Masahito Oh-e - Academia.edu (original) (raw)

Papers by Masahito Oh-e

Emerging Liquid Crystal Technologies XVIII

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1997

We have investigated the switching and response mechanism of the in-plane switching (IPS) mode wh... more We have investigated the switching and response mechanism of the in-plane switching (IPS) mode which is a novel technique for wide viewing-angle liquid crystal displays. In the IPS mode, an in-plane electric field is applied to the liquid crystals along the direction parallel to the plane of the substrates. First, it was made clear that it was the electric field and not the voltage that drove the liquid crystals in the IPS mode. An inversely proportional relationship between the threshold voltage and the cell gap was found to hold. Second, the relaxation time of the liquid crystals when removing the electric field was described as a proportional relationship to the square of cell gap. A thinner cell gap also proved to be effective to obtain fast response time in the IPS mode. In contrast, the electric field strength governed the switching-on time when applying the in-plane electric field.

Scientific Reports

A comprehensive understanding of controlling the iridescence of cellulose films by manipulating t... more A comprehensive understanding of controlling the iridescence of cellulose films by manipulating the alignment and helical pitch of cellulose nanocrystals (CNCs) is required to advance cellulose photonics and its optoelectronic applications. Aqueous suspensions of CNCs exhibit a cholesteric liquid crystal (LC) phase with structural color; however, attaining a uniformly colored film is extremely difficult. Presumably, because multiple interrelated factors influence the CNC molecular alignment and helical pitch, existing models are not necessarily conclusive and remain a subject of debate. To eventually achieve homogeneously colored films, we compare aqueous CNC suspensions as a lyotropic liquid LC with thermotropic ones, and we spectroscopically confirm that the coloration of CNC droplets originates from the periodic CNC structure. The suspension drying process significantly influences the quality of iridescence of CNC films. Rapidly drying a droplet of a CNC suspension forms a concen...

Preprints of symposium on liquid crystals, 1997

Interactions between hydrated Ce 3+ and various carboxylates are of fundamental interest. Anomalo... more Interactions between hydrated Ce 3+ and various carboxylates are of fundamental interest. Anomalously strong interactions with Ce 3+ occur when diglycolic acid (DGA) is added into a Ce 3+ aqueous solution, unlike various other carboxylic acids. Herein, the complex-formation constants of Ce 3+ with these acids are evaluated via absorption and emission spectra. Hydrated Ce 3+ emits fluorescence with unity quantum yield; however, addition of various carboxylates statically quenches the fluorescence when Ce 3+ −carboxylate complexes form because the fluorescence lifetime is constant irrespective of the carboxylate concentration. In the observed static quenching, the complex-formation constants obtained from the absorption and emission spectra (K abs and K em) agree well. The binding of Ce 3+ by the conjugate Lewis bases, i.e., carboxylates, is approximately inversely proportional to the pH. Adding DGA into the system also statically quenches the fluorescence, but far more efficiently, even in a much weaker solution. We rigorously deduce K abs and K em of Ce 3+ with DGA without any approximation using comparable concentrations. Careful fittings provide equivalent K em and K abs values, and by varying the pH and ionic strength, we confirm that this equivalence is an inherent property of the Ce 3+ −DGA system. The Lewis acid−base theory cannot explain why DGA binds to Ce 3+ ∼1000 times more strongly than the other carboxylates. This anomalously strong binding may be due to a chelate effect caused by the DGA's central oxygen atom, which forms a five-membered ring with the conjugate Lewis bases of DGA; double chelate rings can also form, while bis-deprotonated DGA binds to Ce 3+ , facilitated by the central oxygen. Therefore, DGA enables efficient quenching through the chelate effect when it binds to Ce 3+ .

Molecular Crystals and Liquid Crystals, 1991

Abstract X-ray diffraction studies on the field induced distortion of the layer structure in ferr... more Abstract X-ray diffraction studies on the field induced distortion of the layer structure in ferroelectric liquid crystals are reported. Depending on the liquid crystal materials and alignment layers, electric fields produced reversible or irreversible distortions. Bistable electrooptical switching was observed only in the samples with the irreversibly distorted layer structure. Experimental results on the light transmissions indicated that a bookshelf-like structure was formed in the above bistable sample. It seemed that this structure formation was essential to the bistability of the ferroelectric liquid crystals.

Preprints of symposium on liquid crystals, 1994

Journal of Applied Physics, 2019

Theoretically probing the physics underlying the photoluminescence of phosphors and predicting th... more Theoretically probing the physics underlying the photoluminescence of phosphors and predicting their thermal quenching properties are significant issues in the field of phosphor research. The electronic ground states of a series of Eu(II)-doped alkaliearth sulfide phosphors, i.e., MS:Eu 2+ (M = Mg, Ca, Sr, Ba), have been analyzed using density functional theory calculations to characterize and analyze their photoluminescence properties in terms of quantum efficiency and its thermal decay tendency. Anderson's impurity model to MS:Eu 2+ enables devising a physical picture of how the electronic ground states jψ EuÀ5d i representing the Eu(II)-5d orbitals are mixed with those of the conduction bands (CBs) of host materials. The focus is on quantitatively deducing the electron delocalization nature of jψ EuÀ5d i over |CB〉, especially P k jψ MÀdk k i, which represents the bands formed by the d orbitals of M atoms. The ratio of the probability amplitudes of jψ EuÀ5d i and P k jψ MÀdk k i, i.e., C EuÀ5d =C MÀd , proves to be correlated with the electron localization nature of jψ EuÀ5d i, thereby suggesting that this ratio can be an effective parameter for evaluating the thermal quenching tendency of photoluminescence without more precise information on the electronic excited states. Energetically small gaps and large spatial overlaps between jψ EuÀ5d i and |CB〉 delocalize electrons in a hybridized state, which gives these electrons the tendency to dissipate without luminescence. The results explain the rankings of the quantum yield and its temperature dependence in the MS:Eu 2+ (M = Ca, Sr, Ba) systems, which follow the Dorenbos thermal quenching model, while MgS:Eu 2+ does not have the same mechanistic origin.

Journal of the Korean Physical Society, 2008

We investigated the uorescence characteristics of hemicyanine dye molecules in conventional solve... more We investigated the uorescence characteristics of hemicyanine dye molecules in conventional solvents and in the isotropic phase of liquid-crystal 4-pentyl-4'-cyanobiphenyl. Fluorescence decay lifetime of hemicyanine in liquid crystal decreased monotonically as the temperature was increased. As compared to glycerol, the uorescence decay lifetime of hemicyanine in the isotropic phase of liquid crystal was appreciably longer. This longer decay lifetime of hemicyanine in liquid crystal can be explained by a restricted internal rotational motion of the hemicyanine molecule due to strong interaction between the dye molecule and the liquid crystal molecules as compared to other solvents.

Scientific Reports, 2022

To unveil a novel switching mechanism in liquid crystal (LC)-based phase shifters for the THz ran... more To unveil a novel switching mechanism in liquid crystal (LC)-based phase shifters for the THz range, we analyse how the dimensions of the electrode structures enable a new type of switching, namely, THz in-plane and THz out-of-plane (TIP–TOP) switching. Specifically, we determine how varying these electrode dimensions influences the LC in-plane states with the corresponding phase shifts by calculating these effects in virtual devices. Interestingly, we found that significant dimensional effects of the in-plane electrode structures statically and dynamically influence the phase shift and response time of LC switching. Analysing the electromagnetic fields in the TIP–TOP cell clearly reveals that these dimensional effects are due to changes in the electric field strengths caused by lateral bus-line electrodes that were originally assumed not to contribute to the switching. Further, we discover that the ultimate dimensional effect produces a novel type of LC switching, which results in ...

Preprints of symposium on liquid crystals, 2004

Journal f�r Praktische Chemie, 1991

The decomposition of tert-butyl hydroperoxide by photochemically induced reactions in DMSO*) and ... more The decomposition of tert-butyl hydroperoxide by photochemically induced reactions in DMSO*) and water was investigated by cw-e.s.r. spectroscopy. The products tert-butylperoxyl, methyl and sulfur-centered free radicals were identified. The tert-butoxyl free radical is involved in the primary process as shown by time-resolved e.s.r. technique. On the basis of directly identified radical species, a mechanism for the photochemically induced reactions of tert-butyl hydroperoxide in DMSO is proposed. At concentrations below 0.8 mol * I-' the radical formation from tert-butyl hydroperoxide proceeds by cleavage of the 0-0 bond rather than by hydrogen abstraction.

Nanotechnology, 2008

In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processe... more In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processed by nanoimprint lithography technology (NIL), we propose to design a hybrid-type homeotropic polymer material consisting of two distinct moieties with largely different thermo-mechanical properties and surface activity. Surface contact angle measurements and sum-frequency vibrational spectroscopy allow us to conclude that the polymer film is a functionally separated composite suitable for the homeotropic LC alignment processed by NIL. As one of the potential applications using the hybrid-type homeotropic polymer, we demonstrate that the nanoimprinted grooves at the polymer surface can achieve a zenithal nematic LC bistability.

Emerging Liquid Crystal Technologies XVIII

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1997

We have investigated the switching and response mechanism of the in-plane switching (IPS) mode wh... more We have investigated the switching and response mechanism of the in-plane switching (IPS) mode which is a novel technique for wide viewing-angle liquid crystal displays. In the IPS mode, an in-plane electric field is applied to the liquid crystals along the direction parallel to the plane of the substrates. First, it was made clear that it was the electric field and not the voltage that drove the liquid crystals in the IPS mode. An inversely proportional relationship between the threshold voltage and the cell gap was found to hold. Second, the relaxation time of the liquid crystals when removing the electric field was described as a proportional relationship to the square of cell gap. A thinner cell gap also proved to be effective to obtain fast response time in the IPS mode. In contrast, the electric field strength governed the switching-on time when applying the in-plane electric field.

Scientific Reports

A comprehensive understanding of controlling the iridescence of cellulose films by manipulating t... more A comprehensive understanding of controlling the iridescence of cellulose films by manipulating the alignment and helical pitch of cellulose nanocrystals (CNCs) is required to advance cellulose photonics and its optoelectronic applications. Aqueous suspensions of CNCs exhibit a cholesteric liquid crystal (LC) phase with structural color; however, attaining a uniformly colored film is extremely difficult. Presumably, because multiple interrelated factors influence the CNC molecular alignment and helical pitch, existing models are not necessarily conclusive and remain a subject of debate. To eventually achieve homogeneously colored films, we compare aqueous CNC suspensions as a lyotropic liquid LC with thermotropic ones, and we spectroscopically confirm that the coloration of CNC droplets originates from the periodic CNC structure. The suspension drying process significantly influences the quality of iridescence of CNC films. Rapidly drying a droplet of a CNC suspension forms a concen...

Preprints of symposium on liquid crystals, 1997

Interactions between hydrated Ce 3+ and various carboxylates are of fundamental interest. Anomalo... more Interactions between hydrated Ce 3+ and various carboxylates are of fundamental interest. Anomalously strong interactions with Ce 3+ occur when diglycolic acid (DGA) is added into a Ce 3+ aqueous solution, unlike various other carboxylic acids. Herein, the complex-formation constants of Ce 3+ with these acids are evaluated via absorption and emission spectra. Hydrated Ce 3+ emits fluorescence with unity quantum yield; however, addition of various carboxylates statically quenches the fluorescence when Ce 3+ −carboxylate complexes form because the fluorescence lifetime is constant irrespective of the carboxylate concentration. In the observed static quenching, the complex-formation constants obtained from the absorption and emission spectra (K abs and K em) agree well. The binding of Ce 3+ by the conjugate Lewis bases, i.e., carboxylates, is approximately inversely proportional to the pH. Adding DGA into the system also statically quenches the fluorescence, but far more efficiently, even in a much weaker solution. We rigorously deduce K abs and K em of Ce 3+ with DGA without any approximation using comparable concentrations. Careful fittings provide equivalent K em and K abs values, and by varying the pH and ionic strength, we confirm that this equivalence is an inherent property of the Ce 3+ −DGA system. The Lewis acid−base theory cannot explain why DGA binds to Ce 3+ ∼1000 times more strongly than the other carboxylates. This anomalously strong binding may be due to a chelate effect caused by the DGA's central oxygen atom, which forms a five-membered ring with the conjugate Lewis bases of DGA; double chelate rings can also form, while bis-deprotonated DGA binds to Ce 3+ , facilitated by the central oxygen. Therefore, DGA enables efficient quenching through the chelate effect when it binds to Ce 3+ .

Molecular Crystals and Liquid Crystals, 1991

Abstract X-ray diffraction studies on the field induced distortion of the layer structure in ferr... more Abstract X-ray diffraction studies on the field induced distortion of the layer structure in ferroelectric liquid crystals are reported. Depending on the liquid crystal materials and alignment layers, electric fields produced reversible or irreversible distortions. Bistable electrooptical switching was observed only in the samples with the irreversibly distorted layer structure. Experimental results on the light transmissions indicated that a bookshelf-like structure was formed in the above bistable sample. It seemed that this structure formation was essential to the bistability of the ferroelectric liquid crystals.

Preprints of symposium on liquid crystals, 1994

Journal of Applied Physics, 2019

Theoretically probing the physics underlying the photoluminescence of phosphors and predicting th... more Theoretically probing the physics underlying the photoluminescence of phosphors and predicting their thermal quenching properties are significant issues in the field of phosphor research. The electronic ground states of a series of Eu(II)-doped alkaliearth sulfide phosphors, i.e., MS:Eu 2+ (M = Mg, Ca, Sr, Ba), have been analyzed using density functional theory calculations to characterize and analyze their photoluminescence properties in terms of quantum efficiency and its thermal decay tendency. Anderson's impurity model to MS:Eu 2+ enables devising a physical picture of how the electronic ground states jψ EuÀ5d i representing the Eu(II)-5d orbitals are mixed with those of the conduction bands (CBs) of host materials. The focus is on quantitatively deducing the electron delocalization nature of jψ EuÀ5d i over |CB〉, especially P k jψ MÀdk k i, which represents the bands formed by the d orbitals of M atoms. The ratio of the probability amplitudes of jψ EuÀ5d i and P k jψ MÀdk k i, i.e., C EuÀ5d =C MÀd , proves to be correlated with the electron localization nature of jψ EuÀ5d i, thereby suggesting that this ratio can be an effective parameter for evaluating the thermal quenching tendency of photoluminescence without more precise information on the electronic excited states. Energetically small gaps and large spatial overlaps between jψ EuÀ5d i and |CB〉 delocalize electrons in a hybridized state, which gives these electrons the tendency to dissipate without luminescence. The results explain the rankings of the quantum yield and its temperature dependence in the MS:Eu 2+ (M = Ca, Sr, Ba) systems, which follow the Dorenbos thermal quenching model, while MgS:Eu 2+ does not have the same mechanistic origin.

Journal of the Korean Physical Society, 2008

We investigated the uorescence characteristics of hemicyanine dye molecules in conventional solve... more We investigated the uorescence characteristics of hemicyanine dye molecules in conventional solvents and in the isotropic phase of liquid-crystal 4-pentyl-4'-cyanobiphenyl. Fluorescence decay lifetime of hemicyanine in liquid crystal decreased monotonically as the temperature was increased. As compared to glycerol, the uorescence decay lifetime of hemicyanine in the isotropic phase of liquid crystal was appreciably longer. This longer decay lifetime of hemicyanine in liquid crystal can be explained by a restricted internal rotational motion of the hemicyanine molecule due to strong interaction between the dye molecule and the liquid crystal molecules as compared to other solvents.

Scientific Reports, 2022

To unveil a novel switching mechanism in liquid crystal (LC)-based phase shifters for the THz ran... more To unveil a novel switching mechanism in liquid crystal (LC)-based phase shifters for the THz range, we analyse how the dimensions of the electrode structures enable a new type of switching, namely, THz in-plane and THz out-of-plane (TIP–TOP) switching. Specifically, we determine how varying these electrode dimensions influences the LC in-plane states with the corresponding phase shifts by calculating these effects in virtual devices. Interestingly, we found that significant dimensional effects of the in-plane electrode structures statically and dynamically influence the phase shift and response time of LC switching. Analysing the electromagnetic fields in the TIP–TOP cell clearly reveals that these dimensional effects are due to changes in the electric field strengths caused by lateral bus-line electrodes that were originally assumed not to contribute to the switching. Further, we discover that the ultimate dimensional effect produces a novel type of LC switching, which results in ...

Preprints of symposium on liquid crystals, 2004

Journal f�r Praktische Chemie, 1991

The decomposition of tert-butyl hydroperoxide by photochemically induced reactions in DMSO*) and ... more The decomposition of tert-butyl hydroperoxide by photochemically induced reactions in DMSO*) and water was investigated by cw-e.s.r. spectroscopy. The products tert-butylperoxyl, methyl and sulfur-centered free radicals were identified. The tert-butoxyl free radical is involved in the primary process as shown by time-resolved e.s.r. technique. On the basis of directly identified radical species, a mechanism for the photochemically induced reactions of tert-butyl hydroperoxide in DMSO is proposed. At concentrations below 0.8 mol * I-' the radical formation from tert-butyl hydroperoxide proceeds by cleavage of the 0-0 bond rather than by hydrogen abstraction.

Nanotechnology, 2008

In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processe... more In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processed by nanoimprint lithography technology (NIL), we propose to design a hybrid-type homeotropic polymer material consisting of two distinct moieties with largely different thermo-mechanical properties and surface activity. Surface contact angle measurements and sum-frequency vibrational spectroscopy allow us to conclude that the polymer film is a functionally separated composite suitable for the homeotropic LC alignment processed by NIL. As one of the potential applications using the hybrid-type homeotropic polymer, we demonstrate that the nanoimprinted grooves at the polymer surface can achieve a zenithal nematic LC bistability.