Search

Biocompatible and biodegradable silk fibroin films show promise as an eco-friendly biomaterial with excellent mechanical, thermal, and optical transparency properties. In contrast, polyimide (PI) f...

The Tamm-plasmon-polariton (TPP) occurs at the interface between a metallic film and the photonic-crystal (PC) substrate. Unlike conventional surface-plasmon-polariton (SPP), TPP can be directly ex...

We demonstrate a circularly polarized optical microscope (POM) by incorporating a hole-patterned electrode (HPE) liquid crystal (LC) lens fabricated by photoalignment. The focal plane is controlled by voltages on the HPE LC lens with a tuning range of 2.2 mm without any mechanical movement. The diopter can be controlled from 0 to − 5.0 D , and the wavefront optical path difference is less than 0.25 λ for our proposed HPE LC lens. Such a low aberration is obtained, because the LC directors are well aligned along with the axially symmetrical electrical field, and there is no observed twist deformation of the LC directors. Finally, we applied our circularly polarized POM to inspect the reflectance properties of several beetles, and we find that the “Chrysochroa toulgoeti” beetle exhibits right circularly polarized reflectance from some small areas on its wings.

The dielectric properties of SiO2 nanoparticles and their mixture with Fe3O4 nanoparticles in 5CB liquid crystal were studied by using capacitance-voltage measurements. The prepared colloidal systems exhibited a soft memory effect detected by dielectric hysteresis in nematic phase at ambient temperature. In case of homogeneous SiO2 nanoparticles as dopants, the doped liquid crystal showed the improvement of the effect, sensitive to increasing the nanoparticles concentration. The presence of magnetic nanoparticles caused decreasing the memory effect that was concentration dependent. Additional studies revealed that the temperature erased the observed effect as well as the fact that the different oriented magnetic field changed the magnitude of memory effect. The potential application of these composites leads to a fabrication of non-volatile and low power electro-optical memory devices suitable for information storage applications.

The anisotropy of a thin film can be created by a wide variety of methods and it has found many applications. Liquid crystal (LC) molecules are aligned in a specific orientation on a rubbed polyimide film for conventional LC displays (LCDs). The rubbing process on the polyimide film controls the azimuthal and polar angles of the LCs, and it can cause physicochemical anisotropy on the polyimide film and produce the birefringence Δ n in the azimuthal direction. Knowing the rubbing-induced optical axis of polyimide films is crucial for achieving optimum electro-optical properties of LCDs. The rubbing-induced Δ n and the resolution less than 2 deg for determining the optical axis of the rubbed polyimide are obtained by applying Tamm plasmon polaritons in this Letter.

Different morphologies of ZnO nanorods were synthesized by using the two-step hydrothermal method, and they were applied to liquid crystal (LC) alignment films. The morphology of the ZnO nanorods, including length, diameter, and density, were controlled by the growth time, which ranged from 16 to 26 min. The morphology and the chemical features both contributed to the surface wettability of the ZnO nanorods. The LC pretilt angle on the ZnO nanorods was successfully controlled from homeotropic (∼89.0°) to homogeneous (∼1.7°) alignments, as the contact angle of water on ZnO nanorods was changed from 93 to 28° with the growth time. The analysis of X-ray diffraction and X-ray photoelectron spectroscopy showed that the crystallite size of ZnO nanorods increased with the growth time, while the oxygen vacancy decreased. The ZnO nanorods grown on the ITO glass substrate also improve the transmission of LCDs due to the antireflection effect.

It is observed that the anchoring of LC molecules aligned on the ZnO film depends on the surface wettability. We demonstrate that the surface wettability of ZnO films fabricated by sol–gel process can be modified by annealing. The observations using the scanning electron microscope, photoluminescence and X-ray photoelectron spectroscopy for ZnO films have shown that the annealing can modify both the morphologies and chemical compositions of ZnO films, which in turn produces influences on the surface wettability. The surface wettability of as-prepared ZnO film can be controlled from 102° to 60° (contact angle (CA) of water) as the annealing temperature increases from 190 to 250 °C. Our experimental results show that the pretilt angles of LCs on ZnO films can be modified over a wide range from 89.5° to 0.5° as the CA of water on the ZnO films changes from 102° to 60°.

The surface wettability of ZnO films prepared by a sol–gel process is altered from hydrophobicity to hydrophilicity via ultraviolet (UV) light irradiation. The results indicate that hydrophilicity of the ZnO films is enhanced along with the increase of UV irradiation energy. The measurements of X-ray photoelectron spectroscopy and photoluminescence show that the amount of oxygen vacancies in ZnO films is increased with the UV irradiation. The results of UV-vis absorption spectroscopy and X-ray diffraction also show that the crystalline quality of the ZnO films is slightly changed after UV treatment. The increase in oxygen vacancies means that water molecules can easily coordinate into the oxygen vacancy sites, leading to the increase of surface wettability. It is observed that liquid crystal (LC) molecules can be aligned on the UV-treated ZnO films, and the orientation of LCs on the UV-treated ZnO films can be tuned from homeotropic to homogeneous alignment by controlling the surface wettability of ZnO films. Our results show that the pretilt angle of LCs on ZnO films depends on their surface wettability, and it can be successfully adjusted over a wide range from 89.5° to 0.5° as the contact angle of water on ZnO films changes from 97° to 60°.

A low-aberration hole-patterned-electrodes (HPE) liquid crystal (LC) lens with positive and negative focal lengths is demonstrated in this Letter by using four hybrid-aligned nematic LC layers filled with dual-frequency LC materials. The diopter can be controlled from the positive lens ( 0 D ∼ 1.1 D ) to the negative lens ( 0 D ∼ − 1.25 D ). The aberration is analyzed using the Zernike polynomial, and the wavefront optical path difference is improved from 2 λ for the conventional one-layer HPE LC lens to less than 0.25 λ for our proposed LC lens. The proposed LC lens does not require the use of a polarizer, increasing the optical efficiency two times compared with the conventional LC lens.

For the surface electronic states of a metal, the Tamm plasmonic (TP) mode can be excited without an additional phase-matching component, but in a typical device the TP resonance wavelength is fixed, which is quite limiting. This work develops an approach to tuning TP resonance by incorporating a thin layer of liquid crystal (LC) into the design. Here phase retardation by the LC layer is an ensemble effect, due to the entire layer, not just the molecules at the metal's surface, as in devices based on surface-plasmon polaritons (SPPs). Also unlike SPP systems, the proposed structure is highly amenable to mature thin-film processing, for scalability to lengths of several meters.

The control of the liquid crystal (LC) alignment is very important for both academic research and practical applications. LC molecules aligned on the ZnO nanoparticle arrays (ZnO NPAs) are demonstrated and the pretilt angles of LCs can be controlled by using ZnO NPAs with different surface wettability. The wettability of ZnO NPAs fabricated by the solution-based hydrothermal method can be controlled by changing the annealing temperature of the as-prepared ZnO NPAs. The measurements of the energy-dispersive spectra and photoluminescence have shown that the chemical properties of ZnO NPAs have been changed with the annealing temperature. Our results show that the pretilt angle of LCs can be tuned continuously from ∼0 to ∼90° as the contact angle of water on ZnO NPAs changes from 33 to 108°.

The particular thermally induced phase separation (TIPS) method was developed by using poly(N-vinyl carbazole) (PVK) dissolved in liquid crystal (LC) layer recently. Permanent scattering is produced via the particular TIPS due to the formation of poly-domain LCs. In this work, we applied the particular TIPS to a conventional cholesteric LC (CLC) device. A broadband CLC device with a poly-domain structure was demonstrated by using the particular TIPS of CLC and PVK. The CLC device fabricated by two indium tin oxide glass substrates coated with PVK films generated the rough PVK layers and microstructures when the device was cooled from a temperature higher than the clear point of CLCs. The produced poly-domain planar texture of CLCs still preserved the bistability. A high cooling rate and PVK concentration both increased the reflection bandwidth of the CLC devices.

Polyimide (PI) films are widely used in the liquid crystal display (LCD) industry to align liquid crystal (LC) molecules in a specific orientation with a pretilt angle θ p on the PI alignment films. It was observed that physical dispersion of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in commercial homogenous PIs decreases the surface energy of the PI alignment films and generates a controllable θ p in the range 0° θ p

The study of liquid crystal (LC) alignment is important for fundamental researches and industrial applications. The tunable pretilt angles of liquid crystal (LC) molecules aligned on the inorganic zinc oxide (ZnO) nanostructure films with controllable surface wettability are demonstrated in this work. The ZnO nanostructure films are deposited on the ITO- glass substrates by the two-steps hydrothermal process, and their wettability can be modified by annealing. Our experimental results show that the pretilt angles of LCs on ZnO nanostructure films can be successfully adjusted over a wide range from ~90° to ~0° as the surface energy on the ZnO nanostructure films changes from ~30 to ~70 mJ/m. Finally we have applied this technique to fabricate a no-bias optically-compensated bend (OCB) LCD with ZnO nanostructure films annealed at 235 °C.

We proposed a method that is, driving waveforms were added basic waveforms whose characteristics were obtained by analyzing the lateral observation indexes. We improved the performance of electrophoretic displays (EPDs) by eliminating the resistant force. EPD's response time, ghost image and bi-stability were further enhanced.

The surface energy of a conventional homeotropic polyimide (PI) alignment layer was altered via ultraviolet (UV) light irradiation, and the pretilt angle of the PI was changed along with the surface energy. The surface energy can be controlled by either UV exposure time or irradiation intensity. A switchable liquid crystal Fresnel lens (LCFL) was created by the UV-treated alignment layers to form a Fresnel zone-distribution hybrid alignment, vertically aligned and hybrid aligned LC in the odd and even zones, respectively. The LCFL was made polarization-independent by circular buffing, and it had a diffraction efficiency of ∼22% at a low driving voltage of ∼1.2 V.

The intent of this study is to determine the minimum ambient illumination requirement for legible electronic-paper display. Not only the young but also the elderly were included as research subjects. Through the method of character-search task, the results indicated that the significant performance improvement of all subjects occurred at 52 lux on the search time and at 62 lux on the subjective visual fatigue. Therefore, the minimum ambient illumination requirement for legible electronic-paper display can be synthesized at 62 lux. This minimum point of ambient illumination for the young and the elderly represents that the reflective-type display started presenting its better legibility and the subjective visual fatigue started decreasing. As electronic-paper display technology applications gradually expand, product designers need notice this fundamental limit of electronic-paper display when they continue to create possible applications in the future.

This study employs simulated electronic paper to investigate critical issues and focuses on improving legibility of display and reducing users' visual fatigue. Three critical factors--choice of surface treatment, ambient illumination, and bending curvature--are evaluated through the method of a letter-search task. The results show that subjects performed better on legibility and felt less visual fatigue with an anti-glare treatment. Choosing the better anti-glare treatment instead of the anti-reflection series can save significant cost for manufacturers. In addition, ambient lighting of 1500 lux is more appropriate for reading on electronic paper than an environment with extreme illumination (e.g., 8000 lux). The present study also found that curvature had no impact on legibility or visual fatigue. These evaluations of simulated electronic paper may provide manufacturers useful information in fulfilling ergonomic requirements for product design.

The Enriched Xenon Observatory (EXO) will search for double beta decays of 136Xe. We report the results of a systematic study of trace concentrations of radioactive impurities in a wide range of raw materials and finished parts considered for use in the construction of EXO-200, the first stage of the EXO experimental program. Analysis techniques employed, and described here, include direct gamma counting, alpha counting, neutron activation analysis, and high-sensitivity mass spectrometry., Comment: 32 pages, 6 figures. Expanded introduction, added missing table entry. Accepted for publication in Nucl. Instrum. Meth. A

This study examined the effects of anti-glare surface treatment, ambient illumination and bending curvature on legibility and visual fatigue in reading electronic papers. Results showed that surface treatment significantly affected legibility and visual fatigue, and surface treatment can improve legibility and reduce visual fatigue under intense ambient illumination. However, there is no significant difference on bending curvature. In addition, due to no significant difference between anti-glare 43% haze and anti-glare 7.5% haze, it is suggested that electronic paper manufacturers may use cheaper options for cost consideration.

The study used the simulated e-paper to investigate how the bending radius of curvature (−10 cm, plane, and 10 cm) and 12 text/background color-combinations of e-paper affect subjects’ visual performance and subjective preference under various ambient illuminance conditions (200 and 500 lx). Analysis results indicated that the bending curvature and ambient illuminance did not significantly affect subjects’ visual performance. However, subjects visual performance differed significantly for different text/background color combinations of the simulated e-paper. When the background color of the simulated e-paper was set to yellow-like condition and the luminance of the text was low (2.2 and 4.6 cd/m 2 ), subjects’ visual performance was best. Regarding the subjective preferences of subjects, the results of this research also demonstrated that the bending curvature, text/background color combinations and ambient illuminance all significantly affected the subjective preferences of subjects. Subjects exhibited the best preference under the following settings: bending curvature of the simulated e-paper set to plane; background color of the simulated e-paper set to yellow-like condition and low text luminance (2.2 or 4.6 cd/m 2 ); high ambient illuminance (500 lx).

This work proposes a refractive index sensing concept of a Tamm plasmon (TP) device by using spectroscopic ellipsometry and phase detection. A TP device is generally composed of a 1-D photonic crystal (PC) with a metallic film on top of it. We found that the sensing performance can be improved by adjusting the parameters of the incident angle of polarized light, the top layer thickness, and the central wavelength of the PC. By designing proper parameters, it was found that the change of the phase difference of p-polarized and s-polarized lights, δ∆, can reach 34° when the ambient environment is changed from air (n = 1.00028) to carbon dioxide (n = 1.00045). A sensitivity of δ∆/δn ~2 × 105 °/RIU can then be obtained for the proposed TP device.

The zinc oxide (ZnO) nanowire arrays on the indium tin oxide (ITO) glass substrates were fabricated by using the two-step hydrothermal method. A high transmittance ~92% of ZnO nanowire arrays on ITO substrate in the visible region was obtained. It was observed that the liquid crystal (LC) directors were aligned vertically to the (ZnO) nanowire arrays. The properties of ZnO nanowire arrays as vertical liquid crystal (LC) alignment layers and their applications for hybrid-aligned nematic LC modes were investigated in this work.

We investigate the sub-Doppler lines of 133 Cs 2 using the FM spectroscopy and stabilize the 1064 nm Nd:YAG laser to 133 Cs 2 lines. We measure the absolute frequencies of thirty-one transitions of 133 Cs 2 with respect to a frequency-doubled Nd:YAG/I2 reference. Our measurements have an accuracy of 120 kHz. Our results show a discrepancy of 2 MHz with respect to previous work. This indicates that the reproducibility of 133 Cs 2 -locked Nd:YAG laser is worse than 1 MHz although it shows good stability (better than 1×10−10). These measurements provide a well-distributed reference line within the tuning range of a Nd:YAG laser near 1064 nm.

Influences of anti-reflection and anti-glare surface treatments, radius of curvature and ambient illuminance on legibility and visual fatigue of reflective-type displays were studied. The results showed that legibility and visual fatigue mainly depended on the surface treatment, and better surface treatment can improve legibility and reduce visual fatigue especially in the intense ambient illumination. Surface treatments of 0.8% anti-reflection and 44% anti-glare show the same visual performance.

Bistable hybrid-aligned nematic (HAN) liquid crystal devices (LCDs) with silica nanoparticle-coated polyimide alignment films were investigated. It was observed that the existence of the internal electric field produced from the triboelectrically charged silica nanoparticles layer and impurity ions in the LC reduced the total free energy of the HAN-LCD and stabilized the cell in the homeotropic state. The stable homeotropic state can be switched back to the HAN state by changing the ion distribution through a voltage pulse with proper polarity. The capability of controlling bistability through modification of ion density in the LC layer may have some applications, such as displaying a one-time password requiring a specific stable time.

Liquid crystal (LC) devices have been popular for use in photonics products, such as displays for mobile phones, televisions and computers. As shown in Fig. 1, a typical LC device consists of a thin LC layer sandwiched between a pair of indium tin oxide (ITO) conducting glass substrates with a cell gap of few micrometers. Polyimide (PI) as a polymeric material characterized by its outstanding mechanical, thermal and electrical properties at moderate high temperature has been widely applied in the LC displays (LCDs) industry as the alignment layers to align LC molecules in a certain orientation and conformation with a specific pretilt angle, the angle between the director of the LC molecules and the PI alignment layer. The pretilt angle is very important and required for LC devices to obtain a defect-free alignment and also to improve their electro-optical performance, such as driving voltage, response time, color performance and viewing angle. However, the applications of conventional PIs in LCDs are limited by a small tuning range of pretilt angle (~ few degrees) either by controlling the rubbing depth or the number of rubbings (Paek et al., 1998).

We have developed two approaches for controlling the pretilt angles of liquid crystal molecules by using conventional polyimide (PI) alignment materials either doping homogeneous PIs with Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles or treating homeotropic PIs with ultraviolet light. These techniques are very simple and are compatible with current methods familiar in the LCD industry. The characteristics of modified PI alignment films and their applications for photonic devices are demonstrated in this paper.

A broadband cholesteric liquid crystal (CLC) device with a multi-domain structure is demonstrated by using an aggregation of polyhedral oligomeric silsesquioxane (POSS) nanoparticles in the CLC layer. The aggregation pattern of the self-assembled POSS nanoparticles depends on the concentration of POSS doped in the mixture of POSS/CLC and the cooling rate of the mixture from a temperature higher than the clear point. POSS-induced changes in the bulk and surface properties of the cholesteric cells, such as a promotion of homeotropic alignment, help to form a cholesteric structure with a broadband reflection of light; the latter can be used for improvement of bistable CLC devices. A higher POSS concentration and a higher cooling rate both improve the appearance of the black-white CLC device.

The pretilt angles of liquid crystal molecules can be controlled by using conventional polyimide (PI) alignment material doped with different concentrations of Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles, which have been observed to spontaneously induce vertical alignment. The addition of POSS in the homogenous PI changes the surface energy of the alignment layer and generates a variable pretilt angle. Experimental results demonstrate that the pretilt angle thetap is a function of the POSS concentration, and can be tuned continuously over the range of 0 degreesthetap90 degrees. The polar anchoring energy of POSS/PI alignment layer is almost constant regardless of the POSS concentration. This technique is very simple and is compatible with methods familiar in the current LCD industry.

The nanoparticles-induced vertical alignment (NIVA) of the nematic liquid crystals (LC) was proposed to make a tunable liquid-crystal flat microlens with hybrid-aligned nematic (HAN) mode, which was fabricated using micro drop technology. The minute amount of nanoparticle solution was dropped on the selective area, which was surrounded by homogeneous alignment layer. Due to vertical alignment induced by the nanoparticles, the liquid-crystal concave microlens with concentric non-uniform distribution of the refractive index was then formed in the planar LC cell. The divergence effect of this flat lens was observed and its focal length can be electrically controlled at applied voltages.

The technique, nanoparticles-induced vertical alignment (NIVA), was applied to fabricate a guest-host liquid crystal display (GH-LCD) without conventional alignment layers. The GH-LCD produced by NIVA exhibited a high reflectance of approximately 59% in the voltage-off state and a low threshold voltage of approximately 2.1 V(rms). NIVA is very suitable to be applied for fabricating a plastic LCD requiring a low temperature process, and a flexible timepiece by using NIVA was demonstrated.

A polarizer-free flexible and reflective electro-optical switch using dye-doped liquid crystal (LC) gels is demonstrated. The electro-optical performances of both scattering and absorption based dye-doped LC gels depend on curing temperatures due to domain sizes of polymer networks. Such flexible electro-optical switch is bendable and trim-able because of the vertical polymer networks and gel-like materials. The dye-doped LC gel shows good reflectance ~55%, good contrast ratio~450:1 and fast response~6.4 ms at curing temperature 10 degrees C. The bending curvature is 21 mm. The dye-doped LC gels open a new window for trim-able electronic papers, decorative displays, electrically switchable curtains, and electrically switchable sun control film for the automobiles, homes or commercial buildings.

A flexible and reflective polarizer-free display using dye-doped liquid crystal (LC) gels is demonstrated. The electro-optical performances of both scattering and absorption based dye-doped LC gels depend on curing temperatures. The dye-doped LC gel shows good reflectance ~55%, good contrast ratio~450:1 and fast response~6.5ms at curing temperature 10 °C when UV curing intensity is 2.6 mW/cm2. The EO performance depends on the curing temperature. The hysteresis is independent of sampling time duration. The bending curvature is 21 mm. The response of dye-doped LC gels is faster under bending due to the bending-induced sheared force of polymer networks. The dye-doped LC gels open a new window for trimable electronic papers, decorative displays and switchable curtains.