福室 直樹

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the further wide commercialization of PEMFCs. Therefore, carbon-free catalysts are required for PEMFCs. In this study, highly crystallized conducting Sb-doped SnO2 (Sb-SnO2) nanoparticles (smaller than 7 nm in size) were synthesized using an ozone-assisted hydrothermal synthesis. Pt nanoparticles were loaded on Sb-SnO2 supporting particles by polyol method to be “Pt/Sb-SnO2 catalyst”. The Pt/Sb-SnO2 catalyst showed a high oxygen reduction reaction (ORR) mass activity (178.3 A g−1-Pt @ 0.9 V), compared to Pt/C (149.3 A g−1-Pt @ 0.9 V). In addition, the retention ratio from the initial value of electrochemical surface area (ECSA) during 100,000-voltage cycles tests between 1.0 V and 1.5 V, Pt/SnO2 and Pt/Sb-SnO2 catalyst exhibited higher stability (90% and 80%), respectively, than that of Pt/C catalyst (47%). Therefore, the SnO2 and Sb-SnO2 nanoparticles synthesized using this new ozone-assisted hydrothermal method are promising as carbon-free catalyst supports for PEMFCs.

The thermal stability of electroless nickel-phosphorus (Ni-P) film and cobalt-tungsten–phosphorus (Co-W-P) film deposited on GaAs substrate was investigated. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicated that the Ni-P film changed from amorphous to crystalline by annealing at 240°C for 1 h due to the diffusion of Ni into the GaAs substrate and the increase in P concentration in the Ni-P film. On the other hand, the crystallinity of the Co-W-P film did not change by annealing at 240°C for 1 h. Cross-sectional observation showed that the thickness of the crystallized Ni-P film did not change from 3 to 1000 h of high-temperature storage at 270°C, and no void was observed in the Ni-P film. Migration of Ni atoms could be suppressed by the crystallization of the Ni-P film. On the other hand, voids were formed in the Co-W-P film after high-temperature storage at 270°C for 100 h. Since the Co-W-P film consists of nanoscale crystalline and amorphous phases, atoms diffuse from the amorphous portion to the GaAs substrate. Graphical Abstract: [Figure not available: see fulltext.].

In the present study, the effect of electro zinc plating on environmental hydrogen embrittlement of 7075–T6 aluminum alloys was investigated by using a slow strain rate testing device which can detect quantitively the amount of hydrogen generated during deformation and fracture. The testing device can also detect traces of hydrogen gas as low as 5 ppb by using a semiconductor gas sensor at ambient pressure. It was revealed that the environmental hydrogen embrittlement of 7075–T6 aluminum alloys was highly suppressed by zinc–based electroplating, while not fully by anodization. The suppression of the hydrogen embrittlement by zinc plating was caused by the protection of original aluminum surfaces during plastic deformation.

The effect of electropolishing conditions on the outgassing properties of austenitic stainless steel (SUS316L) electropolished by a wiping method (WiEP) and an immersion method (ImEP) was investigated using thermal desorption spectroscopy. In the case of electropolishing by the WiEP in which the metal surface was wiped with an electrolyte–solution–impregnated felt wiper cathode, the SUS316L surface became smoother and the amount of outgassing decreased as the applied voltage (4–8 V) increased. In the case of electropolishing by the ImEP, the SUS316L surface became smoother and the amount of outgassing decreased as the current density (8–15 A dm−2) increased. After electropolishing by the WiEP at higher applied voltages and the ImEP at higher current densities, diffusible hydrogen desorbed from the SUS316L surface below 723 K was almost completely removed, however most of the non–diffusible hydrogen remained. These results suggest that the migration of diffusible hydrogen to the SUS316L surface is enhanced by the increase in the applied voltage of electropolishing. ［doi:10.2320/jinstmet.J2022032］

Surface and outgassing properties of 304 stainless steel samples were studied after electropolishing by a wiping method (WiEP) using felt that is attached to a cathode electrode and impregnated with an electrolyte. Surface morphology observed with an atomic force microscope suggests that WiEP yields a smoother surface with fewer pits compared with the conventional electropolishing method of immersing the samples in an electrolyte. The thickness of the oxide layer after either of the electropolishing processes was 3-4 nm as estimated by x-ray photoelectron spectroscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. Furthermore, no significant difference was found in the chemical state of the surface and oxide film in the two cases. Thermal desorption spectroscopy of the samples revealed that the amount of desorbed H2O and H2 was significantly low in the case of WiEP. The low outgassing was attributed to the formation of a smooth and dense oxide film on the sample surface after electropolishing by WiEP.

The existing states of co-deposited hydrogen in copper films electrolessly deposited from an ethylenediaminetetraacetatic acid complex bath were investigated using thermal desorption spectroscopy. Small desorption peaks at 500-700 K and large desorption peaks at 900-1300 K were observed in the as-deposited copper film, and these were attributed to the break-up of vacancy-hydrogen clusters and the desorption of molecular hydrogen from nanovoids, respectively. Moreover, an unknown desorption peak appeared at around 390 K. The total amount of desorbed hydrogen from the copper film in atomic ratio was 1.2 × 10−2, most of which was non-diffusible hydrogen desorbed above 800 K. A large number of nanovoids distributed in the grains were observed in the copper film. After 7 days, no significant change in hydrogen desorption above 500 K was observed, while the unknown desorption peak around 390 K disappeared. The as-deposited copper film showed lattice expansion and compressive residual stress, which were reduced after 7 days. Therefore, we attributed the unknown desorption peak appearing at around 390 K to the desorption of hydrogen atoms trapped by regular interstitial sites in the copper lattice.

The structural changes in electrodeposited palladium (Pd) films with desorption of co–deposited hydrogen were investigated, and the existing states of hydrogen in the Pd film were analyzed. The Pd films were electrodeposited from an alkaline bath consisted of palladium (II) chloride, ammonium chloride, and citric acid. Two pronounced desorption peaks at around 500 K and 880 K were observed in the thermal desorption spectrum of hydrogen from as–deposited Pd film. For the Pd films with lower hydrogen concentrations, the lattice contraction proceeded concurrently with hydrogen desorption at room temperature. The lattice parameter of Pd film decreased with increasing heat treatment temperature up to 500 K, and then increased with grain growth above 550 K. An exothermic peak corresponding to the hydrogen desorption at around 500 K was observed in the differential scanning thermal analysis curve. A large number of nano–voids were observed in the Pd film. These results suggested that the hydrogen desorption peaks observed at around 500 K and 880 K were ascribed to the break–up of vacancy–hydrogen clusters and the desorption of hydrogen molecules from nano–voids, respectively.

In this study, hydrogen incorporated into 7075 aluminum alloy substrates by electroless Ni-P plating was investigated. In the cross-sectional transmission electron microscope images, a low phosphorus content (5.7mass%) film consisted of fine grains and a high phosphorus content (12.1mass%) film consisted of an amorphous phase were observed on the 7075 alloy substrates. Depth profile analysis by glow discharge optical emission spectrometry revealed that the intensity of hydrogen increased in the 7075 alloy substrate after electroless Ni-P plating, and was higher at the interface between the Ni-P film and the 7075 alloy substrate. In the thermal desorption spectra of hydrogen from the 7075 alloy substrates with low and high phosphorous content Ni-P films, a pronounced desorption peak and a series of desorption peaks were observed. Such desorption peaks were not observed in the 7075 alloy substrate before electroless Ni-P plating and in the Ni-P films on the copper substrates. These results indicate that the hydrogen incorporated into the 7075 alloy substrate by electroless Ni-P plating exists in various trap sites such as interstitial sites, vacancies, grain boundaries, and the incoherent interface between the precipitates and the aluminum basal phase.

In this study, A2017-T4 aluminum alloy was plated with electroless NiP with different phosphorus content and rotary bending fatigue test was conducted to investigate the effect of hydrogen by plating on fatigue properties. The fatigue strength of the low-phosphorus type NiP plated specimen was higher than that of the untreated specimen, while that of the high-phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. The decrease in fatigue strength of the high phosphorus type plating specimen was attributed to hydrogen induced by plating from hydrogen analysis. Thus, despite the previous report that 2000 series aluminum alloys do not exhibit hydrogen embrittlement in slow strain rate tensile tests under wet condition, it was found that A2017-T4 aluminum alloy undergo hydrogen embrittlement when the alloy is plated with high-phosphorus type electroless NiP and fatigue-tested on rotary bending machine.

In this study, with the aim of improving the fatigue characteristics of the A7075 aluminum alloy, A7075-T6511 alloy rod specimens were plated with electroless NiP with different compositions, and the fatigue characteristics were evaluated by a rotary bending fatigue test. The fatigue strength of the specimen plated with low-P type was higher than that of the un-plated specimen. However, the fatigue strength of the specimen plated with high-P type was significantly lower than that of the un-plated specimen, and the fatigue strength of the specimen plated with medium-P type was also lower though the extent was not so significant. It was speculated that these reductions in fatigue strength were due to hydrogen embrittlement by the hydrogen introduced into the specimen during the plating.

We found that an AAA-type battery (min. 750 mAh) pressurized with Ar or N₂ at pressures of up to 5 MPa exhibited a significant durability enhancement even under high-current conditions.

A nickel-metal hydride (Ni-MH) prototype battery completely immersed in an aqueous electrolyte solution of KOH under high-pressure was fabricated to examine the effects of high-pressure on the quality of Ni-MH batteries. The small battery cell comprised positive and negative electrode materials, as used in electric vehicles, and an Ag/AgO reference electrode. The electric capacity of the Ni-MH battery was measured at different temperatures and pressures with small currents and charge/discharge voltages of 1.6-1.0 V. High-pressure was found to clearly and effectively enhance the electric capacity of the Ni-MH battery at larger currents. The considerable effect of high-pressure on the Ni-MH battery was elucidated by the change in internal resistance during the charge/discharge cycle life experiment, indicating that the voltage of the positive electrode did not appreciably change under high-pressure compared to that of the negative electrode. Moreover, the use of large currents in rapid charge/discharge cycle tests at high pressures of up to 30 MPa resulted in charge/discharge cycles that were five times faster and a quick recovery of capacity was achieved in the 0.5-2.1 V range.

Pt is an excellent and widely used hydrogen evolution reaction (HER) catalyst. However, it is a rare and expensive metal, and alternative catalysts are being sought to facilitate the hydrogen economy. As tungsten carbide (WC) has a Pt-like occupied density of states, it is expected to exhibit catalytic activity. However, unlike Pt, excellent catalytic activity has not yet been observed for mono WC. One of the intrinsic differences between WC and Pt is in their magnetic properties; WC is non-magnetic, whereas Pt exhibits high magnetic susceptibility. In this study, the WC lattice was doped with ferromagnetic Co nanocrystals to introduce an ordered-spin atomic configuration. The catalytic activity of the Co-doped WC was ~30% higher than that of Pt nanoparticles for the HER during the hydrolysis of ammonia borane (NH3BH3), which is currently attracting attention as a hydrogen fuel source. Measurements of the magnetisation, enthalpy of adsorption, and activation energy indicated that the synergistic effect of the WC matrix promoting hydrolytic cleavage of NH3BH3and the ferromagnetic Co crystals interacting with the nucleus spin of the protons was responsible for the enhanced catalytic activity. This study presents a new catalyst design strategy based on the concept of an internal magnetic field. The WC-Co material presented here is expected to have a wide range of applications as an HER catalyst.

6061-T6 aluminum alloys (Al-Mg-Si alloys) are known to show low environmental hydrogen embrittlement sensitivity. However, this alloy containing 0.1% of iron shows a decrease in ductility when a large amount of hydrogen is previously charged in an atmosphere containing water. In this study, we investigated the effect of electroless Ni-P plating involved the removal of oxide film on the absorption of hydrogen and the hydrogen embrittlement sensitivity of a 6061-T6 aluminum alloy. It was shown that the ductility decreased immediately after Ni-P plating because a large amount of hydrogen was introduced into the alloys. In addition, the hydrogen embrittlement sensitivity changed according to the holding time after Ni-P plating at room temperature. The 6061-T6 alloy showed better resistance for hydrogen embrittlement when the alloy was kept at room temperature for 50 days after Ni-P plating.

Al-Zn-Mg alloys with a high amount of Zn (10%) were subjected to high-speed compressive deformation after solution heat treatment, and a slow strain rate tensile test (SSRT) was performed under peak-aging condition. The SSRT under a humid air atmosphere revealed that grain boundary cracks near the surface are highly suppressed when the peak-aged Al-Zn-Mg alloy was pre-deformed with a high-speed.

In this study, A2017-T4 aluminum alloy was plated with electroless Ni-P with different phosphorus content and rotary bending fatigue test was conducted to investigate the effect of hydrogen by plating on fatigue properties. The fatigue strength of the low-phosphorus type Ni-P plated specimen was higher than that of the untreated specimen, while that of the high-phosphorus type plated specimen was much lower. It is clear that the fatigue strength differs greatly depending on the phosphorus content in the plating film. The decrease in fatigue strength of the high phosphorus type plating specimen was attributed to hydrogen induced by plating from hydrogen analysis. Thus, despite the previous report that 2000 series aluminum alloys do not exhibit hydrogen embrittlement in slow strain rate tensile tests under wet condition, it was found that A2017-T4 aluminum alloy undergo hydrogen embrittlement when the alloy is plated with high-phosphorus type electroless Ni-P and fatigue-tested on rotary bending machine. (Received May 19, 2021 Accepted August 15, 2021)

In this study, with the aim of improving the fatigue characteristics of the A7075 aluminum alloy, A7075-T6511 alloy rod specimens were plated with electroless Ni-P with different compositions, and the fatigue characteristics were evaluated by a rotary bending fatigue test. The fatigue strength of the specimen plated with low-P type was higher than that of the un-plated specimen. However, the fatigue strength of the specimen plated with high-P type was significantly lower than that of the un-plated specimen, and the fatigue strength of the specimen plated with medium-P type was also lower though the extent was not so significant. It was speculated that these reductions in fatigue strength were due to hydrogen embrittlement by the hydrogen introduced into the specimen during the plating.

© 2020 Elsevier B.V. Superstoichiometric hydrides PdHx have been synthesized by the electrochemical method. The H concentrations, x = H/Pd = 1.13–1.97, have been determined directly by thermal desorption. From X-ray diffraction, the structure is found to be face-centered cubic, with the lattice parameter changing smoothly over the concentration range, x = 0.7–2.0. Surprisingly, however, the lattice parameter goes through a maximum at x ∼1.0 and decreases at higher concentrations. It is suggested from electronic and Monte Carlo calculations that these unique features of the structure and formation process should be the consequence of partial replacement of Pd atoms with H2, namely, the formation of superabundant vacancies filled with H2 molecules.

In electroless nickel-phosphorus plating (ENPP), growth of the plated layer under high pressure was found to be faster than under ambient pressure. To quantitatively elucidate the effect of high pressure on the mechanism of the ENPP reaction, we propose a kinetic model that takes into account both mass transfer and reaction of the chemical species present in the plating solution. We solved the mass balance equations between the chemical species to calculate the transient changes in the thickness of the plated layer as well as the concentrations of the chemical species in the plating solution. By fitting the calculated results to the experimentally acquired results based on the nonlinear least square method, we determined such parameters as the film mass transfer coefficient, the adsorption constants, and the reaction rate constants of the chemical species in the model. As a result, we found that the film mass transfer coefficient under high pressure was greater than that under ambient pressure and revealed the dependence of the coefficient on pressure. The transient changes in the concentrations of the chemical species in the plating solution that we calculated based on the kinetic model employing our estimated parameters closely modeled the experimental results with the determination coefficients being mostly over 99%.

Using an electroless nickel/electroless palladium/immersion gold (ENEPIG) surface finish with a thick palladium–phosphorus (Pd-P) layer of 1 μm, the intermetallic compound (IMC) growth between the ENEPIG surface finish and lead-free solders Sn-3.5Ag (SA) or Sn-3.0Ag-0.5Cu (SAC) after reflow soldering and during solid-state aging at 150°C was investigated. After reflow soldering, in the SA/ENEPIG and SAC/ENEPIG interfaces, thick PdSn4 layers of about 2 μm to 3 μm formed on the residual Pd-P layers (~ 0.5 μm thick). On the SA/ENEPIG interface, Sn was detected on the upper side of the residual Pd-P layer. On the SAC/ENEPIG interface, no Sn was detected in the residual Pd-P layer, and Cu was detected in the interface between the Pd-P and PdSn4 layers. After 300 h of aging at 150°C, the residual Pd-P layers had diffused completely into the solders. In the SA/ENEPIG interface, an IMC layer consisting of Ni3Sn4 and Ni3SnP formed between the PdSn4 layer and the nickel–phosphorus (Ni-P) layer, and a (Pd,Ni)Sn4 layer formed on the lower side of the PdSn4 layer. On the SAC/ENEPIG interface, a much thinner (Pd,Ni)Sn4 layer was observed, and a (Cu,Ni)6Sn5 layer was observed between the PdSn4 and Ni-P layers. These results indicate that Ni diffusion from the Ni-P layer to the PdSn4 layer produced a thick (Pd,Ni)Sn4 layer in the SA solder case, but was prevented by formation of (Cu,Ni)6Sn5 in the SAC solder case. This causes the difference in solder joint reliability between SA/ENEPIG and SAC/ENEPIG interfaces in common, thin Pd-P layer cases.

Electroless plating has several advantages over electroplating, such as uniformity of the plated layer, corrosion resistance, and applicability to an electrically non-conductive surface. In this study, to study the effect of high pressure on both the plating rate and the surface structure of the plated layer prepared by electroless nickel-phosphorus plating, we changed the pressure applied to the plating bath in the range from 0 to 400 MPa. As a result, we confirmed the reproducibility of the plating rate under the same plating conditions. It was found that the plating rate increased significantly when the applied pressure was increased from 0 to higher than 20 MPa but gradually decreased with further increase in pressure.

© 2017 Institute of Materials Finishing. Metallisation of silicon carbide (SiC) wafers is a key technology for producing efficient power devices. Conventional autocatalytic electroless deposition cannot produce adherent metal films directly on SiC substrates. The authors applied their recently developed surface-activation process for electroless metal-film deposition on silicon wafers to SiC wafers. Gold nanoparticles were produced on 4H-SiC substrates by displacement deposition after immersing the substrates in a tetrachloroauric(III) acid solution that includes hydrofluoric acid or potassium hydroxide. The size and the particle density of the deposited gold are changed with deposition parameters such as the surface condition of the substrates, the solution composition, and the UV-light illumination. The gold nanoparticles work not only as catalysts to initiate autocatalytic electroless deposition but also as binding-points between the metal film and the SiC surface. Adherent and uniform nickel-phosphorus alloy films are produced on such SiC substrates by autocatalytic electroless deposition without any further treatments.

© 2016 The Japan Society of Applied Physics,. Ferromagnetic magnetite (Fe3O4) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi3.25Nd0.64Eu0.10)Ti3O12 (BNEuT)/(101) Nb:TiO2 substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5- heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe3O4/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe3O4 with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400-420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76-89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment-magnetic field curves for Fe3O4 thin films deposited at 400-500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

Ferromagnetic magnetite (Fe<inf>3</inf>O<inf>4</inf>) thin films for magnetoelectric multiferroic applications were deposited on (200) (Bi<inf>3.25</inf>Nd<inf>0.65</inf>Eu<inf>0.10</inf>)Ti<inf>3</inf>O<inf>12</inf>(BNEuT)/(101) Nb:TiO<inf>2</inf>substrates by metalorganic chemical vapor deposition (MOCVD) using an iron(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) precursor as the iron source. The BNEuT film utilized as a ferroelectric template material was in the form of freestanding nanoplates with narrow spaces between them. The effects of deposition conditions such as the deposition time and substrate temperature on the magnetic and structural characteristics of the Fe<inf>3</inf>O<inf>4</inf>/BNEuT composite films were investigated. All the films consisted of mostly single-phase Fe<inf>3</inf>O<inf>4</inf>with a cubic inverse-spinel structure. When deposition was carried out at temperatures of 400–420 °C, the filling rates of particles introduced into the narrow spaces between the BNEuT nanoplates exhibited high values of 76–89% including the amorphous phase. This suggested that the deposition in this temperature range made progress according to the growth mechanism of MOCVD in the surface reaction rate determining state. Room-temperature magnetic moment–magnetic field curves for Fe<inf>3</inf>O<inf>4</inf>thin films deposited at 400–500 °C for 60 min exhibited narrow rectangular hysteresis loops, indicating typical soft magnetic characteristics.

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By immersion of silicon into a solution containing metal-salt and hydrofluoric acid, fine metal particles are deposited onto the silicon surface by electroless displacement reaction. The particle density of deposited metal varies widely depending on the kind of metal and the surface condition of silicon substrates. The platinum particle density changes to an especially large degree according to silicon surface conditions. This study revealed the relation of deposition time to platinum particle density deposited by electroless displacement deposition on argonplasma-etched Si surfaces. Single-crystalline n-Si（100）wafers were chemically pretreated and were then etched with argon plasma using a radiofrequency glow discharge spectrometer. The electroless displacement deposition of platinum particles onto the silicon surface proceeds by immersion of silicon wafers into a hexachloroplatinic（IV）acid solution containing hydrofluoric acid. Platinum particles were deposited in the progressive mode until 450 s, and reached 10¹¹ cm^－2. The particle density was decreased by immersion longer than 450 s, and was maintained at 10¹⁰ cm^－2 after 900 s. Dimples appeared on the silicon surface by immersion for 600 s and longer. Dimples were formed by local anodic dissolution of silicon under the platinum particles. The initial increase and posterior decrease in the particle density are explained, respectively, as the influence of argon-plasma etching and the dissolution of the influenced region of a silicon wafer.

The influence of hydrogen adsorption on the electrodeposition of platinum was investigated using an electrochemical quartz crystal microbalance (EQCM) method and thermal desorption spectroscopy (TDS). Three types of hydrogen adsorption were observed in a tetrachloroplatinate(II) solution by the EQCM method: UPD-H1, UPD-H2, and OPD-H in order from positive to negative potential. Platinum films were electrodeposited potentiostatically at 0 for UPD-H1, -0.1 and -0.2 for UPD-H2, and -0.3 V vs. Ag/AgCl for OPD-H. The amount of hydrogen desorbed by TDS, that is, the hydrogen incorporated into the films by electrodeposition, depended on the deposition potential. At the potential for UPD-H1, no hydrogen was incorporated into the bulk of the platinum films. At the UPD-H2 potential, hydrogen was uniformly incorporated in the platinum films at the content of ca. 0.02 in an atomic ratio of H/Pt. At the OPD-H potential, a fairly large amount of hydrogen, 0.1 of content, was incorporated uniformly in the platinum films.

The influence of hydrogen adsorption on the electrodeposition of platinum was investigated using an electrochemical quartz crystal microbalance (EQCM) method and thermal desorption spectroscopy (TDS). Three types of hydrogen adsorption were observed in a tetrachloroplatinate(II) solution by the EQCM method: UPD-H1, UPD-H2, and OPD-H in order from positive to negative potential. Platinum films were electrodeposited potentiostatically at 0 for UPD-H1, -0.1 and -0.2 for UPD-H2, and -0.3 V vs. Ag/AgCl for OPD-H. The amount of hydrogen desorbed by TDS, that is, the hydrogen incorporated into the films by electrodeposition, depended on the deposition potential. At the potential for UPD-H1, no hydrogen was incorporated into the bulk of the platinum films. At the UPD-H2 potential, hydrogen was uniformly incorporated in the platinum films at the content of ca. 0.02 in an atomic ratio of H/Pt. At the OPD-H potential, a fairly large amount of hydrogen, 0.1 of content, was incorporated uniformly in the platinum films.

© 2015 The Japan Society of Applied Physics. (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT-0.1) films with a- and b-axis orientations and thicknesses of 1.8-2.3μm were sputter-deposited on conductive Nb:TiO2(101) substrates containing 0.79 mass% Nb. The deposition temperature was fixed at 650 °C, and the sputtering gas pressure was varied from 0.4 to 5.0Pa in order to examine its effect on the structural, ferroelectric and piezoelectric properties of the films. The films were found to have a mostly single-phase orthorhombic structure, with a high degree of a- and b-axis orientations (93-98%). The films had a nanoplate microstructure, with the plates being aligned along the [100]/[010] direction, and porosities of 15-25%. A maximum room-temperature remanent polarization (2Pr) of 93 μC/cm2 was obtained for a sputtering gas pressure of 5.0 Pa. All the films were strongly a-axis oriented, according to the results of X-ray diffraction measurements and vertical amplitude images in piezoresponse force microscopy. The optimal sputtering gas pressure for heteroepitaxial growth of BNEuT-0.1 nanoplates with a high degree of a-axis orientation of 96.5%, a maximum orthorhombicity of 0.0017, a comparatively large remanent polarization of 2Pr = 66 μC/cm2, and a high porosity of 24% was found to be 0.4 Pa.

© 2015 Elsevier Ltd. Abstract The electrodeposition of Pt from aqueous solutions of K<inf>2</inf>PtCl<inf>4</inf> (Pt(II)), H<inf>2</inf>PtCl<inf>6</inf> (Pt(IV)), and a mixture of Pt(II) and Pt(IV) was studied using the electrochemical quartz crystal microbalance (EQCM) method. Pt deposition and cathode current flow began at the same potential in the Pt(II) solution. On the other hand, in the Pt(IV) solution, the cathode current increased at a more positive potential followed by Pt deposition at a more negative potential than in the Pt(II) solution. This difference in the potentials is due to the reduction reaction of Pt(IV) to Pt(II). Thus, Pt deposition in the Pt(IV) solution occurred in two potential ranges. In the first range, which was more positive than the second one, Pt was deposited via the reduction of Pt(II) to Pt(0). In the second range, direct deposition from Pt(IV) to Pt(0) proceeded, but was followed by hydrogen adsorption, which inhibited further Pt deposition.

© 2015 The Japan Institute of Metals and Materials. We proposed that the grain growth observed in electrodeposited Cu films at room temperature is caused by hydrogen-induced superabundant vacancy-hydrogen clusters. In this study, the relation between grain growth and hydrogen behavior in the electrodeposited Cu films was investigated using different types of plating baths. The Cu films were electrodeposited from an acid sulfate bath, an acid sulfate bath containing chloride ion, polyethylene glycol, and bis (3-sulfopropyl) disulfide (additive-containing bath), a pyrophosphate bath, and a chloride bath containing citric acid. Thermal desorption spectroscopy revealed that extremely high concentration of hydrogen is contained in the Cu films deposited from the additive-containing bath and the chloride bath. The room-temperature grain growth was observed in these Cu films with passage of time after deposition, concurrently with hydrogen desorption. Such grain growths were not observed in the Cu films with low hydrogen content deposited from the acid sulfate bath and the pyrophosphate bath. The changes in crystal orientation and internal stress during the grain growth of the Cu films differed between the additive-containing bath and the chloride bath. These results suggest that the room-temperature grain growth was induced by the co-deposited hydrogen in films.

©The Electrochemical Society. Electrolessly deposited metal films on silicon substrates using gold nanoparticles as catalysts yield much higher adhesion than that by using palladium or silver nanoparticles. In this study, the structure of the gold nanoparticles is analyzed by X-ray diffraction and transmission electron microscopy. Single crystalline gold nanoparticles are epitaxially deposited on silicon substrates and silicon-gold alloy is formed at the interface. Those epitaxially grown gold nanoparticles cause the high adhesion of electrolessly deposited nickel films on silicon substrates.

© The Electrochemical Society. Antireflection of Si surface is an important technology to increase the photocurrent density of solar cells. Recently, porous Si has been researched for replacing Si nitride which is common material of antireflective coating (ARC). In this study, we have investigated the optical properties of porous Si thin films, thinner than doped layers for p-n junction formation of Si solar cells, produced by metal-assisted etching. The structure of porous Si is changed with the size of catalytic Ag nanoparticles, composition of etching solution, and etching time. The reflection of porous film formed Si wafers is much lower than that of mirror polished wafers. Reflectance spectra and ellipsometric analysis indicate that the thin porous Si films act as optical films and they are expected to function as suitable ARC for crystalline Si solar cells.

© The Electrochemical Society. Metal-assisted etching of Si is an electroless method that can produce porous Si by immersing metal-modified Si in a HF solution without electric bias. We reported that the etching rate of noble metal-modified Si in a simple HF solution including oxygen under dark conditions depended on the catalytic activity of metal for oxygen reduction. Only palladium exhibits high activity for the etching under dissolved oxygen-free and dark conditions. In this study, the catalytic activity of Ru for the etching of Si has been investigated. Ru nanoparticles are electrodeposited on Si substrates. Electroless displacement deposition using RuCl3 solution including HF can form Ru nanoparticles not on mirror-polished n-Si substrate but on roughed one. The etching rate of Ru-particledeposited Si is similar to that of Rh case which is changed with dissolved oxygen concentration. On the roughed Si substrates, the Ru nanoparticles assist the etching even under oxygen-free and dark conditions.

By immersion of Si into a solution containing metal-salt and HF, fine metal particles are deposited onto the Si surface by electroless displacement reaction. The density of the deposited metal particles on the surface varies widely according to the metal-salt and Si pretreatment. The Pt particle density depends particularly strongly on the Si pretreatment. This study assessed the Pt electroless displacement deposition process. Single-crystalline n-Si(100) wafers were pretreated using the following three methods: immersion in a mixture of HF, HNO₃, CH₃COOH, and H₂O(3:5:3:22 in volume)(CP4A), ordinary RCA method, and oxidization of the Si surface by immersion in HNO₃ after RCA(RCA+HNO₃). The electroless displacement deposition of Pt particles onto the Si surface proceeds by immersion of Si wafers into a H₂PtCl₆ solution containing HF for 5-900 s. On the Si surface pretreated using the CP4A method, Pt particles were deposited in the progressive mode. For the RCA method, Pt particles were deposited in two-stage progressive mode, which is separated at 180 s. For pretreatment of RCA+HNO₃, Pt particles deposited in two-stage progressive mode were separated at 120 s. These two-stage progressive modes result from the local anodic reaction, which dissolved the Si surface in electroless displacement deposition solution. However, irrespective of the pretreatment method, Pt particles were deposited on the order of 10⁹ cm⁻² particle density by deposition for 900 s.