Browsing by Author "Chang, HL"

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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.
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
;
交大名義發表
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.
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.
Effect of silane flowing time on W volcano and plug formation
(2002-05-01)
Chang, HL
;
Juang, FL
;
Kuo, CT
;
交大名義發表
;
National Chiao Tung University
W volcano is one of the defects in semiconductor devices. The presence of defects causes metal line bridges and thus device malfunction. The decomposition of SiH4 gas into Si atoms as nucleation sites is crucial for W film deposition. Here, we investigate the phenomenon in which the flowing time of SiH4 gas appears to dominate both W volcano formation and the degree of W film filling in a hole; the density of W volcanoes is increased with an increase of SiH4 flowing time. The volcano-free process and step-coverage of a W plug with various SiH4 flowing times are evaluated, and a formation mechanism is also proposed.
Effect of thin film coating of Au on joint strength in Invar-Invar packages
(1996-11-01)
Wang, SC
;
Wang, CM
;
Wang, C
;
Chang, HL
;
Tu, YK
The effect of a thin film coating of Au on the joint strength, weld width, and penetration depth in laser welding techniques for Invar-Invar packages is investigated experimentally. It is found that the joint strength, weld width, and penetration depth are strongly dependent on the coating of Au thickness on the Invar material. The welded joints with thick Au coating show narrower weld width, shallower penetration, and hence less joint strength than those of the packages with thin Au coating. The increase in both the thermal conductivity and the vapor volume in the welded joints as the coating of Au thickness increases are the possible mechanisms for the reduction. Detailed knowledge of the effect of thin film coatings of Au on the welded materials, which gives both the highest joint strength and good adhesion, is essential for practical design and fabrication of reliable optoelectronic packaging.
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).
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.
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.
Factors affecting the safety performance of bus companies - The experience of Taiwan bus deregulation
(2005-06-01)
Chang, HL
;
Yeh, CC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study was undertaken to explore the factors affecting the safety performance of bus companies in Taiwan. A conceptual framework was developed based on the theory of organizational accidents. Environmental and organizational factors were assumed to determine the safety performance of bus companies. Since the deregulation of intercity passenger transportation in 1995 the bus transportation industry in Taiwan has been restructured, and this provides an opportunity to gain insight into the factors that influence the safety performance of bus companies. The study results show that the bus companies on joining intercity bus services in Taiwan did experience higher risks of being involved in major injury and minor injury accidents. The study results provide convincing evidence that organizational factors, including driver-specific, vehicle-specific and general management factors, have significant effects on the safety performance of bus companies. Therefore, if the economic deregulation was implemented with some safety regulation policies, we might have the opportunity to pursue a better safety performance by the bus transport industry as a whole, rather than just prevent the deterioration of the existing safety performance. Furthermore, the limited resources available to monitor the safety performance of bus companies are suggested to focus on those companies that run intercity services as well as those companies of small size, having older fleets, and a higher traffic conviction rate. (c) 2005 Elsevier Ltd. All rights reserved.
Field emission, structure, cathodoluminescence and formation studies of carbon and Si-C-N nanotubes
(2002-03-01)
Chang, HL
;
Lin, CH
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Catalyst growth carbon and Si-C-N nanotubes have been synthesized successfully by microwave plasma chemical vapor deposition (MPCVD) method using CH4 + H-2 or CH4 + N-2 as gas sources, Si columns as additional Si solid sources, and Fe, Fe-Y, Co-Ni as catalysts. Nanotubes consisting of Si, C and N were made under process gases of CH4 + N-2, and with or without additional Si columns. Well-aligned and nested nanotubes were observed dependent on the catalyst materials. Besides, Si-C-N nanotubes were observed as bamboo-Eke structure. The as-grown nanotubes were purified in an air furnace to investigate their CL signal shift for potential application involving blue light emission. The field emission results indicate that the emission current densities can be above 10 mA/cm(2) at 10 V/mum, and aligned nanotubes belong to better current stability at a constant electric field than nested nanotubes. Nanotubes with a low I-D/I-G ratio (=0.23) via Raman analysis are achieved. The mechanisms of formation for carbon nanotubes and Si-C-N nanotubes are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
Forming silicon carbon nitride crystals and silicon carbon nitride nanotubes by microwave plasma-enhanced chemical vapor deposition
(2002-06-17)
Chang, HL
;
Hsu, CM
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Catalyst-assisted silicon carbon nitride (SiCN) nanotubes and SiCN crystals are prepared. The SiCN nanotubes and SiCN crystals are formed by gaseous sources of CH4/N-2/H-2 and CH4/N-2, respectively, and using solid Si columns arranged symmetrically around the specimen as additional Si sources. The formation of the tubular structure is related to the ambient of process that includes H-2 gas, which is considered to delay the action of the so-called catalyst poisons and keep the tube end open during growth. Analysis shows that the SiCN crystals exhibit tetragonal or hexagonal shapes with sizes of about several microns, and multibonding structures. In contrast, the SiCN tubes are randomly orientated with various diameters, and graphitelike structure. The growth mechanisms of SiCN crystals and SiCN nanotubes are discussed. (C) 2002 American Institute of Physics.
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.
Growth of the large area horizontally-aligned carbon nanotubes by ECR-CVD
(2002-12-02)
Hsu, CM
;
Lin, CH
;
Chang, HL
;
Kuo, CT
;
材料科學與工程學系
For potential applications of carbon nanotubes (CNTs) as connectors in microelectronic devices, the process to synthesize the large area horizontally-aligned CNTs on 100 mm (4 inch) Si wafers was developed, using electron cyclotron resonance chemical vapor deposition, with CH, and H, as the source gases and Co as the catalyst. The results show that vertical and horizontal CNTs can be obtained by manipulating the electric field applied on the substrate and flow direction of the gases. In the present deposition conditions, the horizontal CNTs show better field emission properties than vertical CNTs. This may be due to the blocking effect of catalysts at the tips and to the diminishment of the effective emission area from defects of vertical CNTs body. (C) 2002 Elsevier Science B.V. All rights reserved.
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.
Iron and cobalt silicide catalysts-assisted carbon nanostructures on the patterned Si substrates
(2002-12-02)
Chang, HL
;
Lin, CH
;
Kuo, CT
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Catalyst-assisted carbon nanotubes (CNTs) and carbon nano-rods were synthesized on the patterned or un-patterned Si wafer by microwave plasma chemical vapor deposition, using iron or cobalt silicide catalysts. Controllable carbon nanostructures were achieved by manipulating carbon and nitrogen concentration in the source gases, catalyst materials, and patterned wafer application. CNTs were synthesized under a high ratio of CH4/H-2 = 0.1, while carbon nano-rods were synthesized under a low ratio of CH4/H-2=0.01. Introducing N-2 gas into CH4/H-2 source gases gives rise to bamboo-like CNTs formation. Selective CNTs depositions were applied on (a) parallel Fe-coated line arrays, (b) CoSix-coated hole arrays. This is a novel method that is compatible with Si microelectronic device manufacturing. The field emission results indicate that the emission current density can be above 1 mA/cm(2) at 3.97 V/mum, and hollow like CNTs belong to better emission current than bamboo-like CNTs. Growth models of different carbon nanostructures are proposed. (C) 2002 Elsevier Science B.V. All rights reserved.
Is rigorous punishment effective? A case study of lifetime license revocation in Taiwan
(2006-03-01)
Chang, HL
;
Woo, TH
;
Tseng, CM
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study investigated the effectiveness of administrative lifetime driver's license revocation (ALLR) and its impact on offenders, based on a two-stage survey of 768 offenders. It was found that after ALLR had been imposed, 23.4% of these offenders were still driving almost the same as before, 59.8% drove significantly less frequently, and only 16.8% of the offenders gave up driving completely. The results of logistic regression models showed that offenders' compliance with ALLR was significantly correlated with their personal characteristics (age, income), penalty status (incarceration, duration of ALLR), and the need to drive for working, commuting and shopping. Elderly and low-income offenders were more likely to abide by the ALLR restriction. The application of the generalized estimating equations (GEE) model was used to identify the determinant factors affecting offenders' driving mileage, and to effectively estimate the driving mileage reduction as a result of the ALLR. It was found that ALLR is fairly effective in keeping offenders off the road, but that it may reduce their ability to make a living. resulting in the less fortunate becoming more helpless. (c) 2005 Elsevier Ltd. All rights reserved.
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.
Risk factors to driver fatalities in single-vehicle crashes: Comparisons between non-motorcycle drivers and motorcyclists
(2006-03-01)
Chang, HL
;
Yeh, TH
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
Single-vehicle crash data for 2000 from Taiwan's Road Accident Investigation & Reporting System were employed to compare fatality risk factors between non-motorcycle drivers and motorcyclists. Oil average, Motorcyclists had approximately a three times higher fatality risk than non-motorcycle drivers after adjusting for the driving mileage. Two respective logistic regression models for these two categories of drivers indicated that some common features, such as being Male, a higher age. and crashes occurring between the hours of 2200 and 0600 revealed a greater likelihood of fatality. Oil the other hand, the risk discrepancies between these two drivers included the restraint-use effect, speeding, and impairment as the main crash cause, roadway class, and vehicle type. To reduce the high risk of fatality sustained by these two classes of drivers, enhancing the driver's seatbelt-use rate, the management of running speed, the rider's risk perceptions, and the road quality and facilities of the lowest roadway class are particularly recommended.
The life cycle of the policy for preventing road accidents: an empirical example of the policy for reducing drunk driving crashes in Taipei
(2004-09-01)
Chang, HL
;
Yeh, CC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
The purpose of this paper is to examine the temporal variation of the effect of preventive policy on reducing traffic accidents. The life cycle theory was introduced to describe the safety effect of the intervening policy over time. Poisson regression models with dummy-based and time-based specifications were used to evaluate the effect of an intervening policy over an observation period following its implementation. The policy of "Criminal sanction for drunk driving (CSFDD)" in Taipei city was evaluated as an empirical example to determine whether the temporal variation of safety effect happened to the CSFDD policy. The study results showed that alcohol consumption, arresting the drunk driving offenders, and the implementation of the CSFDD were the significant factors affecting the rate of occurrence of fatal accidents involving drunk driving. The effect of the CSFDD policy appeared to be a rapid initial response followed by a lowerrate of decay. The existence of the life cycle implies that employing different observation periods following the implementation of a specific policy to evaluate its performance may obtain different effects. The results of this study are crucial for policy evaluation. The effects of safety policy should be carefully interpreted in order to avoid misleading the relevant authorities in coming to the wrong conclusions and as such make the wrong decisions. 9 (C) 2003 Elsevier Ltd. All rights reserved.
The relationship between the working pressure and accident risks for aggregate-hauling vehicle drivers in Taiwan
(2001)
Chang, HL
;
Yeh, CC
;
運輸與物流管理系註：原交通所+運管所
;
Department of Transportation and Logistics Management
This study is undertaken to explore the sources of stress which enhance the accident risk of AHV drivers and try to develop corresponding strategies to improve the driving safety for AT-TV drivers. In this paper, we introduce the relationship between work pressure and accident risk and develop a conceptual model based on this relationship. An empirical study was conducted by using the data collected from a face to face interview with AHV drivers to verify our hypothetical relationship. The findings of this study provide a set of valuable information to help setting effective policies and strategies.