Large-scale 3-D interconnected Ni nanotube networks with controlled structural and magnetic properties

Tuning Au/SiO2 nanostructures from 1D to 3D interconnected nanotube networks using polycarbonate porous templates

We report a simple process, based on the combination of sol-gel deposition and nano-templating with polycarbonate membranes, for the synthesis of 1D to 3D free-standing silica (SiO2) interconnected nanotube (NT) networks. The thickness and porosity of the SiO2 nanotube walls can be, respectively, controlled by adjusting the ethanol amount in the sol-gel reaction mixture and by the addition or not of a porogen agent during the synthesis. Internal functionalization of 1D and 3D porous and non-porous SiO2 NTs by Au nanoparticles (NPs) was then performed using electroless deposition leading to particle sizes ranging from 15 to 20 nm. Characterization of all these systems by SEM-EDX, TEM, ICP and XPS clearly demonstrated the impact of the porosity of SiO2 on the amount and localization of Au NPs. Selective functionalization of the inner or the inner + outer surfaces of SiO2 NTs was achieved by keeping or freeing the SiO2 NTs from the template prior to electroless deposition, respectively. Moreover, UV-visible analysis confirmed plasmon resonance associated with Au NPs in all functionalized systems, paving the way to applications in many fields such as nano-medicine or (photo-)catalysis. In particular, the free-standing interconnected silica-based nanotube systems provide unique features of great interest for use in nanoscale fluidic bioseparation, sensing, and flow (photo)-catalytic chemistry, as demonstrated herein for the photodegradation of methylene blue.

Tunable Magnetic Properties of Interconnected Permalloy Nanowire Networks

In this study, we investigate the magnetic properties of interconnected permalloy nanowire networks using micromagnetic simulations. The effects of interconnectivity on the hysteresis curves, coercivity, and remanence of the nanowire networks are analyzed. Our results reveal intriguing characteristics of the hysteresis curves, including nonmonotonic behaviors of coercivity as a function of the position of horizontal nanowires relative to vertical nanowires. By introducing horizontal nanowires at specific positions, the coercivity of the nanowire networks can be enhanced without altering the material composition. The normalized remanence remains relatively constant regardless of the position of the horizontal wires, although it is lower in the interconnected nanowire arrays compared to nonconnected arrays. These findings provide valuable insights into the design and optimization of nanowire networks for applications requiring tailored magnetic properties.

Magnetic Properties of 2D Nanowire Arrays: Computer Simulations

The paper considers a nanowires 2D array located in the nodes of a square lattice. Computer simulations use the Heisenberg model and Metropolis algorithm. The array consists of small nanowires that are monodomain. The exchange interaction orders the spins within a single nanowire. Dipole-dipole forces act between neighboring nanowires. The shape of an individual nanowire affects its magnetic anisotropy. Computer simulations examine the phase transition temperature and magnetization behavior of the system. The type of magnetic moments ordering in the array of nanowires depends on the orientation of their long axis. We consider two types of systems. The nanowires' long axes are oriented perpendicular to the plane of their location in the first case. A dipole-dipole interaction results in first-type superantiferromagnetic ordering of the nanowires' magnetic moments for such orientation. The nanowires' long axes are oriented in the plane of the system in the second case. Dipole-dipole interaction results in second-type superantiferromagnetic ordering in such systems. The dependence of the phase transition temperature on the dipole-dipole interaction intensity is investigated.

3D Interconnected Magnetic Nanowire Networks as Potential Integrated Multistate Memristors

Interconnected magnetic nanowire (NW) networks offer a promising platform for three-dimensional (3D) information storage and integrated neuromorphic computing. Here we report discrete propagation of magnetic states in interconnected Co nanowire networks driven by magnetic field and current, manifested in distinct magnetoresistance (MR) features. In these networks, when only a few interconnected NWs were measured, multiple MR kinks and local minima were observed, including a significant minimum at a positive field during the descending field sweep. Micromagnetic simulations showed that this unusual feature was due to domain wall (DW) pinning at the NW intersections, which was confirmed by off-axis electron holography imaging. In a complex network with many intersections, sequential switching of nanowire sections separated by interconnects was observed, along with stochastic characteristics. The pinning/depinning of the DWs can be further controlled by the driving current density. These results illustrate the promise of such interconnected networks as integrated multistate memristors.

Ni80Fe20 nanotubes with optimized spintronic functionalities prepared by atomic layer deposition

Permalloy Ni₈₀Fe₂₀ is one of the key magnetic materials in the field of magnonics. Its potential would be further unveiled if it could be deposited in three dimensional (3D) architectures of sizes down to the nanometer. Atomic Layer Deposition, ALD, is the technique of choice for covering arbitrary shapes with homogeneous thin films. Early successes with ferromagnetic materials include nickel and cobalt. Still, challenges in depositing ferromagnetic alloys reside in the synthesis via decomposing the constituent elements at the same temperature and homogeneously. We report plasma-enhanced ALD to prepare permalloy Ni₈₀Fe₂₀ thin films and nanotubes using nickelocene and iron(iii) tert-butoxide as metal precursors, water as the oxidant agent and an in-cycle plasma enhanced reduction step with hydrogen. We have optimized the ALD cycle in terms of Ni : Fe atomic ratio and functional properties. We obtained a Gilbert damping of 0.013, a resistivity of 28 μΩ cm and an anisotropic magnetoresistance effect of 5.6 % in the planar thin film geometry. We demonstrate that the process also works for covering GaAs nanowires, resulting in permalloy nanotubes with high aspect ratios and diameters of about 150 nm. Individual nanotubes were investigated in terms of crystal phase, composition and spin-dynamic response by microfocused Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and magnonic devices in curved and complex topology operated in the GHz frequency regime.

Giant Magnetoresistance and Magneto-Thermopower in 3D Interconnected NixFe1-x/Cu Multilayered Nanowire Networks

The versatility of the template-assisted electrodeposition technique to fabricate complex three-dimensional networks made of interconnected nanowires allows one to easily stack ferromagnetic and non-magnetic metallic layers along the nanowire axis. This leads to the fabrication of unique multilayered nanowire network films showing giant magnetoresistance effect in the current-perpendicular-to-plane configuration that can be reliably measured along the macroscopic in-plane direction of the films. Moreover, the system also enables reliable measurements of the analogous magneto-thermoelectric properties of the multilayered nanowire networks. Here, three-dimensional interconnected NixFe1−x/Cu multilayered nanowire networks (with 0.60≤x≤0.97) are fabricated and characterized, leading to large magnetoresistance and magneto-thermopower ratios up to 17% and −25% in Ni80Fe20/Cu, respectively. A strong contrast is observed between the amplitudes of magnetoresistance and magneto-thermoelectric effects depending on the Ni content of the NiFe alloys. In particular, for the highest Ni concentrations, a strong increase in the magneto-thermoelectric effect is observed, more than a factor of 7 larger than the magnetoresistive effect for Ni97Fe3/Cu multilayers. This sharp increase is mainly due to an increase in the spin-dependent Seebeck coefficient from −7 µV/K for the Ni60Fe40/Cu and Ni70Fe30/Cu nanowire arrays to −21 µV/K for the Ni97Fe3/Cu nanowire array. The enhancement of the magneto-thermoelectric effect for multilayered nanowire networks based on dilute Ni alloys is promising for obtaining a flexible magnetic switch for thermoelectric generation for potential applications in heat management or logic devices using thermal energy.

Magneto-Transport in Flexible 3D Networks Made of Interconnected Magnetic Nanowires and Nanotubes

Electrochemical deposition of interconnected nanowires and nanotubes made of ferromagnetic metals into track-etched polycarbonate templates with crossed nanochannels has been revealed suitable for the fabrication of mechanically stable three-dimensional magnetic nanostructures with large surface area. These 3D networks embedded into flexible polymer membranes are also planar and lightweight. This fabrication technique allows for the control of the geometric characteristics and material composition of interconnected magnetic nanowire or nanotube networks, which can be used to fine-tune their magnetic and magneto-transport properties. The magnetostatic contribution to the magnetic anisotropy of crossed nanowire networks can be easily controlled using the diameter, packing density, or angle distribution characteristics. Furthermore, the fabrication of Co and Co-rich NiCo alloy crossed nanowires with textured hcp phases leads to an additional significant magnetocrystalline contribution to the magnetic anisotropy that can either compete or add to the magnetostatic contribution. The fabrication of an interconnected nanotube network has also been demonstrated, where the hollow core and the control over the tube wall thickness add another degree of freedom to control the magnetic properties and magnetization reversal mechanisms. Finally, three-dimensional networks made of interconnected multilayered nanowire with a succession of ferromagnetic and non-magnetic layers have been successfully fabricated, leading to giant magnetoresistance responses measured in the current-perpendicular-to-plane configuration. These interconnected nanowire networks have high potential as integrated, reliable, and stable magnetic field sensors; magnetic devices for memory and logic operations; or neuromorphic computing.

Novel Nanofluidic Cells Based on Nanowires and Nanotubes for Advanced Chemical and Bio-Sensing Applications

Since the first introduction of one-dimensional nanochannels for single-molecule detection, there has been increasing interest in modern nanofluidic systems, such as chemical and biological sensing applications. Recently developed nanowires (NWs) and nanotubes (NTs) have received tremendous attention due to their unique geometrical, physical and chemical properties, which are very attractive in this field. Here, we review the recent research activities in the field of novel nanofluidic cells based on NWs and NTs. First, we give a brief introduction of this field. Then the common synthesis methods of NWs and NTs are summarized. After that, we discuss the working principle and sensing mechanism of nanofluidic devices, which is fundamental to the interaction between these nanostructures and small molecules. Finally, we present the NW- and NT-based devices for chemical and bio-sensing applications, such as gas sensing, pathogen detection, DNA sequencing, and so forth.

Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes

We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures’ electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.

Magnetic Nanowires

Magnetic nanowires are attractive materials because of their morphology-dependent remarkable properties suitable for various advanced technologies in sensing, data storage, spintronics, biomedicine and microwave devices, etc. The recent advances in synthetic strategies and approaches for the fabrication of complex structures, such as parallel arrays and 3D networks of one-dimensional nanostructures, including nanowires, nanotubes, and multilayers, are presented. The simple template-assisted electrodeposition method enables the fabrication of different nanowire-based architectures with excellent control over geometrical features, morphology and chemical composition, leading to tunable magnetic, magneto-transport and thermoelectric properties. This review article summarizing the work carried out at UCLouvain focuses on the magnetic and spin-dependent transport properties linked to the material and geometrical characteristics.

Metal Nanotube/Nanowire-Based Unsupported Network Electrocatalysts

Combining 1D metal nanotubes and nanowires into cross-linked 2D and 3D architectures represents an attractive design strategy for creating tailored unsupported catalysts. Such materials complement the functionality and high surface area of the nanoscale building blocks with the stability, continuous conduction pathways, efficient mass transfer, and convenient handling of a free-standing, interconnected, open-porous superstructure. This review summarizes synthetic approaches toward metal nano-networks of varying dimensionality, including the assembly of colloidal 1D nanostructures, the buildup of nanofibrous networks by electrospinning, and direct, template-assisted deposition methods. It is outlined how the nanostructure, porosity, network architecture, and composition of such materials can be tuned by the fabrication conditions and additional processing steps. Finally, it is shown how these synthetic tools can be employed for designing and optimizing self-supported metal nano-networks for application in electrocatalysis and related fields.