Hitoshi Matsuda

Formation of porous silicon by metal particle enhanced chemical etching in HF solution and its application for efficient solar cells

Abstract 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.

Electrochemical deposition of fine Pt particles on n-Si electrodes for efficient photoelectrochemical solar cells

Abstract 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 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 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 (VOC) 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.

Effect of Surfactants Addition on the Suspension of PTFE Particles in Electroless Plating Solutions

SummaryThis study examines the effect of the presence of a variety of surfactants on the suspension of PTFE particles in electroless nickel plating solutions. It has been identified that the suspension of the particles was improved by the addition of non-ionic surfactants especially in the case of polyoxyethylene nonyl phenyl type surfactants.

High Catalytic Activity of Palladium for Metal-Enhanced HF Etching of Silicon

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.

Effect of Cationic Surfactant on Deposition Behaviour in Electroless Ni-P-PTFE Composite Plating

SUMMARYThis paper describes the effects of the presence of cationic surfactants upon the deposition behaviour of electrolessly deposited composite films. Polytetrafluoroethylene (PTFE) particles were codeposited in electroless nickel phosphorus plated films. In this study, it was found that the zeta potential of the particle surface in the plating solutions and the content of the particles in the films both depend upon the surfactant type, with a specific correlation also observed between the PTFE content in the film and the zeta potential.

Influence of hydrogen on room temperature recrystallisation of electrodeposited Cu films: thermal desorption spectroscopy

Abstract 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.

Microstructural feature of crystalline–amorphous transition layer in structurally graded Co–P films produced by an electroless plating process

Abstract 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.

Uniform dispersibility of PTFE particles in electroless composite plating

Electroless nickel plating has been studied from acidic bath solution containing ethylenediamine and/or sodium potassium tartrate as complexing agents at various pH, temperatures and concentrations of sodium hypophosphite. Ni-P alloys with various amounts (1-18%) of phosphorus are obtained under different plating and bath conditions. Cyclic voltammetric studies of the bath solution revealed that the extent of complexation of nickel ions with the complexing agents is in the order of EDA > SPT > EDA & SPT. The functional properties of Ni-P alloys are found to depend on structure, composition and post-treatments. The high % in P in the alloy gave a high corrosion resistance. The X-ray diffraction studies revealed the existence of multiphase Ni-P, Ni 3 P 2 and Ni 5 P 2 films on the surface. Working conditions are optimised to get good quality deposits with high plating rate at sufficiently low temperature from a stable plating bath solution.

Effects of deposition temperature on characteristics of ferroelectric Sr2Bi4Ti5O18 nanoplates fabricated by RF sputtering

Sr2Bi4Ti5O18 (SBTO) films with a- and b-axis orientations, and thicknesses of 0.9–1.2 µm were sputter-deposited on conductive Nb:TiO2(101) substrates containing 0.79 mass % Nb. The deposition temperature was varied from 575 to 700 °C under a fixed gas pressure of 0.4 Pa, and the structural and ferroelectric characteristics of the films were investigated. SBTO films deposited at 625–700 °C had a mostly single-phase orthorhombic structure, with a high degree of a- and b-axis orientations [α(h00)/(0k0)] of 99.0–99.8%. In addition, the full width at half maximum of the (200) diffraction peak was 0.69–0.86°, which indicated good crystallinity. SBTO films deposited at 625–650 °C had a nanoplate-like microstructure with the plates aligned along the [010] direction. The real room-temperature remanent polarization , taking the porosity between the nanoplates into account, exhibited a maximum of 40 µC/cm2 at 650 °C. Thus, the optimal deposition temperature for heteroepitaxial growth of SBTO nanoplates with a high α(h00)/(0k0) of ≥99.0% and excellent ferroelectric properties on conductive Nb:TiO2 substrates is 650 °C under a gas pressure of 0.4 Pa.

Confirmation of hydroxide in electroless cobalt alloy films by GDOES

Abstract 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.