八重 真治

Metal-particle-assisted hydrofluoric acid etching of silicon (Si) is a unique method of preparing Si nanopores with metal nanoparticles at the bottom of each nanopore. Autocatalytic electroless deposition, which is the conventional method to metalize nonmetallic substrates, requires catalyzation of the substrates before deposition. For Si substrates, obtaining adhesive metal films with conventional catalyzation pretreatments is difficult. We recently developed a new method to produce adhesive metal films on Si substrates using catalytic nanopores that consists of three steps: 1) displacement deposition of metal nanoparticles; 2) Si nanopore formation by metal-particle-assisted hydrofluoric acid etching; and 3) autocatalytic electroless deposition of metal films. In this study, the new method is applied not only to previously reported p-Si (100) 1 Ω cm substrates but also to various Si substrates, such as low and high resistibility, p- and n-types, (100), (111), and (110) planes, and single-, multi- and micro-crystalline substrates. Adhesive and bright metal films were formed on all Si substrates. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal-assisted HF etching of Si has attracted considerable attention as a new electroless method that can produce porous Si by immersing metal-modified Si in a HF solution without bias. Such etching generally uses not only metal-modified Si but also an oxidizing agent. Palladium exhibits high activity in assisted etching under dissolved-oxygen-free and dark conditions. In this study, we investigate the Pd assisted HF etching of n-Si by electrochemical measurements. The potential of Pd metal on Si is more negative than the potential of hydrogen evolution at open circuit conditions. Anodic current generation of Pd-modified Si electrodes at positive bias and the localization of etching under Pd films at low thickness indicate that Pd catalyzes the anodic dissolution of Si and the cathodic hydrogen evolution. ©The Electrochemical Society.

The displacement reaction, which is the immersion of Si wafers into a metal-salt solution containing HF, has been applied to prepare catalytic fine metal particles for metal-assisted HF etching, photoelectrochemical solar cells, and autocatalytic plating. The particle density of Pt particles deposited by displacement reaction on n-Si was different based on the solution used for Si chemical oxidation prior to the deposition. Particle density correlates not with the electrical state density at the SiOx/Si interface but with the contact angle of pure water and the microroughness of the oxidized n-Si surface. A model of the deposition process of Pt particles on an oxidized n-Si surface is proposed. ©The Electrochemical Society.

In this paper, we investigate electrodeposition of Pt, Pd and Au particles on n-Si using a double potential step method that applies single pulse potential of -1 to -8 V vs. SCE and then maintains constant potential at -0.3 V. An aqueous solution of H₂PtCl₆, PdCl₂ or HAuCl₄ at pH 1.7 is used for the electrodeposition of each metal. The particle density of Pt is increased with a negative shift of the pulse potential and then remains nearly constant. The Pd particle density changes with the pulse potential in a similar manner to the Pt particle case. The particle density of Au is much higher than that of Pt, and it is independent of the pulse potential. Immersion of bare n-Si wafers in the H₂PtCl₆ solution under the open-circuit condition deposits no particles but produces silicon oxide. Immersion in a H₂PtCl₄ (Pt(II)) solution, under the same condition as the H₂PtCl₆ (Pt(IV)) case, deposits Pt particles on n-Si. Immersion in a HAuCl₄ solution deposits almost the same particle density of Au as electrodeposition. These displacement reactions, which involve cathodic reduction of metal ions and anodic oxidation of Si, influences the electrodeposition behavior.

The depositing conditions were investigated for obtaining a modulated structure that appeared between an amorphous structure and a columnar structure in electroless Co-P alloy films. The microstructure of electroless Co-P films was found to be sensitively dependent on the variation of the deposition rate controlled by both the solution pH and the stirring strength. Uniform modulated structure Co-P film was formed in the limited deposition rate range. Cross-sectional transmission electron microscopy clarified that the modulated structure Co-P film consists of a periodic array of granules less than 100 nm separated by amorphous channels enriched with phosphorous. The modulated structure Co-P film was comprised of hard and soft magnetic components.

Electro deposition technology has been utilized widely in various industries. However, the internal stress generated in the plated film during deposition often results in peeling and crack of the thin film. The investigation of generation mechanism of the internal stress is indispensable for improving the plating film. Measurements of internal stress are required during the early stages of film growth. In this study, TV holographic interferometry, which can capture holographic images at TV frame rates, was used to sensitively measure with the accuracy of λ/2 the deflection of the cantilever beam during the deposition on the substrate. Internal stress is calculated in-situ by substituting the deformation date in Stoney's equation. In this experiment, to examine the influence of the substrate on internal stress of electroplating, the epitaxial growth of plating was compared with the plating growth on an amorphous substrate. Next, internal stress was measured in various plating (Zn, Cu and Ni) without the additive. The generation mechanism of the internal stress was considered by the surface morphology (SEM) and the cross-sectional (TEM) observation of the plating film. The main results are as follows. 1) Internal stress during the early stage of film growth changes greatly on the surface of amorphous substrate compared with the epitaxial growth. But, the difference of both becomes small as the film grows up. 2) In general, internal stress rapidly changes in the initial stage of film growth, and changes gradually afterwards. 3) The compression stress is generated in Zn plating, the tensile stress is generated in Ni plating and in Cu plating, a tensile stress is generated in the initial stage of film growth, which immediately changes to compressive stress.

The objective of this study is to elucidate the relationship between the total amount of hydrogen absorbed in electrodeposited cobalt films and their microstructure. The electrodeposited cobalt films were produced by such different depositing conditions as a solution pH, bath temperature, and current density. Structure analysis with XRD and TEM and hydrogen analysis with TDS reveal that the cobalt films with higher absorbed hydrogen content have a structure with coarse grain that consisted of hcp(100) preferred orientation. On the other hand, the cobalt films with lower absorbed hydrogen content have a stacking fault structure of hcp(110)/fcc(220). The total amount of absorbed hydrogen has a liner relationship with the stacking fault ratio and the grain size. ©The Electrochemical Society.

The behavior of Pt electrodeposition on n-Si is different between H 2PtC16 (Pt(IV)) and K2PtCl4 (Pt(II)) aqueous solutions. Immersion of bare n-Si wafers in a Pt(II) solution under an open-circuit condition deposits Pt particles on n-Si, but immersion in the Pt(IV) solution deposits no particles. In the Pt(IV) solution, silicon oxide is produced with holes injected into the Si valence band by the reduction reaction of Pt(IV) to Pt(II). The quantity of electrodeposited Pt on the glassy carbon at +0.10 V vs. SCE in the Pt(IV) solution was smaller than that of the Pt(II) case. Cyclic voltammetry shows that the electeroeposition behavior of Pt in the early stage is influenced by the substrates. ©The Electrochemical Society.

In situ stress measurements of electrodeposited Ni films from a sulfate bath during deposition were carried out by television holographic interferometry. The effect of the addition of saccharin sodium on the internal stress in the Ni films was studied. Structure change with film growth was investigated by cross-sectional TEM observation. Quantitative analysis of impurities and hydrogen in films was performed. The stress behaviors of Ni films changed drastically from a tensile direction to a compressive direction with an increase of the concentration of saccharin sodium. ©The Electrochemical Society.

Metal-enhanced HF etching of Si is an electroless method used to produce porous Si. Such etching generally uses not only metal-modified Si but also an oxidizing agent, such as hydrogen peroxide or metal ions. Pd exhibits high activity in enhancing the HF etching of Si without an oxidizing agent even under dissolved-oxygen-free and dark conditions. Electrolessly deposited Pd particles on n-type Si enhance the HF etching of Si but produce no porous layer. Patterned Pd films localize the etching under the boundary of the Pd deposited areas, and thus Pd can produce a microetch pattern on Si with a simple immersion in the HF solution. This etching reaction is explained by electron injection into the conduction band of Si due to the Pd-enhanced anodic oxidization of Si with water and the cathodic hydrogen evolution on Pd with the injected electrons.

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 pretreatments is difficult. In this study, we develop a new method to produce adhesive metal films on Si substrates by an electroless process that consists of three steps: 1) electroless displacement deposition of metal nanoparticles; 2) Si nanopore formation by metal-particle-enhanced 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 Si act as catalytic nanoanchors to promote autocatalytic electroless metal deposition and improve the adhesion of metal films on Si substrates. ©The Electrochemical Society.

We investigated the relationship between adhesion and internal stress to improve the adhesion of electroless pure Ni plating on a smooth alumina substrate, focusing on the energy balance in the interface between the substrate and the film. We measured both parts for unified energy (J/m 2 ) and found the ideal adhesion energy. In the measured results, peel energy G p is dependent on film thickness, and thicker film reduced the G p of the Ni plating. Since the thickness of columnar crystal pure Ni plating film is more than 0.2 /urn, columnar crystal pure Ni plating is highly adhesive on smooth alumina substrates. Interfacial adhesion energy G ad which is the ideal adhesion energy is not simply the sum of peel energy G p (adhesion) and internal strain energy Gin (internal stress); we also must consider bending energy Gbend, elastic energy G el , and fracture energy G f . The gains achieved reflect the high adhesion property of columnar crystal pure Ni plating compared to nano crystalline pure Ni plating. In this study we successfully controlled both the appearance of the void for the interface between the substrate and the film to minimize internal strain energy Gin, and the strength around the interface between the substrate and the film to minimize elastic energy Gel and fracture energy Gf.

Metal filled Si nanopores, that is, metal nanorods in an Si matrix, are produced by an electroless process that consists of three steps: (1) electroless displacement deposition of metal nanoparticles from a metal salt solution containing HF; (2) Si nanopore formation by metal-particle-enhanced HF etching; and (3) metal filling in nanopores by autocatalytic electroless deposition. Ag nanoparticles produce Si nanopores whose sizes are a few tens of nm in diameter and ca. 50 nm deep. Au nanoparticles produce finer and straighter nanopores on Si than the Ag case. These nanopores are filled with a Co or a Co-Ni alloy by autocatalytic deposition using dimethylamine-borane as a reducing agent. Phosphinate can be used as a reducing agent for the Au-deposited-and-pore-formed Si. The important feature of this process is that the metal nanoparticles, that is, the initiation points of the autocatalytic metal deposition, are present on the bottoms of the Si nanopores. (C) 2008 Elsevier B.V. All rights reserved.

Metal-enhanced HF etching of Si is an electroless method to produce porous Si. Such etching generally uses not only metal-modified Si but also an oxidizing agent, such as hydrogen peroxide. Pd exhibits high activity for enhancing the HF etching of Si without an oxidizing agent, even under dissolved oxygen free and dark conditions. Electrolessly deposited Pd particles on n-Si enhance the HF etching of Si, but produce no porous layer. Patterned Pd films localize the etching under and the boundary of the Pd deposited areas, and thus Pd can produce a micro-etch pattern on Si with simple immersion in the HF solution. This etching reaction is explained by electron injection into the conduction band of Si due to Pd-enhanced anodic oxidization of Si with water. © The Electrochemical Society.

Pd-particle-modified n-Si can be etched at a high rate in a hydrofluoric acid solution without a particular oxidizing agent under dissolved oxygen free and dark conditions. In this study, Pd thin film patterned n-Si is used. The etching is localized at the boundary between the 29-nm-thick-Pd film and the non-Pd-deposited area of the n-Si surface at the initial stage. Then Pd particles form on the non-Pd-deposited area toward which the etched area extends. Thin (4.3 nm) Pd films localize the etching under the films.

© 2009 by Nova Science Publishers, Inc. All rights reserved. We have been investigating electrochemical deposition of metal nanoparticles on silicon. The metal nanoparticles play a tremendously important role in photoelectrochemical solar cells for photovoltaic and photochemical conversion of solar energy, and in micro- to nano-processing of silicon with metal-enhanced hydrofluoric acid (HF) etching. The kind, particle density and size of nanoparticles influence the stability and conversion efficiency of solar cells, and the etching behavior of silicon. Electrochemical deposition from an aqueous solution of metal ions is one of the simplest methods to produce metal nanoparticles on silicon. This article describes the results of our study on (1) double potential step electrodeposition and (2) electroless displacement deposition of metal nanoparticles on silicon. (1) Double potential step electrodeposition: Fine platinum (Pt) particles were electrodeposited on n-type silicon (n-Si) electrodes from an aqueous solution of hydrogen hexachloroplatinate(IV) by the single potential step (SPS) and double potential step (DPS) methods. The particle density of Pt on n-Si was 108 cm-2 for the SPS method, whereas it increased from 109 to 1010 cm-2 by a shift of the pulse potential at the initial step of the DPS method. The size of the Pt particles enlarged from smaller than 30 nm with the charge density passing across the electrode surface. (2) Electroless displacement deposition: Various kinds of metal nanoparticles were deposited on n-Si by the immersion of Si substrates in a simple metal-salt solution containing HF. The particle density of metals varies widely from 106 to 1011 cm-2, depending on the kind of metal. Deposited metals can be classified into two types of nucleation behavior. One consists of the platinum group elements, including Pt, rhodium, and palladium, which display lower particle densities than elements of the other group and depend on the type of pretreatment of the n-Si, and thus the surface conditions of Si substrates. The second group consists of the copper group elements, including copper, silver, and gold, which display higher particle density than the first group and are independent of pretreatment. The size of deposited particles decreases from hundreds of nm to ten nm as the particle density increases. The displacement deposition of the Pt and silver particles onto n-Si are in progressive and instantaneous nucleation modes, respectively.

Porous silicon (Si) has a wide range of pore sizes between nanometers and tens of micrometers. Microporous Si that consists of nanometer-sized pores has attracted considerable attention due to its visible light emissions and large surface areas. Macroporous Si that consists of micrometer-sized pores is expected to reduce silicon reflectivity to improve the conversion efficiency of solar cells. Porous Si is usually prepared by such methods as electrochemical (p-type) or photoelectrochemical (n-type) anodic etching and chemical (stain) etching. Recently, we reported that porous Si is formed on Si wafers modified with fine metal particles by simply immersing the wafers in a hydrofluoric acid (HF) solution without a bias or a particular oxidizing agent. This chapter describes the structure of porous silicon produced by metal particle enhanced HF etching and its application for the antireflection of multicrystalline Si solar cells. The metal particles are deposited onto Si wafers by electroless displacement deposition from a metal salt solution that includes HF. The metal particle deposited Si wafers are immersed in a simple aqueous HF solution. For n-type Si, a porous layer is only formed on the metal particle deposited area of the wafers. Etching rate increases with oxygen concentration or photoillumination intensity. Both macro and microporous layers are formed on n-Si wafers modified with platinum (Pt), gold, or silver particles. In the case of palladium particles, the n-Si wafers are polish-etched at a rate ten times higher than other metal particles. For Pt-particle-deposited p-type Si, porous layers are formed by HF immersion. Under continuous photoillumination, porous Si is formed mainly on the nonphotoirradiation side surface of p-Si, as opposed to the photoirradiation side of n-Si. Such etching behavior can be described by the mechanism based on the formation of local cells on the surface and the energy band profile of metal particle deposited Si. For Pt-particle deposited multicrystalline n-Si wafers, uniform porous layers are formed by HF immersion. The porous layers reduce the visible light reflectance of the wafers from 30% to 6%. The photocurrent density of porous multicrystalline Si solar cells has a 25% higher value than the non-porous Si cells.© 2009 by Nova Science Publishers, Inc. All rights reserved.

We investigate the nucleation behavior in the electroless displacement deposition of metal particles (Pt, Rh, Pd, Cu, Ag, and Au) onto n-Si wafers from a metal-salt solution containing HE The particle density of metals varies widely from 106 (pt) to loll (Au) cm(-2), depending on the kind of metal. Deposited metals can be classified into two types of nucleation behavior. One consists of the platinum group elements, including Pt, Rh, and Pd, which display lower particle densities than elements of the other group and depend on the type of pretreatment of the n-Si wafer, and thus the surface conditions of Si. The second group consists of the copper group elements, including Cu, Ag, and An, which display higher particle density than the first group and are independent of pretreatment. The size of deposited particles decreases from hundreds nm to tens nm as the particle density increases. Moreover, the displacement deposition of the Pt and Ag particles onto n-Si are in progressive and instantaneous nucleation modes, respectively. (C) 2007 Elsevier Ltd. All rights reserved.

Hydrogen production using water splitting by photoelectrochemical solar cells equipped with a TiO2 photoelectrode has been attracting much attention. However, TiO2 encounters serious difficulty in achieving hydrogen evolution. One solution to this difficulty is using a hydrogen-producing semiconductor, such as silicon, and an oxidation reaction other than oxygen evolution, such as oxidation of iodide ions into iodine (triiodide ion). In this study, microcrystalline silicon (μc-Si:H) thin films are used as photoelectrodes in the photodecomposition of HI for low-cost and efficient production of solar hydrogen. An n-μc-3C-SiC:H and an i-μc-Si:H layer are deposited on glassy carbon substrates using the hot-wire cat-CVD method. The μc-Si:H electrodes are modified with platinum nanoparticles through electroless displacement deposition. The platinum nanoparticles improve the electrode's stability and catalytic activity. The electrodes produce hydrogen gas and iodine via photoelectrochemical decomposition of HI with no external bias under simulated solar illumination. We also attempt solar water splitting using a multi-photon system equipped with the μc-Si:H thin film and TiO2 photoelectrodes in series.

Electrodeposited. Co-P multilayer films were formed by means of controlling stirring conditions and current density under DC electrolysis. The multilayer films comprise amorphous and nanocrystalline layers having a periodicity of several tens of nanometers. The measurement results of the magnetic property of the films are consistent with the above result. (c) 2007 Elsevier B.V. All rights reserved.

The objective of the present study was to confirm the presence of the hydroxide in electrolessly deposited cobalt alloy films. The existence of Mn hydroxide in Co-Mn-P films was confirmed by glow discharge optical emission spectroscopy (GDOES). The results of the electrical resistivity and magnetic coercivity measurements of the films are also consistent with the above results.

Microcrystalline silicon (mu c-Si:H) thin films, which are prospective low-cost semiconductor materials, are used as photoelectrodes for the direct conversion of solar energy to chemical energy. An n-type microcrystalline cubic silicon carbide layer and an intrinsic mu c-Si:H layer are deposited on glassy carbon substrates using the hot-wire cat-CVD method. The mu c-Si:H electrodes are modified with platinum nanoparticles through electroless displacement deposition. The electrodes produce hydrogen gas and iodine via photoelectrochemical decomposition of hydrogen iodide with no external bias under solar illumination. Surface modification with platinum nanoparticles and surface termination with iodine improve the conversion efficiency. (c) 2006 Elsevier B.V. All rights reserved.

With a measurement technique called television holographic interferometry, we investigated the internal stress generated at the initial deposition stage in electrolessly deposited Cu films on silicon substrates. In a region of film thickness less than 100 nm, two inflection points, at which the direction of stress was reversed, were observed on the film thickness-stress curve. From cross-sectional transmission electron microscopy observation of these films, it was found that the films grew in the Volmer-Weber mode and that the above inflection points related to specific stages observed, such as islands growth, islands coalescence, the formation of continuous film, and grain growth. (c) 2007 The Electrochemical Society.

Antireflection of silicon (Si) surface is one key technology for the manufacture of efficient solar cells. Metal particle enhanced HF etching is applied to produce uniform antireflecting porous layer on multicrystalline Si wafers that cannot be uniformly texturized by anisotropic etching with an alkaline solution. Fine platinum (Pt) particles are deposited on multicrystalline n-Si wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. Both macroporous and luminescent microporous layers are uniformly formed by immersing the Pt-particle-deposited multicrystalline Si wafers in a HF solution. The reflectance of the wafers is reduced from 30% to 6% by the formation of porous layer. The photocurrent density of photoelectrochemical solar cells using porous multicrystalline n-Si has a 25% higher value than non-porous Si cells. (c) 2005 Elsevier Ltd. All rights reserved.

Metal-particle deposited Si can be etched by simply immersion in HF aqueous solution without a bias or a particular oxidizing agent. Both macroporous and luminescent microporous Si are formed by this metal particle enhanced etching. The present work applies this method to p-type Si and investigates structural changes in porous Si by controlling photoillumination intensity and dissolved O2 concentration during etching. Fine Pt particles are deposited on p-Si wafers by simple immersion in the HF solution containing H 2PtCl6. Both macroporous and luminescent microporous layers are formed on the Pt particle deposited p-Si wafer by immersion in HF solution under intermittent photoirradiation. Continuous photoirradiation and O2 gas bubbling increase the etching rate of Si. Ar gas bubbling decreases the rate under photoirradiation and stops the etching in the dark. The similarities and differences in the etching behavior between p- and n-type Si are discussed.

The objective of this study was to clarify the microstructure of crystalline-amorphous transition layers formed in electrolessly deposited Co-P films. Structurally graded Co-P films, including the transition layers, were prepared by controlling the solution pH in electroless plating solutions. TEM analysis indicated that the layers featured a modulated structure comprised of two phases, namely a crystalline phase with low P content and an amorphous phase with high P content.

The objective of this study is to clarify the effect of the composition of electroless pure Ni solutions on the microstructure and electrical conductivity of deposited films. The carbon, sulfur and boron contents included as impurities in the samples have been measured, showing changes in the carbon content ranging from 0. 01 to 0. 19% by mass. The crystal structure of the deposited films was investigated by means of cross-sectional TEM observation, and investigation of the obtained electron diffraction patterns reveals that the crystals of the deposited films are generally oriented randomly. The grain size is uniform throughout the investigated film (1 μm), though the diameter varies from 10 nm to 120 nm with changes in the solution composition: relatively coarse grains are observed in films deposited from a solution with a high hydrazine concentration. The addition of saccharin sodium generally induces grain growth. The results of the measurements suggest an adequate correlation between the carbon content and the grain size, and it has become evident that the electrical conductivity of the films decreases linearly with an increase of the carbon content. © 2005, The Japan Institute of Electronics Packaging. All rights reserved.

We have developed an autocatalytic plating solution for pure nickel deposits using hydrazine as a reducing agent. The solution is characterized by its extended lifetime, high deposition rate and high deposit brightness. In this study, we have found that a simple solution consisting of nickel acetate and hydrazine can deposit black nickel films with stability. The deposition rate was 0.79 nm/sec. The addition of a small amount of formaldehyde to the plating solution gave bright nickel films. The purity of the deposited nickel was higher than 99.7%. Its electrical conductivity increased with purity.

The electroless plating method has a particular advantage in that it accepts non-conductive substrates as its substrate materials. The catalyzation pretreatment process is essential for initiating electroless deposition. The most common two-step pretreatment process prior to electroless nickel plating was studied here, which includes the sensitizing step and the activating step. The objective of this study is to investigate the morphological changes of the adsorbate produced on the non-conductive substrates during the period before and after the deposition is initiated. The results obtained are as follows :<br> By using an ICP for the nickel precipitate weight gain measurement when the glass substrate which conducted the catalyzation process was immersed in an electroless Ni-P plating bath, the results show that deposition is already initiated with a low deposition rate even before the deposition can be confirmed with a visual inspection.<br> The observations of the catalyzed surfaces using SEM detect the aggregates of adparticles with sizes grown to reach several microns. The incidence of the grown aggregates has a tendency to be higher as the solubility of Sn in the activating solution is increases. Comparing the results of the morphological observation before and after the initiation of the deposition, it should be concluded that the aggregates produced during the activation step play the starting point of the massive nodular grains that exist on the surface of deposits.<br>

Electroless Plated Ni-P/TiO₂ composite films were deposited from an acidic solution or an alkaline solution containing photocatalytic TiO₂ particles (P-25). The dispersion of particles in the films was investigated by cross-sectional observation with a transmission electron microscope. The particle content in the films increased with an increase of its amount in the solutions. The deposition rate of composite films was independent of the amount of TiO₂ particles in the solutions(0˜100g dm⁻³). Photocurrent density of the films in 0.1M NaOH aqueous solution rose with particle content in the films.<br>

This paper describes the formation process and chemical state of adsorbates produced during the two-step catalysation pre-treatment prior to electroless deposition. Tin species adsorbed during sensitisation are divided into two types, namely one that adsorbs weakly and one that adsorbs strongly. The former exists in equilibrium with Sn2+ in the sensitising solution. It easily desorbed from the substrate during the following 110 immersion, and the loss is recovered during an ensuing sensitising step. The latter is not desorbed during the HCl immersion step. A dry process after sensitisation, which should promote oxidation, induces the transition from Sn2+ to Sn4+. In the activating step, two reactions proceed independently of each other; that is, an oxidation-reduction reaction between Sn2+ and Pd2+ takes place, which produces Pd-0 and Sn4+. Simultaneously, some Sn2+ is desorbed from the substrate. XPS analysis confirms that tin oxide (or hydroxide) and metallic palladium are the final products in the two-step catalysation pre-treatment.

SnCl₂ aqueous solution including HCl is used as a sensitizer of two-step catalyzation (sensitization-activation) pretreatment for electroless metal plating onto non-conducting substrates. The sensitizer is inactivated by aging. In this study, the relationships among the Sn²⁺ concentration of sensitizer, amount of adsorbates formed on the substrates, induction period of electroless Ni-P deposition and aging time have been investigated quantitatively. As the aging proceeded, the Sn²⁺ concentration decreased, while the amount of adsorbates, including Sn species formed by sensitization, increased. With the decrease of Sn²⁺ concentration, the amount of Pd adsorbates formed during activation decreased, and the induction period was extended. An independent investigation using mixture solutions of SnCl₂ and SnCl₄ gave similar results for aging. These results show that the aging of sensitizer induces the decrease of divalent Sn species and the rise of tetravalent Sn species, which is inactive for the formation of Pd adsorbates. Thus, the aging decreases the Pd adsorbates and extends the induction period.<br>

Electroless plating is recently used for electronic industry. But, during the deposition of thin films large internal stresses are frequently built into the films. The internal stress in films has been extensively investigated but its origin has not been clarified yet. In order to determine the origin of stress, measurements of stress are required in the initial stage of film growth. In this study, TV holography, which can capture holographic image at TV frame rates, is used to measure sensitively the change in the internal stress in films by recording the change in deflection of the free end of a cantilever beam. The dependence of internal stress upon film thickness for a Cu plating bath on a Be-Cu substrate was discussed. As the results, large stress variation is generated right after the plating, which occurred simultaneously with the adhesion of the plating particle on the substrate by SEM observation. The stress variation is large different in commercial bath and basic bath which removed small additives. This study shows that present method is useful as "in-situ measurement" of internal stress of electroless plating.

Porous Si was formed on n-Si wafers, modified with fine Pt particles, by simply immersing the wafers in a HF solution without a bias or an oxidizing agent. The Pt particles were deposited onto n-Si wafers by electrodeposition or electroless displacement deposition. SEM images show that many pores, ranging between 0.1 and 0.8 μm in diameter and covered with a luminescent nanoporous layer, were formed only on the Pt-modified area of the n-Si surface by immersion in 7.3 M HF solution for 24 h. The weight loss of Pt-electrodeposited n-Si wafer was 0.46 mg cm -2 , corresponding to ca. 2 μm in thickness. The weight loss and the structure of porous Si changed with the etching conditions, such as concentration of dissolved oxygen in the HF solution, distribution density of metal particles, and different kinds of metal particles. A photoelectrochemical solar cell equipped with a Pt-particle-modified porous n-Si electrode gave 13.3 mW cm -2 of maximum output power, which corresponds to a 13% conversion efficiency and is higher than that for the Pt-particle-modified flat n-Si electrode. ©2003 Elsevier Science B.V. All rights reserved.

For electroless Co-P based alloy films, corrosion resistance increases with increased W content due to passivity, but decreases with increasing Zn content. The coercivity of the films increases with the Zn content, and is independent of the W content. The measurement of film magnetisation using a magnetic balance is effective for the determination of quantitative corrosion loss of ferromagnetic films, such as Co alloys. The electroless Co-W-Zn-P film, about 3 mum in thickness, containing 1.2 atom % of W and 1.6 atom % of Zn gave high coercivity of 69 kA m(-1) and high corrosion resistance, three times that of Co-Zn-P films. XPS analysis indicated that an oxide of Co and WO3 were formed on, and Zn was eluted from, the surface of the Co-W-Zn-P film by the corrosion. The passive WO3 layer improves the corrosion resistance of films.

Electroless deposition of metal onto nonconductors, such as ceramics, glass and plastics, requires a catalyzation pretreatment of substrates. Adsorbates formed on glass or mica substrates by two-step catalyzation (sensitization-activation) have been investigated by quantitative analysis of Sn and Pd on substrates, XPS and AFM. Adsorbates, formed on the substrate by the sensitization, included divalent Sn and O, and no Cl was included. There were two kinds of Sn adsorbates, weak adsorbed ones and strong adsorbed ones. The former was in an equilibrium state to Sn²⁺ in the sensitizer, therefore, it was desorbed from the substrate by immersion into HCl solution, and was recovered to the same amount by the sensitization after the immersion into HCl solution. Elemental Pd which included no Cl was produced on the substrate by the activation after the sensitization. The amounts of Sn and Pd adsorbates were increased by the repetition of sensitization and activation. The activity of the catalyzed substrate for the electroless deposition was lost by the sensitization. AFM inspection showed that fine particles (10–15nm in size, 0.5–1.0nm in height, 4–5×10³ particles μm^-2 in density) were formed on the substrate by the sensitization, and the height and density of particles were enlarged by the activation. The process of two-step catalyzation was explained by using a model based on these results.

Fine platinum (Pt) particles were deposited electrochemically on n-type silicon (n-Si) electrodes from an aqueous hexachloroplatinic acid(IV) solution by the single potential step (SPS) and double potential step (DPS) methods. The distribution density of the Pt particles on n-Si was 10(8) cm(-2) for the SPS method, whereas it increased from 10(9) to loll cm(-2) by a shift of the pulse potential at the initial step of the DPS method from -1.0 to -4.0 V versus SCE and remained nearly constant at more negative potentials. The size of the Pt particles enlarged with the charge density passing across the electrode surface at a potential of -0.70 V versus SCE, which was applied throughout for the SPS method and at the second step for the DPS method. Photoelectrochemical (PEC) solar cells equipped with Pt-electrodeposited n-Si electrodes generated open-circuit photovoltages (V-OC) of 0.51-0.61 V, much higher than those for n-Si electrodes coated with continuous Pt layers (ca. 0.2-0.3 V). Solar cell characteristics changed with the pulsed potential and charge density passing across the electrode surface which changed the size and distribution density of the Pt particles. The characteristics were explained well by our previous theory on metal-dot coated n-Si electrodes. (C) 2001 Elsevier Science Ltd. All rights reserved.