Browsing by Author "Tseng, Tseung Yuen"

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A Collective Study on Modeling and Simulation of Resistive Random Access Memory
(2018-01-10)
Panda, Debashis
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Sahu, Paritosh Piyush
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Tseng, Tseung Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this work, we provide a comprehensive discussion on the various models proposed for the design and description of resistive random access memory (RRAM), being a nascent technology is heavily reliant on accurate models to develop efficient working designs and standardize its implementation across devices. This review provides detailed information regarding the various physical methodologies considered for developing models for RRAM devices. It covers all the important models reported till now and elucidates their features and limitations. Various additional effects and anomalies arising from memristive system have been addressed, and the solutions provided by the models to these problems have been shown as well. All the fundamental concepts of RRAM model development such as device operation, switching dynamics, and current-voltage relationships are covered in detail in this work. Popular models proposed by Chua, HP Labs, Yakopcic, TEAM, Stanford/ASU, Ielmini, Berco-Tseng, and many others have been compared and analyzed extensively on various parameters. The working and implementations of the window functions like Joglekar, Biolek, Prodromakis, etc. has been presented and compared as well. New well-defined modeling concepts have been discussed which increase the applicability and accuracy of the models. The use of these concepts brings forth several improvements in the existing models, which have been enumerated in this work. Following the template presented, highly accurate models would be developed which will vastly help future model developers and the modeling community.
An ultra-compact blackbody using electrophoretic deposited carbon nanotube films
(2018-01-01)
Lin, Albert
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Yang, Chien-Chih
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Parashar, Parag
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Lin, Chien-Yung
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Jian, Ding Rung
Carbon nanotubes (CNTs) possesses decent optical properties and thus can be considered as a candidate for perfect absorbers due to their close-to-air refractive index and minimal extinction. However, weak absorption in porous materials, due to the low extinction coefficients, requires an inevitably thick absorption layer (similar to 100 mu m) for the perfect opaque absorbers. Thus, the requirement of large thicknesses of CNTs prohibits them from being used as miniaturized integrated photonic devices. Here, we propose an electrophoretic deposited (EPD) CNT resonant cavity structure on tantalum (Ta) to enhance optical absorption. Efficient random light scattering along with the resonant cavity structure using Ti/SiO2 stacking enhances the absorption in our proposed EPD-CNT film while maintaining the total device thickness to <1 mu m. The experiment results reveal that the absorption band covers the entire UV-VIS-NIR spectrum (lambda = 0.3-2.6 mu m), using resonant-cavity EPD-CNT design. The EPD deposition process is done at relatively low temperature < 120 degrees C. We believe that this proposal is very promising for sensing, antenna, and thermophotovoltaics (TPV), in terms of bandwidth, compactness and cost.
Electrophoretic Fabrication and Characterizations of Manganese Oxide/Carbon Nanotube Nanocomposite Pseudocapacitors
(2011)
Hung, Chung Jung
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Hung, Jeng Han
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Lin, Pang
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Tseng, Tseung Yuen
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材料科學與工程學系
This study reports the electrochemical performance and stability of MnO(x)-multiwall carbon nanotubes (MWCNTs) nanocomposite/Ni pseudocapacitor electrodes fabricated by a modified electrophoretic deposition (EPD) method. The nanocomposite electrode consisting of highly dispersed manganese oxide on MWCNTs was synthesized by a redox titration method at room temperature. The electrochemical properties of the electrode were demonstrated by cyclic voltammetry. The mean specific capacitances at a constant scan rate of 100 mV/s of MnO(x)-MWCNTs nanocomposites without and with heat treatment at temperatures 150, 200, and 250 degrees C for 2 h are 378, 402, 445, and 469 F/g, respectively, which indicate an increase with increasing annealing temperature. During stability tests, the as-grown MnO(x)-MWCNTs nanocomposite electrode can preserve 80% of its original capacitance after 6000 cycles of operation which can be increased to 86% after annealing at 200 degrees C for 2 h. The EPD MnO(x)/MWCNTs coaxial nanocomposite pseudocapacitors with manganese oxide ionized by H(+) ion process exhibit high specific capacitance, fast reaction rate, high stability, and have high potential for practical applications. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3601862] All rights reserved.
Electrophoretic fabrication and pseudocapacitive properties of graphene/manganese oxide/carbon nanotube nanocomposites
(2013-12-01)
Hung, Chung Jung
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Lin, Pang
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Tseng, Tseung Yuen
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材料科學與工程學系
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電子工程學系及電子研究所
Hybrid nanocomposites provided a synergistic improvement on electrochemical performance and stability for pseudocapacitor. Designed graphene/carbon nanotubes (CNTs)/MnO2 nanocomposites with CNTs electrode (in short, GMC + C) with highly nanoporous framework surface structure are fabricated by a modified electrophoretic deposition (EPD) method. Scanning electron microscopy and transmission electron microscopy analysis demonstrate that the flake-like MnO2 thickness (about less than 10 nm) and uniformly distributed on the porous graphene/CNTs framework. X-ray diffraction shows the formation of birnessite-type MnO2. Pseudocapacitances of the GMC + C electrode calculated by cyclic voltammetry having different scan rates of 5, 20, 50, 100, and 300 mV s(-1) exhibit high specific capacitances of 481, 436, 413, 398, and 372 F g, respectively. Sodium ion diffusion coefficients of the GMC + C electrode show a higher intercalation value of 3.647 x 10(-8) cm(2) s(-1) and deintercalation value of 2.899 x 10(-8) cm(2) s(-1) using chronoamperometry. Moreover, the GMC + C electrode maintains a high specific capacitance of 346 F g(-1), and is about 833% of the initial capacitance after 15,000 charge/discharge cycles. The designed hybrid GMC + C nanocomposites pseudocapacitor electrode using EPD route with the high specific capacitance, fast reaction rate, and high stability, exhibits high potential for practical applications. (C) 2013 Elsevier B.V. All rights reserved.
Fabrication of carbon nanotube/cobalt oxide nanocomposites via electrophoretic deposition for supercapacitor electrodes
(2016-03-01)
Kumar, Nagesh
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Yu, Yun-Cheng
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Lu, Yi Hsuan
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Tseng, Tseung Yuen
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電子工程學系及電子研究所
The cobalt oxide and carbon nanotubes (Co3O4/CNTs) nanocomposites are successfully synthesized using hydrothermal method. The as-synthesized nanocomposite materials are utilized in the electrophoretic deposition (EPD) to fabricate the electrodes, whose electrochemical properties are investigated in a three-electrode configuration cell with 1 M KOH electrolyte. By adjusting the precursor concentration, reaction time in hydrothermal process, and annealing temperature, the optimum conditions are obtained. From the experimental results, when the cobalt nitrate concentration is taken as 2 mmol, reaction time is 8 h, and the temperature is maintained at 180 A degrees C in the hydrothermal process, the synthesized Co3O4/CNTs nanocomposites shows the highest specific capacitance of 705 F g(-1) at a charging current of 3 A g(-1). Besides, the binder-free electrode preparation through EPD has effectively reduced the inner resistance of the electrode and makes the cycle stability excellent.
Facile synthesis of mesoporous NiFe2O4/CNTs nanocomposite cathode material for high performance asymmetric pseudocapacitors
(2018-03-01)
Kumar, Nagesh
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Kumar, Amit
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Huang, Guan-Min
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Wu, Wen-Wei
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Tseng, Tseung Yuen
Morphology and synergistic effect of constituents are the two very important factors that greatly influence the physical, chemical and electrochemical properties of a composite material. In the present work, we report the enhanced electrochemical performance of mesoporous NiFe2O4 and multiwall carbon nanotubes (MWCNTs) nanocomposites synthesized via hexamethylene tetramine (HMT) assisted one-pot hydrothermal approach. The synthesized cubic phase spinel NiFe2O4 nanomaterial possesses high specific surface area (148 m(2)g(-1)) with narrow mesopore size distribution. The effect of MWCNTs addition on the electrochemical performance of nanocomposite has been probed thoroughly in a normal three electrode configuration using 2 M KOH electrolyte at room temperature. Experimental results show that the addition of mere 5 mg MWCNTs into fixed NiFe2O4 precursors amount enhances the specific capacitance up to 1291 Fg(-1) at 1 Ag-1, which is the highest reported value for NiFe2O4 nanocomposites so far. NiFe2O4/CNT nanocomposite exhibits small relaxation time constant (1.5 ms), good rate capability and capacitance retention of 81% over 500 charge-discharge cycles. This excellent performance can be assigned to high surface area, mesoporous structure of NiFe2O4 and conducting network formed by MWCNTs in the composite. Further, to evaluate the device performance of the composite, an asymmet-ric pseudocapacitor has been designed using NiFe2 04/CNT nanocomposite as a positive and N-doped graphene as a negative electrode material, respectively. Our designed asymmetric pseudocapacitor gives maximum energy density of 23 W h kg(-1) at power density of 872W kg(-1). These promising results assert the potential of synthesized nanocomposite in the development of efficient practical high-capacitive energy storage devices. (C) 2017 Published by Elsevier B.V.
Formation of Core/Shell-Type ZnO/CeO(2) Nanorods and CeO(2) Nanotube Arrays by Aqueous Synthesis and Wet-Etching
(2008-06-01)
Chen, Yung Sheng
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Tseng, Tseung Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Aqueous synthesis and wet-etching process for fabricating core/shell-type ZnO/CeO(2) nanorods and CeO(2) nanotube arrays without any chemical modification or assisted surfactant are reported. Ce ions are adsorbed on ZnO to form core/shell-type ZnO/CeO(2) nanorods and polycrystalline CeO(2) nanotubes are fabricated by wet-etching the ZnO cores with a dilute hydrochloric acid solution. The as-synthesized ZnO/CeO(2) nanorods reveal that the ZnO cores are coated with CeO(2) shells to form a plastered layer. The obtained CeO(2) nanotubes show a perfect hexagonal structure and large cavities. The possible formation mechanism for the core/shell-type ZnO/CeO(2) nanorods and CeO(2) nanotube arrays is discussed.
Formation of Core/Shell-Type ZnO/CeO2 Nanorods and CeO2 Nanotube Arrays by Aqueous Synthesis and Wet-Etching
(2008-06-01)
Chen, Yung Sheng
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Tseng, Tseung Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Aqueous synthesis and wet-etching process for fabricating core/shell-type ZnO/CeO2 nanorods and CeO2 nanotube arrays without any chemical modification or assisted surfactant are reported. Ce ions are adsorbed on ZnO to form core/shell-type ZnO/CeO2 nanorods and polycrystalline CeO2 nanotubes are fabricated by wet-etching the ZnO cores with a dilute hydrochloric acid solution. The as-synthesized ZnO/CeO2 nanorods reveal that the ZnO cores are coated with CeO2 shells to form a plastered layer. The obtained CeO2 nanotubes show a perfect hexagonal structure and large cavities. The possible formation mechanism for the core/shell-type ZnO/CeO2 nanorods and CeO2 nanotube arrays is discussed.
High energy density asymmetric pseudocapacitors fabricated by graphene/carbon nanotube/MnO2 plus carbon nanotubes nanocomposites electrode
(2014-08-01)
Hung, Chung Jung
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Lin, Pang
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Tseng, Tseung Yuen
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材料科學與工程學系
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電子工程學系及電子研究所
Novel graphene/carbon nanotubes (CNTs)/manganese oxide (MnO2) nanocomposites plus CNTs (GMC + C) and graphene/CNTs hybrid (GC) thin-film electrodes are prepared by electrophoretic deposition (EPD). These nanocomposite electrodes exhibit high surface area and interconnected pore networks. The GMC + C nanocomposite electrode shows excellent specific capacitance of 964 F g(-1) at 1 A g (-1), rate capability with the residual capacitance of 529 F g(-1), at 500 mV s(-1), and fast Na+ diffusion with intercalation value of 6.34 x 10(-7) cm(2) s(-1), and deintercalation value of 8.86 x 10(-7) cm(2) s(-1). Such excellent pseudocapacitive performances are attributed to low ion/electron transport resistances and short ion/electron diffusion lengths. Furthermore, novel aqueous electrolyte-based asymmetric pseudocapacitor having 1.8 V cell voltage is successfully fabricated using GMC + C nanocomposite as a cathode and GC nanocomposite as an anode. The optimized asymmetric pseudocapacitor possesses superior performance with a maximum energy density of record high 304 Wh kg(-1) and retaining 56.2% of its initial specific energy density at the power density up to 242 kW kg(-1). In addition, the asymmetric cell configuration also shows excellent cycling stability with 89% specific capacitance maintained after 10,000 cycles. These results suggest that our designed asymmetric pseudocapacitors have a high potential for practical applications. (C) 2014 Elsevier B.V. All rights reserved.
Hydrothermal Formation of Tungsten Trioxide Nanowire Networks on Seed-Free Substrates and Their Properties in Electrochromic Device
(2014-05-01)
Hung, Chung Jung
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Huang, Yi Hsuan
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Chen, Chih Hao
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Lin, Pang
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Tseng, Tseung Yuen
Facile and cost-efficient hydrothermally grown 3-D tungsten trioxide (WO3) nanowires (NWs) network film on seed-free fluorine-doped tin oxide (FTO) substrates without using additive or capping agent is reported. The NW networks are hexagonal phase and the morphologies are changed by adjusting the pH of precursor solutions. Growth mechanism of WO3 NWs is also extensively discussed. The designed porous film exhibits remarkable enhancement of the electrochromic (EC) properties. In particular, a significant optical modulation (57% at 632 nm), fast color switching speed (bleaching: 7 s and coloration: 21 s), high coloration efficiency (120.3 cm(2) C-1 at 632 nm), high Li+ diffusion coefficient (2.14 x 10(-9) cm(2) s(-1)), and excellent cycling stability (87% after 1000 cycles) are achieved for the 3-D NWs film. The improved EC properties are mainly attributed to the highly porous film, which makes the Li+ diffusion becomes easier and provides larger specific surface area for charge-transfer reactions. Furthermore, we also reported an EC device (50 mm x 50 mm) with a simple two-electrode configuration showing high optical contrast. The 3-D WO3 NWs network film acts as an excellent EC material.
Porous carbon materials derived from areca palm leaves for high performance symmetrical solid-state supercapacitors
(1970-01-01)
Le, Phuoc-Anh
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Nguyen, Van-Truong
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Saho, Sumanta Kumar
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Tseng, Tseung Yuen
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Wei, Kung-Hwa
Areca palm leaves derived porous carbon material as the electrode for symmetrical solid-state supercapacitors (SSCs). The areca palm leaves biomass was processed using a fast carbonization method followed by in situ chemical activation. The structures and compositions of these biomass-derived carbon materials were characterized using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. One of the biomass-derived porous carbon materials, AR2, was a lightweight carbon material that possessed a large surface area of 876 m(2) g(-1). Electrochemical studies revealed that AR2 possessed a high specific capacitance of 262 F g(-1) at a scan rate of 5 mV s(-1). We fabricated symmetrical SSCs featuring these carbon material as major (80 wt%) components of the electrodes and poly(vinyl alcohol)-Li2SO4 as gel polymer electrolyte. The optimal supercapacitor (SAR2) involving AR2 exhibited a specific capacitance of 132 F g(-1) at a current density of 0.5 A g(-1) and an energy density of 10.3 W h kg(-1) at a power density of 375 W kg(-1), and durability of retaining 92% of its initial capacitance after 5000 cycles-performance that is the excellent values reported for devices featuring derived from biomass.
Probing the electrochemical properties of an electrophoretically deposited Co3O4/rGO/CNTs nanocomposite for supercapacitor applications
(2016-01-01)
Kumar, Nagesh
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Huang, Chun-Wei
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Yen, Po-Jen
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Wu, Wen-Wei
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Wei, Kung-Hwa
This study reports the electrochemical performance of pseudosupercapacitor electrodes composed of cubic phase Co3O4 nanoparticles, reduced graphene oxide (rGO) and functionalized MWCNTs based nanocomposites. The Co3O4/rGO/CNTs nanocomposites have been synthesized using a hydrothermal method and the EPD technique has been used to make binder free electrodes of the nanocomposite materials for supercapacitor applications. The effects of graphene oxide (GO) concentration and the ratio of GO/CNTs on the electrochemical performance of the nanocomposite material have been investigated. From the experimental results, the Co3O4/rGO/CNTs nanocomposite synthesized with 2 mg mL (1) GO concentration and 10 : 1 GO/CNT ratio exhibits a good specific capacitance of 850 F g (1) at a 5 mV s(-1) scan rate and 790 F g(-1) at 1 A g(-1), excellent rate capability and good cyclability in 1 M KOH. Furthermore, we have successfully designed an aqueous electrolyte-based asymmetric pseudocapacitor using Co3O4/rGO/CNTs nanocomposite as an anode and N-doped graphene nanocomposite as a cathode. The operating voltage of our optimized asymmetric pseudocapacitor is 1.4 V and it exhibits the maximum energy density and power density of 19.6 W h kg(-1) and 7250 W kg(-1), respectively. These results suggest that our EPD grown nanocomposite binder free electrode and our designed asymmetric pseudocapacitor have a good potential for practical applications.
Synthesis of Free-Standing Flexible rGO/MWCNT Films for Symmetric Supercapacitor Application
(2019-08-06)
Kumar, Amit
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Kumar, Nagesh
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Sharma, Yogesh
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Leu, Jihperng
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Tseng, Tseung Yuen
Herein, we report a novel, simple, and cost-effective way to synthesize flexible and conductive rGO and rGO/MWCNT freestanding films. The effects of MWCNT addition on the electrochemical performance of rGO/MWCNT nanocomposite films are investigated in some strong base aqueous electrolytes, such as KOH, LiOH, and NaOH via three-electrode system. The supercapacitor behavior of the films is probed via cyclic voltammetry, galvanostatic charging-discharging, and electrochemical impedance spectroscopy. The structural and morphological studies of the films are performed by X-ray diffractometer, Raman spectrometer, surface area analyzer, thermogravimetric analysis, field emission scanning electron microscope and transmission electron microscope. The rGO/MWCNT film synthesized with 10 wt% MWCNTs (GP10C) exhibits high specific capacitance of 200 Fg(-1), excellent cyclic stability with 92% retention after 15,000 long cycle test, small relaxation time constant (similar to 194 ms), and high diffusion coefficient (7.8457 x 10(-9) cm(2) s(-1)) in 2 M KOH electrolyte. Furthermore, the symmetric supercapacitor coin cell with GP10C as both anode and cathode using 2 M KOH as electrolyte demonstrates high energy density of 29.4 Whkg(-1) and power density of 439 Wkg(-1) at current density 0.1 Ag-1 and good cyclic stability with 85% retention of the initial capacitance at 0.3 Ag-1 after 10,000 cycles. Such a high performance of the GP10C film in the supercapacitor can be ascribed to the large surface area and small hydration sphere radius and high ionic conductivity of K+ cations in KOH electrolyte.
Ternary Au/ZnO/rGO nanocomposites electrodes for high performance electrochemical storage devices
(2017-10-31)
Chaudhary, Manchal
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Doong, Ruey-an
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Kumar, Nagesh
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Tseng, Tseung Yuen
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環境工程研究所
The combination of metal and metal oxide nanoparticles with reduced graphene oxides (rGO) is an active electrode material for electrochemical storage devices. Herein, we have, for the first time, reported the fabrication of ternary Au/ZnO/rGO nanocomposites by using a rapid and environmentally friendly microwave-assisted hydrothermal method for high performance supercapacitor applications. The ZnO/rGO provides excellent electrical conductivity and good macro/mesopore structures, which can facilitate the rapid electrons and ions transport. The Au nanoparticles with particle sizes of 7-12 nm are homogeneously distributed onto the ZnO/rGO surface to enhance the electrochemical performance by retaining the capacitance at high current density. The Au/ZnO/rGO nanocomposites, prepared with the optimized rGO amount of 100 mg exhibit a high specific capacitance of 875 and 424 F g(-1) at current densities of 1 and 20 A g-1, respectively, in 2 M KOH. In addition, the energy and power densities of ternary Au/ZnO/rGO can be up to 17.6-36.5 Wh kg(-1) and 0.27-5.42 kW kg(-1), respectively. Results obtained in this study clearly demonstrate the excellence of ternary Au/ZnO/rGO nanocomposites as the active electrode materials for electrochemical pseudocapacitor performance and can open an avenue to fabricate metal/metal oxide/rGO nanocomposites for electrochemical storage devices with both high energy and power densities. (C) 2017 Elsevier B.V. All rights reserved.
The External Light Trapping for Perovskite Solar Cells Using Nanoimprinted Polymer Metamaterial Patterns
(2016-01-01)
Lin, Albert
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Fu, Sze Ming
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Chen, Bo-Ruei
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Yan, Sheng-Lun
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Zhong, Yan Kai
In this work, we develop the process flow for nano-imprinted metamaterial patterns for perovskite solar cell light trapping. Nanoimprint can be scaled for large-area photovoltaics at low cost, compared to conventional lithography techniques. While conventional grating is normally underneath the solar cell active layers, the degraded electrical characteristic can be a problem. On the other hand, the external light trapping separates the electrical and optical designs and, therefore, it is more promising for complex photonic management without sacrificing the diode characteristics. We demonstrate the concept by perovskite solar cells with metamaterial patterns. Imprinting a deeper metamaterial pattern is suggested to enhance the far field effect for further efficiency improvement.
The External Light Trapping Using Down-Conversion Polymer and Diffuse Trench Reflectors
(2016-01-01)
Lin, Albert
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Han, Hau-Vei
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Huang, Chien-Yao
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Chen, Bo-Ruei
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Fu, Sze Ming
External light trapping has been proposed as an alternative to internal light trapping. The advantage is that the electrical and optical characteristics can be designed separately. This enhances the degree of improvement that nano-photonics can contribute to the solar cell efficiency and J(SC). In this work, we use diffuse trench reflectors with down-conversion polymer to demonstrate the concepts of a low-cost, widely applicable scheme for the external light trap. A >50% enhancement of the J(SC) can be observed with proper designs and configurations. The proposed external light trap can be applied to nearly all thin-film solar cell technologies since the external optical components do not affect the electrical diode characteristic of the solar cells. The efficient external light trap is attributed to the high reflectance of the disuse mirror and its wide-angle diffractions, optical confinement due to the trench reflector, and the additional short-wavelength spectral enhancement by the down-conversion mechanism.