Browsing by Author "Lin, Yan-Gu"

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Deep-Ultraviolet Photodetectors Based on Epitaxial ZnGa(2)O(4 )Thin Films
(2018-09-19)
Tsai, Si-Han
;
Basu, Sarbani
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Huang, Chiung-Yi
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Hsu, Liang-Ching
;
Lin, Yan-Gu
A single-crystalline( )ZnGn(2)O(4) ( )epilayer was successfully grown on c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition. This epilayer was used as a ternary oxide semiconductor for application in high-performance metal-semiconductor-metal photoconductive deep-ultraviolet (DUV) photodetectors (PDs). At a bias of 5V, the annealed ZnGn(2)O(4) PDs showed better performance with a considerably low dark current of 1 pA, a responsivity of 86.3 A/W, cut-off wavelength of 280 nm, and a high DUV-to-visible discrimination ratio of approximately 10(7) upon exposure to 230 nm DUV illumination than that of as-grown ZnGn(2)O(4 )PDs. The as-grown PDs presented a dark current of 0.5 mA, a responsivity of 2782 A/W at 230 nm, and a photo-to-dark current contrast ratio of approximately one order. The rise time of annealed PDs was 0.5 s, and the relatively quick decay time was 0.7 s. The present results demonstrate that annealing process can reduce the oxygen vacancy defects and be potentially applied in ZnGn(2)O(4) film-based DUV PD devices, which have been rarely reported in previous studies.
Effect of Postdeposition Annealing Temperatures on Electrical Characteristics of Molecular-Beam-Deposited HfO2 on n-InAs/InGaAs Metal-Oxide-Semiconductor Capacitors
(2012-02-01)
Trinh, Hai-Dang
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Lin, Yueh-Chin
;
Wang, Huan-Chung
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Chang, Chia-Hua
;
Kakushima, Kuniyuki
The electrical characteristics of molecular-beam-deposited HfO2/n-InAs/InGaAs metal-oxide-semiconductor capacitors with different postdeposition annealing (PDA) temperatures (400-550 degrees C) are investigated. Results show that the sample with the PDA temperature of 500 degrees C exhibits the best capacitance-voltage (C-V) behavior with small frequency dispersion and small hysteresis. The X-ray photoelectron spectroscopy (XPS) spectra show the reduction of the amount of As-related oxides to below the XPS detection level when the PDA temperature is up to 500 degrees C. As the PDA temperature was increased to above 500 degrees C, As and In atoms seem to diffuse significantly into HfO2, resulting in the degradation of C-V behavior. (C) 2012 The Japan Society of Applied Physics
Effective hydrogenation of TiO2 photocatalysts with CH3OH for enhanced water splitting: A computational and X-ray study
(2019-09-15)
Wang, Tsai-Te
;
Raghunath, Putikam
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Lin, Yu-Chang
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Lin, Yan-Gu
;
Lin, Ming-Chan
We have investigated computationally and experimentally the efficacy of CH3OH treatment of anatase TiO2 nanoparticles (NPs) and compared the results obtained with H-2 as the hydrogenation source. The results indicate that TiO2 NPs heated at 300 degrees C in 120 Torr of CH3OH vapor is more effective than the samples heated under 800 Torr of H-2 at the same temperature. Ultraviolet-visible spectroscopy (UV-VIS), Photoluminescence spectroscopy (PL) and X-ray diffraction spectroscopy (XRD) were employed to study the optical property. The effect of temperature of hydrogenation has been systematically studied for NPs in the 200-450 degrees C range for both H-sources based on H-2 evolution, employing Xe lamp as the light source. The hydrogenated TiO2 NPs using H-2 and CH3OH have been analyzed by soft X-ray absorption near-edge structure analyses with and without Xe lamp irradiation in situ. The result indicates that CH3OH hydrogenation can induce a much stronger Ti-O interaction along direction d(z)(2) and increase the unoccupied DOS of Ti t(2g) states. This is why the CH3OH treated TiO2 exhibits a greater photo-activity. The crucial role of the hydrogenation using CH3OH was also investigated systematically and confirmed by quantum-chemical calculations with complementary synchrotron-based X-ray techniques. The results are consistent with the predicted barriers for the formation of H atoms on the TiO2 surface, 4-9 kcal/mol, considerably lower than that in the H-2 case, 48 kcal/mol.
Efficient hydrogen production using Cu-based catalysts prepared via homogeneous precipitation
(2009)
Lin, Yu-Kai
;
Su, Yi-Han
;
Huang, Yun-Hsin
;
Hsu, Chia-Jung
;
Hsu, Yu-Kuei
We report here preparation of multi-composition Cu/ZnO/Al(2)O(3) (CZA) catalyst by homogeneous precipitation (HP) method using urea treatment. Compared to the conventional co-precipitation (CP) method, the HP method used here improves the uniformity of metal mixing through homogeneous generation of hydroxide ions as a result of hydrolysis of urea in the solution. In this study, optimization of the conditions to prepare CZA catalyst was achieved by adjusting the urea concentration, amount of water, reaction temperature and reaction time; to control the pH value. The HP-derived CZA particles exhibited a characteristic flower-like morphology with a higher surface area, typically 78.5 m(2)/g as measured by the BET analysis, as compared to the CP-derived CZA catalysts. Induction coupled plasma and energy dispersive spectroscopy mapping results further confirmed the homogeneity of HP-CZA components and highly uniform dispersion of the active metal. Significantly lowering and a narrower range of the reduction temperature for HP-CZA is observed. An improved performance in methanol reforming reaction, in terms of methanol conversion, yield of hydrogen production, and higher carbon dioxide selectivity, has been achieved. Furthermore, the concentration of carbon monoxide can be further reduced by employing CeO(2) and ZrO(2) to modify the support, which also results in reduced reduction temperature and improved performance. Among the modified catalysts, HP-CZCZ catalyst showed the highest methanol conversion and rate of hydrogen production, simultaneously with reduced concentration of CO. Moreover, only 20 mg of catalyst loading yielded 98% methanol conversion rate under more than 8500 h(-1) GHSV. In future, not only can this method be used to synthesize other multi-composition materials with high homogeneity, but also our approach presents opportunity for production of a highly active catalyst for efficient generation of hydrogen for fuel cell applications.
Electrodeposited Fe2TiO5 nanostructures for photoelectrochemical oxidation of water
(2016-09-20)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
Electrodeposition was used to fabricate nanostructured films of Ti-containing hematite for application to the photoelectrochemical (PEC) splitting of water. The morphology and microstructure of Ti-doped hematite were examined with a scanning electron microscope, X-ray diffraction, Raman spectra and X-ray photoelectron spectra. Optical absorption spectra indicated an enhanced light absorbance in Ti-doped hematite. This Ti doping increased the carrier concentration about ten-fold, confirmed with a Mott-Schottky analysis. The prepared Ti-doped hematite showed a photocurrent enhanced four-fold relative to pristine hematite. Synchrotron-based soft X-ray absorption spectra clearly revealed that a local Fe2TiO5 structure in hematite formed a heterojunction, which decreased the accumulation of photogenerated holes and improved the performance. (C) 2016 Elsevier Ltd. All rights reserved.
Electrodeposited Fe2TiO5 nanostructures for photoelectrochemical oxidation of water
(2016-09-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
Electrodeposition was used to fabricate nanostructured films of Ti-containing hematite for application to the photoelectrochemical (PEC) splitting of water. The morphology and microstructure of Ti-doped hematite were examined with a scanning electron microscope, X-ray diffraction, Raman spectra and X-ray photoelectron spectra. Optical absorption spectra indicated an enhanced light absorbance in Ti-doped hematite. This Ti doping increased the carrier concentration about ten-fold, confirmed with a Mott-Schottky analysis. The prepared Ti-doped hematite showed a photocurrent enhanced four-fold relative to pristine hematite. Synchrotron-based soft X-ray absorption spectra clearly revealed that a local Fe2TiO5 structure in hematite formed a heterojunction, which decreased the accumulation of photogenerated holes and improved the performance. (C) 2016 Elsevier Ltd. All rights reserved.
Electrophoretic deposition of PtRu nanoparticles on carbon nanotubes for methanol oxidation
(2009-02-01)
Hsu, Yu-Kuei
;
Yang, Ju-Lan
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Lin, Yan-Gu
;
Chen, San-Yuan
;
Chen, Li-Chyong
Electrophoretic deposition technique was successfully utilized to deposit the PtRu nanoparticles on carbon nanotubes, which were directly grown on carbon cloths (CNTs/CC). We applied an external dc field to drive the PtRu nanoparticles. which were surrounded by negatively charged glycolate in an ethylene glycol process, toward the positively biased CNTs. Systematic studies to achieve optimal size and loading amount by varying the bias potential and deposition time have been carried out. An average PtRu particle size of 2.08 nm with catalytic activity of 1.6 A/cm(2)/mg in electro-oxidation methanol could be achieved, which is highly desirable for fuel cell applications. (C) 2008 Published by Elsevier B.V.
Hierarchical Fe2O3 nanotube/nickel foam electrodes for electrochemical energy storage
(2016-10-20)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
An iron-oxide (Fe2O3) nanotube (NT) array is grown directly as a hierarchical nanoarchitecture on a nickel-foam (NF) surface via a simple and cost-effective immersive process. The morphology and microstructure of Fe2O3 NT arrays are systematically examined by scanning electron, transmission electron, Raman, and X-ray photoelectron spectroscopies. The results reveal that the walls of Fe2O3 NT are composed mainly of agglomerated small alpha-Fe2O3 (hematite) monocrystalline nanoparticles filled with a few ZnO monocrystalline particles. The microstructural influence on the pseudocapacitive performance of the obtained Fe2O3 NT/NF electrodes is also investigated via in-situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in-situ XAS results regarding charge storage mechanisms of the Fe2O3 NT/NF electrodes show that a Li+ can reversibly insert/desert into/from the 3D mesoporous textures between the Fe2O3 subunits depending on the applied potential. The electrochemical results indicate that the Fe2O3 NT/NF electrode shows highly reversible features and satisfactory rate abilities. Most significantly, the excellent specific capacitance achieved in Fe2O3 NT/NF nanoelectrodes is as great as 300.1 Fg(-1); energy density 75 W h kg(-1) and power density 4.5 kW kg(-1) are obtained, and the Fe2O3 NT/NF nanoelectrode has acceptable cycling stability after 3000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.
Hierarchical Fe2O3 nanotube/nickel foam electrodes for electrochemical energy storage
(2016-10-20)
Lin, Yan-Gu
;
Hsu, Yu-Kuei
;
Lin, Yu-Chang
;
Chen, Ying-Chu
;
材料科學與工程學系
An iron-oxide (Fe2O3) nanotube (NT) array is grown directly as a hierarchical nanoarchitecture on a nickel-foam (NF) surface via a simple and cost-effective immersive process. The morphology and microstructure of Fe2O3 NT arrays are systematically examined by scanning electron, transmission electron, Raman, and X-ray photoelectron spectroscopies. The results reveal that the walls of Fe2O3 NT are composed mainly of agglomerated small alpha-Fe2O3 (hematite) monocrystalline nanoparticles filled with a few ZnO monocrystalline particles. The microstructural influence on the pseudocapacitive performance of the obtained Fe2O3 NT/NF electrodes is also investigated via in-situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in-situ XAS results regarding charge storage mechanisms of the Fe2O3 NT/NF electrodes show that a Li+ can reversibly insert/desert into/from the 3D mesoporous textures between the Fe2O3 subunits depending on the applied potential. The electrochemical results indicate that the Fe2O3 NT/NF electrode shows highly reversible features and satisfactory rate abilities. Most significantly, the excellent specific capacitance achieved in Fe2O3 NT/NF nanoelectrodes is as great as 300.1 Fg(-1); energy density 75 W h kg(-1) and power density 4.5 kW kg(-1) are obtained, and the Fe2O3 NT/NF nanoelectrode has acceptable cycling stability after 3000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.
KSCN-activation of hydrogenated NiO/TiO2 for enhanced photocatalytic hydrogen evolution
(2020-05-01)
Wang, Tsai-Te
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Chiang, Chao-Lung
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Lin, Yu-Chang
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Srinivasadesikan, Venkatesan
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Lin, Ming-Chang
It was investigated the efficiency of hydrogen production from NiO-loaded TiO2 treated by methanol hydrogenation and functionalized by SCN ligand (SCN-M:(NiO/TiO2)). The effects of a p-n junction created between NiO and TiO2 were demonstrated to enhance significantly the overall photocatalytic performance. The optical and microstructural properties of SCN-M:(NiO/TiO2) were studied with ultraviolet-visible spectra (UV-Vis), photoluminescence (PL), Raman spectra, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS). The atomic and electronic configurations of SCN-M:(NiO/TiO2) were investigated with analysis of the X-ray absorption near-edge structure (XAS) in situ under irradiation with Xe lamp incorporating a filter (AM 1.5G). An effective quantum yield of 1.34% for hydrogen production was attained with SCN-M:(NiO/TiO2). Quantum-chemical calculations revealed a synergistic decrease of the band gap upon loading Ni, Ni-linked O-2 and anionic SCN-ligand binding. The optimal energy bandgap was decreased to 2.70 eV for (SCN/O-2)-3Ni@TiO2, which reasonably supported the enhancement of H-2 evolution.
Microwave-activated CuO nanotip/ZnO nanorod nanoarchitectures for efficient hydrogen production
(2011)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Chen, Li-Chyong
;
Chen, Kuei-Hsien
Microwave treatment of CuO nanotip/ZnO nanorod catalyst precursors has been demonstrated to remarkably enhance their activity in methanol reforming reactions. Studies using XRD, Raman, XPS, XAS, and HRTEM analyses conclude that comparative to conventional heating, microwave treatment significantly enhances the activity and stability of the catalysts, which might be attributed to defect and microstrain formation and strong metal support interaction at the Cu/ZnO interface.
N,P co-coordinated Fe species embedded in carbon hollow spheres for oxygen electrocatalysis
(2019-06-28)
Zhu, Xiaofeng
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Tan, Xin
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Wu, Kuang-Hsu
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Chiang, Chao-Lung
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Lin, Yu-Chang
The increasing interest in fuel cell technology and metal-air batteries has led to the need for stable and effective catalyst materials to replace noble metal (such as Pt) based benchmarks for the oxygen reduction reaction (ORR). In this study, carbon hollow spheres with highly dispersed nitrogen and phosphorus co-coordinated iron atoms (FeNPC) on their surface have been successfully fabricated, exhibiting exceptional ORR activity in both alkaline and acidic solutions. Specifically, the obtained FeNPC catalyst is capable of catalyzing the ORR with an onset potential of 1.03 V and a half-wave potential of 0.88 V (both vs. the reversible hydrogen electrode) in alkaline solution, outperforming the commercial Pt/C catalyst under identical conditions. Experimental results and theoretical simulations reveal that the quasi-octahedral O-2-FeNxPy species are the active sites of the FeNPC composite. These species modify the electronic configuration of Fe centers and weaken the adsorption of the OH* intermediate, thereby promoting the ORR process. Additionally, the FeNPC catalyst also displays a catalytic activity towards the anodic oxygen evolution reaction (OER), making it an active air electrode catalyst in rechargeable Zn-air batteries with a high peak power density of 233.2 mW cm(-2) and an excellent cycling stability at 3 mA cm(-2) for over 15 h.
Nanostructured Zinc Oxide Nanorods with Copper Nanoparticles as a Microreformation Catalyst
(2009)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Lin, Yu-Kai
;
Chen, Li-Chyong
Nitrogen-Doped Graphene Quantum Dots for Remarkable Solar Hydrogen Production
(2020-06-22)
Tsai, Kai-An
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Hsieh, Ping-Yen
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Lai, Ting-Hsuan
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Tsao, Chun-Wen
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Pan, Hui
We synthesized nitrogen (N)-doped graphene quantum dots (N-GQDs) using a top-down hydrothermal cutting approach. The concentration of N dopants was readily controlled by adjusting the concentration of the N source of urea. When N dopants were incorporated into GQDs, visible absorption was induced by C-N bonds, which created another pathway for generating photoluminescence (PL). Time-resolved PL data revealed that the carrier lifetime of GQDs was increased upon doping with the optimized N concentration. The photoelectrochemical properties of N-GQDs toward water splitting were studied, and the results showed that 2N-GQDs prepared with 2 g of urea produced the highest photocurrent. The photocatalytic activity of 2N-GQDs powder photocatalyst for hydrogen production was also examined under AM 1.5G illumination, showing substantial enhancement over that of pristine GQDs. Electrochemical impedance spectroscopy data further revealed a significant improvement in charge dynamics and reaction kinetics and an increased carrier concentration as a result of N doping.
O(2) plasma-activated CuO-ZnO inverse opals as high-performance methanol microreformer
(2010-01-01)
Lin, Yan-Gu
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Hsu, Yu-Kuei
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Chen, San-Yuan
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Chen, Li-Chyong
;
Chen, Kuei-Hsien
We report the use of oxygen vacancy-rich CuO-ZnO inverse opals to strikingly enhance the performance of catalytic methanol reforming reaction with a ratio of 1 : 0.125 : 1 (H(2)O/O(2)/MeOH) at a low reaction temperature of only 230 degrees C, yielding complete conversion of methanol, high hydrogen production rate, ultralow CO formation, and outstanding stability.
O-2 plasma-activated CuO-ZnO inverse opals as high-performance methanol microreformer
(2010-01-01)
Lin, Yan-Gu
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Hsu, Yu-Kuei
;
Chen, San-Yuan
;
Chen, Li-Chyong
;
Chen, Kuei-Hsien
We report the use of oxygen vacancy-rich CuO-ZnO inverse opals to strikingly enhance the performance of catalytic methanol reforming reaction with a ratio of 1 : 0.125 : 1 (H2O/O-2/MeOH) at a low reaction temperature of only 230 degrees C, yielding complete conversion of methanol, high hydrogen production rate, ultralow CO formation, and outstanding stability.
Reversible phase transformation of MnO(2) nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy
(2011-01-01)
Hsu, Yu-Kuei
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Chen, Ying-Chu
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Lin, Yan-Gu
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Chen, Li-Chyong
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Chen, Kuei-Hsien
The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na(+) between MnO(2) nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na(+) diffusion process in MnO(2) nanosheets and cause phase retention during the self-discharge process.
Reversible phase transformation of MnO2 nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy
(2011-01-01)
Hsu, Yu-Kuei
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Chen, Ying-Chu
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Lin, Yan-Gu
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Chen, Li-Chyong
;
Chen, Kuei-Hsien
The reversible phase transformation is reported from hexagonal to monoclinic structure responding to the intercalation/deintercalation of Na+ between MnO2 nanosheets upon potential cycling in aqueous electrolyte via an in situ Raman technique. This structural evolution will influence the Na+ diffusion process in MnO2 nanosheets and cause phase retention during the self-discharge process.
Room-temperature fabrication of Cu nanobrushes as an effective surface-enhanced Raman scattering substrate
(2016)
Hsu, Yu-Kuei
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Chen, Zhong-Bo
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Lin, Yu-Chang
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Chen, Ying-Chu
;
Chen, San-Yuan
A facile route to manufacture an active surface-enhanced Raman-scattering (SERS) substrate based on brush-like Cu nanostructures directly grown on a Cu foil at 23 degrees C was systematically investigated. A hierarchical Cu nanobrush substrate was fabricated in two cycles of electro-oxidation and chemical reduction in sequence; Cu(OH)(2) nanowires (NW) were formed on electro-oxidation, and converted on chemical reduction to Cu NW. Two cycles of this process achieved a brush-like Cu nanostructure; its structure, morphology and composition were examined by XRD, SEM, HRTEM and XPS, respectively. With 4-mercaptobenzoic acid (4-MBA) and chlorothalonil as probe molecules, the SERS experiments showed that the brush-like Cu nanostructures exhibit excellent detection performance, which could serve as effective SERS substrates for ultrasensitive detection. This novel hierarchical SERS substrate shows satisfactory reproducibility and a linear dependence between the analyte concentration and intensity, revealing the advantage of this method for easily scaled production.
Sandwich-Nanostructured n-Cu2O/AuAg/p-Cu2O Photocathode with Highly Positive Onset Potential for Improved Water Reduction
(2019-10-23)
Lin, Yu-Chang
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Hsu, Liang-Ching
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Lin, Chia-Yu
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Chiang, Chao-Lung
;
Chou, Che-Min
An n-Cu2O layer formed a high-quality buried junction with p-Cu2O to increase the photovoltage and thus to shift the turn-on voltage positively. Mott-Schottky measurements confirmed that the improvement benefited from a positive shift in flat-band potential. The obtained extremely positive onset potential, 0.8 V-RHE in n-Cu2O/AuAg/p-Cu2O, is comparable with measurements from water reduction catalysts. The AuAg alloy sandwiched between the homo-junction of n-Cu2O and p-Cu2O improved the photocatalytic performance. This alloy both served as an electron relay and promoted electron-hole pair generation in nearby semiconductors; the charge transfer between n-Cu2O and p-Cu2O in the sandwich structure was measured with X-ray absorption spectra. The proposed sandwich structure can be considered as a new direction for the design of efficient solar-related devices.