Fe-Ni Alloy Films Research Articles

Electrodeposition of Fe-Ni Alloy Films having Invar Compositions with Fe3+ as the Sole Iron Source

Fe-Ni alloy films with invar alloy compositions were electrodeposited from a stable citrate bath containing trivalent iron ions (Fe3+) as the sole iron source. This bath was prepared based on determining the equilibrium constants for acid dissociation, complex formation and precipitation reactions. Electrodeposition was conducted under galvanostatic conditions at 25 °C without agitation and an investigation was carried out into the effects of pH and current density on the composition and microstructure of the films. The results showed that ferric hydroxide (Fe(OH)3), which is normally poorly soluble, did not precipitate after electrodeposition. Fe-Ni alloy films containing 31‒42 mass% Ni (including Fe-36 mass% Ni) were formed with a current efficiency of approximately 70%. The films were smooth and were made up of grains with sub-micron sizes, although some cracks were observed. Fe and Ni were distributed homogeneously throughout the films and the Fe-Ni solid solutions exhibited both face-centered cubic and body-centered cubic structures.

Fabrication of Large-Sized Invar Alloy Film with Low Thermal Expansion by Pulse Reverse Electrodeposition

Invar alloy film with low thermal expansion is a key substrate for high-resolution organic light-emitting diodes (OLEDs). The preparation of Invar alloy film by electrodeposition has attracted increasing attention due to its low cost and simple process. In this work, a large-sized (8 × 10 cm) uniform Fe-Ni alloy film was fabricated by pulse reverse electrodeposition. The effects of the electrodeposition parameters on the chemical composition and microstructure of Fe-Ni alloy films were investigated. Results showed that greater Ni2+/Fe2+ in the electrolyte, lower pulse frequency (f), smaller reverse pulse coefficient (x), and lower electrodeposition temperature (T) favored the iron content. The Invar alloy film (64 wt% Fe) was electrodeposited at T = 50 °C, x = 0.2, f = 10 Hz, and Ni2+/Fe2+ = 1.9 when the average pulse current density was 30 mA cm−2. The structure of the film was composed of a mixture of fcc and bcc phases, where (110) and (111) preferential orientations were predominant. After heat treatment in H2 at 800 °C for 120 min, the bcc phase transformed into the fcc phase, and the grain size increased (>2 μm). As a result, the coefficient of thermal expansion of the film decreased from 11 × 10−6 to 1.5 × 10−6/°C, which is close to the standard for commercial application.

Uniaxial in-plane magnetic anisotropy mechanism in Ni, Fe, and Ni-Fe alloy films deposited on single crystal Y-cut 128° LiNbO3 using magnetron sputtering

We investigated the mechanism of induced in-plane uniaxial magnetic anisotropy (Ku) in Nickel (Ni), Iron (Fe), and Ni-Fe alloy films deposited in situ on a single-crystal 128° Y-cut LiNbO3 (LNO) substrate at various substrate heating temperatures (Th) in the range 30–400 °C through radio frequency magnetron sputtering or co-sputtering. The results show that the Ku values for the Ni, Fe, and Ni-Fe alloy films are induced in the (01.2) or (21¯.0) planes of the LNO substrate. The highest value of Ku for the Ni films was observed at Th = 200 °C, which is owing to the increased orientation of the fcc Ni (311) plane. The Ni film with thickness t ∼ 20 nm deposited on the LNO substrate at Th = 200 °C possesses the highest value of Ku. Density functional theory calculations show that the magnetic anisotropic energy on the fcc Ni (311) plane differs depending on the magnetization direction in the in-plane direction in the model. Meanwhile, the value of Ku for the Fe films decreases with an increase in the value of Th because the films with higher Th are polycrystalline and have an oxide layer. The composition dependence of Ku for Ni-Fe alloy films at Th = 30 °C shows a trend similar to the crystal magnetic anisotropy for bulk Ni-Fe alloy. The induced Ku on LNO is attributed to the magnetostriction effect with the change in the crystal orientation of the ferromagnetic metal owing to a strain from the LNO substrate through the thermal expansion during sputtering. These results indicate the origin of the induced Ku in the Ni and Fe based metallic material films deposited on the LNO substrate.

Magnetic Permeability of Co–Ni–Fe Alloy Films Obtained by Electrochemical Deposition

Magnetic Permeability of Co–Ni–Fe Alloy Films Obtained by Electrochemical Deposition

FeNi alloy films prepared by directional magnetic field assistance and their degradation and adsorption on azo dyes

Synthetic dyes in the aquatic environment caused various ecological and health problems that are detrimental to sustainable development. To solve these problems, we designed a dense Fe3Ni2 phase alloy film (FeNi-M) on copper substrate by the directional magnetic field-assisted wet chemical film formation method. The degradation and adsorption of Congo red (CR) in water were achieved by using the surface activity of the film. The degradation rate of FeNi-M alloy film reached 99.5% at 48 h and the kobs is 0.10982 h−1, which is 2.1 and 7.5 times of FeNi alloy film (0.05147 h−1) and Ni film （0.01465 h−1）, respectively. The degradation processes of all three films were in accordance with the pseudo-first-order kinetic model. In addition, FeNi-M alloy films have excellent cycling performance with more than 90% removal rate after 5 cycles. We also discussed the possible degradation mechanism and pathway of CR. We speculated that the main part of alloy responsible for providing electrons were iron atoms and very few electrons were produced by nickel. However, nickel was beneficial to increase the activity of iron atoms and played a catalytic role, thereby greatly enhancing the efficiency of iron atoms on the reaction.

The influence of saccharin adsorption on NiFe alloy film growth mechanisms during electrodeposition.

This article deals with the effects of current modes on saccharin adsorption during NiFe electrodeposition, and, as a consequence, its effect on chemical composition, crystal structure, and microstructure of deposited films. For this purpose, we obtained NiFe films using direct, pulse, and pulse-reverse electrodeposition modes. The deposit composition, crystal structure, and surface microstructure are studied. Direct current (DC) and pulse current (PC) films have a smooth surface, while a pulse-reverse current (PRC) film surface is covered by a volumetric cauliflower-like microstructure. The mechanism of the film surface development was considered from the point of view of saccharin adsorption and its action as an inhibitor of vertical grain growth during different current modes. During the DC and PC modes, saccharin is freely adsorbed on the growth centers and restrains their vertical growth. Whereas in the case of the PRC electrodeposition, saccharin adsorbs during cathodic pulses and desorbs during anodic pulses. Therefore, its inhibiting action decreases, vertical grain growth rises, and a rougher surface develops.

(Invited) Highly Active OER Electrodes Derived from Fe-Doped Ni Oxyfluoride Formed by Anodizing of NiFe Electrodeposits

Because of the limited availability of fossil fuels and pertinent global environmental issues, hydrogen production via electrochemical water splitting using renewable resources is an important alternative for future energy economies. For efficient alkaline water electrolysis to produce hydrogen, we need to develop highly active and durable electrocatalysts, particularly for oxygen evolution reaction (OER) because of high overpotential. Anodizing of metals and alloys is a promising means of directly fabricating an OER electrocatalyst on a metallic current collector. Binder-free electrocatalysts are readily formed by anodizing. Since Fe-doped Ni oxyhydroxides and hydroxides are recently reported as highly active OER electrocatalysts in alkaline media. Here, we report anodizing of NiFe electrodeposits in fluoride-containing ethylene glycol electrolyte and the conversion of resultant nanoporous Fe-doped Ni oxyfluoride to highly OER active hydroxide during OER (1).NiFe alloy films containing 7.2 – 21.1 at% Fe were obtained by electrodeposition on Ni substrate. Then, the alloys were anodized at 10 V in ethylene glycol electrolyte containing ammonium fluoride and water. The anodizing developed a porous layer consisting of crystalline NiF2 phase. XPS analysis revealed the presence of Fe and O as well as Ni and Fe. Thus, porous Fe-doped Ni oxyfluoride was developed by anodizing. The as-anodized NiFe alloys were initially less active for OER in 1.0 mol dm-3 KOH, but during potential cycling to OER potential, the OER activity was gradually enhanced. The enhancement was dependent upon Fe content, and the highest activity was obtained for the Ni-11.8 at% Fe. After activation, the porous layer was converted to amorphous hydroxide, and the fluoride content was highly reduced. Thus, anodically formed Fe-doped oxyfluoride on the NiFe electrodeposits is a suitable precursor of highly active OER electrocatalyst. The galvanostatic durability test exhibited the stable overpotential, disclosing the high durability of this electrocatalyst.Reference N. Yamada, S. Kitano, Y. Yato, D. Kowalski, Y. Aoki and H. Habazaki, ACS Applied Energy Materials, in press, doi.org/10.1021/acsaem.0c02362.

Ni-based 3D hierarchical heterostructures achieved by selective electrodeposition as a bifunctional electrocatalyst for overall water splitting

The fabrication of efficient, cost-effective and stable bifunctional electrocatalysts for electrocatalytic water splitting is an important way of energy conversion and storage. In this work, ultrathin NiFe alloy layers are coated on the surface and the up-sidewalls of the Ni(Cu) nanotubes by a selective electrodeposition and used as a bifunctional electrocatalyst. Having a 3D honeycomb-like structure, superlarge ECSA of Ni(Cu)/NF and NiFe alloy films simultaneously fabricated on the surface of Ni foam, the NiFe@Ni(Cu)/NF catalyst shows a Pt-like performance in hydrogen evolution reaction and efficient oxygen evolution reaction activity in alkaline medium. The fabricated NiFe@Ni(Cu)/NF electrode delivers current densities of 10 mA cm−2 at overpotentials of merely 36 and 209 mV for HER and OER. Furthermore, the water electrolysis cell assembled with the as-prepared catalyst requires an energy input as low as 1.525 V to deliver 10 mA cm−2. The bifunctional NiFe@Ni(Cu)/NF also presents remarkable stability in alkaline solution with negligible degradation rate in potential. This study provides a new approach for rational design of hetero-hierarchical structures of bifunctional electrocatalysts for energy storage and conversion applications.

Microstructure Characterization of Electrodeposited Invar Fe–Ni Alloy

In Fe–Ni alloys, coefficients of thermal expansion (CTEs) of Fe–Ni alloys with 30 to 40 mass% Ni are small compared to that of Fe (CTE = 12 ppm/K) or Ni (CTE = 13 ppm/K) at near room temperature. In particular, the Fe–Ni alloys with 36 mass% Ni exhibit the lowest CTE (approximately 1 ppm/K) among the Fe–Ni alloys. These Fe–Ni alloys with 30 to 40 mass% Ni are called “Invar alloys.” An Fe–Ni alloy electroplating can be used as the high-throughput Invar alloy fabrication process, furthermore, an Fe–Ni alloy electroforming process can provide precise micrometer-sized three-dimensional structures of Invar alloys with excellent thermal dimensional stability, e.g., MEMS (microelectromechanical systems).We already have prepared electrodeposited Invar Fe–Ni alloys with 36 mass% Ni from plating baths containing saccharin as a stress reducer and containing Fe2+ and Ni2+ ions with various concentration ratios. The electrodeposited Invar Fe–Ni alloys contained of small amount of S (~0.02 mass%) which was originated from saccharin.It was confirmed that as-deposited Invar Fe–Ni alloys were mainly composed of metastable bcc phases, resulting in larger CTEs. When the alloys were annealed at 400°C or above, the equilibrium fcc phases became the predominant phases, accompanied by a drastic decrease of the CTEs. The bcc-to-fcc transformation led to a decrease of the CTEs.In general, electrodeposited fcc Ni and Ni-rich Fe–Ni alloys containing small amounts of S are often embrittled upon annealing. An S (sulfide) in the as-deposited fcc films is dispersed at grain boundaries (2). During recrystallization and grain growth of the fcc grains by heat treatment, the S (sulfide) is extruded into recrystallized an fcc grain boundary with segregating as a thin layer form. The S thin layer coats the fcc grain boundaries and causes grain boundary weakening; therefore, distinct embrittlement occurs, and the embrittlement is promoted by rapid grain growth during annealing (3).With respect to our electrodeposited Invar Fe–Ni alloys with S, in contrast, ductile behavior was confirmed, irrespective of whether the alloys were heat-treated. Upon heat treatment at 400 to 500°C, the Invar Fe–Ni alloys exhibited high strength with good ductility, consistent with their low CTE (1). Moreover, we observed that the S in the Invar Fe–Ni alloys heat-treated at 600°C existed not as a filmy sulfide but as a granular sulfide at grain boundaries. However, the microstructures containing the granular sulfide generated in the film during heat treatment have not been sufficiently explored.In this study, we investigated microstructure of the electrodeposited Invar alloys with and without heat treatment in detail. In particular, morphology and composition of the sulfide were evaluated in the Invar alloys with changing of microstrucutre during an annealing.A galvanostatic electrolysis was conducted for preparation of the Invar Fe–Ni alloy film with 36 mass% Ni from the plating bath (1).A transmission electron microscopy (TEM) was are used for microstructure characterization of the obtained films. A focused-ion-beam (FIB) system have given choice to fabricate cross-sectional TEM specimen.From the results of cross-sectional TEM observation of the electrodeposited Invar Fe- 36 mass%Ni alloys with and without heat treatment at 300 to 600°C, it was found that the as-deposited bcc electrodeposited Invar alloys exhibited a columnar microstructure composed of micrometer-sized coarse grains and submicrometer-sized grains.After the heat treatment at 300 to 400°C, where the proportion of fcc phase increased, the columnar structure became indistinct and the fraction of the submicrometer-sized fine grains increased. Furthermore, no substantial segregated sulfide was detected at the Fe–Ni alloy from elemental mapping by energy dispersive spectroscopy (EDS) in TEM.Heat treatment at 500°C led to grain growth; the alloys treated at this temperature were fully composed of the fcc phase, accompanied by a decrease in the CTE.Our TEM results suggest that S in the Invar Fe-36 mass%Ni alloy became highly concentration upon heat treatment at 500°C and formed granular Fe-rich Fe–Ni–S in grain-boundary triple-points.In our research, the formation of granular sulfide in the film after heat treatment at 500 ° C and its composition were confirmed for the first time.Upon heat treatment at 600°C, Fe-Ni matrix grains grew up as recrystallized grains, accompanied by grain growth of the Fe–Ni–S compound in the matrix grains or grain-boundary triple-points. T. Nagayama, T. Yamamoto and T. Nakamura, Electrochim. Acta, 205, 178 (2016). I. Tabakovic, S. Riemer, K. Tabakovic, M. Sun and M. Kief, J. Electrochem. Soc., 153, C586 (2006). Y. M. Wang, S. Cheng, Q. M. Wei, E. Ma, T. G. Nieh and A. Hamza, Scripta Mater., 51, 1023 (2004).

Epitaxial L1-FeNi films with high degree of order and large uniaxial magnetic anisotropy fabricated by denitriding FeNiN films

L10-orderd FeNi alloy films with a high degree of order (S) and a large uniaxial magnetic anisotropy energy (Ku) were realized by denitriding FeNiN films. FeNiN films with the a-axis perpendicular to the film plane were epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy by changing the growth temperatures (TS) to 200, 250, and 350 °C. The a-axis oriented epitaxial L10-FeNi films were fabricated by annealing the FeNiN films in a H2 gas atmosphere at 300 °C. S and Ku of the denitrided L10-FeNi films were characterized by anomalous x-ray diffraction using synchrotron radiation and magnetic torque measurements, respectively. A high S of 0.87 and a Ku of 5.9 × 105 J/m3 were realized in the L10-FeNi film with a TS of 350 °C. This high S value exceeds the values reported on L10-FeNi to date, but the Ku value was comparable to those of c-axis oriented L10-FeNi films with S ∼ 0.5 grown by alternate monoatomic deposition of Fe and Ni layers. A possible origin for the suppressed macroscopic Ku in a-axis oriented L10-FeNi films is discussed, and denitriding FeNiN is a promising method for the fabrication of L10-FeNi with a high S and a large Ku.

Measurement of hysteresis loop based on weak measurement.

In this Letter, we propose a technique for hysteresis loop measurement based on weak measurement. By using the photonic spin Hall effect (PSHE) as a probe and combining the quantum weak measurement, the technique's noise can be suppressed greatly. A theoretical model to describe the numerical relation between the amplified shift and Kerr rotation angle is established. Through detecting the amplified shift of the PSHE based on weak measurement, we experimentally measure the hysteresis loops of Ni-Fe alloy film, iron-phthalocyanine (FePc) monolayer film, and Co/FePc double-layer film. The results show that the precision can reach about $ \sim {10^{ - 6}} \;{\rm rad} $∼10-6rad under ordinary experimental conditions, which may have an important application prospect in magneto-optic parameters measurement.

Electrodeposition of Fe–Ni alloy on Au(111) substrate: Metastable BCC growth via hydrogen evolution and interactions

The electrodeposition of Fe–Ni alloy is usually complicated by the effects of anomalous codeposition and hydrogen evolution. Although the influence of the deposition conditions on the alloy composition has been studied extensively, very few works considered the influence of growth conditions on the phase constitution. In this work, various electrodeposition conditions were investigated to grow Fe–Ni alloy films (<30 nm) with similar compositions in the Invar-to-equiatomic range on Au (111) substrate. Highly (110) oriented BCC phase Fe–Ni with a Ni fraction (ca. 40 at.% Ni) well beyond the equilibrium solubility limit (5 at.% Ni) was obtained with a significant alloy deposition partial current. An increase in the fraction of the BCC phase was found to be associated with a higher alloy deposition partial current, but not necessarily with an increase in the hydrogen evolution partial current. Motivated by the findings from this work, the formation of the metastable BCC phase is speculated to depend on the competing kinetics between the inclusion and desorption of hydrogen adatoms at the electrodeposited growth front.

Electrochemical Deposition of NiFe Alloy Films of Chloride Electrolyte Containing Low Concentration of Basic Salts

Electrochemical Deposition of NiFe Alloy Films of Chloride Electrolyte Containing Low Concentration of Basic Salts

The Effect of a Substrate Material on Composition Gradients of Fe-Ni Films obtained by Electrodeposition

The electrodeposition of FeNi alloy films was performed galvanostatically in the sulfate solution (Fe2+/Ni2+ mass ratio 1:2) in order investigate their co-deposition mechanism. The FeNi layers were deposited at variable substrates (copper, brass, silver) under the same chemical (electrolyte composition) and electric plating (current density value) conditions. After applying various time, substrates and external magnetic field orientation, the quality of the obtained film was examined. The surface morphology and crystallographic texture variation were investigated by the Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Wavelength Dispersive X-ray Fluorescence (WDXRF) and Laser Confocal Scanning Microscope (LCSM). The anomalous co-deposition of iron group metals is evidently dependent on the substrate.

Electroplating and Characterization of Invar Fe–Ni Alloy Films from Plating Baths Containing Organic Acids

In Fe–Ni alloys, coefficients of thermal expansion (CTEs) of Fe–Ni alloys with 30 to 45 mass% Ni are small compared to that of Fe (CTE = 12 ppm/K) or Ni (CTE = 13 ppm/K) at near room temperature. In particular, the Fe–Ni alloy with 36 mass% Ni exhibits the lowest CTE (approximately 1 ppm/K) among the Fe–Ni alloys. These Fe-Ni alloys with 30 to 45 mass% Ni are called “Invar alloys.” The Fe–Ni alloy electroplating can allow lower cost of Invar alloy production compared with the conventional rolling process. Furthermore, the electroforming process can provide precise micrometer-sized three-dimensional structures of Invar alloys with excellent thermal dimensional stability, e.g., MEMS (microelectromechanical systems). An acidic Fe–Ni alloy electroplating bath usually contains an organic acid, which acts as a masking agent for Fe3+ generated via electrochemical and air oxidation and pH buffer agent. However, it is known that an organic additive addition often effects on properties, e.g. internal stress in the Fe–Ni alloy electroplated films. For MEMS applications in particular, internal stress should be minimized. So far, the internal stresses in the electroplated Fe–Ni alloy films in the Invar composition range obtained from the alloy plating baths containing various organic acids have not been studied in detail. In this study, we investigated the influence of the type of organic acid added to the alloy plating bath on composition, current efficiency and internal stress in the Fe–Ni alloy films electroplated from various Fe2+ concentration baths. Electroplating of the Fe–Ni alloy was carried out using sulfate/chloride bath (modified Watts-type Ni plating bath) with additives at a current density of 40 mA/cm2. Bath compositions were as follows: FeSO4 (0 to 0.4 mol/L), NiSO4 (0.95 mol/L), NiCl2 (0.17 mol/L), boric acid (0.49 mol/L), sodium saccharin (0.008 mol/L) and organic acid (0.05 mol/L). Organic acids were selected based on the stability constant (log KMA) of the complex with Fe3+: tartaric acid (log KMA = 6.49), malonic acid (log KMA = 7.52), or citric acid (log KMA = 11.5). The bath temperature was maintained at 50 °C and the bath pH was adjusted to pH 2.5. Pure Ni sheets were used as anodes. Internal stress in the films was estimated by the bending strip method using a Cu–Be foil as a substrate, and the value of internal stress was calculated based on Stoney’s equation. The composition of the electroplated Fe–Ni alloy film was determined by the fundamental parameter method. Regardless of the presence or absence of an organic acid, the Fe content in the electroplated Fe–Ni alloy film increased with the increase in the concentration of Fe2+ in the plating bath, and at the Fe2+ concentration of 0.3 to 0.4 mol/L, Fe–Ni alloy electroplated film with a Ni content of 30 to 45 mass%, in the Invar composition range, was obtained. Without addition of an organic acid, current efficiency showed high efficiency of 95 % or more at any Fe2+ concentration. In contrast, the current efficiency decreased to approximately 90 % due to the addition of the organic acid. Citric acid added bath exhibited lower current efficiency than those form baths with tartaric acid or malonic acid at the Fe2+ concentration of 0.3 to 0.4 mol/L. The decrease in the current efficiency in the Fe–Ni alloy plating reaction was related to hydrogen evolution as a side reaction. Organic acids promoted hydrogen evolution during Fe–Ni alloy plating reaction. Citric acid most promoted hydrogen evolution at 0.3 to 0.4 mol/L of Fe2+ to obtain an Invar Fe–Ni alloy electroplated film. Without addition of saccharin, micro cracks occurred in the Invar Fe–Ni alloy electroplated films because the films generated very large internal stresses (tensile). Addition of tartaric acid or malonic acid to Fe–Ni alloy plating bath including saccharin kept the internal stress in Invar Fe–Ni alloy electroplated film relatively low (tensile, approximately 200 MPa), and furthermore, may prevent a decrease in toughness of the film by masking Fe3+. Consequently, these optimized Invar plating baths can be used for MEMS electroforming. In contrast, due to the addition of citric acid to form a more stable complex with Fe3+, internal stresses in the Invar Fe-Ni alloy electroplated films became very high (tensile, 300 MPa or more) and micro cracks occurred in the films; it was difficult to provide the obtained films as MEMS materials. It is expected that the internal stress behavior in the Invar electroplated films depending on the type of organic acid added to bath will be related to hydrogen evolution and impurity incorporation to the film during the Invar electroplating.

Preparation and Characterization of Electroless Deposited Fe-Ni Alloy Films

The higher reliability of high-density packaging for electronic devices is considered to be the issue to achieve the sustainable semiconductor manufacturing. Fe–Ni alloy thin films exhibit an excellent wettability and a low reaction rate with lead-free solders compared with Ni thin films [1]. The Fe–Ni alloy films are thus promising as a highly reliable metallize material for semiconductor packaging. An electroless Fe-Ni alloy plating process is of current interest because it is also possible to form films metallized on non-conductive material such as an insulating substrate. Pyrometallurgically produced Fe-Ni alloys with 55 to 70 wt% Fe contents exhibited low coefficients of thermal expansion (CTEs) and are termed “Invar alloys” [2]. Therefore, electroless deposited Fe-Ni alloy films can be also expected to have a low CTE comparable with those of semiconductor and insulating substrates used in power semiconductor devices. We have prepared Fe–Ni–Boron (B) alloy thin films by using the electroless plating method, and their thermal-expansion properties have been evaluated [3]. The CTE of electroless deposited Ni–5wt%B alloy film was approximately 13 ppm/K, while those of the electroless deposited Fe–Ni–B alloy films with an Fe content of 55 and 64 wt% in the Invar composition range exhibited lower CTEs, approximately 8 ppm/K, than that of a conventional electroless deposited Ni film [3]. So far, stress generations in the electroless deposited Fe–Ni–B alloy films associated with those microstructure have not been studied extensively despite their importance in high-density package reliability. In this study, we produced a variety of electroless deposited Fe–Ni–B alloy films with different amounts of Fe/Ni ratio and investigated the internal stress in the alloy films. The electroless Fe–Ni alloy plating bath compositions were as follows: FeSO4 ·7H2O 0 to 0.02 mol/L, NiSO4·6H2O 0.03 to 0.05 mol/L, Tri-potassium citrate monohydrate 0.1 mol/L, Potassium pyrophosphoric 0.005 mol/L, and dimethylamine borane 0.025 mol/L as the reducing agent [3]. The pH of the electroless Fe–Ni alloy plating bath was adjusted to pH 10.0 using a KOH solution. The bath temperature was kept at 70 °C in a water bath. Ni/Cr/Si wafers (with thicknesses of approximately 10 nm, 10 nm, and 525 μm, respectively) contacted with pure aluminum plate were used as a substrate. The electroless plating was carried out with adjusting a plating time to obtain a film thickness of about 500 nm. The composition of the electroless deposited Fe–Ni alloy films was determined by an EPMA. The thickness of the electroless deposited film was measured by the fluorescent X-ray-FP method. The internal stress (σ film) of the electroless deposited film was calculated using Stoney’s equation from the change in the film's curvature at room temperature. Fig.1 shows the alloy composition and the deposition rate of the electroless deposited Fe–Ni–B alloy film obtained from the plating bath, where the ratio of Fe2+/(Fe2++Ni2+) was varied from 0 to 0.4. An electroless deposited Ni–B alloy film that contained approximately 5 wt%B was obtained from the plating bath without Fe2+ addition. When Fe2+ was added to the bath, the Ni and B contents of the resulting film decreased gradually, and the Fe content increased to 62 wt%. When the Fe2+/(Fe2++Ni2+) ratio was 0.3 or more, the B content was less than 0.3 wt% and hardly detectable. When the Fe2+/(Fe2++Ni2+) concentration ratio was 0.3 or more, electroless deposited Fe–Ni–B alloy films in the Invar composition region were obtained. Fig.2 shows effect of Fe content on the internal stress value (σ film) in an electroless deposited Ni–B alloy film and electroless deposited Fe–Ni–B alloy films. The stresses (σ film) of electroless deposited Ni–Fe alloy films with an Fe content of 0 to 10 wt% were approximately 100 to 200 MPa (tensile). For Fe content of 20 to 40 wt%, the stresses (σ film) increased significantly to approximately 800 MPa (tensile). In contrast, with respect to the Fe–Ni–B alloy films with an Fe content of 55 to 64 wt% in the Invar composition range with lower CTEs, the stresses (σ film) decreased and exhibited relatively low values, approximately 500 MPa (tensile). It is believed that the change of the stress in the electroless deposited film with the various film composition corresponds to the microstructural conversion in the film. Reference [1] H. Zhou, J. Guo, and J. Shang, J. Electrochem. Soc., 160, D233, (2013). [2] C. É. Guillaume, CR Acad. Sci., 125, 235 (1897). [3] T. Yamamoto, T. Nagayama, and T. Nakamura, J. Electrochem. Soc. (in press). Figure 1

Electroplating and Characterization of Invar Fe–Ni Alloy Films from Plating Baths Containing Organic Acids

Practical plating baths and plating conditions for preparing Fe–Ni alloy electroplated films with compositions in the Ni content range 36–100 mass% have been proposed. The addition of saccharin in sulfate-chloride bath is indispensable for preparation of Fe-30–45 mass% Ni alloy electroplated films, i.e., those in invar composition region. The addition of tartaric acid or malonic acid to Fe–Ni alloy plating baths (containing saccharin) prevents a reduction in the toughness of the plated film by masking Fe3+ generated by oxidation. It was possible to suppress the internal stress in invar Fe–Ni alloy electroplated films to low levels. Resultantly, the invar electroplated films obtained from these optimized plating baths show promise for electroforming. On the contrary, the addition of citric acid, which forms a more stable complex with Fe3+, causes very large internal stress in the resultant invar Fe–Ni alloy electroplated films, making them unsuitable as MEMS materials. It was confirmed that Fe–Ni alloy electroplated films with Ni contents of 45–100 mass% comprise a single-phase alloy having an fcc structure but the invar Fe-36–42 mass% Ni alloy electroplated film is a metastable bcc phase or a mixture of bcc and fcc phases. Therefore, to impart low thermal expansion characteristics to as-plated invar alloy films, it is necessary to induce phase transformation to an fcc phase, which is the equilibrium phase at high temperature, by the means of heat treatment.

Controllable electrodeposition of binary metal films from deep eutectic solvent as an efficient and durable catalyst for the oxygen evolution reaction.

In this work, we present an easy and scalable electrodeposition protocol that operates in a deep eutectic solvent, used to prepare self-supported Ni-Fe alloy films directly grown on copper foils. Unlike electrodeposition in aqueous baths, alloy compositions deposited in deep eutectic solvent are found to be the same as in plating solution owing to the enlargement of the deposition window and secondary reaction suppression. By rationally tuning the Ni/Fe ratio in deep eutectic solvent plating solution, the best oxygen evolution reaction performance was achieved by a Ni75Fe25 catalyst, which requires only a 316 mV overpotential to reach a current density of 10 mA cm-2, while its Tafel slope is as low as 62 mV dec-1. This catalyst can operate at 10 mA cm-2 with negligible activity degradation for over 10 h, promising its potential use as a low-cost, high-performance and stable electrocatalyst in water splitting devices.

The Properties of Cr–Co–Cu–Fe–Ni Alloy Films Deposited by Magnetron Sputtering

In spite of great efforts undertaken to produce and examine the properties of new high-entropy alloys (bulk or film alloys), the available information is still insufficient for creating scientific ideas that would connect the properties and process parameters of these alloys. We studied the dependence of the composition and structure of Co–Cr–Cu–Fe–Ni films deposited by magnetron sputtering on the physical parameter such as energy flux delivered to the growing film surface. This parameter is directly related to process parameters such as magnetron discharge current (Id) and substrate bias voltage (Ub). The films have a nanocrystalline microstructure and crystallize as a two-phase fcc and bcc solid solution with the following lattice parameters: a = 0.363 nm for the fcc phase and a = 0.294 nm for the bcc phase. Ion bombardment of the growing film induced by bias voltage Ub varying from 0 to –300 V in the substrate influences the film structure and composition. Thus, the films deposited at ~300 eV are noticeably depleted of copper, while the composition of the films deposited without ion bombardment is the same as that of the target. Greater energy flux delivered to the growth surface (higher Id and/or Ub in the substrate) increases the growth surface temperature, leading to grain coarsening and film texturing. The bcc phase also substantially decreases in volume, vanishing in the films deposited at Ub = –300 V. The films formed by the bombardment of ions with ≈100 eV energy showed the maximum (~19 GPa) microhardness.

Controlled Growth of Large-Area Uniform Multilayer Hexagonal Boron Nitride as an Effective 2D Substrate.

Multilayer hexagonal boron nitride (h-BN) is an ideal insulator for two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides, because h-BN screens out influences from surroundings, allowing one to observe intrinsic physical properties of the 2D materials. However, the synthesis of large and uniform multilayer h-BN is still very challenging because it is difficult to control the segregation process of B and N atoms from metal catalysts during chemical vapor deposition (CVD) growth. Here, we demonstrate CVD growth of multilayer h-BN with high uniformity by using the Ni-Fe alloy film and borazine (B3H6N3) as catalyst and precursor, respectively. Combining Ni and Fe metals tunes the solubilities of B and N atoms and, at the same time, allows one to engineer the metal crystallinity, which stimulates the uniform segregation of multilayer h-BN. Furthermore, we demonstrate that triangular WS2 grains grown on the h-BN show photoluminescence stronger than that grown on a bare SiO2 substrate. The PL line width of WS2/h-BN (the minimum and mean widths are 24 and 43 meV, respectively) is much narrower than those of WS2/SiO2 (44 and 67 meV), indicating the effectiveness of our CVD-grown multilayer h-BN as an insulating layer. Large-area, multilayer h-BN realized in this work will provide an excellent platform for developing practical applications of 2D materials.