Ni Filaments Research Articles

The Formation of Nanosized Ferromagnetic Ni Filaments in Films of ZrO2(Y)

The Formation of Nanosized Ferromagnetic Ni Filaments in Films of ZrO2(Y)

Формирование наноразмерных ферромагнитных филаментов Ni в пленках ZrO-=SUB=-2-=/SUB=-(Y)

In thin ZrO2 (Y) / Ni films, with used of an atomic force microscope (AFM) probe, conductive ferromagnetic filaments of nanometer sizes, consisting of Ni atoms, are formed. Memristor structures based on such films, the upper electrode of which was the AFM probe, demonstrated bipolar-type resistive switching (RP) associated with the destruction and reduction of Ni filaments. The area where the conducting filament emerges on the surface of the ZrO2 (Y) film manifested itself in the magnetic force image as a single-domain ferromagnetic particle.

Effects of Resistance States on the Magnetoresistance in Ni/Al2O3/Ni by Resistive Switching

Formation and rupture of conductive filaments is one of the main mechanisms for unipolar resistive switching (URS), which can be manifested by the observation of magnetoresistance (MR) effect if ferromagnetic metallic filaments are formed. In this work, ferromagnetic metallic Ni is used as top and bottom electrodes on Al2O3 film, and stable URS behavior is observed after a forming process. By inserting a series resistor in the circuit during the set process, the resistance value at low resistance state (LRS) increases with increasing resistance of the series resistor. The URS behavior can be attributed to the formation and rupture of metallic Ni filaments penetrating through the thin Al2O3 layer, which has been confirmed by the observation of tunneling magnetoresistance. However, the MR value decreases continuously with increasing resistance in LRS, which is due to that the diameter of Ni conductive filaments becomes smaller. Thus, the nonmagnetic scattering at the surfaces of filaments increases, leading to the decrease of MR.

Resistive switching in FeNi/Al2O3/NiO/Pt structure with various Al2O3 layer thicknesses

Abstract Noble metals are generally used as electrodes in resistive switching devices. In this work, ferromagnetic metallic NiFe is used as top electrode on NiO films, and stable unipolar resistive switching (URS) behavior has been observed after a forming process. By inserting a thin Al2O3 layer between NiFe and NiO, URS persists with increasing the thickness of Al2O3 layer up to 20 nm. The URS behavior can be attributed to the formation and rupture of metallic Ni filaments in NiO layer, which penetrate through the thin Al2O3 layer, and have been confirmed by the observation of anisotropic magnetoresistance. With further increasing the thickness of Al2O3 layer up to 30 nm, forming free bipolar resistive switching (BRS) behavior is observed, which is due to the oxygen vacancy accumulation and dissipation at the interface because the thick Al2O3 layer blocks the penetration of Ni filaments. By inserting a thin Al2O3 layer with thickness below 20 nm, the distribution of the reset voltages in URS is significantly narrowed.

Ni‐Coated SiC Particles: Synthesis and Densification

The mechanofusion process, a dry particle coating route, has been successfully applied to coat micrometric SiC particles with submicrometric Ni filaments. In a first step, the mechanofusion parameters were optimized to form a continuous Ni coating onto SiC particles. In a second step, the Ni‐coated SiC particles were sintered by hot isostatic pressing. The temperature and pressure cycles were determined to ensure a good densification of the material. Such a densification process leads to the formation of a δ‐Ni2Si bilayer at the SiC/Ni interface; the inner δ‐Ni2Si layer in contact with SiC being more rich in carbon than the one in contact with the matrix. From X‐ray diffraction, wavelength‐dispersive X‐ray spectrometry and scanning electron microscopy characterizations, a mechanism is proposed to explain the microstructure of the end‐product.

Formation of linear Ni nanochains inside carbon nanotubes: Prediction from density functional theory

First principles calculations have been performed to investigate the ground state properties of monoperiodic single-walled carbon nanotubes (CNTs) containing nanochain of aligned Ni atoms inside. Using the PBE exchange-correlation functional (Exc) within the framework of density functional theory (DFT) we predict the clusterization of Ni filaments in (n,0) CNTs for n⩾9 and for (n,n) CNTs for n⩾6. The variations in formation energies obtained for equilibrium defective nanostructures allow us to predict the most stable Ni@CNT compositions. Finally, the electronic charge redistribution has been calculated in order to explore intermolecular properties leading to stronger Ni–Ni bond formation.

Switching Mode and Mechanism in Binary Oxide Resistive Random Access Memory Using Ni Electrode

Resistive-switching (RS) modes in different CMOS-compatible binary oxides have been shown to be governed by the interplay with the Ni top electrode. Unipolar RS and metallic low-resistance state in polycrystalline HfO2 and ZrO2 are distinct from the preferential bipolar RS and semiconductive low-resistance state in amorphous Al2O3 and SiO2. Backside secondary ion mass spectrometry (SIMS) has shown the formation of Ni filaments in HfO2, in contrast to the formation of oxygen-vacancy filaments in Al2O3. The differences have been explained by strong dependence of Ni migration on the oxide crystallinity. Additionally, the RS mode can be further tailored using bilayer structures. The oxide layer next to the Si bottom electrode and its tendency of forming Ni filaments play significant roles in unipolar RS in the bilayer structures, in support of the conical-shape Ni filament model where the connecting and rupture of filaments for unipolar RS occur at the smallest diameter near the bottom electrodes.

Electrically Conductive Epoxy Adhesives

Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive matrix viscosity on the electrical conduction behavior of epoxy-based adhesives are presented in this work. For this purpose, epoxy-based adhesives were prepared using conductive fillers of different size, shape, and types, including Ni powder, flakes, and filaments, Ag powder, and Cu powder. The filaments were 20 μm in diameter, and 160 or 260 μm in length. HCl and H3PO4 acid solutions were used to etch and remove the surface oxide layers from the fillers. The plane resistance of filled adhesive films was measured using the four-point method. In all cases of conductive filler addition, the planar resistivity levels for the composite adhesive films increased when the film thickness was reduced. The shape of resistivity-thickness curves was negative exponential decaying type and was modeled using a mathematical relation. The relationships between the conductive film resistivities and the filler volume fractions were also derived mathematically based on the experimental data. Thus, the effects of surface treatment of filler particles, the type, size, shape of fillers, and the uncured epoxy viscosity could be included empirically by using these mathematical relations based on the experimental data. By utilizing the relations we proposed to model thickness-dependent and volume fraction-dependent conduction behaviors separately, we were able to describe the combined and coupled volume fraction-film thickness relationship mathematically based on our experimental data.

Resistive switching in NiSi gate metal-oxide-semiconductor transistors

Both unipolar and bipolar resistive switchings are demonstrated on NiSi gate transistors after gate dielectric percolation. Nanoscale Ni filaments and oxygen ion conduction are found in the percolation path as the physical defects responsible for resistive switching. Memory cells can be fabricated together with the metal gate transistors for ease of integration.

Reactions Between Bi-2212 and Silver-Nickel Composite Sheath

The use of a Ag-Ni composite sheath has been proposed as a means to improve the mechanical performance and reduce the cost of Bi-2212 conductor. However, Bi-2212 is highly reactive with metals other than Ag and the precious metals. Previous work has also shown that the Cu-oxide in Bi-2212 will react with oxides applied to the exterior of the Ag sheath. To investigate the feasibility of using a Ni reinforced composite sheath, a monocore tape was fabricated using a Ag sheathing tube reinforced with 44 volume percent Ni filaments. The tape was melt processed in oxygen and argon atmospheres and the structure of the Ni filaments and oxide core was examined. The Ni filaments were found to completely oxidize and incorporate Cu from the core. The oxide in the core was depleted in Cu as a result, which affected 2212 phase formation.

Characterization of a ferromagnetic porous silicon-based Ni/Si nanocomposite with a novel strong high-field anisotropy

Ferromagnetic (Ni) filaments are embedded into a porous silicon template by an electrochemical deposition process. During cathodic deposition using NiCl 2 as electrolyte the channels of the meso-/macroporous silicon structure are filled with metallic Ni. The resulting nanocomposite system consists of silicon as base material as well as of implemented Ni-structures, especially of highly oriented Ni-wires perpendicular to the surface showing an exceptionally high aspect ratio (>300) and is of interest for applications in microtechnology. The length of the Ni-wires is in the range of a few tens of micrometers. Concomitant with the growth of wires, spheres or ellipsoidally shaped particles are formed during the Ni-filling procedure, whose spatial frequency and distribution become tunable. Structural investigations of this system, using SEM and EDX as well as investigations of the magnetic behaviour using SQUID-magnetometry, demonstrate the dependency of the magnetic properties on the filling status of the samples. The hysteresis loops in the low-field regime up to 500 Oe as well as magnetization curves in the high-field range of a few tesla display a strong magnetic anisotropy due to magnetic rearrangements. At fields around 5 T, a decline of the magnetization followed by a steep increase is observed. This magnetic field-induced anisotropy depends on the detailed growth of the Ni within the pores which can be controlled by the deposition process. It is governed by yet unknown antiferromagnetic exchange between the wires, and inherently connected with the shape of the magnetic nano-objects.

Thickness-dependent conduction behavior of various particles for conductive adhesive applications

In order to gain insight into the film thickness-dependent conduction behavior of adhesives containing conductive particles of different sizes, shapes, and types, the effect of adhesive film thickness was studied. Epon 830 resin was used as the base resin and 4-7 μm silver powder was used as the base particle for comparative purposes. Adhesive films of length 2.0 cm and width 0.7 cm were cast subsequent to mixing with conductive particles in the amount of 25% by volume. The conductive particles were 100% Ag or a 50% by weight mixture of Ag with Ni powder, flakes, or filaments. Silver-coated Ni flakes of size 20 μm were also mixed in 50% proportion with Ag powder to assess the effect of silver coating. Subsequent to cure, the resistance of the filled films was measured by the four-point method and resistivities were calculated based on these measurements. In general, the addition of flake and filament material (Ni) to the conductive mixture in epoxy films resulted in distinct thickness thresholds for transition from three-dimensional to two-dimensional conductivity with a considerable increase in resistivity when the film thicknesses were smaller than these threshold values. This behavior is attributed to the specific geometry of the flake and filament particles which, when added to a thin film resin, are likely to align flat in planar directions, thus reducing the number of three-dimensional conduction paths.

Ferromagnetic filaments fabrication in porous Si matrix (invited)

We have fabricated Ni filaments by nickel precipitation into a porous silicon matrix, making Ni filaments of about 200 Å in diameter and 30 μm in length separated by ∼500 Å silicon walls. This composite material demonstrates strong magnetic anisotropy perpendicular to the surface due to shape anisotropy of the Ni filaments.

In-line Gas Analyzer for UF6and F2through Differential Thermal Conductivity Measurements

For the purpose of analyzing UF6 and F2 continuously in the fluorination of U, a system of differential thermal conductivity cells (TCC), equipped with shock absorber, and also NaF and KCl traps, has been trially constructed. Mixed flow-through/diffusion type katharometers are used, provided with four and two Ni filaments (∼30Ω) on the UF6 and F2 cells, respectively. Based on data obtained from preliminary operating tests, the standard conditions for operating the system were established i.e., 500 mmHg abs. Cell pressure, 200 ml/min flow rate and 80 mA bridge current. Under these operating conditions and for UF6 and F2 concentrations of 2 and 20 v/o respectively, the overall out-put variations are below 1%. The total response time of the system including the transport lag is below 1 and 2.5 min for UF6 and F2 cells, respectively. The dead time due to blow-back noise is observed to have about the same period as the above response time. The sensitivities for UF6 and F2 are found respectively to be 11.5 and 0.37 mV/v/o, for which the limits of analytical determination are 0.01 and 0.05 v/o;, respectively. By practical application to uranium fluorination, the TCC system thus devised, has proven to possess the requisite characteristics for measurements of reaction rate, fluorine utilization and end of reaction in fluid-bed fluorination of uranium oxides. The system has possibilities of application to the study of reaction steps.

In-line Gas Analyzer for UF6 and F2 through Differential Thermal Conductivity Measurements

For the purpose of analyzing UF6 and F2 continuously in the fluorination of U, a system of differential thermal conductivity cells (TCC), equipped with shock absorber, and also NaF and KCl traps, has been trially constructed. Mixed flow-through/diffusion type katharometers are used, provided with four and two Ni filaments (∼30Ω) on the UF6 and F2 cells, respectively. Based on data obtained from preliminary operating tests, the standard conditions for operating the system were established i.e., 500 mmHg abs. Cell pressure, 200 ml/min flow rate and 80 mA bridge current. Under these operating conditions and for UF6 and F2 concentrations of 2 and 20 v/o respectively, the overall out-put variations are below 1%. The total response time of the system including the transport lag is below 1 and 2.5 min for UF6 and F2 cells, respectively. The dead time due to blow-back noise is observed to have about the same period as the above response time. The sensitivities for UF6 and F2 are found respectively to be 11.5 and 0.37 mV/v/o, for which the limits of analytical determination are 0.01 and 0.05 v/o;, respectively. By practical application to uranium fluorination, the TCC system thus devised, has proven to possess the requisite characteristics for measurements of reaction rate, fluorine utilization and end of reaction in fluid-bed fluorination of uranium oxides. The system has possibilities of application to the study of reaction steps.

Energy accommodation during oxygen atom recombination on metal surfaces

The recombination coefficient, γ′H and the energy accommodation coefficient, βH were simultaneously determined for hydrogen atom recombination on Ag, Au, Co, Cu, W, Fe, Ni and Pt filaments. Values of βH of 0.87, 0.65 and 0.43 were observed for Ag, Au and Cu, respectively, while values between 0.08 and 0.28 were observed for the other metals. In general, the relative values of βH for these filaments were similar to the values of β previously determined for oxygen atom recombination.

Energy accommodation during hydrogen atom recombination on metal surfaces

The recombination coefficient, γ′H and the energy accommodation coefficient, βH were simultaneously determined for hydrogen atom recombination on Ag, Au, Co, Cu, W, Fe, Ni and Pt filaments. Values of βH of 0.87, 0.65 and 0.43 were observed for Ag, Au and Cu, respectively, while values between 0.08 and 0.28 were observed for the other metals. In general, the relative values of βH for these filaments were similar to the values of β previously determined for oxygen atom recombination.