Over the last two decades it was well documented that the formation of ultrafine-grained (UFG) structures with the grain sizes in submicron (< 1 μm) or nanometer (< 100 nm) range in metallic materials increases strength but typically also leads to decrease in ductility. However, recent studies demonstrated that extraordinarily high strength and enhanced ductility can be obtained in the UFG metals and alloys when it is possible to control not only grain sizes but also the formation of various nanostructured elements, such as nanoparticles, nanotwins and grain boundary structures (states) by means of severe plastic deformation (SPD) techniques. These new trends applied to different metallic materials with superior strength and high ductility are considered and discussed in the present paper.
We prepared the spent coffee grounds (SCG) and controlled the steam activation process for them in order to develop SCG-derived activated carbon with uniform micropores that were similar to those of KOH-activated phenolic resin carbon (MSP-20). The SCG-derived activated carbon that we obtained had a high yield, a high specific surface area, and uniform-sized micropores, and it exhibited characteristics different from those of conventional structures containing both micropores and mesopores. The laminated multi-layer EDLC cells achieved a capacitance of higher than 75 F/g. They were produced with only small variations. The Nyquist plot generated from the impedance measurements showed a fairly vertical rise that can be attributed to the blocking electrode in the low frequency range. This confirms that the pores in the electrodes were used effectively. It was demonstrated that the electric double layer characteristics and impedance characteristics of the SCG capacitors can be changed by controlling the raw material preparation and its activation conditions.
The present authors have developed a Time-dependent Ginzburg-Landau (TDGL) model for microstructural evolution of D019 type ordering, taking into account the crystal symmetry of the ordered phase. The D019 structure based on hcp is divided into four equivalent sublattices. The site occupation probabilities are given as a function of three order parameters and a composition parameter. Multiple types of variants of the structures are represented by the order parameters. Mean-field free energies are defined in a form of Landau type expansion with the order parameters and the composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. We distinguish characteristic off-phase boundaries observed in Transmission Electron Microscopy (TEM) images in such as Cu3Sn and Ti3Al, and performed three-dimensional numerical simulations based on the kinetic equations.
Gold- and silver-nanoparticle-incorporated inverted-type organic thin-film solar cells were fabricated and evaluated. The incorporation of gold nanoparticles, silver nanoparticles, and the gold:silver mixed nanoparticles in poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) layer, improved the photoelectric conversion efficiency of the organic thin-film solar cells under irradiation of simulated sunlight.
We investigated the effects of the introduction of helical structures into a host liquid crystal on the viscoelastic properties of particle/liquid-crystal composite gels. A composite gel using a cholesteric liquid crystal as a host matrix was found to become soft compared to that using a nematic liquid crystal. With reducing the half-pitch length of a helical structure of cholesteric liquid crystals, a storage modulus of the composite gels showed a linear decrease. On the other hand, a crossover point which is a mechanical quasi-solid–quasi-liquid transition point exhibited no significant changes when the half-pitch length was larger than the radius of a particle used in this study. However, a decrease of the crossover points was observed when the half-pitch length was shorter than the particle radius. We qualitatively discussed the origin of helical-structure-induced softening of particle/liquid-crystal composite gels based on the differences in self-organization behavior of particles in nematic and cholesteric liquid crystals.
A dichiral azobenzene mesogenic compound was found to exhibit the electric-induction of birefringence in the optically isotropic liquid phase. The anomalous emergence of the birefringence is attributed to the formation of the liquid-crystalline organization stabilized by the polar structure of the electrically-induced ferroelectric molecular assembly. The application of the in-plane electric field in the liquid phase produces a homogenous birefringent texture, which thus can be considered as a new type of light valve applicable for displays or switching devices. The electrically-induced birefringence can be erased by the irradiation of UV light, due to the photoinduced isomerization of the azobenzene compound, thus dual controlled birefringent structure, by the irradiation of light and/or by the application of the electric field, is obtained.
Neodymium magnets contain rare earth elements. In this study, rare earth elements were recovered from neodymium magnets using the molten salt electrolysis process, thereby making the existing recycling processes for neodymium magnets obsolete. Using anodic polarization, rare earth elements were leached by controlled potential electrolysis, without leaching iron and other elements. The composition of rare earth elements in the molten salt was more than 99 mass% from the controlled potential electrolysis process, not accounting for the molten salt component. Rare earth elements were leached from the boundary phase first. After electrolysis, the boundary phase disappeared from the residual, and rare earth elements were not detected in the residual. The Nd2Fe14B alloy was converted to other materials. The neodymium magnet decomposed with the leaching of the boundary phase and became brittle. It was shown that rare earth elements were leached in preference to other elements using controlled potential electrolysis.
We demonstrated formation of magnetic nanodots (NDs) made of FePt alloy by exposing a metal bi-layer stack to remote H2 plasma and characterized their magnetization properties. Pt/Fe bi-layer stacked structures formed on SiO2 were exposed to remote H2 plasma generated by inductive coupling with an external single-turn antenna connected to a 60-MHz generator. After the remote H2 plasma exposure, the formation of electrically isolated FePt-NDs with an areal density of ～1011 cm-2 was confirmed. These results imply that surface migration and agglomeration of Fe and Pt atoms induced by remote H2 plasma is promoted simultaneously with the alloying reaction. The FePt-alloy NDs exhibited a large perpendicular anisotropy with an out-of-plane coercivity of ～4.8 kOe, while the in-plane and out-of-plane coercivities of the Pt/Fe bi-layer were almost zero, reflecting the small magneto-crystalline anisotropy of the Fe layer.
We have examined the formation of the undoped polycrystalline Si1-x-yGexSny (poly- Si1-x-yGexSny) layers grown on SiO2 by using the solid phase crystallization method. We have investigated the electrical property of poly-Si1-x-yGexSny layers with the Hall effect measurement. We clarified the effects of the Sn incorporation into Si1-xGex and the two-step solid phase crystallization on the Hall mobility. We found that the Si1-x-yGexSny layers are crystallized over 475 ºC-annealing. No Sn precipitation is observed after the crystallization of the Si1-x-yGexSny layer with a Sn content of 1.3%. We can see that a large grain size can be achieved with the lower annealing temperature for Si1-x-yGexSny with a lower content of Sn. On the other hand, a higher mobility is obtained with the higher annealing temperature for the sample at a Sn content of 1.3%. We performed the additional 2nd-step annealing at 700ºC for 10 min, and the mobility was effectively improved to be 1.5 times higher (129 cm2/V-s) than that before the 2nd-step annealing.
We carried out X-ray fluorescence holography at an undulator beamline of SPring-8 to investigate the local structure around the La atoms in Sr0.95La0.05TiO3 single crystal at 297 K. The weak La Lγ1 radiation was detected separately from the radiations Ti Kα1, Ti Kα2 and Ti Kβ1. The La Lγ holograms were collected in the inverse mode at seven incident X-ray energies from 7.00 keV to 10.00 keV. By the holograms the clear atomic images of Sr(La) and Ti are reconstructed around the La atom. On the other hand, no images of the O atoms were discriminated from the intensities of artifacts. The atomic image around the La atom demonstrates that the La atoms are substituted for the Sr atoms in the cubic perovskite structure of SrTiO3.
We investigated the ion-track grafting of vinylbenzyl chloride (VBC) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film using different grafting media for applications as anion exchange membranes for fuel cells. In an attempt to increase the grafting yield, we applied a poor solvent system as the grafting medium, i.e., a mixture of water and isopropyl alcohol (H2O-iPrOH mixture). The optimum H2O-iPrOH composition was identified by the kinetic parameters including the initial polymerization rate (rp0), the radical recombination rate (γ) and the grafting efficiency (rp0/γ). These parameters changed depending on the VBC-grafting/chain-transfer reaction competition for the radicals on ETFE and the Trommsdorff effect; the swelling of the grafting substrate gave an additional effect.
We investigated the effect of hyperthermal atomic oxygen beam irradiation on hydrogenated Si-doped Diamond-Like Carbon (hydrogenated Si-DLC) films for the purpose of use as a solid lubrication material in space. We found that film thickness of hydrogenated Si-DLC was constant after the exposure to atomic oxygen beam. From this result, the hydrogenated Si-DLC films have resistance to etching by the irradiation of atomic oxygen, unlike hydrogenated non-dope DLC films. In addition bulk composition of hydrogenated Si-DLC film kept constant. Especially, hydrogen content in Si-DLC film did not decrease. Therefore, hydrogenated Si-DLC film is expected to keep low fiction properties in a vacuum. Furthermore, the atomic oxygen beam fluence dependence of X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectra of hydrogenated Si-DLC films were measured. From these studies, it was found that the C atoms on the hydrogenated Si-DLC surface were desorbed, but Si atoms were remained on the hydrogenated Si-DLC surface as the SiOx by the collision of atomic oxygen. This SiOx layer was considerable to disturb the erosion of bulk film against atomic oxygen. From the element distribution in depth direction, it was found that the thickness of SiOx was about 5 nm.
In the conventional X-ray reflectivity (XRR) analysis, the reflectivity is calculated based on the Parratt formalism, accounting for the effect of roughness by the theory of Nevot-Croce. However, the calculated results of the XRR done in this way often showed strange results where the amplitude of the oscillation due to the interference effects would increase for a rougher surface. For the solution to this problem, we have developed an improved formalism in which the effects of the roughness-induced diffuse scattering are included correctly. In this paper, for deriving more accurate formalism of XRR, we introduce the effective roughness depending on the angle of incidence X-ray in XRR measurement. The new improved XRR formalism derives more accurate surface and interface roughness with depending on the size of coherent X-rays probing area, and derives the roughness correlation function and the lateral correlation length.
The structure, transport coefficients, and thermal properties of the sodium chloride (NaCl) aqueous solution in similar concentration to the seawater, where the bicarbonate (HCO3-) anion is dissolved to the saturated concentration, has been investigated by molecular dynamics simulation (MD). The effects of pressure have been investigated to the corresponding pressure to the 12000m in depth. The negative pressure dependence of the thermal conductivity has been detected in the depth of more than 8000m. The shear viscosity has also been obtained using the Green-Kubo formula.
Amorphous carbon (a-12C) and amorphous isotopic carbon (a-13C) films were deposited from carbon and 13C targets, respectively to investigate isotopic effects on the electronic properties of amorphous carbon films. The 13C target was obtained by sintering 13C charcoal. The structure of the films was evaluated by Raman spectroscopy. The density of paramagnetic defects was evaluated by electon spin resonance, and ultraviolet-visible spectroscopy was carried out to determine the optical band gap of the films. There were no significant differences between the graphite structures of a-12C and a-13C films. On the other hand, the defect density of the a-13C film (1.1×1020 cm-3) was more than 10 times higher than that of the a-12C film (1.0×1019 cm-3) and the Tauc gap of the a-13C film (1.9 eV) was lower than that of the a-12C film (2.1 eV). These results indicated that 13C affects the electronic properties of amorphous carbon films.
Bismuth telluride thin films were prepared on nickel plate by galvanostatic electrodeposition from hydrochloric acid-based electrolyte. It was found that the structural and thermoelectric properties of the thin films were strongly dependent on the Te content in the electrolyte. All thin films with various Te contents exhibited peaks in their X-ray diffraction patterns corresponding to the reflections of the rhombohedral phase of Bi2Te3. The surface morphology of the thin films with nearly stoichiometric composition was formed by dendritic crystallites, and that of the Te-rich thin film revealed a granular structure. The electrical conductivity of these thin films seemed to be influenced by both the Te content and the morphology. The Seebeck coefficient of the thin films exhibited both negative and positive values in dependence of the quantity of Te in the electrolyte. This behavior is advantageous because only by changing the Te content of the electrolyte, the material composition can be manipulated to yield either p-type or n-type semiconductors suitable for thermoelectric devices.
The authors investigate the effects of surface smoothness on the fatigue characteristics of Ti-Ni SMA wire. The surface smoothness varies according to physical-polishing and electro-polishing. When the bending strain range is more than 3%, the fatigue characteristics are improved by the electro-polishing, but fatigue characteristics are not improved by the physical-polishing. From the results of SEM observations, it is supposed that the fracture origin develops from the residual surface cracks of the physical-polished specimen, if the bending strain range is more than 3%. Due to this, the difference in the fatigue characteristics between the non-polished specimen and physical-polished specimen will be reduced. When the bending strain range is less than 3%, it is assumed that the development of the fracture origin from the residual cracks in the surface of physical-polished specimen is less likely to occur. Owing to this, the fatigue characteristics is improved by the physical-polishing and electro-polishing, and the difference in fatigue characteristics between the physical-polished specimen and electro-polished specimen is reduced.
We optimized AlN growth conditions for hydride vapor phase epitaxy by using simulation. In the simulations, the growth temperature and growth pressure were 1500 °C and 100 kPa, respectively. We studied on growth rate distribution using different separation gas species and NH3 flow rates in order to obtain uniform AlN deposition. High uniformity AlN growth was achieved by using N2 as the separation gas and lowering NH3 flow rates.
Nonadiabatic quantum molecular dynamics (NAQMD) simulations are performed to understand the fast photoexcited phase change of Ge2Sb2Te5 (GST), which is widely used for data storage. NAQMD approach, which simulates energy transfer from excited electrons to the finite temperature ionic system, shows that GST is fast heated up in few picoseconds toward the melting point. This result is considered to be one of the realistic phase change processes through the liquid phase, and also provides an insight on the non-thermal phase change, which is a promising property to improve the speed of phase change.
We report on the effect of nano-sized Ag and Al layer on the electrical and optical properties of the ITO/Ag/ITO (IAI) multilayer films as well as a work function. With increasing the thickness of the Ag and Al layer, we investigated the change of electrical and optical properties of the IAI multilayer in detail. Regardless of thickness of the Ag and Al top layer, the IAI multilayer showed a constant sheet resistance of ～5 Ohm/square and a high transmittance of ～87%. However, the surface morphology and microstructure of the IAI multilayer were affected by the nano-sized Al and Ag cover layer due to different oxidation behavior. The work function of the IAI multilayer with nano-sized Ag cover layer is constant (～4.95 eV) regardless of Ag thickness, while the work function of the IAI multilayer with Al layer decreased from 4.95 eV to 4.75 eV with increasing Al thickness. This indicates that the coating of the nano-sized Al is effective way to decrease the work function of the IAI multilayer films.
Single-walled carbon nanotube (SWNT) growth using Pt as catalysts was carried out by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD), and the properties of SWNTs grown from Pt catalysts were compared to those grown from Co catalysts. Raman results showed that the diameters of SWNTs grown at 700ºC from Pt catalysts were distributed between 0.6 and 1.6 nm, which were much smaller than those from Co catalysts. The SWNT diameters decreased as the growth temperature was reduced, and the diameters of most SWNTs grown at 400ºC from Pt were below 0.9 nm. We also investigated the effects of catalyst deposition method on the SWNT growth and showed that the electron beam (EB) deposition is suitable for growth of SWNTs with smaller diameters under lower ethanol pressures.
(1-2x)(Ba0.8Sr0.2)TiO3-x(Bi(Mg0.5Ti0.5)O3-NaNbO3) (x = 0 - 0.33) ceramics were prepared by solid-state synthesis and the dielectric properties were investigated. At x = 0, the ceramics showed a ferroelectric behavior, and thus the dielectric properties were strongly dependent on electric field and temperature. With increasing x, the ferroelectric behavior became weak, and the electric field and temperature dependence became smaller. For the ceramics with x = 0.25 and 0.33, the dc bias and temperature dependence of the dielectric constant was small, that is, the dielectric constant was 310 – 573 under dc bias fields of 0 - 180 kV/cm and temperatures of 25 - 400 ˚C. Moreover, at x = 0.33, the grain size dependence was also small; the dielectric constant at 25 ˚C and no dc bias was 481 – 561 at grains sizes of 1.0 – 3.2 μm. These stable dielectric properties indicated that the ceramics could be candidate materials for high temperature, dc-bias-free capacitor applications.
Nanocube has attracted interest regarding its synthesis by the wet chemical process. Recently, nanocube with perovskite structure such as barium titanate (BaTiO3) and strontium titanate (SrTiO3) has been studied. In this study, sodium niobate (NaNbO3) was prepared by the solvothermal method and its morphology was investigated. The synthesis was carried out using niobium oxide (Nb2O5) and sodium hydroxide (NaOH) as starting materials, also using ethanol as solvent. X-ray diffraction (XRD) confirmed the presence of perovskite NaNbO3 particles and indicated that the phase is orthorhombic NaNbO3. Scanning electron microscopy (SEM) observation revealed the form of NaNbO3 to be nanocube. Reaction times and concentrations of reaction solutions are important factors for synthesis of nanoparticles. The particle size increases with the reaction times, while the particle size decreases with the concentration of the reaction solutions. The smaller crystals were synthesized in a shorter reaction time at the higher concentration of the reaction solutions.
The synthesis of graphene films on Cu foils was investigated by the thermal annealing with and without ethanol vapor flow. It should be noted that graphene films are synthesized on Cu foils even without ethanol flow. In the case, a small amount of contaminations, probably remaining ethanol, in the flow pipe and reaction chamber can be utilized as carbon source for the synthesis of graphene films. Additionally, carbon impurities dissolved in Cu foils can also play a role as carbon source. The graphene films synthesized without ethanol flow are shown to be bilayer ones which are characterized by Raman spectroscopy and optical transmittance measurements.
A micro-periodic structure composed of polymer and liquid crystal (LC) phases is called holographic polymer dispersed liquid crystal (HPDLC) grating. The HPDLC grating has been applied for grating formation to obtain both high optical efficiency and electric switching function. Moreover, HPDLC grating shows polarization dependence in diffraction efficiencies against the incident polarization state of laser light. The anisotropic diffraction is modulated by the distribution of submicrometer-scale LC droplet in a polymer matrix using interferometric laser exposure. The refractive-index modulations in grating medium corresponding to the three dimensional directions are obtained by applying theoretical calculation based on the anisotropy for the experimental results of angular dependence of diffraction efficiencies in various grating structures. The anisotropy in grating medium is analyzed by connecting the experimental results of angular dependence of diffraction efficiencies with SEM observations in different grating spacing.
LaLnO3 (Ln = Dy, Ho, Y, Er, and Yb) and La(Ln, Ln')O3 (Ln, Ln' = Dy, Ho, Er, and Yb) systems were synthesized by solid state reaction method and characterized by X-ray diffraction and Rietveld analysis. In order to investigate the size effect of Ln site ion in ABO3-type compound, the phase relationship in the LaLnO3 system. When Ln = Er or Yb which has smaller ionic radius than that of Y3+ (0.900 Å), the LaLnO3 showed an orthorhombic perovskite-type structure, while when Ln = Dy or Ho which has larger ionic radius than that of Y3+, it showed a monoclinic B-type rare earth structure. Next, the solid solution system of LaHoxYb1-xO3 was investigated in order to clarify the crystallochemical factor affecting the structural transformation. The XRD experiments revealed that the samples with x = 0.90 (rav.=0.8977Å) showed the orthorhombic perovskite-type structure, changed to the mixed phases of monoclinic B-type rare earth, and orthorhombic perovskite-type structures with increasing x, and then the samples with x ≧ 0.95 (rav.=0.8994Å) showed the monoclinic B-type rare earth structures, where rav. represents the average ionic radii of Ln and Ln'. Therefore, in order to search into process of phase transformation from orthorhombic perovskite-type structure to monoclinic B-type rare earth structure, LaHoxYb1-xO3 (0.90≦x≦0.95) system was performed Rietveld analysis.
The Ru5+ and Y3+-doped BaCeO3 (BaCe0.85Ru0.05Y0.10O3-δ: BCRY) thin film has been prepared on (0001) Al2O3 substrate by RF magnetron sputtering. The BCRY thin film crystallized at 600°C exhibits a- and c-axes orientations. The electrical conductivity of BCRY thin film is higher than that of BaCe0.90Y0.10O3-δ (BCY) thin film. The activation energy (EA) of BCRY thin film is ～0.25 eV, which corresponds to half EA of BCY thin film, below 400°C. The conductivity depends on oxygen partial pressure. The Fermi level (EF) of BCRY thin film shifts to the conduction band side, although the EF of BCY thin film locates at the valence band side. The above results indicate that the BCRY thin film occurs the electron-ion mixed conductions below 400°C.