Rozprawy doktorskie na temat „Interfacial defect”

Les revêtements d'hydrogel sont des réseaux de polymères transparents et hydrophiles capables d’abosrber plusieurs fois leur épaisseur en eau. Cependant, les contraintes induites par le gonflement du film peuvent entraîner un décollement préjudiciable de l'hydrogel ce qui peut limiter l’utilisation pratique des ces revêtements. Dans cette étude, nous proposons de décrire les mécanismes de décollement de films minces d’hydrogel en fonction de leur densité de greffage à l'interface film/substrat. Le but est de pouvoir contrôler et prédire la dégradation des revêtements hydrogel pendant le gonflement ou sous des contraintes de contact. Dans ce but, nous avons développé une méthodologie permettant de mesurer l'initiation et la propagation de la délamination induite par le gonflement de films minces d’hydrogel à partir de défauts d'interface préexistants bien contrôlés.Des films minces d'hydrogel de poly(diméthylacrylamide) (PDMA) attachés à la surface sont préparés sur des plaquettes de silicium à partir de la réticulation et du greffage simultanés (CLAG) de chaînes polymères fonctionnalisées par la chimie click thiol-ène. Cette stratégie permet de faire varier l'épaisseur du film (0.1 - 2 µm) et de contrôler le taux de gonflement du réseau, ici fixé à 2, tout en assurant une densité de réticulation homogène. Afin de faire varier la résistance de l'interface film/substrat, le substrat en silicium est greffé avec des mélanges de mercaptosilane (réactif) et de propylsilane (inerte) dans différentes proportions avant le dépôt du film mince. Alors que le mercaptosilane est capable de former des liaisons covalentes avec le réseau PDMA, le propylsilane ne réagit pas, ce qui permet de contrôler le taux de greffage du film mince d’hydrogel sur le substrat. Nous caractérisons la fraction de surface de mercaptosilane ainsi obtenue par des analyses XPS et TOF-SIMS. Par ailleurs, toujours à l’interface subtrat/film, des défauts linéaires bien contrôlés ayant une faible adhérence (largeur entre 10 et 100 µm) sont créés sur le substrat en passivant de façon localisée les groupes thiol réactifs par microlithographie. Ces défauts nucléent le décollement des films de façon bien localisée, ce qui permet ensuite de suivre la propagation de la décohésion à partir de ces défauts.Le décollement du film induit par le gonflement est réalisé sous un flux de vapeur constant assurant la saturation du film en eau. En observant le décollement progressif du film à partir des défauts linéaires préexistants, nous retrouvons un motif d’instabilité classique dit de fil de téléphone et nous montrons que le décollement résulte de contraintes de gonflement localisées proche de la ligne de décollement. Nous mesurons la vitesse de propagation du décollement dans la zone où le film est greffé sur le substrat et nous observons qu’elle augmente de deux ordres de grandeur lorsque la quantité de propylsilane dans le mélange de silanes réactifs passe de 0 à 90 %, c’est-à-dire lorsque le taux de greffage du film décroit. Un seuil d'épaisseur pour le décollement est également observé, les films pouvant se décoller étant d’autant plus minces que le taux de greffage du film ets faible. Les mesures de ce seuil sont discutées à partir d'un argument simple de mécanique de la rupture qui permet de rendre compte semi quantitativement de nos mesures
Hydrogel coatings are transparent and hydrophilic polymer networks that absorb a lot of water and can be suitable candidates for anti-mist coatings. However, swelling-induced stresses within the film can result in detrimental debonding of hydrogel and may fail. In this study, these debonding processes are investigated in the relation to the grafting density at the film/substrate interface, so as to control and predict the failure of the coatings during swelling or under contact stresses. For that purpose, we have developed a methodology consisting in monitoring the initiation and the propagation of swelling-induced delamination from well-controlled preexisting interface defects.Surface-attached poly(dimethylacrylamide) (PDMA) hydrogel thin films are prepared on silicon wafers from the simultaneous Cross-Linking And Grafting (CLAG) of functionalized polymer chains by thiol-ene click chemistry. This strategy allows to tune the film thickness (0.1-2 µm) while ensuring a homogeneous crosslinking density. In order to vary the strength of the film/substrate interface, the silicon wafer is grafted by mixing reactive mercaptosilane and unreactive propylsilane in various proportions prior to the formation of the hydrogel film. We characterize the mercaptosilane surface fraction thus obtained by XPS and TOF-SIMS analyses. Well-controlled line defects (width between 2 and 100 µm) are also created to nucleate delamination of the hydrogel from the substrate.Swelling-induced debonding of the film is achieved under a constant vapor flow ensuring water saturation. Optical observations show the progressive debonding of the film from the pre-existing line defects under the action of localized swelling stresses. We obtain a delamination pattern of typical so-called telephone cord instability. We measure the debonding propagation velocity where the hydrogel is grafted to the substrate. The debonding rate is found to decrease over two orders of magnitude when the amount of mercaptosilane in the reactive silane mixture is increased from 10% to 100% while increasing the covalent bonds between hydrogel and substrate. A threshold thickness for debonding is also observed. This threshold thickness increases with the amount of mercaptosilane used to graft the substrate. We derived quantitative values of the interface fracture energy from the measured thickness threshold with a simple fracture mechanics model

O carbeto de silício (SiC) é um semicondutor com propriedades adequadas para substituir o silício em dispositivos eletrônicos em aplicações que exijam alta potência, alta frequência e/ou alta temperatura. Além disso, é possível crescer termicamente um filme de dióxido de silício (SiO2) sobre o SiC de maneira análoga ao silício. Porém, esses filmes apresentam maior densidade de defeitos eletricamente ativos na região interfacial SiO2/SiC que no caso do SiO2/Si, o que limita a qualidade dos dispositivos formados. Assim, compreender a origem da degradação elétrica e desenvolver métodos para passivar os defeitos na região interfacial SiO2/SiC são importantes passos para o desenvolvimento da tecnologia do SiC. Buscando uma melhor compreensão da natureza dos defeitos presentes na região interfacial SiO2/SiC, a interação de estruturas SiO2/SiC com vapor d’água enriquecido isotopicamente (D2 18O) e a interação com monóxido de carbono (CO), um dos subprodutos da oxidação térmica do SiC, foram investigadas. Observou-se que a interação com CO gera cargas positivas na estrutura e que a incorporação de deutério proveniente da água é fortemente dependente da rota de formação do filme de SiO2. Sabendo que a incorporação de nitrogênio e de fósforo na região interfacial SiO2/SiC são eficientes métodos para reduzir o número de defeitos eletricamente ativos nessa região, investigou-se a incorporação de nitrogênio em estruturas de SiC através de tratamentos térmicos em amônia enriquecida isotopicamente (15NH3) e desenvolveu-se um novo método de incorporação de fósforo, fazendo sua deposição por pulverização catódica (sputtering) Os métodos de incorporação propostos resultaram em maiores quantidades de nitrogênio e de fósforo na região interfacial SiO2/SiC do que os encontrados na literatura, tornando-os promissores candidatos na passivação elétrica do SiC. Além da caracterização físico-química utilizando diferentes técnicas, também foi feita a caracterização elétrica de capacitores Metal-Óxido-Semicondutor (MOS) testando filmes de SiO2 obtidos por sputtering ou por crescimento térmico. Adicionalmente, desenvolveu-se uma rota de síntese de padrões de 18O mais estáveis ao longo do tempo para serem utilizados em análises por reação nuclear. Também foi proposta uma metodologia de quantificação de fósforo via análise por reação nuclear. Dos resultados obtidos neste doutorado, uma melhor compreensão da natureza e da origem dos defeitos presentes na região interfacial SiO2/SiC foi alcançada. Também obteve-se uma melhor compreensão de como os elementos passivadores nitrogênio e fósforo interagem nessa região.
Silicon carbide (SiC) is a semiconductor with adequate properties to substitute silicon in electronic devices in applications that require high power, high frequency, and/or high temperature. Besides, a silicon dioxide (SiO2) film can be thermally grown on SiC in a similar way to that on Si. However, these films present higher density of electrical defects in the SiO2/SiC interfacial region when compared to the SiO2/Si interface, which limits the quality of the fabricated devices. Thus, it is important to understand the origin of the electrical degradation and to develop methods to passivate the defects in the SiO2/SiC interfacial region in order to develop the SiC technology. Aiming at a better understanding of the nature of defects at the SiO2/SiC interfacial region, the interaction of SiO2/SiC structures with water vapor isotopically enriched (D2 18O) and the interaction with carbon monoxide (CO), one of the SiC thermal oxidation by-products, were investigated. It was observed that the interaction with CO generates positive charges in the structure and that the deuterium incorporation from the water vapor is strongly dependent on the formation route of the SiO2 film. Knowing that nitrogen and phosphorous incorporation in the SiO2/SiC interfacial region are efficient methods to reduce the number of electrical defects in this region, the nitrogen incorporation in SiC structures by isotopically enriched ammonia (15NH3) annealings was investigated and a new method to incorporate phosphorous, by sputtering deposition was developed The proposed incorporation methods resulted in higher amounts of nitrogen and phosphorous then those found in literature, making them promising candidates to the electrical passivation of SiC. Besides the physico-chemical characterization using different techniques, the electrical characterization of Metal-Oxide-Semiconductor (MOS) capacitors was also performed, testing SiO2 films obtained by sputtering deposition or thermally grown. Additionally, a route to synthesize 18O standards for nuclear reaction analyses that are more stable over time was developed. Besides, a methodology to quantify phosphorous by nuclear reaction analysis was proposed. From the results obtained in this PhD thesis, a better understanding of the nature and the origin of defects present in the SiO2/SiC interfacial region was obtained, as well as a better understanding on how the passivating elements nitrogen and phosphorous interact in this region.

The aim of this work was to develop a solid knowledge on formulation effects controlling offset ink-paper coating adhesion and to identify key factors of the coating and printing process affecting it. Focus lay on comprehending the impact of pigment dispersant on ink-paper coating adhesion and ultimately on the print quality of offset prints. The work covers laboratory studies, a pilot coating trial designed to produce coated material with a span in surface chemistry and structure, and an industrial offset printing trial. The lab scale studies quantified ink-paper coating adhesion failure during ink setting with a developed laboratory procedure based on the Ink-Surface Interaction Tester (ISIT) and image analysis. Additional polyacrylate dispersant resulted in slower ink setting and reduced ink-paper coating adhesion, with a dependence on its state of salt neutralisation and cation exchange, mainly in the presence of moisture/liquid water. The industrial printing trial on pilot coated papers was designed to study how these laboratory findings affected full scale offset print quality. These trials confirmed the dispersant-sensitive effect on ink-paper coating adhesion, especially at high water feeds. Evaluation of prints from the printing trial resulted in two fundamentally different types of ink adhesion failure being identified. The first type being traditional ink refusal, and the second type being a novel mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off adhesion failure occurs when ink is initially deposited on the paper but then lifted off in a subsequent print unit. In this work, ink adhesion failure by this ink-lift-off mechanism was observed to occur more often than failure due to ink refusal. Print quality evaluation of the industrial prints suggested that water induced mottle was caused by a combination of ink-surface adhesion failure, creating white spots on the print, together with variation in ink layer thickness due to emulsified ink.

QC 20161019

Apres avoir elabore un potentiel semi-empirique adapte aux alliages fe - al de structures b2 et d0#3, nous avons etudie les defauts ponctuels et les joints de grains dans ces composes. A basse temperature, l'ecart a la stchiometrie b2 est accommode par des defauts d'antisite ; a plus haute temperature, des lacunes de fer apparaissent et les defauts tendent a former des complexes dont la structure est tres sensible a l'ecart a la stchiometrie. Nos calculs, reposant sur les energies de formation a temperature nulle, indiquent les types des defauts predominants, mais conduisent a des predictions quantitatives sous-estimees, ce qui souligne probablement l'importance des vibrations atomiques. Dans le compose b2 equiatomique, la diffusion des deux especes s'effectue conjointement par des cycles a quatre sauts de lacunes de fer. Bien que les energies d'activation calculees soient comparables a celles deduites de l'experience, les coefficients de diffusion calcules se revelent inferieurs aux mesures experimentales. La difference peut la encore etre attribuee a la non-prise en compte des vibrations atomiques. La seconde application concerne les structures atomiques du joint de grains symetrique de flexion autour de 001 et de plan (310) dans les composes b2 et d0#3. A basse temperature, nous obtenons, dans le compose b2 equiatomique, une unique structure stable (pseudo-symetrique) enrichie en fer, ainsi qu'une forte influence de la composition globale sur cette structure (avec segregation intergranulaire de l'element majoritaire). Dans le compose d0#3 stchiometrique, il existe une grande multiplicite de structures, celles-ci etant toujours enrichies en aluminium. L'etude structurale du joint de grains dans l'alliage b2 a haute temperature revele une transition de phases stabilisant une structure symetrique. Celle-ci etant tres energetique a basse temperature, son apparition met une fois encore en evidence l'importance des vibrations atomiques dans les composes fe - al b2.

This dissertation describes the impact of defects on monolayer properties for self-assembled monolayers (SAMs) created by interfacial patterning methods. When forming a two-dimensional interfacial pattern with n-alkanethiols on gold, the desired electrochemical properties are those of a homogeneous, solution adsorbed monolayer. However, even well-ordered SAMs contain a small degree of defects, especially at domain boundaries where two nucleating domains converge. Patterning a surface creates user-defined domain boundaries within the monolayer, potentially having a significant impact on the properties of the interface. This dissertation investigates the effect that user-created domain boundaries have on the properties of a monolayer, as studied by electrochemical impedance spectroscopy. Two patterning methods are investigated for creating user-defined domain boundaries: the soft lithography method of contact printing and site-selective reductive desorption. The electrochemical properties of homogeneous contact printed monolayers are measured and compared to those of monolayers prepared by solution adsorption. The contact printed monolayers are found to have dramatically different impedance behavior from the solution prepared monolayers, consistent with the contact printed monolayers having greater defect density. In addition, these studies show that the overall defect density depends on the concentration of the solutions used for contact printing. In this work, simple patterns are created by contact printing a pattern onto the substrate and then backfilling the remaining gold substrate by solution adsorption. Backfilling with the same alkanethiol used to create the pattern generates a homogeneous monolayer; however, it is found that the contact printed/backfilled monolayer has an impedance intermediate between the homogeneous contact printed and the homogeneous solution adsorbed monolayer. This result suggests that the backfilling process also saturates the pinhole defects associated with the contact printed areas. In addition to exploring defects that arise from contact printing, simple patterns with user-defined defects, created by site-selective reductive desorption (SSRD), were also investigated. Following the backfill step, the impedance behavior of the SSRD produced patterns was similar to that of the impedance of the initial pattern before backfilling. This important result implies that the domain boundaries play the most important role in defining the overall impedance of the patterned interface.
Ph. D.

Le procédé de coextrusion permet de combiner à l’état fondu plusieurs couches de polymères dans une même structure. La compatibilisation des différentes couches est généralement réalisée à l’aide de liants qui réagissent in-situ. Bien que la compatibilisation puisse permettre de réduire ou même supprimer les instabilités macroscopiques d’écoulement, un nouveau défaut qualifié de « granité » peut apparaitre. Très peu de travaux de la littérature traitent les mécanismes gouvernant ce type de défaut. Les phénomènes mis en jeu sont particulièrement complexes puisqu’ils impliquent de façon couplée des phénomènes hydrodynamiques via l’écoulement, la rhéologie des différentes couches et des phénomènes physico-chimiques via la diffusion et la réaction chimique aux interfaces polymère/polymère. Ce mémoire s’articule autour d’une étude multi-échelle du rôle des copolymères aux interfaces sur la stabilité des écoulements stratifiés. L’étude a été réalisée à la fois sur des systèmes non-réactifs et réactifs constitués d’une couche barrière, le polyamide 6 (PA6) ou le poly(éthylène-co-alcool vinylique) (EVOH), avec un polypropylène (PP) ou un polypropylène greffé anhydride maléique (PP-g-AM). Le défaut de « granité » a été mis en évidence en coextrusion. Les paramètres procédé et matériaux influençant son apparition ont été identifiés. Il a pu être différencié des défauts et des instabilités interfaciales généralement rencontrées en coextrusion. Le phénomène de compatibilisation a également été étudié via les caractérisations morphologiques (MET, MEB, AFM) et physico-chimiques (XPS) aux interfaces. Le comportement rhéologique en cisaillement et élongation en viscoélasticité linéaire et non linéaire s’est révélé très sensible à l’effet la présence de copolymères aux interfaces et à leur architecture moléculaire. Cette étude a permis de déterminer les propriétés intrinsèques de l’interface/interphase en fonction du copolymère formé entre le liant et le PA6 ou l’EVOH. Elles ont pu être corrélées aux défauts macroscopiques observés dans les films multicouches coextrudés. La stabilité de ces écoulements stratifiés résulte d’un couplage de phénomènes qui se produisent à différentes échelles : nano (réaction de copolymérisation), micro (interphase) et macro (écoulement dans le procédé)
Several polymers can be combined in one multilayer structure by reactive coextrusion. Tie-layers are often used to compatibilize the adjacent layers and may reduce or suppress the interfacial instabilities and the defects in the multilayer coextrusion flow. However, an additional defect defined as the “grainy” defect can be observed. In the best of our knowledge, no study in literature has been devoted to understand its origin. The phenomena are quite complex due to the coupling of the effects of flow and the physico-chemical mechanisms at the interface. The aim of this work is to understand the relations between the instabilities and the defects encountered in multilayer coextruded films and the role of the copolymer formed in-situ between tie and barrier layers. Polyamide 6 (PA6) and ethylene-vinyl alcohol copolymer (EVOH) were used as the barrier layers sandwiched in a polypropylene (PP) with or without a polypropylene grafted maleic anhydride (PP-g-MA) as a tie-layer. The effect of the process parameters and the structure of the polymers on the generation of the “grainy” defect was assessed in correlation with the rheological and the physicochemical properties of the layers. These experiments have shown that this defect appeared mainly in the compatibilized EVOH system and could be distinguished from the usual coextrusion instabilities. The interfacial properties between tie and barrier layers were investigated. The characterization of the interfacial morphology by TEM and AFM highlighted an irregular and rough interface between PP-g-MA and EVOH while a flat interface was observed with PA6 and PP-g-MA. Step shear and startup elongation rheology was shown to be sensitive to the copolymer at the polymer/polymer interface. The study of the interfacial properties highlighted that the copolymer architecture significantly impacts the interfacial roughness and the rheology of the multilayer stuctures. Hence, relations between the relaxation process, the interfacial morphology and the copolymer architecture were established in correlation with the generation of the macroscopic grainy defect in coextrusion

This project investigated the synthesis of hybrid nanoparticles of gold and zinc oxide by using photodeposition and crystal seeding approach. The study extended our understanding of the factors that determine nanocrystal size, shape and ratio of gold and zinc oxide in the hybrid system. Control at this scale is important from a materials-engineering viewpoint and for technological applications such as nonlinear optics, photocatalysis and photovoltaics. This research found that nonlinear optical absorption of zinc oxide can be enhanced by several orders of magnitude by coupling zinc oxide nanoparticles to gold nanoparticles.

Ce travail de thèse a pour objet l'étude de l'influence de la plasticité sur le délaminage et le flambage de films minces déposés sur substrats. Il repose sur une approche mixte combinant des simulations atomistiques et des calculs analytiques basés sur la théorie des plaques minces de Föppl-von Kármán (FvK). Les simulations ont permis de caractériser, au cours de la formation d'une ride droite, un mécanisme de glissement localisé dans l'interface en pied de cloque entraînant une augmentation de la déflexion maximale de la ride. Ce mécanisme de glissement est également présent lorsque le délaminage piloté par le flambage du film mince est lui aussi observé. En l'intégrant dans le modèle élastique de FvK, la forme de la ride droite ainsi que le processus de délaminage ont ensuite été caractérisés. Le bon accord trouvé entre les simulations atomistiques et le modèle explique notamment le délaminage des cloques sans introduire de dépendance entre l'énergie d'adhésion et la mixité modale. L'initiation du cloquage à partir d'une marche d'interface créée par des dislocations venant du substrat a également été étudiée. Les simulations révèlent qu'avant flambage, le film se décolle à la fois sur le haut et sur le bas de la marche. Un mécanisme de glissement est là aussi identifié. Une déformation critique de flambage qui tient compte de ces phénomènes a été déterminée en modélisant le film mince sur la marche dans le formalisme de FvK. Les résultats des simulations couplés au modèle élastique expliquent, comme il est par ailleurs observé expérimentalement, pourquoi les cloques se forment préférentiellement au-dessus de défauts tels que des marches.

Thesis (M.S.)--Florida State University, 2006.
Advisor: Anter El-Azab, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed June 9, 2006). Document formatted into pages; contains xi, 64 pages. Includes bibliographical references.

博士
國立臺灣科技大學
材料科學與工程系
107
In order to establish the relationship between interface structure and magnetic properties, in this study, defect structure of different types of cerium oxide-metal composite structures were analyzed and their room temperature ferromagnetic properties were discussed. Two composite structures were chosen: one was using silver as the core, the ceria nanoparticle as the shell; the other was using ceria hollow sphere as the substrate on which the silver nanoparticle was deposited. The main microstructure analysis techniques used were transmission electron microscopy, electron energy loss spectroscopy and X-ray absorption spectroscopy. In the silver/ceria core/shell structure, X-ray absorption spectroscopy results demonstrated electron transfer in p-orbital and the d-orbital of silver. The valence state of Ce was decreased after the interface formation. The proportion of Ce3+ was increased from 6% to 14%. The scanning transmission electron microscope and electron energy loss spectrum analysis of the further pointed out the distribution of Ce3+ was inhomogeneous. At the interface, the Ce3+ ratio was up to 40% and concentrated in a thin area of 7 Å; on the surface of the ceria shell, the Ce3+ ratio was 80%, and the Ce3+-rich region extended to 4 nm thick. Further changing the thickness of the shell layer from 15 nm to 35 nm effectively enhanced the saturation magnetization of the silver/ceria core shell structure. In the hollow composite structure, ceria hollow spheres were synthesized by spray pyrolysis at first. The sphere size was about 100 nm to 1 m, and the shell thickness was about 30 nm. Electron energy loss spectroscopy indicated that the cerium oxide hollow sphere had a high defect content, and the Ce3+ ratio was over 99% at a surface depth of 2.5 nm; the Ce3+ ratio inside the hollow sphere was also as high as 37%. The defect content and distribution could be controlled by post-annealing and treatment with an acidic solution. After annealing, the Ce3+ content on the surface of the hollow sphere was reduced to 22%, and the width of defect-rich region was reduced to 1.2 nm. On the other hand, the acidic solution treatment will further increase the Ce3+ content of the hollow sphere, especially in the hollow sphere. In this study, Ag nanoparticle deposition was performed on the ceria hollow spheres which were annealed for 2 hours to form a hollow composite structure. The electron transfer phenomena of silver was also observed at this interface by X-ray absorption spectroscopy. However, the electron energy loss spectrum analysis indicated that the Ce3+ concentration was about 56% at the interface of the hollow composite structure, and the defect-rich region was about 1 nm. It was worth noting that the Ce3+ concentration at the interface and the depth of the defect-rich region were lower than those of the exposed hollow sphere. Magnetic analysis indicated that the contribution of this interface to magnetism was smaller than that of the surface. Finally, the interface analysis results of the two composite structures were compared. It was found that the defect structure at the interface closely depended on the interface formation process, not only relate to the material. In addition, magnetic analysis results confirmed that the formation of the interface benefit to concentrate the defects, thereby enhancing the ferromagnetic strength. Combined the analysis of hollow composites, it was also demonstrated that as the defects were concentrated at the surface of the sphere had the greatest contribution to the formation of ferromagnetism. This result could be used as a reference for subsequent process development and theoretical calculations.

Billions of people rely solely on groundwater for drinking and daily use. In the last few decades, groundwater was shown to be contaminated with arsenic in high concentrations, especially in Asian countries such as Bangladesh. Arsenic (As) is ranked the first among 20 toxic substances by the Agency for Toxic Substances and Disease Registry (ATSDR) and United States Environmental Protection Agency (USEPA). Because many diseases and deaths were linked to consumption of arsenic-contaminated groundwater, the world health organization (WHO) reduced the arsenic standard level for drinking water from 50 to 10 µg L-1. Urgent demands for safe drinking water lead to developing potential technologies for removal of arsenic from groundwater. Arsenic is mainly present as uncharged As(III) in groundwater, which makes it difficult to be efficiently removed by conventional treatment methods. Therefore, membrane technology could be a promising potential solution. Because membrane technology has not been widely tested for arsenic removal, a novel in-house defect-free interfacially-polymerized (IP) cross-linked polyamide thin-film composite (TFC) nanofiltration membrane, namely, PIP-KRO1, was tested in this research. Two commercial TFC membranes, namely Dow NF270 and Sepro RO4, were also tested and compared to PIP-KRO1. The membranes were tested at four different pH conditions (4, 6, 8, and 10) in a cross-flow flat sheet membrane unit. The experiments were divided into two parts: (i) the membranes were tested for water permeance and salt (NaCl) removal and (ii) tested for As(III) removal in the presence of 250 ppm NaCl. The results in this study showed strong size sieving rejection for RO4 and a combination of size sieving and charge exclusion mechanisms for PIP-KRO1 and NF270. In general, the rejection trend was RO4 > PIP-KRO1 > NF270 for both NaCl and As(III). In contrast, the trend for water permeance was NF270 > PIP-KRO1 > RO4. The minimum and maximum salt rejection at pH 4 and pH 10, respectively, were 85 and 98.8% for RO4, 57 and 89% for PIP-KRO1, and 34 and 76.8% for NF270. In addition, the TFC membranes demonstrated a maximum As(III) rejection of 98.7, 69.5, and 46.3% for RO4, PIP-KRO1, and NF270, respectively. Based on the characterizations of the membranes, PIP-KRO1 had the highest cross-linking (N/O ratio) followed by RO4 and NF270, respectively. The same trend was observed for the thickness of the polyamide selective layer (PIP-KRO1 > RO4 > NF270). The zeta potential for NF270 was slightly higher than that for PIP-KRO1; RO4 had much lower membrane surface charge. In terms of surface roughness, the following trend was observed: RO4 > PIP-KRO1 > NF270.

This research was undertaken to develop state-of-the-art interfacially polymerized (IP) defect-free thin-film composite (TFC) membranes and understand their structure-function-performance relationships. Recent research showed the presence of defects in interfacially polymerized commercial membranes which potentially deter performance in liquid separations and render the membranes inadequate for gas separations. Firstly, a modified method (named KRO1) was developed to fabricate interfacially polymerized defect-free TFCs using m-phenylene diamine (MPD) and trimesoyl chloride (TMC). The systematic study revealed the ability to heal defects in-situ by tweaking the reaction time along with considerably improving the membrane crosslinking by controlling the organic solution temperature. The two discoveries were combined to produce highly crosslinked, defect-free MPD-TMC polyamide membranes which showed exceptional performance for separating H2 from CO2. Permeance and pure-gas selectivity of the membrane increased with temperature. H2 permeance of 350 GPU and H2/CO2 selectivity of ~100 at 140 °C were obtained, the highest reported performance for this application using polymeric materials to date. Secondly, the membranes produced using KRO1 were tested for reverse-osmosis (RO) performance which revealed significantly improved boron rejection compared to commercial membranes reaching a maximum of 99% at 15.5 bar feed pressure at pH 10. The study also unveiled direct correlations between membrane crosslinking and salt separation performance in addition to the membrane surface roughness. Thirdly, this was followed by replacing the conventional IP TMC monomer with a large, rigid and contorted tetra-acyl chloride (TripTaC) monomer to enhance the performance of IP TFCs. The fabricated TFCs showed considerable performance boosts especially for separating of small solutes from organic solvents such as methanol. A rise in H2 permeance was also observed compared to the conventional MPD-TMC TFCs while reaching a maximum H2/CO2 selectivity of 9 at 22 °C. Finally, the research was completed by showing the potential of KRO1 for fabrication of defect-free TFCs using a range of aqueous diamine monomers. KRO1 enabled defect-free gas properties for all monomers used showing exceptional performance for separating H2-CO2 and O2-N2 mixtures. It was further shown that the formulation could also improve the RO separation of interfacially polymerized polyamide TFCs beyond those shown by commercially available TFCs.

碩士
國立清華大學
材料科學工程學系
101
Exchange bias(EB) is an interfacial magnetic phenomenon. After a bilayer film made of a ferromagnet and antiferromagnet goes through a field-cooling process from above the antiferromagnet's Néel temperature, these two materials will couple magnetically at their interface. Thus, a nickel-iron/nickel-oxide bilayer can magnetically couple and enable EB. This phenomenon is related to the interfacial arrangement of atomic magnetic moments. However, it is quite difficult to experimentally observe the direction of magnetic moments for individual atoms, and even harder to resolve the necessary atomic arrangement in polycrystalline films such as NiFe/NiO. Thus, we try to simulate the magnetic moments of each atom coupling to permit EB at the interface of nickel-iron/nickel-oxide system by theoretical simulations and mapping these results onto experiments on the films grown on a crystalline MgO substrate. According to random-field model, we can obtain the exchange bias from the difference of interfacial energies before and after the change of magnetic field direction, then incorporating the thickness effects of the ferromagnetic layer and its magnetization. Afterwards, we compared the simulated results with the experimental data and determined reasonable configurations of atomic magnetic moments by comparison with results from HRTEM (high resolution transmission electron microscopy). The result of VASP simulations for exchange bias without roughness and with two kinds of roughness (2.20Å and 4.43Å) at the interface is 3.08±4.59(Oe), -24.27±3.13(Oe) and -195.53±10.88(Oe), respectively, and 0.00±3.88(Oe), -4.17±1.96(Oe) and -11.02±3.12(Oe) for different directions of applied field. All simulations revealed that interfacial roughness can strengthen the EB, which is consistent with experimental results. Thus, we can conclude that the configuration of atomic magnetic moments is similar to real case with the interfacial roughness as also shown from HRTEM. Afterwards, we calculated for the effect of interfacial dislocations on EB. When dislocations appear around the interface with 2.20Å roughness, EB increased from -24.27±3.13(Oe) to -143.46±4.37(Oe), and from -4.17±1.96(Oe) to -82.30±7.29(Oe) for different directions of applied field. As EB is essentially a spin-spin interaction between ferromagnet and antiferromagnet at the interface, any kind of modification of the interfacial spin configuration (e.g. quantity of the uncompensated interfacial antiferromagnetic spins and the relative orientation between antiferromagnetic and ferromagnetic spins) will affect the final exchange coupling. Thus, it is reasonable to conclude that an interface roughness can strengthen the interfacial exchange coupling by enhancing the defect-generated uncompensated condition. This is in agreement with recent Monte Carlo simulations [J. Spray and U. Nowak, J. Phys. D: Appl. Phys. 39, 4536 (2006)].

碩士
國立清華大學
材料科學工程學系
102
The diamagnetic semimetal CoSi presents unanticipated ferromagnetism as CoSi/SiO2 nanowires.[1] Using first-principles calculations, we offer physical insights into the origins of this unusual magnetism. Due to the distorted and dangling bonds near the nanowire surface with different bond lengths, the transition metal (Co) d-orbital electron spin up and spin down populations become asymmetric from the exchange interactions, providing the mechanism for some of the measured magnetization. However, the distorted and dangling bonds are clearly not the only factor contributing to the magnetization of the nanowires. The transmission electron microscopy selected area diffraction (SAD) analysis of the CoSi region suggested a superlattice structure existed in the cubic CoSi, and defects existing as ordered vacancies in the CoSi resulted in the observed SAD lower contrast image components. The simulation’s results for the Co moment in the CoSi nanowires without these ordered vacancies, but incorporating the surface and internal spin moments, is only 0.1638μB/atom, which is a ~80% shortfall compared to the experimental value of 0.8400μB/atom. When the effects of ordered vacancies are incorporated into the simulation, 0.8074μB per Co atom, a much better match with the experimental value (within ~3.881%) results, indicating that the internal ordered vacancies in the CoSi nanowires is a dominant mechanism of the ferromagnetism. Investigation on the density of states (DOS) of Co atoms around the ordered vacancies shows that the Co atoms with lower coordination number induce more magnetization due to the unpaired electrons created by the break of Co-Si bonds, which cause the unbalance between spin up and spin down states. But in some cases, the magnetization of Co in the structure without ordered vacancies is higher than the Co in the structure with ordered vacancies. In such case, the bond length of Co in the structure without ordered vacancies falls in a range that leads to stronger interacting spin-exchange through the overlap between magnetic orbitals.

abstract: With the increasing focus on developing environmentally benign electronic packages, lead-free solder alloys have received a great deal of attention. Mishandling of packages, during manufacture, assembly, or by the user may cause failure of solder joint. A fundamental understanding of the behavior of lead-free solders under mechanical shock conditions is lacking. Reliable experimental and numerical analysis of lead-free solder joints in the intermediate strain rate regime need to be investigated. This dissertation mainly focuses on exploring the mechanical shock behavior of lead-free tin-rich solder alloys via multiscale modeling and numerical simulations. First, the macroscopic stress/strain behaviors of three bulk lead-free tin-rich solders were tested over a range of strain rates from 0.001/s to 30/s. Finite element analysis was conducted to determine appropriate specimen geometry that could reach a homogeneous stress/strain field and a relatively high strain rate. A novel self-consistent true stress correction method is developed to compensate the inaccuracy caused by the triaxial stress state at the post-necking stage. Then the material property of micron-scale intermetallic was examined by micro-compression test. The accuracy of this measure is systematically validated by finite element analysis, and empirical adjustments are provided. Moreover, the interfacial property of the solder/intermetallic interface is investigated, and a continuum traction-separation law of this interface is developed from an atomistic-based cohesive element method. The macroscopic stress/strain relation and microstructural properties are combined together to form a multiscale material behavior via a stochastic approach for both solder and intermetallic. As a result, solder is modeled by porous plasticity with random voids, and intermetallic is characterized as brittle material with random vulnerable region. Thereafter, the porous plasticity fracture of the solders and the brittle fracture of the intermetallics are coupled together in one finite element model. Finally, this study yields a multiscale model to understand and predict the mechanical shock behavior of lead-free tin-rich solder joints. Different fracture patterns are observed for various strain rates and/or intermetallic thicknesses. The predictions have a good agreement with the theory and experiments.
Dissertation/Thesis
Ph.D. Mechanical Engineering 2011