Ni Layer Thickness Research Articles

Achieving better strength-toughness synergy in heterogeneous Cu/Ni/graphene composites: A molecular dynamics simulation

The non-wetting nature of copper (Cu) and graphene, coupled with the brittle behavior of graphene, impedes the strength-toughness synergy in graphene-reinforced Cu matrix (Cu/graphene) composites, limiting their practical applications. Benefiting from interface modification engineering and heterogeneous structure strengthening effects, here a novel strengthening and toughening strategy for Cu/graphene composites by introducing a variable-thickness nickel (Ni) modification layer sandwiched between Cu and graphene (Cu/Ni/graphene) was proposed, and the influence of layer thickness-related structural heterogeneity on mechanical properties and underlying deformation mechanisms were investigated via molecular dynamics simulations. The results revealed that an optimal Ni thickness of 2.44 nm within increased Ni layer thickness enhanced the strength-toughness synergy in the Cu/Ni/graphene composites. This was attributed to altered interface structure, stress distribution, and graphene fracture behaviors due to layer thickness-related deformation behavior. In addition to common strengthening mechanisms like graphene load-bearing effect, interface dislocation nucleation, and interface dislocation blockage strengthening, the layer thickness-dependent semi-coherent Cu/Ni and Ni/graphene heterogeneous interface stress strengthening contributed to extra strength enhancement. Furthermore, cooperative deformation behavior among heterogeneous components improved toughness. The interfacial engineering strategy, achieved by tailoring the modification layer thickness, may pave the way for producing nanostructured metallic composites with extraordinary mechanical properties.

NiO surface reduction by Nd overlayers

Metal/metal oxide interfaces have significant impact on modern technologies like microelectronics, solar cells, magnetic storage, and sensors due to their distinct electronic and structural properties. Such interfaces sometimes deviate from ideal bulk-termination which influences the system's overall performance. Here, we present the study of the interfacial electronic structure formed by the deposition of Nd layers onto NiO thin films utilizing X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoemission spectroscopy (UPS). Our study indicates that the interface between the rare earth metal (Nd) and NiO differs from the ideal sharp interface. The portion of NiO surface reduced to metallic Ni while the deposited Nd metal is oxidized, indicating the interfacial oxidation/reduction process. The thickness of this interfacial Ni layer increases with increase in Nd metal deposited and reaches maximum depth of 3.0 Å when effective Nd overlayer thickness reaches 7.9 Å. Such an interface reaction could be utilized in heterostructures where an intentional reduction of the oxides is desired.

Experimental and model study of LIBS depth profile for multilayer deposition materials

The patterns of erosion and deposition occurred in the plasma-facing materials (PFMs) of a magnetic confinement fusion device are crucial for the investigation of plasma-wall interaction (PWI). The deposition behavior can be identified by the elemental depth profile of the deposition layer. As an effective remote monitoring method for the wall in nuclear fusion devices, laser-induced breakdown spectroscopy (LIBS) shows excellent potential for the depth profiling of the deposition layer on the PFMs. However, some potentially influencing factors lead to the difficulty of distinguishing and identifying the interfaces between the deposition layers and substrate. The measuring accuracy of the deposition layer thickness plays an essential role in PWI research. In this paper, depth profiling of multilayer samples with Ni layers on Cu were performed using LIBS with an ns-pulse laser. The experiment was carried out under 5 × 10−5 mbar to simulate the operation of a nuclear fusion device. Meanwhile, a two-dimensional model for multi-pulse LIBS depth analysis based on the laser beam profile factor and interface roughness factor was established to reconstruct and predict the elemental depth profile distribution of NiCu multilayer materials. The correlation coefficients between the experimental and modeling data were all >0.99. We introduced a locating approach for the interface based on model prediction, and the relative errors of all Ni layer thicknesses were < 5.1%, demonstrating the feasibility and accuracy of the model. All the results show that the two-dimensional numerical model can improve the accuracy of LIBS depth profile on layer thickness analysis and further promote the application of in situ LIBS diagnosis in PWI research.

Spin–orbit torque in perpendicularly magnetized [Pt/Ni] multilayers

The performance of spin–orbit torque (SOT) in heavy metal/ferromagnetic metal periodic multilayers has attracted widespread attention. In this paper, we have successfully fabricated a series of perpendicular magnetized [Pt(2–t)/Ni(t)]4 multilayers, and studied the SOT in the multilayers by varying the thickness of Ni layer t. The current induced magnetization switching was achieved with a critical current density of 1 × 107 A/cm2. The damping-like SOT efficiency ξ DL was extracted from an extended harmonic Hall measurement. We demonstrated that the ξ DL can be effectively modulated by t Pt/t Ni ratio of Pt and Ni in the multilayers. The SOT investigation about the [Pt/Ni] N multilayers might provide new material candidates for practical perpendicular SOT-MRAM devices.

Structural and Magnetic Properties of Ni Nanoparticles Embedded in Vinyl Polymer Nanocomposite Films

Ni nanoparticles layer of nominal thickness in the range of 5–40[Formula: see text]nm were deposited on polyvinyl alcohol (PVA) film by using the ion beam sputtering (IBS) technique. PVA films were made on a quartz substrate by the solution casting technique. Grazing incidence X-ray diffraction (GIXRD) results reveal Ni is present in a metallic form in the FCC phase. AFM shows that roughness increases with increase in thickness of Ni layer and corresponding MFM images of magnetic domains were recorded. Soft X-ray absorption spectroscopy (SXAS) studies on the PVA/Ni nanocomposites films were recorded using synchrotron radiation. This study is used to study the electronic structure of the as-prepared nanocomposite films and reveals that Ni nanoparticles are present in their metallic form. Magnetic properties were measured using the magneto-optical Kerr effect (MOKE) magnetometer and the films were found to be magnetically soft with higher value of coercivity at lower thickness of Ni nanoparticles layer. The results of magnetic studies are discussed in light of the microstructure and morphological features of PVA/Ni nanocomposite films. The PVA/Ni nanocomposites showed interesting anisotropic magnetic behavior; thus the investigative results may be useful for the development of futuristic flexible functional magnetic material system.

Design and fabrication of energetic Al/Ni exploding foil with enhanced energy efficiency and plasma density for direct ignition

In order to lower the firing voltage, an energetic Al/Ni exploding foil (Al/Ni-EF) with enhanced energy efficiency and plasma density was prepared in this study, to realize the direct ignition of pyrotechnics. An Al/Ni reactive multilayer foil (Al/Ni-RMF) was firstly synthesized by magnetron sputtering and wet etch method, and its structure and exothermic behavior were investigated. Scanning Electron Microscopy, Atomic Force Microscope and X-ray Diffraction characterizations confirmed the periodic layer structure of Al/Ni-RMF with a total thickness of 4 μm. The highest heat release in Al/Ni-RMF could be achieved theoretically when the ratio of Al and Ni was 1.5, and thus the thickness of single Al and Ni layer was determined to be 300 nm and 200 nm, respectively. The obtained Al/Ni-RMF was subsequently fabricated to be an exploding foil, and its electric explosion performance was further studied. Energy efficiency of the Al/Ni-EF was measured to be 85.9% during the electric explosion process, which was 30.9% higher than that of Cu exploding foil (Cu-EF). The plasma generated at Al/Ni-EF had larger volume, longer duration time and higher temperature than Cu-EF due to the intermetallic reaction between Al and Ni, which was beneficial for the direct ignition of Boron/Potassium Nitrate composition (B/KNO3, BPN). Afterwards, a special Al/Ni-EF ignitor without slapper was constructed, and the fierce ignition of BPN at the minimum discharge voltage of 800 V was observed. Above results confirmed the feasibility of direct ignition, such a unique strategy was beneficial for the development of low-energy, low-cost and miniaturized ignitor.

Improvement of Heat Dissipation in Ag/Ni Substrates for Testing Cu-TiO2/TiO2-Modified Filters Using SERS Spectroscopy

Surface-enhanced Raman scattering (SERS) spectroscopy is used to investigate a composition of wash swabs from the Cu-TiO2/TiO2-modified filters with disinfecting ability. Macroporous Si chips coated with conformal 800 nm thick Ni layer and Ag particles (Ag/Ni) are engineered to act as SERS-active substrates. Such substrates are characterized by a moderate reflection band in the visible range and provide an improved heat dissipation from contaminants in wash swabs during SERS study. This prevents thermal-induced destruction of analyzing media for reliable assessment of its composition. The anatase Cu-TiO2 and TiO2 nanoparticles are synthesized using the sol-gel method and characterized via Raman spectroscopy and X-ray diffractometry. The filters are modified with Cu-TiO2/TiO2 nanoparticles and embedded in three-valve facial masks that are worn by a volunteer to breathe for 4 h. Comparative SERS analysis of the filters shows that they slightly destroy chemical bonds in the molecules constituting airborne contaminations upon ceiling day lights, which can be associated with Cu-TiO2 photocatalytic activity. The filters additionally exposed to near-ultraviolet light prominently decrease the intensity of Raman signatures of airborne contaminant due to the presence of pure TiO2.

Morphology control in Ni/Ti multilayer neutron mirrors by ion-assisted interface engineering and B4C incorporation

The optical contrast and minimum layer thickness of Ni/Ti broadband neutron multilayer supermirrors is usually hampered by an interface width, typically 0.7 nm, caused by nanocrystallites, interdiffusion, and/or intermixing. We explore the elimination of nanocrystallites in combination with interface smoothening by modulation of ion assistance during magnetron sputter deposition of 0.8 to 6.4 nm thick Ni and Ti layers. The amorphization is achieved through incorporation of natural B4C where B and C preferably bond to Ti. A two-stage substrate bias was applied to each layer; -30 V for the initial 1 nm followed by -100 V for the remaining part, generating multilayer mirrors with interface widths of 0.40-0.45 nm. The results predict that high performance supermirrors with m-values as high as 10 are feasible by using 11B isotope-enriched B4C combined with temporal control of the ion assistance.

Mechanical properties and strengthening mechanism of Ni/Al nanolaminates: Role of dislocation strengthening and constraint in soft layers

This work focuses on the mechanical properties and strengthening mechanism of Ni/Al nanolaminates, where dislocation strengthening and constraint dominate in the soft Al nanolayers. Nanoindentation and micropillar compression experiments highlight a constrained plasticity of Al nanolayers, which endows Ni/Al nanolaminates with a strain hardened behavior. Plasticity of Ni/Al nanolaminate begins with yielding of Al, and the Al yield strength depends on the individual layer thickness. Based on an inverse methodology, the Al yield strength as a function of Al grain size is determined. The results evidence a significant strengthening in the Al nanolayers. Specially, when Al layer thickness decreases from ≈110 nm to ≈16 nm, its yield strength is increased for ≈68 %, from ≈0.69 GPa to ≈1.16 GPa. The strengthening rule follows a confined layer slip model that is developed based on confining of single dislocation loops in nanolayers. Both the dislocation strengthening and the constraint effects in the Al layers contribute to a more sensitivity of Ni/Al strength with the variation of Al layer thickness, instead of Ni layer thickness. The work may forward the fundamental understanding in the strengthening mechanism and mechanical behavior of metallic nanolaminates with large elastoplastic mismatch.

A NiCo bimetallic hydroxide electrode-based flexible Ni//Zn battery with smart electrochromic function for visually monitoring battery residual electricity

Flexible battery with a smart electrochromic function of changing color in the electrochemical process reveals great application potentials in the field of intelligent electronics. However, Ni//Zn battery with an electricity visual alerting function has seldom been reported by now. Herein, we designed a flexible Ni//Zn battery, assembled by the NiCo bimetallic hydroxide/Ni/indium tin oxide (NiCo BH/Ni/ITO) flexible electrode with an electrochromic feature. By optimizing the thickness of the middle Ni layer, the NiCo BH/Ni/ ITO electrode shows a coloration efficiency of 59.89 cm2 C−1 and a capacity of 7.15 µA h cm−2 at a current density of 0.1 mA cm−2. Correspondingly, the flexible electrochromic Ni//Zn battery shows a high energy density of 12.69 µW h cm−2 at a power density of 160 µW cm−2, outperforming those of transparent flexible supercapacitors and electrochromic batteries reported in literatures. Moreover, the flexible electrochromic Ni//Zn battery displays reversible color change during charging and discharging processes, rendering it a novel function to monitor the battery residual electricity by visual inspection.

Magnetic and optical properties of ZnO/Ni/ZnO multilayer film on Si(100) and sapphire substrates

The optical absorption, band gap, and magnetic properties of ZnO/Ni(t)/ZnO multilayer film structures were investigated in various Ni layer thicknesses and substrates. We deposited 1, 4, and 5 nm of Ni film by thermal evaporation technique that sandwiched between ZnO films (~15 nm) via radio frequency magnetron sputtering method on both Si(100) and sapphire substrates. Although x-ray diffraction (XRD) analysis confirmed the (002) crystalline plane of ZnO without any Ni crystal phases on Si(100) surface, the better crystalline directions of ZnO, hexagonal wurtzite structure, was observed on the sapphire substrate. In the XRD analysis, we observed the cubic structure of NiO film formation due to thermally oxidation of Ni ions with interactions ZnO layer. Atomic force microscopy images confirmed the effect of the Ni layer on the average island size of 23.9 ± 2.9 nm and 25.6 ± 6.2 of ZnO films on 4 and 5 nm Ni films, respectively. Energy dispersive x-ray spectroscopy data confirmed that there is no other atom or impurity in the sample structure. The optical transparency of the multilayer films was reduced with increasing Ni layer thickness and maximum transparency was obtained as 97% at 800 nm of wavelength for the film with 1 nm Ni. The direct optical band gap of ZnO/Ni(t)/ZnO films was found to be 3.25, 3.20, and 3.12 eV with the contribution of 1, 4, and 5 nm Ni film in the multilayer film stack. The maximum Hc is found to be 1000 Oe for Si substrates and this value is reduced to around 400 Oe due to the crystal formation of the NiO layer for sapphire substrate samples.

Structural and Electrical Characterization of Ni-Based Ohmic Contacts on 4H-SiC Formed by Solid-State Laser Annealing

Laser annealing process for ohmic contact formation on 4H-SiC has attracted increasing attention in the last years, because it enables the fabrication of SiC power devices on very thin substrates. We have investigated the formation of Nickel-based ohmic contact on 4H-SiC by using a Yb:YAG laser in scanning mode, with a wavelength of 515 nm and a pulse duration of 1200 ns. A 100 nm thick Ni layer has been deposited on SiC and irradiated at different process conditions. The reaction process has been studied, as a function of fluence and scan number of laser annealing, by means of X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) analyses. The electrical properties of the annealed layers have been evaluated on Schottky Barrier Diodes (SBDs) devices, confirming the ohmic behavior of the reacted contact and showing improved performances respect to RTA approach. The compatibility of thermal budget of the process in the front side has been verified by means process simulation. A strong relationship between structural properties of reacted layers and electrical behavior of SBDs devices has been revealed. Solid-state laser annealing process, with wavelength in green light region, can indeed represent a suitable solution for ohmic contact formation of 4H-SiC power devices, fabricated on thin substrates.

Magnetic properties affected by structural properties of sputtered Ni/Cu multilayer films with different thicknesses of Ni layers

Magnetic properties affected by structural properties of sputtered Ni/Cu multilayer films with different thicknesses of Ni layers

Effect of Ni(P) Layer Thickness on Interface Reaction and Reliability of Ultrathin ENEPIG Surface Finish.

Electroless Ni(P)/electroless Pd/immersion Au (ENEPIG) is a common surface finish in electronic packaging, while the Ni(P) layer increases the impedance of solder joints and leads to signal quality degradation in high-frequency circuits. Reducing the thickness of the Ni(P) layer can balance the high impedance and weldability. In this paper, the interfacial reaction process between ultrathin ENEPIG substrates with different Ni layer thicknesses (0.112 and 0.185 μm) and Sn–3.0Ag–0.5Cu (SAC305) solder during reflow and aging was studied. The bonding ability and reliability of solder joints with different surface finishes were evaluated based on solder ball shear test, drop test and temperature cycle test (TCT), and the failure mechanism was analyzed from the perspective of intermetallic compound (IMC) interface growth. The results showed that the Ni–Sn–P layer generated by ultrathin ENEPIG can inhibit the growth of brittle IMC so that the solder joints maintain high shear strength. Ultrathin ENEPIG with a Ni layer thickness of 0.185 μm had no failure cracks under thermal cycling and drop impact, which can meet actual reliability standards. Therefore, ultrathin ENEPIG has broad prospects and important significance in the field of high-frequency chip substrate design and manufacturing.

Origin of Perpendicular Magnetic Anisotropy Enhancement in Co/Ni Bilayer Due to Plasma Oxidation

In spintronics and magnonics, materials that offer tunable perpendicular magnetic anisotropy (PMA) along with low Gilbert damping and high spin polarization are particularly important. Therefore, a lot of studies are performed on Co/Ni films, that aim at satisfying all these requirements. Moreover, the Dzyaloshinskii−Moriya interaction is induced in them by surrounding the magnetic layers with heavy metal or oxide layers. For this reason, the study of the oxidation of Co/Ni is of particular interest. Therefore, the magnetic properties of Co/Ni bilayers after plasma oxidation (PO) are investigated. It is shown that the magnetic anisotropy of these bilayers can be tuned, not only by the thicknesses of Co and Ni layers, but also by oxidation time varied in the range between 15 and 220 s. After PO, the effective thickness of ferromagnetic Ni is reduced, but it does not oxidize more than ≈2 nm, even for longer oxidation. However, the contribution to PMA increases for the entire range of oxidation times. This indicates that the thickness reduction of the Ni layer is not the only source of PMA enhancement. This additional contribution is attributed to the exchange bias coupling between the ferromagnetic (Co/Ni) and the antiferromagnetic NiO layers.

Analysis of the Piezoelectric Properties of Aligned Multi-Walled Carbon Nanotubes

Recent studies reveal that carbon nanostructures show anomalous piezoelectric properties when the central symmetry of their structure is violated. Particular focus is given to carbon nanotubes (CNTs) with initial significant curvature of the graphene sheet surface, which leads to an asymmetric redistribution of the electron density. This paper presents the results of studies on the piezoelectric properties of aligned multi-walled CNTs. An original technique for evaluating the effective piezoelectric coefficient of CNTs is presented. For the first time, in this study, we investigate the influence of the growth temperature and thickness of the catalytic Ni layer on the value of the piezoelectric coefficient of CNTs. We establish the relationship between the effective piezoelectric coefficient of CNTs and their defectiveness and diameter, which determines the curvature of the graphene sheet surface. The calculated values of the effective piezoelectric coefficient of CNTs are shown to be between 0.019 and 0.413 C/m2, depending on the degree of their defectiveness and diameter.

Optical properties of Ni metal nanoparticles embedded poly (vinyl alcohol) films

This paper reports the effect of Ni layer thickness on the optical properties of the PVA/Ni nanocomposite films prepared by embedding Ni nanoparticles into the PVA (polyvinyl alcohol) film matrix using ion beam sputtering technique. UV–Vis-NIR spectra have been used to determine the optical parameters like absorption bands, absorption edge, transmission, bandgap, refractive index (RI), extinction coefficient and optical conductivity. As observed, all the above optical parameters were found to have changed remarkably on incorporation of Ni nanoparticles in the PVA film; for example, indirect band gap reduced from 5.01 to 4.38 eV, and RI increased from 1.21 to 10.04.

Room temperature CPP-giant magnetoresistance in Ni/Cu multilayered nanowires

Current-flow perpendicular to the layer planes giant magnetoresistance (CPP-GMR) of Ni/Cu multilayered nanowires (NWs) grown by an alternating current (AC) pulsed electrodeposition technique into anodic aluminum oxide (AAO) template with a pore diameter of 50 ± 5 nm is studied at room temperature. The method used for obtaining GMR percentage is the 2-probe resistance measurement of the contact of released and aligned NWs on a glass substrate in the presence of a magnetic field. The structure and thickness of layers are investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), indicating the formation of well-ordered multilayers. The magnetic properties are studied by a vibrating sample magnetometer (VSM) and the first-order reversal curve (FORC) analysis. The maximum CPP-GMR of Ni/Cu multilayered NWs is obtained to be 2.6% for 17 and 2.7 nm thick Ni and Cu layers, respectively. The results show that Ruderman–Kittel–Kasuya–Yosida (RKKY) variation behavior of GMR values as a function of Cu spacer thickness is in accordance with theoretical models.

Thickness and metallization layer effect on interfacial and vertical cracking of sintered silver layer: A numerical investigation

Cracking of sintered silver layer always leads to the reliability issues in power devices. In this paper, the cracking behaviors of sintered silver layer have been investigated through numerical analysis with fracture based method. Energy release rate of various interfacial cracks and vertical cracks in sintered silver are computed. It is found that the energy release rate of interfacial crack and vertical crack are significantly influenced by their thickness. The thinner of the sintered silver layer, the higher of the energy release rate it will meet. For interfacial crack, the adding of the metallization layer does not improve the energy release rate significantly. For vertical crack, two conditions are considered, i.e., vertical crack emanating from the chip sider or emanating from the copper baseplate side, and it is found that the energy release rate is strongly dependent on its location and the existence of metallization layer. The increase of the thickness of Ni layer enables to lower down the entire level of energy release rate for vertical crack. Otherwise, the energy release rate of vertical crack near the edge region of the sintered silver layer is much higher than other locations. It implies that the cracking risk is higher for thinner sintered silver layer around the edge region which should be avoided. It is also found that the porosity effect on interface cracking and vertical cracking of sintered silver is also important.

Enhanced output power of thermoelectric modules with reduced contact resistance by adopting the optimized Ni diffusion barrier layer

The diffusion barrier layers in thermoelectric generators (TEGs) are widely used to improve their mechanical/thermal stabilities and energy generation performance; however, thickness dependence of diffusion barrier was rarely reported. In this study, we prepared Bi2Te3-based thermoelectric (TE) modules and Ni diffusion barrier with a thickness of 0–30 µm to investigate the correlation between the thickness of Ni layers and TE output performance. A TE module with 1 μm-thick Ni layer harvests a maximum output power of 2.79 mW under a temperature difference (ΔT) of 200 K, which is a higher value than that of a module without a diffusion barrier. Regarding the dependence of TE output performance on the diffusion barrier’s thickness, TEGs based on the thicker Ni layers showed lower output performance for all ΔT ranges compared with a 1 µm-Ni layer TEG. The degradation of TE conversion efficiency was related to the increment of contact resistance (Rc) with the thickness of the diffusion barrier. This Ni thickness-dependent Rc was explored using the transmission line method. The results from this study prove that the thickness of optimized diffusion barriers would maximize the output performance of TEGs, which could be used as a guide for improving the performance of TEGs.