Browsing by Author "Huang, J. C."

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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 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]
Designing novel lightweight, high-strength and high-plasticity Ti-x(AlCrNb)(100-x) medium-entropy alloys
(2020-02-01)
Liao, Y. C.
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Li, T. H.
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Tsai, P. H.
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Jang, J. S. C.
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Hsieh, K. C.
Due to the demand for reduced energy consumption by transportation vehicles, lighter weight high-entropy alloys (with density comparable to that of commercial Ti alloys around 4.5-5 g/cm(3)) are attracting more attention in terms of alloy design and application as structural materials. In this study, a nonequiatomic quaternary alloy system, Ti-x(AlCrNb)(100-x), was designed through the calculation of phase diagrams. Simulation results reveal that a single body-centered cubic (BCC) phase can be formed and can be stable at temperatures above 950 degrees C. Accordingly, a series of Ti-x(AlCrNb)(100-x), (x = 45-80) alloys containing a BCC structure were prepared through vacuum arc melting and rapid cooling. The designed alloys can exhibit desirable mechanical properties with high compression yield strength about 1500 MPa, high compression fracture strength about 1800 MPa and high compression plasticity more than 30% at room temperature. Moreover, the Ti65 alloy can demonstrate a tensile strength of 1200 MPa with a tensile elongation of 32%, after a homogenization treatment for 24 h. The specific compression and tensile strength can reach 0.36 and 0.24 GPa cm(3)/g.
Dual heterogeneous structures lead to ultrahigh strength and uniform ductility in a Co-Cr-Ni medium-entropy alloy
(2020-05-13)
Du, X. H.
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Li, W. P.
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Chang, H. T.
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Yang, T.
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Duan, G. S.
Alloys with ultra-high strength and sufficient ductility are highly desired for modern engineering applications but difficult to develop. Here we report that, by a careful controlling alloy composition, thermomechanical process, and microstructural feature, a Co-Cr-Ni-based medium-entropy alloy (MEA) with a dual heterogeneous structure of both matrix and precipitates can be designed to provide an ultra-high tensile strength of 2.2GPa and uniform elongation of 13% at ambient temperature, properties that are much improved over their counterparts without the heterogeneous structure. Electron microscopy characterizations reveal that the dual heterogeneous structures are composed of a heterogeneous matrix with both coarse grains (10 similar to 30 mu m) and ultra-fine grains (0.5 similar to 2 mu m), together with heterogeneous L1(2)-structured nanoprecipitates ranging from several to hundreds of nanometers. The heterogeneous L1(2) nanoprecipitates are fully coherent with the matrix, minimizing the elastic misfit strain of interfaces, relieving the stress concentration during deformation, and playing an active role in enhanced ductility. Improving both strength and ductility simultaneously in structural metals and alloys remains a challenge. Here, the authors design a heterogeneous structure in a Co-Cr-Ni alloy that results in ultrahigh strength and significant uniform elongation.
Enhanced electrical behavior from the galvanic effect in Ag-Cu alloy electrode conductive bridging resistive switching memory
(2018-07-30)
Tseng, Yi-Ting
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Chen, I-Chieh
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Chang, Ting-Chang
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Huang, J. C.
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Shih, Chih-Cheng
In this study, an Ag-Cu alloy was chosen as the electrode in conductive bridging random access memory (CBRAM), with results indicating a significant decrease in forming voltage. In addition, resistive switching characteristics as well as a retention test indicated better stability and a resistive switching window of at least an order, The switching time of the Ag-Cu alloy CBRAM is shorter than that of both Ag and Cu electrode CBRAMs under fast current-voltage (fast I-V). The experimental result indicated that the mechanism was dominated by the galvanic effect. Active atoms (Ag) captured electrons of inactive atoms (Cu) and generated metallic ions (Cu ions) in the alloy electrode, Cu ions drifted into the insulator and generated a conductive path when applying voltage bias, The use of this alloy as an electrode in CBRAM can significantly decrease forming voltage and enhance CBRAM characteristics. Published by AIP Publishing.
Hybrid Dendrimer/Semiconductor Nanostructures with Efficient Energy Transfer via Optical Waveguiding
(2015-03-05)
Lin, T. N.
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Huang, J. C.
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Shen, J. L.
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Chu, C. M.
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Yeh, J. M.
In this study, we demonstrated a nonradiative energy transfer between InGaN quantum wells (QWs) and polyamidoamine (PAMAM) dendrimers through optical waveguiding by detecting a reduction in the photoluminescence lifetime. The maximum energy transfer efficiency of this system is similar to 72%, which is promising for sensor applications. The energy transfer efficiency depends on the distance between the InGaN QWs and PAMAM dendrimers by a factor of 1/d(2), revealing layer-to-layer dipole interactions. Upon increasing the generation of PAMAM dendrimers, the transfer energy efficiency increases exponentially, which can be explained by the increased surface coverage for the higher generation.
Interfacial reactions of Pt-based Schottky contacts on nGaP
(2008-02-25)
Chu, L. H.
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Chang, E. Y.
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Wu, Y. H.
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Huang, J. C.
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Chen, Q. Y.
We have investigated the interfacial reaction between platinum and InGaP in a Schottky diode structure. There was a 7.5-nm-thick amorphous layer formed at the interface between Pt and InGaP after metal deposition. After annealing at 325 degrees C for 1 min, this amorphous layer increased to 12.8 nm and the reverse leakage current also decreased. The diffusion of Pt atoms and the crystallization of amorphous layer took place after annealing at 325 degrees C for 10 min. Prolonging the annealing to 3 h led to formation of Ga(2)Pt and GaPt(3) phases in InGaP and Schottky diodes degraded after these new phases were observed. (C) 2008 American Institute of Physics.
Microstructure and elastic modulus evolution of TiTaNb alloys
(2018-10-01)
Wei, T. Y.
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Huang, J. C.
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Chao, Chih-Yeh
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Wei, L. L.
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Tsai, M. T.
In order to develop Ti based alloys with promising biocompatibility and matching mechanical response wit} human bone, TiTaNb alloys with 15, 23 and 30 mass% Ta are designed and systematically examined in terms 01 microstructural evolution and mechanical response. The Ti-30mass%Ta-10mass%Nb is demonstrated to be sa tisfactory with an elastic modulus similar to 60 GPa, hardness similar to 3.1 GPa, and strength similar to 1250 MPa. The evolution trenc of the resulting microstructure and phases as a function of Ta content and annealing temperature are established The relationship between the various phase amounts and alloy moduli is explored.
Nanoindentation-Induced Structural Deformation in GaN/AIN Multilayers
(2010-12-01)
Jian, Sheng-Rui
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Juang, Jenh-Yih
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Chen, Nie-Chuan
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Jang, Jason S. -C.
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Huang, J. C.
The mechanical responses of GaN/AIN multilayers grown on Si(111) substrates by using the metal-organic vapor phase epitaxy (MOVPE) were investigated by combining the Berkovich nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. The prominent mechanical parameters such as the hardness and Young's modulus of GaN/AIN multilayers were obtained to be 21.6 +/- 0.8 GPa and 285.7 +/- 12.1 GPa, respectively by operating the Berkovich nanoindenter with the continuous contact stiffness measurements (CSM) mode. The structural deformation behaviors were delineated by XTEM observations taken in the vicinity regions just underneath the indenter tip. It was revealed that the "pop-ins" observed in the load displacement curve during loading are due primarily to the activities of dislocation nucleation and propagation. There is no evidence of either phase transformation or micro-crack formation observed in XTEM images of GaN/AIN multilayers, which is consistent with no distinct "pop-out" event displayed in unloading curves.
The nanoindentation responses of nickel surfaces with different crystal orientations
(2007)
Ju, S. -P.
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Wang, C. -T.
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Chien, C. -H.
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Huang, J. C.
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Jian, S. -R.
Molecular dynamics (MD) simulations are applied to elucidate the anisotropic characteristics in the material responses for crystallographic nickel substrates with (100), (110) and (111) surface orientations during nanoindentation, compensating for the experimental limitation of nanoindentation-particularly for pure nickel substrates of three crystallographic orientations. This study examines several factors under indentation: three-dimensional phases of plastic deformation which correspond to atomic stress distributions, pile-up patterns at maximum indentation depth, and extracted material properties at different crystallographic orientations. The present results reveal that the strain energy of the substrate exerted by the tip is stored by the formation of the homogeneous nucleation, and is dissipated by the dislocation sliding of the {111} plane. The steep variations of the indentation curve from the local peak to the local minimums are affected by the numbers of slip angle of {111} sliding plane. The pile-up patterns of the three nickel substrates prove that the crystalline nickel materials demonstrate the pile-up phenomenon from nanoindentation on the nano-scale. The three crystallographic nickel substrates exhibit differing amounts of pile-up dislocation spreading at different crystallographic orientations. Finally, the effects of surface orientation in material properties of FCC nickel material on the nano-scale are observable through the slip angle numbers of {111} sliding planes which influence hardness values, as well as the cohesive energy of different crystallographic surfaces that indicate Young's modulus.