Showing papers by "National Institute of Advanced Industrial Science and Technology published in 1996"

Spectroscopic studies of nile red in organic solvents and polymers

Abstract: We have studied the spectroscopic properties of nile red (NR), a highly fluorescent laser dye, in organic solvents, binary solvent mixtures and polymers. Spectroscopic studies reveal remarkable changes in the absorption and emission band positions and intensities as a function of the polarity of the medium. Such large changes have been attributed to the twisted intramolecular charge transfer (TICT) state of the molecule in polar medium. Experimental results show that the molecule is sensitive to the polarity of its microenvironment and is an excellent probe for systems presenting restricted geometries. We have incorporated NR into thin films of poly (methyl methacrylate) (PMMA) and poly (vinyl alcohol) (PVA); it is found that the micropolarity in PVA is greater than that in PMMA; in PVA, the micropolarity corresponds to that of a binary mixture of acetonitrile and water, whereas in PMMA, the micropolarity corresponds closely to that of pure acetonitrile.

Ultrasonic Atomic Force Microscope with Overtone Excitation of Cantilever

Abstract: We propose a novel atomic force microscope (AFM) combined with ultrasonic frequency vibration of a cantilever excited at its support. This method enables both topography and elasticity imaging of stiff samples such as metals and ceramics, without a need for bonding a transducer to the sample. When the sample surface is contacted with a tip attached to the cantilever, the cantilever vibration mode is changed according to the sample properties. It is theoretically predicted that the amplitude and resonant frequency of vibration at higher-order modes are useful parameters for elasticity evaluation of stiff samples. A preliminary experimental verification of this principle is presented using a glass-fiber-reinforced plastic sample. Clear elastic contrast was successfully obtained using a soft cantilever only when it was vibrated at MHz frequency higher-order modes.

Linear approximate dynamic model of ICPF (ionic conducting polymer gel film) actuator

Abstract: The ionic conducting polymer gel film (ICPF) actuator is a perfluorosulfonic acid membrane plated with platinum on its both surfaces. It bends in water and in wet condition by applying a low voltage of 1.5 V to its surfaces. This phenomenon was discovered in 1992. The principle of the motion is still unknown. This paper discusses 2-dimensional linear approximate modelling of the ICPF actuator. The authors are proposing a dynamic model of the actuator consisting of an electrical stage, a stress generation stage and mechanical stage. In the stress generation stage, time derivative of current generates the internal stress with a second degree delay. Expansion and contraction of each surface induce bending motion in the mechanical stage. Simulation results were in agreement with actual responses.

Optical absorption and photoluminescence studies of β‐FeSi2 prepared by heavy implantation of Fe+ ions into Si

Abstract: Mass‐separated 56Fe+ ions were implanted into Si(100) at 350 °C using three different energies and doses of 140 keV (1.32×1017 cm−2), 80 keV (6.20×1016 cm−2), and 50 keV (3.56×1016 cm−2). Their optical properties were investigated as a function of subsequent annealing temperature and its duration time. X‐ray diffraction analysis revealed that polycrystalline semiconducting β‐FeSi2 layers are formed in the as‐implanted and annealed samples. From Rutherford backscattering spectrometry analysis, the formation of β‐FeSi2 up to the surface was confirmed, and the average thickness and composition of the layers at peak concentration were estimated to be 70–75 nm and Fe:Si=1:2.0–2.2, respectively. The types of optical transition and the inverse logarithmic slope (E0) of the Urbach tail were investigated using room temperature optical absorption measurements. All the synthesized β‐FeSi2 layers exhibited a direct transition with direct band‐gap energies (Egdir) of 0.802–0.869 eV and with high optical absorption coe...

Extended Van Hove singularity in a noncuprate layered superconductor Sr2RuO4.

Abstract: Angle-resolved photoemission spectroscopy was performed on a ruthenate superconductor S${\mathrm{r}}_{2}$Ru${\mathrm{O}}_{4}$ ( ${T}_{c}\ensuremath{\sim}1$ K) which has the same crystal structure as L${\mathrm{a}}_{2}$Cu${\mathrm{O}}_{4}$, but with Ru${\mathrm{O}}_{2}$ layers replacing Cu${\mathrm{O}}_{2}$ layers. S${\mathrm{r}}_{2}$Ru${\mathrm{O}}_{4}$ shows an extended Van Hove singularity (VHS) at $20\ifmmode\pm\else\textpm\fi{}2$ meV below ${E}_{F}$ just like the cuprates, regardless of the character of the electronic states at ${E}_{F}$. This suggests that the extended VHS is a general feature of a two-dimensional correlated d-electron metal. The observed Fermi surface is in contrast to local-density-approximation calculations.

Humidity-sensitive optical absorption of Co3O4 film

Abstract: Cobalt oxide (Co3O4) films prepared by pyrolysis of an organometallic precursor show a humidity-sensitive absorbance change in the visible wavelength region at room temperature. The light absorbance change is strongest at wavelengths around 350–400 nm. The reversible absorbance change and the relatively fast response time (within a few minutes) make the Co3O4 film a potential candidate for optical humidity detection.

Oxidation and Steam Reforming of CH 4 on Ni and Fe Anodes under Low Humidity Conditions in Solid Oxide Fuel Cells

Abstract: Oxidation and steam reforming of on Ni/YSZ and Fe/YSZ cermet anodes were examined, primarily under the condition of . In the fuel system, steam reforming occurs on anodes, generating CO and . The steam reforming activity of on Ni/YSZ was much higher than on Fe/YSZ at open circuit. The anodic polarization curves of an Ni/YSZ cermet electrode, both in dry and fuel systems, could be divided into two parts; one due to direct oxidation of C in the low overvoltage region, the other due to oxidation of and/or CO at higher overvoltages. On the other hand, the anodic polarization curves of an Fe/YSZ cermet electrode in fuel showed behavior different from that for Ni/YSZ in the dry or the fuel systems. The polarization curve in the dry fuel system showed multiple reaction slopes, while that in the fuel system showed only one slope. A thermochemical calculation was made to estimate the anode surface state and the equilibrium oxygen partial pressure between the anode/YSZ interface and the gas phase.

Dynamic underactuated nonprehensile manipulation

Abstract: By exploiting centrifugal and Coriolis forces, simple, low-degree-of-freedom robots can control objects with more degrees-of-freedom. For example, by allowing the object to roll and slip, a one-degree-of-freedom revolute robot can take a planar object to a full-dimensional subset of its state space. We present a dynamic manipulation planner that finds manipulator trajectories to move an object from one state to another without grasping it. The trajectories have been successfully implemented on a one-degree-of-freedom direct drive arm to perform dynamic tasks such as snatching an object from a table, rolling an object on the surface of the arm, and throwing and catching.

Laser induced microexplosions of a photosensitive polymer

Abstract: Laser ablation of a photosensitive triazene polymer was studied in a micro region by means of a nanosecond imaging technique. The propagation of a blast wave, 100 ns after laser irradiation, sufficiently matched a planar blast wave model including the decomposed source mass which indicates characteristics of a microexplosion. The measured velocities of the fronts indicates two blast waves: an initially fast unsupported wave around the peak of the laser pulse, and a relatively slow supported wave involving the main component of the decomposition.

Scanning Tunneling Microscopy Observations of α,ω-Bis(mercaptomethylthienyl)alkane Derivatives Self-Assembled on Au(111)

Abstract: 1,8-Bis(5-mercaptomethyl-2-thienyl)octane (1a), 1,8-bis(5‘-mercaptomethyl-2,2‘-bithienyl-5-yl)octane (1b), 1-(5-mercaptomethyl-2-thienyl)-4-(2-thienyl)butane (1c), 1,8-bis(2,2‘-bithienyl-5-yl)octane (2), 1,12-dodecanedithiol (3), and 1,4-bis(mercaptomethyl)benzene (4) were prepared, and their adsorption states on a gold single crystal surface were studied by using scanning tunneling microscopy under ultrahigh-vacuum condition. Two ordered phases were observed for the mercaptomethylthiophene derivatives 1: The first phase is composed of one-dimensional molecular rows with spacings smaller than those for other monothiols and the second one has a previously unknown two-dimensional honeycomb structure. In both of the two phases, the molecules were arranged with end-on configuration in which only one end thiol is attached to the gold substrate. The absence of the honeycomb structure for 3 and 4 suggests the important role of the mercaptomethylthienyl moiety for the formation of the specific structures.

High quality CuInSe2 films grown on pseudo-lattice-matched substrates by molecular beam epitaxy

Abstract: CuInSe2 films have been grown by molecular beam epitaxy on pseudo‐lattice‐matched substrates that consist of a 1‐μm‐thick In0.29Ga0.71As layer grown on a linearly composition‐graded InxGa1−xAs buffer (0≤x≤0.29) grown in turn on GaAs (001). The properties of these films have been compared with those of the films grown directly on GaAs (001). High resolution x‐ray diffraction analysis on CuInSe2 grown on pseudo‐lattice‐matched substrates indicated substantial reduction on residual strain in the CuInSe2 films. A photoluminescence spectrum dominated by sharp free exciton emissions has been observed for the first time from CuInSe2 films indicative of significant improvement in crystalline quality and substantial reduction in the point defect density.

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 1. Comparison between H2SO4 and NaOH solutions

Abstract: Anodic oxidation of high modulus coal tar pitch-based carbon fibre in alkaline and sulfuric solutions was investigated. X-ray photoelectron spectroscopy (XPS) analysis was used to evaluate the oxygen concentration (O 1S /C 1S ) and surface functional groups (OH, CO and COOH). The interfacial shear strength between the epoxy matrix and carbon fibre was measured by a fragmentation test. The results showed that the oxygen concentration on fibre surfaces increased rapidly as electrical charge increased, in both alkaline and acidic solution. The best bonding between epoxy matrix and carbon fibre was achieved in alkaline solution. The Raman spectra of carbon fibre oxidized in alkaline and sulfuric solutions suggested that the weak adhesive strength between the epoxy resin and oxidized carbon fibre in sulfuric solution was due to the existence of an oxidized graphite layer, which might easily come off the surface.

Significant densification of sol-gel derived amorphous silica films by vacuum ultraviolet irradiation

Abstract: Structural changes in sol‐gel derived amorphous silica films were investigated using vacuum ultraviolet light emitted from an undulator. A significant increase in the refractive index and a decrease in the thickness for the silica films were induced by photons with energies above ∼9 eV. The frequency shift of ω4 (transverse optical mode) of infrared absorption to a lower wave number with the irradiation indicates a decrease in the average Si–O–Si bridging angle. These results suggest that the silica films were densified by the irradiation with the energetic photons. The densification of silica gel films dried at 50 °C was accompanied by a decrease of OH groups in a manner similar to thermal treatments. On the other hand, the structure of the irradiated silica was similar to that of silica glass densified under high pressures. Although silica gel films annealed at 600–1000 °C were also densified by the irradiation, the structural changes were relatively small for the films annealed at temperatures above 70...

Phase Transition in Glycolipid Monolayers Induced by Attractions between Oligosaccharide Head Groups

Abstract: The surface property of two kinds of synthetic glyceroglycolipids was investigated to confirm the stereoeffect of sugar residues on the phase behavior in monolayers: one is the maltooligosaccharide-containing lipids [MalN(C12)2] and the other is cellooligosaccharide-containing lipids [CelN(C12)2]. The two kinds of glycolipids exhibit the opposite dependence of the surface pressure−area (Π−A) isotherm on the number of glucose residues (N), in that MalN(C12)2 tends to be more expanded as N increases, while CelN(C12)2 tends to be more condensed. The liquid-expanded/liquid-condensed phase transition in Cel4(C12)2 was evaluated by the Brewster angle microscopy and the latent heat analysis with the Clausius−Clapeyron equation, as a model of film condensation induced by the attraction between oligosaccharide head groups. The film morphology of Cel4(C12)2 was unique in that it exhibits the optically isotropic and flexible fluid type of the LC phase, while Glc(C16)2 forms a two-dimensional tilted crystalline phase...

Effect of anodic oxidation of coal tar pitch-based carbon fibre on adhesion in epoxy matrix: Part 2. Comparative study of three alkaline solutions

Abstract: Anodic oxidation of coal tar pitch-based carbon fibre was performed in various alkaline solutions, such as NaOH, NaHCO 3 and Na 2 CO 3 , to examine the effect of various kinds of electrolytes on the surface chemical nature of treated fibres and the adhesive strength between treated fibres and epoxy resin. Evaluation of the oxygen concentration and surface functional groups of the carbon fibre surface was conducted by X-ray photoelectron spectroscopy (XPS). A fragmentation test was adopted for evaluation of the adhesive strength between the carbon fibre and epoxy matrix. As a result, it was shown that the highest O 1S /C 1S value was obtained in NaOH aqueous solution, and the highest interfacial shear strength (IFSS) was also obtained from the carbon fibre oxidized in NaOH solution. It was recognized that the IFSS values increase with increasing of O 1S /C 1S in every solution at the initial stage of oxidation below 1.0 × 10 −3 C mm −2 . However, above this level of electrical charge in NaOH solution, decreasing IFSS values may occur, regardless of an increasing O 1S /C 1S value. SEM analysis inferred that in the case of the fibre treated in NaOH solution, grooves on the carbon fibre surfaces had become deeper over 1.0 × 10 −3 C mm −2 . Presumably, the amorphous part of the carbon fibres could be oxidized intensively, and the remaining graphite layer become very thin and easy to break when a shear stress is loaded on its interface.

Combining probabilistic map and dialog for robust life-long office navigation

Abstract: A design of mobile robot for robust life-long navigation in office environment is proposed and evaluated. The key idea is combining probabilistic map and dialog with humans for reducing the location uncertainty. Bayesian inference with the map represented by probabilistic automata is used in order to reduce the number of queries and to evaluate the success rate of planned paths. We experimentally implemented the design using a simple Bayesian network with continuous nodes and demonstrated its effectiveness in a real environment.

Langmuir−Blodgett Films of Nonamphiphilic N,N‘-Bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide: A Spectroscopic Study

Abstract: Mixed films of nonamphiphilic N,N‘-bis (2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (DBPI) and stearic acid (SA) have been studied at the air−water interface and as Langmuir−Blodgett (LB) films deposited on glass substrates. Our studies reveal that DBPI forms excellent LB mono- and multilayers mixed with SA that are highly fluorescent. Spectroscopic studies indicate the formation of organized aggregates in the LB films that is evident from the broadening of the absorption spectral profile and the appearance of a broad band excimer-like emission that originates from a loosely bound dimer of DBPI. While freshly prepared LB films exhibit the excimer-like broad band maximum at 602 nm, aging of the films results in a shift of the excimer-like band maximum from 620 nm for a three week old film to 636 nm for a film that is twelve weeks old. The observed spectroscopic changes are attributed to the changes in the packing configuration of the DBPI moieties in the LB films with time.

Band‐edge photoluminescence of CuGaSe2 films grown by molecular beam epitaxy

Abstract: Slightly Cu‐rich CuGaSe2 films were grown on [001] oriented GaAs substrates by molecular beam epitaxy. Photoluminescence of the films showed a remarkable emission peaked at 1.71 eV at low temperature, which is attributed to recombination of free excitons and bound excitons. The dissociation energy of free excitons and their localization energy to a center are found to be 16.2 and 3.3 meV, respectively. The band‐gap energy Eg is estimated to be 1.7310 eV at low temperature. It is suggested that the temperature variation of Eg is dominated by interaction with phonons of 26 meV which corresponds to the mean energy of the optical phonons in CuGaSe2.

Uptake and reduction of arsenate by Dunaliella sp.

Abstract: Uptake and reduction of arsenate [AS(V)] by Dunaliella sp. cells were determined to investigate the metabolic processes of arsenic in the alga. Cellular uptake of arsenic by Dunaliella sp. cells was markedly affected by the form of arsenic in the medium. The content of arsenic taken up by Dunaliella sp. cells increased rapidly with time on addition of As(V) to the medium. However, in the case of addition of arsenite [As(III)], the gradient of arsenic uptake by Dunaliella sp. cells was low, and arsenic content was small. In the water-soluble fraction of arsenic taken up by Dunaliella sp. cells with exposure to As(V), arsenic was in the forms of organic arsenic, As(V) and As(III). The content of As(V) in the water-soluble fraction increased with exposure time. The content of As(III) also increased with time, but remained constant after 5h of exposure. On the other hand, organic arsenic content was small and did not increase with time. It was found that Dunaliella sp. takes up As(V) and readily reduces it to As(III).