Browsing by Author "Juang, Jenh-Yih"

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A Comprehensive Study of One-Step Selenization Process for Cu(In1-xGax) Se-2 Thin Film Solar Cells
(2017-03-21)
Chen, Shih-Chen
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Wang, Sheng-Wen
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Kuo, Shou-Yi
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Juang, Jenh-Yih
;
Lee, Po-Tsung
In this work, aiming at developing a rapid and environmental-friendly process for fabricating CuIn1-xGaxSe2 (CIGS) solar cells, we demonstrated the one-step selenization process by using selenium vapor as the atmospheric gas instead of the commonly used H2Se gas. The photoluminescence (PL) characteristics indicate that there exists an optimal location with superior crystalline quality in the CIGS thin films obtained by one-step selenization. The energy dispersive spectroscopy (EDS) reveals that the Ga lateral distribution in the one-step selenized CIGS thin film is intimately correlated to the blue-shifted PL spectra. The surface morphologies examined by scanning electron microscope (SEM) further suggested that voids and binary phase commonly existing in CIGS films could be successfully eliminated by the present one-step selenization process. The agglomeration phenomenon attributable to the formation of MoSe2 layer was also observed. Due to the significant microstructural improvement, the current-voltage (J-V) characteristics and external quantum efficiency (EQE) of the devices made of the present CIGS films have exhibited the remarkable carrier transportation characteristics and photon utilization at the optimal location, resulting in a high conversion efficiency of 11.28%. Correlations between the defect states and device performance of the one-step selenized CIGS thin film were convincingly delineated by femtosecond pump-probe spectroscopy.
A lighting mechanism for flat electron emission lamp
(2009-03-02)
Li, Jung-Yu
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Chen, Shih-Pu
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Li, Chia-Hung
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Lin, Yi-Ping
;
Chou, Yen-I
We propose a lighting mechanism for generating uniform planar light. The device integrates electron beams induced by gas discharge with cathodoluminescence at the anode, where the spectra of the emitted light depend entirely on the phosphor materials coated on the anode. Consequently, ultraviolet is not required and the usage of mercury can be avoided. In addition, the features of double-side lighting, transparency, and gray-scale images indicate that the flat electron emission lamp might become potential candidate for the next generation green lighting source.
A Nanostructuring Method to Decouple Electrical and Thermal Transport through the Formation of Electrically Triggered Conductive Nanofilaments
(2018-07-12)
Retamal, Jose Ramon Duran
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Kang, Chen-Fang
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Lien, Der-Hsien
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Kuo, Wei-Cheng
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Juang, Zhen-Yu
Transforming thermal energy into electric energy and vice versa needs the decoupling of electrical transport from thermal transport. An innovative strategy is proposed by forming/disrupting electrically triggered conductive nanofilaments within semiconducting thin films to switch thermoelectric properties between two states without further material modification and manufacturing processes. It can also controllably adjust the degree of decoupling, providing a potential resolution and performance adjustability for heat/coldness control or power consumption reduction on demand.
Annealing-Driven Microstructural Evolution and Its Effects on the Surface and Nanomechanical Properties of Cu-Doped NiO Thin Films
(2019-02-01)
Wang, San-Ho
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Jian, Sheng-Rui
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Chen, Guo-Ju
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Cheng, Huy-Zu
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Juang, Jenh-Yih
The effects of annealing temperature on the structural, surface morphological and nanomechanical properties of Cu-doped (Cu-10 at %) NiO thin films grown on glass substrates by radio-frequency magnetron sputtering are investigated in this study. The X-ray diffraction (XRD) results indicated that the as-deposited Cu-doped NiO (CNO) thin films predominantly consisted of highly defective (200)-oriented grains, as revealed by the broadened diffraction peaks. Progressively increasing the annealing temperature from 300 to 500 degrees C appeared to drive the films into a more equiaxed polycrystalline structure with enhanced film crystallinity, as manifested by the increased intensities and narrower peak widths of (111), (200) and even (220) diffraction peaks. The changes in the film microstructure appeared to result in significant effects on the surface energy, in particular the wettability of the films as revealed by the X-ray photoelectron spectroscopy and the contact angle of the water droplets on the film surface. The nanoindentation tests further revealed that both the hardness and Young's modulus of the CNO thin films increased with the annealing temperature, suggesting that the strain state and/or grain boundaries may have played a prominent role in determining the film's nanomechanical characterizations.
Berkovich nanoindentation and deformation mechanisms in GaN thin films
(2008-01-30)
Tsai, Chien-Huang
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Jian, Sheng-Rui
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Juang, Jenh-Yih
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電子物理學系
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Department of Electrophysics
The deformation mechanisms of GaN thin films obtained by metal-organic chemical vapor deposition (MOCVD) method were studied using nanoindentation with a Berkovich diamond indenter, micro-Raman spectroscopy and the cross-sectional transmission electron microscopy (XTEM) techniques. Due to the sharpness of the tip of Berkovich indenter, the nanoindentation-induced deformation behaviors can be investigated at relatively lower load and, hence, may cover wider range of deformation-related phenomena over the same loading range. The load-displacement curves show the multiple "pop-ins" during nanoindentation loading. No evidence of nanoindentation-induced phase transformation and cracking patterns were found up to the maximum load of 300 mN, as revealed from the micro-Raman spectra and the scanning electron microscopy (SEM) observations within the mechanically deformed regions. In addition, XTEM observation performed near the cross-section of the indented area revealed that the primary deformation mechanism in GaN thin film is via propagation of dislocations on both basal and pyramidal planes. The continuous stiffness measurement (CSM) technique was used to determine the hardness and Young's modulus of GaN thin films. In addition, analysis of the load-displacement data reveals that the values of hardness and Young's modulus of GaN thin films are 19 +/- 1 and 286 +/- 25 GPa, respectively. (C) 2007 Elsevier B.V. All rights reserved.
Broadband antireflection and field emission properties of TiN-coated Si-nanopillars
(2014-08-21)
Chang, Yuan-Ming
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Ravipati, Srikanth
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Kao, Pin-Hsu
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Shieh, Jiann
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Ko, Fu-Hsiang
Broadband antireflection and field emission characteristics of silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma were systematically investigated. In particular, the effects of ultrathin (5-20 nm) titanium nitride (TiN) films deposited on Si-NPs by atomic layer deposition (ALD) on the optoelectronic properties were explored. The results showed that by coating the Si-NPs with a thin layer of TiN the antirefiection capability of pristine Si-NPs can be significantly improved, especially in the wavelength range of 1000-1500 nm. The enhanced field emission characteristics of these TiN/Si-NP heterostructures suggest that, in addition to the reflectance suppression in the long wavelength range arising from the strong wavelength-dependent refractive index of TiN, the TiN-coating may have also significantly modified the effective work function at the TiN/Si interface as well.
Broadband Omnidirectional Light Trapping in Gold-Decorated ZnO Nanopillar Arrays
(2017-04-05)
Chang, Yuan-Ming
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Lin, Man-Ling
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Lai, Tung-Yen
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Chen, Chang-Hung
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Lee, Hsin-Yi
The photoluminescence (PL) and reflectivity characteristics of zinc oxide nanopillars- (ZnO-NPs) grown on indium tin oxide (ITO)-coated glasses were investigated. The room temperature PL showed bright -white -light emission for the undoped ZnO-NPs grown at 600 degrees C, suggesting the close relation between the optical characteristic and "the growth conditions being, carried out for,obtaining the present ZnO-NPs. The reflectivity of the as -grown ZnO-NPs array was about, similar to 29% with the wavelength of the incident light ranging from 200 to 1800 nm. Nevertheless, the reflectance reduced significantly to less than 9.9% when a layer of gold (Au) was deposited on ZnO=NPg by sputtering for 5 min, corresponding to more than 65% reduction in Au -coated ZnQ-NPs (Au/ZnO-NPs). Moreover, the angle -resolved reflectance measurement's on the present Au/ZnO-NPs array show an omnidirectional light -trapping characteristic. These remarkable characteristics, broadband and omnidirectional light -trapping -of Ati/ZnO-NPs, are attributed to the extended effective optical path of the incident light due to subwavelength scattering resulting,from the presence of Au nanoparticics.
Complex Oxide-Noble Metal Conjugated Nanoparticles
(2013-04-11)
Guo, Jun-Ling
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Chiou, Yao-De
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Liang, Wen-I
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Liu, Heng-Jui
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Chen, Ying-Jiun
Hybrid nanoparticles (NPs) composed of multiple components offer new opportunities for next-generation materials. In this study, a paradigm for the noble metal/ternary complex oxide hybrid NPs is reported by adopting pulsed laser ablation in liquids. As model hybrids, gold-spinel heterodimer (Au-CoFe2O4) and gold-pervoskite heterodimer (Au-SrTiO3) NPs are investigated. This work has demonstrated the diverse playgroup of NP conjugation enlarged by complex oxides.
Cross-sectional transmission electron microscopy observations of structural damage in Al(0.16)Ga(0.84)N thin film under contact loading
(2008-02-01)
Jian, Sheng-Rui
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Juang, Jenh-Yih
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Lai, Yi-Shao
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電子物理學系
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Department of Electrophysics
This article reports a nanomechanical response study of the contact-induced deformation behavior in Al(0.16)Ga(0.84)N thin film by means of a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. Al(0.16)Ga(0.84)N thin film is deposited by using the metal-organic chemical vapor deposition method. Hardness and Young's modulus of the Al(0.16)Ga(0.84)N films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements mode. The obtained values of the hardness and Young's modulus are 19.76 +/- 0.15 and 310.63 +/- 9.41 GPa, respectively. The XTEM images taken in the vicinity just underneath the indenter tip revealed that the multiple "pop-ins" observed in the load-displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. The absence of discontinuities in the unloading segments of the load-displacement curve suggests that no pressure-induced phase transition was involved. (c) 2008 American Institute of Physics.
Cross-sectional transmission electron microscopy observations on the Berkovich indentation-induced deformation microstructures in GaN thin films
(2007-07-07)
Chien, Chi-Hui
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Jian, Sheng-Rui
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Wang, Chung-Ting
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Juang, Jenh-Yih
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Huang, J. C.
Nanoindentation-induced mechanical deformation in GaN thin films prepared by metal-organic chemical-vapour deposition was investigated using the Berkovich diamond tip in combination with the cross-sectional transmission electron microscopy (XTEM). By using focused ion beam milling to accurately position the cross-section of the indented region, the XTEM results demonstrate that the major plastic deformation was taking place through the propagation of dislocations. The present observations are in support of attributing the pop-ins that appeared in the load-displacement curves to the massive dislocation activities occurring underneath the indenter during the loading cycle. The absence of indentation-induced new phases might have been due to the stress relaxation via the substrate and is also consistent with the fact that no discontinuity was found upon unloading.
Deformation behaviors of Au nanotubes under torsion by molecular dynamics simulations
(2018-08-01)
Hwang, Yeong-Maw
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Pan, Cheng-Tang
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Lu, Ying-Xu
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Jian, Sheng-Rui
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Juang, Jenh-Yih
In this study, the mechanical deformation behaviors of Au nanotubes (Au-NTs) under torsional stress are investigated using molecular dynamics (MD) simulations. The inter-atomic interaction is modeled using the embedded-atom potential. In particular, the effects of loading rate, thickness and length of the nanotube, as well as the thermal effects were systematically explored. The results indicated that higher loading rate, longer length and thinner wall thickness all led to a larger value of critical torsional angle (theta(cr)), which signifies the onset of plastic deformation. On the other hand, theta(cr) decreases with increasing temperature in all simulated results. Moreover, the torsional buckling deformation behavior and geometrical instability are found to strongly depend on the length of Au-NTs, the applied strain rate and temperature with vastly different underlying mechanisms. (C) 2018 Author(s).
Deformation behaviors of InP pillars under uniaxial compression
(2012-10-08)
Jian, Sheng-Rui
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Sung, T. -H.
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Huang, J. C.
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Juang, Jenh-Yih
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電子物理學系
We report the deformation behavior of single-crystal InP(100) micropillars, measuring about 1 mu m in diameter and 2 mu m in height, subjected to uniaxial compression at room temperature. The engineering stress-strain results indicated that the yield strength of InP pillar is about 2.5 GPa, and the presence of a drastic strain burst right after yielding. Cross-sectional transmission electron microscopy microstructural observations reveal the formation of extremely dense twins. The results indicate that the plastic deformation in InP micropillars is dominated by explosive generation of deformation twins under the high stress state. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4758479]
Deformation mechanisms in ultrahigh-strength and high-ductility nanostructured FeMnAlC alloy
(2014-02-15)
Lin, Chih-Lung
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Chao, Chuen-Guang
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Juang, Jenh-Yih
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Yang, Jenn-Ming
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Liu, Tzeng-Feng
The deformation mechanisms of a bulk nanostructured Fe-30Mn-9.5Al-2.0C (in wt.%) alloy were investigated. After aging at 450 degrees C for 9-12 h, the alloy exhibits an exceptional strength-ductility combination (e. g. yield strength similar to 1406 MPa with elongation similar to 32%). The aged alloy exhibits a novel microstructure with isolated austenite nano-channels bounded by an extremely high volume fraction of directional nano-sized (Fe,Mn)(3)AlC carbides (kappa'-carbides). The plastic deformation was found to be dominated by bursting dislocation nucleation within the isolated austenite nano-channels. (C) 2013 Elsevier B. V. All rights reserved.
Deviatoric deformation kinetics in high entropy alloy under hydrostatic compression
(2019-07-05)
Huang, E-Wen
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Lin, Chih-Ming
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Juang, Jenh-Yih
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Chang, Yao-Jen
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Chang, Yuan-Wei
An equiatomic CoCrFeMnNi high-entropy alloy under hydrostatic compression is investigated using insitu angular-dispersive X-ray diffraction to explore the polymorphism in high entropy alloy systems. The metallic system is of face-centered-cubic structure at ambient condition and applied hydrostatic pressures up to 20 GPa via diamond anvil cell. The angle-resolved diffraction-intensity evolutions of multiple diffraction peaks were collected simultaneously to elucidate the phase stability examinations. The phase transformation from face-centered-cubic to hexagonal-close-packed structure was evidently observed in CoCrFeMnNi alloy accompanied by a deviatoric strain subjected to the hydrostatic compression. We found lattice-asymmetric crossover before and after the phase transformation subjected to hydrostatic compression surroundings. Deviatoric strain triggers fcc-hcp phase transformation as local heterogeneity-driven lattice distortion is significant for CoCrFeMnNi alloy. (c) 2019 The Authors. Published by Elsevier B.V.
Discharge and photo-luminance properties of a parallel plates electron emission lighting device
(2011-01-03)
Li, Chia-Hung
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Liu, Ming-Chung
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Chiang, Chang-Lin
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Li, Jung-Yu
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Chen, Shih-Pu
The gas discharge and photo-luminance properties of a planar lighting source featuring highly uniform light emission and mercury-free design were studied. The current density-voltage characteristics and the associated gas discharge of the devices operating with the values of the ratio of electric field to gas pressure (E/p) between 4.3 kV/Torr-cm and 35.7 kV/Torr-cm indicate that the width of the cathode fall extends over the entire gap between the two electrodes and the device is mostly in the obstructed discharge regime. The optical emission analysis confirmed the electron collision-induced gas emissions and strong effect of gas pressure on the phosphor emission when operated at constant current density, both are indicative of the primary roles played by the electron energy. (C)2011 Optical Society of America
Dislocation Energetics and Pop-Ins in AlN Thin Films by Berkovich Nanoindentation
(2013-09-01)
Jian, Sheng-Rui
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Tseng, Yu-Chin
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Teng, I-Ju
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Juang, Jenh-Yih
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電子物理學系
Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD) analyses. Instead XTEM observations suggest that these "instabilities" resulted from the sudden nucleation of dislocations propagating along the slip systems lying on the {0001} basal planes and the {10 (1) over bar1} pyramidal planes commonly observed in hexagonal compound semiconductors. Based on this scenario, an energetic estimation of dislocation nucleation is made.
Effects of Cr doping on physical properties of amorphous In-Ga-Zn-O films
(2011-09-15)
Liu, Shiu-Jen
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Su, Shih-Hao
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Fang, Hau-Wei
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Hsieh, Jang-Hsing
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Juang, Jenh-Yih
Amorphous thin films of InGaZnO(4) (a-IGZO) doped with Cr have been fabricated by using pulsed-laser deposition (PLD). The electrical, optical and magnetic properties of Cr-doped a-IGZO films grown at 25 degrees C and 150 degrees C were investigated. The conductivity, optical transmission and band gap of films are remarkably enhanced by increasing the growth temperature. Conductivity, carrier concentration and mobility decrease with increasing the Cr content. However, the optical transmission and band gap are not significantly affected by Cr doping. Moreover, all Cr-doped films exhibit room-temperature ferromagnetism. (C) 2011 Elsevier B.V. All rights reserved.
Effects of growth temperature on Mg-doped ZnO films fabricated by pulsed-laser deposition
(2017-01-01)
Fang, Hau-Wei
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Juang, Jenh-Yih
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Liu, Shiu-Jen
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材料科學與工程學系
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電子物理學系
Magnesium-doped zinc oxide (MZO) films were fabricated by pulsed-laser deposition (PLD) at various substrate temperatures (T-s). The substitution of Mg for Zn sites (Mg-Zn) in the films was confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and room-temperature photoluminescence (RTPL) measurements. Characteristic deep-level emissions (DLE) observed in the RTPL spectra further indicate the presence of Zn vacancies (V-Zn) in the MZO films. Moreover, it was found that the intensity of the blue emission corresponding to V-Zn increases with increasing T-s, indicating the important role played by T-s on the incorporation of Mg into ZnO matrix. Hall effect measurements reveal the p-type conduction of the MZO films grown at 400 degrees C. The p-type characteristic is attributed to the formation of nMg(Zn) - V-Zn complex which could act as acceptor for MZO films.
Effects of indium concentration on the efficiency of amorphous In-Zn-O/SiOx/n-Si hetero-junction solar cells
(2014-02-01)
Fang, Hau-Wei
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Hsieh, Tsung-Eong
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Juang, Jenh-Yih
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材料科學與工程學系
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電子物理學系
Semiconductor-insulator-semiconductor (SIS) hetero-junction solar cells comprising of the amorphous indium zinc oxide (a-IZO) layer directly deposited onto the n-type Si substrates by pulsed laser deposition were fabricated. Characterizations on the physical properties of the a-IZO layer and the a-IZO/SiOx interface as a function of In/(Zn + In) ratio were carried out to delineate their influences on the photovoltaic performance of SIS solar cells. The optical and electrical analyses indicated that the resistivity of a-IZO films decreased with increasing In concentration, reaching 4.5 x 10(-4) Omega-cm for In/ (Zn+In)=0.5, which also exhibited a transmittance higher than 80% in the visible-light wavelength range. Moreover, combining with an optimally controlled insulating SiOx layer (about 2.0 nm), the device exhibited excellent SIS solar cell performance with open-circuit voltage of 0.38 V, short-circuit current density of 45.1 mA cm(-2), fill factor of 49.7% and a conversion efficiency of 8.4% under the AM1.5 illumination condition. The dramatic performance enhancement was attributed to the reduction of effective interface trap densities at the a-IZO/SiOx interface and the increase of carrier mobility in the a-IZO layer resulted from the increase of In/(In+Zn) ratio. (C) 2013 Elsevier B.V. All rights reserved.
Effects of pillar size modulation on the magneto-structural coupling in self-assembled BiFeO3-CoFe2O4 heteroepitaxy
(2020-01-21)
Amrillah, Tahta
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Chen, Yu-Xun
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My Ngoc Duong
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Abdussalam, Wildan
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Simanjuntak, Firman Mangasa
The magneto-structural coupling of BiFeO3 (BFO)-CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated. A structural phase transformation of the BFO matrix was observed when the pillar size of CFO was increased to exceed 200 nm. Such structural transformation led to modification of magneto-elastic coupling behavior and magnetic anisotropy in the BFO-CFO/LAO system. The flexibility of tuning the pillar size of CFO, and hence, the strain and interfacial effect on the multiferroic system have significant application implications in these functional oxide nanocomposites.