The high corrosion behavior of the sputter-deposited amorphous or/and nanocrystalline W-Cr-(4-15)Ni alloys was investigated by corrosion tests, electrochemical measurements and X-ray photoelectron spectroscopy (XPS) including angle-resolved measurements in 12 M HCl at 30℃, open to air. Particular attention was paid to the effects of tungsten, chromium and nickel metals addition on the surface composition of the passive films formed on the ternary alloys which is related to the corrosion-resistant as well as the anodic passivity of the alloys. Corrosion rates of the alloys (～0.85-3.00 x 10^-2 mm/y) are about four and three orders of magnitude lower than pure chromium and nickel, respectively, and even slightly lower than tungsten metal. Surface analyses by XPS including angle-resolved measurements revealed that the high corrosion resistance of the ternary W-Cr-(4-15)Ni alloys is mostly due to the formation of homogeneous passive oxyhydroxide films consisting of all alloying cations of the alloys. The beneficial effect of the simultaneous addition of chromium and tungsten is based mainly on the synergistic interaction between chromium and tungsten cations in the homogeneous oxyhydroxide passive films to improve the corrosion behavior as well as the passivity of the W-Cr-(4-15)Ni alloys in 12 M HCl.

View full abstract

We investigated a microwave heating technique to prepare transparent conducting ZnO thin films in air within a few minutes. A microwave was directly irradiated to a glass substrate by a commercial kitchen microwave oven with an output power of 2.45GHz and 1000 W. The substrate temperature went up as high as 550°C in a few tens seconds with increasing the thickness of a microwave absorbing layer attached on the back of the substrate. The electrical resistivity of ZnO film reached the minimum value of 4.1×10^-3 Ω・cm by optimizing a dopant indium concentration.

View full abstract

Superconducting oxide REBa₂Cu₄O₈ (RE124; RE=Y, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb) were synthesized by a molten hydroxide method under an ambient pressure. Rare earth oxide, barium carbonate and copper oxide powder were used as starting materials and potassium hydroxide (KOH) was used as a solvent material. The synthesis was carried out by a heating treatment at 715°C. XRD peaks of RE124 using small ionic radius elements such as Y and Dy-Yb were obtained to be intense and sharp. The effect of RE substitution in superconductivity and lattice constant was investigated by SQUID and XRD. Superconducting critical temperature (Tc) increased and c-axis length decreased as the ion radius decreased. In order to investigate relationship between heating temperature and synthesized phases, Y124 were prepared at different heating temperature from 500°C to 800°C. Y124 phase appeared in the rage between 600°C and 800°C, and the most intense at 700°C. No Y124 phase was observed at 500°C. From these results, it was considered that small ion radius elements such as Y and Dy-Yb are appropriate to easily synthesize RE124 by this method, and the optimal heating temperature is about 700°C.

View full abstract

The optical emission spectra induced by plasma discharge in a supercritical carbon dioxide were measured. The Swan band associated with carbon dimers (C₂) was detected in addition to carbon monoxide, atomic carbon, and atomic oxygen, suggesting the decomposition of the carbon dioxide by the plasma discharge. The Swan band was found to broaden as the carbon dioxide pressure was increased. It was shown that the active C₂ species can be used for the synthesis of carbon-based materials.

View full abstract

Gold nanoplates were prepared in high yield at room temperature using the Fe(III)-reducing bacterium Shewanella algae. The cell extract, prepared by sonicating a suspension of S. algae cells, plays an important role in improving productivity of gold nanoplates. S. algae cell extract was capable of reducing aqueous AuCl₄^- ions into elemental gold within 60 min when H₂ gas was provided as an electron donor. Gold nanoplates with an edge length of 100 nm appeared after 6 hours, and compact gold nanoplates with an edge length of 100-200 nm were obtained after 24 hours. The prepared nanoplates had diffraction spots characteristic of single-crystalline (111)-oriented gold nanocrystal. Using S. algae cell extract, the yield of gold nanoplates relative to the total nanoparticle population was 60 %, which was four times higher than that obtained with a suspension of resting cells. Following centrifugal ultrafiltration of the S. algae extract, only the fraction containing biomolecules greater than 50 kDa successfully produced gold nanoplates.

View full abstract

We report on the synthesis of nanoporous Ni (NP Ni) materials, discuss their morphology, and investigate their electrocatalytic properties in alkaline electrolytes. NP Ni was obtained by the electrochemical dealloying of co-sputtered, X-ray amorphous Ni-Al alloy films in diluted KOH. The solution pH and applied potential were chosen so that Al would selectively dissolve while Ni would remain immune and would not form a passive layer. Upon dealloying, NP Ni develops a nanofibrous morphology, different from the 3-D network of interconnected ligaments observed for nanoporous Au. This is likely due to the inhomogeneity of the Ni-Al precursor, which may tend to form Al-enriched grain boundaries. Relative to smooth Ni, NP Ni showed little or no catalytic enhancement towards the hydrogen evolution and oxygen evolution reactions. We attribute this effect to either i) the pore occlusion caused by nascent gas, and/or ii) the presence of oxides on the surface which may passivate potential active sites.

View full abstract

Transient mass transfer rate of Ag⁺ ion associated with natural convective electrolyte flow developing along the vertical plane electrodes immersed in a stagnant AgNO₃ aqueous electrolyte solution is numerically analyzed under both direct and pulsed current conditions. The cathodic concentration profile of Ag⁺ ion caused by silver electrodeposition was measured by the holographic interferometer. Calculated results are compared with the measured values. Under direct current condition, it is found that quantitative agreement between calculated and measured results is obtained at the lower current density, while an obvious deviation is noticed at the higher one due to the laser beam deflection effect as well as the concentration dependence of transport properties. Additionally, it may be related to the fact that the effective cathode surface area apparently increases due to the roughening of the cathode surface by silver electrodeposition. Under pulsed current condition, reasonable agreement is obtained even at the higher pulse current density. It may be ascribed to the fact that pulse electrolysis reduces the nodular growth, edge build up, and surface roughness development.

View full abstract

Multilayered polymer solar cells were fabricated by a combination of spin-coating and layer-by-layer (LbL) deposition techniques. A light-harvesting layer was precisely designed by LbL assembly of poly(p-phenylenevinylene) (PPV) and an anionic PPV derivative, poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV). The remaining hole-transporting and electron-transporting layers were prepared by the spin-coating method. In order to improve optical properties of the MPS-PPV LbL film, dimethylsulfoxide (DMSO) was added to an aqueous solution of MPS-PPV. As a result, the absorption of PPV/MPS-PPV LbL films increased at around 500 nm compared with that of the reference LbL films fabricated from an aqueous solution of MPS-PPV. The short-circuit current density of the multilayered polymer solar cell was improved by > 10% compared to the reference cell with PPV/MPS-PPV LbL layers fabricated from the aqueous solution. Furthermore, the external quantum efficiency at around 500 nm was also improved, suggesting the increase in the light-harvesting efficiency of the LbL layer fabricated from the water/DMSO mixed solution of MPS-PPV.

View full abstract

Electrodeposition of tungsten has been achieved at 150°C, which is the lowest temperature to this day, by using a new molten salt (ionic liquid), N-ethyl-N-methylpyrrolidinium chloride (EMPyrCl)-ZnCl₂. Metallic tungsten was electrodeposited on a nickel substrate by potentiostatic electrolysis at 0.01 V vs. Zn(II)/Zn in an equimolar EMPyrCl-ZnCl₂ melt after adding KF and WCl₄. A denser and smoother tungsten film was obtained by the same electrolysis condition when WCl₆ was used as a tungsten ion source.

View full abstract

Photoluminescence properties are studied on scandia-stabilized zirconia for 8, 11 and 12 mol%-scandia-doped samples. Temperature dependence of multiple sub-bands observed under irradiation of He-Cd laser light (3.81 eV) is investigated and shows a clear contrast between 11 and 12 mol%-doped samples. A model is presented, which explains by thermal properties for both ground and excited electronic states of oxygen vacancies under photo-excitation.

View full abstract

The electrodeposition of ternary Al-Mo-Ti alloy was examined in the Lewis acidic 66.7-33.3 percent mole fraction aluminum chloride–1-ethyl-3-methylimidazolium chloride (AlCl₃–EtMeImCl) room-temperature ionic liquid containing both (Mo₆Cl₈)Cl₄ and TiCl₂. All of the electrodeposited Al-Mo-Ti alloys were dense and compact, and they adhered well to the copper substrate. In simulated body fluid, e.g., Ringer’s solution, the Al-Mo-Ti alloy showed better corrosion resistance than pure nickel although it was somewhat inferior to 316 L stainless steel that is one of typical metallic biomaterials. Open circuit experiments in Ringer’s solution suggested that amorphous Al-Mo alloy is superior to Al-Ti and Al-Mo-Ti alloys as a metallic biomaterial because of the formation of more stable passivation layer.

View full abstract

Amorphous SiO₂ powder refined from diatomaceous earth (DE-SiO₂) was pressed into pellets, and the electrolytic reduction of them has been investigated in molten CaCl₂ at 1123 K. The DE-SiO₂ pellets were successfully reduced to Si by electrolysis at 1.00 and 1.20 V vs. Ca²⁺/Ca. Observations with a scanning electron microscope revealed that the reduced Si has the rod-like nanostructure, and that the reduction rate for the DE-SiO₂ pellet is higher at more negative electrode potential. Furthermore, the reduction rate for the DE-SiO₂ pellet is higher than that for the fumed-SiO₂ pellet. The high reduction rate of the DE-SiO₂ pellet and the evolution of rod-like nanostructure are probably derived from its peculiar porous structure. DE-SiO₂ will be one of the most promising Si sources in the industrial-scale electrolytic reduction in both aspects of the reduction rate and the abundance of the resources.

View full abstract

We report in this paper the observation of a transition between two different dendritic growth mechanisms in the electrodeposition of a metal from a binary electrolyte. This transition is associated with a change in the current density regime. Our results, in particular concerning the dendritic growth velocities and ionic concentrations in the electrolyte, are well explained in terms of models previously proposed in the literature.

View full abstract

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.

View full abstract

The oxygen incorporation reaction, and its opposite, the oxygen deletion reaction, may be rate limiting reactions in solid oxide fuel cells. This study examines the insertion and deletion reactions in the popular solid oxide fuel cell electrolyte and electrode materials (Y₂O₃)_x(ZrO₂)_1−x (YSZ), (Y₂O₃)_x(CeO₂)_1−x (YDC), (Gd₂O₃)_x(CeO₂)_1−x (GDC), LaMnO₃ (LMO), (La_xSr_1−x)MnO₃ (LSM), and (La_xSr_1−x)(Co_xFe_1−y)O₃ (LSCF). A Kröger-Vink diagram is constructed for SOFC anode and cathode operating conditions, and defect equilibrium considerations are used to explain the experimental result that oxygen incorporation in bilayer electrolytes shows higher surface exchange rates. Quantum simulations of the incorporation reaction and vacancy formation energetics support this conclusion.
  Simulations of oxygen incorporation in perovskites agree with experimental trends in reactivity LSCF > LSM > LMO, and suggest the reason to be due to structural rather than electronic properties. A new model of oxygen deletion at the anode is proposed and shown to have lower energy barriers than sequential deletion and reaction with hydrogen to form the hydroxide ion.

View full abstract

  The electrochemical anodization of silicon films in aqueous solutions containing hydrofluoric acid was investigated. The films were deposited onto fused quartz chips from poly-crystalline, phosphorous doped silicon using magnetron physical vapor deposition in argon plasma. X-ray diffraction from these films showed that the atomic structure of silicon was amorphous. Current-potential profiles of the films in hydrofluoric acid solutions showed a linear increase in current with increasing anodic potential, unlike the diffusion limited profiles obtained from arsenic-doped silicon (100) crystals. In order to form microstructures within selected regions of the silicon, an epoxy resin was lithographically patterned onto the surface of the silicon prior to anodization. Three-dimensional profiles of the film’s surface after removal of the resin revealed that the regions of silicon protected by the resin had formed microstructures.

View full abstract

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.

View full abstract

The method as described below enables us to synthesize a continuous film of Mg₂Si with the thickness up to 10 μm. By conducting potentiostatic electrolysis of a silicon cathode in a molten LiCl-KCl-MgCl₂ melt, electrochemical formation of magnesium silicide proceeded according to the following reaction steps; Mg(II) + 2e^- → Mg (Reduction of Mg(II) on a Si cathode), 2Mg + Si → Mg₂Si (Formation of silicide film). From XRD and SEM results, a polycrystalline Mg₂Si with a thickness of 20 μm was uniformly formed on Si (001) surface, after conducting potentiostaic electrolysis at 0.8 V (vs. Li⁺/Li). Absorption edge of the sample was exhibited at around 0.8 eV through transformation of reflectance spectra with Kubelka-Munk function.

View full abstract

Effects of external bubble supply on the discharge characteristics in water have been investigated. The external bubble supply reduces discharge ignition and sustain voltage. This can be explained as a consequence of increase of availability of primary electrons required for igniting electrical discharges.

View full abstract

We describe a light-controlled template-directed reversible DNA photoligation via carbazole tethered 5-carboxyvinyluracil. Carbazole tethered 5-carboxyvinyl-2´-deoxyuridine (^CVU)-containing oligodeoxynucleotide (ODN) can be ligated by irradiation at 366 nm in the presence of template ODN, and the ligated ODN can be split by irradiation at 366 nm in the absence of the template ODN.

View full abstract

Molecular membranes of the amphiphilic graft peptide (PAAgPLLeu) consisted of polyallylamine main chain and hydrophobic poly(L-Leu) graft chains, as a model of lipid molecules were prepared at water-water interface. Under acidic conditions, PAAgPLLeu formed a regular and dense thin molecular membrame, with the poly(L-Leu) graft chains took a β-sheet structure at the water-water interface. Under this condition, the molecular membrane shows chiral selectivity for an amino acid having the same optical activity as the graft chains of the amphiphilic copolymer. The permeability of L-Leu through the nano-sheet was 26 times greater than that of D-isomer.

View full abstract

  Temperature dependences of poled dielectric constants ε₃₃^T/ε₀ of [001] 0.70 Pb(Mg_1/3Nb_2/3)O₃-0.30 PbTiO₃ (PMN-PT) single crystals with different poling fields were measured to investigate the cause of the fluctuation of the ε₃₃^T/ε₀. Anomalous ε₃₃^T/ε₀ > 50,000 at phase-transition temperature between rhombohedral and tetragonal phases (Trt) with a specific poling field (twice coercive field; E_c) were observed in some samples. Those samples also showed higher ε₃₃^T/ε₀ = 7,700 and piezoelectric constant d₃₃ = 2,000 pC/N at room temperature than those of other samples. Because each sample had the same Curie temperature T_c, the fluctuations are not derived from the variation in crystal composition variation. Easily or not easily polarized crystal parts may exist in the same wafer. And different domain configurations, defects and impurity levels within the wafer may cause the different mobility of polarization. The temperature dependence of ε₃₃^T/ε₀ measurement is an effective method to investigate the cause of the fluctuation of dielectric and piezoelectric properties of single crystal transducer. Thus, the results of this study provide important guidelines for controlling the fluctuation of these properties of single crystal medical array probes.

View full abstract

Depth dependency of local structure of SrTiO₃ thin film was investigated by X-ray absorption fine structure (XAFS). In epitaxial thin films, a large strain exists between substrates and grown films. The expitaxial strain is the largest in the interface and it is relaxed as parting from the substrate. The lattice parameter of the grown film changes depending on the lattice strain. We performed depth-resolved XAFS measurements on SrTiO₃ thin film grown on LaAlO₃ substrate. The depth-resolved XAFS can extract the local structures around the surface and inner regions separately. It was clarified that the bond distance between Sr and O changed greatly depending on the depth. On the other hand, the bond distance between Sr and Ti unchanged.

View full abstract

A careful observation of X-ray diffraction in the ferroelectric crystals such as BaTiO₃ reveals that a new physical picture of the ferroelectric transition in these crystals may rather be regarded as an order-disorder transition. A strong local order in the disordered phase is a characteristic feature. The model gives natural interpretation of the occurrence of a micro cluster phase in the phase transition to explain the existence of the depolarization phase, and this micro cluster phase existed just behind the phase transition temperature in the tetragonal phase.

View full abstract

  The doping effect of Cd ions on the giant dielectric response in Ca_1−xCd_xCu₃Ti₄O₁₂ ceramics with x=0, 0.01, 0.03, 0.05 and 0.1 was studied in the frequency range of 10 kHz–1 MHz over the temperature range of 300–850 K. It is found that the chemical substitution of Cd ions at the Ca sites results in decrease in dielectric constant by 9% – 55% for Cd-doped CaCu₃Ti₄O₁₂, at room temperature. Although the decrease in the dielectric constant was observed by Cd doping, no drastic suppression of dielectric response could be observed by Cd-doping. The dielectric anomaly was found at T₁ (727 K for x=0.05), which suggests a phase transition. This T₁ decreases linearly with increasing x. CdCu₃Ti₄O₁₂ is still a member of high-dielectric materials.

View full abstract

High-pressure synthesis of bismuth based perovskite (Bi_0.5Na_0.5-xLi)TiO₃ (BNLT) (=0.1, 0.15, 0.2, 0.25, 0.4, 0.5) was demonstrated. Single phase BNLTs with perovskite structure were successfully synthesized for x≤0.1 by the solid state reaction method. The solid phase reaction occurred in the pressure range of 6–10 GPa, and in the temperature range of 800–1200°C. Two thermal anomalies were observed in single phase perovskite BNLT(x=0.1) as well as (Bi,Na)TiO₃. The cusp like anomaly at 210°C was assigned to a rhombohedral-tetragonal structural phase transition. The finished products of x≥0.2 included three kinds of impurities, which were affected by the selection of starting materials.

View full abstract

Biomimetic deposition of hydroxyapatite (HAp) on polystyrene (PS) surfaces under body fluid conditions was evaluated. It was found that introduction of adsorption layers of serum proteins such as human serum albumin (HSA) and human immunoglobulin G (hIgG) on PS surfaces using solution casting techniques resulted in formation of HAp deposits on these surfaces when immersed in 1.5SBF, a solution having 1.5 times higher ion concentrations than those of simulated body fluid (SBF). Experimental results including physical characterizations of the HAp deposits support that the ionic amino acid side chains displayed on the surface of these serum proteins induced heterogeneous nucleation and growth of bone-like HAp. Both HSA and hIgG exhibited HAp deposition ability under the current experimental conditions.

View full abstract

Allergic substances, which have higher stability to heat and an inhibition of an enzyme activity, such as ovomucoid, histamine and albumin, were treated by RF oxygen plasma. As a result of that, it was found that RF plasma, especially oxygen plasma, has ability of reducing the persistent allergic substances. Almost all of ovomucoid existing in egg white was removed by oxygen plasma. It was indicated that histamine was also removed by oxygen plasma irradiation. The reduction rate of allergen strongly relates to the irradiation period and was tended to be irrespective of the bond energy. The reduction rate of allergic proteins is indicated high in lower concentration and was significantly dependent on the initial concentration. It was suggested that plasma reacted to only the surface or surface layer of the allergic substances. The targets of plasma treatment in practical application are highly lower concentration because it is washed with water before exposure of plasma treatment process. The plasma irradiation is effective to treat an allergic substance and could be applied in practice.

View full abstract

To prepare bone and cartilage substituent, soft materials with heterogenic surfaces were prepared, that is, hybrid matrix composed of poly(2-methacryloyloxyethyl phosphorylcholine (MPC)-co-2-methacryloyloxyethyl phosphate (MEP)) (PMP) hydrogel and hydroxyapatite (HAp), namely PMP/HAp. The PMP hydrogel provides tissue non-adhesive and high lubricious surface and HAp layer on the matrix provides bone-connecting properties. The PMP hydrogel was synthesized by random copolymerization of MPC and MEP with a little cross-linking reagent in an aqueous medium. Some properties of the PMP hydrogel could be controlled by the composition of monomers. To deposit HAp on/in PMP, the alternative soaking process using CaCl₂ and Na₂HPO₄ aqueous solutions was carried out. Deposition of white calcium phosphate was visually obvious, and identification to HAp was done by X-ray diffraction measurement and scanning electron microscopy observation. Cell adhesion and growth on the hybrid matrix was evaluated using osteoblast-like MC3T3-E1 cells. After 3-days incubation, the cells did not adhere on the PMP hydrogel, however adhesion of the cells was observed on the PMP/HAp matrix. The number of cells adhered on the PMP/HAp matrix increased and cells took more spread morphology after 7-days incubation. We concluded that the HAp layer is important to make adhetion to bone and MPC unit rich layer may be compatible to cartilage tissue.

View full abstract

We prepared a new biointerface for obtaining specific recognition of glycoproteins having polysaccharide chains to capture corresponding cells by a phospholipid polymer having phenylboronic acid moiety (PMBV), so-called artificial lectin. The PMBV was coated on the surfaces of Au substrate and tissue culture polystyrene. The affinity of the PMBV toward the glycoproteins and its effects on cell adhesion were evaluated. X-ray photoelectron spectroscopic analysis revealed that the PMBV existed on both substrates. Although adsorption of protein without polysaccharide chain was suppressed, glycoprotein as fibronectin (FN) adsorbed effectively, which was confirmed by surface plasmon resonance. Kinetic parameters calculated by SPR measurements showed high affinity between PMBV and FN, 1.4×10⁵ (M^-1). Cell adhesion and growth behavior on PMBV was observed using L-929 fibroblast cells. It was demonstrated that cells proliferated well on PMBV surface and maintained their sphere morphology. Also, the activity of cells was kept in higher level on the PMBV surface compared with conventional surface.

View full abstract

Poly(trimethylene carbonate) (PTMC) is of great interest from the viewpoint of applications in various biomedical materials. Ring-opening polymerization of trimethylene carbonate (TMC) can yield PTMC by the activation of the hydroxyl group in the presence of organic catalysts. By using hydrophilic or hydrophobic compounds as initiation points, we can evaluate a state of surface enrichment for each initiation compound. In the present study, cholesterol derivatives and a series of poly(ethylene glycol) were selected as initiation points. Cholesterol derivatives, including cholesterol, lithocholic acid, and cholic acid, were used. A series of poly(ethylene glycol), including hydroxyl groups on both terminals and monomethyl ether, were used. The resulting polymers were coated on a substrate. By measuring the static contact angle, we observed that PTMC including a hydrophobic segment, had a hydrophobic surface. On the other hand, PTMC including hydrophilic initiation points had a hydrophilic surface. This paper reports the surface enrichment of the hydrophilic or hydrophobic segment by changing the surrounding environment. For fine connecting biointerfaces, initiation points, including carboxyl groups, may be used to synthesize new materials by connecting with another molecule with an amino group via an amide bond.

View full abstract

When the materials get contact with blood, non-specific protein adsorption occurs on the surface and the protein adsorption layer induces much severe biological responses including cellular reactions. Therefore, evaluating the first protein adsorption is important for preparing the nonbiofouling surfaces. Atomic force microscopy (AFM) makes it possible to directly measure the forces generated from protein-surface interaction in aqueous media down to few piconewtons range. In this study, we evaluated the adsorption force between bovine serum albumin (BSA)-immobilized AFM cantilever and well-defined polymer brush surface with three kinds of hydrophilic monomers, which are 2-methacryloyloxyethyl phosphorylcholine (MPC), poly (ethylene glycol) methacrylate (PEGMA) and 2-hydroxyethyl methacrylate (HEMA) by surface-initiated atom transfer radical polymerization (SI-ATRP) on initiator-immobilized silicon wafer in buffer solution. We found that the protein adsorption forces depended on the both chemical structure and thickness of the polymer brush layer. In particularly, the thickness was important to reduce protein adsorption force. From these results, thick polymer brush surface is one of the candidate surfaces with nonbiofouling characteristics.

View full abstract

Hydroxyapatite (HAp), Ca₁₀(PO₄)₆(OH)₂, is known to precipitate on bioactive materials such as TiO₂ and CaTiO₃ by soaking in simulated body fluid (SBF). The formation of HAp on TiO₂ surfaces under continuous ultraviolet (UV) irradiation was investigated. Anatase-type TiO₂ film was synthesized on pure Ti substrates by a combined chemical-hydrothermal treatment. The specimens were immersed in SBF in darkness or under UV irradiation with a centered wavelength of λ = 365 nm. Under dark conditions, a thin homogeneous HAp film was formed, with just a few spherical clusters of HAp. The UV irradiation promoted the formation of HAp clusters, which may be due to the generation of functional Ti-OH or Ti-OH^- groups on the TiO₂ surface. The UV light produces electron-hole pairs in the TiO₂. When an n-type semiconductor is immersed in an aqueous solution, an up-hill potential gradient is produced towards the surface in the conduction and the valence bands. Therefore, the photogenerated holes migrate to the surface and repel the Ca²⁺ ions in the solution near the surface of TiO₂. As a consequence, the UV irradiation suppressed the formation of a HAp thin film.

View full abstract

  To control functions of cells during their culture period in vitro is important for providing cells in the cell engineering fields. We designed a novel soft biodevice for realizing cell engineering. That is, spontaneously forming and highly cytocompatible hydrogel system composed of poly (2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate-co-p-vinylphenylboronic acid) (PMBV) and poly (vinyl alcohol) (PVA), was prepared to encapsulate cells as “Cell Container”. This hydrogel was reversibly dissociated by addition of sugar derivatives. When mouse fibroblast (L929) cell lines and human hepatocellular liver carcinoma (HepG2) cell lines were encapsulated in the PMBV/PVA hydrogel, the cells could proliferate slowly compared with those on conventional tissue culture plate and form cell clusters derived by expansion of the single cells, without forming aggregations. After the dissociation of the PMBV/PVA hydrogel, the distribution of cell cycle phase of L929 cells was analyzed. It was found that the PMBV/PVA hydrogel lead a synchronization of cell cycle phase of L929 cells to G0/G1 phase. As other cell-specific function of HepG2, albumin production and releasing from HepG2 was evaluated. The PMBV/PVA hydrogel did not induce a significant reduction of albumin production from HepG2. The PMBV/PVA hydrogel could preserve cells for long term inhibiting the excessive proliferation, provide normalized cells with uniformly cell cycle phase, and maintain the cell-specific function. Thus, we concluded that the PMBV/PVA hydrogel will be a novel and powerful device to control cell functions in cell engineering fields.

View full abstract

  To determine the location of molecules during uptake process by cells, a new nanoparticle-type fluorescence probe whose fluorescence behavior can change in response with surrounding pH was prepared. The nanoparticles was composed of quantum dot (QD) core and block-type water-soluble phospholipid polymer with pH responsible poly(2-diethylamino methacrylate (DEAEMA)) segment as a shell. A small amount of fluorescent dye bounded to the polymer. For detecting the pH circumstances, fluorescence resonance energy transfer (FRET) mechanism between QD as a donor and a fluorescent dye as an accepter was used. The block-type phospholipid polymer was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization method to control molecular weight and polymer sequence. After solubilizing QD into water by the polymers to form nanoparticles, Alexa 594 cadaverine was immobilized on the nanoparticles. It was observed the change in fluorescence spectra dramatically in the pH range between pH 6.6 and pH 7.4. This was due to the morphology of the block-type phospholipid polymer chains was dramatically changed in this pH range. The poly(DEAEMA) segment in the polymer was shrunken at pH 7.4, while the segment was stretched at pH 5.0 related to the protonation of the polymer. The nanoparticles were added in the culture medium under HeLa cell culturing, the nanoparticles were accepted cell-uptake. During this process, the fluorescence property was changed. We considered that this fluorescence change is corresponded to releasing of the nanoparticles from endosome to cytoplasm. Thus, the nanoparticles are good pH probe to detect the location of molecules inside of cells.

View full abstract

Thin films of the infinite layer insulator CaCuO₂ with (001) orientation were prepared by MOCVD at different growth temperatures (650-800°C). At lower temperatures, growth is through a 3D mechanism, while at temperatures above 770°C it changes into a 2D one. Epitaxial films composed of uniform square-shape grains showing high crystal quality and low roughness were obtained for a optimum growth temperature of 790°C. Mean square roughness (RMS) was around 1.5nm. This value is about half of the best values determined for the films of Ca_0.5Sr_0.5CuO₂ from the Ca_1-xSr_xCuO₂ and Ca_1-xBa_xCuO₂ films series (x=0-1) reported earlier. The result suggests that these films are suitable for device fabrication or integration. Some details of the anisotropic growth are discussed.

View full abstract

α and γ Al₂O₃ doped sintered ZnO (n-type) and sintered CuAlO₂ (p-type) pellets were prepared by conventional solid state synthesis starting from the oxides. 2% γ Al₂O₃ doped ZnO was the best n-type sample showing a thermoelectric figure of merit ZT = 0.17 at 800℃. In the case of p-type CuAlO₂ sample, ZT = 0.035 at 800℃ was obtained by application of melt-textured growth (MTG) process to the sintered pellet. In this work, MTG was recognized for the first time as effective way for the enhancement of thermoelectric properties of CuAlO₂.

View full abstract

Nanocrystalline NiFe₂O₄ (Nickel Ferrite) particles were synthesized using the coprecipitation technique and subsequently their nonlinear optical properties were studied using the open aperture Z-Scan experiment employing nanosecond and femtosecond laser pulses. A significant optical limiting is observed in both cases showing that NiFe₂O₄ is a potential optical limiter having a broad temporal response, useful for device applications.

View full abstract

Electrical conduction occurs and optical absorbance increases in a high resistive and transparent WO₃ film with oxygen deficiencies. Both phenomena were caused by the generation of conduction electrons and electron transition from the valence band to the conduction band. Resistivity depends on the O₂ flow rate of sputtering gas and on sputtering power. The absorbance of a tungsten oxide film increases after annealing. Resistivity can be controlled with the O₂ flow rate of the sputtering gas and the sputtering power. It increases after annealing in air or vacuum because the oxygen deficiency is compensated and the carrier mobility increases.

View full abstract

Nickel copper oxide ((Ni_1-xCu_x)O) thin films, where the Cu content x was changed in the range from 0 to 1, were prepared by pulsed laser deposition. The copper content of the thin films was determined by energy-dispersive X-ray analysis with scanning electron microscopy. Transmission electron microscope observations of the thin film with x=0.52 revealed that the unit cell was distorted from cubic to tetragonal according to the Jahn-Teller effect by Cu²⁺ ions dissolved in the NiO lattice.

View full abstract

  Ga-doped TiO₂ films were prepared by spin-coating method and optical properties of non-doped and Ga-doped TiO₂ films were investigated. In the films prepared using low concentration of Ga to Ti in the solution, few Ga₂O₃ crystals existed in the TiO₂ films. The thickness of Ga-doped TiO₂ films increased and the refractive index of the films decreased with increasing the ratio of Ga to Ti in the solution. In the reflectance measurements, there was little dependency of doping concentration as long as the concentration was not too high. The transmittance increased with increasing the ratio of Ga to Ti in the solution. The bandgap of the non-doped and Ga-doped TiO₂ films were obtained using absorption coefficients calculated with reflectance and transmittance spectra. The bandgap of the films was almost constant regardless of the ratio of Ga to Ti in the solution.

View full abstract

In this study, well-ordered Ga doped/undoped ZnO nanorods were synthesized on the conductive ITO glass substrate using hydrothermal method, and its piezoresistive properties were measured. In the measurement, linearity of the piezoresistive change was ovserved. By the Ga doping, semiconductive resistivity of the nanorod was decreased. However, piezoresistive change ratio of both Ga doped/undoped nanorods remained almost the same. Such ZnO nanorods have a potential to serve as a nanosized force sensors.

View full abstract

Electrical properties of (Ba_x,Sr_1-x)Ta₂O₆ (x=0, 0.5, 1) thin films fabricated by the Sol-Gel method were investigated. SrTa₂O₆ and (Ba_0.5,Sr_0.5)Ta₂O₆ thin films were found to have similar crystal structures in this study. The quadratic voltage capacitance coefficients (VCC) and the temperature coefficients of capacitance (TCC) were found to be very close for these two thin films. However, a higher dielectric constant of about 130 was obtained for the (Ba_0.5,Sr_0.5)Ta₂O₆ thin film. A low VCC of about 26 ppm/V² and TCC of about -230 ppm/℃ were obtained for the BaTa₂O₆ thin film. The lowest leakage current density of about 10^-8 A/cm² at 500 kV/cm was obtained in SrTa₂O₆ thin film among all thin films investigated. It is considered to be due to the best surface morphology.

View full abstract

ZnO thin films were deposited with changing oxygen gas pressure and their microstructures were investigated by the glancing incident X-ray reflectivity measurement. It was found that the ZnO thin films exhibited higher packing density and smoother surface morphology, when they were deposited in lower oxygen gas pressure. These microstructure improvements of ZnO thin films with decreasing in oxygen gas pressure should come from the increase in the kinetic energy of sputtered Zn atoms and gas particles such as oxygen negative ions recoiled from the sputtering target surface. Furthermore, the double-layered low-emissivity coatings consisting of glass/ZnO/Ag were also prepared and the correlation between the microstructure of ZnO thin films and the electrical property of the Ag thin films was clarified. The Ag thin films exhibited low electrical resistivity when the ZnO thin films deposited in low oxygen gas pressure were used. It can be considered that this improvement in the Ag resistivity is attribute to the high packing density and smooth surface of the ZnO thin film.

View full abstract

Local deposition of carbon containing SiO_X was studied by using a very-high-frequency (VHF) inductive coupling microplasma jet (MPJ) from a tetraethoxysilane ((Si(OC₂H₅)₄), TEOS) and argon mixture. Two distinct thickness profiles were observed in the product, i.e., the dome shaped profiles with and without a hollow at the center region. The products showed a strong white photoluminescence emission. The gas flow dependent deposition profile of products is discussed in terms of the film thickness, chemical composition, and photoluminescence characterizations.

View full abstract

Biaxially oriented polyethylene terephthalate (PET) films were exposed to oxygen-implicated plasma. They were pressed at 100℃ with their exposed surfaces faced, then bonded tightly without using glue. X-ray photoelectron spectroscopy showed increase in C=O group at the exposed surface, and gas chemical modification method showed increases in -OH and -COOH groups. They might indicate that a mechanism of the two-sheets bonding is related to hydrogen bond or condensation reactions concerning these functional groups

View full abstract

High quality grain boundary junction of NdBa₂Cu₃O_7-δ (NBCO) thin films was fabricated by Tri-Phase Epitaxy technique. Current flows in the film with the junction and artificial defects were investigated by Scanning SQUID microscopy. Magnetic signals generated by the current in the sample were clearly observed. Quantized magnetic vortices close to the grain boundary were also studied.

View full abstract

A polymer-supported terpyridine copper(I) complex was prepared and found to promote the Huisgen’s [3+2] cycloaddition reaction in water between azides and alkynes. Thus, terpyridine ligand was prepared from p-hydroxybenzaldehyde, propane sultone, and 2-acetylpyridine for 2 steps. Immobilization of terpyridine ligand onto a polystyrene-poly(ethylene glycol) (PS-PEG) resin through ionic bonds to sulfonate group took place and the complexation of amphiphilic PS-PEG resin-bound terpyridine ligand with Cu(I) underwent to give PS-PEG-terpyridine-Cu(I) complex 1 as green solid. This polymeric catalyst showed high catalytic activity for the Huisgen 1,3-dipolar cycloaddition reaction of organic azides with acetylenes. This catalyst was recovered and reused for several times without any loss of catalytic activity.

View full abstract