Dissertations / Theses on the topic 'Laser hybrid deposition'

Au catalyst ZnO nanostructures have been grown on the a- and c-plane sapphire substrate by PLD. Influence of substrate lattice orientation, substrate surface and different substrate annealing temperature have been characterized by AFM, SEM and XRD. This report shows that a-plane sapphire substrate annealed at 1000 degree C and 1200 degree C improves the growth condition of Au catalyst ZnO nanostructures. For c-plane sapphire; annealing at 1200 degree C and 1400 degree C enhances the nanostructure growth. The better growth condition is a result of the terrace-and-step morphology seen on the substrate surface prior to growth. This report also indicates a correlation between the azimuthal in-plane alignment of the grown nanostructures and the sapphire substrate lattice orientation.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 18, 2008) Includes bibliographical references.

The arrival on the market of a new kind of CNC machines which can both add and remove material to an object paved the way to a new approach to the problem of repairing damaged components. The additive operation is performed by a Direct Laser Deposition (DLD) tool, while the subtractive one is a machining task. Up to now, repair operations have been carried out manually and for this reason they are errors prone, costly and time consuming. Refurbishment can extend the life of a component, saving raw materials and resources. For these reasons, using a precise and repeatable CNC machine to repair valuable objects is therefore very attractive for the sake of reliability and repeatability, but also from an economical and environmental point of view. One of the biggest obstacles to the automation of the repairing process is represented by the fact that the CAM software requires a solid CAD model of the damage to create the toolpaths needed to perform additive operations. Using a 3D scanner the geometry of the damaged component can be reconstructed without major difficulties, but figuring out the damage location is rather difficult. The present work proposes the use of octrees to automatically detect the damaged spot, starting from the 3D scan of the damaged object. A software named DUOADD has been developed to convert this information into a CAD model suitable to be used by the CAM software. DUOADD performs an automatic comparison between the 3D scanned model and the original CAD model to detect the damaged area. The detected volume is then exported as a STEP file suitable to be used directly by the CAM. The new workflow designed to perform a complete repair operation is described placing the focus on the coding part. DUOADD allows to approach the repairing problem from a new point of view which allows savings of time and financial resources. The successful application of the entire process to repair a damaged die for injection molding is reported as a case study. In the last part of this work the strategies used to apply new material on the worn area are described and discussed. This work also highlights the importance of using optimal parameters for the deposition of the new material. The procedures to find those optimal parameters are reported, underlying the pros and cons. Although the DLD process is very energy efficient, some issues as thermal stresses and deformations are also reported and investigated, in an attempt to minimize their effects.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.
Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).

La thèse de doctorat présentée dans ce travail est consacrée à une méthode innovante de production de moules d'injection plastique. Cette méthode combine la technologie additive laser, notamment le rechargement par injection coaxiale de poudre (LMD) et la technique de traitement laser visant à réduire les contraintes résiduelles. Par conséquent, l'objectif principal du présent travail est d'optimiser et d'analyser la méthode de fabrication proposée en ce qui concerne les propriétés finales des pièces déposées. L'étude paramétrique de LMD des "simples cordons", des structures de type "mur" et des "cubes" a été réalisée. La LMD d'échantillons cubiques a été analysée en fonction de la densité, des contraintes résiduelles et de la microstructure afin d’obtenir les paramètres optimaux de LMD. Les paramètres optimaux de LMD ont été vérifiés lors du dépôt à long terme d'échantillons cubiques et cylindriques en une seule et plusieurs fois. La tenue en fatigue ainsi que la densité, la microdureté et la microstructure ont ensuite été évaluées. La simulation numérique a également été réalisée pour prédire les champs thermiques générés pendant le procédé LMD. Enfin, cette thèse comprend l'étude numérique et expérimentale du processus de traitement laser (de détentionnement) visant à réduire les contraintes résiduelles et à éviter les post-traitements durables tels que le vieillissement
The PhD thesis presented in this work is dedicated to the innovative method of plastic injection mould production. This method combines laser additive technology, namely, the Laser Metal Deposition (LMD) and technique of laser treatment aiming to reduce the residual stresses. Therefore, the main objective of the present work is to optimize and analyze the proposed fabrication method regarding the final properties of deposited parts. The parametrical study of “single-bead”, multi-bead “wall” and multi-bead “cube” LMD has been carried out. The LMD of cubic specimens has been analyzed with respect to the density, residual stresses and microstructure in order to find the optimal deposition parameters. The optimal LMD parameters have been verified during the longtime deposition of cubic and cylindrical specimens in a single operating session and after multiple pauses. The fatigue resistance as well as the density, microhardness and microstructure were then evaluated. The numerical simulation has been also performed to predict the thermal fields generated during LMD. Finally, this thesis includes the numerical and experimental study of laser treatment process aiming to reduce the residual stresses and avoid the possible long-lasting post-treatment such as aging

L’émergence des satellites très haut débit pour la couverture des zones rurales s’accompagne de nombreuses contraintes technologiques. Dans le cadre du plan France très haut débit, le projet THD-sat proposé par le CNES se base sur l’utilisation des bandes Q et V pour assurer les liaisons avec les stations au sol et libérer de la ressource sur la bande Ka communément utilisée par les satellites ancienne génération. Avec la montée en fréquence, les besoins en termes de filtrage deviennent très stricts nécessitant des considérations particulières. Le premier chapitre reprend le contexte de l’étude et expose les différents éléments permettant de justifier le choix de la technologie SIW qui profite à la fois des bons facteurs de qualité des modes volumiques se propageant dans le substrat et de l’aisance du procédé technologique et de l’intégration des structures planaires. Les performances des cavités SIW restent néanmoins intimement liées à l’épaisseur de substrat qui doit être augmentée pour atteindre de meilleurs facteurs de qualité. L’augmentation de l’épaisseur de substrat s’accompagne de deux principales limitations : le rallongement des fils de « bonding » utilisés pour le câblage du filtre à son environnement MIC d’épaisseur 254 μm et l’élargissement de la ligne d’accès 50 Ω induisant des problèmes de discontinuités et d’excitations de modes parasites. L’approche suivie consiste à considérer des formes 3D permettant l’adaptation de mode et d’épaisseur entre une ligne microruban sur substrat de 254 μm d’épaisseur et le SIW d’épaisseur plus importante. Une nouvelle transition 3D est dès lors imaginée. Le chapitre II reprend les différents procédés technologiques utilisés pour la mise en forme et la métallisation des substrats 3D. Les substrats considérés sont l’alumine et la silice fondue mis en forme par ablation laser et le thermoplastique COP mis en forme par moulage. La principale limitation de l’ablation laser concerne les épaisseurs de substrat accessibles. Nous nous limitons à 635 μm dans le cas de l’alumine et à 500 μm dans le cas de la silice fondue. Le moulage polymère permet de s’affranchir de cette limitation et de viser des substrats plus épais (2 mm pour la solution COP).Le chapitre III reprend les étapes de conception des différentes solutions de filtrage avec la nouvelle transition 3D. Des résultats de mesures de différents prototypes réalisés sont par ailleurs présentés. Ces résultats sont globalement encourageants mais nécessitent d’être davantage développés pour être mieux exploitables
The emergence of satellite high-speed internet for the coverage of rural zones is accompanied by numerous technological constraints. The current trend is to use higher frequency bands to release the satellite capacity for users. The increasing frequency requires new considerations especially for filtering needs which become notably strict in terms of performance and integration in small integrated circuits. This work introduces filtering solutions based on high quality factor Substrate Integrated Waveguides (SIW) using a novel 3D transition for a better integration in widely planar Hybrid ICs.The first chapter introduces the study’s context and the different elements justifying the use of the SIW technology.In fact, these structures profit from both the good quality factors of TE-modes propagating in the substrate and the easy fabrication process and integration of planar circuits. However, to increase the SIW quality factor, the substrate’s height should be increased which induces interconnection limitations such as long bond wires with high parasitic effects and large microstrip access lines with discontinuity problems and the propagation of parasitic modes. The adopted approach consists in imagining 3D shapes providing both mode and thickness matching between a microstrip line etched on a thin substrate and a high substrate SIW.The second chapter introduces the different manufacturing processes used for the substrate’s shaping and metallization. Three substrates are considered: Alumina, fused Silica and Cyclo Olefin Polymer COC. Alumina is widely used in space applications and has a well-mastered process. For equivalent dielectric losses, fused silica has a lower permittivity for bigger structures with less manufacturing tolerance sensitivity. Both Alumina and fused silica substrates are shaped using a laser ablation. The reachable substrate’s height using this machining method is relatively low. The polymer solution (COP) is elaborated using a molding process allowing higher substrates heights.The last chapter outlines the design steps of the different solutions and the measurement results of the first prototypes. These results are on the whole encouraging but require further development

Hybridsolarzellen werden sowohl aus ZnO-Schichten als auch ZnO-Nanostrukturen und Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophen)-alt-4,7(2,1,3-benzothiadiazol)] (PCPDTBT) hergestellt. Das Wachstum der ZnO-Schichten und Nanostrukturen wird mittels gepulster Laserdeposition (PLD) auf Saphirsubstraten durchgeführt. Die Schichten weisen eine c-Achsenorientierung auf. Die Polarität einer ZnO-Schicht bestimmt die Morphologie der nachfolgend gewachsenen ZnO-Nanostrukturen. Dabei kann die Morphologie kontrolliert zwischen Nanostäbchen auf einer O-terminierten ZnO-Schicht und Nanowänden auf einer Zn-terminierten ZnO-Schicht eingestellt werden. Untersuchungen mittels konvergenter Elektronenbeugung zeigen, dass die Nanostrukturen immer Zn-terminiert sind. Die Grenzfläche zwischen ZnO und PCPDTBT wird mit Photoelektronenspektroskopie untersucht und ergibt eine Vakuumniveauangleichung zwischen beiden Materialien. Prinzipiell ist der Übergang für photovoltaische Aktivität geeignet, jedoch sind die erzielten Wirkungsgrade sehr niedrig. Die Ursache ist eine niedrige Exzitonendissoziationseffizienz, die durch die Benutzung von sol-gel ZnO, kleinen organischen Molekülen und einer niedrigeren Leitfähigkeit vom PLD-ZnO verbessert werden kann. Dennoch beträgt der maximale Wirkungsgrad der Hybridsolarzellen nur 0,21 %.
Hybrid solar cells are built from ZnO layers and ZnO nanostructures and Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT). The growth of the ZnO layers and nanostructures is performed with pulsed laser deposition (PLD) on sapphire substrates. The samples exhibit a c-axis orientation. The polarity of a ZnO layer determines the morphology of subsequently grown ZnO nanostructures. One can control the morphology between ZnO nanorods on an O-terminated layer and nanowalls on a Zn-terminated layer. Studies with convergent electron beam diffraction reveals that the ZnO nanostructures are always Zn-terminated. The interface between ZnO and PCPDTBT is studied with photoelectron spectroscopy and shows a vacuum level alignment between both materials. In principle, the interface is suitable for photovoltaic activity, however, the achieved power conversion efficiencies are very low. This is due to a low exciton dissociation efficiency, which can be improved by the use of sol-gel ZnO, small organic molecules, and a lower conductivity of the PLD ZnO. Nevertheless, the maximum power conversion efficiency amounts to 0.21 %, only.

Mestrado em Engenharia de Materiais
O presente trabalho aborda o processo de funcionalização por via seca de nanopartículas de óxido de grafeno (nano-GO) visando o estabelecimento de ligações a polietilenoglicol (PEG) na sua superfície. Atualmente utilizam-se métodos químicos de funcionalização por via húmida com esta finalidade, no entanto são demorados e resultam em perdas significativas de amostra. O trabalho foi realizado em duas fases: o GO foi primeiramente sintetizado em forma de filme e pó utilizando um método “Hummers” modificado, sendo caracterizado por FTIR, SEM e DLS; em seguida o GO foi exposto aos precursores do PEG num reator de deposição por camada molecular (MLD) sob condições de vácuo. Utilizaram-se temperaturas diversas de deposição, tendo-se observado uma adsorção ótima entre 90-100° C. Primeiramente, a deposição de PEG em pó de GO, com terminações de amina, confirmou por FTIR a presença dos picos característicos de PEG, aproximadamente aos 2925 cm-1 e 2850 cm-1, corroborando a funcionalização a seco do GO por um mecanismo de vaporização-condensação. A via MLD, usando TMA e EG como precursores foi então realizada no pó de GO, tendo proporcionado uma camada de passivação inicial rica em alumínio, na qual ciclos subsequentes de exposição ao monómero EG resultaram na sua adsorção e polimerização, tal como demonstrado por FTIR e análises EDS. O nano-GO-PEG é vantajoso para aplicações na área da biomedicina, incluindo sistemas de administração de fármacos, biossensores e terapia fototérmica. O PEG permite ao nano-GO ser reconhecido como biocompatível, estabelecendo uma superfície repelente e incrementando o transporte citoplasmático, permitindo assim características essenciais, tais como alta absorvância óptica, fluorescência e estabilidade em meio fisiológico, essenciais para os sistemas biológicos. O sucesso da produção do nano-GO funcionalizado com PEG pela via a seco aqui proposta poderá será favorável para outros tipos de funcionalização e copolimerização de nanopartículas.
This research aims to achieve a dry functionalization approach for covalently attaching polyethylene glycol (PEG) onto the surface of nano-graphene oxide (GO). Currently, wet chemical methods are used to achieve this, being characteristically time consuming and resulting in significant loss of sample. This work is carried out in two stages; GO is first synthesized using a modified Hummers’ method, and then characterized by FTIR, SEM and DLS; it is then produced in film and powder form, for exposure to precursors in an MLD reactor under rough vacuum conditions. GO films were exposed to PEG at variable temperatures, determining that at 90oC and 100oC the optimal adsorption occurred. Deposition of amine-terminated PEG on GO powder confirmed the presence of characteristic PEG peaks around 2925cm-1 and 2850cm-1 via FTIR, substantiating the dry functionalization of GO via vaporization-condensation. An MLD route, using TMA and EG precursors was then performed on GO powder, delivering an initial passivation layer of Al, onto which subsequent cycles of EG adsorbs, demonstrated by FTIR and EDS analysis. PEGylated-nano-GO is advantageous for applications in the area of biomedicine; including drug delivery systems, biosensors and photothermal therapy. PEG permits nano-GO to be recognized as biocompatible; establishing on it a non-fouling surface and increasing its cytoplasmic transport, thereby allowing its inherent characteristics such as high optical absorbance, fluorescence, and stability in physiological media to be pertinent to biological systems. Successful production of PEG functionalized nano-GO via the proposed method will be favourable for other possibilities of nanoparticle surface functionalization and copolymerization.

La croissance de nanotubes de carbone (NTC) sur particules micrometriques d'alumine (Al2O3) permet d'obtenir une dispersion uniforme des NTC dans des matrices sans enchevêtrement de NTC. Ce type de structure hybride NTC-Al2O3 fournit également une solution prometteuse au problème de sécurité de NTC car ils intègrent NTC avec des particules micrométriques, étendant la dimension des NTC à partir de nano-échelle au micro-échelle. Cependant, l'adhérence entre les NTC et les Al2O3 particules ne permet pas de fixer efficacement les NTC. Par ailleurs, une autre préoccupation essentielle de NTC est de savoir comment créer une forte adhésion interfaciale entre les NTC et les matrices polymères pour obtenir de bonnes propriétés mécaniques et de ne pas diminuer la conductivité électrique de NTC. Motivé par ces considérations, cette thèse vise à proposer plusieurs techniques concernant le dépôt d'une nano-couche conductrice sur la surface des structures hybrides NTC-Al2O3. De plus, les impacts de la nano-couche déposée sur la fixation des NTC à la surface d’Al2O3, sur la conductivité électrique des hybrides NTC-Al2O3, et sur l'adhésion interfaciale des systèmes NTC-Al2O3/epoxy composites sont étudiés en détail
Growth of carbon nanotubes (CNTs) on micro-sized alumina (Al2O3) particles helps to achieve a uniform dispersion of CNTs in matrices without CNT entanglement. This kind of CNT-Al2O3 hybrids also provides a promising solution to the CNT safety problem since they integrate CNTs with micrometric particles, extending dimension of CNT fillers from nano-scale to micro-scale. However, the adhesion between the CNTs and the Al2O3 particles doesn’t sufficiently enable to fix the CNTs firmly and stably. Besides, another crucial concern of CNTs is how to create a strong interfacial adhesion between CNTs and polymer matrices for good mechanical properties and meanwhile not to degrade CNTs’ electrical conductivity. Motivated by these considerations, this PhD thesis aims to establishing several techniques for deposition of an electrically conductive nano-layer on the surface of CNT-Al2O3 hybrids. And the impacts of the deposited nano-layer on the fixing the CNTs on the Al2O3 surface, on bulk electrical conductivity of the CNT-Al2O3 hybrids, and on the interfacial adhesion of CNT-Al2O3/epoxy composite systems are investigated in detail

Mestrado em Química
A técnica de deposição por camada atómica (ALD) permite a deposição de filmes finos em fase de vapor de alta qualidade com um controlo de espessura à nano-escala. No presente trabalho foi demonstrado a deposição de filmes finos de óxido de zinco (ZnO) por ALD de elevada uniformidade em diferentes substratos, incluído nano-estruturas como por exemplo, nanotubos de carbono. Demonstrou-se por difracção de raio-X que o processo de deposição do ZnO originou a formação da estrutura da hexagonal, na fase wurtzite, com uma taxa de crescimento por ciclo de 1.9 Å. A deposição de filmes finos de natureza inorgânica (e.g. óxidos metálicos) por ALD está bem estabelecida contrariamente à emergente deposição por camada molecular (MLD) de filmes finos puramente orgânicos. Actualmente, a combinação de ALD/MLD começa a ganhar importância na criação de estruturas híbridas do tipo orgânica-inorgânicas. Nomeadamente, através da selecção adequada dos precursores, é possível obter diferentes arquitecturas funcionais em forma de filme fino, incluindo nano-laminados, superestruturas e redes metalo-orgânicas (MOFs) nano-porosas. A deposição de MOFs por ALD/MLD surge como uma alternativa para superar as desvantagens dos métodos convencionais de deposição de filmes finos baseados em soluções. Este trabalho contempla também a revisão da literatura no que diz respeito à síntese de este tipo de filmes finos obtidos em fase de vapor. Procedeu-se à reprodução dos resultados da literatura tendo como objectivo a síntese de filmes finos híbridos orgânico-inorgânicos (e.g. MOFs). Numa primeira fase efectuou-se a transformação vapor-sólido de um filme de ZnO crescido por ALD por exposição ao vapor de 2-metilimidazol. Posteriormente usou-se um processo ALD/MLD com o propósito de depositar uma estrutura do tipo zeólito (ZIF-8) a partir da reacção do dietilzinco (DEZ) e o 2-metilimidazol. Finalmente realizou-se a síntese de dois sistemas de filmes finos híbridos com base no ácido tereftálico como precursor orgânico e os seguintes precursores organometálicos: DEZ e Eu(TMHD)3. Para o caso do sistema DEZ/TPA, a formação da ligação Zn-TP nos filmes híbridos, foi observada por espectroscopia de FTIR
Atomic layer deposition is a state-of-the-art vapor phase deposition method for the creation of high quality thin films with nanoscale thickness control. As demonstrated in this work by the deposition of ZnO with a home-built reactor, ALD enables uniform and conformal film deposition even on complex nanostructures like carbon nanotubes. Deposition of hexagonal wurtzite ZnO proven by GIXRD with a growth-per-cycle of 1.9 Å, determined from XRR thickness measurements, was demonstrated. While the ALD synthesis of inorganic thin films, such as metal oxides is widely established, the organic counterpart molecular layer deposition (MLD) is still emerging. Recently, combining ALD/MLD has attracted great interest for the creation of organic-inorganic hybrid structures. By choice and adaptation of suitable precursors a great versatility of functional thin film architectures is achievable, spanning from novel multilayer nanolaminates and superstructures for thermoelectrics, over luminescent lanthanide hybrid films for optical application to even crystalline, nanoporous metal-organic frameworks (MOFs) as low-κ dielectrics in microdevices. Especially in the field of MOFs, a clean and precise synthesis route by ALD/MLD is desirable for device implementation in order to overcome the drawbacks of conventional, solution-based thin film deposition techniques. In this work, recent advances towards these vapor-processed hybrids are reviewed. Then, the reproduction of literature results leading to the deposition of organic-inorganic hybrid thin films (e.g. MOFs) was studied. The feasibility of a vapor-solid transformation of a sacrificial ALD-grown ZnO film by exposure to 2-methylimidazole (HMIM) and a direct ALD/MLD method using HMIM and diethylzinc (DEZ) towards a zeolitic imidazole framework (ZIF-8) have been attempted. Finally, the synthesis of two different hybrid films was studied involving the organic precursor terephthalic acid (TPA) combined with the organometallic precursors DEZ or Eu(TMHD)3. In case of the DEZ/TPA system, the deposition of a hybrid thin film with Zn-terephthalate bondings was evidenced by FTIR spectroscopy.

An electrical driven organic solid state laser is a very challenging goal which is so far well beyond reach. As a step towards realization, we monolithically implemented an Organic Light Emitting Diode (OLED) into a dielectric, high quality microcavity (MC) consisting of two Distributed Bragg Reflectors (DBR). In order to account for an optimal optical operation, the OLED structure has to be adapted. Furthermore, we aim to excite the device not only electrically but optically as well. Different OLED structures with an emission layer consisting of Alq3:DCM (2 wt%) were investigated. The External Quantum Efficiencies (EQE) of this hybrid structures are in the range of 1-2 %, as expected for this material combination. Including metal layers into a MC is complicated and has a huge impact on the device performance. Using Transfer-Matrix-Algorithm (TMA) simulations, the best positions for the metal electrodes are determined. First, the electroluminescence (EL) of the adjusted OLED structure on top of a DBR is measured under nitrogen atmosphere. The modes showed quality factors of Q = 60. After the deposition of the top DBR, the EL is measured again and the quality factors increased up to Q = 600. Considering the two 25-nm-thick-silver contacts a Q-factor of 600 is very high. The realization of a suitable encapsulation method is important. Two approaches were successfully tested. The first method is based on the substitution of a DBR layer with a layer produced via Atomic Layer Deposition (ALD). The second method uses a 0.15-mm-thick cover glass glued on top of the DBR with a 0.23-µm-thick single-component glue layer. Due to the working encapsulation, it is possible to investigate the sample under ambient conditions.

L'hydrogène s'avère être un vecteur d'énergie stockable et non carboné particulièrement séduisant. Une approche prometteuse pour la production propre et durable d'H2 est la photoélectrolyse de l'eau. Ce projet vise à modifier les propriétés du TiO2 utilisé comme photoanode dans une cellule photoélectrochimique, pour améliorer la production d'H2 sous lumière solaire. La nanostructuration du TiO2 sous forme de nanotubes (NTs) est un bon moyen d'améliorer sa réactivité et la séparation spatiale des charges. Une étude basée sur une stratégie de co-alliage, consistant à introduire une grande quantité d'anions (N3-) et de cations (Nb5+,Ta5+) dopants, a permis de réduire l'énergie de la large bande interdite du TiO2. Une étude paramétrique sur la décoration par ablation laser pulsé de NTs de TiO2avec des co-catalyseurs (cobalt, nickel) a été réalisée. Les conditions optimales de dépôt ont été identifiées, menant à une amélioration considérable de la production photoélectrochimique d'H2. En combinant l'approche de co-alliage et de dépôt de co-catalyseur, la production d'H2 sous lumière solaire est triplée. Des études plus spécifiques ont été réalisées afin de mieux comprendre les mécanismes mis en jeu
Hydrogen is an attractive non-carbonaceous storable fuel. A promising approach for clean and sustainable hydrogen production is solar driven photoelectrochemical water-splitting. This project aims to modify the properties of TiO2 used as a photoanode, in order to enhance the photoelectrochemical hydrogen production. Designing TiO2 at the nanometric scale with nanotubes is an interesting way to enhance both its reactivity and spatial separation of photogenerated carriers. A co-alloying strategy was investigated. The large introduction of anions (N3-) and cations (Nb5+,Ta5+) in the lattice was found to be an efficient way to reduce the band gap energy of TiO2, allowing absorption of photons in the visible range. A parametric study on the pulsed laser deposition of co-catalysts (cobalt, nickel) on TiO2 NTs was performed. The chemical composition of the co-catalysts can be controlled with the background atmosphere used during the deposition. Under the optimal conditions determined after this study, a significant improvement of photoelectrochemical hydrogen production under both solar and visible light was reached. Combining the co-alloying approach and the co-catalysts deposition leads to tripling the hydrogen production under solar light. In order to have a better understanding of the mechanisms involved, more specific studies have been performed

L’application de la technologie OLED (diode électroluminescente organique) pour l’affichage est actuellement principalement portée par le marché des écrans de télévision et des smartphones. Les matériaux et les substrats utilisés permettent de produire des dispositifs légers, compacts, voire flexibles, possédant un excellent contraste image et une fréquence de rafraîchissement élevée. Les contraintes technologiques limitant l’industrialisation concernent la durée de vie des dispositifs. D’une part, les matériaux utilisés dans les structures OLEDs sont dégradés en présence d’eau et d’oxygène, il est donc essentiel de passiver le dispositif avec une structure de haute qualité barrière à l’atmosphère. D’autre part, il est nécessaire d’ajouter une protection mécanique en surface, sous forme de capot ou de protection monolithique, modulable en fonction de l’application visée. Ces travaux de thèse visent à développer une nouvelle conception de packaging, intégrant des nanocomposites organiques-inorganiques au sein de l’architecture d’encapsulation multicouche développée au CEA-LETI, et appliquée aux écrans de petite taille (microdisplays) OLED réalisés sur substrat silicium. Ces matériaux permettent de cumuler des propriétés d’ordinaire antagonistes ; celles de la phase organiques (flexible, déposable par voie liquide) et celles de la phase inorganique (barrière au gaz, résistance mécanique et chimique). Les résultats reposent sur le contrôle fin de la morphologie ; le procédé sol-gel a donc été choisi pour sa versatilité. Nous avons montré qu’il était possible de définir plusieurs formulations composites. L’une en particulier, basée sur des nanoparticules de silice intégrées dans une matrice polymère, s’est révélée compatible avec l’encapsulation monolithique des substrats OLED, permettant notamment la reprise de contact électrique. L’ajout de ce matériau au sein de l’architecture de passivation augmente la résistance barrière au gaz et, par extension, la durabilité des dispositifs en conditions climatiques sévères. Utilisé en tant que protection mécanique de surface, cette solution en couche mince n’atteint pas la résistance mécanique des capots de verre, mais permet malgré tout de protéger les substrats pendant toutes les phases de fabrication et de manipulation. L’avantage principal de cette solution packaging réside dans la diminution de l’épaisseur totale, augmentant le contraste en limitant fortement les pertes lumineuses, et ouvrant la porte aux substrats et dispositifs flexibles
Due of the ongoing growth of smartphones and TVs displays markets, the application of OLED (Organic Light Emitting Diode) technology for displays has become a major center of interest. The materials and substrates used in such architectures allow to develop lightweight, compact and even foldable displays, demonstrating an excellent image quality and fast refresh rates. Currently, the technological drawbacks restricting the exploitation on industrial scale mainly concern the lifespan of the devices. First, materials used in OLED architecture are highly sensitive to moisture and oxygen ingress and require a high barrier encapsulation. In addition, a specific protection needs to be included to secure the device from mechanical failures. As so various options from glass lids to flexible barriers are likely to be considered depending on the intended use. This work deals with the production of OLED microdisplays deposited on silicon substrates, and aims to develop an alternative packaging solution, based on organic-inorganic nanocomposite layers, both on top and embedded into the multi-barrier passivation architecture previously developed at the CEA-LETI. Synergistic properties can be obtained from composite materials, enhancing the advantages of both the organic (flexibility, processability) and inorganic phase (barrier properties, mechanical and chemical resistance). As a high control on the morphology in required, the sol-gel process was therefore selected for its versatility. Several composite materials were designed. One selected formulation, based on silica nanoparticles dispersed in a polymer matrix, proved to be fully compatible with the monolithic encapsulation of OLED circuits, including, among other properties, the recovery of the electrical bonding. Passivation architectures using the composite as interface layer showed improved barrier properties as well as an enhanced durability of devices stored in warm and damp environment. Obviously, a thin hard-coat layer does not equal a glass lid in terms of mechanical resistance, yet our formulation provided a sufficient protection during the overall process and handling of the displays. The main advantages of this alternative packaging rely on the reduced thickness, increasing the contrast by minimizing the loss of luminous efficacy through guided mode and offering the prospect of flexible substrate manufacturing

Cette thèse en cotutelle entre la France et le Canada a pour objectif de développer une méthode innovante d’élaboration de couches minces nano-composites de ZnO:V, basée sur la mise en vol et le dépôt de nanoparticules (NPs) de ZnO :V par des Décharges à Barrière Diélectrique (DBDs) double fréquence. Cette méthode de dépôt vise à réduire le coût de production par l’utilisation de nanoparticules synthétisées par méthode sol-gel et de DBDs dans une configuration permettant le dépôt de couches minces en continu à pression atmosphérique. Les travaux se sont déroulés en trois phases :- L’étude des OTC obtenus par ablation laser à partir d’une cible de NPs de ZnO:V(1 %at.) et de cibles métalliques de ZnV. La résistivité la plus faible (4 x 10 4 Ω.cm) est observée pour les dépôt faits à 250 °C à partir d’une cible de Zn :V(3 %at.) alors que les meilleures propriétés optiques sont celles d’une couche mince quasi-amorphe obtenue à 20 °C à partir de la cible de NPs de ZnO:V. Ces couches minces présentent une transmission de 40% dans l’UV à 250 nm, 90% dans le visible et 80% dans le PIR à 2500 nm) avec une résistivité de 6 x 10-2 Ω.cm. - La recherche et l’optimisation d’une source plasma DBD pour mettre en vol des NPs de ZnO:V dans une configuration compatible avec le dépôt de couches minces contrôlées. La démarche a consisté à chercher à accroître le flux et l’énergie des ions à la cathode en appliquant, sur une des électrodes, une tension radiofréquence (5 MHz) qui génère une forte densité d’ions (~2 x 1011/cm3) et sur l’autre électrode une tension basse fréquence (50 kHz) afin de transporter les ions vers la cathode. La première étape a été de bien comprendre la physique de la DBD RF-BF en couplant la caractérisation optique de la décharge et la modélisation fluide 1D. Lorsque la tension BF augmente, la décharge initialement RF en régime α bascule en régime α-γ durant 1/5 du cycle BF. Les résultats montrent qu’en régime γ la décharge est auto-entretenue dans la gaine et le flux d’ions à la cathode est multiplié par un facteur 7 alors que leur énergie s’accroit d’un facteur 4. L’étude expérimentale montre que lorsqu’une cible de NPs interagit avec une DBD RF-BF, des NPs sont mises en vol.- La conception et le test d’une configuration de réacteur DBD comprenant 2 zones plasmas successives : la première pour mettre en vol les NPs d’une cible, la deuxième pour déposer les NPs sur un substrat. Cette dernière est basée sur une DBD double fréquence BF-BF obtenue par application d’une tension 50 kHz qui génère des électrons pour charger les NPs et une tension 1 kHz dont on sait qu’elle peut assurer le transport des NPs chargées du volume vers les surfaces. La faisabilité a été montrée par l’observation de NPs sur le substrat
This thesis jointly supervised by France and Canada aims to develop an innovative method for the development of thin nanocomposite layers of ZnO: V, based on the sputtering and deposition of ZnO: V nanoparticles (NPs) using Double Frequency Dielectric Barrier Discharges (DBDs). This deposition method aims to reduce the cost of production by using nanoparticles synthesized by the sol-gel method and DBD in a configuration allowing the deposition of thin films continuously at atmospheric pressure. The work took place in three phases:- The study of TCO obtained by pulsed laser deposition from a target of NPs of ZnO: V (1% at.) and metal targets of ZnV. The lowest resistivity (4 x 10-4 Ω.cm) is observed for the deposits made at 250 ° C from a Zn: V target (3% at.) While the best optical properties are those of a quasi-amorphous thin layer obtained at 20 ° C from the NPs target of ZnO: V. These thin films have a transmission of 40% in UV at 250 nm, 90% in the visible and 80% in the PIR at 2500 nm) with a resistivity of 6 x 10-2 Ω.cm.- Research and optimization of a DBD plasma source to sputter ZnO: V NPs in a configuration compatible with the deposition of controlled thin films. The approach consisted in increase the flow and energy of the ions at the cathode by applying, on one of the electrodes, a radiofrequency voltage (5 MHz) which generates a high density of ions (~ 2 x 1011 / cm3) and on the other electrode a low frequency voltage (50 kHz) in order to transport the ions to the cathode. The first step was to understand the physics of the DBD RF-BF by coupling the optical characterization of the discharge and the 1D fluid modeling. When the LF voltage increases, the initially RF discharge in the α regime switches to the α-γ regime for 1/5 of the LF cycle. The results show that in γ regime the discharge is self-sustaining in the sheath and the flow of ions at the cathode is multiplied by a factor of 7 while their energy increases by a factor of 4. The experimental study shows that when an NPs target interacts with an RF-BF DBD, NPs are brought into flight.- The design and testing of a DBD reactor configuration comprising 2 successive plasma zones: the first to launch the NPs of a target, the second to deposit the NPs on a substrate. The latter is based on a double frequency BF-LF DBD obtained by applying a 50 kHz voltage which generates electrons to charge the NPs and a 1 kHz voltage which we know can ensure the transport of charged NPs from the volume to surfaces. The feasibility was shown by the observation of NPs on the substrate

Cette étude a pour objet les piles à combustible à haute température qui se différencient par la nature de l’électrolyte : oxyde solide (SOFC) et carbonates fondus (MCFC). Malgré la maturité actuelle de ces technologies, la dégradation à haute température des matériaux freine un développement à grande échelle. Nous nous sommes essentiellement penchés l’évolution des systèmes SOFC. Ce travail s’intéresse tout d’abord à l’élaboration par dépôt de couches atomiques (ALD) d’oxyde de cérium dopé à l’yttrium (connu pour ses propriétés électrocatalytiques à l’anode) et leur caractérisation électrochimique, afin de mettre en évidence l’influence de leur microstructure sur la réactivité sous atmosphère réductrice d’hydrogène. L’orientation de ces couches a montré une augmentation significative de leur réactivité. Dans un deuxième temps nous avons étudié des électrolytes composites oxyde-carbonates et, plus particulièrement, l’évolution de leur comportement électrique sous différentes conditions expérimentales se rapprochant du fonctionnement des SOFC. Nous avons pu en déduire les mécanismes régissant la conductivité ionique sous atmosphères variées et mis en évidence l’intérêt d’une couche mince entre anode et électrolyte dans une cellule unitaire. Dans les deux cas des résultats très significatifs ont été obtenus permettant d’envisager des systèmes hybrides SOFC/MCFC, incluant des couches minces fortement orientées, compétitifs par rapport aux dispositifs existants
This study deals with high-temperature fuel cells that differ in the nature of the electrolyte: solid oxide (SOFC) and molten carbonates (MCFC). Despite the current maturity of these technologies, the high temperature degradation of materials slows down large-scale development. We mainly focused on the evolution of SOFC systems. This work investigates first the deposition of atomic layers (ALD) of cerium oxide doped with yttrium (known for its electrocatalytic properties at the anode) and their electrochemical characterization, in order to show the influence of their microstructure on the reactivity under a reducing atmosphere of hydrogen. The orientation of these layers showed a significant increase in their reactivity. In a second time we studied composite electrolytes oxide-carbonates and, more particularly, the evolution of their electrical behavior under different experimental conditions approaching the operation of the SOFC. We have been able to deduce the mechanisms governing the ionic conductivity under various atmospheres and highlighted the interest of a thin layer between anode and electrolyte in a single cell. In both cases, very significant results have been obtained allowing SOFC / MCFC hybrid systems, including highly oriented thin films, to be considered as competitors with existing devices

This dissertation develops a novel application of the resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) technique toward the end goal of conjugated-polymer-based optoelectronic device fabrication. Conjugated polymers are attractive materials that are being investigated in the development of efficient optoelectronic devices due to their inexpensive material costs. Moreover, they can easily be combined with inorganic nanomaterials, such as colloidal quantum dots (CQDs), so as to realize hybrid nanocomposite-based optoelectronic devices with tunable optoelectronic characteristics and enhanced desirable features. One of the most significant challenges to the realization of optimal conjugated polymer-CQD hybrid nanocomposite-based optoelectronics has been the processes by which these materials are deposited as thin films, that is, conjugated polymer thin film processing techniques lack sufficient control so as to maintain preferred optoelectronic device behavior. More specifically, conjugated-polymer-based optoelectronics device operation and efficiency are a function of several attributes, including surface film morphology, internal polymer chain morphology, and the distribution and type of nanomaterials in the film bulk. Typical conjugated-polymer thin-film fabrication methodologies involve solution-based deposition, and the presence of the solvent has a deleterious impact, resulting in films with poor charge transport properties and subsequently poor device efficiencies. In addition, many next-generation conjugated polymer-based optoelectronics will require multi-layer device architectures, which can be difficult to achieve using traditional solution processing techniques. These issues direct the need for the development of a new polymer thin film processing technique that is less susceptible to solvent-related polymer chain morphology problems and is more capable of achieving better controlled nanocomposite thin films and multi-layer heterostructures comprising a wide range of materials. Therefore, this dissertation describes the development of a new variety of RIR-MAPLE that uses a unique target emulsion technique to address the aforementioned challenges.

The emulsion-based RIR-MAPLE technique was first developed for the controlled deposition of the conjugated polymers poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly[2-methoxy-5-(2'ethylhexyloxy)-1,4-(1-cyanovinylene) phenylene] (MEH-CN-PPV) into homogenous thin films. Therein, it was identified that target composition had the most significant influence on film surface morphology, and by tuning the concentration of hydroxyl bonds in the target bulk, the laser-target absorption depth could be tuned so as to yield more or less evaporative deposition, resulting in films with tunable surface morphologies and optical behaviors.

Next, the internal morphologies of emulsion-based RIR-MAPLE-deposited MEH-PPV thin films were investigated by measuring their hole drift mobilities using the time-of-flight (TOF) photoconductivity method in the context of amorphous materials disorder models (Bässler's Gaussian Disorder model and the Correlated Disorder model) in order to provide a quantitative measure of polymer chain packing. The polymer chain packing of the RIR-MAPLE-deposited films was demonstrated to be superior and more conducive to charge transport in comparison to spin-cast and drop-cast MEH-PPV films, yielding enhanced hole mobilities.

The emulsion-based RIR-MAPLE technique was also developed for the deposition of different classes of inorganic nanoparticles, namely un-encapsulated nanoparticles and ligand-encapsulated nanoparticles. These different classes of nanoparticles were identified to have different film growth regimes, such that either rough or smooth films were obtained, respectively. The ligand-encapsulated nanoparticles were then co-deposited with MEH-PPV as conjugated polymer-CQD hybrid nanocomposites, wherein the distributions of the constituent materials in the film bulk were identified to be tunable, from homogeneous to highly clustered. The RIR-MAPLE deposition regime determined the said distributions, that is, if the polymer and CQDs were sequentially deposited from a sectioned target or simultaneously deposited from a single target, respectively. The homogeneous conjugated polymer-CQD nanocomposites were also investigated in terms of their charge transport properties using the TOF photoconductivity technique, where it was identified that despite the enhanced dispersion of CQDs in the film bulk, the presence of a high concentration of CQDs degraded hole drift mobility, which indicates that special considerations must be taken when incorporating CQDs into conjugated-polymer-based nanocomposite optoelectronics.

Finally, the unique capability of RIR-MAPLE to enable novel conjugated polymer-based optical heterostructures and optoelectronic devices was evaluated by the successful demonstration of a conjugated polymer-based distributed Bragg reflector (DBR), a plasmonic absorption enhancement layer, and a conjugated polymer-based photovoltaic solar cell featuring a novel electron-transporting layer. These optical heterostructures and optoelectronic devices demonstrate that all of the constituent polymer and nanocomposite layers have controllable thicknesses and abrupt interfaces, thereby confirming the capability of RIR-MAPLE to achieve multi-layer, conjugated polymer-based heterostructures and device architectures that are appropriate for enhancing specific desired optical behaviors and optoelectronic device efficiencies.

Dissertation

碩士
國立清華大學
材料科學工程學系
103
Crustacean exoskeleton, a natural composite consisting of chitin, proteins and minerals, has gradient constituent and microstructure which provide excellent hardness and fracture toughness. The major toughening mechanism is the crack deflection at the interface between the hard exocuticle and tough endocuticle so that the crack cannot propagate through the exoskeleton directly. The twisted plywood (or Bouligand) structure which possesses elastic modulus mismatch and oscillation could further prevent cracks from propagation. A novel hybrid system combining reactive RF sputtering and pulsed laser deposition is designed and utilized to synthesize bio-inspired ceramic/polymer multilayer coatings. In order to mimic the exocuticle and endocuticle in crustacean exoskeleton, multilayer coatings composed of hard ZrO2 outer layers and tough TiO2/polyimide inner layers were synthesized. The thickness ratio of TiO2/polyimide layers is kept 10 to 1 (100 nm/10 nm), and the thickness of ZrO2 was altered from 100 nm to 500 nm to investigate the effect of the elastic modulus gradient on the mechanical properties. Nanoindentation was conducted to evaluate the mechanical performance of multilayer films. The fracture toughness of bio-inspired coatings was further evaluated by the energy-based indentation method. Results show that the multilayer film with specific thickness ratio of ZrO2 has the highest fracture toughness. Toughening mechanisms were elucidated and optimal bio-inspired designs were proposed in this study.

碩士
國立清華大學
材料科學工程學系
102
Abalone nacre is a natural ceramic-based composite consists of 95 wt% stacked CaCO3 tiles and 5 wt% organic layers organized into a unique multilayer structure, which leads to exceptional fracture toughness. The major toughening mechanism is the crack deflection at the organic/inorganic interfaces so that the crack cannot propagate through the shell directly. Furthermore, interfacial roughness and interconnected mineral bridges between tiles can further prevent plastic deformation. Inspired from abalone nacre, multilayer films of zirconia and polyimide layers are synthesized by the hybrid PVD system combining sputtering and pulsed laser deposition. Zirconia is an intrinsically tough ceramic material. By introducing the polyimide interlayer, the fracture toughness of multilayer films can be significantly enhanced, six times higher than that of zirconia monolayer. The thickness ratio of zirconia and polyimide is kept 10:1, and the period thickness is altered to investigate effect the interfaces on the mechanical properties. Results show that multilayer structure can enhance the fracture toughness of thin film: fracture toughness increases with increasing number of interlayers yet the hardness decreases. SEM observation verifies that the major toughening mechanism of bio-inspired multilayer films is crack deflection at organic/inorganic interfaces, which prevent crack from direct propagation. The interfacial roughness can also enhance mechanical properties in certain situations and the mechanisms are discussed.

Optical metamaterials have triggered extensive studies driven by their fascinating electromagnetic properties that are not observed in natural materials. Aside from the extraordinary progress, challenges remain in scalable processing and material performance which limit the adoption of metamaterial towards practical applications. The goal of this dissertation is to design and fabricate nanocomposite thin films by combining nitrides with a tunable secondary phase to realize controllable multi-functionalities towards potential device applications. Transition metal nitrides are selected for this study due to the inherit material durability and low-loss plasmonic properties that offer stable two-phase hybridization for potential high temperature optical applications. Using a pulsed laser deposition technique, the nitride-metal nanocomposites are self-assembled into various geometries including pillar-in-matrix, embedded nanoinclusions or complex multilayers, that possess large surface coverage, high epitaxial quality, and sharp phase boundary. The nanostructures can be further engineered upon precise control of growth parameters.

This dissertation is composed of a general review of related background and experimental approaches, followed by four chapters of detailed research chapters. The first two research chapters involve hybrid metal (Au, Ag) - titanium nitride (TiN) nanocomposite thin films where the metal phase is self-assembled into sub-20 nm nanopillars and further tailored in terms of packing density and tilting angles. The tuning of plasmonic resonance and dielectric constant have been achieved by changing the concentration of Au nanopillars, or the tuning of optical anisotropy and angular selectivity by changing the tilting angle of Ag nanopillars. Towards applications, the protruded Au nanopillars are demonstrated to be highly functional for chemical bonding detection or surface enhanced sensing, whereas the embedded Ag nanopillars exhibit enhanced thermal and mechanical stabilities that are promising for high temperature plasmonic applications. In the last two chapters, dissimilar materials candidates beyond plasmonics have been incorporated to extend the electromagnetic properties, include coupling metal nanoinclusions into a wide bandgap semiconducting aluminum nitride matrix, as well as inserting a dielectric spacer between the hybrid plasmonic claddings for geometrical tuning and electric field enhancement. As a summary, these studies present approaches in addressing material and fabrication challenges in the field of plasmonic metamaterials from fundamental materials perspective. As demonstrated in the following chapters, these hybrid plasmonic nanocomposites provide multiple advantages towards tunable optical or biomedical sensing, high temperature plasmonics, controllable metadevices or nanophotonic chips.

碩士
國立臺灣科技大學
材料科學與工程系
107
In recent years, the passivated emitter rear cell (PERC) solar cell has benefits such as easy fabrication and high conversion efficiency which demonstrate a promising cell structure of Si-based solar cells. In general, the alumina oxide was deposited on the emitter region of PERC for passivation purpose. It is well known that the DLC thin films exhibits many advantages such as high hardness, transparency in visible-light and IR-light and high resistivity etc. In this study, the diamond like carbon (DLC) thin films is tried to grow on the p-type Si substrate by combined electron-cyclotron resonance (ECR) plasma and radio-frequency (RF) plasma chemical vapor deposition (CVD), namely hybrid plasma CVD (HPCVD) system. The growth parameters of DLC thin films such as precursors flow ratio of CH4 and H2, working pressure and RF power are optimized in order to find a better passivation result. The capacitance-voltage (C-V) measurement of samples constructed by metal Al/DLC/p-Si/metal Al are used for studied the fix-charge density, trap-center density and interface defect density of DLC passivation layer by techniques of the flat-band voltage, hysteresis behavior and conductance. The quasi steady state photoconductivity (QSSPC) is also be used for carrier lifetime measurement. In addition, the leakage current of sample structure is studied by the current-voltage (I-V) measurement. Finally, an optimized DLC passivation layer with growth conditions: working pressure of 1 torr, CH4/H2 flow ratio of 10/90 sccm, RF power of 150 W is used for achieving the lowest surface recombination rate (0.23 cm/s), interface defect density (2.25×〖10〗^10 〖eV〗^(-1) 〖cm〗^(-2)). In addition, the carrier lifetime is increased from 2.99 s for p-Si substrate to 9.85 s for DLC passivated p-Si substrate.