%. Weakening the magnetizing coupling of the FM segments through increasing NFM thickness is recognized by a ridge along the coercivity axis of the FORC diagram. With increasing the NFM thickness, the demagnetizing interactions decrease which can be a direct consequence of decreasing the magnetizing NFM thickness. Increasing the NFM thickness also leads to increasing the magnetic reversibility which is characterized on FORC diagrams by a shift in the FORC distribution to the lower coercivity values.

Nanobeam X-ray Fluorescence Dopant Mapping Reveals Dynamics of in Situ Zn-Doping in Nanowires.

The properties of semiconductors can be controlled using doping, making it essential for electronic and optoelectronic devices. However, with shrinking device sizes it becomes increasingly difficult to quantify doping with sufficient sensitivity and spatial resolution. Here, we demonstrate how X-ray fluorescence mapping with a nanofocused beam, nano-XRF, can quantify Zn doping within in situ doped III-V nanowires, by using large area detectors and high-efficiency focusing optics. The spatial resolution is defined by the focus size to 50 nm. The detection limit of 7 ppm (2.8 × 1017 cm-3), corresponding to about 150 Zn atoms in the probed volume, is bound by a background signal. In solar cell InP nanowires with a p-i-n doping profile, we use nano-XRF to observe an unintentional Zn doping of 5 × 1017 cm-3 in the middle segment. We investigated the dynamics of in situ Zn doping in a dedicated multisegment nanowire, revealing significantly sharper gradients after turning the Zn source off than after turning the source on. Nano-XRF could be used for quantitative mapping of a wide range of dopants in many types of nanostructures.

The Role of Cu Length on the Magnetic Behaviour of Fe/Cu Multi-Segmented Nanowires.

A set of multi-segmented Fe/Cu nanowires were synthesized by a two-step anodization process of aluminum substrates and a pulsed electrodeposition technique using a single bath. While both Fe segment length and diameter were kept constant to (30 ± 7) and (45 ± 5) nm, respectively, Cu length was varied between (15 ± 5) and (120 ± 10) nm. The influence of the non-magnetic layer thickness variation on the nanowire magnetic properties was investigated through first-order reversal curve (FORC) measurements and micromagnetic simulations. Our analysis confirmed that, in the multi-segmented Fe/Cu nanowires with shorter Cu segments, the dipolar coupling between Fe segments controls the nanowire magnetic behavior, and its performance is like that of a homogenous Fe nanowire array of similar dimensions. On the other hand, multi-segmented Fe/Cu nanowires with larger Cu segments act like a collection of non-interacting magnetic entities (along the nanowire axis), and their global behavior is mainly controlled by the neighbor-to-neighbor nanodisc dipolar interactions.

Probing the interplay between reversibility and magnetostatic interactions within arrays of multisegmented nanowires

Ordered arrays of NiFe/Cu multisegmented nanowires (NWs) are fabricated by ac pulse electrodeposition method into the 25-µm thick anodic aluminum oxide templates with a pore diameter of about 40–100 nm inter-pore distance. The behavior of magnetostatic interactions between neighboring NiFe/Cu NWs as well between magnetic segments of the same wire related to the NW length and the magnetic segment thickness is presented. The first-order reversal curves (FORCs) results for two given magnetic shape anisotropies, a nearly disk-shaped and a rod-shaped one, reveal a single domain magnetic state along with a constant peak value of FORC coercivity distribution (H FORC ). However, the Major Hysteresis Loop coercivity (H MHL ) shows a significant reduction with an increase in length. In addition, the magnetostatic interaction distribution along the Hu axis of FORC diagrams shows a weakly decreasing behavior, in disagreement with existing phenomenological model. In order to resolve this contradiction, the reversible and irreversible components of magnetization were measured. For arrays of multisegmented NWs, the contribution of the reversible components of magnetization rises up to about 70% as NW’s length increases which is in contrast for arrays of uniform NWs where a nearly zero reversibility is reported.

Angular Magnetoresistance of Nanowires with Alternating Cobalt and Nickel Segments

Magnetization reversal in segmented Co/Ni nanowires with varying number of segments was studied using angular magnetoresistance (MR) measurements on isolated nanowires. The MR measurements offer an insight into the pinning of domain walls (DWs) within the nanowires. Angular MR measurements were performed on nanowires with two and multiple segments by varying the angle between the applied magnetic field and nanowire ( $- 90 {^{\circ }} \le \theta \le 90^{\circ }$ ). The angular MR measurements reveal that at lower values of $\theta $ , the switching fields are nearly identical for the multisegmented and two-segmented nanowires, whereas at higher values of $\theta $ , a decrease in the switching field is observed in the case of two-segmented nanowires. The two-segmented nanowires generally exhibit a single DW pinning event, whereas an increased number of pinning events are characteristic of the multisegmented nanowires at higher values of $\theta $ . In situ magnetic force microscopy substantiates reversal by DW nucleation and propagation in multisegmented nanowires.

Multisegmented Nanowires: a Step towards the Control of the Domain Wall Configuration

Cylindrical nanowires synthesized by controlled electrodeposition constitute excellent strategic candidates to engineer magnetic domain configurations. In this work, multisegmented CoNi/Ni nanowires are synthesized for tailoring a periodic magnetic structure determined by the balance between magnetocrystalline and magnetostatic energies. High-resolution Transmission Electron Microscopy confirms the segmented growth and the sharp transition between layers. Although both CoNi and Ni segments have similar fcc cubic crystal symmetry, their magnetic configuration is quite different as experimentally revealed by Magnetic Force Microscopy (MFM) imaging. While the Ni segments are single domain with axial magnetization direction, the CoNi segments present two main configurations: a single vortex state or a complex multivortex magnetic configuration, which is further interpreted with the help of micromagnetic simulations. This original outcome is ascribed to the tight competition between anisotropies. The almost monocrystalline fcc structure of the CoNi segments, as revealed by the electron diffraction patterns, which is atypical for its composition, contributes to balance the magnetocrystalline and shape anisotropies. The results of MFM measurements performed under in-plane magnetic field demonstrate that it is possible to switch from the multivortex configuration to a single vortex configuration with low magnetic fields.