Browsing by Author "Yang, Chia-Ming"

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Bidirectional All-Optical Synapses Based on a 2D Bi2O2Se/Graphene Hybrid Structure for Multifunctional Optoelectronics
(1970-01-01)
Yang, Chia-Ming
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Chen, Tsung-Cheng
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Verma, Dharmendra
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Li, Lain-Jong
;
Liu, Bo
Neuromorphic computing has been extensively studied to mimic the brain functions of perception, learning, and memory because it may overcome the von Neumann bottleneck. Here, with the light-induced bidirectional photoresponse of the proposed Bi2O2Se/graphene hybrid structure, its potential use in next-generation neuromorphic hardware is examined with three distinct optoelectronic applications. First, a photodetector based on a Bi2O2Se/graphene hybrid structure presents positive and negative photoresponsibility of 88 and -110 A W-1 achieved by the excitation of visible wavelength and ultraviolet wavelength light at intensities of 1.2 and 0.3 mW cm(-2), respectively. Second, this unique photoresponse contributes to the realization of all optically stimulated long-term potentiation or long-term depression to mimic synaptic short-term plasticity and long-term plasticity, which are attributed to the combined effect of photoconductivity, bolometric, and photoinduced desorption. Third, the devices are applied to perform digital logic functions, such as "AND" and "OR," using full light modulation. The proposed Bi2O2Se/graphene-based optoelectronic device represents an innovative and efficient building block for the development of future multifunctional artificial neuromorphic systems.
BIOSENSOR
(2010-11-18)
Meng, Hsin- Fei
;
Hong, Sheng-Fu
;
Chao, Yu-Chiang
;
Horng, Yun-Ru
;
Tsai, Pei-Yu
A biosensor applicable to an environment suitable for biosensing is provided, which is a solid-state element for performing detections in an aqueous environment. The biosensor at least includes a biosensing layer, a light-emitting diode and a photodiode. The biosensing layer causes changes in the light-emitting property thereof after absorbing, adsorbing and/or bonding with a biological substance released during in vivo signal transduction in an organism, and the rays of light generated by excitation of the light-emitting diode causes the biosensing layer to emit fluorescence. After the fluorescence is absorbed by the photodiode, it can be converted into an interpretable photocurrent signal. Afterwards, the meaning of the in vivo signal transduction can be understood by interpretation of the photocurrent signal.
Current injection and transport in polyfluorene
(2007-08-27)
Yang, Chieh-Kai
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Yang, Chia-Ming
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Liao, Hua-Hsien
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Horng, Sheng-Fu
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Meng, Hsin-Fei
A comprehensive numerical model is established for the electrical processes in a sandwich organic semiconductor device with high carrier injection barrier. The charge injection at the anode interface with 0.8 eV energy barrier is dominated by the hopping among the gap states of the semiconductor caused by disorders. The Ohmic behavior at low voltage is demonstrated to be not due to the background doping but the filaments formed by conductive clusters. In bipolar devices with low work function cathode it is shown that near the anode the electron traps significantly enhance hole injection through Fowler-Nordheim tunneling, resulting in rapid increases of the hole carrier and current in comparison with the hole-only devices. (c) 2007 American Institute of Physics.
Deep blue light-emitting diode based on high molecular weight poly(9,9-dioctylfluorene) with high efficiency and color stability
(2008-06-01)
Tseng, Shin-Rong
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Li, Shiuan-Yi
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Meng, Hsin-Fei
;
Yu, Yi-Hsiang
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Yang, Chia-Ming
A highly efficient deep blue polymer light-emitting diode based on poly(9,9-dioctylfluorene) is demonstrated. The performance is found to increase significantly with the molecular weight. Two different molecular weights are compared, one is 71,000 and the other is 365,000. The electroluminescent efficiency and color stability are improved by slightly doping hole traps into the emission layer and bilayer structure. The maximum efficiency is 3.8 cd/A with the corresponding external quantum efficiency of 3.7% at deep blue with Commission Internationale de L'Eclairage (CIE) coordinate at (0.15, 0.09). Stable blue emission is maintained up to 6600 cd/m(2) without growth of green shoulder in emission spectrum. (C) 2007 Elsevier B.V. All rights reserved.
Dynamics and reversibility of oxygen doping and de-doping for conjugated polymer
(2008-05-15)
Liao, Hua-Hsien
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Yang, Chia-Ming
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Liu, Chien-Cheng
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Horng, Sheng-Fu
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Meng, Hsin-Fei
We perform comprehensive long-time monitoring of the p-doping and de-doping of poly(3-hexyl thiophene) under changing external conditions of oxygen, light, and temperature. They are shown to be controlled by the complex adsorption and desorption process with time scales ranging from seconds to weeks. The oxygen doping at atmospheric pressure takes several hours in the dark. The doping is dramatically accelerated to be within seconds with light of wavelength of 500-700 nm. Even at low oxygen pressure of 10(-4) torr doping occurs within minutes with light. The de-doping by oxygen desorption takes as long as weeks at room temperature and vacuum of 10(-4) torr, but when the temperature is raised to near the polymer glass temperature of 370 K, the de-doping is accelerated to minutes as the enhanced chain motion releases the trapped oxygen. Even though visible and near infrared light causes very efficient doping within seconds or minutes depending on vacuum level, such light-induced doping is not a chemical reaction and is fully reversible by thermal annealing at the end without sacrificing the mobility. For the polymer field-effect transistors, only the carrier density is changed while the mobility remains roughly a constant for all the conditions. (c) 2008 American Institute of Physics.
Electron mobility and electroluminescence efficiency of blue conjugated polymers
(2008-01-01)
Yang, Chia-Ming
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Liao, Hua-Hsien
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Horng, Sheng-Fu
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Meng, Hsin-Fei
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Tseng, Shin-Rong
We study systematically the underlying property which determines the electroluminescence efficiency of blue polymers based on polyfluorene and its copolymers. The photoluminescence efficiency is high (40-50%) for all the selected polymers, but the electroluminescence efficiency varies in a wide range. The hole mobility is measured by transient electroluminescence. The electron mobility is obtained from the current in electron-only device using space-charge-limited current equation. All polymers share roughly the same results, whereas electron mobility is the critical factor for electroluminescence. In general, low efficiency results from the low electron mobility. (C) 2007 Elsevier B.V. All rights reserved.
Enhanced photovoltaic response of organic solar cell by singlet-to-triplet exciton conversion
(2007-03-26)
Yang, Chia-Ming
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Wu, Chi-Hui
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Liao, Hua-Hsin
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Lai, Kuei-Yuan
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Cheng, Hong-Ping
Ir complex was doped to conjugated polymers, and the photoinduced absorption of triplet excitons in host materials was examined. A greatly enhanced intersystem crossing rate was observed, despite the decrease in triplet exciton lifetime. The authors find that the steady-state triplet exciton population in host polymer would increase by an order of magnitude. Conjugated polymer/colloidal CdSe nanocrystal hybrid solar cells were fabricated and the effect of Ir-complex doping on photovoltaic response was studied. It was found that due to the enhanced singlet-to-triplet conversion, greatly enhanced photovoltaic response of these hybrid organic solar cells was observed. The results suggest that triplet solar cells may be achieved by doping conventional photovoltaic materials with transition-metal complexes. (c) 2007 American Institute of Physics.
High-efficiency blue multilayer polymer light-emitting diode based on poly(9,9-dioctylfluorene)
(2007-04-15)
Tseng, Shin-Rong
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Li, Shiuan-Yi
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Meng, Hsin-Fei
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Yu, Yi-Hsiang
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Yang, Chia-Ming
A highly efficient blue polymer light-emitting diode based exclusively on commercial poly(9,9-dioctylfluorene) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4(')-(N-(4-s-butylphenyl)) diphenylamine)] is demonstrated. High electroluminescent efficiency is achieved by enhancing electron currents and making devices in multilayered structures. CsF/Al is used as the efficient electron injection cathode, and the fabrication process is in the glove box to enhance electron mobility by reducing oxygen adsorption. The multilayer structure is prepared by the liquid buffer layer technique. The maximum efficiency is 2.5 cd/A at deep blue with the corresponding external quantum efficiency of 2%.
Interface effect of oxygen doping in polythiophene
(2009-06-01)
Liu, Chien-Cheng
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Yang, Chia-Ming
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Liu, Wen-Hsing
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Liao, Hua-Hsien
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Horng, Sheng-Fu
Long-time evolution of the electrical characteristics for two-terminal and transistor of poly(3-hexylthiophene) film with various gate dielectric interfaces are measured. The oxygen doping is found to depend sensitively on the amount of hydroxyl groups of the interface and irreversible after long time in vacuum except for quartz. For a given interface, dip-coated film always has a higher doping level and slower de-doping than spin-coated films because of higher porosity. With careful control of the oxygen level transistor with mobility of 0.12 cm(2)/V s and on-off ratio of 29,000 are obtained for dip-coated film on glass substrate. (C) 2009 Elsevier B.V. All rights reserved.
Large enhancement of intersystem crossing in polyfluorenes by iridium-complex doping
(2007-01-01)
Liao, Hua-Hsien
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Yang, Chia-Ming
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Wu, Chi-Hui
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Horng, Sheng-Fu
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Lee, Wei-Shan
Photoinduced absorption is used to study the intersystem crossing (ISC) rate of two polyfluorenes doped with iridium (III) tris[2-(4-totyl)pyridinato-N,C2]. It is found that the triplet exciton lifetime of polyfluorene is reduced by the dopants. But instead of decreasing, the population density of polyfluorene triplet exciton increases by almost one order of magnitude. The finding shows that the ISC rate can increase over 100 times due to the spin-orbital interaction with the Ir ion even though it is covered by the ligands. Specifically, the ISC lifetime changes from the intrinsic value of 62 ns to as short as 0.28 ns upon 10% doping.
Lnfrared photocurrent response of charge-transfer exciton in polymer bulk heterojunction
(2008-02-25)
Yang, Chia-Ming
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Tsai, Pei-Yu
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Horng, Sheng-Fu
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Lee, Kuan-Chen
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Tzeng, Shin-Rong
We study the charge-transfer exciton absorption and photocurrent response in solution-processed bulk heterojunction based on poly(3-hexylthiophene) donor and (6,6)-phenyl-C(61)-butyric acid methyl ester acceptor in the near-infrared wavelength region. While the exciton absorption exists only for wavelength below 650 nm, direct generation of charge-transfer exciton formed between the donor and acceptor extends the absorption wavelength to 950 nm. For films with micrometer thickness, the photon-to-electron conversion efficiency is about 60% at 750 nm wavelength under reverse voltage bias and the photocurrent to dark current ratio is about 8.6 at 900 nm and remains 3.6 even at 1000 nm. Photodetector with high sensitivity covering exclusively the 650-1000 nm near infrared region can therefore be made without a low bandgap material. The charge-transfer exciton absorption coefficient and photocurrent sensitivity depend on the annealing condition which controls the donor-acceptor morphology. (c) 2008 American Institute of Physics.
Organic semiconductor infrared distance sensing apparatus and organic infrared emitting apparatus thereof
(2010-06-03)
Meng, Hsin-Fei
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Horng, Sheng-Fu
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Tseng, Hsin-Rong
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Yang, Chia-Ming
;
Chen, En-Chen
An organic semiconductor infrared distance sensing apparatus and an organic infrared emitting apparatus thereof are disclosed. The organic semiconductor infrared distance sensing apparatus comprises an organic infrared emitting apparatus and an organic infrared receiving apparatus. The organic infrared emitting apparatus has a positive electrode layer and a negative electrode layer to form an electric field, and organic light emitting molecules are sandwiched between the two layers and correspond to the positive electrode layer and the negative electrode layer. Under a positive bias, a plurality of electrons and holes are respectively injected from electrodes and recombine with each other to emit photons. An infrared organic conversion layer absorbs and transfers the energy to infrared emitting molecules to emit infrared light. The organic infrared receiving apparatus receives the infrared light reflected by an obstacle to generate photocurrent which varies with distance, thereby sensing the distance between the obstacle and the apparatus.
Organic-semiconductor-based infrared receiving device
(2009-11-26)
Meng, Hsin-Fei
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Horng, Sheng-Fu
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Yang, Chia-Ming
An organic-semiconductor-based infrared receiving device comprises an electrode layer having a positive layer and a negative layer to form an electric field, and a transport layer located between the positive and negative layers and having a first and a second predetermined material combined in a predetermined ratio. The energy of infrared light from a light source is received at an interface between the first and second materials. The thickness of the transport layer can be increased to enhance the light absorbance in the infrared light range to form electron-hole pairs, which are then parted to form a plurality of electrons and holes driven by the electric field to move to the negative layer and the positive layer, respectively, so that a predetermined photocurrent is generated.
Polymer infrared proximity sensor
(2008-08-11)
Chen, En-Chen
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Tseng, Shin-Rong
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Ju, Jia-Hong
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Yang, Chia-Ming
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Meng, Hsin-Fei
A proximity sensor that combines a polymer light-emitting diode and a polymer photodiode is presented. The operation wavelength is in the near infrared from 700 to 850 nm. The infrared emission is obtained by adding a color conversion film of polyvinylpyrrolidone polymer matrix blended with infrared dye 1,1-diethyl-2,2-dicarbocyanine iodide to a red polymer light-emitting diode. The photodetector relies on the direct charge-transfer exciton generation in a donor-acceptor polymer blend of poly(3-hexylthiophene) and (6,6)-phenyl-C(61)-butyric acid methyl ester. The detection distance is up to 19 cm for objects with various colors and roughness under ambient indoor lighting. (C) 2008 American Institute of Physics.
Reducing Fine Particulate to Improve Health: A Health Impact Assessment for Taiwan
(2013-01-01)
Yang, Chia-Ming
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Kao, Kai
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
Recently various countries have adopted the new standards for PM2.5 (particulate matter <2.5 mu m in aerodynamic diameter), but Taiwan still maintains an old set of air quality guidelines for particulate matter; therefore, the authors quantified the public health impact of long-term exposure to PM2.5 in terms of attributable number of deaths and the potential gain in life expectancy by reducing PM2.5 annual levels to 25, 20, 15, and 10 mu g/m3. When the guideline for PM2.5 long-term exposure was set at 25 mu g/m3, 3.3% of all-cause mortality or 4,500 deaths in 2009 could be prevented. The potential gain in life expectancy at age 30 of this reduction would increase by a range between 1 and 7 months in Taiwan. This study shows that guidelines for PM2.5, especially for long-term exposure, should be adopted in Taiwan as soon as possible to protect public health.