Nickel Films Research Articles

Maximizing Performance of a Hybrid MnO2/Ni Electrochemical Actuator through Tailoring Lattice Tunnels and Cation Vacancies.

Electrochemical actuators play a key role in converting electrical energy to mechanical energy. However, a low actuation stress and an unsatisfied strain response rate strongly limit the extensive applications of the actuators. Here, we report hybrid manganese dioxide (MnO2) fabricated by introducing ramsdellite (R-MnO2) and Mn vacancies into birnessite (δ-MnO2) nanosheets, which in situ grew on the surface of a nickel (Ni) film, forming a hybrid MnO2/Ni actuator. The actuator demonstrated a rapid strain response of 0.88% s-1 (5.3% intrinsic strain in 6 s) and a large actuation stress of 244 MPa owing to the special R-MnO2 with a high density of sodium ion (Na+)-accessible lattice tunnels, Mn vacancies, and also a high Young's modulus of the hybrid MnO2/Ni composite. Besides, the cyclic stability of the actuator was realized after 1.2 × 104 cycles of electric stimulation under a frequency of 0.05 Hz. The finding of the novel hybrid MnO2/Ni actuator may provide a new strategy to maximize the actuating performance evidently through tailoring the lattice tunnel structure and introducing cation vacancies into electrochemical electrode materials.

Observation of perfect diamagnetism and interfacial effect on the electronic structures in infinite layer Nd0.8Sr0.2NiO2 superconductors

Nickel-based complex oxides have served as a playground for decades in the quest for a copper-oxide analog of the high-temperature superconductivity. They may provide clues towards understanding the mechanism and an alternative route for high-temperature superconductors. The recent discovery of superconductivity in the infinite-layer nickelate thin films has fulfilled this pursuit. However, material synthesis remains challenging, direct demonstration of perfect diamagnetism is still missing, and understanding of the role of the interface and bulk to the superconducting properties is still lacking. Here, we show high-quality Nd0.8Sr0.2NiO2 thin films with different thicknesses and demonstrate the interface and strain effects on the electrical, magnetic and optical properties. Perfect diamagnetism is achieved, confirming the occurrence of superconductivity in the films. Unlike the thick films in which the normal-state Hall-coefficient changes signs as the temperature decreases, the Hall-coefficient of films thinner than 5.5 nm remains negative, suggesting a thickness-driven band structure modification. Moreover, X-ray absorption spectroscopy reveals the Ni-O hybridization nature in doped infinite-layer nickelates, and the hybridization is enhanced as the thickness decreases. Consistent with band structure calculations on the nickelate/SrTiO3 heterostructure, the interface and strain effect induce a dominating electron-like band in the ultrathin film, thus causing the sign-change of the Hall-coefficient.

Polarized phonons carry angular momentum in ultrafast demagnetization.

Magnetic phenomena are ubiquitous in nature and indispensable for modern science and technology, but it is notoriously difficult to change the magnetic order of a material in a rapid way. However, if a thin nickel film is subjected to ultrashort laser pulses, it loses its magnetic order almost completely within femtosecondtimescales1. This phenomenon is widespread2-7 and offers opportunities for rapid information processing8-11 or ultrafast spintronics at frequencies approaching those of light8,9,12. Consequently, the physics of ultrafast demagnetization is central to modern materials research1-7,13-28, but a crucial question has remained elusive: if a material loses its magnetization within mere femtoseconds, where is the missing angular momentum in sucha short time? Here we use ultrafast electron diffraction to reveal in nickel an almost instantaneous, long-lasting, non-equilibrium population of anisotropic high-frequency phonons that appear within 150-750 fs. The anisotropy plane is perpendicular to the direction of the initial magnetization and the atomic oscillation amplitude is 2 pm. We explain these observations by means of circularly polarized phonons that quickly absorb the angular momentum of the spin system before macroscopic sample rotation. The time that is needed for demagnetization is related to the time it takes to accelerate the atoms. These results provide an atomistic picture of the Einstein-de Haas effect and signify the general importance of polarized phonons for non-equilibrium dynamics and phase transitions.

Iodide-induced galvanic replacement of nickel film on copper as activator for electroless nickel-phosphorus plating

Galvanic replacement provides a convenient route to synthesize metallic films and nanostructures. However, metals commonly reduce more noble metal ions. In this work, nickel film was deposited on copper through an iodide-assisted galvanic replacement method. It was found copper had a lower electrode potential than nickel in high concentration of iodide solution, so nickel film could be obtained through the unusual galvanic replacement. The experimental results revealed increasing iodide concentration was conducive to the galvanic replacement rate between copper and nickel ions, and complete nickel film could be obtained in solution with 1200 g·L−1 sodium iodide in 10 min. The as-prepared nickel film showed good activation ability for electroless nickel-phosphorus plating, for the nickel-phosphorus coatings obtained on the nickel and traditional palladium films possessed similar morphology, structure and corrosion resistance.

Atomic-scale observation of spontaneous hole doping and concomitant lattice instabilities in strained nickelate films

Thin oxide films are of vast opportunities for modern electronics and can facilitate emergent phenomena by factors absent in the bulk counterparts, such as the ubiquitous epitaxial strain and interfacial charge doping. Here, we demonstrate the twisting of intended bulk-metallic phases in 10-unit-cell LaNiO3, PrNiO3, and NdNiO3 films on (001)-oriented SrTiO3 into distinct charge-lattice entangled states by epitaxial strains. Using atomically-resolved electron microscopy and spectroscopy, the interfacial electron doping into SrTiO3 in the conventional context of band alignments are discounted. Instead, spontaneously doped holes that are localized and at the order of 1013 cm−2 are atomically unraveled across all three heterointerfaces and associated with strain mitigations by the accompanied atomic intermixing with various ionic radii. The epitaxial strains also lead to condensations of monoclinic-C2/c lattice instabilities, which are hidden to the bulk phase diagram. The group-theoretical analysis of characteristic transition pathways unveils the strain resurrection of the hidden C2/c symmetry. While this strain-induced monoclinic phase in LaNiO3 remains metallic at room temperature, those in PrNiO3 and NdNiO3 turn out to be insulating. Such strain-induced monoclinic lattice instabilities and parasitic localized holes go beyond the classical elastic deformations of films upon epitaxial strains and hint on plausible hidden orders in versatile oxide heterostructures with unexpected properties, of which the exploration is only at the infancy and full of potentials.

Optical characteristics of LaNiO3 thin films in the terahertz–infrared frequency range

Transparent semiconducting oxides are widely used as conductive electrodes in optoelectronic devices in the near-infrared and visible ranges. However, their applications in the THz frequency range devices are limited because of the absorption by free carriers in this range and the low-frequency tail of the optical phonon modes. In this study, we investigated the optical and electrodynamic parameters of lanthanum nickelate films using contactless and nondestructive methods, including submillimeter coherent spectroscopy, terahertz pulsed spectroscopy, and infrared Fourier transform spectroscopy. Evidently, the film transmission deviates from the Hagen–Rubens relation by as much as 30%, and the temperature dependence of the conductivity exhibits a dominantly semiconducting behavior. A decrease in the plasma frequency of the free carriers to approximately 2000 cm−1 (0.25 eV) increases the intensity of the vibrational absorption bands of the film. Further, films with a reduced conductivity and a thickness of 100–200 nm are expected to transmit at least half of the incident radiation in the THz range. These results demonstrate the prospect of employing lanthanum nickelate films with decreased conductivity as electrode layers in optoelectronic converters in the THz frequency range.

A study on wafer scalable, industrially applicable CNT based nanocomposites of Al-CNT, Cu-CNT, Ti-CNT, and Ni-CNT as thermal interface materials synthesised by thin film techniques

Heat dissipation is one of the major factors that inhibit the miniaturisation of electronic components. Thermal interface materials (TIMs) that dissipate heat help in improving device performance. Commercially available conformal TIMs such as indium foils, thermal pads, polymer matrix with thermal conductive films are not very useful in heat transfer due to low thermal conductivity and high thermal expansion coefficient. This research focuses on developing novel thin-film nanocomposites consisting of Carbon nanotubes (CNTs) as TIMs. CNTs based nanocomposites behave as nano fins for heat dissipation. CNTs that are almost vertically aligned are deposited on silicon (Si) substrates using Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD). Metallic thin films of Aluminium, Copper, Titanium, and Nickel are sputtered using a Direct Current Magnetron target-based Physical Vapour Deposition on the CNT films to form a nanocomposite sandwich. The nanocomposite morphology is studied using SEM, structure using TEM, polycrystalline and elemental determination using XRD. The produced nanocomposite is modelled using Solid Works software, and thermal simulation of the same is performed using ANSYS. The equivalent thermal conductivity of Ni/CNT/Si, Al/CNT/Si, Cu/CNT/Si, and Ti/CNT/Si network is 1045.6 W/mK, 1120.8 W/mK, 886.56 W/mK and 463.6 W/mK when derived using mathematical modelling. The thermal conductivity values after experimentation for CNT/Si, Al/CNT/Si, Cu/CNT/Si, Ti/CNT/Si and Ni/CNT/Si nanocomposites were found to be 255–282 W/mK, 52–15 W/mK, 195–236 W/mK, 15–20.5 W/mK and 7.7–9.1 W/mK, respectively.

Universal spin-glass behaviour in bulk LaNiO2, PrNiO2 and NdNiO2

Motivated by the recent discovery of superconductivity in infinite-layer nickelate thin films, we report on a synthesis and magnetization study on bulk samples of the parent compounds RNiO2 (R = La, Pr, Nd). The frequency-dependent peaks of the alternating current magnetic susceptibility, along with remarkable memory effects, characterize spin-glass states. Furthermore, various phenomenological parameters via different spin glass models show strong similarity within these three compounds as well as with other rare-earth metal nickelates. The universal spin-glass behaviour distinguishes the nickelates from the parent compound CaCuO2 of cuprate superconductors, which has the same crystal structure and d 9 electronic configuration but undergoes a long-range antiferromagnetic order. Our investigations may indicate a distinctly different nature of magnetism and superconductivity in the bulk nickelates than in the cuprates.

The effect of thickness and deposition angle on structural, chemical and magnetic properties of nickel slanted columns

In this work, the influence of different deposition angles on the structural, chemical and magnetic properties of nickel (Ni) thin films was investigated. Nickel samples were deposited by glancing angle deposition technique at two different angles, 65o and 85o. Characterization of the thin films was carried out by scanning electron microscopy, X-ray photoelectron spectroscopy and magneto-optical Kerr effect microscopy. Structural analysis was found that the changes in the deposition angle have a great influence on the porosity of the film as well as on the amount of the present nickel oxide (NiO) in the samples. On the other hand, we have also found that different deposition angle changes the magnetic response of nickel film. The coercivity of the samples deposited at the angle of 85o is significantly higher compared to the samples deposited at lower angle which could be correlated with the higher porosity and the amount of NiO in the thin films.

Improvement of electric insulation in dielectric layered perovskite nickelate films via fluorination

Epitaxial films of La3/2Sr1/2NiOxFy with a wide range of fluorine content (y), 0.4–3, were prepared. The fluorinated film exhibited high electric insulation due to the large and random bond distortions provided by the fluorination.

Полупроводниковые свойства полимерных пленок на основе комплекса никеля с лигандом саленового типа

Complexes of metals with Schiff bases are considered as promising materials for creating energy storage and photovoltaic devices. In this work, the semiconducting properties of a polymer nickel film with a salen-type ligand (poly-Ni(CH3O-Salen)) were studied by spectrophotometric and Faraday impedance spectroscopy. The Mott-Schottky analysis showed that the polymer film is a semiconducting material with a fairly narrow band gap, high charge carrier density and p-type conductivity. Using the method of Faraday impedance spectroscopy, the limiting stage of the oxygen photoelectroreduction reaction, the process of charge transfer from the film to molecular oxygen, has been established.

Effect of Thiourea Containing Composite Additives on Nickel Electrodeposition in Ammoniacal Solution

Composite additives have an important influence on the process of metal electrodeposition and the quality of a metal deposited layer. In this work, the additive thiourea (TU) was compounded with cetyltrimethyl ammonium chloride (CTAC), sodium dodecyl sulfate (SDS) and polyethylene glycol 20,000 (PEG20000), and their effect on the cyclic voltammetric behavior, electrochemical nucleation mechanism, crystallographic orientations and surface morphology of the nickel electrodeposition in ammoniacal solution were experimentally investigated. The results show that the introduction of composite additives resulted in a stronger cathodic polarization and increased the nucleation overpotential (NOP) values significantly, which had an important impact on forming compact and smooth nickel deposits. The chronoamperometry analysis indicated that the reduction in nickel followed the 3D progressive nucleation mechanism in the presence of composite additives at the step potential of −1.16 V and −1.18 V. Smoother and finer nickel films were found using scanning electron microscopy (SEM) images as the composite additives were used. X-ray diffraction revealed that all nickel deposit samples had the face-centered cubic structure, and five main crystal planes were displayed by the presence of composite additives in the electrolyte. Furthermore, the diffraction peaks of (111) and (200) crystal planes were slightly shifted toward lower 2θ values when thiourea was used in combination with additive CTAC or PEG20000. These results were beneficial for understanding the mechanisms and facilitating the rational design of additives for metal nickel electrodeposition.

Spin dependent charge transfer in MoSe2/hBN/Ni hybrid structures

We present magneto-photoluminescence measurements in a hybrid two-dimensional semiconductor/ferromagnetic structure consisting of MoSe2/hBN/Ni. When the nickel layer is magnetized, we observe circularly polarized photoluminescence of the trion peak in the MoSe2 monolayer under linearly polarized excitation. This build-up of circular polarization can reach a measured value of about 4% when the magnetization of Ni is saturated perpendicularly to the sample plane and changes its sign when the magnetization is reversed. The circular polarization decreases when the hBN barrier thickness increases. These results are interpreted in terms of a spin-dependent charge transfer between the MoSe2 monolayer and the nickel film. The build-up of circular polarization is observed up to 120 K, mainly limited by the trion emission that vanishes with temperature.

A Nickelate Renaissance

The 2019 discovery of high temperature superconductivity in layered nickelate films, Nd1-xSrNiO2, has galvanized a community that has been studying nickelates for more than 30 years both as cuprate analogs and in their own right. On the surface, infinite layer nickelates, and their multilayer analogs, should be promising candidates based on our understanding of cuprates: square planar coordination and a parent d9 configuration that places a single hole in a dx2-y2 planar orbital makes nickelates seem poised for superconductivity. But creating crystals and films of sufficient quality of this d9 configuration in Ni1+ has proven to be a synthetic challenge, only recently overcome. These crystalline specimens are opening windows that shed new light on the cuprate-nickelate analogy and reveal nuances that leave the relationship between cuprates and nickelates very much an area open to debate. This Perspective gives a qualitative, phenomenological account of these newly discovered superconductors and multilayer members of the infinite layer nickelate family. The focus is on our current understanding of electronic and magnetic properties of these materials as well as some future opportunities, explored from the viewpoint of synthetic challenges and some suggested developments in materials discovery and growth to make further progress in this rejuvenated field.

Thermally grown oxide formation on Ni2Al3 aluminide coating: The effect of nanocrystalline nickel film on oxide scale adhesion

The Ni2Al3 coatings were prepared by aluminizing with and without nanocrystalline (NC) Ni film using the pack cementation process for 5 h at 620 °C. After oxidation at 900 °C, the results demonstrate that the alumina formed on two Ni2Al3 coatings composed of θ-Al2O3 on the basis of investigations of scanning electron microscopy (SEM), x-ray diffraction (XRD) and photo-stimulated luminescence spectroscopy (PSLS). The transmission electron microscopy (TEM) investigations combined with the electron diffraction pattern revealed that a small grain of α-Al2O3 nucleated on the Ni2Al3 coating with Ni film at the alumina scale/coating interface. Moreover, the Ni2Al3 coating with Ni film, in comparison to Ni2Al3 coating without Ni film control the size and density of the cavities formation at the scale/coating interface resulted in better adhesion of the alumina scale on aluminide.

Observation of Josephson-like Tunneling Junction Characteristics and Positive Magnetoresistance in Oxygen Deficient Nickelate Films of Nd0.8Sr0.2NiO3-δ.

Nickelate films have recently attracted broad attention due to the observation of superconductivity in the infinite layer phase of NdSrNiO (obtained by reducing Sr doped NdNiO films) and their similarity to the cuprates high temperature superconductors. Here, we report on the observation of a new type of transport in oxygen poor NdSrNiO films. At high temperatures, variable range hopping is observed while at low temperatures a novel tunneling behavior is found where a Josephson-like tunneling junction characteristic with serial resistance is revealed. We attribute this phenomenon to coupling between superconductive (S) surfaces of the grains in our Oxygen poor films via the insulating (I) grain boundaries, which yields SIS junctions in series with the normal (N) resistance of the grains themselves. The similarity of the observed conductance spectra to the tunneling junction characteristic with Josephson-like current is striking, and seems to support the existence of superconductivity in our samples.

Orbital and spin character of doped carriers in infinite-layer nickelates

The discovery of superconductivity in infinite-layer nickelate thin films has produced fervent theoretical research about the doping evolution of their electronic structure. Here, by means of x-ray spectroscopy and atomic multiplet calculations, the authors show that doped holes are mainly introduced in Ni sites in a spin-singlet configuration. The dominant role of the Ni 3${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ band implies that infinite-layer nickelates are likely a strongly correlated electronic system, reminiscent of their cuprate siblings.

Thermal Atomic Layer Etching of Nickel Using Sequential Chlorination and Ligand-Addition Reactions

The thermal atomic layer etching (ALE) of nickel was demonstrated using sequential chlorination and ligand-addition reactions. Nickel chlorination was achieved using SO2Cl2 (sulfuryl chloride) as the chlorine reactant. PMe3 (trimethylphosphine) was employed as the ligand-addition reactant. Sequential exposures of SO2Cl2 and PMe3 led to Ni thermal ALE. This procedure was inspired by the covalent bond classification (CBC) method that categorizes the most common compounds of various metals. Based on the CBC method, the surface reactions during thermal Ni ALE were performed to form NiX2L2 products, where Cl is the X ligand and PMe3 is the L ligand. Using this strategy, thermal Ni ALE was observed at temperatures from 75–200 °C. The etch rates were determined from in situ quartz crystal microbalance (QCM) measurements. The average etch rates determined from the mass changes were 0.14 ± 0.13, 0.57 ± 0.36, 0.67 ± 0.45, 1.30 ± 0.68, and 3.07 ± 1.56 Å/cycle for the temperatures 75, 100, 125, 150, and 175 °C, respectively. The QCM investigations revealed that there was a mass increase on every SO2Cl2 exposure and a mass loss on every PMe3 exposure, resulting in a net mass loss. The amount of chlorination for a given SO2Cl2 exposure increased with increasing temperature. The amount of mass lost on each PMe3 exposure also increased with increasing temperature. The etch rates were also confirmed using ex situ X-ray reflectivity measurements on Ni films on silicon wafers. The etch rates varied from 0.39 ± 0.10 Å/cycle at 125 °C to 2.16 ± 0.47 Å/cycle at 200 °C. Mass spectrometry analysis revealed that the volatile etch product was NiCl2(PMe3)2 as expected from the CBC method. In addition, scanning electron microscopy revealed that the nickel surface morphology had negligible changes after ALE. Atomic force microscopy analysis showed that thin nickel films remained smooth during initial etching and may experience some slight roughening with progressive etching. Using the CBC method to create novel thermal ALE procedures can be generalized for the thermal ALE of many different metals.

Providing a Specified Level of Electromagnetic Shielding with Nickel Thin Films Formed by DC Magnetron Sputtering

Nickel films of 4–250 nm thickness were produced by DC magnetron sputtering onto glass and silicon substrates. The electrical properties of the films were investigated by the four-probe method and the surface morphology of the films was studied by atomic force microscopy. To measure the shielding effectiveness, a portable closed stand based on horn antennas was used. A theoretical assessment of the shielding effectiveness of nickel films of various thickness under electromagnetic radiation of a range of frequencies was carried out using two different approximations. The results demonstrate the shielding effectiveness of up to 35 dB of the nickel thin films in the frequency range of 2–18 GHz.

Study of Copper-Nickel Nanoparticle Resistive Ink Compatible with Printed Copper Films for Power Electronics Applications.

This paper is focused on copper–nickel nanoparticle resistive inks compatible with thick printed copper (TPC) technology, which can be used for power substrate manufacturing instead of conventional metallization techniques. Two types of copper–nickel inks were prepared and deposited by Aerosol Jet technology. The first type of ink was based on copper and nickel nanoparticles with a ratio of 75:25, and the second type of ink consisted of copper–nickel alloy nanoparticles with a ratio of 55:45. The characterization of electrical parameters, microstructure, thermal analysis of prepared inks and study of the influence of copper–nickel content on electrical parameters are described in this paper. It was verified that ink with a copper–nickel ratio of 55:45 (based on constantan nanoparticles) is more appropriate for the production of resistors due to low sheet resistance ~1 Ω/square and low temperature coefficient of resistance ±100·10−6 K−1 values. Copper–nickel inks can be fired in a protective nitrogen atmosphere, which ensures compatibility with copper films. The compatibility of copper–nickel and copper films enables the production of integrated resistors directly on ceramics substrates of power electronics modules made by TPC technology.