Browsing by Author "Tu, GC"

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A study on the hardness variation of alpha- and beta-pure titanium with different grain sizes
(2005-05-25)
Kao, YL
;
Tu, GC
;
Huang, CA
;
Liu, TT
;
材料科學與工程學系
In this study, the hardness and the microstructure of alpha and beta-pure Ti treated with different grain sizes were investigated. The alpha-Ti specimens were obtained by heating pure Ti at 750 degrees C for various periods and then quenched in water, while the beta-Ti specimens by heating at 1000 degrees C for various periods and then quenched in water. Experimental results show that the hardness of a-Ti decreased with increasing the grain size; whereas, the hardness of beta-Ti tends to increase with increasing grain size. From the microstructures examined with transmission electron microscope, it can be realized that the strengthening mechanisms of alpha- and beta-Ti are quite different. Grain boundary could be the main strengthening microstructure of alpha-Ti and the smaller grain size the higher hardness. The major strengthening microstructure of beta-Ti was martensitic twin with a very high dislocation density. The amount of martensitic twin increased with increasing the grain size of beta-Ti and, therefore, the larger grain size the higher hardness. (c) 2005 Elsevier B.V. All rights reserved.
Characteristics of the rough-cut surface of quenched and tempered martensitic stainless steel using wire electrical discharge machining
(2004-04-01)
Huang, CA
;
Tu, GC
;
Yao, HT
;
Kuo, HH
;
交大名義發表
This article studies the surface characteristics of quench- and temper-treated AISI 440A martensitic stainless steels, which were rough cut using wire electrical discharge machining (WEDM). The microstructure of the recast layer on the cut surface was investigated using scanning and transmission electron microscopes, and the phase compositions were analyzed with an energy-dispersive X-ray (EDX) spectrometer. Experimental results showed that the thickness of the recast layer varied with the heat-treatment condition of the workpiece, the largest thickness was obtained with a quenched specimen, and the thickness decreased with increasing tempering temperature. Intergranular surface cracks were observed only from the as-quenched specimen, whereas surface cracks were not found in the rough-cut specimens after tempering above 200 degreesC. It is reckoned that reliefing of the thermal residual stress in the quenched workpiece induced the surface intergranular cracks. Microstructures of the recast layer on the rough-cut surfaces of the 600 degreesC tempered specimen were examined using cross-sectional transmission electron microscopy (TEM) specimens. An amorphous layer exists at some parts of the outermost cut surface. A high density of wire electrode droplets of spherical shape, approximately 10 to 60 nm in size, was found throughout the porous recast layer. Besides, many high-chromium containing sigma spheres with sizes of approximately 120 to 200 nm were precipitated at the bottom part of the recast layer, and its formation mechanism was proposed. Adjacent to the recast layer was a heat-affected zone (HAZ) with a thickness of about 4 mum, in which temper-induced carbides were fully dissolved. The HAZ comprised basically two distinct regions: the first region adjacent to the recast layer was composed of a lath martensite structure, while the other region was an annealed ferrite structure.
CoSix thermal stability on narrow-width polysilicon resistors
(2006-01-01)
Chen, YM
;
Tu, GC
;
Wang, YL
;
Hwang, GJ
;
Lo, CY
In this study, the thermal stability of polysilicon lines with various widths and different dopant types in 90-nm processes is investigated. The thermal behavior of silicides formed on N+ polyresistors and P+ polyresistors is very different. The worst thermal stability is found on the narrower N+ polyresistors, while an abnormal thermal behavior is observed on P+ polyresistors. This anomalous thermal-stability change with different drawn linewidths of P+ polyresistors is related to the C Grain-size distribution and the actual polyresistor linewidth. Also, it is interesting to find that the voids formed in P+ polyresistors lead to a stepped increase in sheet resistance. (c) 2006 American Vactatin Society.
Effect of catalyst on growth behavior of carbon nanotube synthesizing by microwave heating thermal chemical vapor deposition process
(2001-05-01)
Chen, SC
;
Shih, LY
;
Chang, YC
;
Tu, GC
;
Lin, IN
A modified chemical vapor deposition process, which utilizes a susceptor to absorb the microwave and to self generate the heat, for heating up the Si substrate, was used for growing carbon nanotubes (CNTs). The advantage of such a process is that the deposition chamber can be maintained at around room temperature with only the substrates localized heated, such that the deposition temperature can be more precisely controlled. The influence of the pretreatment process for catalyst-coated Si substrates on growth behavior of CNTs and the related electron field emission properties were systematically examined. Among the form of catalyst used, the Fe(NO3)(3)-ethythersilicate mixture performs much better than the de sputtered Fe films. The higher the concentration of Fe species in the catalyst mixture, the denser the CNTs formed on the subs;rates, resulting in better held emission properties. Thus grown CNTs can be turned on at a very low field (E(0)congruent to0.78 V/mum), achieving a very large emission current density (J(e)congruent to 13 mA/cm(2)) at 5.5 V/mum applied field. (C) 2001 American Vacuum Society.
Fabrication and characterization of Cu-SiCp composites for electrical discharge machining applications
(2001)
Shu, KM
;
Tu, GC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Cu-SiCp composites made by the powder metallurgy method were investigated. To avoid the adverse effect of Cu-SiCp reaction, sintering was controlled at a reaction temperature less than 1032 K. Electroless plating was employed to deposit a copper film on SiCp powder before mixing with Cu powder in order to improve the bonding status between Cu and SiC particles during sintering. It was found that a continuous copper film could be deposited on SiCp by electroless copper plating, and a uniform distribution of SiCp in Cu matrix could be achieved after the sintering and extrusion process. The mechanical properties of Cu-SiCp composites with SiCp contents from 0.6 to 10 wt% were improved evidently, whereas electrical properties remained almost unchanged as compared with that of the pure copper counterpart. In the electrical discharge machining (EDM) test, the as-formed composite electrodes exhibited a character of lower electrode wear ratio, justifying its usage. The optimum conditions for EDM were Cu-2 wt% SiC. composite electrode operating with a pulse time of 150 mu sec.
Fabrication and microstructure of the dc-magnetron-sputtered YBa2Cu3O7-x superconducting thin films
(1996-04-01)
Koo, HS
;
Tseng, TY
;
Chang, WR
;
Tu, GC
;
材料科學與工程學系
Systematic investigations were conducted to determine the effect of deposition conditions on the microstructure and superconducting properties of YBa2Cu3O7-x thin films produced by d.c. magnetron sputtering on (001) MgO substrate. The films were c-axis preferentially oriented with respect to the (001) MgO surface at substrate temperatures of 680-700 degrees C. X-ray diffraction patterns clearly indicated the existence of the c-axis alignment normal to the substrate surface and some second phases. The second phases, including a Cu-rich phase and Y2O3, were identified by energy dispersive X-ray spectrometer and the microstructures were analysed by electron and;atomic force microscopes.
Hard chromium plating on cold swaged Cr-Mo steel using rotating cylinder electrode
(2000-08-01)
Huang, CA
;
Tu, GC
;
Liao, MC
;
Kao, YL
;
材料科學與工程學系
Microstructural study of the effect of chloride ion on electroplating of copper in cupric sulfate-sulfuric acid bath
(2005)
Kao, YL
;
Li, KC
;
Tu, GC
;
Huang, CA
;
材料科學與工程學系
The purpose of this work is to study the electrocrystallization behavior of the copper deposit on pure titanium substrate. The electroplating was conducted at 0.7 A/cm(2), 65 degrees C in cupric sulfate-sulfuric acid bath with various chloride additions (45-350 ppm). Initial growth morphology and microstructure of the deposit were examined with a field-emission scanning electron microscope (FESEM) and a high-resolution transmission electron microscope integrated with an energy-dispersive X-ray spectrometer. Results of cathodic polarization and galvanostatic plating experiments show that the increasing concentration of chloride ions in the plating bath would significantly increase the cathodic potential. This cathodic potential increase was found to be induced by the presence of CuCl precipitates on the cathodic surface as well as on the copper cluster formed during the electrocrystallization process. At the initial plating stage, both copper and hexagonal-shaped CuCl precipitates were produced simultaneously. Eventually, the pyramid-shaped CuCl precipitates were observed, which consisted of many parallel hexagonal planes stemming from a screw dislocation. The polarization effect of CuCl precipitate on the Ti substrate was further confirmed and clarified. Through measurement of the electrode response and investigation of the deposit using FESEM, it was observed that under identical electroplating conditions, much less CuCl forms on a copper substrate in the initial stages than on a titanium substrate, leading to lower polarization. (c) 2005 The Electrochemical Society.
Nanomechanical properties of nanocrystalline Ni-Fe mold insert
(2004-06-09)
Yeh, YM
;
Tu, GC
;
Fang, TH
;
材料科學與工程學系
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Department of Materials Science and Engineering
Nanocrystalline Ni-Fe alloy micro-mold inserts were fabricated by UV lithographic technology and pulse current electroforming process. The structure, surface and mechanical properties of Ni-Fe alloys were evaluated under different pulse current electroforming processes via X-ray diffraction (XRD), scanning probe microscope (SPM), nanoindentation, and scanning transmission electron microscope (STEM). The results show that when Fe content of the alloys increase by over 10% the grain size of Ni-Fe alloys was < 20 nm. The finer the grain of Ni-Fe alloys the higher the hardness, which is above 9 GPa. By controlling the variation of current density and duty cycle, the surface roughness of Ni-Fe alloys is < 10 nm and the surface friction coefficient is about 0.2. The results of the microelectroforming process revealed that the Fe contents was able to suppress grain growth and induced the formation of dense Ni-Fe alloys and improved the mechanical properties of the Ni-Fe alloys. (C) 2003 Elsevier B.V. All rights reserved.
Oxide-mediated fort-nation of epitaxy silicide on heavily doped Si surfaces and narrow width active region
(2006-03-01)
Chen, YM
;
Tu, GC
;
Wang, YL
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Oxide-mediated epitaxy (OME) is a highly promising means of forming epitaxial CoSi2. In this work, various chemical treatments were applied to grow chemical oxides on heavily doped Si substrates and narrow width active region. The effects of the treatment on the OME performance were investigated. Both the thickness and the quality of the oxide varied with the chemicals and dopants, resulting in various levels of junction leakage current. The junction leakage current was minimized by choosing the most favorable chemical treatment and optimizing the annealing temperature. (c) 2005 Elsevier B.V. All rights reserved.
Reverse CoSi(2) thermal stability and digitized sheet resistance increase of sub-90 nm polysilicon lines
(2005-04-01)
Lo, CY
;
Peng, YC
;
Chen, YM
;
Tu, GC
;
Lin, SS
An equation for quantifying the CoSi(2) thermal stability of polysilicon lines ranging from 50 nm to 2 mu m is proposed for the first time. In contrast to the intuitive thinking of narrower lines having a worse thermal stability, the equation predicts the weakest thermal stability occurring at the super nominal line in 90nm technology. An interesting phenomenon of digitized resistance increase is also reported for the first time.
Simulation analysis and experimental verification of LIGA-like process for Ni-Fe micromold insert with taper angle
(2004-11-01)
Fu, MN
;
Yeh, YM
;
Tu, GC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The LIGA (a German acronym for lithographic, gavanoformung, abformung) (or LIGA-like) process involving lithography, electroforming, and molding is one of the most important microfabrication technologies for fabricating high-aspect-ratio 3-D microstructures. In this study we use CFX software to simulate the flow field in the micromold insert electroforming process and investigate the mass transfer effect, as well as the flow field and mass transfer for different taper angles and aspect ratios for a microtemplate under different flow speeds, in order to understand the effect of the geometrical shape of the template on the electroforming process, thus to obtain the optimum physical electroforming model. In this study, we will also perform a practical electroforming process at different aspect ratios and different taper angles of the microtemplate, in order to verify the results of the simulation. From the results of the simulation, it is found that the taper angle increases the speed of the plating solution at the vent, and a good equilibrium is achieved at a taper angle of 30degrees-45degrees. Since taper angle significantly affects the mass transfer effect, it can be used to increase the mass transfer effect in high-aspect-ratio and small holes. This result has been verified using a practical electroforming Ni-Fe micromold insert.
Simulation analysis and experimental verification of UV-LIGA process for high-aspect-ratio Ni-Fe micro-mold insert
(2003-10-01)
Yeh, YM
;
Tu, GC
;
Fu, MN
;
材料科學與工程學系
;
Department of Materials Science and Engineering
UV (ultra violet)-LIGA (a German acronym for lithographic, gavanoformung, abformung), a low-cost microcomponent manufacturing technology for micro-electromechanical systems (MEMS), combines the UV patterning of thick photoresist layers with the molding of the resulting patterns by electroforming. It enables mass production of microcomponents using microinjection molding or hot embossing technology. This paper addresses the characteristics of the flow field and the mass transfer effect during micro-electroforming processes. A micro-electroforming experiment is conducted and a simulation is performed to determine optimal conditions for fine surface forming by micro-electroforming. Results show that a smaller diameter of a hole corresponds to poorer plating bath transfer. Plating bath can be replenished by increasing the rotation speed of the electrodes. However, mass transfer is still limited in holes with a high aspect ratio. The theoretical results of simulation analysis were verified by conducting practical electroforming experiments.
Study of electrical discharge grinding using metal matrix composite electrodes
(2003-06-01)
Shu, KM
;
Tu, GC
;
材料科學與工程學系
;
Department of Materials Science and Engineering
An investigation was made into the combined technologies of electrical discharge machining and grinding (EDMG). A metal matrix (Cu/SiCp) electrode with a rotating device was made and employed to study the EDMG technology. It was found that 3-7 times the normal electrical discharge machining (EDM) material removal rate (MRR) could be achieved in EDMG under suitable conditions of electrode rotating speed, SiCp particle size and current. This novel achievement is attributed to the fact that, under appropriate conditions, the hump-shaped melted material created by the EDM mechanism is vulnerable to attack by the grinding mechanism during the EDMG operation, greatly increasing the removal rate. Conversely, under inappropriate conditions, in which hump-shaped material solidifies prior to the non-conductive ceramic particle grinding, the above function becomes negligible and results in much lower MRR. (C) 2003 Elsevier Science Ltd. All rights reserved.
The annealing behavior of copper deposit electroplated in sulfuric acid bath with various concentrations of thiourea
(2004-09-25)
Kao, YL
;
Tu, GC
;
Huang, CA
;
Chang, JH
;
材料科學與工程學系
The annealing behavior of electroplated copper deposits is reported in this study. The copper deposits were electroplated with a current density of 0.7 A/cm(2) at 53 degreesC in a sulfuric acid bath containing various concentrations of thiourea. The hardness values of the copper deposits were measured before and after annealing, and the differential scanning calorimetry (DSC) diagrams of the as-electroplated copper deposits were recorded. An improvement of the softening resistance of the copper deposits was observed when the bath contained thiourea greater than or equal to3 mg/L. By adding thiourea in the plating bath, smaller grain size of the copper deposits can be achieved. As thiourea content increased greater than or equal to3 mg/L, the twin boundary of the copper deposits was significantly increased, and many sulfur-rich particles were deposited along the grain boundaries and a few within the grains of the deposit. These sulfur-rich particles are capable of impeding migration of the grain boundaries and improving the softening resistance of the copper deposits during annealing. The aforementioned microstructures of the copper deposits were examined with transmission electron microscope (TEM) integrated with energy-dispersive X-ray spectrometer (EDX) for chemical composition analysis. (C) 2004 Elsevier B.V. All rights reserved.
The effect of 180 degrees C-annealing on the electrochemical behavior of nano-thick zinc-electroplated copper in aqueous solutions with different pH
(2006-02-01)
Kao, YL
;
Tu, GC
;
Huang, CA
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The anodic polarization and a.c. impedance measurements of 4 nm- and 25 nm-zinc-electroplated copper specimens were conducted in aqueous solutions with four different pH-values. The nano-thick zinc-electroplated copper was tested after electroplating and annealing at 180 degrees C for 1, 2 and 3 h, respectively. The results showed that the open-circuit potential (OCP) of 25 nm-zinc electroplated copper shifted toward noble potential after annealing. A more noble OCP of 25 nm zinc-electroplated copper could be achieved when zinc plated copper was annealed at 180 degrees C up to 1 h. Similar change was found for 4 nm-zinc electroplated copper only in neutral and alkaline solutions. The a.c. impedance response of all nano-thick zinc-electroplated copper corresponded to two Randle's circuits in series, in which the circuit measured in a high frequency region of their Nyquist diagrams revealed the electrochemical behavior of nano-thick zinc deposits. The charge transfer resistance of the nano-thick zinc electroplated copper was significantly raised after annealing at 180 degrees C when tested in pH 9.5 solution. Microstructures of the aforementioned nano-thick zinc electroplated copper were examined with cross-sectional TEM specimens. A distinct phase interface between zinc and copper was observed for as plated specimens, while alloying of zinc and copper at the interface was detected after annealing at 180 degrees C for 1 h. Electroplated zinc diffused into the copper foil during the 180 degrees C-annealing and the corrosion potential of the anodic polarization curve indicated the condition of the alloy surface. The annealing effect of 4 nm- and 25 nm-zinc eleetro-plated copper specimens could be related to the results of electrochemical measurement. (C) 2005 Elsevier Ltd. All rights reserved.
The effect of indium impurity on the DC-etching behaviour of aluminum foil for electrolytic capacitor usage
(1997-09-01)
Lin, W
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Tu, GC
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Lin, CF
;
Peng, YM
;
材料科學與工程學系
The effects of indium impurity on the etched morphology of high purity aluminium foils for electrolytic capacitor usage were investigated. The indium impurity was present either in as-received aluminium foils or deposited purposely on the foil surface through immersion-reduction reaction. The rolling line effect can be improved through introducing deposited indium on foil surfaces by immersion of the foil into In(NO3)(3) solution prior to DC-etching. Under a high immersion temperature and more concentrated Ir(NO3)(3) condition, surface etching competes with tunnel etching, and the foil thickness clearly decreases. Under low temperature and dilute In(NO3)(3) condition, surface etching is inhibited and tunnel etching prevails. The different DC-etching behaviour under the two In-deposition conditions is explained through the energy state difference between the two deposited-In and the activation energy difference between surface etching and tunnel etching. The modification of etchability by indium on aluminium surface is stronger than that of lead. This facilitates employing lower temperature and dilute In(NO3)(3) condition in the immersion-reduction process to optimize the etchability. (C) 1997 Elsevier Science Ltd.
The effect of lead impurity on the DC-etching behaviour of aluminum foil for electrolytic capacitor usage
(1996-06-01)
Lin, W
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Tu, GC
;
Lin, CF
;
Peng, YM
;
材料科學與工程學系
The effects of lead impurity on the etched morphology of high purity aluminum foils for electrolytic capacitor applications were investigated in this work. The lead impurity was either present in as-received aluminum foils or deposited purposely on the foil surface through an immersion-reduction reaction. The amount and distribution of deposited lead varies with the lead content in as-received foil. The as-received foil with higher lead content gave a higher concentration and a more uniform distribution of deposited lead. Uniformly distributed vertical tunnel etchings were obtained when high lead foil, formed by immersion as-received high lead foil in Pb(NO3)(2) solution, was subject to DC-etching. For the as-received lower lead foils, the deposited lead was concentrated in rolling lines which resulted in surface etching along rolling lines. Both the surfacial and cross-sectional etching morphologies are presented in this study, together with the etching mechanism discussed. Copyright (C) 1996 Elsevier Science Ltd.
The effect of lead impurity on the DC-etching behaviour of aluminum foil for electrolytic capacitor usage
(1996-06-01)
Lin, W
;
Tu, GC
;
Lin, CF
;
Peng, YM
;
材料科學與工程學系
The effects of lead impurity on the etched morphology of high purity aluminum foils for electrolytic capacitor applications were investigated in this work. The lead impurity was either present in as-received aluminum foils or deposited purposely on the foil surface through an immersion-reduction reaction. The amount and distribution of deposited lead varies with the lead content in as-received foil. The as-received foil with higher lead content gave a higher concentration and a more uniform distribution of deposited lead. Uniformly distributed vertical tunnel etchings were obtained when high lead foil, formed by immersion as-received high lead foil in Pb(NO3)(2) solution, was subject to DC-etching. For the as-received lower lead foils, the deposited lead was concentrated in rolling lines which resulted in surface etching along rolling lines. Both the surfacial and cross-sectional etching morphologies are presented in this study, together with the etching mechanism discussed. Copyright (C) 1996 Elsevier Science Ltd.
The electrochemical behavior of tin-doped indium oxide during reduction in 0.3 M hydrochloric acid
(2003-10-30)
Huang, CA
;
Li, KC
;
Tu, GC
;
Wang, WS
;
材料科學與工程學系
The electrochemical behavior of tin-doped indium oxide (ITO) on SiO2 in 0.3 M HCl was studied using voltammetric scanning method. The result showed that an obvious reduction current peak occurred during the first cathodic potential scanning. The reduction reaction became less active after annealing ITO at 500 C for 1 h. The result was attributed to the replenishment of oxygen-deficient site, which acts as current carrier, by the annealing treatment. Many spherical In-Sn particles with sizes about 100-500 nm were formed on the ITO surface adjacent to the grain boundary when the reduction current took place. The In-Sn particles initiated preferentially on the ITO surface near grain boundaries attending the dissolution of ITO grain boundary. In the scanning period, after completion of the reduction current peak, reduction of hydrogen ions occurred in more negative potential region. A schematic illustration for the formation mechanism of the In-Sn reduction particle was postulated based on the metallographical and electrochemical results in this work. (C) 2003 Elsevier Ltd. All rights reserved.