Madoka Takai

A soft magnetic CoNiFe film with high saturation magnetic flux density and low coercivity

Magnetic materials are classed as ‘soft’ if they have a low coercivity (the critical field strength Hc required to flip the direction of magnetization). Soft magnetic materials are a central component of electromagnetic devices such as step motors, magnetic sensors, transformers and magnetic recording heads. Miniaturization of these devices requires materials that can develop higher saturation flux density, Bs, so that the necessary flux densities can be preserved on reducing device dimensions, while simultaneously achieving a low coercivity. Common high-Bs soft magnetic films currently in use are electroplated CoFe-based alloys electroplated CoNiFe alloys and sputtered Fe-based nanocrystalline and FeN films. Sputtering is not suitable, however, for fabricating the thick films needed in some applications, for which electrochemical methods are preferred. Here we report the electrochemical preparation of a CoNiFe film with a very high value of Bs (2.0–2.1 T) and a low coercivity. The favourable properties are achieved by avoiding the need for organic additives in the deposition process, which are typically used to reduce internal stresses. Our films also undergo very small magnetostriction, which is essential to ensure that they are not stressed when an external magnetic field is applied (or conversely, that external stresses do not disrupt the magnetic properties). Our material should find applications in miniaturization of electromechanical devices and in high-density magnetic data storage.

Significance of Antibody Orientation Unraveled: Well-Oriented Antibodies Recorded High Binding Affinity

To investigate the effect of antibody orientation on its immunological activities, we developed a novel and versatile platform consisting of a well-defined phospholipid polymer surface on which staphylococcal protein A (SpA) was site-selectively immobilized. The application of a biocompatible phospholipid-based platform ensured minimal denaturation of immobilized antibodies, and the site-selective immobilization of SpA clarified the effect of antibody orientation on immunological activities. The phospholipid polymer platform was prepared on silicon substrates using the surface-initiated atom transfer radical polymerization (SI-ATRP) technique. An enzymatic reaction was performed for orientation-selective coupling of SpA molecules to the polymer brush surface. Orientation-controlled antibodies were achieved using enzymatic reactions, and these antibodies captured 1.8 ± 0.1 antigens on average, implying that at least 80% of immobilized antibodies reacted with two antigens. Theoretical multivalent binding analysis further revealed that orientation-controlled antibodies had antigen-antibody reaction equilibrium dissociation constants (K(d)) as low as 8.6 × 10(-10) mol/L, whereas randomly oriented and partially oriented antibodies showed K(d) values of 2.0 × 10(-7) and 1.2 × 10(-7) mol/L, respectively. Strict control of antibody orientation not only formed an approximately 100-fold stronger antigen-antibody complex than the controls but also sustained the native antibody K(d) (10(-10)-10(-9) mol/L). These findings support the significance of antibody orientation because controlling the orientation resulted in high reactivity and theoretical binding capacity.

Effects of Saccharin and Thiourea on Sulfur Inclusion and Coercivity of Electroplated Soft Magnetic CoNiFe Film

During the course of our recent work performed to develop an electroplated CoNiFe temary alloy with high saturation magnetic flux density and low coercivity for use in magnetic recording heads, it was observed that two common sulfur-containing additives, saccharin and thiourea, behave differently with respect to the dependence of sulfur inclusion and coercivity of the alloy film on the additive concentration in the plating bath. To understand the cause of this difference, scanning tunneling microscopy (STM) was performed, using Au(111) as the substrate, to examine the structure of the adsorbed layers of the additive molecules. The result revealed that the nature of adsorption is fundamentally different for the two different additives; i.e., the adsorption of saccharin is physical and reversible, whereas thiourea undergoes irreversible chemisorption. This finding is consistent with the known behaviors of the two additives in the electroplating of nickel. In this paper the different effects of saccharin and thiourea in the electrodeposition of CoNiFe alloy are interpreted based on the STM results and relevant information available in the literature on the electrodeposition of nickel.

Protein adsorption and cell adhesion on cationic, neutral, and anionic 2-methacryloyloxyethyl phosphorylcholine copolymer surfaces

Protein adsorption and cell adhesion on cationic, neutral, and anionic water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer surfaces were compared. These model MPC copolymers coated SiO(2) surfaces exhibited comparable surface zeta-potentials of 26.1 mV, near 0 mV, and -24.2 mV, respectively. X-ray photoelectron spectroscopy analyses indicated the similarities and the differences in the surface composition between the sample surfaces. Atomic force microscopy analyses revealed that the type of the charged moiety did not affect the surface roughness. Static contact angle measurements and dynamic contact angle analyses not only indicated that the surfaces were very hydrophilic in general, but also provided information on the surface mobility and the dominant role of MPC at the surface in aqueous conditions. Comparing with the SiO(2) substrates on which protein seriously adsorbed and cell heavily adhered, three MPC copolymers coated surfaces, despite their different charge properties, exhibited significantly low adsorbed amounts of different proteins having various electrical natures and totally no cell adhesion. This suggested that the incorporation of charged moieties in the MPC copolymers did not significantly inspire both the protein adsorption and cell adhesion. The MPC moieties were predominant at the surface when in contact with aqueous conditions and thereby dominated the bio-adsorptions, while the possible effect from electrostatic interactions would be too small and too limited to influence the overall situation. Therefore, these MPC copolymer surfaces can satisfy those biological applications requiring not only electrical but also non-biofouling properties.

Polymer Nanoparticles Covered with Phosphorylcholine Groups and Immobilized with Antibody for High-Affinity Separation of Proteins

Novel polymer nanoparticles were prepared for the selective capture of a specific protein from a mixture with high effectiveness. The nanoparticle surface was covered with hydrophilic phosphorylcholine groups and active ester groups for easy immobilization of antibodies. Phospholipid polymers (PMBN) composed of 2-methacryloyloxyethyl phosphorylcholine, n-butyl methacrylate, and p-nitrophenyloxycarbonyl polyethyleneglycol methacrylate, were synthesized for the surface modification of poly( l-lactic acid) nanoparticles. Surface analysis of the nanoparticles using laser-Doppler electrophoresis and X-ray photoelectron spectroscopy revealed that the surface of nanoparticles was covered with PMBN. Protein adsorption was evaluated with regard to the nonspecific adsorption on the nanoparticles that was effectively suppressed by the phosphorylcholine groups. The immobilization of antibodies on nanoparticles was carried out under physiological conditions to ensure specific binding of antigens. The antibody immobilized on the nanoparticles exhibited high activity and strong affinity for the antigen similar to that exhibited by an antibody in a solution. The selective binding of a specific protein as an antigen from a protein mixture was relatively high compared to that observed with conventional antibody-immobilized polymer nanoparticles. In conclusion, nanoparticles having both phosphorylcholine and active ester groups for antibody immobilization have strong potential for use in highly selective separation based on the biological affinities between biomolecules.

Effect of higher-silane formation on electron temperature in a silane glow-discharge plasma

Electron temperature measured by an optical-emission spectroscopy shows a strong substrate temperature dependence in a silane glow-discharge plasma. The electron temperature increases with time after turning on the plasma at a low substrate temperature of 150 °C, while it stays constant at a high substrate temperature of 400 °C. The electron temperature is drastically reduced when the source gas silane is diluted with hydrogen at low substrate temperatures. These results suggest that the electron temperature in silane plasma is strongly affected by an electron-attachment process to higher-order silane molecules whose formation reactions show negative activation energies with gas temperature and are also suppressed by the presence of hydrogen molecules.

New soft magnetic CoNiFe plated films with high B/sub s/=2.0-2.1 T

A CoNiFe film with saturation magnetic flux density (B/sub s/) greater than 2.0 tesla (T) has been prepared for the first time as a soft magnetic film; the coercivity (H/sub c/) of the film is less than 160 A/m (2.0 Oe). This success was achieved by formulating a new plating bath and operating conditions to form fine grains. The film has a low H/sub c/ of less than 160 A/m, a low saturation magnetostriction (/spl lambda//sub s/) of approximately 10/sup -6/, and a high B/sub s/ of 2.0-2.1 T. The present invention is expected to contribute to accelerating the development of not only the technology of high-density magnetic recording but also the field of magnetic materials in general.

Super-hydrophilic silicone hydrogels with interpenetrating poly(2-methacryloyloxyethyl phosphorylcholine) networks.

We synthesized silicone hydrogels from 2-methacryloyloxyethyl phosphorylcholine (MPC) and bis(trimethylsilyloxy)methylsilylpropyl glycerol methacrylate (SiMA) using two methods: random copolymerization with a small amount of cross-linker (P(SiMA-co-MPC)) and construction of an interpenetration network (IPN) structure composed of cross-linked poly(MPC)(PMPC) chains and cross-linked poly(SiMA)(PSiMA) chains (PSiMA-ipn-PMPC). The polymerization was carried out by photoreaction. The surface hydrophilicity and water absorbability of P(SiMA-co-MPC) increased with an increase in the MPC unit composition. On the other hand, in the case of PSiMA-ipn-PMPC, a super-hydrophilic surface was obtained by the surface enrichment of MPC units. The optical and mechanical properties of PSiMA-ipn-PMPC are suitable for use as a material for preparing contact lenses. In addition, the oxygen permeability of PSiMA-ipn-PMPC remains high because of the PSiMA chains. The MPC units at the surface of the hydrogels reduce protein adsorption effectively. From these results for PSiMA-ipn-PMPC, we confirmed that it has the potential for application to silicone hydrogel contact lenses.

Amorphous silicon solar cells deposited at high growth rate

Abstract A series of investigations was performed to improve stabilized efficiency of hydrogenated amorphous silicon (a-Si:H) solar cells deposited at a high growth rate of 15–20 A/s by the plasma-enhanced chemical vapor deposition method. The deterioration of film stability accompanied by an increase of deposition rate was found to be closely correlated with the increase of Si–H 2 bond hydrogen content in the deposited film. Plasma diagnosis results by quadrupole mass spectrometry and optical emission spectroscopy showed that reduction of electron temperature of plasma can effectively suppress the formation of higher-order silane-related species in the plasma and can improve film stability. According to the guiding principles deduced from the plasma diagnosis, we successfully improved the stability of cell performance and obtained a considerably improved stabilized efficiency of 8.2% at a high rate of 20 A/s. Key issues for improving stabilized efficiency of high growth-rate a-Si:H solar cells, by making the best use of plasma diagnostic techniques, are presented and discussed.

Bioinspired interface for nanobiodevices based on phospholipid polymer chemistry

This review paper describes novel biointerfaces for nanobiodevices. Biocompatible and non-biofouling surfaces are designed largely based on cell membrane structure, and the preparation and functioning of the bioinspired interface are evaluated and compared between living and artificial systems. A molecular assembly of polymers with a phospholipid polar group has been developed as the platform of the interface. At the surface, protein adsorption is effectively reduced and the subsequent bioreactions are suppressed. Through this platform, biomolecules with a high affinity to the specific molecules are introduced under mild conditions. The activity of the biomolecules is retained even after immobilization. This bioinspired interface is adapted to construct bionanodevices, that is, microfluidic chips and nanoparticles for capturing target molecules and cells. The interface functions well and has a very high efficiency for biorecognition. This bioinspired interface is a promising universal platform that integrates various fields of science and has useful applications.