Browsing by Author "Cheng, SY"

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Characterization and composition evolution of multiple-phase nanoscaled ceramic powders produced by laser ablation
(2004-10-20)
Lin, SC
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Chen, SY
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Cheng, SY
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交大名義發表
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National Chiao Tung University
Nanosized ceramic powder was prepared by laser ablation under different atmospheres using a ceramic target composed of ZrO2, TiO2, ZnO and Al2O3. Physical characteristics and microstructure of nanoparticles, including particle morphology, phase transformation, powder compositions and far-infrared emissivity, have been investigated. The laser-ablated nanoparticles exhibit two kinds of particle size distribution with 7-15 (70-90%) and 40-100 nm (10-30%). Nanoparticles synthesized at lower laser fluences show poor crystallinity but rich Zn composition. While increasing laser fluence, better crystalline nanoparticles with rich Zr composition were obtained. It was found that both composition and morphology of nanoparticles change with laser fluence. The average far-infrared emissivity of the nanoparticles varies with crystallinity of nanoparticles. (C) 2004 Elsevier B.V. All rights reserved.
Critical length of nanowires for hydrophobic behavior
(2004-10-11)
Cheng, YH
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Chou, CK
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Chih, C
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Cheng, SY
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材料科學與工程學系
This Letter investigates the wetting behavior on surface with well-controlled nanoscale structure. Water and water-alcohol droplets were brought to contact the surface electroplated by Ag nanowires. It is found that hydrophobic behavior becomes more pronounced as the length of the nanowires increases. A critical length of approximately 100 nm is observed, beyond which the contact angle approaches a steady value of 130degrees. In addition, the contact angle of water levels off around 160degrees when the length of the fluorine-coated Ag nanowires exceeds the critical value of 100 nm. The mechanism of the hydrophobic behavior on surface with nanoscale structure is proposed. (C) 2004 Elsevier B.V. All rights reserved.
Effect of metal oxide precursor on sintering shrinkage, microstructure evolution and electrical properties of silver-based pastes
(2002-01-01)
Chen, SY
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Chou, CH
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
Since the shrinkage behavior of silver-based films has been correlated with the characteristics of oxide additives used, the relative role of metal oxides and metal-organic precursors in sintering shrinkage and microstructure evolution of silver films was investigated and compared in this work. Films with an oxide powder additive exhibit two-stage shrinkage behavior in contrast to one-stage continuous shrinkage, which occurs in silver films with metal-organic precursors, added. Furthermore, metal-organic precursors are less effective than metal oxide powders in reducing shrinkage of silver-based films. That can be reasonably explained that metal-organic precursors can be effectively decorated around silver powder to inhibit the sintering densification. The Zr-based organic precursor among the metal-organic precursors exhibits optimal retardation in sintering densification of silver film, which is probably interrelated to refractory characteristics of ZrO2. The unique conductivity and grain growth of silver film with 1.0 wt% tungsten-organic precursor added was possibly due to the partial dissolution of W into Ag. (C) 2002 Kluwer Academic Publishers.
Effects of phase transformation on photoluminescence behavior of ZnO : Eu prepared in different solvents
(2006)
Yang, CC
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Cheng, SY
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Lee, HY
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Chen, SY
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材料科學與工程學系
Europium doped zinc oxide (Eu:ZnO) powder has been prepared by mixing ZnO and Eu2O3 in deionized water and acetone solvents. The influence of phase transformation of Eu-doped ZnO powders mixed in different solvents on the luminescence behavior has been investigated. When the powder was mixed in deionized water and then sintered at high temperatures, Eu3+ ions were detected in the ZnO matrix. The intrinsic red photoluminescence (D-5(0)->F-7(2)) of Eu3+ was easily shielded by the ZnO intrinsic defect as the samples were excited with 325 nm short wavelength as a consequence of the energy level of Eu-Zn(circle) (0.19 eV) being closer to conduction band than the one of Zn-1(circle circle) (0.22 eV). Therefore, no red emission can be detected. In contrast, as the Eu-doped ZnO powder was mixed in acetone solvent (without OH-), no Eu3+ ions could be detected in the ZnO matrix. In addition, the red emission could be detected not only under excitation with long wavelength (532 nm) but also at short wavelength (325 nm). (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
LOG filter based inspection of cluster Mura and vertical-band Mura on liquid crystal displays
(2005)
Chen, HC
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Fang, LT
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Lee, L
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Wen, CH
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Cheng, SY
In this paper, we propose the use of Laplacian of Gaussian (LOG) filters in the detection of Cluster Mura defects and Vertical-Band Mura defects on Liquid Crystal Displays. To detect Cluster Mura defects, 2-D LOG filters with their shapes matching the shapes of Cluster Mura are adopted. The optimal threshold for the detection of Cluster Mura is determined based on the SEMU formula. On the other hand, to detect Vertical-Band Mura, a 1-D LOG filter is used over the projected I-D intensity profile to check if the variation tendency of the intensity profile is changed. The portions with inconsistently intensity variation are regarded as the portions where V-Band Muras occur. The simulation results demonstrate the LOG filters are very useful in the detection of Mura defects.
Luminescent and structural characteristics of ZnO nanorods fabricated by postannealing
(2006-01-01)
Lin, CC
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Liao, HC
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Chen, SY
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Cheng, SY
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材料科學與工程學系
Well-aligned ZnO nanorods grown on silicon substrates buffered with ZnO film were postannealed at 200-1000 degrees C in various atmospheres. The optical properties of ZnO nanorods were much improved by annealing at high temperatures in both atmospheres of N-2 and O-2. This improvement was ascribed to the decrease in structure defects as compared to as-grown ZnO nanorods. However, for the ZnO nanorods annealed in H-2/N-2, a stronger UV emission occurs at 600 degrees C; above that the UV emission rapidly disappeared, which was attributed to the collapse of the ZnO nanorods due to H-2 etching during a higher-temperature annealing in H-2/N-2. The crystallinity and optical properties of the ZnO nanorods can be controlled by postannealing treatment. (c) 2006 American Vacuum Society.
Nucleation and growth behavior of well-aligned ZnO nanorods on organic substrates in aqueous solutions
(2005-09-15)
Lin, CC
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Chen, SY
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
A low-temperature synthetic route was used to prepare well-aligned arrays of oriented ZnO nanorods on organic substrates coated with polystyrene beads (PS) in an aqueous solution. The corresponding growth behavior and photoluminescence properties of ZnO nanorods were analyzed. It was found that the ZnO nanorods are initially nucleated from the ZnO monolayer under the concave regions of the PS layers and preferentially grown along [0 0 0 1] direction. High-resolution transmission electron microscopy (HRTEM) observation reveals that the ZnO nanorods tend to coalesce together with other adjacent nanorods to form a larger ZnO crystal in the later growth stage. The room-temperature photoluminescence spectra demonstrate that a stronger ultraviolet (UV) emission with a broad yellow emission around 575 nm was observed for the ZnO nanorods grown on the organic substrates and the relative intensity ratio of ultraviolet emission to yellow emission depends on the growth periods of time. This simple approach demonstrates great potential for optoelectronic devices because it can produce large-scale highly well-aligned ZnO nanorods on the flexible organic substrates at lower temperatures. (c) 2005 Elsevier B.V. All rights reserved.
Physical characteristics and photoluminescence properties of phosphorous-implanted ZnO thin films
(2004-11-15)
Lin, CC
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Chen, SY
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
ZnO films were implanted with phosphorus in the range from 5 x 10(12) to 5 x 10(15) cm(-2). Effect of phosphorus concentration on structural characteristics and photoelectric behavior of phosphorus-implanted ZnO films under different atmosphere and annealing treatment was investigated. It has been demonstrated that below solubility (1.5 x 10(18) ions/cm(3)), the defect formation will be dominated by annealing atmosphere and more defects can be formed in oxygen ambient than in nitrogen atmosphere as revealed from PL spectra. However, excess phosphorus doping, above solubility (1.5 x 10(18) ions/cm(3)), will induce the formation of the phosphide compounds in ZnO films and seriously deteriorate the crystallinity and optical property of the films. However, a high-resistive but not p-type ZnO film is obtained by phosphorus doping. (C) 2004 Elsevier B.V. All rights reserved.
Pilot power ratio design for hierarchical CDMA systems in supporting multi-class services
(2004)
Wanc, LC
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Cheng, SY
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電信工程研究所
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Institute of Communications Engineering
Multi-class services change the design paradigm and pose new challenges for the future wireless networks. In the future, a voice-oriented macrocell and a data-oriented microcell will co-exist to support multi-class services. In this paper, we develop an analytical framework to determine the optimal pilot power ratio for the CDMA system considering the impact of hierarchical cellular structure, co-channel interference, shadowing, and multi-class service requirements. An analytical approach for determining the pilot power in the hierarchical cellular system is developed to maximize system capacity in supporting multi-class traffic. Based on this analytical approach, we find that to maximize the system capacity, it is necessary to increase the pilot power of the microcell, but lower the pilot power of the macrocell.
PL dependence of ZnO films grown on Si with various buffer layers by RF magnetron sputtering
(2004)
Lin, CC
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Chen, SY
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
Peculiar photoluminescence (PL) emission properties of ZnO films on Si buffered with SiO2 and Si3N4 were found. The ZnO films deposited on SiO2/Si substrate show two double peaks in the room-temperature PL spectra, one double (374 and 394 nm) in the ultraviolet region and the other double (495 and 605 nm) located in the visible region. If the ZnO film was grown on Si3N4/Si, a very strong UV along with invisible deep-level emission was detected because the Si3N4 can effectively reduce the defect formation of oxygen vacancies and Zn interstitials compared to ZnO on SiO2/Si and Si. (C) 2004 The Electrochemical Society.
Properties of nitrogen-implanted p-type ZnO films grown on Si3N4/Si by radio-frequency magnetron sputtering
(2004-06-14)
Lin, CC
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Chen, SY
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Cheng, SY
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Lee, HY
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材料科學與工程學系
An nitrogen-implanted p-type ZnO film has been grown on a Si substrate buffered with Si3N4 using radio-frequency magnetron sputtering. The Si3N4 buffer layer can effectively improve film stoichiometry and reduce the formation of oxygen vacancies compared to ZnO on Si. The electrical properties of the p-type ZnO films implanted with 5x10(12)-1x10(14) cm(-2) N+ dose show a hole concentration of 5.0x10(16)-7.3x10(17) cm(-3), hole mobility of 2.51-6.02 cm(2)/V s, and resistivity of 10.11-15.3 Omega cm. The p-type ZnO films also showed an excellent crystallinity and a strong ultraviolet emission peak near 3.30 eV at room temperature. Moreover, as evidenced by extended x-ray absorption fine structure analysis, the local structure of the p-type ZnO films was changed due to the substitution of nitrogen ions for oxygen ions in p-type ZnO films. Our finding of p-type ZnO films grown on a Si3N4/Si substrate could provide a simple method to fabricate reproducible p-type ZnO films on silicon substrate for the development of large-scale optoelectronic integration device. (C) 2004 American Institute of Physics.
Reaction kinetics and mechanism of BaPbO3 formation
(2000-06-15)
Chang, MC
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Wu, JM
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Cheng, SY
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Chen, SY
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材料科學與工程學系
The influence of starting materials on the formation of BaPbO3 is studied. The reaction kinetics of perovskite BaPbO3 phase formation depends greatly on the phase of lead oxide raw materials. Kinetics of BaPbO3 formation is analyzed by the Johnson-Mehl-Avrami model. The experimental results reveals that the reaction of BaCO3-PbO2 raw materials has a reaction order of n = 5/2, and the reaction is controlled by diffusion. On the other hand, in the case of BaCO3-PbO system, the reaction order n is equal to 1. The formation is controlled by the interface reaction. In the final stage of both systems, the reaction orders are the same of about 0.5. The phases left in the final stage are BaPbO3 and BaCO3. (C) 2000 Elsevier Science S.A. All rights reserved.
Role of perovskite PMN in phase formation and electrical properties of high dielectric Pb[(Mg-x, Zn1-x)(1/3)Nb-2/3]O-3 ceramics
(1998-03-01)
Chen, SY
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Wang, CM
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
The structural evolution of perovskite phase Pb[(MgxZn1-x)(1/3)Nb-2/3]O-3 (abbreviated to PZMN) was found to be highly dependent on its precursors' strong tendency of forming pyrochlore phase in the mixture of raw materials. Three major pyrochlore compositions, Pb2Nb2O7, Pb3Nb2O8 and Pb3Nb4O13, were characterized and analyzed to understand their roles in the formation of the perovskite PZMN phase. Based on phase structure evolution, a preparation method for forming high dielectric constant PZMN ceramics without using common stabilizers such as SrTiO3 was proposed. By using pre-synthesized perovskite PMN, a Zn-rich PZMN composition with an almost 100% perovskite content and a maximum dielectric constant of 22 000 at 1 kHz is obtained. The formation mechanism of PZMN perovskite phase was also reported in this research. The pre-synthesized perovskite PMN acts as stabilizer and nuclei to initiate PZMN perovskite formation through the reaction in the PMN/ZnO interface. A ternary phase diagram of PMN-PZN-SrTiO3 was further constructed to investigate the perovskite development and its related electrical properties. (C) 1998 Elsevier Science S.A.
Synthesis and magnetic properties of highly arrayed nickel-phosphate nanotubes
(2005-07-01)
Lin, SC
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Chen, SY
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Cheng, SY
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Lin, JC
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交大名義發表
In this study, nanotube arrays of nickel-phosphate have been developed by electroless deposition into sub-micro to nanometer sized pores of the porous alumina templates by hypophosphite electrolytic solution composed of NiSO4, NaH2PO2, NaC2H3O2 and Na3C6H5O7 at 80-100 degrees C and PH = 3-6. The dimension of the formed nanotubes has 1 mu m in length, 200-300 nm in diameter and 80-150 nm in thickness of tube walls. Transmission electron microscopy examination of the nanotubes clearly show amorphous hallow structure with a average grain size of similar to 5 nm. The hysteresis loops of the nanotube arrays show a coercive field of about 200 Oe under treatment in 95%N-2/5%H-2 atmosphere at 500 degrees C as the magnetic field was applied along parallel and perpendicular to tube axis. The nanotube arrays also exhibit an anisotropic magnetic property with easier saturation along the perpendicular direction. However, both coercive field and saturation of remanent magnetization of the nanotube arrays become lower while continually increasing heat treatment temperature up to 900 degrees C. (c) 2005 Elsevier SAS. All rights reserved.
The effect of ball-milling solvent on the decomposition properties of Ba(Pb1-xBix)O-3
(2001-03-01)
Chang, MC
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Wu, JM
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Cheng, SY
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Chen, SY
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材料科學與工程學系
Ba(Pb1-xBix)O-3 compound, which exhibits perovskite structure is a superconducting material. It can be a useful material for resistor when x value equals 0. The conducting behavior of BaPbO3 is liable to be affected during aqueous processing. In contrast, the phenomenon is not found in Ba(Pb0.8Bi0.2)O-3 The milling solvents of water and ethanol have different effect on the stability of perovskite phase. The decomposition of BaPbO3 into BaCO3 and PbO2 is found when CO32- ion exists. The partial substitution of Bi3+ stabilizes the perovskite phase. The stabilization and decomposition of perovskite phase explain the resistivity change with different milling solvents. (C) 2001 Elsevier Science B.V. All rights reserved.
The effect of pyrochlore phase on formation mechanism and electrical properties of perovskite PZMN relaxors
(1997-06-15)
Chen, SY
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Wang, CM
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
The reaction mechanism and electrical properties of phase formation of the perovskite Pb[(Mg-x,Zn1-x)(1/3)Nb-2/3]O-3-SrTiO3 (PZMN-ST) were studied. Three major pyrochlore phase types, Pb2Nb2O7, Pb3Nb2O8 and Pb3Nb4O13 were characterized and analyzed to understand their roles in the formation of perovskite PMN, PZN and PZMN phases. The formation of a perovskite phase within PMN relaxors requires the presence of either Pb2Nb2PO7 or Pb3Nb2O8 pyrochlore phases in the mixture and is only slightly dependent on the presence of the stabilizer. On the other hand, the formation of a perovskite phase within PZN or PZMN relaxors requires the presence of both Pb3Nb2O8 pyrochlore phase and stabilizer. The maximum dielectric constant for PMN, PZN and PZMN systems can be obtained with the Pb3Nb2O8 phase present in the starting raw materials because of the benefit of Pb3Nb2O8 to perovskite phase formation.
The effect of pyrochlore phase on formation mechanism and electrical properties of perovskite PZMN relaxors
(1997-06-15)
Chen, SY
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Wang, CM
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Cheng, SY
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材料科學與工程學系
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Department of Materials Science and Engineering
The reaction mechanism and electrical properties of phase formation of the perovskite Pb[(Mg-x,Zn1-x)(1/3)Nb-2/3]O-3-SrTiO3 (PZMN-ST) were studied. Three major pyrochlore phase types, Pb2Nb2O7, Pb3Nb2O8 and Pb3Nb4O13 were characterized and analyzed to understand their roles in the formation of perovskite PMN, PZN and PZMN phases. The formation of a perovskite phase within PMN relaxors requires the presence of either Pb2Nb2PO7 or Pb3Nb2O8 pyrochlore phases in the mixture and is only slightly dependent on the presence of the stabilizer. On the other hand, the formation of a perovskite phase within PZN or PZMN relaxors requires the presence of both Pb3Nb2O8 pyrochlore phase and stabilizer. The maximum dielectric constant for PMN, PZN and PZMN systems can be obtained with the Pb3Nb2O8 phase present in the starting raw materials because of the benefit of Pb3Nb2O8 to perovskite phase formation.
Ultraviolet emission in ZnO films controlled by point defects
(2004)
Lin, CC
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Hsiao, CS
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Chen, SY
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Cheng, SY
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材料科學與工程學系
The undoped ZnO films were grown on silicon (001) substrates by radio frequency magnetron sputtering. The dependence of defect formation and photoluminescence (PL) of ZnO films on the annealing temperature and oxygen mole ratio (OMR) were investigated using X-ray diffraction and PL spectra. A sharp ZnO (002) peak with a strong UV emission peak around 3.28 eV can be obtained for the films annealed in O-2 and N-2 atmospheres. However, the films annealed in nitrogen show strong deep-level emission peaks that vary with the annealing temperature. Below 850 degreesC, Zn interstitials become the dominant point defects, but for the ZnO films annealed at higher temperatures such as 1000 degreesC, oxygen vacancies become the predominant point defects. In contrast, in an oxygen atmosphere, a strong UV emission along with invisible deep-level peaks can be detected for ZnO films sputtered at an OMR of 5% and annealed at 850 degreesC. This result is attributed to the enhanced crystallization and a reduced defect concentration. (C) 2004 The Electrochemical Society.