Microstructuring of silicon is performed to alter its optical and electrical properties for use in photonic devices. Femtosecond lasers are a favourable structuring tool because they are extremely precise due to the confinement of their interaction to the focal volume. Experiments were carried out on N-type, P-type, and intrinsic silicon with a femtosecond laser operating at 800 nm, with pulse duration of 40 fs, and 1 kHz repetition rate. A single pulse produced a micro-ring structure surrounding a crater. It is caused by the motion of material according to the pressure gradient induced by the Gaussian profile of the laser. Multiple-pulse structures were similar to the single pulse except for the central protrusion of material. Two factors are responsible for multiple-pulse structures: (1) geometrical difference of the plasma compared to the single pulse (2) reflections of shockwaves produce protruding structures. Polarization dependence of all structures was observed.

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a cost- and time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal.

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a cost- and time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal.

La texturisation de matériaux par irradiation laser ultracourt est un procédé permettant de modifier les propriétés optiques et électriques de la matière en formant des nano et microstructures en surface, apparaissant au cours des irradiations successives. Le contrôle du procédé et le développement des applications nécessitent une compréhension des mécanismes mis en jeu. Les processus intervenant sont étudiés à l'aide de simulations numériques, et sont comparés à des résultats expérimentaux. L'étude est menée dans le cadre de l'augmentation du rendement des cellules photovoltaïques basées sur du silicium massif. / Ultrashort laser pulsed texturing is a process which allows to modify optical and electrical properties of matter, through formation of nano and micro structures on surface, appearing from pulse to pulse. Control of the process and developments of the potential applications need a good knowledge of the formation mechanisms. Processes occuring during the interaction are studied using numerical simulations and are compared to experimental results. The study aims to increase the efficiency of solar cells based on bulk silicon.

Neste trabalho exploramos o uso de diferentes técnicas de microestruturação de materiais poliméricos a laser, visando a obteção de superfícies que podem ser aplicadas tanto no desenvolvimento de dispositivos fotônicos quanto de materiais biomédicos. Primeiramente, estudamos a influência da energia de pulso e velocidade de translação sobre as microestruturas produzidas na superfície de filmes de poli(2-metóxi-5-(2-etil-hexiloxi)-1,4-fenileno vinileno) (MEH-PPV). Observamos que a rugosidade da superfície microestruturada aumentou significativamente com o aumento da energia de pulso e velocidade de translação. Além disso, determinamos o limiar de energia para remoção de material, distinguindo o intervalo de energia para a remoção do polímero daquele que causa somente alterações morfológicas. Uma vez que as condições de microestruturação com pulsos laser de femtossegundos foram determinadas, aplicamos tal abordagem para fabricar um dispositivo eletroluminescente microestruturado, sem danificar o polímero e a camada de óxido de índio-estanho, utilizada como contato. Em uma segunda vertente do trabalho, estudamos a influência da energia do pulso ultracurto sobre as propriedades físico-químicas de filmes de quitosana. Neste caso, determinamos o limiar de energia para que ocorra mudança estrutural e remoção de material polimérico. Com isso, produzimos microestruturas com características mais hidrofílicas, além de superfícies com diferentes estruturações superficiais, que foram utilizadas para investigar seu potencial no estudo da formação de biofilme de Staphylococcus aureus. Neste caso, produzimos microestruturas com dimensões de 500 μm2 e diferentes periodicidades (variando de 4 a 12 μm) na superfície de filmes de quitosana e polimetilmetacrilato (PMMA). Com essas microestruturas, observamos distintos comportamentos para a formação de biofilme; no caso do PMMA, não houve distinção de desenvolvimento; quanto às amostras de quitosana, observamos uma preferência das bactérias por superfícies mais rugosas e regiões de bordas das microestruturas. Por fim, em uma terceira vertente do trabalho, utilizamos o método de estruturação direta por interferência para fabricar microestruturas periódicas em membranas de poliuretano, usando pulsos de nanossegundos. Com esse método, produzimos microestruturas de alta qualidade na superfície de membranas de poliuretano, com diferentes periodicidades (variando de 500 nm até 5 μm). Essa microestruturação permitiu a obtenção de amostras com comportamento de molhamento anisotrópico. De maneira geral, os resultados aqui apresentados, além de demonstrar a potencialidade das técnicas de microfabricação a laser, fornecem importantes informações sobre os parâmetros ótimos para microfabricação em filmes poliméricos, visando aplicações tanto em dispositivos fotônicos e optoeletrônicos quanto em biomateriais. / In this work we explored the use of laser micromachining methods to structure polymeric materials, aiming to obtain surfaces that can be applied in the development of photonic devices as well as biomedical materials. Firstly, we investigated the influence of pulse energy and translation speed on microstructures fabricated on the surface of poly[2-methoxy-5- (2\'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) films. We observed that the roughness of the microstructured surface significantly increased with the pulse energy and translation speed. Besides, we determined the energy threshold for material removal, distinguishing the energy range for polymer removal from that causing only structural changes. Once the proper laser micromachining conditions were determined, we were able to apply such approach to fabricate a functional microstructured electroluminescent device, without disrupting the indium tin oxide layer used as the contact for the devices. In the second part of the work, we studied the influence of femtosecond pulses on the structuring process of chitosan films. In this case, we determined the threshold energy that leads to structural change and material removal. We have been able to produced microstructures with hydrophilic characteristics, in addition to surfaces with different structuring that were used to study the formation of Staphylococcus aureus biofilm. For such purpose we produced microstructured areas of 500 μm2 and different periods (ranging from 4 to 12 μm) on the surface of chitosan and poly(methyl methacrylate)(PMMA) films. With these microstructures we observed different behaviors in the biofilm formation; in the case of PMMA, there was not distinction of development; concerning the chitosan samples we observed preferential bacterial growth on the rougher regions of the microstructures. Lastly, in a third part of the study, we used the method of direct laser interference patterning to fabricate periodic microstructures on polyurethane membranes, using nanosecond pulses. With this method, we produced high quality microstructures on the surface of polyurethane with different periodicity (from 500 nm to 5.0 μm). This approach allowed obtaining samples with anisotropic wetting behavior. In general, the results presented here, in addition to demonstrating the potential of the laser micromachining methods to structure polymeric samples, provides important information about the optimal parameters to micromachining of polymer films, aiming at applications in photonic devices, optoelectronics and biomaterials.

Neste trabalho investigamos as modificações na morfologia superficial e estrutura de filmes finos de silício amorfo hidrogenado, resultantes da irradiação com pulsos ultracurtos de femtossegundos (150 fs, 775 nm e 1 kHz). Os processos de microfabricação foram conduzidos varrendo, a velocidade constante, um feixe laser com diferentes fluências (1,8 a 6,2 MJ/m2) sobre a amostra. Os espectros de transmissão apresentaram queda para amostras irradiadas, cujas imagens de microscopia eletrônica de varredura mostraram estruturas superficiais condizentes com o fenômeno de LIPSS (Laser Induced Periodic Surface Structures). Uma análise estatística das imagens de microscopia de força atômica foi realizada com um programa que identifica e caracteriza os domínios (picos) produzidos pela microfabricação. O histograma de altura da amostra irradiada com uma fluência de 3,1 MJ/m2 mostrou que a altura média dos picos produzidos é de 15 nm, menor que o centro da distribuição de alturas para uma amostra não irradiada. Porém, para fluências acima de 3,7 MJ/m2 a morfologia é dominada pela formação de agregados. Medidas de espectroscopia Raman revelaram a formação de uma fração de silício cristalino, após a irradiação com pulsos de femtossegundos, de até 77% para 6,2 MJ/m2. Determinamos ainda uma diminuição da dimensão dos nanocristais produzidos com o aumento da fluência do laser de excitação. Portanto, nossos resultados mostram que há um compromisso entre as propriedades obtidas pela microfabricação (transmissão, distribuição de picos, fração de cristalização e tamanho dos nanocristais produzidos) que deve ser levado em conta ao aplicar a técnica de microestruturação com laser de femtossegundos. / In this work we investigated surface morphology and structural modification on hydrogenated amorphous silicon (a-Si:H) thin films, resulting from femtosecond laser irradiation (150 fs, 775 nm and 1 kHz). Microfabrication processes were carried out scanning sample´s surface, at constant speed, with distinct laser fluencies (from 1.8 to 6.2 MJ/m2). A decrease was observed in the transmission spectra of irradiated samples, whose scanning electron microscopy images revealed surface structures compatible with the Laser Induced Periodic Surface Structure (LIPSS) phenomenon. A statistical analyzes of Atomic Force Microcopy images was performed using a specially developed software, that identifies and characterizes the domains (spikes) produced by the laser irradiation. The height histogram for a sample irradiated with 3.1 MJ/m2 reveals that the average height of the produced spikes is at 15 nm, which is smaller than the center of height distribution for non-irradiated sample. For fluencies higher than 3.7 MJ/m2, however, aggregation of the produced spikes dominates the sample morphology. Raman spectroscopy revealed the formation of a crystalline fraction of 77% for laser fluence irradiation of 6.2 MJ/m2, as well as a decrease in size of the produced crystals as a function of fluence. Therefore, our results indicate that there is a compromise of the sample transmission, spikes distribution, crystallization fraction and size of nanocrystals obtained by fs-laser irradiation, which has to be taken into consideration when using this material processing method.

In the current PhD thesis a thorough study is performed on the design, fabrication and analysis of microstructures created by use of laser methods. The work comprises the design and fabrication of organic, inorganic and hybrid microstructures for use in photonics applications. In addition, several techniques are applied for the fabrication and replication of photonic diffractive microstructures. Fabricated structures are tested as potential functional photonic sensors for humidity, ammonia and temperature detection. Furthermore, a detailed study on polymer-based microstructures creation by laser radiation forces is attempted both theoretically and experimentally. The created 2D and 3D free-standing micro/nanostructures are optically characterized. / Στην παρούσα διδακτορική διατριβή παρουσιάζεται μια ενδελεχής μελέτη στην σχεδίαση, κατασκευή και ανάλυση μικροδομών που δημιουργούνται με τη χρήση δέσμης λέιζερ. Η εργασία περιλαμβάνει τον σχεδιασμό και την κατασκευή οργανικών, ανόργανων και υβριδικών μικροδομών για χρήση τους σε εφαρμογές φωτονικής. Επιπρόσθετα, εφαρμόζονται διάφορες τεχνικές για την κατασκευή και αναπαραγωγή φωτονικών περιθλαστικών μικροδομών. Οι δομές ελέγχονται ως λειτουργικοί φωτονικοί αισθητήρες για την ανίχνευση υγρασίας, αμμωνίας και θερμοκρασίας. Ακόμα, πραγματοποιείται μια λεπτομερής μελέτη πάνω στη δημιουργία μικροδομών βασισμένων σε πολυμερή με χρήση δυνάμεων ακτινοβολίας λέιζερ τόσο σε θεωρητικό όσο και σε πειραματικό επίπεδο. Οι δημιουργούμενες δισδιάστατες και τρισδιάστατες μικρο/νανοδομές ελεύθερου χώρου χαρακτηρίζονται οπτικά.

Neste trabalho exploramos o uso de diferentes técnicas de microestruturação de materiais poliméricos a laser, visando a obteção de superfícies que podem ser aplicadas tanto no desenvolvimento de dispositivos fotônicos quanto de materiais biomédicos. Primeiramente, estudamos a influência da energia de pulso e velocidade de translação sobre as microestruturas produzidas na superfície de filmes de poli(2-metóxi-5-(2-etil-hexiloxi)-1,4-fenileno vinileno) (MEH-PPV). Observamos que a rugosidade da superfície microestruturada aumentou significativamente com o aumento da energia de pulso e velocidade de translação. Além disso, determinamos o limiar de energia para remoção de material, distinguindo o intervalo de energia para a remoção do polímero daquele que causa somente alterações morfológicas. Uma vez que as condições de microestruturação com pulsos laser de femtossegundos foram determinadas, aplicamos tal abordagem para fabricar um dispositivo eletroluminescente microestruturado, sem danificar o polímero e a camada de óxido de índio-estanho, utilizada como contato. Em uma segunda vertente do trabalho, estudamos a influência da energia do pulso ultracurto sobre as propriedades físico-químicas de filmes de quitosana. Neste caso, determinamos o limiar de energia para que ocorra mudança estrutural e remoção de material polimérico. Com isso, produzimos microestruturas com características mais hidrofílicas, além de superfícies com diferentes estruturações superficiais, que foram utilizadas para investigar seu potencial no estudo da formação de biofilme de Staphylococcus aureus. Neste caso, produzimos microestruturas com dimensões de 500 μm2 e diferentes periodicidades (variando de 4 a 12 μm) na superfície de filmes de quitosana e polimetilmetacrilato (PMMA). Com essas microestruturas, observamos distintos comportamentos para a formação de biofilme; no caso do PMMA, não houve distinção de desenvolvimento; quanto às amostras de quitosana, observamos uma preferência das bactérias por superfícies mais rugosas e regiões de bordas das microestruturas. Por fim, em uma terceira vertente do trabalho, utilizamos o método de estruturação direta por interferência para fabricar microestruturas periódicas em membranas de poliuretano, usando pulsos de nanossegundos. Com esse método, produzimos microestruturas de alta qualidade na superfície de membranas de poliuretano, com diferentes periodicidades (variando de 500 nm até 5 μm). Essa microestruturação permitiu a obtenção de amostras com comportamento de molhamento anisotrópico. De maneira geral, os resultados aqui apresentados, além de demonstrar a potencialidade das técnicas de microfabricação a laser, fornecem importantes informações sobre os parâmetros ótimos para microfabricação em filmes poliméricos, visando aplicações tanto em dispositivos fotônicos e optoeletrônicos quanto em biomateriais. / In this work we explored the use of laser micromachining methods to structure polymeric materials, aiming to obtain surfaces that can be applied in the development of photonic devices as well as biomedical materials. Firstly, we investigated the influence of pulse energy and translation speed on microstructures fabricated on the surface of poly[2-methoxy-5- (2\'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) films. We observed that the roughness of the microstructured surface significantly increased with the pulse energy and translation speed. Besides, we determined the energy threshold for material removal, distinguishing the energy range for polymer removal from that causing only structural changes. Once the proper laser micromachining conditions were determined, we were able to apply such approach to fabricate a functional microstructured electroluminescent device, without disrupting the indium tin oxide layer used as the contact for the devices. In the second part of the work, we studied the influence of femtosecond pulses on the structuring process of chitosan films. In this case, we determined the threshold energy that leads to structural change and material removal. We have been able to produced microstructures with hydrophilic characteristics, in addition to surfaces with different structuring that were used to study the formation of Staphylococcus aureus biofilm. For such purpose we produced microstructured areas of 500 μm2 and different periods (ranging from 4 to 12 μm) on the surface of chitosan and poly(methyl methacrylate)(PMMA) films. With these microstructures we observed different behaviors in the biofilm formation; in the case of PMMA, there was not distinction of development; concerning the chitosan samples we observed preferential bacterial growth on the rougher regions of the microstructures. Lastly, in a third part of the study, we used the method of direct laser interference patterning to fabricate periodic microstructures on polyurethane membranes, using nanosecond pulses. With this method, we produced high quality microstructures on the surface of polyurethane with different periodicity (from 500 nm to 5.0 μm). This approach allowed obtaining samples with anisotropic wetting behavior. In general, the results presented here, in addition to demonstrating the potential of the laser micromachining methods to structure polymeric samples, provides important information about the optimal parameters to micromachining of polymer films, aiming at applications in photonic devices, optoelectronics and biomaterials.

Neste trabalho investigamos as modificações na morfologia superficial e estrutura de filmes finos de silício amorfo hidrogenado, resultantes da irradiação com pulsos ultracurtos de femtossegundos (150 fs, 775 nm e 1 kHz). Os processos de microfabricação foram conduzidos varrendo, a velocidade constante, um feixe laser com diferentes fluências (1,8 a 6,2 MJ/m2) sobre a amostra. Os espectros de transmissão apresentaram queda para amostras irradiadas, cujas imagens de microscopia eletrônica de varredura mostraram estruturas superficiais condizentes com o fenômeno de LIPSS (Laser Induced Periodic Surface Structures). Uma análise estatística das imagens de microscopia de força atômica foi realizada com um programa que identifica e caracteriza os domínios (picos) produzidos pela microfabricação. O histograma de altura da amostra irradiada com uma fluência de 3,1 MJ/m2 mostrou que a altura média dos picos produzidos é de 15 nm, menor que o centro da distribuição de alturas para uma amostra não irradiada. Porém, para fluências acima de 3,7 MJ/m2 a morfologia é dominada pela formação de agregados. Medidas de espectroscopia Raman revelaram a formação de uma fração de silício cristalino, após a irradiação com pulsos de femtossegundos, de até 77% para 6,2 MJ/m2. Determinamos ainda uma diminuição da dimensão dos nanocristais produzidos com o aumento da fluência do laser de excitação. Portanto, nossos resultados mostram que há um compromisso entre as propriedades obtidas pela microfabricação (transmissão, distribuição de picos, fração de cristalização e tamanho dos nanocristais produzidos) que deve ser levado em conta ao aplicar a técnica de microestruturação com laser de femtossegundos. / In this work we investigated surface morphology and structural modification on hydrogenated amorphous silicon (a-Si:H) thin films, resulting from femtosecond laser irradiation (150 fs, 775 nm and 1 kHz). Microfabrication processes were carried out scanning sample´s surface, at constant speed, with distinct laser fluencies (from 1.8 to 6.2 MJ/m2). A decrease was observed in the transmission spectra of irradiated samples, whose scanning electron microscopy images revealed surface structures compatible with the Laser Induced Periodic Surface Structure (LIPSS) phenomenon. A statistical analyzes of Atomic Force Microcopy images was performed using a specially developed software, that identifies and characterizes the domains (spikes) produced by the laser irradiation. The height histogram for a sample irradiated with 3.1 MJ/m2 reveals that the average height of the produced spikes is at 15 nm, which is smaller than the center of height distribution for non-irradiated sample. For fluencies higher than 3.7 MJ/m2, however, aggregation of the produced spikes dominates the sample morphology. Raman spectroscopy revealed the formation of a crystalline fraction of 77% for laser fluence irradiation of 6.2 MJ/m2, as well as a decrease in size of the produced crystals as a function of fluence. Therefore, our results indicate that there is a compromise of the sample transmission, spikes distribution, crystallization fraction and size of nanocrystals obtained by fs-laser irradiation, which has to be taken into consideration when using this material processing method.

To meet the new challenges of the chemical indutries, the developpement of new heterogeneous catalytic reactors and their understanding are mandatory. From these perspectives, new reactor designs based on structuring at micro or millimeter scales have emerged. They have sparked interest for their ability to decrease physical limitations for heat and mass transfers. Thus, two advanced reactor technologies for gas-liquid-solid catalysed reactions are studied. The first reactor is a micro-structured falling film (FFMR) in which vertical sub millimetric grooves are etched and coated with a catalyst. This structuration allows stabilizing the gas-liquid interface of a down flow liquid phase. A thin liquid film is generated leading to high specific surface areas. Commercially available, it represents a very good potential for performing demanding reactions (i.e.fast, exothermic) for small scale productions such as pharmaceuticals. In a second part, a new reactor concept is proposed. Open cell foams are used as catalyst support and inserted in a milli-square channel. The reactor is then submitted to a preformed gas-liquid Taylor flow. In both cases, hydrodynamics features are studied by using microscopy based methods. Their potential in terms of mass transfers are also studied by performing catalyzed α-methylstyren hydrogenation. For both reactors, it comes out that the particular flow induced by micro or milli structures leads to at least one order of magnitude higher mass transfers performances than mutliphase reactors currently used in the industry albeit it remains to be demonstrated at such scale. From all these studies, correlations, models and methods for chemical engineers (hydrodynamics, pressure drops, mass transfer) are proposed for the two reactors