Browsing by Author "Wang, Yi-Chung"

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An indoor light-activated 3D cone-shaped MoS2 bilayer-based NO gas sensor with PPb-level detection at room-temperature
(2019-06-07)
Chen, Yu-Ze
;
Wang, Sheng-Wen
;
Yang, Chun-Chuan
;
Chung, Chieh-Han
;
Wang, Yi-Chung
Utilization of light to boost the performance of gas sensors allows us to operate sensor devices at room temperature. Here, we, for the first time, demonstrated an indoor light-activated 3D cone-shaped MoS2 bilayer-based NO gas sensor with ppb-level detection operated at room-temperature. Large-area coneshaped (CS)-MoS2 bilayers were grown by depositing 2 nm-thick MoO3 layers on a 2'' three-dimensional (3D) cone-patterned sapphire substrate (CPSS) followed by a sulfurization process via chemical vapor deposition. Because the exposed area of MoS2 bilayers is increased by 30%, the CS-MoS2 gas sensor (GS) demonstrated excellent performance with a response of 470% and a fast response time of 25 s after exposure to 1 ppm of NO gas illuminated by ultraviolet (UV) light with a wavelength of 365 nm. Such extraordinary performance at room temperature is attributed to the enhanced light absorption because of the light scattering effect caused by the 3D configuration and photo-desorption induced by UV illumination. For NO concentrations ranging from 2 ppm down to 0.06 ppm, the CS-MoS2 GS demonstrated a stable sensing behavior with a high response and fast response time (470% and 25 s at 2 ppm NO) because of the light absorption enhanced by the 3D structure and photo-desorption under constant UV illumination. The CS-MoS2 GS exhibits a high sensitivity (189.2 R% ppm-1), allowing the detection of NO gas at 0.06 ppm in 130 s. In addition, the 3D cone-shaped structure prolonged the presence of sulfur vapor around MoO3, allowing MoO3 to react with sulfur completely. Furthermore, the CS-MoS2 GS using an indoor lighting to detect NO gas at room temperature was demonstrated for the first time where the CS-MoS2 GS exhibits a stable cycling behavior with a high response (165% at 1 ppm NO) in 50 s; for concentration as low as 0.06 ppm, the response of 75% in 150 s can be achieved.
Design and realization of a digital multiphase-interleaved VRM controller using FPGA
(2007)
Wang, Yi-Chung
;
Tzou, Ying-Yu
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Voltage Regulator Modules (VRM) are used for low-voltage, high-current dc-dc converters used for high-performance microprocessors and graphic processors. This paper describes the development of a digital PWM controller architecture in applications to multiphase-interleaved VRM. A digital current control technique with interleaved PWM generation and synchronous current sampling has been developed to improve the transient response under large load disturbances. The proposed control scheme for the interleaved multiphase buck converter employs feedback signals of output voltage, output current, and per-phase inductor current. By using a synchronous over-sampling, technique for the detection per-phase inductor current and double-edge PWM modulation technique, the current response can reach a deadbeat performance for step current command. Current sharing control is used to equalize the current of each phase converter under possible parameters mismatch. A computer simulation study has been carried out to illustrate the feasibility and performance of the proposed digital control technique.
Design of novel TiO2-SiO2 core-shell helical nanostructured anti-reflective coatings on Cu(In,Ga)Se-2 solar cells with enhanced power conversion efficiency
(2019-05-14)
Chen, Chia-Wei
;
Tsai, Hung-Wei
;
Wang, Yi-Chung
;
Su, Teng-Yu
;
Yang, Chen-Hua
Introducing an anti-reflective coating (ARC) is the last step of fabricating Cu(In,Ga)Se-2 solar cells with enhanced photo-generated current by reducing the reflectance of visible light. The use of nanostructures in ARC has been intensively investigated because this can prolong the optical path length by a scattering effect or by the formation of a refractive index gradient. Herein, we proposed the use of TiO2 helical nanostructures using glancing angle deposition (GLAD), and then synthesized SiO2 surrounding the helical nanostructures to further decrease the reflectance by producing a refractive index gradient. The optimized values of TiO2 and SiO2 thicknesses are 150 nm and 3 nm determined by the finite-difference time-domain (FDTD) simulation on Cu(In,Ga)Se-2 solar cells. The suppression of reflectance led to enhanced light absorption across a broad wavelength range, and boosted the J(SC) from 20.66 to 22.51 mA cm(-2), resulting in improved power conversion efficiency (PCE) from 6.32 to 7.00% after applying the TiO2-SiO2 core-shell nanostructures as the ARC. This 10.75% PCE enhancement suggests that the novel TiO2-SiO2 core-shell nanostructures have great potential as ARC for Cu(In,Ga)Se-2 solar cells, and it would be beneficial for development in the photovoltaic field in both research and applications.
Electrochemically active novel amorphous carbon (a-C)/Cu3P peapod nanowires by low-temperature chemical vapor phosphorization reaction as high efficient electrocatalysts for hydrogen evolution reaction
(2019-09-20)
Manikandan, Arumugam
;
Sriram, Pavithra
;
Hsu, Kun-Chieh
;
Wang, Yi-Chung
;
Chen, Chia-Wei
Toward finding low-cost electrocatalysts with high catalytic properties to replace noble metals as high efficient electrocatalysts in electrochemical hydrogen evolution reaction (HER) of total water splitting plays a vital role to approach the green and sustainable energy supply. Here, we demonstrate the direct growth of novel copper phosphide coated with amorphous carbon, namely heterostructured a-C/Cu3P peapod nanowires from chemically synthesized copper nanowires (Cu NWs) followed by a chemical vapor phosphorization reaction (CVPR) process at a low temperature of 400 degrees C. The heterostructured a-C/Cu3P peapod nanowires exhibit a superior electrocatalytic activity by a lower overpotential of 287 mV at a current density of 10 mA cm(-2) with a low Tafel slope of 72 mV dec(-1) and excellent stability over 1000 cycles. The superior electrocatalytic performance can be explained by the superior contact of the electrolyte with active sites on the heterostructured a-C/Cu3P due to the high surface area of peapod nanowire structure covered by defective edges of graphene with the encapsulated amorphous carbon layer, which can tremendously enhance electrical conductivity at the surface. (C) 2019 Published by Elsevier Ltd.
Environmentally and Mechanically Stable Selenium 1D/2D Hybrid Structures for Broad-Range Photoresponse from Ultraviolet to Infrared Wavelengths
(2018-10-17)
Chen, Yu-Ze
;
You, Yen-Ting
;
Chen, Pin Jung
;
Li, Dapan
;
Su, Teng-Yu
Selenium (Se) is one of the potential candidates as photodetector because of its outstanding properties such as high photoconductivity (similar to 8 x 10(4) S cm(-1)), piezoelectricity, thermoelectricity, and nonlinear optical responses. Solution phase synthesis becomes an efficient way to produce Se, but a contamination issue that could deteriorate the electric characteristic of Se should be taken into account. In this work, a facile, controllable approach of synthesizing Se nanowires (NWs)/films via a plasma-assisted growth process was demonstrated at the low substrate temperature of 100 degrees C. The detailed formation mechanisms of nanowires arrays to thin films at different plasma powers were investigated. Moreover, indium (In) layer was used to enhance the adhesive strength with 50% improvement on a SiO2/Si substrate by mechanical interlocking and surface alloying between Se and In layers, indicating great tolerance for mechanical stress for future wearable devices applications. Furthermore, the direct growth of Se NWs/films on a poly(ethylene terephthalate) substrate was demonstrated, exhibiting a visible to broad infrared detection ranges from 405 to 1555 nm with a high on/off ratio of similar to 700 as well as the fast response time less than 25 ms. In addition, the devices exhibited fascinating stability in the atmosphere over one month.
Fabrication of large-scale single-crystal Cu(In, Ga)Se-2 nanotip arrays solar cell by one-step ion milling processes
(2013-11-01)
Wang, Yi-Chung
;
Yen, Yu-Ting
;
Liu, Chin-Hung
;
Chen, Chia-Hsiang
;
Kuo, Wei-Chen
Template-free, one step formation of Cu(In, Ga)Se-2 (CIGS) nanotip arrays (NTRs) to enhance device efficiency were discussed. Through Ar+ ion milling process, the CIGS NTRs could be formed directly on the CIGS layer. The angles and lengths of CIGS NTRs could be precisely controlled by incident angle of Ar+ beam and milling time, respectively. Mechanisms were proposed to be a self-masking effect by Cu segregation formed at early stage confirmed by Transmission Electron Microscopy, Grazing Incidence X-ray Diffraction, Energy Dispersive Spectroscopy, and Auger Electron Spectroscopy. Measurements of devices on various KCN washing time and thickness of CdS buffer layer were reported to achieve the highest efficiency of CIGS NTRs devices. This approach provides one-step fast process without templates, easy integration with in-line sputtering process, and no post-selenizatoin process for the formation of CIGS nanostructure, which can stimulate great attention not only in academic investigations but also in industrial side for practical applications. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Non-antireflective Scheme for Efficiency Enhancement of Cu(In,Ga)Se-2 Nanotip Array Solar Cells
(2013-08-01)
Liao, Yu-Kuang
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Wang, Yi-Chung
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Yen, Yu-Ting
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Chen, Chia-Hsiang
;
Hsieh, Dan-Hua
We present systematic works in characterization of CIGS nanotip arrays (CIGS NTRs). CIGS NTRs are obtained by a one-step ion-milling process by a direct-sputtering process of CIGS thin films (CIGS TF) without a postselenization process. At the surface of CIGS NTRs, a region extending to 100 nm in depth with a lower copper concentration compared to that of CIGS TF has been discovered. After KCN washing, removal of secondary phases can be achieved and a layer with abundant copper vacancy (V-Cu) was left. Such compositional changes can be a benefit for a CIGS solar cell by promoting formation of Cd-occupied Cu sites (Cd-Cu) at the CdS/CIGS interface and creates a type-inversion layer to enhance interface passivation and carrier extraction. The raised V-Cu concentration and enhanced Cd diffusion in CIGS NTRs have been verified by energy dispersive spectrometry. Strengthened adhesion of Al:ZnO (AZO) thin film on CIGS NTRs capped with CdS has also been observed in SEM images and can explain the suppressed series resistance of the device with CIGS NTRs. Those improvements in electrical characteristics are the main factors for efficiency enhancement rather than antireflection.
Resistive switching of Au/ZnO/Au resistive memory: an in situ observation of conductive bridge formation
(2012-10-08)
Peng, Chung-Nan
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Wang, Chun-Wen
;
Chan, Tsung-Cheng
;
Chang, Wen-Yuan
;
Wang, Yi-Chung
A special chip for direct and real-time observation of resistive changes, including set and reset processes based on Au/ZnO/Au system inside a transmission electron microscope (TEM), was designed. A clear conducting bridge associated with the migration of Au nanoparticles (NPs) inside a defective ZnO film from anode to cathode could be clearly observed by taking a series of TEM images, enabling a dynamic observation of switching behaviors. A discontinuous region (broken region) nearby the cathode after reset process was observed, which limits the flow of current, thus a high resistance state, while it will be reconnected to switch the device from high to low resistance states through the migration of Au NPs after set process. Interestingly, the formed morphology of the conducting bridge, which is different from the typical formation of a conducting bridge, was observed. The difference can be attributed to the different diffusivities of cations transported inside the dielectric layer, thereby significantly influencing the morphology of the conducting path. The current TEM technique is quite unique and informative, which can be used to elucidate the dynamic processes in other devices in the future.
Single-chip FPGA implementation of a digital VRM controller with interlaced sampling and control technique
(2007)
Lin, Yu-Tzung
;
Wang, Yi-Chung
;
Tzou, Ying-Yu
;
電控工程研究所
;
Institute of Electrical and Control Engineering
This paper presents the design and implementation of a singe-chip FPGA based digital VRM controller for multi-phase synchronous buck converters with interlaced current sampling and load current feed-forward compensation techniques. The sampling of the inductor current is synchronized with the middles of leading and trailing edges of the PWM signal of each synchronous buck converter for both turn-on and turn-off. The proposed sampling scheme has a high noise immunity to the common-mode switching noises induced by the switching of the MOSFET and its parasitic junction capacitances resulted by the heat sink. A true average current signal with minimum response time can be measured with accuracy within a switching period. The timing clocks for the digital controller and the digital PWM generator are interlaced with each other to achieve a minimum delay at a same sampling and switching frequency. A digital interface is designed for the connected microprocessor load to adjust the output voltage and provide feed-forward load current compensation according to its clock rate, loading factor, and pipeline scheduling. The realization scheme for the proposed digital VRM controller has been described. Simulation analysis and experimental verifications are given to illustrate the fast dynamic response control of VRM for advanced microprocessors.
Wafer Scale Phase-Engineered 1T-and 2H-MoSe2/Mo Core-Shell 3D-Hierarchical Nanostructures toward Efficient Electrocatalytic Hydrogen Evolution Reaction
(2016-11-23)
Qu, Yindong
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Medina, Henry
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Wang, Sheng-Wen
;
Wang, Yi-Chung
;
Chen, Chia-Wei
The necessity for new sources for greener and cleaner energy production to replace the existing ones has been increasingly growing in recent years. Of those new sources, the hydrogen evolution reaction has a large potential. In this work, for the first time, MoSe2/Mo core-shell 3D-hierarchical nanostructures are created, which are derived from the Mo 3D-hierarchical nanostructures through a low-temperature plasma-assisted selenization process with controlled shapes grown by a glancing angle deposition system.