A reverse mode liquid crystal (LC) characteristic which shows a transparent voltage off-state and a light scattering on-state can be obtained by two light scattering mechanisms. One is using an index mismatching between LC and polymer matrix and another is using a micro-lens array with a short focal length. Here, we combine two reverse mode technologies in one LC cell. We investigate relations between the cell thickness and the lens diameter of a hole array patterned electrode and successfully obtained the stronger light scattering with low driving voltage. Not only an extraordinary ray but an ordinary ray can also be scattered by non-uniform electric field which is caused by using hole pattered electrodes on both side of the substrates.

Three oligothiophenes containing alkoxy groups were synthesized, and their optical, electrochemical, and electrical properties were investigated. The oligothiophenes were soluble in common organic solvents owing to the presence of flexible alkyl chains in their alkoxy groups. The introduction of alkoxy groups induced a red-shift in the absorption and emission bands and a negative shift in the oxidation potentials observed for the compounds. The extension of the π-conjugation system enhanced the stability of the oxidized states of the oligothiophenes due to a reduction in the Coulombic repulsion. The electrochemically oxidized dodecathiophene showed excellent electrical conductivity.

High performance and easily processable wettable/repellent patterns formation were achieved using photo-induced surface control materials (PISC) by conventional i-line exposure and annealing. Functional inks can be patterned spontaneously on exposed surface which realize high resolution patterning by drop-coating methods. Fine silver lines of 10-μm width were achieved by inkjet printing with Ag nanoparticle (AgNP) inks on this pattern. Using this technique, silver source-drain electrodes of organic thin film transistor (OTFT) were successfully fabricated. A novel patterning method using alkali-developable type PISC was also devised for formation of high resolution, aspect patterns and high thickness microlenses, which difficult to be formed by photolithography technique.

A long lifetime organic light emitting diode (OLED) display at high temperature was developed with optimization of each layer organic materials. We clarified that charge-carrier balance between hole and electron inside the emission layer (EML) affects the lifetime of OLEDs, especially for blue-OLED. We also clarified that the lifetime becomes long with increasing the density of hole in the EML. The lifetimes of the blue-, green, and red-OLEDs developed in this study were achieved over 1,000 hours at 85 ℃ under a driving of 600 cd/m² white luminance. A prototype 12.3 inch flexible OLED display was fabricated with using the new electron-blocking layer, hole-blocking layer, and hole-transport layer materials. We believe that the OLED display that we developed would be useful for automotive application.

Metal halide perovskite nanocrystals (PeNCs) have ionic crystal structures, and their optical properties are greatly affected by polar solvents owing to the formation of cation- and anion-defects. Herein, we fabricated low driving voltage and high efficiency NC light emitting devices (LEDs) using gel permeation chromatography (GPC) with nonpolar solvents to remove impurities such as excess ligands and reaction solvents. We confirmed that these impurities may be removed completely via the one-cycle GPC purification process in contrast to the conventional reprecipitation purification process having two-cycles. In addition, we demonstrated the effect of interfacial engineering between the hole transport layer and PeNC layer using alkyl ammonium salts containing Br anion, i.e., oleylamine bromide (OAm-Br), to passivate both cation- and anion-defects in PeNCs. The LEDs based on PeNCs with GPC purification achieved the maximum external quantum efficiency of 4.3% with OAm-Br layer.

In perovskite solar cells, the morphology of perovskite active layers is one of important factors for obtaining high energy conversion efficiency (PCE). We investigate the morphology of the crystals and grains of perovskite layer fabricated by a 1-step method incorporated with the air-flow and solvent annealing. Although the crystal and grain sizes of perovskite layer became smaller than the as-grown perovskite layer, the former film quality advanced because of less pinhole. In addition, after the solvent annealing, the crystals and grains of perovskite layer grew promptly in the air-flow treated perovskite layer. The crystal and grain sizes in the air-flow treated perovskite layer were twice larger than those in the as-grown perovskite layer. Finally we fabricated the higher PCE perovskite solar cells by incorporating the air-flow and solvent annealing processes.

We fabricated electrochromic devices (ECDs) with an Fe(II)-based metallo- supramolecular polymer (polyFe) and a gel electrolyte and revealed the influence of the electrolyte components and the fabrication process on thermal stability. Four electrolytes (G1-4) were prepared by mixing of polymer matrix (poly(methyl methacrylate) (PMMA) or poly(ethylene oxide) (PEO)), lithium salt (LiClO₄), and plasticizer (propylene carbonate (PC) or ionic liquid (BMP-TFSI)) (G1: PMMA/PC; G2: PEO/PC; G3: PMMA/BMP-TFSI: G4: PEO/BMP-TFSI). The ECDs with G1,2,4 showed good EC properties upon applying ±3 V. We also found that the electrochromic (EC) properties were improved by thermal annealing of the device at 150 ℃. The ECDs with G3 showed the best EC properties with fast response (t_b = 2.65 sec, t_d = 0.15 sec), high repeating stability (∆T₁₀₀/∆T_i > 99%), large color contrast (∆T = 32%) and good thermal stability (T_d > 150 ℃). In addition, when viologen was added in the gel as ion storage material, the repeating stability at high temperature was further improved.

Stretchable light-emitting sources have attracted attention for various applications such as deformable displays and health care devices that can be attached on non-flat shapes such as the human body. One conventional method of making stretchable devices is by designing stretchable wavy structures by attaching thin functional films on pre-stretched elastomers. However, this method requires a special apparatus to stretch the elastomer because of which printed electronics cannot be applied for film coating and patterning. In this study, we proposed a method that utilizes a plastic deformation, stretchable wrinkle structure consisting of conductive polymer electrodes which are patterned using printed electronics technique. Here, we present the fabrication method and the experimental results of the proposed material. Using this method, stretchable comb-shape electrodes were patterned on an elastomer/electroluminescent powder composite, and a light-emitting device stretchable up to an equi-biaxial stretch λ = 1.4 was fabricated. Our method will help in the fabrication of stretchable light sources.

The surface treatment using atomic hydrogen genareted by a heated tungsten mesh was investigated for the cleaning of the optical elements used in the synchrotron facility. We call the surface-tretament by the atomic hydrogen annealing (AHA). The Au and Ni mirors and Ni and Mo diffraction gratings with carbon contamination were cleaned by the chemical reaction and thermal effect due to the recombination of the atomic hydrogens during AHA. The carbon contamination was removed and the reflactance of the Au and Ni mirrors was recovered by AHA. The AHA conditions could be optimaized for cleaning of Mo/Si multilayer mirrors from the relationship between the treatment condition and degradation. In addition, to clarify the removal reaction of the carbon contamination, the two-types of amorphous carbon (a-C) films were used. The etching rate of the a-C film by AHA was strongly related to the hydrogen content, atomic density and sp²/sp³ component of a-C film.

We have previously demonstrated that photoresist removal rate comparable to oxygen plasma is accomplished by optimizing the removal conditions with H radicals produced on hot metal filament surfaces from H₂/N₂ mixtures (H₂:N₂ = 10:90 vol%). N₂ gas was used to dilute the concentration of the H₂ gas and to reduce the risk of explosion. However, it is not clear how the dilution of H₂ by N₂ affects the removal rate. In this paper, we examined the relationship between the removal rate and the H₂ content; the flow rate ratio of H₂ to H₂+N₂. The removal rate increased with increasing the H₂ content. In addition, the removal rate increased with increasing the substrate temperature according to an Arrhenius equation, when the H₂ content was over 90%. However, below 60%, the removal rate decreased with increasing the temperature over 230 ± 5 ℃. Denaturation of photoresist, e.g. hardening and/or crosslinking, may be induced by substrate heating when the H-radical density is low. The removal rate decreases not only by the deficiency of H radicals but also by the denaturation of films in H₂/N₂ mixed systems.

We have previously demonstrated that photoresist removal rate is enhanced by adding a trace amount of O₂ to the atmosphere in which H radicals are produced from H₂ on a hot metal filament. In this case, not only H radicals but also O and OH radicals are produced. The populations of O and OH radicals are a few hundredth parts of that of H radicals, but these radicals must play important roles. It is not clear which radicals contribute more to the enhancement of the removal rate. We used He/O₂ mixtures in this study, instead of H₂/O₂, to produce O radicals without co-producing H and OH to make clear the contribution of O radicals on the removal rate. The removal rate increased slightly with increasing the O₂ additive amount when the filament was unheated. This may be caused by thermal oxidation. On the other hand, the removal rate with a hot filament decreased by the addition of O₂. In short, the removal rate is not enhanced by O radicals. The enhancement in H₂/O₂ mixtures must only be ascribed to OH radicals.

Photo amphoteric compound generators (PAmGs), which are onium salts used to generate 2-aminoethane-1-sulfonate (taurine) in photo decomposition, were prepared as a mixture and compared with the absorption spectra, photo generation of taurine, and photo pH changes in aqueous solution. One of these photo taurine generators (PtaurineGs) with bis(4-methoxyphenyl)iodonium was designed and prepared for environmentally-friendly photo-reactive materials. These PtaurineGs were water-soluble and photo-decomposable. The photo induced gelling of the aqueous solution drop including casein, which were derived from natural compounds, were demonstrated for stereolithography.

Hydroxyl groups of dextrin, which is a base polymer, were modified with photosensitive groups to the extent that water solubility could be maintained, and water-soluble plant-derived photosensitive materials were created. This material can be applied to a silicon wafer using spin coating, exposed by a mask contact exposure system (LTCET-500: Litho Tech Japan), and then developed with water to enable fine processing, which is derived from plants for photolithography. It has been demonstrated that adaptation to water-soluble nanopatterning materials is possible. Since the base polymer is derived from plants and does not use organic solvents or highly toxic strong alkaline developers, it is useful as a low environmental load patterning material.

The rail track is one of the most important structures for maintenance among railway structures. The rail track is subjected to repeated loads by the wheels directly, causing track deviation. Track irregurality causes unsafety and uncomfortable running of train. There is a method of measuring orbital deviation. By installing a recursive target for image measurement on the rail of the train, the coordinates of the center of gravity are measured with a digital camera. Track distortion caused by repeated train running is measured. However, since the train repeatedly travels, deposits are attached due to external environmental factors, and the target becomes black. In this study, the attached matter was analyzed and the kind of attached matter was confirmed. By analyzing the attached matter, various materials are found, and it is possible to infer a blackened state. Knowing the actual condition of the adhering matter enables countermeasures and prevention, leading to a reduction in maintenance work.

In quartz crystal microbalance (QCM) analysis, dopamine acrylamide (DopAm) accumulated on the surface of SiO₂, ITO, and Ag over time. These results suggest that the scaffolds on these surfaces are formed with the catechol groups and DopAm accumulates by the intermolecular hydrogen bondings. And in the investigation of the surface adhesion and the tackiness, by adding only 1% of DopAm to UV curing monomers, DopAm was effective to several materials and several pairs of dissimilar materials. Considering the behavior of the QCM, these results suggest that DopAm has the effect of resin reinforcement by intermolecular hydrogen bondings with the functional groups of other monomers as well as scaffolding by catechol groups. To further applications, a redox characterization of DopAm was investigated by a cyclic voltammogram (CV).

In this study, we synthesized hydroxypropyl cellulose (HPC) derivatives possessing alkyl ether side chains through Williamson ether synthesis. Such HPC ether derivatives exhibited thermotropic cholesteric liquid crystals (CLCs) with Bragg reflection. The temperature dependence of reflection wavelength could be controlled by changing the side chain lengths and etherification degrees in the HPC derivatives. Moreover, the thermal stability of both HPC ester and ether was evaluated before and after heating at 60 ℃ for 20 days. The reflection peak of HPC ester shifted to the longer wavelength upon the heating treatment due to the hydrolysis of ester linkage. On the other hand, we found that the reflection peak of HPC ether can be robustly preserved even after the prolonged heating treatment, arising from the thermal stability of ether linkage. The rational approach addressed here provides promising clues to fabricate the stable photonic CLC devices with refection features by exploiting anti-hydrolysis of the cellulose ether derivatives.

In this study, we fabricated the reflective color films of lyotropic cholesteric liquid crystals (CLCs) by using a hydroxypropyl cellulose (HPC) derivative and water. When HPC derivatives possessing acryloyl esters in the side chains (HPC-AcE) were completely dissolved in water to form the lyotropic CLC (HPC-AcE_H₂O), we could observe Bragg reflection in the visible wavelength range at room temperature. Furthermore, after the lyotropic CLC mixtures were irradiated with UV light, the reflection colors could be preserved at room temperature. This report has established an important guideline to fabricate the colored CLC cellulose films with safety and low risks for both human being and global environment from naturally occurring polymers and water.

In this report, we describe the syntheses of monodispersed microparticles of silica, that is, polysilicate, in a microreactor based on Stöber method for fabrication of the well-organized colloidal photonic crystal (CPC) films with visible reflection properties. Although the bath synthesis of silica microparticles gave the relatively high coefficient of variation (CV) value of 14.1% in the particle diameter, we successfully improved the CV value from 14.1% to 5.5% by the microfluidic synthesis of silica microparticles in a flow reactor, arising from the separation of nucleation and growth processes. When we fabricated various CPC films of the silica microparticles by the vertical deposition technique, each CPC film showed a characteristic peak of Bragg reflection with a high reflectance over ~60% in the visible wavelength range. Moreover, we found that the experimental reflection spectra of CPC films have consistent with the theoretical spectra calculated by the scalar wave approximation (SWA) technique.