Browsing by Author "Lee, Sheng-Wei"

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Design of multifold Ge/Si/Ge composite quantum-dot heterostructures for visible to near-infrared photodetection
(2015-05-15)
Kuo, Ming-Hao
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Lai, Wei-Ting
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Lee, Sheng-Wei
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Chen, Yen-Chun
;
Chang, Chia-Wei
We demonstrate an effective approach to grow high-quality thin film (>1 mu m) ofmultifold Ge/Si/Ge composite quantum dots ( CQDs) stacked heterostructures for near infrared photodetection and optical interconnect applications. An otherwise random, self-assembly of variable-fold Ge/Si CQDs has been grown on Si through the insertion of Si spacer layers to produce micron-scale-thick, stacked Ge/Si CQD layers with desired QD morphology and composition distribution. The high crystalline quality of these multifold Ge CQD heterostructures is evidenced by low dark current density of 3.68 pA/mu m(2), superior photoresponsivity of 267 and 220 mA/W under 850 and 980 nm illumination, respectively, and very fast temporal response time of 0.24 ns measured on the Ge/Si CQD photodetectors. (C) 2015 Optical Society of America
Effects of TiO2 and SDC addition on the properties of YSZ electrolyte
(2019-11-12)
Shen, Chin-Tien
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Lee, Kan-Rong
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Hsieh, Yu-Pin
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Lee, Sheng-Wei
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Chang, Jeng-Kuei
In this study, we investigate the effects of adding titanium dioxide (TiO2) and samarium doped cerium oxide (SDC) on the properties of yttrium-stabilized zirconia (YSZ) electrolyte. The microstructure, mechanical, and electrochemical properties of the electrolyte are investigated. The performance in CO2 electrolysis is measured by supplying carbon dioxide to Ni-YSZ electrode and nitrogen to LSM electrode. Results show that TiO2 and SDC addition can reduce the sintering temperature and increase grain size. The ionic conductivity is 0.123 S cm(-1) at 1000 degrees C. In addition, the thermal expansion coefficient at 1000 degrees C is 8.25 x 10(-6)K(-1). The current density of the cell is 439 mA cm(-2) at 1.3 V and 1000 degrees C in solid oxide electrolysis cell. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Enhancement of NiSi-Based Nanocrystal Formation by Incorporating Ge Elements for Nonvolatile Memory Devices
(2009)
Hu, Chih-Wei
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Chang, Ting-Chang
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Tu, Chun-Hao
;
Chiang, Cheng-Neng
;
Lin, Chao-Cheng
In this work, a NiSiGe mixed film was deposited by the cosputtering approach. The rapidly thermal treatment condition was executed at 600 degrees C for 30 s in nitrogen ambient to form the nanocrystal structure. From the results of the transmission electron microscopy, the annealed NiSiGe film reveals a larger nanocrystal size and density distribution than pure NiSi. X-ray photoelectron spectroscopy analyses were used to confirm that the Ge elements provide the additional nucleation centers and enhance the nanocrystal formation during the thermal process. Raman spectroscopy and an energy-dispersive spectrometer also exhibit the compositions of nanocrystals including Ni, Si, and Ge elements. With the better formation process, a remarkable improvement of memory effect is observed by comparing with the NiSi and NiSiGe nanocrystal memory devices. Also, the NiSiGe nanocrystal device shows a better retention characteristic due to the lower quantum confinement effect.
Enhancing the Seebeck effect in Ge/Si through the combination of interfacial design features
(2019-11-08)
Nadtochiy, Andriy
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Kuryliuk, Vasyl
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Strelchuk, Viktor
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Korotchenkov, Oleg
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Li, Pei-Wen
Due to their inherent physical properties, thin-film Si/SiGe heterostructures have specific thermal management applications in advanced integrated circuits and this in turn is essential not only to prevent a high local temperature and overheat inside the circuit, but also generate electricity through the Seebeck effect. Here, we were able to enhance the Seebeck effect in the germanium composite quantum dots (CQDs) embedded in silicon by increasing the number of thin silicon layers inside the dot (multi-fold CQD material). The Seebeck effect in the CQD structures and multi-layer boron atomic layer-doped SiGe epitaxial films was studied experimentally at temperatures in the range from 50 to 300 K and detailed calculations for the Seebeck coefficient employing different scattering mechanisms were made. Our results show that the Seebeck coefficient is enhanced up to approximate to 40% in a 3-fold CQD material with respect to 2-fold Ge/Si CQDs. This enhancement was precisely modeled by taking into account the scattering of phonons by inner boundaries and the carrier filtering by the CQD inclusions. Our model is also able to reproduce the observed temperature dependence of the Seebeck coefficient in the B atomic layer-doped SiGe fairly well. We expect that the phonon scattering techniques developed here could significantly improve the thermoelectric performance of Ge/Si materials through further optimization of the layer stacks inside the quantum dot and of the dopant concentrations.
Fabrication of anode-supported thin BCZY electrolyte protonic fuel cells using NiO sintering aid
(2019-09-03)
Lee, Kan-Rong
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Tseng, Chung-Jen
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Jang, Shian-Ching
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Lin, Jing-Chie
;
Wang, Kuan-Wen
A thin and fully dense BaCe0.6Zr0.2Y0.2O3-delta(BCZY) electrolyte for the use of anode-supported protonic fuel cells has been successfully prepared by spin coating using NiO sintering aid. The effects of NiO addition on the electrolyte microstructures and fuel cell performances are also investigated. An appropriate NiO addition has a significant positive contribution to the densification and grain growth of thin BCZY electrolytes. However, too much NiO addition gives rise to NiO aggregation in BCZY electrolyte and deteriorates the cell performance. The enhanced sintering mechanism can be mainly attributed to the oxygen vacancies generated from the NiO decomposition and bulk diffusion of Ni into BCZY perovskites. The fuel cell with a BCZY-3%NiO electrolyte exhibits the highest maximum power density of similar to 106.6 mW/cm(2) at 800 degrees C among all fuel cells in this study. The electrochemical impedance characteristics of thin BCZY electrolyte fuel cells are further discussed under open circuit conditions. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Germanium-assisted growth of titanium dioxide nanowires for enhanced photocatalytic and electron emission performance
(2020-11-15)
Chen, Chih-Yen
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Lin, Tzu-Chien
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Chuang, Wen-Shuo
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Chang, Jeng-Kuei
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Lee, Sheng-Wei
In this study, free-standing and well-aligned titanium dioxide (TiO2) nanowires were grown on a Ti foil by precisely controlling the growth temperature and the thickness of the Ge catalyst layer. The catalyst layer played an important role in activating the surface of the Ti foil, facilitating the growth of TiO2 nanowires on it in a chemical vapor deposition furnace system. The structure of the TiO2 nanowires was investigated using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The photocatalytic experiment results showed that the optimum Ge catalyst layer thickness significantly improved the rhodamine B (RhB) degradation efficiency of the nanowires. The TiO2 nanowires grown using a 40-nm-thick Ge layer could degrade 74% of RhB after 5 h of ultraviolet irradiation. In addition, the TiO2 nanowires exhibited excellent electron field emission performance as compared to the TiO2 nanocrystals grown without the Ge catalyst layer. The results suggested that TiO2 nanowires grown using a Ge catalyst layer are promising materials for next-generation electronic emitters and photocatalytic systems.
Highly concentrated carbonate electrolyte for Li-ion batteries with lithium metal and graphite anodes
(2020-02-29)
Xie, Jian-De
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Patra, Jagabandhu
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Rath, Purna Chandra
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Liu, Weng-Jing
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Su, Ching-Yuan
Highly concentrated lithium bis(fluorosulfonyflimide (LiFSI) salt dissolved in carbonate solvent is employed as a high-performance and robust organic electrolyte for Li-ion batteries. The influences of Li salt type, concentration, and solvent type (such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethylene carbonate (EC)) on the electrochemical properties of Li metal and graphite anodes are systematically assessed. A superior electrolyte composition of 5.5 M LiFSI-DMC/EC is achieved, enhancing the anti-flammability, coulombic efficiency, and high rate capability. The optimal efficiency values of Li electrodeposition/stripping utilizing 5.5 M LiFSI-DMC/EC are 97.0% and 94.5% at 0.4 and 6 mA cm(-2), respectively. Such an enhanced performance is due to the formation of a three-dimensional ion network, composed of contact ion pairs (CIPs) and ion aggregates (AGGs) in the highly concentrated LiFSI electrolyte, which effectively decreases the number of free solvent molecules and inhibits the formation of undesired dendritic Li structures. Raman spectroscopy is employed to confirm the formation of CIP and AGG compounds within the electrolyte. The electrochemical data of the 5.5 M LiFSI-DMC/EC electrolyte cell demonstrates a remarkable improvement in the specific capacity and rate capability of a graphite anode.
Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors
(2020-07-01)
Xie, Jian-De
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Hsu, Kai-Hsiang
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Patra, Jagabandhu
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Su, Ching-Yuan
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Lee, Sheng-Wei
In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2-Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 degrees C preserves a large fraction of hydrous RuO2 center dot xH(2)O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2-Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg(-1) at a power density of 8720 W kg(-1) (or 8.3 Wh L-1 at 15,000 W L-1). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO2-Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.
Local anodic oxidation kinetics of chemical vapor deposition graphene supported on a thin oxide buffered silicon template
(2013-04-01)
Chuang, Min-Chiang
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Chien, Hsiao-Mei
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Chain, Yuan-Hong
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Chi, Gou-Chung
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Lee, Sheng-Wei
Study of local anodic oxidation (LAO) of single layer graphene (SLG) supported on thin oxide buffered silicon template is reported. Centimeter scaled SLG sheet grown through chemical vapor deposition on Cu foil is transferred onto patterned silicon template covered with thin oxide steps. LAO are performed on the supported SLG through contact mode atomic force microscopy in ambient condition. LAO bumps with heights exceed physical carbon-oxygen stacking are formed on thin oxide buffered samples. Micro-Raman spectroscopy reveals the coexistence of surface graphene oxide formation and local strain near the LAO patterns. The writing speed dependence of LAO bump shows a multi-exponent behavior, indicating inhomogeneous chemical profiles involved in the LAO process. The observation points to a sequential kinetics of surface SLG oxidation prior to subsurface silicon oxide protrusion formation. Our work shows the necessity to consider oxidation of substrate through the subsurface buffer layer during nano-scaled field effect device fabrication with LAO method. The strain generation from the subsurface protrusion suggests possible tuning knob for local distortion of SLG structure. (c) 2012 Elsevier Ltd. All rights reserved.
Microstructures and electrical properties of zirconium doped barium cerate perovskite proton conductors
(2019-08-09)
Jhuang, Jhe-Wei
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Lee, Kan-Rong
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Lee, Sheng-Wei
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Chang, Jeng-Kuei
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Jang, Shian-Ching
In this work, we vary the Zr to Ce ratio to investigate the microstructures and electrical properties of zirconium doped barium cerates. The solid state reaction is used in synthesizing the BaCe0.8-xZrxY0.2O3 (X = 0.1-0.5). The electron backscatter diffraction (EBSD) is successfully applied to identify the crystal structure of the barium cerates. EBSD results indicate that all samples have the orthorhombic structure. Conductivity measurement results show that for temperatures below 700 degrees C, Zr-doped barium cerates have higher protonic conductivities than oxygen-ion/electron-hole conductivities. The protonic conductivity increases with the Zr content initially, but decreases after the Zr content is higher than 0.3. The protonic conductivity of BCZY0.3 reaches 8.8 mS/cm at 700 degrees C in dry hydrogen atmosphere. Stability test results show that, for stable operation in CO2 atmosphere, the Zr content in barium cerates should be greater than 0.2. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Nano-fibrous SrCe0.8Y0.2O3-delta-Ni anode functional layer for proton-conducting solid oxide fuel cells
(2019-10-01)
Lee, Kan-Rong
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Tseng, Chung-Jen
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Chang, Jeng-Kuei
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Wang, Kuan-Wen
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Huang, Yu-Shuo
This study presents a nanofiber-derived functional anode consisting of proton-conducting SrCe0.8Y0.2O3-delta nanofibers and electro-catalytic Ni for proton-conducting solid oxide fuel cells. Fuel cell testing with the nano fibrous SrCe0.8Y0.2O3-delta-Ni anode exhibits a maximum power density of 201.0 mW/cm(2) at 800 degrees C, which is significantly higher than those of cells with a powder-derived Ba0.8Sr0.2Ce0.6Zr0.2Y0.2O3-delta-Ni anode or a nano fibrous SrCe0.8Y0.2O3-delta anode. Its relatively lower ohmic resistance can be explained in terms of protonic and electronic "highways" throughout the nano-fibrous SrCe0.8Y0.2O3-delta-Ni anode. The significantly lower polarization resistance elements, R-1 and R-2, further indicate that the nano-fibrous SrCe0.8Y0.2O3-delta-Ni anode has superior catalytic activity for the hydrogen oxidation reaction and thus generates more protons that can participate in the cathode reactions. The results show that the performance enhancement in the fuel cell with the nano-fibrous SrCe0.8Y0.2O3-delta-Ni anode can be attributed to its low ohmic resistance, excellent electrode catalytic activity, and good gas transport property.
Nanomechanical Properties and Fracture Behaviors of Ba1-xKxCe0.6Zr0.2Y0.2O3-delta Electrolytes by Nanoindentation
(2014-08-01)
Jian, Sheng-Rui
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Lee, Sheng-Wei
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Chang, Jeng-Kuei
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Tseng, Chung-Jen
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Juang, Jenh-Yih
The nanomechanical characteristics and fracture behaviors of the Ba1-xKxCe0.6Zr0.2Y0.2O3-delta (K-doped BCZY, 0.0 <= x <= 0.15) oxides were investigated by using nanoindentation techniques. The BKCZY samples were prepared by the citrate-ethylenediaminetetraacetic acid (EDTA) complexing sol-gel process, followed by uniaxial pressure pressing and sintering at 1600 degrees C for 4 h. The XRD results indicated that the BKCZY samples occurred predominantly in perovskite-type cubic structures. The hardness and Young\'s modulus of BKCZY samples were measured by a Berkovich nanoindenter operated in continuous contact stiffness measurements (CSM) mode. Results indicated that the hardness and Young\'s modulus of BKCZY sample decreased substantially with increasing the K doping concentration, presumably due to doping-enhanced grain growth. Furthermore, the SEM observations indicated that Berkovich nanoindentation-induced fracture mode was mostly transgranular and the fracture toughness exhibited a similar doping dependence as that of the hardness and Young\'s modulus.