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Now showing 1 - 10 of 27

Elastic interaction between screw dislocations and a circular surface crack
(1997-03-31)
Lin, KM
;
Lin, HC
;
Chen, KC
;
Chang, HL
;
材料科學與工程學系
The behaviour of a screw dislocation around a circular surface crack was analyzed using the conformal mapping method. The effects of the crack length l and its radius of curvature R on the shielding effect and the strain energy were discussed in detail. It was found that for a dislocation being fixed at a constant distance from the crack tip and located on a plane tangent to crack surface at the tip, there exists a critical crack length l* corresponding to a maximum shielding effect induced by the dislocation on the circular surface crack. The l* increases with R and approaches infinity as the crack becomes planar (i.e. R --> infinity). The shielding effect vanishes as the crack disappears. It increases rapidly with l if 0 < l much less than l*, regardless of R. After reaching the maximum, it decreases slightly for larger R but significantly for smaller R as the crack becomes longer. The shielding is more pronounced for larger R than that for smaller R, with the difference increasing with crack length. As a result, a surface microcrack propagates initially in a rather brittle manner then becomes more ductile. When the crack gets longer, it still keeps ductile for a less curved or a planar crack but becomes relatively brittle for a severely curved crack. In addition, the strain energy is also significantly influenced by crack length and increases rapidly with l when l is rather small, regardless of R. With increasing l, it becomes less affected by l, and the variation with R is still not obvious, with larger R corresponding to a slightly higher strain energy. (C) 1997 Elsevier Science S.A.
Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups
(1997-09-30)
Hsu, CS
;
Chu, PH
;
Chang, HL
;
Hsieh, TH
;
應用化學系
The synthesis of side-chain liquid crystalline polysiloxanes containing either 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-[(S)-2-methyl-1-butoxy] phenyl 4-(alkenyl oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an Sd phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the technique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. (C) 1997 John Wiley & Sons Inc.
Thermally stimulated deporization current and DSC studies of the dual glass transitions in side-chain liquid crystalline copolysiloxanes
(1996-08-25)
Chang, HL
;
Hsu, CS
;
應用化學系
;
Department of Applied Chemistry
High resolution and energy filtering TEM study of interfacial structure and reaction in advanced materials processing
(1998-04-10)
Chang, HL
;
Chang, L
;
Chen, FR
;
Kai, JJ
;
Tzou, E
High resolution TEM becomes more powerful when coupled with a Gatan imaging filler (GIF). It gives both structural and compositional information simultaneously with subnanometer and nanometer resolution. respectively. By means of these combined techniques, the failure mechanism of diffusion barrier layers in IC devices, having the structure of Al-1%Si-0.5%CuiTiNITi/Si substrate, was investigated. In non-oxygen stuffed samples thermally stressed at 550 degrees C for 1 h serious Al spikes below contacts were observed where metal layer Ti also reacted with Si substrate to form C49-TiSi2 and was consumed completely. TiN and Al become unstable due to high temperature thermal stress and reacted into TiAl3 and AlN. Decomposition of TiN degraded the function of the barrier layer, and so a diffusion path at the weakest point of the contact corner was opened for metal Al alloy to diffuse through the barrier layer and to form a spike below the TiN layer. We also showed that the oxygen-stuffing processes after each TiN/Ti deposition enhances the barrier capability against Al/Si diffusion in thermal stress. It was found that Ti and TiN were oxidized to form titanium oxide which reacted with the Al alloy. As a result, Al2O3 and TiAl3 were found above the TiN layer. Therefore, it is concluded that oxidation during oxygen-stuffing processes provides a means to inhibit diffusion in thermal stress processes, and maintains integrity of the stack structure. (C) 1998 Acta Metallurgica Inc.
Using a weight-assessing model to identify route choice criteria and information effects
(2001-03-01)
Chen, TY
;
Chang, HL
;
Tzeng, GH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Shortest-path (minimum travel time) routing has been adopted over the past few decades. However, many studies have shown that a driver's route and the shortest path differ widely in significant ways, and that most drivers use several criteria in selecting their routes. Since route choice criteria have been the subject of controversy, this study develops an individual behavioral-based mechanism for exploring the crucial criteria affecting drivers' route-selection decisions. On the basis of the weight-assessing model and the habitual domain theory, this study presents the dynamic change of route choice criteria according to their dynamic weights. Furthermore, the effects of information on drivers' route-formulating behaviors are investigated as well in order to provide some valuable suggestions for implementing Advanced Traveler Information Systems (ATIS) in the future. An empirical study in Taipei City was conducted to show the feasibility and applicability of our proposed method and the empirical results indicate excellent performance in practice. (C) 2001 Elsevier Science Ltd. All rights reserved.
Analytical model for design criteria of passively Q-switched laser
(2001-03-01)
Chen, YF
;
Lan, YP
;
Chang, HL
;
電子物理學系
;
光電工程學系
A general and straightforward model was developed for the design of passively Q-switched lasers. With the second-threshold criterion and using a numerically fitting procedure, the output pulse energy was expressed as an analytical function of the initial transmission of the saturable absorber and the reflectivity of the output coupler. An analytical expression for the optimal output reflectivity was also obtained for maximizing the output pulse energy of a passively Q-switched laser with a given initial transmission of the saturable absorber. Excellent agreement was studied between the present results and detailed theoretical computations. A Nd:YAG laser with Cr4+:YAG as a saturable absorber was performed to illustrate the use of the present model.
Properties of Si-C-N films prepared on Si substrate using cobalt interfacial layers
(2001-11-01)
Chang, HL
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A microwave plasma chemical vapor deposition (MPCVD) process was successfully used to synthesize Si-C-N films. The film properties were tuned by deposition parameters and engineering interfacial Co layers on Si substrates. The films were deposited by using CH4, N-2, and additional solid Si columns as raw material sources. The films were characterized by scanning electron microscopy (SEM) for film morphologies, X-ray photo-emission spectroscopy (XPS) and cathodoluminescence (CL) spectroscopy for bonding structure and band gap analyses. The results show that the application of Co interlayer can have the following effects: (1) it can change film morphology from (100) preferred orientation to become pyramidal structure, and the band gap from 2.93 to 4.00 eV; (2) it may possess the additional Si(2p)-Si bonding in the films. By adding additional Si source, the atomic ratio of Si:C:N can change significantly with the decrease in carbon content of films, the film structure may vary from amorphous to crystalline and possess additional C(1s)=N bonding (or N(1s)=C bonding). In summary, the composition, morphology, bonding and crystal structures of Si-C-N films have been successfully demonstrated to be manipulated through applications of Co interlayer and additional Si source. (C) 2001 Elsevier Science B.V. All rights reserved.
Effects of substrate pretreatments and catalyst applications on Si-C-N films and nanotube formations
(2001-12-01)
Chang, HL
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The Si-C-N films were synthesized on Si substrates by a microwave plasma chemical vapor deposition (MPCVD) system with CH4, H-2 and N-2 as the source gases. Metal coating on Si columns were placed around the specimen and acted as catalyst and additional source of Si. Some of the Si substrates were mechanically polished or chemically etched with HF-KIO3-H2O solutions to obtain different surface roughness before film depositions. Effects of the substrate pretreatment and the action of catalysts on surface morphologies, compositions, band structure, field emission of the films were examined. Nanotubes or nanowires structures were found for films deposited on no-treatment substrate using Fe, Co and Pt catalysts. However, chemical etching substrate can enhance formation of crystals and film nucleation with or without the addition of catalyst. This was the first work to demonstrate the possibility of fabricating the Si-C-N nanotubes through use of the catalysts and by controlling the deposition conditions by MPCVD. Under the present deposition conditions and by using Fe catalyst, the lowest turn-on voltage of the films can be as low as 1.3 V/mum, while the corresponding emission current density at field strength of 20 V/mum can go beyond 2000 muA/cm(2).
Using fuzzy measures and habitual domains to analyze the public attitude and apply to the gas taxi policy
(2002-02-16)
Chen, TY
;
Chang, HL
;
Tzeng, GH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Public acceptance and support are the crucial keys for implementing public policies successfully. Thus, the understanding of public acceptance or rejection towards the policy, as well as the important attributes of concern, could be very helpful to implementing the policy. However, most conventional attitude models could not approximate people's subjective evaluation process exactly by virtue of the additivity and independence assumptions. Additionally, people's decision behavior is deeply affected by their existing habits. Since habitual domains exist in the decision process, if the government can change or extend people's habitual thinking in favor of the public policy, the policy will receive satisfactory acceptance. Therefore, this study uses the habitual domain theory to analyze the public's attitude towards public policies. Furthermore, general fuzzy measures and fuzzy integrals, which require only boundary conditions and monotonicity, are also applied to develop a public attitude analysis model. An empirical study on the compress natural gas (CNG) taxi policy in Taipei City is conducted to show the applicability of the proposed model. The empirical results indicate that there are significant differences between the public's concern and governmental publicity, and some valuable strategies are suggested to the government. (C) 2002 Elsevier Science B.V. All rights reserved.
Growth mechanism and properties of the large area well-aligned carbon nano-structures deposited by microwave plasma electron cyclotron resonance chemical vapor deposition
(2002-03-01)
Lin, CH
;
Chang, HL
;
Tsai, MH
;
Kuo, CT
;
材料科學與工程學系
Large area (4-inch diameter) well-aligned carbon nano-structures on Si substrate were successfully synthesized by using a catalyst-assisted microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 as source gas. The catalysts include Fe, Co and Ni. The catalysts and the deposited nano-structures were characterized by scanning electron microscopy (SEM) transmission electron microscopy (TEM), Raman and field emission I-V measurements. Effects of process parameters on morphologies, structures and properties of the nano-structures were examined. The results show that the deposited nano-structures can include normal nano-tubes, split catalyst nano-tubes, seaweed-like nano-sheets and carbon film, depending mainly on substrate temperature and bias, catalyst materials and their application methods. Deposition mechanisms for different nano-structures, especially, the unique split catalyst nano-tubes and seaweed-like nano-sheets, were proposed. The differences in oxidation resistance and field emission proper-ties between different nano-structures will be compared and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

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