八重 真治

The objective of this study is to reveal the atomistic state of hydrogen in electrodeposited Ni-P films by thermal desorption spectroscopy. Two peaks corresponding to the desorption of hydrogen occupying regular interstitial sites and the break-up of vacancy-hydrogen (Vac-H) clusters were observed in electrodeposited pure Ni film. With an increase in phosphorus content, the crystallinity of electrodeposited Ni-P films decreased and the hydrogen desorption from the interstitial sites and Vac-H clusters disappeared. The amount of diffusible hydrogen increased abruptly with the increase in the amorphous phase in Ni-P film. ©The Electrochemical Society.

© 2019 Elsevier B.V. Fiber-optic laser-induced breakdown spectroscopy (LIBS) can be used for on-site chemical analysis in harsh environments with a flexible light delivery system. In this work, the use of a long-pulse laser (100 ns) is proposed for the detection of molecular emission signals, instead of a normal-pulse laser (6 ns). We show a significant enhancement of AlO signals using an aluminum metal target in air. We also elucidate the enhancement mechanism of the AlO formation by measuring species-specific images of the emission from aluminum atoms, oxygen atoms, and AlO molecules in the plasma. The internal structure of the plasma suggests that the formation origin of AlO molecules in the long-pulse-produced plasma is essentially different from that in the normal-pulse-produced plasma. The long-pulse laser causes a rise of the ablation plume and facilitates the flow of oxygen from the ambient air. This is a key factor to enhance the molecular emission signals.

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.

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.

A nitrobenzene droplet put on an Au electrode moves spontaneously during Sn electrodeposition, which has been reported previously. The driving force of the motion is an imbalance of the interfacial tension of solid-water interface (γSW): the droplet moves when γSW acting on the front side of droplet is larger than that on the rear side. The electrodeposition, which increases γSW, is supressed by a side reaction such as hydrogen evolution reaction. Thus, if the electrode surface is non-uniform, the electrodeposition as well as the side reaction takes place non-uniformly on the electrode surface, resulting in the droplet motion. In other words, the non-uniform surface is one of the factors that create the interfacial tension imbalance. However, we have recently found that the droplet moves spontaneously on a uniform surface. This motion is initiated when nitrobenzene molecules are adsorbed non-uniformly on the surface, as discussed in this study.

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.

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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.

<p>Antireflection of a silicon surface is an important means of increasing the photocurrent density and thereby improving solar cell conversion efficiency. We have produced thin nanohole arrays on silicon solar cells using metal-assisted-etching with electrolessly deposited silver nanoparticles. The nanohole array acts as an optical film, decreasing silicon surface reflectance, increasing photocurrent, and causing no damage to the pn-junction.</p>

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.

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.

Fe-C alloy films containing supersaturated C and H were prepared by electrodeposition, and investigated for the hydrogen behavior in annealing processes utilizing X-ray diffraction and thermal desorption spectroscopy. The H content x(H) (x(H) = H/Fe) in the films increased from about 0.031 in pure Fe to about 0.36 in Fe-C alloy (x(C) = C/Fe = 0.073) in proportion to the C content. The lattice contraction of about 0.2% was observed in pure Fe films, whereas the lattice expansion increasing with C content was observed in Fe-C alloy films. Both the lattice contraction of the Fe films and the lattice expansion of the Fe-C alloy films were decreased as H was desorbed during heat treatments. The atomistic structure of vacancy-hydrogen and vacancy-carbon-hydrogen clusters in Fe-C alloy films is discussed, based on these experimental results. (C) 2014 Elsevier B.V. All rights reserved.

The electrodeposition of Pt from aqueous solutions of K2PtCl4 (Pt(II)), H2PtCl6 (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. (C) 2015 Elsevier Ltd. All rights reserved.

© 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.

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.

Recently, we reported on autocatalytic electroless metallization of silicon using gold nanoparticles. This technology is expected to be a useful, low-cost, and reliable method to form electrodes on silicon for several devices, such as solar cells and power devices. For the fabrication of electrodes, it is important that the resistance, consisting of the sheet resistance of the metal patterns and the contact resistance between the metal and silicon, is low. In this study, we measure the contact resistance of metal electrodes on silicon prepared by autocatalytic electroless metallization using gold nanoparticles. The transfer length method is suitable to evaluate the contact resistance between electrolessly plated nickelphosphorus alloy thin films and silicon. The values obtained for the contact resistivity decrease as the film thickness increases from 0.5 to 2.3 μm. This decrease is caused by the decrease of the sheet resistance of the metal films. Reliable values for the contact resistivity were determined to be 0.9 and 1.2 mω cm2 for p+- And n+-doped wafers, respectively. The contact resistivity depends on the gold nanoparticle coverage.

We developed a new surface-activation process for autocatalytic electroless metallization of silicon using gold nanoparticles. The gold nanoparticles provide much higher adhesion of electrolessly deposited nickel-boron alloy films on silicon substrates than do silver and palladium nanoparticles. TEM observation and XPS analysis indicate that the electrolessly deposited nickel-phosphorus alloy film directly contacts the gold nanoparticles, silicon-gold metallic alloy is formed at the interface between the silicon substrate and the gold nanoparticles even at room temperature, and an amorphous layer exists between the metals and silicon substrate.

We developed a simple recovery method of all noble metals from aqueous solutions by adding silicon (Si) powder and fluoride. This method is expected to be low-cost, because the Si powder and the fluoride solution can be supplied from semiconductor industries, such as the sawdust Si of wafering or dicing and the waste hydrofluoric acid solution of wafer cleaning or etching. In this study, we investigated the recovery of noble metals using a lowtoxic agent instead of a toxic hydrofluoric acid, or sawdust Si powder. This method can recover noble metals using ammonium fluoride or sodium fluoride. The recovery rate with sawdust Si is as high as that using pure Si powder. We found that the recovery of noble metals by this method from aqueous solutions including aqua regia is also possible.

For the direct electroless deposition of adhesive metal films on Si substrates, we have developed a surface-activation process that forms metal nanorods in Si using electroless displacement metal nanoparticle deposition, metal-nanoparticle-assisted HF etching of Si, and autocatalytic electroless Ni deposition. The metal film adhesion increases with the metal nanorod length.

The hydrogen-induced enhancement of atomic diffusion in electrodeposited Pd films on Cu substrate has been investigated with thermal desorption spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrogen content in Pd films (x = H/Pd) was 2.2-7.7 x 10(-2) and decreased with time at room temperature. For Pd films with lower hydrogen contents (x &lt;= 4.0 x 10(-2)), lattice contraction and grain growth proceeded as hydrogen desorption proceeded. For Pd films with higher hydrogen contents (x &gt;= 5.8 x 10(-2)), fine grains became large columnar grains, and a large-grained Cu-Pd interlayer was formed by interdiffusion between the Cu substrate and the Pd film. (C) 2013 Elsevier B.V. All rights reserved.

We deposit fine metal particles on silicon (Si) by a displacement reaction, which is the immersion of Si wafers into a metal-salt solution containing hydrofluoric acid, that consists of a local cathodic reduction of metal ions and a local anodic dissolution of Si. In this study, the displacement deposition of silver (Ag) nanoparticles on the Si(111) surface with an atomic step-terrace structure is investigated by atomic force microscopy. Ag particles are uniformly deposited on the Si surface without influence of the step-terrace structure. The particle density of the deposited Ag decreases and then increases with immersion times between 1 and 15 s. The step-terrace structure disappears and nanoholes are formed by an immersion time of 15 s. We propose a model of Ag particle density and Si surface changes with time. © The Electrochemical Society.

Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a HF solution without electrical bias. We have been studying this etching using dissolved oxygen as an oxidizing agent and recently reported that the catalytic activity of noble metal particles including silver, gold, platinum, and rhodium, influences the cathodic reduction of oxygen and controls the etching rate. In this paper, we investigate the influence of the HF concentration on the etching rate and the pore morphology. In the case of high HF concentration, the etching rate is independent of the HF concentration and depends on the oxygen concentration and the catalytic activity of the metal particles. In the low HF concentration case, the etching rate depends on the HF concentration and is independent of the oxygen concentration and the catalytic activity. The pore morphology is also changed by the HF concentration. © The Electrochemical Society.

Gold nanoparticles on silicon work not only as catalysts to initiate autocatalytic electroless metal deposition but also as binding-points between the deposited metal film and the silicon surface. Conventional catalysts of autocatalytic electroless metal deposition, such as palladium and silver, require heat treatments or anchor formation to obtain practical adhesion of deposited metal films on silicon. Gold nanoparticles can directly produce adhesive metal films on flat silicon surfaces without any treatments. Cross-sectional transmission electron microscopic observation reveals that gold nanoparticles form an alloy with silicon at the room temperature. This alloy is expected to improve the adhesion of metal film on silicon. © The Electrochemical Society.

We developed a low-cost, efficient method to recover all noble metals including gold, silver, palladium, rhodium, platinum, osmium, ruthenium, and iridium from aqueous solutions by simply adding hydrofluoric acid (HF) and silicon (Si) powder. The recovery rate depends on the specific surface area of Si, the HF concentration, and the solution temperature. Our method selectively recovers noble metals and copper from a mixture solution of noble and base metal ions, such as nickel, cobalt, and iron, and obtains pure noble metal powder by dissolving Si. The Si powder and the HF solution are expected to be supplied from semiconductor industries, such as the sawdust Si of wafering or dicing and the waste HF solution of wafer cleaning or etching. This new method recovers noble metals from waste (urban mines) using other waste; it also has green electroless deposition. © The Electrochemical Society.

Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias. We have been studying the metal-assisted hydrofluoric acid etching of silicon using dissolved oxygen as an oxidizing agent. Three major factors control the etching reaction and the porous silicon structure: photoillumination during etching, oxidizing agents, and metal particles. In this study, the influence of noble metal particles, silver, gold, platinum, and rhodium, on this etching is investigated under dark conditions: the absence of photogenerated charges in the silicon. The silicon dissolution is localized under the particles, and nanopores are formed whose diameters resemble the size of the metal nanoparticles. The etching rate of the silicon and the catalytic activity of the metals for the cathodic reduction of oxygen in the hydrofluoric acid solution increase in the order of silver, gold, platinum, and rhodium.

The influence of hydrogen on the microstructure of Pt films electrodeposited from a dinitrosulfatoplatinate(II) solution was investigated with thermal desorption spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. Two pronounced desorption peaks were observed in the thermal desorption spectrum of hydrogen from the Pt films. The total amount of desorbed hydrogen in the range from 300 to 1100 K in the atomic ratio (H/Pt) was 0.1. The deposited Pt film consisted of fine grains (∼10 nm) and many nano-voids. The lattice parameter of the Pt grains was lower than that of bulk Pt. Drastic grain growth and reduction in the lattice contraction occurred from heat treatment at a temperature corresponding to the first hydrogen desorption peak of 500 K. © The Electrochemical Society.

A new recycling electroless nickel plating system has been developed using nickel hypophosphite as the source of metallic ions and as a reducing agent. In the system, phosphite ions, which are deleterious for the plating process, are fixed as the precipitate of calcium phosphite. Then they are removed from the solution. During repetitive plating operations, we maintained the plating solution composition and pH as almost constant values. The quantitative change of the reaction products provides theoretical confirmation that the system can be characterized as a 'zero-emission-type recycling model'.

Autocatalytic electroless deposition, which is a conventional method to metalize nonmetallic substrates, requires catalyzation of substrates before deposition. For silicon (Si) substrates, obtaining adhesive metal films with conventional catalyzation pretreatment is difficult. In this study, we develop a new surface-activation process for the direct electroless deposition of adhesive metal films on Si substrates that consists of three steps: (1) metal nanoparticle formation by electroless displacement deposition; (2) Si nanopore formation by metal-particle-assisted hydrofluoric acid etching; and (3) metal filling in nanopores and metal-film formation on the whole Si surface by autocatalytic electroless deposition. The metal nanorods in the Si act as catalytic nanoanchors to promote autocatalytic electroless metal deposition and improve the adhesion of the metal films on the Si substrates. This process was successfully applied not only to nickel-boron alloy but also to copper film deposition on Si substrates. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3610221] All rights reserved.

The mechanism of recrystallisation observed at room temperature in electrodeposited Cu films has been examined in light of the enhancement of metal atom diffusion by hydrogen induced superabundant vacancies. Thermal desorption spectroscopy revealed that Cu films electrodeposited from acid sulphate bath containing some specific additives showed a pronounced peak, which was ascribed to the break- up of vacancy-hydrogen clusters. The amount of desorbed hydrogen was comparable to that of vacancy type clusters estimated in previous positron annihilation experiments. The grain size of Cu films increased as hydrogen desorption proceeded. Such grain growths were not observed in the films deposited from the baths without additives. These results indicate that the room temperature recrystallisation of electrodeposited Cu films is caused by hydrogen induced superabundant vacancies.