Browsing by Issue Date, starting with "2018-08-29"

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Efficient Defect Healing of Transition Metal Dichalcogenides by Metallophthalocyanine
(2018-08-29)
Ahn, Hyeyoung
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Huang, Yu-Chiao
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Lin, Chang-Wei
;
Chiu, Yi-Lun
;
Lin, Erh-Chen
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted great attention as alternatives to graphene with semiconducting band gaps. Mono- or few-layer TMDCs can be prepared by various methods, but regardless of the fabrication methods [such as mechanical exfoliation and chemical vapor deposition (CVD)], TMDCs contain many structural defects, which significantly affect their physical properties and limit their performance in applications. Metallophthalocyanines (MPcs) are organic semiconductors, and as dopants, they are capable of modulating the optical and electrical properties of other semiconducting materials. Here, we report that besides the ability to modulate the optoelectronic properties of 2D TMDCs, MPc molecules can be used to heal defects and improve the physicochemical properties of TMDCs. Doping of planar MPc molecules to TMDCs is achieved by a simple solution dip-coating method and results in a significant improvement in the optical properties and thermal responses of CVD-grown TMDCs, even comparable to those of mechanically exfoliated counterparts. Study of carrier dynamics shows that the adsorption of MPc on the TMDC surface leads to the complete suppression of the mid-gap defect-induced absorption in TMDCs. Furthermore, MPc molecules with a large lateral size are found to effectively reduce the point defects in mechanically exfoliated TMDCs introduced during the preparation process. Our results not only clarify the optoelectronic modulation mechanism of chemical doping but also offer a simple method to control the nanosized defects in 2D TMDCs.
Wound Healing in Streptozotocin-Induced Diabetic Rats Using Atmospheric-Pressure Argon Plasma Jet (vol 8, 12214, 2018)
(2018-08-29)
Cheng, Kuang-Yao
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Lin, Zhi-Hua
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Cheng, Yu-Pin
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Chiu, Hsien-Yi
;
Yeh, Nai-Lun
Electronic Structure Evolution in Tricomponent Metal Phosphides with Reduced Activation Energy for Efficient Electrocatalytic Oxygen Evolution
(2018-08-29)
Wang, Miao
;
Dong, Chung-Li
;
Huang, Yu-Cheng
;
Li, Yanrui
;
Shen, Shaohua
Non-noble metal catalysts for high-active electrocatalytic oxygen evolution reaction (OER) are essential in large-scale application for water splitting. Herein, tricomponent metal phosphides with hollow structures are synthesized from cobalt-contained metal organic frameworks (MOFs), i.e., ZIF-67, by tailoring the feeding ratios of Ni and Fe, followed by a high-temperature reduction and a subsequent phosphidation process. Excellent OER activity and long-time stability are achieved in 1 M NaOH aqueous solution, with an overpotential of 329 mV at 10 mA cm(-2) and Tafel slope of 48.2 mV dec(-1), even superior to the noble metal-based catalyst. It is evidenced that the formed (oxyhydr)oxide/phosphate species by in situ electrochemical surface oxidation are responsible for active OER. Accordingly, the simultaneous introduction of external Ni and Fe elements significantly influences the electronic structures of the parent metal phosphides, leading to the in situ electrochemical formation of surface active layer with decreased OER activation energy for greatly improved water oxidation performance. This electronic structure tuning strategy by introducing multicomponent metals demonstrates a versatile method to use MOFs as precursors for synthesizing high-efficient water splitting electrocatalysts.
Formation of Cu/MnOx composite film by concurrent electroplating and electrophoresis in an organic solvent
(2018-08-30)
Chiang, Wei-Shen
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Huang, Jun-Qian
;
Tso, Kuang-Chih
;
Hung, Pei-Sung
;
Chen, Po-Chun
A composite Cu/MnOx thin film was fabricated by conducting electroplating of Cu and electrophoresis of MnOx colloids simultaneously in an organic electrolyte. The organic electrolyte was prepared by dissolving copper (II) acetylacetonate and manganese (II) acetylacetonate in ethylene glycol, with addition of 10 vol% acetic acid to improve ionic conductivity. Since both Cu ions and MnOx colloids carry positive charges, the formation of a composite film was achieved by a pulse current mode in which a low current pulse was used for Cu2+ reduction, followed by a high current pulse for the electrophoresis of the MnOx colloids. The Cu/MnOx composite film was dense and its X-ray diffraction pattern revealed a mixture of Cu, Mn2O3, and Mn3O4. Both X-ray photoelectron spectroscopy and X-ray absorption spectroscopy show consistent results confirming the metallic nature of Cu and oxidized state of Mn.
Effect of interfacial layer on device performance of metal oxide thin-film transistor with a multilayer high-k gate stack
(2018-08-30)
Ruan, Dun-Bao
;
Liu, Po-Tsun
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Chiu, Yu-Chuan
;
Kuo, Po-Yi
;
Yu, Min-Chin
The amorphous indium gallium zinc oxide thin-film transistors (TFTs) with a multilayer high-k gate stack are investigated in this research. In order to achieve a high quality gate insulator for plastic flexible display application, the multilayer high-k gate stacks (SiO2/TiO2/HfO2) are deposited by a low-temperature physical vapor deposition (PVD) process. On the other hands, an interfacial layer between the high-k stack and metal oxide channel is important for the device performance. The effects of interfacial layer material (SiO2 or Ga2O3) are also discussed in this report. The devices with SiO2 interfacial layer show a high on/off current ratio of similar to 7x10(7) for its low gate leakage current, a small sub-threshold swing of 0.093 V/decade and a high field-effect mobility of similar to 37.8 cm(2)/Vs for its good interface condition and low interface defeats. This research shows that the interface engineering of multilayer PVD gate stacks is necessary for oxide TFT fabrication.
Spin transport in half-metallic ferromagnet-superconductor junctions
(2018-08-30)
Wu, Chien-Te
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Halterman, Klaus
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電子物理學系
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Department of Electrophysics
We investigate the charge and spin transport in half-metallic ferromagnet (F) and superconductor (S) nanojunctions. We utilize a self-consistent microscopic method that can accommodate the broad range of energy scales present, and ensures that proximity effects that account for the interactions at the interfaces are accurately determined. Two experimentally relevant half-metallic junction types are considered: The first is an F1F2S structure, where a half-metallic ferromagnet F-1 adjoins a weaker conventional ferromagnet F-2. The current is injected through the F-1 layer by means of an applied bias voltage. The second configuration involves an SF1F2F3S Josephson junction whereby a phase difference Delta phi between the two superconducting electrodes generates the supercurrent flow. In this case, the central half-metallic F-2 layer is surrounded by two weak ferromagnets F-1 and F-3. By placing a ferromagnet with a weak exchange field adjacent to an S layer, we are able to optimize the conversion process in which opposite-spin triplet pairs are converted into equal-spin triplet pairs that propagate deep into the half-metallic regions in both junction types. For the tunnel junctions, we study the bias-induced local magnetization, spin currents, and spin-transfer torques for various orientations of the relative magnetization angle theta in the F layers. We find that the bias-induced equal-spin triplet pairs are maximized in the half metal for theta approximate to 90 degrees and, as part of the conversion process, are anticorrelated with the opposite-spin pairs. We show that the charge current density is maximized, corresponding to the occurrence of a large amplitude of equal-spin triplet pairs, when the exchange interaction of the weak ferromagnet is about 0.1E(F). For the half-metallic Josephson junctions we often find that the spin current flowing in the half metal is equivalent to the charge supercurrent flowing throughout the junction. This is indicative that the current consists of spin-polarized triplet pairs. The conversion process of the opposite-spin triplet pairs to the equal-spin triplet pairs in the weaker magnets is clearly demonstrated. This is exemplified by the fact that the supercurrent in the half metal was found to be relatively insensitive to its thickness.
Resistive switching behavior of Ga doped ZnO-nanorods film conductive bridge random access memory
(2018-08-30)
Singh, Pragya
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Simanjuntak, Firman Mangasa
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Kumar, Amit
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Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
The influence of Ga dopant on resistive switching behavior of ZnO-nanorods film conducting bridge random access memory was investigated. Using a hydrothermal process, we grew vertically well-aligned and uniform Ga doped ZnO (GZO)-NRs films on transparent glass substrates to fabricate Cu/TiW/GZO-NRs/Indium Tin Oxide/Glass devices. The GZO-NRs film provides a diffusion path for the Cu ions to form a conducting bridge; thus, reducing the formation of a branched filament. The Ga dopant induces a significant improvement in switching distribution of high resistance states (HRS) and low resistance states (LRS). The 1.5 mol% Ga doped device exhibits good retention up to 10(4) s and high HRS/LRS ratio of 30 times. Therefore, our proposed device structure may be a good candidate for future conductive-bridge resistive random access memory application.
Investigation of low operation voltage InZnSnO thin-film transistors with different high-k gate dielectric by physical vapor deposition
(2018-08-30)
Ruan, Dun-Bao
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Liu, Po-Tsun
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Chiu, Yu-Chuan
;
Kan, Kai-Zhi
;
Yu, Min-Chin
Amorphous Indium-Zinc-Tin-Oxide thin-film transistors (a-IZTO TFT) using different types of high-k materials (like HfO2, ZrO2 and Al2O3) as gate dielectric are studied in this work. All gate dielectric films were deposited by physical vapor deposition (PVD) process for better composition control. Compared with the traditional SiO2 gate insulator, a high-k gate dielectric can reduce the operation voltage of TFT device significantly. The TFT device with ZrO2 gate insulator exhibits a small subthreshold swing of 0.126 V/decade, high field-effect mobility of similar to 40.7 cm(2)/Vs, low threshold voltage of -0.05 V, and large On/Off current ratio of similar to 1.01 x 10(7). The mechanisms for electrical improvements are also investigated. These results demonstrate the potential application of PVD-deposited ZrO2 thin film as a promising gate dielectric in oxide-based thin-film transistors.
The impact of TiW barrier layer thickness dependent transition from electro-chemical metallization memory to valence change memory in ZrO2-based resistive switching random access memory devices
(2018-08-30)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Aluguri, Rakesh
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Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
The effect of TiW metal barrier layer thickness on voltage-current characteristics of the Cu/TiW/ZrO2/TiN conductive bridge random access memory device was systematically investigated. The change of reset behavior from abrupt decrease to gradual decrease with increasing TiW thickness was observed. Electronic conduction during the forming process was also analyzed to obtain detailed information about the effect of TiW layer thickness on the nature of the conduction phenomenon. The temperature coefficient of resistance of the conductive filament confirms that an electro-chemical metallization (ECM) based conduction was observed in the devices made with a thinner TiW layer. On the other hand, valence change memory (VCM) based conduction was observed with a thick TiW layer. A conduction mechanism is proposed to explain the ECM to VCM conduction transformation phenomenon.
Effect of surface passivation by a low pressure and temperature environment-grown thermal oxide layer for multi-crystalline silicon solar cells
(2018-08-30)
Liao, Shun Sing
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Chuang, Chuan Lung
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Lin, Yueh Chin
;
Dee, Chang Fu
;
Majlis, Burhanuddin Yeop
In this study, we show that the efficiency and carrier life time of multi-crystalline silicon solar cells were significantly improved by using a low pressure (20,000 Pa) and temperature (650 degrees C similar to 750 degrees C) environment grown thermal oxide (TO) as the surface passivation layer. In this experiment, during the first stage, the oxidation process was done at 650 degrees C and a lower pressure of 20,000 Pa for 2 mins under the flow a gas mixture of N-2/O-2 in ratio of 2:1. In the second stage, a temperature of 750 degrees C was used at the same pressure for the post-growth annealing process under a pure N-2 ambient for 25 mins. Consequently, conversion efficiency was significantly increased by 0.55% with the surface passivation layer grown by low pressure and temperature TO process. The sheet resistance, carrier lifetime, internal quantum efficiency (IQE), increased by 6.32 Omega/sq., 22.18 mu s, 4.33%, respectively, and the average reflection was reduced of 0.62%. Thus, the low pressure and temperature thermal oxidation process was an efficient way to increase the efficiency of the multi-crystalline silicon solar cells.
Differential Expression of Phosphorylated ERK and c-Fos of Limbic Cortices Activities in Response to Tactile Allodynia of Neuropathic Rats
(2018-08-31)
Lin, Hsiao-Chun
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Yen, Chen-Tung
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交大名義發表
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生醫電子轉譯研究中心
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National Chiao Tung University
Neuropathic pain is due to lesion or dysfunction of the somatosensory system. Treating patients with neuropathic pain is difficult because the underlying mechanisms are understood limitedly, especially at the supraspinal level. In this study, we used two kinds of molecular markers to investigate the neuronal activity changes in the anterior cingulate cortex (ACC), insular cortex (IC), and medial prefrontal cortex (mPFC) of the neuropathic rats under tactile allodynia. We used spared nerve injury (SNI) of the sciatic nerve as the neuropathic pain model. Two weeks after SNI surgery, we applied repetitive allodynic stimulation to the conscious rats. After stimulation, the rats were sacrificed, and the immunohistochemistry of phosphorylated extracellular signal-regulated kinase (pERK) and c-Fos was performed. Quantification of immunoreactive cells was carried out by stereological method. For pERK study, the expression of pERK was significantly increased in the mPFC and IC of the SNI rats. For c-Fos study, only mPFC had elevated expression of c-Fos in the SNI rats. The analgesic, gabapentin, reversed the mechanical hyper-sensitivity and the augmented expression of limbic pERK and c-Fos in the SNI rats. Immunofluorescent staining revealed the expression of pERK or c-Fos was restricted to neurons, not glia cells. Our results demonstrated that tactile allodynia represented differential expression of pERK and c-Fos in the limbic cortices of the neuropathic rats.
Pseudopolymorph Control of L-Phenylalanine Achieved by Laser Trapping
(2018-09-01)
Wu, Chi-Shiun
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Hsieh, Pei-Yun
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Yuyama, Ken-ichi
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Masuhara, Hiroshi
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Sugiyama, Teruki
We demonstrate pseudopolymorph control of L-phenylalanine (L-Phe) with laser trapping method by tuning laser power, polarization, and initial solution concentration. When a continuous-wave near-infrared laser beam of 1064 nm was focused at an air/solution interface of L-Phe D2O solutions with different saturation, L-Phe crystallization was always observed within 30 min-irradiation, even from unsaturated solution. Either whisker- or plate-like crystals were generated depending on given conditions, and identified by Raman spectroscopy to be two L-Phe pseudopolymorphs of monohydrate and anhydrous forms, respectively. The absolute control of L-Phe pseudopolymorphism was achieved by changing the initial solution concentration. In unsaturated solution, laser trapping always produced only one anhydrous crystal at the focus, which can never be produced on spontaneous nucleation at ordinary temperatures and pressures, while in supersaturated solution, a number of monohydrate crystals were densely distributed in an area ranging from 500 mu m to 1 mm away from the focus. Moreover, in saturated solution, laser power and polarization contributed to the pseudopolymorphism. As laser power was increased, linearly and circularly polarized laser irradiation increased the formation probability of the anhydrous and monohydrate crystals, respectively. The dynamics and mechanism of laser trapping-induced pseudopolymorphism of L-Phe are discussed in view of the formation of a highly concentrated domain consisting of the liquid-like clusters and the stability of the clusters in the domain under electromagnetic field of trapping laser.
Orthogonally Polarized Self-Mode-Locked Lasers With Repetition Rate Multiplication up to Hundreds of Gigahertz: Observation of Temporal Carpets
(2018-09-01)
Chen, Yung-Fu
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Chang, Ming-Ting
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Huang, Tzu-Lin
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Tung, Jung-Chen
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Huang, Kai-Feng
Mode-locked laser sources with high repetition rates in the range of 10-1000 GHz are of considerable interest in modern communications, optical metrology, and photonic applications. Currently, developed laser systems generally suffer from the hardware complexity and energy loss. Here, we demonstrate a compact robust scheme based on a self-mode-locked monolithic Yb:KGW laser with external feedback coupling to achieve numerous repetition rate multiplications in the range of 25-330 GHz. The output pulse train consists of two orthogonally polarized components to form a vector state that is beneficial to practical applications. More intriguing, the pulse train measured as a function of the distance of the coupling feedback reveals a feature of the fractional recurrence that is like the Talbot carpet. An analytic formula is derived to manifest the formation of the temporal carpets. The developed experiment and formula not only pave a useful way for generating ultrahigh-repetition-rate femtosecond lasers but also provide new perspectives in the fractional recurrences of coherent waves.
Promising Er3+/Yb3+-Codoped GdBiW2O9 Phosphor for Temperature Sensing by Upconversion Luminescence
(2018-09-01)
Dutta, Somrita
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Som, Sudipta
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Chen, Teng-Ming
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應用化學系
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Department of Applied Chemistry
Yb3+/Er3+-codoped GdBiW2O9 phosphors are prepared via the solidstate route for application in upconversion temperature sensors. The structural analyses indicate that all phosphors possess a single-phased orthorhombic structure. Upon the excitation of a laser wavelength of 980 nm, Yb3+/Er3+-codoped GdBiW2O9 phosphors emanate green emission peaks, endorsed to the emission to the I-4(15/2) state from the S-4(3/2) and H-2(11/2) states, respectively, and the weak emission (red) from the F-4(9/2) state to the I-4(15/2) state of Er3+ ion. The upconversion mechanism has been elucidated via the scheme of energy levels conferred from the pump power-induced upconversion characteristics. The temperature-dependent upconversion of GdBiW2O9 phosphors was investigated in detail along with the estimation of the stability and repeatability of the measurement. The obtained sensitivity data for the present materials with the corresponding sensing parameters show their probable outlook in temperature sensing applications.
Employment of silicon-micro-ring resonator and compound-ring architecture for stable and tunable single-longitudinal-mode fiber laser
(2018-09-01)
Hsu, Yung
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Yeh, Chien-Hung
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Cheng, Hao-Yun
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Chang, Yuan-Chia
;
Chow, Chi-Wai
In this work, a wavelength-switchable erbium-doped fiber (EDF) glasses-type compound-ring (GTCR) laser with stable single-longitudinal-mode (SLM) oscillation is proposed and presented. In the experiment, to accomplish wavelength-tunable operation, a silicon-micro-ring-resonator (SiMRR) is utilized inside the ring cavity, when the birefringent loss of EDF laser is adjusted properly. Moreover, the GTCR configuration is proposed to as the mode-filter for suppressing the multi-longitudinal-mode (MLM) to achieve the SLM oscillation. Here, the measured linewidth of output wavelength is 61 kHz. The output stabilities of the proposed SiMRR EDF compound-ring laser are also discussed experimentally. (C) 2018 Elsevier Ltd. All rights reserved.
A Speed- and Power-Efficient SPIHT Design for Wearable Quality-On-Demand ECG Applications
(2018-09-01)
Hsieh, Jui-Hung
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Hung, King-Chu
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Lin, Yu-Ling
;
Shih, Meng-Ju
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生物科技學系
In this paper, a speed and power-efficient set partitioning in hierarchical trees (SPIHT) design is introduced for one-dimensional (1-D) wavelet-based electrocardiography (ECG) compression systems with quality guarantee. To achieve real-time and low-power design objectives toward wearable quality-on-demand (QoD) ECG applications, we first propose a coding-time-and computation-efficient SPIHT algorithm using various types of coding status register files to overcome the disadvantages of low coding speeds and complicated hardware architectures characterizing prior SPIHT algorithms resulting from the necessity of dynamic computation and arrangement in the sorting and refinement processing phase. Second, a highly pipelined and power-efficient very large scale integration (VLSI) architecture is developed to implement a high-performance and low-power SPIHT design based on the proposed algorithm. The final simulation results demonstrate that our proposed algorithm can speed up the average coding time 1.52 to 2.74 times compared to prior work with an identical compression ratio for an 11-level 1024 x 1 1 - D discrete wavelet transform at diverse target percentage root-mean-square differences (PRDT) on various MIT-BIH arrhythmia datasets. Applied to wearable wavelet-based QoD ECG applications, our proposed VLSI architecture attains a working frequency of 740 MHz and consumes an average of 23 mu W of power with Taiwan Semiconductor Manufacturing Company 90-nm CMOS technology, which shows the effectiveness of speed and power over the state-of-the-art designs.
Fundus photography with subpixel registration of correlated laser speckle images
(2018-09-01)
Li, Jie-En
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Tien, Chung-Hao
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光電工程學系
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Department of Photonics
In this paper, we propose multiple modalities based on laser speckle correlation and image registration to enhance the visibility of the fundus without a scanning interferometric scenario, resulting in robustness against intra frame noises induced by inevitable movement. The experimental results showed, with the features from laser speckle contrast imaging (LSCI), that the quality of images obtained using a conventional imaging system could be enhanced. Moreover, by applying the image registration process, we successfully eliminated the inter frame blurring caused by eye movements in an in vivo experiment. The concept was proven when the image contrast of a vascular feature was improved by 1.00x-2.75x. (c) 2018 The Japan Society of Applied Physics
Shake table tests on RC frame infilled by slitted masonry panels
(2018-09-01)
Yuen, Terry Y. P.
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Zhang, Han-hui
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Kuang, J. S.
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Huang, Qunxian
;
土木工程學系
Unreinforced masonry infill walls are widely used as non-structural partitions in RC frames. The effects of infills on the structural responses are often ignored in the design process since they are generally considered as expendable elements. However, recent studies have shown that not only shear damage can be inflicted to the columns braced by the infill walls, but also that the structural stability can be jeopardised by the fall-off of the infills. This paper presents the development of new detailing methods for the infill walls, which features slit panels, isolation gaps between the infills and columns, and anchorage of the infills. The proposed detailing methods were tested and verified experimentally using shake-table tests on five 1/3-scale infilled RC frame specimens with different combinations of the features stated above. The design and construction of the shake-table test specimens have taken into account the similitude requirements. The test results indicate that the proposed detailing method effectively reduced the undesirable interaction between column and infill walls. And the use of proper anchorage could prevent the fall off of infills from the bounding frame. Furthermore, the specimens with slit infill walls displayed better seismic performances, which could be attributed to the rocking behaviour of the sub-panels with increased aspect ratios.
Automatic Optimization of Wayfinding Design
(2018-09-01)
Huang, Haikun
;
Lin, Ni-Ching
;
Barrett, Lorenzo
;
Springer, Darian
;
Wang, Hsueh-Cheng
Wayfinding signs play an important role in guiding users to navigate in a virtual environment and in helping pedestrians to find their ways in a real-world architectural site. Conventionally, the wayfinding design of a virtual environment is created manually, so as the wayfinding design of a real-world architectural site. The many possible navigation scenarios, as well as the interplay between signs and human navigation, can make the manual design process overwhelming and non-trivial. As a result, creating a wayfinding design for a typical layout can take months to several years. In this paper, we introduce the Way to Go! approach for automatically generating a wayfinding design for a given layout. The designer simply has to specify some navigation scenarios; our approach will automatically generate an optimized wayfinding design with signs properly placed considering human agents' visibility and possibility of making mistakes during a navigation. We demonstrate the effectiveness of our approach in generating wayfinding designs for different layouts such as a train station, a downtown and a canyon. We evaluate our results by comparing different wayfinding designs and show that our optimized wayfinding design can guide pedestrians to their destinations effectively and efficiently. Our approach can also help the designer visualize the accessibility of a destination from different locations, and correct any "blind zone" with additional signs.
A versatile low-resistance ohmic contact process with ohmic recess and low-temperature annealing for GaN HEMTs
(2018-09-01)
Lin, Yen-Ku
;
Bergsten, Johan
;
Leong, Hector
;
Malmros, Anna
;
Chen, Jr-Tai
Deeply recessed ohmic contacts for GaN-based high electron mobility transistors (HEMTs) are demonstrated. It is shown that low-resistance ohmic contacts can be achieved with recessing beyond the AlGaN Schottky barrier where the ohmic contacts are formed on the sidewall of the recess. This makes the process versatile and relatively insensitive to the exact recess depth. The ohmic contact is based on a gold-free metallization scheme consisting of a Ta/Al/Ta metal stack requiring a low-temperature annealing. Important parameters for this type of ohmic contact process include the metal coverage, slope of the etched sidewall, bottom Ta-layer thickness, as well as annealing temperature and duration. The optimized contact resistance is as low as 0.24 Omega mm after annealing at 575 degrees C. Moreover, this sidewall contact approach was successfully implemented on different epitaxial heterostructures with different AlGaN barrier thickness as well as with and without AlN exclusion layer. All the samples exhibited excellent contact resistances in a wide range of recess depths. The Ta-based, sidewall ohmic contact process is a promising method for forming an ohmic contact on a wide range of GaN HEMT epitaxial designs.