Browsing by Author "Hsiao, Yu-Cheng"

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A thermally tunable narrowband selector based on a chiral nematic containing a binary thermosensitive chiral dopant mixture
(2017-01-01)
Yang, Zong-Han
;
Hsiao, Yu-Cheng
;
Shen, Dong
;
Lee, Wei
;
光電系統研究所
We employed a thermosensitive chiral dopant (CD), characterized by its thermoinduced change in helical twisting power (HTP) in terms of the handedness and strength, to shift the Bragg reflection band of a CLC. A thermally tunable photonic bandgap (PBG) device was demonstrated using a one-dimensional asymmetric photonic crystal (PC) infiltrated with the CLC as a defect layer. With a temperature controller to shift the PBG of the CLC, two narrow transmission bands can be tuned in the spectrum dominated by the asymmetric PC structure. This optical device can find applications as a tunable narrowband wavelength selector or an intensity controller.
Advanced color-reflective dual-frequency cholesteric liquid crystal displays and the driving matrix
(2017-01-01)
Hsiao, Yu-Cheng
;
Yeh, En-Rong
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
We propose a novel color-reflective, dual-frequency cholesteric liquid crystal display (DFCLCD) by employing hybrid alignment treatment. The switching voltage is significantly lowered to favor the thin-film transistors used in the current display market and the response time is drastically reduced to the millisecond level while the bistability remains. Test cells with three distinct helical pitches were fabricated to demonstrate the concept of color pixels. The DFCLCD can be directly switched from the bright planar state to the light-scattering state by a low-frequency voltage pulse, and reversibly by a high-frequency pulse. A drive scheme is presented for the advanced color DFCLCD.
Chiral liquid crystals as biosensing platforms
(2016-01-01)
Lee, Mon-Juan
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Sung, Yu-Chien
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Hsiao, Yu-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
The texture observation has long been the core technique in liquid crystal (LC)-based bioassays. Its working principle stems from the dark-to-bright texture change induced by the interruption of the initially homeotropic alignment in nematic bulks or from the radial-to-bipolar configuration transition in LC droplets in the presence of biomolecules. One of the drawbacks of this observational scheme, which requires a polarizing optical microscope, is the difficulty in quantitative analysis. In this invited paper, we report on our recent development of alternative optical biosensing techniques based on cholesteric LCs (CLCs) without the use of a polarizer. The increase in structural order in a vertically anchored CLC cell in the quasi-planar state provides a means to allow detection and quantification of the concentration of biomolecules immobilized on the interface between the mesophase and the surfactant DMOAP for LC vertical alignment.
Electrically active nanoantenna array enabled by varying the molecular orientation of an interfaced liquid crystal
(2016-01-01)
Hsiao, Yu-Cheng
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Su, Chen-Wei
;
Yang, Zong-Han
;
Cheypesh, Yevheniia I.
;
Yang, Jhen-Hong
A system comprising a gold nanoantenna array covered with a high-birefringence liquid crystal (LC) material is introduced. By applying voltage across the LC bulk, we demonstrate that the refractive-index and polarization changes significantly modify the hybrid plasmonic-photonic resonances in the system. The hybrid structure enables the active control of the spectrum as well as a large shift in resonance wavelength of the metallic nanoantennas by means of an externally applied electric field. Our modeling supports the observed results, by assuming that the nanoantenna array leads to two orthogonal easy axes with a finite anchoring energy. In combination of the nanostructured surface with birefringent LC, tunability up to 90 nm is achieved in the visible wavelengths, opening the door towards nanoscale displays or nano-optical switches.
Electrically induced red, green, and blue scattering in chiral-nematic thin films
(2015-04-01)
Hsiao, Yu-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
Cholesteric liquid-crystalline materials are abundant in nature such as condensed phases of DNA, plant cell walls, and chiral biopolymers. These self-organized helical structures produce unique optical properties, giving rise to the selective Bragg reflection of colorful light. In this Letter, we focus on the focal conic state of cholesteric liquid crystals and report on stable, tunable, and reversible color switching among red, green, and blue in polymer-stabilized cholesteric films. The experimental results indicate that, with appropriate voltage pulses, the electrically induced color switching of all six routes can be realized in a single cell reflecting green light. The scattered transmissive color persists at zero voltage due to the polymer stabilization. (C) 2015 Optical Society of America
Electrically switchable organo-inorganic hybrid for a white-light laser source
(2016-06-21)
Huang, Jui-Chieh
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Hsiao, Yu-Cheng
;
Lin, Yu-Ting
;
Lee, Chia-Rong
;
Lee, Wei
We demonstrate a spectrally discrete white-light laser device based on a photonic bandgap hybrid, which is composed of a soft photonic crystal; i.e., a layer of dye-doped cholesteric liquid crystal (CLC), sandwiched between two imperfect but identical, inorganic multilayer photonic crystals. With a sole optical pump, a mono-, bi-, or tri-chromatic laser can be obtained and, through the soft photonic crystal regulated by an applied voltage, the hybrid possesses electrical tunability in laser wavelength. The three emitted spectral peaks originate from two bandedges of the CLC reflection band as well as one of the photonic defect modes in dual-mode lasing. Thanks to the optically bistable nature of CLC, such a white-light laser device can operate in quite an energy-saving fashion. This technique has potential to fulfill the present mainstream in the coherent white-light source.
Electrochemical photocatalytic degradation of dye solution with a TiO2-coated stainless steel electrode prepared by electrophoretic deposition
(2013-08-01)
Lin, Wei-Chieh
;
Chen, Chien-Hung
;
Tang, Han-Yu
;
Hsiao, Yu-Cheng
;
Pan, Jill Ruhsing
This study demonstrates a new model for the treatment of azo dye wastewater by means of a heterogeneous photocatalytic degradation coupled with the homogeneous electrochemical Fenton reaction, and is called electrochemical photocatalytic (ECPC) degradation. Titanium dioxide-coated stainless steel (P25-TiO2/SS) mesh was employed as a photo-anode, covered with a uniform layer of P-25-TiO2 using electrophoretic deposition (EPD) in a 2-propanol suspension with 10(-4) M Zn(NO3)(2), at a deposition time of 1 min. After annealing in air at 350 degrees C for 1 h, a crack-free, porous P25-TiO2 layer of ca. 2.14 mu m was obtained. Potential bias was used to enhance the photocatalytic degradation of P25-TiO2/SS towards the target pollutant, azo dye orange G, in an undivided cell under ultraviolet light irradiation. Heterogeneous photocatalytic degradation and a homogeneous electro-Fenton reaction occurred in the system simultaneously when H2O2 and Fe2+ were electrochemically generated on the graphite cathode and photo-anode, respectively, under a suitable potential bias, enhancing the de-colorization and removal of total organic carbon. (C) 2013 Elsevier B.V. All rights reserved.
Electrochemical Photocatalytic Degradation of Orange G Using TiO2 Films Prepared by Cathodic Deposition
(2014-01-01)
Wu, Tsai-Fang
;
Lin, Wei-Chieh
;
Hsiao, Yu-Cheng
;
Su, Chih-Hao
;
Hu, Chi-Chang
Herein, we report that organic dyes with poor adsorption on photocatalysts (e. g., OG (orange G) on TiO2) can only be significantly degraded via the indirect oxidation process by the electrochemical photocatalytic (EPC) or photo-electro-Fenton (PEF) mechanisms because of their enhanced electron-hole separation for generating H2O2. The TiO2/Ti photo-anodes were prepared by cathodic deposition from a bath containing TiCl3, HCl, H2O2, and NaNO3 under a two-electrode mode for EPC dye degradation. Effects of the deposition cell voltage, deposition time, and annealing temperature on the photocatalytic activity of TiO2 films, evaluated by the photocurrent density, are systematically investigated. The surface morphologies and crystalline structure of various TiO2 films were studied using scanning electron microscopic (SEM) and X-ray diffraction (XRD) analyses. The EPC characteristics of TiO2/Ti photo-anodes combined with a graphite cathode toward the OG degradation have also been evaluated. The maximal photocatalytic activity is obtained for the TiO2/Ti photo-anode deposited at a cell voltage of 2.6 V for 20 min and annealed at 700 degrees C in air for 1 hr, which exhibits a photocurrent density of 22.86 mu Amg(-1). The order of degradation modes with respect to decreasing the degradation efficiency of OG is: PEF > EPC > PC (photocatalytic) > EC (electrocatalytic) oxidation. (C) 2014 The Electrochemical Society. All rights reserved.
Electrothermo-optical effect in liquid crystals and its applications
(2017-01-01)
Hsiao, Yu-Cheng
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Lee, Wei
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影像與生醫光電研究所
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Institute of Imaging and Biomedical Photonics
Electro-optical effects in liquid crystals (LCs) have been widely utilized in many optical components and photonic devices, thanks to the anisotropic media that can be easily manipulated by an electric field to modulate the light. In general, dielectric heating in LC applications is negligible because their orientational dielectric relaxations occur at high frequencies. Here we focus on a dual-frequency LC characterized by its much lower relaxation frequency. The field-induced heat strongly affects the LC ordering and optical properties. The electrothermo-optical effect reveals an unusual behavior compared with the well-known electro-optical effect in regular LCs. Based on the electrothermo-optical effect, some applications such as optical modulators or tunable optical shutters are demonstrated.
Evaluating the sensitizing effect on the photocatalytic decoloration of dyes using anatase-TiO2
(2014-04-27)
Hsiao, Yu-Cheng
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Wu, Tsai-Fang
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Wang, Yu-Sheng
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Hu, Chi-Chang
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Huang, Chihpin
This work tries to clarify the contribution of the dye-sensitizing effect on the photocatalytic decoloration of dyes dissolved in aqueous media using an anatase TiO2 (A-TiO2) photocatalyst. The photocurrentvoltage (J-V) curves of a typical dye-sensitized solar cell (DSSC) with the A-TiO2 photoanodes adsorbed with various dyes, including methylene blue (MB), orange G (OG), rhodamine B (RhB), metanil yellow (MY), acid black 24 (AB24), and N719, are employed to demonstrate the sensitizing characteristics of dyes on A-TiO2. Unlike RhB, the MB, OG, MY, and AB24 cannot work as the photo-sensitizer on A-TiO2 from the J-V curves of DSSCs, reasonably due to the unmatched band position between dyes and A-TiO2. In the photocatalytic decoloration test of these dyes on A-TiO2 in aqueous media, dye adsorption onto A-TiO2 becomes the key factors affecting the photocatalytic decoloration rate because the generation of oxidants species (e.g., Oi(2)(-center dot), OH center dot or photo-excited holes) occurs on the A-TiO2 surface. The contribution of dye-sensitizing on the photocatalytic decoloration of RhB is negligible since the dye-sensitizing/electron-injection/dye-regeneration cycle cannot be completed in the degradation media while adsorbed RhB molecules are unstable when few photo-generated electrons have been injected into the conduction band of A-TiO2, probably leading to the decomposition of RhB. (C) 2013 Elsevier B.V. All rights reserved.
Highly sensitive color-indicating and quantitative biosensor based on cholesteric liquid crystal
(2015-12-01)
Hsiao, Yu-Cheng
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Sung, Yu-Chien
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Lee, Mon-Juan
;
Lee, Wei
;
影像與生醫光電研究所
Liquid crystal (LC)-based biosensors employ highly sensitive interfaces between the alignment layers and LCs to detect biomolecules and their interactions. Present techniques based on optical texture observation of the homeotropic-to-planar response of nematic LCs are limited by their quantitative reproducibility of results, indicating that both the accuracy and reliability of LC-based detection require further improvements. Here we show that cholesteric LC (CLC) can be used as a novel sensing element in the design of an alternative LC-based biosensing device. The chirality of the vertically anchored (VA) CLC was exploited in the detection of bovine serum albumin (BSA), a protein standard commonly used in protein quantitation. The color appearance and the corresponding transmission spectrum of the cholesteric phase changed with the concentration of BSA, by which a detection limit of 1 fg/ml was observed. The optical response of the VA CLC interface offers a simple and inexpensive platform for highly sensitive and naked-eye color-indicating detection of biomolecules, and, thus, may facilitate the development of point-of-care devices for the detection of disease-related biomarkers. (C) 2015 Optical Society of America
Hybrid anchoring for a color-reflective dual-frequency cholesteric liquid crystal device switched by low voltages
(2015-11-01)
Hsiao, Yu-Cheng
;
Timofeev, Ivan V.
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Zyryanov, Victor Ya
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Lee, Wei
;
影像與生醫光電研究所
Cholesteric liquid crystal (CLC) materials used in electro-optical (EO) devices are characterized by high operating voltage and slow response speed, which hinders their further development in display applications. Dual-frequency CLCs (DFCLCs) can solve the problem of slow bistable transition, but the operating voltage is still high, especially in color-reflective DFCLC cells. Here we report a simple approach to lowering the switching voltage as well as to shortening the response time. This technique adopts hybrid surface treatment to modulate the structural arrangement of CLC molecules. Both planar-and vertical-alignment layers are employed and coated on one and the other substrates separately to improve the electro-optical properties of DFCLCs. We show that the threshold voltage for switching can be decreased to as low as 5 V and the shortest response time is measured to be 0.8 ms, which renders CLC EO devices including displays more practical for commercial purpose. (C) 2015 Optical Society of America
Influence of methyl red as a dopant on the electrical properties and device performance of liquid crystals
(2014-12-15)
Wu, Po-Chang
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Hou, Chien-Tsung
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Hsiao, Yu-Cheng
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Lee, Wei
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影像與生醫光電研究所
The ionic effect in nematic liquid-crystal (LC) cells containing the azo dye methyl red was investigated by means of dielectric spectroscopy, measurements of voltage holding ratio (VHR) and ultraviolet/visible absorption spectroscopy. The experimental results indicated that incorporating a minute amount of the methyl red (< 0.03 wt%) in the LC host leads to the suppression of the ionic effect caused by impurity ions. Practically, the doped LC cells with a dye content of 0.02 wt% showed improved VHR and promoted lifetime by 15% and 180%, respectively, in virtually no expense of the optical transmittance. (C)2014 Optical Society of America
Lower operation voltage in dual-frequency cholesteric liquid crystals based on the thermodielectric effect
(2013-10-07)
Hsiao, Yu-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
Dual-frequency cholesteric liquid crystal (DFCLC) devices characteristically require high operation voltage, which hinders their further development in thin-film-transistor driving. Here we report on a lower-voltage switching method based on the thermodielectric effect. This technique entails applying a high-frequency voltage to occasion dielectric oscillation heating so to induce the increase in crossover frequency. The subsequent change in dielectric anisotropy of the DFCLC allows the switching, with a lower operation voltage, from the planar state to the focal conic or homeotropic state. The temperature rise incurred by the dielectric heating is described. (C)2013 Optical Society of America
Photo-manipulated photonic bandgap devices based on optically tristable chiral-tilted homeotropic nematic liquid crystal
(2016-10-31)
Huang, Kuan-Chung
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Hsiao, Yu-Cheng
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Timofeev, Ivan V.
;
Zyryanov, Victor Ya.
;
Lee, Wei
We report on the spectral properties of an optically switchable tristable chiral-tilted homeotropic nematic liquid crystal (LC) incorporated as a tunable defect layer in one-dimensional photonic crystal. By varying the polarization angle of the incident light and modulating the light intensity ratio between UV and green light, various transmission characteristics of the composite were obtained. The hybrid structure realizes photo-tunability in transmission of defect-mode peaks within the photonic bandgap in addition to optical switchability among three distinct sets of defect modes via photoinduced tristable state transitions. Because the fabrication process is easier and less critical in terms of cell parameters or sample preparation conditions and the LC layer itself possesses an extra stable state compared with the previously reported bistable counterpart operating on the basis of biased-voltage dual-frequency switching, it has much superior potential for photonic applications such as a low-power-consumption multichannel filter and an optically controllable intensity modulator. (C) 2016 Optical Society of America
Photo-switchable chiral liquid crystal with optical tristability enabled by a photoresponsive azo-chiral dopant
(2017-02-06)
Hsiao, Yu-Cheng
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Huang, Kuan-Chung
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Lee, Wei
;
光電系統研究所
;
影像與生醫光電研究所
A light-driven tristable chiral-tilted homeotropic nematic (TCHN) cell is demonstrated. The liquid-crystal cell is photo-switchable among the three stable states: the tilted-homeotropic, fingerprint, and the tilted-twist states. The inclusion of a photosensitive chiral bis(azobenzene) compound into a typical nematic liquid crystal makes the resulting material possible to switch from one to another stable state directly and reversibly owing to the photoinduced trans-cis isomerization of the azo-chiral dopant and, hence, the configurational change of the liquid crystal via the guest-host effect. By further introducing dichroic dyes into the TCHN system, we devised a polarizer-free display and light modulators. The novel TCHN composite material opens up new possible applications in lightdriven optical elements and devices. (C) 2017 Optical Society of America.
Polymer stabilization of electrohydrodynamic instability in non-iridescent cholesteric thin films
(2015-08-24)
Hsiao, Yu-Cheng
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Lee, Wei
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影像與生醫光電研究所
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Institute of Imaging and Biomedical Photonics
A non-iridescent cholesterol liquid crystal (CLC) thin film is demonstrated by using the polymer-stabilized electrohydrodymanic (PSEHD) method. The photopolymerized cell made from a CLC/monomer mixture exhibits an optically stable gridlike pattern. The helical axis of thus-formed CLC is aligned with the hydrodynamic flow induced by a space charge motion, and the arrayed CLC grid configuration renders a wide viewing angle thanks to the limited color shift at various lines of sight. The formation of the PSEHD structure was verified with polarized optical microscopy, ascertaining that the electrohydrodymanic pattern can be photo-cured or stabilized. The PSEHD CLC is simple to fabricate and potentially suitable for applications in wide-viewing-angle or non-iridescent devices. (C) 2015 Optical Society of America
Red, Green, and Blue Reflections Enabled in an Electrically Tunable Helical Superstructure
(2018-03-05)
Hsiao, Yu-Cheng
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Yang, Zong-Han
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Shen, Dong
;
Lee, Wei
;
光電學院
Materials with tunable optical properties in the visible spectrum are intriguingly important in science and technology. Such desired tunability can be conveniently accomplished by controlling optical materials with electric field. Now an organic film of self-organized helical superstructure producing electrically tunable reflection of visible light is introduced in this work. The composite is a dual-frequency thermosensitive cholesteric (DFTC) material consisting of a liquid crystal host doped with a binary chiral-dopant mixture including a thermosensitive chiral switch. The red, green, and blue reflections in the DFTC film can be obtained by varying the frequencies of a 45 V-rms applied voltage to induce dielectric heating. The resulting variation in temperature and, in turn, in helical pitch length, enables various wavelengths of reflection to render full-color display in a single film without the need of film stacking. As far as it is known, this is the first work to demonstrate broad electrical tuning of cholesteric reflection in red, green, and blue.
Solution-processed conductive interconnecting layer for highly-efficient and long-term stable monolithic perovskite tandem solar cells
(2019-01-01)
Chang, Chih-Yu
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Tsai, Bo-Chou
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Hsiao, Yu-Cheng
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Lin, Min-Zhen
;
Meng, Hsin-Fei
Although stacking of multiple subcells with complementary bandgaps via an interconnecting layer (ICL) to form multi-junction tandem devices appears to be one of the most promising strategies to increase the power conversion efficiency (PCE) of organic-inorganic hybrid perovskite solar cells (PeSCs), the realization of high efficiency and long-term stable tandem devices based on solution-processed ICL remains highly challenging. In this study, a promising solution-processed ICL consisting of cross-linked p-doped hole transport layer (HTL) and n-doped fullerene electron transport layer for efficient and stable monolithic perovskite tandem solar cells is demonstrated. For the first time, high-performance photo-cross-linkable p-doped HTL material based on poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) is developed by incorporating 1,2-bis[4-(azido-methyl)phenyl]-1,2-diphenylethene (TPE-MN3) and molybdenum tris-[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfdCOCF(3))(3)) as the cross-linking agent and p-type dopant, respectively. This HTL exerts multiple positive impact on the device characteristics, including good solvent resistance, appropriate energy level matching, good electrical conductivity, and high compatibility with different perovskite systems. With these desirable characteristics, the series-connected tandem solar cells afford a PCE up to 18.69%, which represents the highest efficiency reported to date for monolithic all-perovskite tandem cells. Additionally, owing to high conductivity of the interfacial layers, a promising PCE up to 16.20% is attained even when the active area is extended to 1.2 cm(2). More encouragingly, the encapsulated tandem cells exhibit remarkable long-term stability, maintaining approximate to 91% of its initial PCE after 9300 h (approximate to 387 days) of air exposure. This work represents an important step forward toward the realization of large-area solution-processed perovskite tandem solar cells with high efficiency and long-term stability.
Temperature-dependent electrical and dielectric properties of nematic liquid crystals doped with ferroelectric particles
(2016-09)
Hsiao, Yu-Cheng
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Huang, Sheng-Miao
;
Yeh, En-Rong
;
Lee, Wei
;
影像與生醫光電研究所
We report on the temperature dependence of dielectric properties of nematic liquid crystals impregnated with BaTiO3 (BTO) ferroelectric nanoparticles. The behavior of ion transport at low frequencies is discussed by means of dielectric spectroscopy, which allows the ionic concentration and the relaxation time of electrode polarization to be deduced. The experimental results imply that the ferroelectric nanopartides can not only increase the traveling time of ions between two electrodes but also suppress the buildup of the electric double layers. Verified by the voltage holding ratio of cells containing various contents of BTO nanoparticles, it is obvious that doping BTO into liquid crystals is a low-cost and easy way to improve the device performance. (C) 2015 Elsevier B.V. All rights reserved.