Ni Layer Thickness Research Articles

Low-Temperature (400 °C) Synthesis of Multilayer Graphene by Metal-Assisted Sputtering Deposition.

Low-temperature synthesis of multilayer graphene (MLG) is essential for combining advanced electronic devices with carbon materials. We investigated the vapor-phase synthesis of MLG by sputtering deposition of C atoms on metal-coated insulators. Ni, Co, and Fe catalysts, which have high C solid solubility, enabled us to form MLG at 400 °C. The domain size and surface coverage of MLG were determined by the supplied amount of C atoms and the thickness of the metal layer associated with the solid solution amount of C. An average domain size of 2.5 μm and surface coverage of approximately 50% were obtained for a 1 μm thick Ni layer. Transmission electron microscopy demonstrated the high crystalline quality of the MLG layer despite the low processing temperature. Therefore, this simple sputtering technique has great potential for integrating graphene-based devices on various platforms.

PENGARUH ENERGI AKTIVASI LOGAM PELAPIS TERHADAP KETEBALAN DAN LAJU KOROSI PLATING

This study aims to study the effect of the activation energy gradient (∆G) of metals on the thickness and corrosion rate of Ni layers; Cr, and Ni-Cr. The layer is obtained through the Ni electroplating process; Cr, and Ni-Cr in carbon steel specimens using a variation of current strength of 1.25; 1.5 and 1.75 Ampere at constant stress and coating time (15 minutes). Nickel plating is obtained in the electric layer process using a watt's bath electrolyte solution in a mixture of 150 g / l NiSO4, 30 g / l NH4Cl, 30 g / l H3BO3 with a temperature of 25-35 oC, pH around 4-6, air agitation, Chromium plating using anode in the form of an alloy of Pb (lead) and Sn (antimony) rods, a solution in the form of an electrolyte mixture of 300 g / l CrO3, 3 g / l H2SO4 in working temperature of 40–55 oC, pH around 0.4 - 0.5 and air agitation. Corrosion thickness was observed using an optical microscope at 200 X magnification while the corrosion rate of observation was carried out based on the method of resistance polarization in the medium of 0.9% Sodium Chlorid Solution. The results showed that, in the same treatment, the thickness of the layer increased in increasing current strength, slower chromium than nickel layer and Nickel-Chromium layer. Sequential thickness of layers is obtained for Ni: 51, Cr: 39 layers, while corrosion rates occur at 1.75 A current in nickel layer 0.0017 mm / year; Chromium layer, 0.0077 mm /year and Nickel-Chromium layer 0.0231 mm / year

Unexpected Development of Perpendicular Magnetic Anisotropy in Ni/NiO Multilayers After Mild Thermal Annealing

We report on the significant enhancement of perpendicular magnetic anisotropy of Ni/NiO multilayers after mild annealing up to 90 min at 250 °C. Transmission electron microscopy shows that after annealing, a partial crystallization of the initially amorphous NiO layers occurs. This turns out to be the source of the anisotropy enhancement. Magnetic measurements reveal that even multilayers with Ni layers as thick as 7 nm, which in the as-deposited state showed in-plane anisotropy with square hysteresis loops, show reduced in-plane remanence after thermal treatment. Hysteresis loops recorded with the field in the normal-to-film-plane direction provide evidence for perpendicular magnetic anisotropy with up and down magnetic domains at remanence. A plot of effective uniaxial magnetic anisotropy constant times individual Ni layer thickness as a function of individual Ni layer thickness shows a large change in the slope of the data attributed to a drastic change of volume anisotropy. Surface anisotropy showed a small decrease because of some layer roughening introduced by annealing.

Thickness effects of Ni on the modified boron doped diamond by thermal catalytic etching for non-enzymatic glucose sensing

Sputtered nickel (Ni) layers modified boron-doped diamond (BDD) electrodes for non-enzymatic glucose sensor were fabricated by the thermal catalytic etching process in the hydrogen ambient. The effect of Ni thickness on the thermal catalytic etching and the electrochemical behavior of Ni/BDD electrodes for glucose oxidation were investigated. Scanning electron microscopy(SEM)and Raman spectroscopy were utilized to characterize the electrode morphology and composition, respectively. Marked by different thickness and morphology of Ni layer, three kinds of surfaces were obtained after thermal catalytic etching. The first is a roughened surface with most Ni nano-particles sinking into the BDD film, the second is with Ni micro-particles presented on the BDD film, the third is with residual lamellar Ni. Electrochemical results indicated that the electrochemical behaviors of those Ni/BDD electrodes were related to the surface structure. The second Ni/BDD electrode has the limit of detection (LOD) of 1.23μM with a sensitivity of 839.3μAmM−1cm−2, which was ascribed to the numerous agglomerated Ni nano- and micro-particles presented on the roughed surface.

Large nucleation barrier for Ni oxide on Rh(110) driving Ni into subsurface sites upon oxidation

The behavior of ultrathin layers of nickel (0.5 ≤ θNi ≤ 1.4 monolayers (ML)) on Rh(110) has been studied in oxidation/reduction experiments with O2 and H2 at T = 770 K. The reaction has been followed with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning photoelectron microscopy (SPEM). The adsorption of oxygen leads to a large decrease (up to 90%) of the Ni signal in AES. Subsequent titration with hydrogen restores nearly the initial Ni signal. The peculiar behavior of Ni on Rh(110) upon O2 adsorption is attributed to a large nucleation barrier for Ni oxide formation on Rh(110). This barrier leads to the preferential formation of chemisorbed oxygen on Rh sites forcing Ni into subsurface sites. SPEM reveals that also small NiO particles with a diameter of ≈1 µm develop during O2 adsorption. For comparison, a Rh(110) surface with a thick Ni layer of an estimated thickness of about 8–9 ML has been prepared. On this thick Ni layer Ni oxide develops spontaneously during O2 adsorption in the in 10−6 mbar range at T = 770 K.

Oscillatory Giant Magnetoresistance of Electrodeposited Fe/Cu/Ni Multilayered Structures—Effect of Non-Magnetic and Magnetic Layer Thicknesses

Giant magnetoresistance (GMR) behavior in electrodeposited N[Fe/Cu/Ni] multilayered (ML) structures is investigated as a function of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers’ thicknesses. Detailed structural and magnetic analyses of the ML structures are studied before looking into the GMR behavior. Structural analyses reveal that all peaks are well matched with Ni (face-centered cubic) being the top most layer during ML deposition. Shifting of preferred orientation, between (220) and (111) planes, is observed with the thickest layer of copper spacer. Refined structural parameters are calculated and details of fittings are discussed with reference to layer thicknesses. Crystallite size, dislocation density, stacking fault probability, and strain all show oscillatory behavior with variation in thicknesses. Magnetic behavior shows strong dependence of magnetization on thickness of each layer. Saturation magnetization ( $M_{s})$ increases up to a value of 10.12 emu/cm3 with increasing Fe and Ni layer thicknesses. Whereas, oscillatory behavior of magnetization is observed with variation in Cu layer thickness. Magnetoresistance (MR) measurements show oscillatory GMR behavior as a function of intervening layer thickness. Highest value of GMR ~12% is observed at a Cu layer thickness of 9.6 nm. Structural, magnetic, and MR properties of N[Fe/Cu/Fe] are observed on the basis of variation of thicknesses of non-magnetic (Cu) and ferromagnetic (Fe and Ni) layers. It is observed that layer thicknesses play a dominant effect on the nature (i.e., oscillatory) and on the value of GMR.

Enhancement of shear stability of a Fe-based amorphous alloy using electrodeposited Ni layers

Tensile and fracture behaviors of sandwich-structured composites consisting of a Fe-based amorphous layer with a constant thickness and ultrafine-grained Ni layers with different thicknesses were investigated. The results indicate that the initiation and the stable propagation of the shear band in the amorphous layer was dominated by the Ni layers due to their strong constraint role. The catastrophic fracture of the amorphous layer was postponed in the sandwich composites through properly increasing the constrained Ni layer thickness, which effectively decreased the shear stress on the shear fracture planes of the amorphous layer, and thus led to stable propagation of the primary SB characterized by the increase in the smooth region size of the shear band.

Improving the Efficiency of AlGaN Deep‐UV LEDs by Using Highly Reflective Ni/Al p‐Type Electrodes

AlGaN‐based deep‐ultraviolet light‐emitting diodes (DUV LEDs) have a wide range of applications and a large market is expected. However, the efficiency of DUV LEDs is still much lower than that of blue LEDs due to the quite low light‐extraction efficiency (LEE). We are developing high LEE DUV LEDs by introducing a transparent contact layer and a highly reflective Ni/Al p‐type electrode. In this work, we investigate optimization of the Ni layer thickness of the highly reflective Ni/Al p‐type electrode for AlGaN DUV LEDs. We find that the reflectivity in the UV region becomes higher as the thickness of the Ni layer becomes smaller; however, the external quantum efficiency (EQE) is reduced if the Ni layer is too thin (<0.8 nm). As a result, we find that the most appropriate Ni thickness for the Ni/Al electrode is 0.9 nm. We fabricate 279 nm AlGaN quantum well (QW) DUV LEDs with the optimized electrodes and demonstrate an enhancement in EQE by a factor of 1.8 and a maximum EQE of 9% under bare wafer measurement conditions. We also demonstrate a high output power of 33 mW under an injection current of 100 mA.

Sign Reversal of Fieldlike Spin-Orbit Torque in an Ultrathin Cr/Ni Bilayer

In this work report unconventional sign change of field like spin orbit torque in ultra-thin Chromium(1.5nm-5nm)/Nickel(8nm) bi-layer. We performed standard spin-torque ferromagnetic resonance (ST-FMR) experiment in Cr/Ni bi-layer by passing radio frequency current and measuring DC voltage. We observe that when thickness of Cr layer is critically low (<6nm) spin orbit torque by Cr on Ni significantly increases. Most importantly the sign of field like torque is opposite to the Oersted field generated torque. To verify interracial nature of this torque, 2 nm thin Cu is inserted between Cr and Ni and field like torque behaves same as Oersted field induced torque. Hence possible origin of such unconventional sign change of field like torque could be inter-facial Rashba like spin orbit interaction which is present between Cr and Ni but vanishes in Cr/Cu/Ni hetero-structure. From our experiment we can estimate that approximately 35 Oe of effective Rashba like magnetic field is created on 8 nm thicker Ni layer, when 1E12 A/m^2 current flows through Cr layer. All experiments are done at room temperature. So Cr thin film is expected to behave like paramagnet (Neel temperature of bulk Cr is 311K). Hence Cr can be a good choice as a heavy metal to employ large spin orbit torque combining bulk spin Hall effect and inter-facial Rashba interaction.

Superconductivity in Bi/Ni bilayer system: Clear role of superconducting phases found at Bi/Ni interface

Bi/Ni bilayers with varying Bi and Ni layer thicknesses have been prepared by (a) pulsed-laser deposition (PLD) at 300 K and (b) thermal evaporation at 4.2 K. A two-step superconducting transition appears on the electrical transport measurements in the samples prepared by PLD. High-resolution transmission and scanning transmission electron microscopy, supported by energy-dispersive x-ray spectroscopy (EDXS) analysis, reveal that two superconducting intermetallic alloys, namely NiBi and ${\mathrm{NiBi}}_{3}$, are formed by interdiffusion, if the bilayers are prepared at 300 K. The ${T}_{c}$ of the two phases behaves very differently in an external magnetic field and the upper critical magnetic fields at zero temperature $[{\mathrm{B}}_{c2}(0)]$ were estimated as 1.1 and 7.4 T, respectively. The lower value corresponds to the ${\mathrm{B}}_{c2}$(0) of ${\mathrm{NiBi}}_{3}$ phase and the higher one is supposed to be of NiBi. These alloys are responsible for the superconductivity and the two-step transition appearing in the Bi/Ni bilayer system. Surprisingly, the Bi-rich phase (${\mathrm{NiBi}}_{3}$) is formed near the Ni layer, while the Ni-rich phase (NiBi) is formed far from the Ni layer. The EDXS analysis at nanometer scale clearly shows an unusual increase of Ni concentration near the interface of Bi/substrate. The limited thickness of Bi layer in the interdiffusion process results in an unexpected distribution of Ni concentration. Samples prepared at 4.2 K after annealing at 300 K do not show any superconductivity, which indicates that a nonepitaxial Bi/Ni interface does not induce superconductivity in the case interdiffusion does not occur. These results offer a deeper understanding of the superconductivity in the Bi/Ni bilayer system.

Nickel-Encapsulated Carbon Nanotubes Modified Boron Doped Diamond Hybrid Electrode for Non-Enzymatic Glucose Sensing

A hybrid non-enzymatic glucose sensor made by incorporating boron doped diamond (BDD) film electrode with nickel (Ni)- encapsulated carbon nanotubes (CNTs) were facilely fabricated. The CNTs were grown directly on BDD films in the presence of pre-sputtered Ni layer as a catalyst by hot-filament chemical vapor deposition. The morphology and composition of the hybrid structure were assessed by scanning electron microscopy and Raman spectroscopy. As Ni layer thickness increased, the CNTs were less covered on the surface and the length of CNTs increased. The Ni particles were encapsulated into a large number of CNTs. Electrochemical results indicated that this hybrid structure significantly improved the electrochemical performance of BDD due to the increased specific surface area and synergistic effect of Ni and CNTs. The optimized glucose sensor revealed two broad linear range of 1.25 μM - 0.49 mM and 0.49 mM- 6.79 mM, with a high sensitivity of 1642.20 μA mM−1 cm−2 (R2 = 0.9988) and 1374.4 μA mM−1 cm−2 (R2 = 0.9969) respectively. In addition, the hybrid electrode exhibited a low limit of detection which was 1.0 μM (S/N = 3), and good selectivity and stability.

Onset of magnetic order in multilayers of Fe and Ni on and embedded in fcc-Cu(100) substrates

We investigate magnetic correlations and local magnetic moments at finite temperatures in some Fe and Ni multilayers on and embedded in Cu(100). Our study is based on a mean-field theory of magnetic fluctuations for layered materials within the first-principles local spin-density functional theory. We find that although there is no significant local moments formation in the Ni layers, the Ni layers are not magnetically dead in the sense that they mediate magnetic interactions between Fe layers separated by Ni layers. The Curie temperature of FenNim/Cu(100) and NinFem/Cu(100) films is almost independent of the Ni layer thickness, however, in Fe1NinFe1/Cu(100) and Fe1CunFe1/Cu(100) films, the Curie temperature exhibits an interesting oscillatory behaviour as the spacer layer thickness is increased. We show that there is a connection between this behaviour and the spin-reorientation transition observed in some Ni films. In the Ni1FenNi1/Cu(100) and Cu1Fen/Cu(100) films we found that the nature and strength of the magnetic correlations depends upon the Fe layer thickness.

Spin currents during ultrafast demagnetization of ferromagnetic bilayers

Ultrafast spin currents induced by femtosecond laser excitation of ferromagnetic metals have been found to contribute to sub-picosecond demagnetization, and to cause a transient enhancement of the magnetization of the bottom Fe layer in a Ni/Ru/Fe layered structure. We analyze the ultrafast magnetization dynamics in such layered structures by element- and femtosecond time-resolved x-ray magnetic circular dichroism, for different Ni and Fe layer thicknesses, Ru and Ta interlayers, and by varying the pump laser fluence. While we do not observe the transient enhancement of the magnetization in Ni/Ru/Fe discovered previously, we do find a reduced demagnetization of the Fe layer compared to a Ni/Ta/Fe layered structure. In the latter, the spin-scattering Ta layer suppresses spin currents from the Ni layer into Fe, consistent with previous results. Any spin current arriving in the lower Fe layer will counteract other, local demagnetization mechanisms such as phonon-mediated spin-flip scattering. We find by increasing the Ni and Fe layer thicknesses in Ni/Ru/Fe a decreasing effect of spin currents on the buried Fe layer, consistent with a mean free path of the laser-induced spin currents of just a few nm. Our results suggest that in order to utilize ultrafast spin currents in an efficient manner, the sample design has to be optimized with these considerations in mind, and further studies clarifying the role of interfaces in the employed layered structures are needed.

Magnetic Anisotropy and Damping for Monolayer-Controlled Co | Ni Epitaxial Multilayer

Structures and magnetic properties were systematically investigated for the monolayer (ML)-controlled Co | Ni multilayers with various Ni layer thicknesses, where the Co and Ni layers were epitaxially grown on a Al2O3 (\(11\bar{2}0\)) single crystal substrate or deposited on a thermally oxidized Si substrate. The epitaxial Co | Ni multilayers exhibited high uniaxial magnetic anisotropy energies (Ku) and low effective magnetic damping constants (αeff), resulting in the perpendicular magnetization with low damping even for the 1 ML-Ni | 1 ML-Co multilayer. By comparing the experimental results with the first principles calculation, we found that the Ni atoms largely contributed to the perpendicular anisotropy for the Co | Ni multilayers. We also discussed the possible mechanism dominating the magnitude of αeff for the Co | Ni multilayers based on the experiments and the calculations. The present results suggest that the epitaxial Co | Ni multilayer is a promising material to achieve high Ku and low magnetic...

Nickel/sulfur composite electroplated nickel foams for the use as 3D cathode in lithium/sulfur batteries – A proof of concept

In this work, a composite electroplating method of manufacturing organic binder and conductive carbon free electrode materials is applied on nickel foam substrates, used as 3D current collector. Thereby, sulfur particles (d50 = 24µm) are functionalized with polythiophene (layer thickness 100–200nm) and brought to the surface of the nickel foam by means of composite electroplating while using nickel as a mechanically stable and electrically well conducting binding matrix for sulfur (Ni layer thickness around the sulfur particles < 1µm). Therefore, organic nonconducting binders such as PVDF and conducting additives such as carbon are redundant. The method of composite electroplating ensures high sulfur loading with additional surface structuring, while keeping all pores accessible to the battery electrolyte. The naturally high surface of the metal foam is thereby further increased, which helps to decrease local current densities in the battery application. Cross-section SEM micrographs and CT images show that the functionalized sulfur particles are uniformly and densely distributed throughout the nickel foam. A battery capacity of about 300mAhg−1sulfur over 100 cycles at a current density of 1mAcm−2 (0.167C) for a cathode containing 3.57mgcm−2 sulfur is achieved. With an additional 50nm thin NiSx alloy coating, the utilization of sulfur is improved by 250–300% (a battery capacity of about 800mAhg−1sulfur over 100 cycles at a current density of 1mAcm−2 (0.162C) for a cathode containing 3.68mgcm−2 sulfur is achieved). Furthermore, a high reversibility and rate capability is found when cycled between 0.1 and 1C, respectively. A stable coulombic efficiency of about 100% is achieved.

Structural dynamics during laser-induced ultrafast demagnetization

The mechanism underlying femtosecond laser pulse induced ultrafast magnetization dynamics remains elusive despite two decades of intense research on this phenomenon. Most experiments focused so far on characterizing magnetization and charge carrier dynamics, while first direct measurements of structural dynamics during ultrafast demagnetization were reported only very recently. We here present our investigation of the infrared laser pulse induced ultrafast demagnetization process in a thin Ni film, which characterizes simultaneously magnetization and structural dynamics. This is achieved by employing femtosecond time resolved X-ray resonant magnetic reflectivity (tr-XRMR) as probe technique. The experimental results reveal unambiguously that the sub-picosecond magnetization quenching is accompanied by strong changes in non-magnetic X-ray reflectivity. These changes vary with reflection angle and changes up to 30$\%$ have been observed. Modeling the X-ray reflectivity of the investigated thin film, we can reproduce these changes by a variation of the apparent Ni layer thickness of up to 1$\%$. Extending these simulations to larger incidence angles we show that tr-XRMR can be employed to discriminate experimentally between currently discussed models describing the ultrafast demagnetization phenomenon.

Tuning the coercivity of Cu/Ni multilayer nanowire arrays by tailoring multiple parameters

Cu/Ni multilayer nanowire arrays with well controlled diameters, Cu and Ni layer thickness and varying periodicity were fabricated by multi potential deposition technique in etched ion-track template at room temperature. A facile method was adopted to confirm the different layer thickness and corresponding component by only removing the Cu layer. The pure Ni and Cu layer were confirmed in the Cu/Ni multilayer nanowires by using the new method and XRD analysis. The relationships between the coercivity and nanowire diameter, layer thickness and periodicity were obtained by carrying out vibrating sample magnetometry (VSM) measurement. The results indicated that the coercivity of multilayer nanowire arrays can be tuned significantly by nanowire diameter, periodicity, Cu and Ni layer thickness. In order to explain the experimental phenomena, Pant's model was modified and adopted to successfully explain the variation of demagnetizing field in Cu/Ni multilayer nanowire arrays after tailoring multiple parameters.

Fast in situ X‐ray analysis of Ni silicide formation

Metal silicides are the preferred contact materials for metal‐oxide semiconductor (MOS) structures. With further technology development, the materials changed within the last decades toward lower resistivity and lower thermal budget. Currently NiSi partly further stabilized with Pt or Pd is the material of choice. The understanding of phase transformation processes and structural features is of great importance for production process optimization. Here we present a fast laboratory‐based in situ X‐ray diffraction method with two different experimental arrangements (Bragg–Brentano and grazing incidence) optimized concerning the materials texture. Its application is demonstrated for the transformation of Ni to different Ni silicide phases starting with a 46 nm thick Ni layer sputtered on a Si(001) substrate and covered with TiN. Activation energies for the Ni to Ni2Si (1.55 ± 0.13) eV and the Ni2Si to NiSi transition (1.30 ± 0.15) eV are measured by repeating fast diffraction scans over a limited angular range under isothermal conditions and analyzing the diffraction peak height versus time.

Formation of nickel germanides from Ni layers with thickness below 10 nm

The authors have studied the reaction between a Ge (100) substrate and thin layers of Ni ranging from 2 to 10 nm in thickness. The formation of metal-rich Ni5Ge3 was found to precede that of the monogermanide NiGe by means of real-time in situ x-ray diffraction during ramp-annealing and ex situ x-ray pole figure analyses for phase identification. The observed sequential growth of Ni5Ge3 and NiGe with such thin Ni layers is different from the previously reported simultaneous growth with thicker Ni layers. The phase transformation from Ni5Ge3 to NiGe was found to be nucleation-controlled for Ni thicknesses &amp;lt;5 nm, which is well supported by thermodynamic considerations. Specifically, the temperature for the NiGe formation increased with decreasing Ni (rather Ni5Ge3) thickness below 5 nm. In combination with sheet resistance measurement and microscopic surface inspection of samples annealed with a standard rapid thermal processing, the temperature range for achieving morphologically stable NiGe layers was identified for this standard annealing process. As expected, it was found to be strongly dependent on the initial Ni thickness.

In Ukrainian

Nanocomposite particles (NCP) structure of "core-shell" composition Ni @ C were obtained by the method of pyrolytic polymer-salt systems on the basis of phenol-formaldehyde and nickel acetate. It has been shown that nanoparticles (NPs) Ni is a single-domain, the magnetization curve is shaped NCP characteristic superparamagnets and its settlements within the framework of the theory of Langevin paramagnetism in satisfactory agreement with the experimental results. It found a method based on magnetic granulometry model "core-shell" that lognormal distributed Ni NP size and have an average diameter (5 - 8) nm. It was calculated the value of the low surface Ni layer thickness with non-collinear with respect to volume, the magnetic moments. Еnsembles surface depending on the specific saturation magnetization was found and the specific area NCP of the average thickness of the carbon shell.