We have proposed reverse mode liquid crystal (LC) cells with a hybrid alignment nematic (HAN). A dual frequency LC which has positive and negative dielectric anisotropies and a reactive mesogen were used to prepare the cell. The reverse mode HAN cell has a transparent state at any incident angle in the voltage off state. The cell scattered a normal incident light by the voltage application and the transmittance, however, becomes high at a certain oblique incident angle like a louver of a window shutter. Such an incident angle can be switched by the frequency of applied voltage since the reoriented LC director changes from perpendicular to parallel to the substrate. Moreover, the incident angle switching was theoretically analyzed using conditions of refractive index matching and mismatching between the LC and the reactive mesogen.

Homogeneously aligned liquid crystal (LC) cell was fabricated using nematic LCs (NLCs) doped with a polymerizable monomer comprising of photocrosslinkable mesogenic side groups, combined with the linearly polarized UV light exposure at elevated temperature. We have clarified that the photosensitive layer forms on the substrates via the thermal polymerization, followed by generating the NLC photoalignment based on the axis-selective photocrosslinking. The LC characteristics of the photosensitive side groups of the polymerizable material play an important role in the defect-free alignment for the NLCs.

A liquid crystal alignment film with fewer processes capable of imparting anisotropy was developed using a polyimide, which utilized the cleavage of a cyclobutane ring by irradiation of polarized UV light at 254 nm. When an aromatic diamine with alkylene in the molecular center was used, an even methylene number of diamines showed superior liquid crystal alignment ability compared with diamines with an odd methylene number. Additionally, a diamine containing a molecular structure with a pre-imidized imide group adjoined to a cyclobutane ring was extremely effective in improving liquid crystal alignment ability and sensitivity to polarized UV light.

Liquid crystal (LC) lens with transparent multiple ring electrodes and circular electrode inside is proposed for controlling spherical and conical lens-like optical phase retardations. Almost circular interference fringes can be smoothly tuned by adjusting the voltage applied across each patterned-electrode and the common flat electrode. The spherical and conical lens-like properties can be obtained, and the focal lengths at an optical axis can also be estimated by a ray tracing calculation resulting from the experimental phase retardation distribution.

The recent development of n-type semiconducting polymers in the author’s group is reviewed. Fullerene polymers are initially described. By introducing a specially designed alkylated comonomer and using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction, highly soluble but high-molecular-weight fullerene polymers with a high fullerene content are obtained. Next, a new attempt to produce n-type polymers by a postfunctionalization reaction is shown. The [2+2] cycloaddition-retroelectrocyclization (CA-RE) between electron-rich alkynes and electron-deficient olefins is employed to construct acceptor units in the polymers. The frontier energy levels of typical p-type polymers containing electron-rich alkynes are lowered by the [2+2] CA-RE with cyano acceptors, such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Finally, rational design of high mobility n-type semiconducting polymers based on benzobisthiadiazole (BBT) and its analogues are described. A series of polymers are designed and synthesized, and their thin film transistor (TFT) performances are investigated. Although the BBT unit is suitable for TFT applications, the comonomer must be carefully selected in order to create unipolar n-type charge-transport properties. Thus, naphthalenediimide (NDI) with a deep highest occupied molecular orbital (HOMO) level is copolymerized with the BBT monomer to produce high-performance n-type polymers.

Organic light-emitting diodes (OLEDs) have showed the unique potentials of display by bendable, foldable and storable panels. In general, since OLEDs consisted of multi organic layers, their electrical conduction would be complicated. Aluminum quinoline (Alq3) was a classical and famous fluorescent material. We studied the conduction properties of inverted Alq3-bilayer OLEDs. Since the barrier height of electron injection from ITO cathode to Alq3 was higher than that from LiF/Al, electrons were little injected into Alq3 and the current density in the absence of EL was controlled by holes. In the specimen using polyethyleneimine as an injection layer, the current density and hole injection were influenced by electron injection for the current continuity. Despite that holes could arrive at the counter cathode through Alq3, the recombination zone was located near a hole transport layer as the conventional bilayer OLED. It was suggested that the carrier transport in an organic layer depends on both carrier injections.

We applied lithium bis(trifluoromethanesulfonyl)imide (Li–TFSI) salt for electron injection layers (EILs) in solution-processed organic light-emitting devices (OLEDs). The application result indicates that the alone Li–TFSI EIL was insufficient. Meanwhile, zinc oxide (ZnO) nanoparticle (NP)/polyethyleneimine ethoxylated (PEIE)/Li–TFSI trilayer was a highly efficient EIL compared with conventional lithium (Li) 8-quinolate and ZnO NPs/PEIE EILs and we realized a low-driving voltage OLED. Possibly, Li cations were reduced to Li atoms by the thermally evaporated aluminum (Al) atoms with adjacent Al cathode, and Li atoms reduced the work function of the cathode, resulting in the driving voltage reduction of the OLED. In the triple EIL structures, Li–TFSI was changed to magnesium and silver salts. Among the three types of TFSI salts, Li–TFSI exhibited the most efficient electron injection property.

Two donor-acceptor-type conjugated polymers comprising alkoxy-substituted bithiophenes were synthesized by both direct C-H arylation polymerization and Stille-type polycondensation. Although these polymers contain the same components, i.e. two alkoxythiophene moieties and one benzothiadiazole moiety in a repeating unit, their optical and electrochemical properties were clearly different owing to their different regioregularities.

B-site-ordered double-perovskite oxide up-conversion phosphors La₂ZnTiO₆, La₂MgTiO₆, and Ba₂LaTaO₆ doped with Yb and Ho, Er, or Tm were synthesized by a citric acid complex gelation method and a polymerizable complex method. Under 980-nm excitation, the double-perovskite oxide phosphors doped with luminescent ions at the A-site (La₂ZnTiO₆ and La₂MgTiO₆) showed stronger up-conversion emission than the phosphor doped with luminescent ions at the B-site (Ba₂LaTaO₆). La₂ZnTiO₆ and La₂MgTiO₆, in which dopants occupied the A-site, showed different up-conversion emission behaviors because of structural distortion resulting from the substitution of B-site cations.

The efficiency of Sn-perovskite solar cells has been dramatically improved by adopting the inverted structure solar cells and is expected to reach the efficiency of lead-based perovskite solar cell. We have observed fluctuations in the efficiency of the same perovskite material due to the type of TCO substrates. In this study, we investigated the influence of TCO substrates on the solar cell characteristics of SnGe-perovskite solar cells. It was found that the efficiency of the SnGe-perovskite solar cell is better with fluorine-doped tin oxide (FTO) substrate (9.24%) than indium-doped tin oxide (ITO) substrate (7.72%). The improvement of the efficiency of the cell with FTO substrate is contributed by the improvement in the short-circuit current J_sc and V_oc. The high transmittance of FTO substrate enhanced the J_sc while the V_oc is influenced by the Fermi level of the transparent conductive oxide film. Although there is a difference in the surface roughness between TCO substrates, there is no direct influence on the device performance that can be observed.

Resist removal phenomena using laser irradiation were compared in the novolak resist and the PVP. Thresholds for stripping from the Si wafer and damaged at the Si wafer were evaluated for the laser irradiating condition in the normal atmosphere and in the water. The PVP was found to be easy to be stripped as compared with the novolak resist. Only in the water, the photoresist material was completely stripped from the Si wafer surface. The size of the changed area by the laser irradiation for the PVP was approximately 2 times larger than that of the novolak resist. Time-resolved images were also acquired in 400 ns and 7500 ns after the laser irradiation. The scattering condition of the PVP in the removal process was completely different from that of the novolak resist.

We examined an environmentally friendly photoresist removal method using radicals produced by decomposing mixtures of hydrogen and oxygen on a hot iridium catalyst. We earlier reported that the decomposition of photoresists was hastened by adding oxygen gas to a hydrogen flow using a tungsten hot-wire catalyst. The rate increased with the oxygen additive amount up to about 1.0% and then decreased gradually. The decrease is caused by the catalytic poisoning of O atoms on the catalyst surface because of its poor oxidation resistance. In present study, we show that oxygen addition without catalytic poisoning is effective to increase the decomposition rate. The poisoning can be avoided by using an Ir catalyst. The decomposition rate increased with the substrate temperature. The rate also increased rapidly with increasing amounts of added oxygen to 1.0% and then the increase became more gradual. OH radicals must play an important role to hasten the decomposition reactions.

Oxidative degradation of poly(ethylene glycol) (PEG) by ozone microbubbles (O₃MBs) was investigated in water. Ozone water are generally effective in oxidation reaction with a variety of organic compounds. O₃MBs have promise to improve the efficiency because it seems that O₃MBs generates hydroxy radicals, resulting in the higher active oxidative degradation. Herein, oxidative decomposition of PEG by O₃MBs in water was carried out and the products were characterized by ¹H nuclear magnetic resonance (NMR) and matrix assisted laser desorption/ionization fourier transform ion cyclotron resonance mass spectrometry (MALDI-FT-ICR-MS). Through the continuous struggles, decomposition of PEG was promoted by O₃MBs. It was found that O₃MBs with hydrogen peroxide added had the largest decomposition effect. The reason has been veiled yet, however, the author reasons that O₃MBs have promise as the novel degradation system.

Diacrylate having a dipyridyl disulfide moiety is synthesized as a cross-linker for photoadhesive materials. The cross-linker has been used with 2-hydroxylethyl acrylate and a photoradical initiator to adhere a glass substrate with various kinds of substrates such as glass, copper, polyvinyl chloride, and aluminum. After 4 J/cm² of UV irradiation at a wavelength of 365 nm, ca. 0.3-1.2 MPa of shear stress is recorded with the adhesive samples, which is superior to control adhesive samples having no dipyridyl disulfide moieties. From the results on XPS spectral measurements, it is indicated that both electron-rich sulfur atom and electron-poor nitrogen atom would contribute to the adhesion behavior.

UV-cured films containing disulfide bonds were fabricated by radical UV curing with a diacrylate monomer. The free standing films were characterized by DSC, XPS, and Raman spectral measurements. Film shrinkage due to volume contraction during radical polymerization reactions was relieved by heating at 60 ℃ for 2 min, which was not observed in the control film sample containing no disulfide bonds. This quick relaxation would be due to relaxing the internal stress by exchange reactions between disulfide bonds.

In the nanoimprint process, the transfer failure due to the air involved from pressing the mold against the transfer material and the gas generated from the transfer material has been reported as a serious problem. We have investigated the relationship between the thickness of the mold and the gas permeation flow rate in a single-layer gas permeable mold with only a low density structure and a two-layer gas permeable mold with a low density structure and a lattice structure manufactured by a 3D printer. Furthermore, we imprinted the transfer material containing volatile solvents using two gas permeable molds, and investigated the presence of transfer defects due to gas. As a result, the gas permeation flow rate increased as the thickness of any gas permeable mold became thinner. In addition, when the gas permeable mold having a two-layer structure and the gas permeable mold having a single-layer structure are compared, the gas permeation flow rate of the two-layer structure is about 20 times as large as that of the single-layer structure. Furthermore, as a result of investigating the presence or absence of transfer failure due to gas in imprint molding, transfer failure due to gas occurred in the non-gas permeable mold, but transfer failure due to gas did not occur in the gas permeable mold having the two-layer structure. Therefore, the lattice structure designed for the gas passage can greatly improve the gas permeation flow rate, and it can be expected to reduce the transfer failure due to the gas at the time of imprint.

This report describes the syntheses and properties of cellulosic derivatives for reflection color films. As hydroxypropyl cellulose (HPC) was reacted with acryloyl chloride, we prepared a series of HPC derivatives tethering acryloyl side chains (HPC-Ac) at their different esterification degrees. When the cell of HPC-Ac was heated in a stepwise manner, we observed thermotropic cholesteric liquid crystal (CLC) feature with Bragg reflection in the full-visible wavelength range. Such temperature dependence of Bragg reflection could be controlled by tuning esterification degree of acryloyl side chains of HPC-Ac. We succeeded in the permanent preservation of periodic helical CLC structure by thermo- or photo-induced crosslinking reaction between the acryloyl side chains of HPC-Ac, resulting in fabrication of reflection color films with thermal stability up to 180 ℃. This report provides promising clues to fabricate the robust multi-colored films, derived from biomass of cellulose, for novel photonic devices.

This report describes the preparation of lyotropic cholesteric liquid crystals (CLCs) with visible reflection by using two kinds of human-friendly materials. We adopted a cellulosic derivative as the main CLC component and α-ionone as the additive liquid. A cellulosic derivative possessing propionyl side chains was dissolved in α-ionone at the concentration between 66 wt% and 86 wt% for the formation of lyotropic CLCs. We confirmed that the visual appearance of lyotropic CLC phase shows iridescent feature such as visible Bragg reflection. The reflection peak wavelengths could be easily tuned not only by controlling the concentration of cellulosic derivative, but also by temperature. Moreover, it turned out that the refection wavelength is influenced by weight average molecular weights of the cellulosic derivatives used in lyotropic CLC mixtures. This report provides promising clues to fabricate environment- and human-friendly photonic devices by using cellulose and ionone.

In this report, we synthesized hydroxypropyl cellulose (HPC) derivatives tethering both ester and carbamate groups by chemical modifications of HPC with both alkanoyl chlorides and alkyl isocyanates. They exhibited thermotropic cholesteric liquid crystal (CLC) phase. The differences in side chain lengths and bonding species of HPC derivatives affected the thermotropic CLC properties. We observed visible Bragg reflection from the HPC ester-carbamate derivatives at lower temperature than from those of the HPC esters. Moreover, the shifting wavelength ranges of Bragg reflection of the HPC ester-carbamate derivatives as heating temperature were narrow rather than those of the HPC esters probably due to their hydrogen bonding between carbamate bonds.

In this study, we fabricated the multi-colored films of lyotropic cholesteric liquid crystals (CLCs) prepared from a hydroxypropyl cellulose (HPC) derivative by photopolymerization of a diacrylate liquid monomer for color image applications. When a hydroxypropyl cellulose derivative tethering propionyl side chains (HPC-PrE) was completely dissolved in a liquid monomer of 1,4-bis(acryloyloxy)butane (BAOB) to prepare lyotropic CLC (HPC-PrE_BAOB), we could observe Bragg reflection in the visible wavelength range at room temperature. Photopolymerization of BAOB in the lyotropic CLC mixture gave rise to fabrication of robust solid-state CLC films with reflection colors. Furthermore, we found that the reflection wavelength is tunable by controlling the light intensity of irradiation UV light, thereby enabling the facile fabrication of multi-colored films by the photolithographic technique. The present report opens promising ways to design and produce intriguing photonic devices by utilizing the environmentally-friendly and safe natural polymer of cellulose.

In this report, we describe the facile fabrication procedure of a flexible photoluminescence (PL) film of CuInS₂ nanocrystals (CIS NCs) embedded in polyacrylates. The CIS NCs with the sizes of 2.2±0.5 nm were synthesized by simple pyrolysis of low-toxic Cu and In acetate precursors in 1-octadecene, and successively were dispersed in a mixture of acrylate monomers. Irradiation of the mixture with UV light brought about the formation of a clear PL film of polyacrylates hybridized with CIS NCs. Moreover, we found excellent mechanical flexibility of the hybrid film. The present report opens promising ways to impart unique photonic devices by combining the inorganic NCs and photopolymers.

The contact angle is measured when evaluating oil repellency in water in the static wettability of a solid. Basically, it is common to observe the shape of a solid water droplet, oil or solid interface with a camera or a telescope and evaluate it from an image. The phenomenon of wetting is whether liquid is likely to adhere to the solid surface or not, and is discussed in terms of the contact angle. Although this method can evaluate the wettability of the surface at an instant, it is difficult to evaluate when maintaining the state of wettability or when changing the environment. Therefore, we considered a method that can evaluate the condition while observing the progress of the wettability on the surface. For surface wettability, we report a new oil repellent evaluation method using the resonance principle. In the near future, this new evaluation method can contribute to dynamic wetness that incorporates the elements of time.

A new display with quantum dot color filter (QD-CF) is attracting attention as a next-generation display. The QD-CF display can achieve high brightness, definition and contrast. It is essential for QD-CF structure to form “banks” separating QD materials.

　In this paper, we introduce the novel photo-sensitive light-shielding banks with high reflectivity, which are suitable for QD-CF display. This bank material contains both TiO₂ pigment and UV transparent black pigment. The material can form gray banks which have a thickness of 10 μm with a good taper angle of 86°. The banks show good light-shielding property (transparency@450 nm<1%), high reflectivity of 50.8% at 550 nm, and high heat resistance (1% weight loss temperature is 353 ℃). This developed material is ideal for application of QD-CF display.

In recent years, we have seen growing numbers of reports on problems associated with outgas generated from resists during ArF exposure, including contaminating of the exposure equipment lens. Scanner manufacturers have apparently begun taking countermeasures—for example, establishing criteria for outgas generated by resists during exposure. In the near future, resist manufacturers will likely be required to attach documents regarding outgassing to their products at the time of shipment. In our earlier studies, we tried to establish methods for evaluating outgassing from KrF resists during KrF (248 nm) exposure. This paper examines an approach to evaluating outgassing from ArF chemically-amplified resists during ArF exposure, with a special focus on sulfate ions (SO₄ ^2－) derived from PAG, based on the outgas analytical techniques that we have built up to date. We used ion chromatography (IC) as the method of analysis.

A color filter (CF) for displays consists of color resists, transmitting red (R), green (G), and blue (B) light, deposited onto a pattern of black matrix (BM) film formed on a thin glass substrate. The BM prevents optical leaks while producing the color black and prevents the mixing of color resists in adjacent pixels of the matrix. The filter also has a structure that forms the ITO (transparent electrode) film, which serves as the common electrode for the TFT array substrate. The BM resist must have high optical density (OD) to prevent optical leaks. Manufacturing goals typically include reducing the unit cost of panels and ensuring high-sensitivity panel design to allow the high throughput production of large panels. The emergence of 8K and 16K technologies in recent years has generated demand for ever higher resolutions, which, in turn, has driven demand for thinner films capable of achieving greater resolution and OD. Thus, the development of BM resists must now meet the highest technological standards. Responding to these issues involves identifying BM lithography characteristics. As a first step, we focused on the lithographic properties of BM resists, particularly on development characteristics. However, it is difficult for conventional development monitors to measure development rates of BM resists. Here we report on an analysis performed by a development monitor based on the QCM method.