Browsing by Author "Jang, Jason S. -C."

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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.
;
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.
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.
Influence of annealing temperature on the structural, optical and mechanical properties of ALD-derived ZnO thin films
(2011-06-15)
Yen, C. -Y.
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Jian, S. -R.
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Chen, G. -J.
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Lin, C. -M.
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Lee, H. -Y.
ZnO thin films grown on Si(1 1 1) substrates by using atomic layer deposition (ALD) were annealed at the temperatures ranging from 300 to 500 degrees C. The X-ray diffraction (XRD) results show that the annealed ZnO thin films are highly (0 0 2)-oriented, indicating a well ordered microstructure. The film surface examined by the atomic force microscopy (AFM), however, indicated that the roughness increases with increasing annealing temperature. The photoluminescence (PL) spectrum showed that the intensity of UV emission was strongest for films annealed at 500 degrees C. The mechanical properties of the resultant ZnO thin films investigated by nanoindentation reveal that the hardness decreases from 9.2 GPa to 7.2 GPa for films annealed at 300 degrees C and 500 degrees C, respectively. On the other hand, the Young's modulus for the former is 168.6 GPa as compared to a value of 139.5 GPa for the latter. Moreover, the relationship between the hardness and film grain size appear to follow closely with the Hall-Petch equation. (C) 2011 Elsevier B. V. All rights reserved.
Influence of Mg-containing precursor flow rate on the structural, electrical and mechanical properties of Mg-doped GaN thin films
(2012-10-15)
Ke, Wen-Cheng
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Jian, Sheng-Rui
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Chen, I-Chen
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Jang, Jason S. -C.
;
Chen, Wei-Kuo
The effects of Mg-containing precursor flow rate on the characteristics of the Mg-doped GaN (GaN:Mg) were systematically studied in this study. The GaN:Mg films were deposited on sapphire substrates by metal-organic chemical-vapor deposition (MOCVD) with various flow rates of 25, 50, 75 and 100 sccm of bis-(cyclopentadienyl)-magnesium (Cp2Mg) precursor. The structural, electrical and nanomechanical properties of GaN:Mg thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM). Hall measurement and nanoindentation techniques, respectively. Results indicated that GaN:Mg films obtained with 25 sccm Cp2Mg possess the highest hole concentration of 3.1 x 10(17) cm(-3). Moreover, the hardness and Young's modulus of GaN:Mg films measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option showed positive dependence with increasing flow rate of Cp2Mg precursor, presumably due to the solution hardening effect of Mg-doping. (C) 2012 Elsevier B.V. All rights reserved.
Mechanical responses of Mg-based bulk metallic glasses
(2010-10-01)
Jian, S. -R.
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Li, J. -B.
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Chen, K. -W.
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Jang, Jason S. -C.
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Juang, J. -Y.
In this study, the mechanical responses of the bonded interface method derived Mg(58)Cu(28.5)Gd(11)Ag(2.5) bulk metallic glasses (BMG) under the micro-/nano-indentation are investigated. A modified expanding cavity model is developed to analyze the morphological observations of shear band by Vickers indentation. Results indicate that the radius ratio of any two adjacent shear band circles is approximately constant. The ratio of the shear band deformation zone to the contact radius induced by indentation is also a constant, which depends on the constraint factor (the ratio of hardness to yield strength) of the material. The features predicted by the present model are consistent with the results obtained from the indentation experiments, indicating the validity of the expanding cavity model for describing the mechanical behaviors of the BMG materials. The cross-sectional transmission electron microscopy (XTEM) observations reveal that the terraced shear bands are formed on the interface of the bonded Mg-based BMG. The microstructures for the Vickers indentation-induced terraced shear bands are also discussed. (C) 2010 Elsevier Ltd. All rights reserved.
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.