Browsing by Author "Jian, Sheng-Rui"

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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.
Atomistic modeling of dislocation activity in nanoindented GaAs
(2006-11-15)
Jian, Sheng-Rui
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Fang, Te-Hua
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Chuu, Der-San
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Ji, Liang-Wen
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電子物理學系
The mechanical behavior of GaAs was investigated by nanoindentation with the aid of molecular dynamics (MD) analysis based on the Tersoff potential. Particular attention was devoted to the evolution characterization of dislocation activity during deformation. The transition from elastic-to-plastic deformation behavior was clearly observed as a sudden displacement excursion occurring during the load-displacement curves of larger loads (single pop-in), faster impact velocity and higher temperature (multiple pop-ins). Even for an ultra-small penetration depth (< 3 nm), the MD simulation shows that GaAs deforms plastically and a good description is given in the results. The plastic deformation occurs due to the anticipated change in the twinning and/or dislocation motion. Dislocation nucleations occurred inside the material near the top of the surface and generated loops in the {111} slip planes. The MD analysis of the deformation behavior shows an agreement with that of previous atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments. (c) 2006 Elsevier B.V. All rights reserved.
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.
Cathodoluminescence and cross-sectional transmission electron microscopy studies for deformation behaviors of GaN thin films under Berkovich nanoindentation
(2008-04-01)
Jian, Sheng-Rui
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Teng, I-Ju
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Lu, Jian-Ming
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材料科學與工程學系
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Department of Materials Science and Engineering
In this study, details of Berkovich nanoindentation-induced mechanical deformation mechanisms of metal-organic chemical-vapor deposition-derived GaN thin films have been systematic investigated with the aid of the cathodoluminescence (CL) and the cross-sectional transmission electron microscopy (XTEM) techniques. The multiple "pop-in" events were observed in the load-displacement (P-h) curve and appeared to occur randomly by increasing the indentation load. These instabilities are attributed to the dislocation nucleation and propagation. The CL images of nanoindentation show very well-defined rosette structures with the hexagonal system and, clearly display the distribution of deformation-induced extended defects/dislocations which affect CL emission. By using focused ion beam milling to accurately position the cross-section of an indented area, XTEM results demonstrate that the major plastic deformation is taking place through the propagation of dislocations. The present observations are in support to the massive dislocations activities occurring underneath the indenter during the loading cycle. No evidence of either phase transformation or formation of micro-cracking was observed by means of scanning electron microscopy and XTEM observations. We also discuss how these features correlate with Berkovich nanoindentation produced defects/dislocations structures.
Characteristics of ZnO thin films prepared by radio frequency magnetron sputtering
(2008-03-01)
Yang, Ping-Feng
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Lai, Yi-Shao
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Wu, Sean
We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto Langasite substrates at 200 degrees C through radio frequency magnetron sputtering with an radio frequency power at 200 W in an O(2)/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal zinc oxide at 31.75 degrees, 34.35 degrees, and 36.31 degrees. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement technique, the hardness and Young's modulus of ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h. In addition, surface acoustic wave properties of ZnO thin films were also presented. (C) 2007 Elsevier Ltd. All rights reserved.
Characterizations of ZnO thin films deposited onto langasite substrates by r.f. magnetron sputtering
(2007)
Yang, Ping-Feng
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Lail, Yi-Shao
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Wu, Sean
We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto langasite substrates at 200 degrees C through r.f. magnetron sputtering with an r.f. power at 200 W in an O2/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal ZnO at 31.75 degrees, 34.35 degrees, and 36.31 degrees. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement (CSM) technique, the hardness and Young\'s modulus of the ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h.
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.
Cross-sectional transmission electron microscopy studies for deformation behaviors of AlN thin films under Berkovich nanoindentation
(2010-08-01)
Jian, Sheng-Rui
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Chen, G. -J.
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Chen, H. -G.
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Jang, Jason S. -C.
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Liao, Y. -Y.
This article reports a nanomechanical response study of the contact-induced deformation behavior in AlN thin film by using a combination of nanoindentation and the cross-sectional transmission electron microscopy (XTEM) techniques. AlN thin films are deposited on Si(1 1 1) substrates by using the helicon sputtering system. The hardness and Young's modulus of the AlN thin film are measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) mode. The obtained values of hardness and Young's modulus are 24.79 +/- 0.33 GPa and 223.92 +/- 5.34 GPa, respectively. XTEM samples are prepared by using focused ion beam (FIB) milling to accurately position the cross-section of the indented area. Although the film's surface was free from fracture, AlN thin film showed evidence of radial crack along the columnar grain boundary underneath the center of Berkovich indentation for an applied load of 100 mN. XTEM results also indicated that the slip bands on {1 1 1} planes and an indentation-induced phase transformation zone of silicon substrate, containing the metastable phases of Si-III and Si-XII, and, the amorphous phases are observed. (C) 2010 Elsevier B.V. All rights reserved.
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]
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 post-annealing on the structural and nanomechanical properties of Ga-doped ZnO thin films deposited on glass substrate by rf-magnetron sputtering
(2011-11-15)
Wang, Szu-Ko
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Lin, Ting-Chun
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Jian, Sheng-Rui
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Juang, Jenh-Yih
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Jang, Jason S. -C.
In this study, the effects of post-annealing on the structure, surface morphology and nanomechanical properties of ZnO thin films doped with a nominal concentration of 3 at.% Ga (ZnO:Ga) are investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) and nanoindentation techniques. The ZnO:Ga thin films were deposited on the glass substrates at room temperature by radio frequency magnetron sputtering. Results revealed that the as-deposited ZnO:Ga thin films were polycrystalline albeit the low deposition temperature. Post-annealing carried out at 300, 400 and 500 degrees C, respectively, has resulted in progressive increase in both the average grain size and the surface roughness of the ZnO:Ga thin film, in addition to the improved thin films crystallinity. Moreover, the hardness and Young's modulus of ZnO:Ga thin films are measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. The hardness and Young's modulus of ZnO:Ga thin films increased as the annealing temperature increased from 300 to 500 degrees C, with the best results being obtained at 500 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
Electrochemical reaction and performance of proton exchange membrane fuel cells with a novel cathode flow channel shape
(2007-04-15)
Chiang, Mu-Sheng
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Chu, Hsin-Sen
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Chen, Cha'o-Kuang
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Jian, Sheng-Rui
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機械工程學系
This study focuses on the investigation of the electrochemical reaction along a novel cathode flow channel of PEM fuel cells with various shoulder/channel (S/C) ratios at the outlet port. A three-dimensional mathematical model, considering conservation principles of mass, momentum, species and electric current is employed. Local variations of important model variables such as reactant concentration and local current density are presented by contour plots to elucidate the effects of channel geometry on transport process, catalyst reaction and cell performance. The potential fields of solid and membrane phases are also resolved in the cell domain and the driving force of the electrochemical reactions - the catalyst activation overpotential - is harnessed in modeling. Numerical calculations reveal the influence of the cathode channel configuration on the local distributions of various model variables. The results also show the dependence between optimal channel configuration and cell operating condition. At a medium reaction rate, the reaction sites underneath the shoulder region generate more current than the channel region. Therefore, a convergent channel configuration with a larger S/C ratio at the outlet port develops more current because such a design facilitates the electron transport and enhances local activation overpotential. However, as the cell voltage decreases and the reaction rate increases, such configuration loses its merit gradually as the requirement for a higher reactant concentration is more important and the reaction sites underneath the channel region have a higher reaction rate. Consequently, the divergent channel configuration with a lower S/C ratio of 0.67 perfonns better at a cell voltage of 0.22 V (c) 2007 Elsevier B.V. All rights reserved.
Enhanced visible photoluminescence from ultrathin ZnO films grown on Si-nanowires by atomic layer deposition
(2010-09-24)
Chang, Yuan-Ming
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Jian, Sheng-Rui
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Lee, Hsin-Yi
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Lin, Chih-Ming
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Juang, Jenh-Yih
Bright room temperature visible emission is obtained in heterostructures consisting of similar to 3.5 nm thick ZnO ultrathin films grown on Si-nanowires produced by means of self-masking dry etching in hydrogen-containing plasma. The ZnO films were deposited on Si-nanowires by using atomic layer deposition (ALD) under an ambient temperature of 25 degrees C. The orders of magnitude enhancement in the intensity of the room temperature photoluminescence peaked around 560 nm in the present ZnO/Si-nanowire heterostructures is presumably due to the high aspect (surface/volume) ratio inherent to the Si-nanowires, which has, in turn, allowed considerably more ZnO material to be grown on the template and led to markedly more efficient visible emission. Moreover, the ordered nanowire structure also features an extremely low reflectance (similar to 0.15%) at 325 nm, which may further enhance the efficiency of emission by effectively trapping the excitation light.
Erbium-Doped Amorphous Carbon-Based Thin Films: A Photonic Material Prepared by Low-Temperature RF-PEMOCVD
(2014-03-01)
Hsu, Hui-Lin
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Leong, Keith R.
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Teng, I-Ju
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Halamicek, Michael
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Juang, Jenh-Yih
The integration of photonic materials into CMOS processing involves the use of new materials. A simple one-step metal-organic radio frequency plasma enhanced chemical vapor deposition system (RF-PEMOCVD) was deployed to grow erbium-doped amorphous carbon thin films (a-C:(Er)) on Si substrates at low temperatures (<200 degrees C). A partially fluorinated metal-organic compound, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) Erbium(+III) or abbreviated Er(fod)(3), was incorporated in situ into a-C based host. Six-fold enhancement of Er room-temperature photoluminescence at 1.54 mu m was demonstrated by deuteration of the a-C host. Furthermore, the effect of RF power and substrate temperature on the photoluminescence of a-C:D(Er) films was investigated and analyzed in terms of the film structure. Photoluminescence signal increases with increasing RF power, which is the result of an increase in [O]/[Er] ratio and the respective erbium-oxygen coordination number. Moreover, photoluminescence intensity decreases with increasing substrate temperature, which is attributed to an increased desorption rate or a lower sticking coefficient of the fluorinated fragments during film growth and hence [Er] decreases. In addition, it is observed that Er concentration quenching begins at similar to 2.2 at% and continues to increase until 5.5 at% in the studied a-C: D(Er) matrix. This technique provides the capability of doping Er in a vertically uniform profile.
Fabrication of cone-shaped CNF/SiC-coated Si-nanocone composite structures and their excellent field emission performance
(2012)
Teng, I-Ju
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Kuo, Cheng-Tzu
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Juang, Jenh-Yih
Novel cone-shaped carbon nanofiber (CNF)/silicon carbide (SiC)-coated Si-nanocone (Si-NC) composite structures with excellent field emission (FE) performance have been fabricated by a simple microwave plasma chemical vapour deposition process. Transmission electron microscopy analyses reveal that the newly developed cone-shaped composite structures are composed of bamboo-like herringbone CNFs grown vertically on the tips of conical SiC layers with a flat-top Si cone embedded underneath. For this CNF/SiC-coated Si-NC composite array, a ultra-low threshold field of 0.32 V mu m(-1) (at 10 mA cm(-2)), a large emission current density of 668 mA cm(-2) at 1.05 V mu m(-1), and a field enhancement factor as high as similar to 48 349 are obtained. In addition, the FE lifetime test performed at a large emission current density of 200 mA cm(-2) under an applied field of 1 V mu m(-1) shows no discernible decay during a period of over 260 minutes. We deduce that this superior FE performance can be attributed to the specific bamboo-like herringbone CNFs with numerous open graphitic edges and a faceted top end, and the conical base SiC/ Si structures with sufficient adhesion to the substrate surface. Such a novel structure with promising emission characteristics makes it a potential material for electron field emitters.
Field emission characteristics of carbon nanotubes post-treated with high-density Ar plasma
(2010-01-15)
Wang, Wen-Pin
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Wen, Hua-Chiang
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Jian, Sheng-Rui
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Cheng, Huy-Zu
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Jang, Jason Shian-Ching
The field emission characteristics of carbon nanotubes (CNTs) grown by thermal chemical vapor deposition (CVD) and subsequently surface treated by high-density Ar plasma in an inductively coupled plasma reactive ion etching (ICP-RIE) with the various plasma powers were measured. Results indicate that, after treated by Ar plasma with power between 250 and 500 W, the emission current density of the CNTs is enhanced by nearly two orders of magnitude (increased from 0.65 to 48 mA/cm(2)) as compared to that of the as-grown ones. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to investigate the structural features relevant to the modified field emission properties of CNTs. The SEM images of CNTs subjected to a 500 W Ar plasma treatment exhibit obvious damages to the CNTs. Nevertheless, the turn-on fields decreased from 3.6 to 2.2V/mu m, indicating a remarkable field emission enhancement. Our results further suggest that the primary effect of Ar plasma treatment might be to modify the geometrical structures of the local emission region in CNTs. In any case, the Ar plasma treatment appears to be an efficient method to enhance the site density for electron emission and, hence markedly improving the electric characteristics of the CNTs. (C) 2009 Elsevier B.V. All rights reserved.
High temperature creep properties of directionally solidified CM-247LC Ni-based superalloy
(2016-02-08)
Chiou, Mau-Sheng
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Jian, Sheng-Rui
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Yeh, An-Chou
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Kuo, Chen-Ming
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Juang, Jenh-Yih
This study explores the effects of cooling rate after solution heat treatment on the high temperature/low stress (982 degrees C/200 MPa) creep properties of CM-247LC Nickel base superalloy. Cooling rate was controlled by blowing argon gas, air cooling, and furnace cooling, which, in turn, gave rise to corresponding cooling rates (from 1260 degrees C to 800 degrees C) of 18.7, 7.4, and 0.19 degrees C/s, respectively. The results indicated that higher cooling rate from the solution heat treatment temperature led to finer gamma\' precipitates and much improved tertiary creep as well as rupture life time in high-temperature creep test. The microstructural analyses using both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that finer gamma\' precipitates and narrower gamma channel width could result in denser rafting structure which might have hindered the climb of dislocations across the precipitates rafts. (C) 2015 Elsevier B.V. All rights reserved.
Highly graphitized laterally interconnected SWCNT network synthesis via a sandwich-grown method
(2011-04-13)
Teng, I-Ju
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Chen, Kai-Ling
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Wang, Li-Chun
We present a sandwich-grown method for growing laterally interconnected single-walled carbon nanotube (SWCNT) networks with a high degree of graphitization by microwave plasma chemical vapour deposition (MPCVD). An Al(2)O(3)-supported Fe catalyst precursor layer deposited on an oxidized Si substrate with an upper Si cover is first pretreated in pure hydrogen, and then exposed to a gas mixture of methane/hydrogen for growth process at a lower growth temperature and a faster rate. The effects of various parameters, such as catalyst film thickness, gas flow rate, working pressure, growth time and plasma power, on the morphologies and structural characteristics of the SWCNT networks are investigated, and therefore provide the essential conditions for direct growth of laterally interconnected SWCNT networks. Analytical results demonstrate that the SWCNT-based lateral architecture comprises a mixture of graphene-sheet-wrapped catalyst particles and laterally interconnected nanotubes, isolated or branched or assembled into bundles. The results also show that the formation of the laterally interconnected SWCNT networks is related to the sandwich-like stack approach and the addition of an Al(2)O(3) layer in the MPCVD process. The successful growth of lateral SWCNT networks provides new experimental information for simply and efficiently preparing lateral SWCNTs on unpatterned substrates, and opens a pathway to create network-structured nanotube-based devices.