Dissertations / Theses on the topic 'Periodic Micron Structures'

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 130-147).
A central pillar of real-world engineering is controlled molding of different types of waves (such as optical and acoustic waves). The impact of these wave-molding devices is directly dependent on the level of wave control they enable. Recently, artificially structured metamaterials have emerged, offering unprecedented flexibility in manipulating waves. The design and fabrication of these metamaterials are keys to the next generation of real-world engineering. This thesis aims to integrate computer science, materials science, and physics to design novel metamaterials and functional devices for photonics and nanotechnology, and translate these advances into realworld applications. Parallel finite-difference time-domain (FDTD) and finite element analysis (FEA) programs are developed to investigate a wide range of problems, including optical micromanipulation of biological systems [1, 2], 2-pattern photonic crystals [3], integrated optical circuits on an optical chip [4], photonic quasicrystals with the most premier photonic properties to date [5], plasmonics [6], and structure-property correlation analysis [7], multiple-exposure interference lithography [8], and the world's first searchable database system for nanostructures [9].
by Lin Jia.
Ph.D.

Patterning, the utilisation and manipulation of geometric properties, is important both for the rational design of technological devices and also to the understanding of many natural phenomena. In this thesis I examine the way in which micro and nano patterning can alter optical properties across a large range of wavelength scales and how these novel phenomena can be utilised. Micro patterned electrodes can tune the geometry of radio frequency electric fields to generate dielectrophoretic microfluidic devices. These devices use the dielectrophoretic force to sort, position and characterise the properties of micro and nano particles. I develop a new image processing algorithm that radically improves experimental efficiency allowing for real-time supervisor free dielectrophoretic characterisation of nanoparticles. Metamaterials are composite structures that have repeating units that are much smaller than the wavelength of radiation they are designed to work with. The optical properties of the materials are derived from these units rather than the bulk characteristics of the materials they are composed of. I demonstrate the development of novel THz metamaterial absorber devices. These devices provide a means to design and control the absorption of THz radiation, modulating bandwidth, polarization dependence and frequency in a form that is readily integrable with other standard fabrication processes. Finally by periodically patterning materials on the nanometer scale I demonstrate the development of novel photonic crystal devices and complementary optical components. In these devices the periodicity of the electromagnetic wave is modulated by the periodicity of the structures themselves resulting in band gaps and resonances analogous to the band gaps and defect states found commonly in semi-conductor physics. I demonstrate the theory, fabrication and measurement of these devices using novel broadband supercontinuum sources and propose a future application for biosensing. Further topics covered in the appendix include the development of a spin out technology, a $100 open source atomic force microscope developed while spending time in China. Finally I examine the role of patterning for optimising the performance of nanomechanical cantilever biosensors, and show how geometrical effects on the microscopic scale are crucial to understanding the workings of the vancomycin family of antibiotics, as screened using microcantilevers. Portions of this report are edited extracts from published articles resulting from this work, a full list of which is given in Appendix A.

The main aim of this work was to develop the formation technique of periodic micro-structures by interference lithography in photosensitive polymeric materials, experimentally investigate possibilities and limitations of the method, and to create micro-structures suitable for practical applications. The shape of the micro-structures fabricated by interference lithography depends on the used laser irradiation dose, laser wavelength, phase, polarization, the angle between interfering beams and the number of the interfering beams, and their rigidity - mainly on the used laser irradiation dose. In this work also the possibility to form micro-tube and scaffolds arrays by using interference lithography was demonstrated and the control of the geometrical parameters of micro-lenses fabricated by interference lithography and manipulating the laser irradiation dose was investigated in depth. The possibility to immobilize the newly synthesized aromatic azides molecules in PEG matrix by photo-grafting technique was also demonstrated and the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) chemical reaction by using azide “MegaStokes dye 673” was realized, in order to show the capability to combine the photo-grafting technique with “click” chemistry. The developed 3D site-specific functionalization method is simple and versatile; it has potential applications in micro-array based proteome analysis, studies of cell-surface interactions, sensing applications, and drug screening.
Disertacijos tikslas buvo sukurti metodą periodinių darinių formavimui interferencinės litografijos būdu, polimerizuojant fotojautrias medžiagas, eksperimentiškai ištirti šio metodo galimybes ir ribojimus bei suformuoti mikrodarinius, tinkamus praktiniams taikymams. Eksperimentų metu buvo pademonstruota, kad interferencinės litografijos metodu formuojamų mikrodarinių forma priklauso nuo: lazerinės apšvitos dozės, bangos ilgio, fazės, kampo tarp interferuojančių pluoštų ir pluoštų skaičiaus, o jų tvirtumas labiausiai priklauso nuo lazerinės apšvitos dozės. Šiame darbe taip pat parodyta, kad naudojant interferencinės litografijos metodą viena lazerine ekspozicija galima formuoti mikrovamzdelių ir mikrolęšių masyvus bei karkasus iš biosuderinamos ir biosuskaidomos PEG-DA-258 medžiagos. Be polimerinių darinių formavimo, šiame darbe pademonstruota ir jų fotomodifikavimo galimybė, naudojant fotoįskiepijimo (angl. photo-grafting) technologiją, o taip pat realizuojant variu katalizuojamos azido alkino ciklizacijos (CuAAC) cheminę reakciją parodyta fotoįskiepijimo technologijos ir „klik“ chemijos apjungimo galimybė. Toks paprastas ir universalus būdas atveria naujas galimybes biojutiklių kūrime ir audinių inžinerijoje, nes molekulių imobilizavimas polimero matricoje vyksta trimatėje erdvėje ir tiksliai norimoje vietoje, o trimatė erdvinė gradientinė kontrolė yra labai svarbi daugybėje biotechnologijos taikymų.

Une approche dynamique discrète (DDM) est proposée dans le contexte de la mécanique des poutres pour calculer les caractéristiques de dispersion des structures périodiques. Cette démarche permet de calculer les caractéristiques de dispersion de milieux périodiques unidimensionnels et bidimensionnels. Il est montré qu’un développement d'ordre supérieur suffisamment élevé des forces et des moments d’éléments structuraux est nécessaire pour décrire avec précision les modes de propagation d’ordre supérieur. Ces résultats montrent dans l’ensemble que les calculs des caractéristiques de dispersion de systèmes structurels périodiques peuvent être abordés avec une bonne précision par la dynamique des éléments discrets. Les comportements non classiques peuvent être capturés non seulement par une expansion d'ordre supérieur mais aussi par des formulations à gradient supérieur. Nous calculons ainsi les paramètres constitutifs macroscopiques jusqu'au deuxième gradient du déplacement en utilisant deux formulations différentes, soit selon une méthode d'homogénéisation dynamique à gradient supérieur (DHGE) prenant en compte les effets de micro-inertie, ou alternativement selon le principe de Hamilton. Nous analysons ensuite la sensibilité des termes constitutifs du second gradient aux paramètres microstructuraux pour des matériaux composites à microstructure périodique de type laminés. En plus, on montre que les modèles du deuxième gradient formulés à partir de l'énergie interne totale en tenant compte des termes de gradient d'ordre supérieur donnent la meilleure description du propagation d’onde à travers ces milieux. On analyse les contributions d'ordre supérieur et de micro-inertie sur le comportement mécanique de structures composites en utilisant une méthode d'homogénéisation dynamique d'ordre supérieur qui intègre les effets de micro-inertie. Nous calculons la réponse effective statique longitudinale à gradient d’ordre supérieur, en quantifiant la différence relative par rapport à la formulation classique de type Cauchy qui repose sur le premier gradient du déplacement. Nous analysons ensuite les propriétés de propagation d’ondes longitudinales en termes de fréquence propre de composites, en tenant compte de la contribution de la micro-inertie. La longueur interne joue un rôle crucial dans les contributions de micro-inertie avec un effet substantiel pour les faibles valeurs de longueur interne, et qui correspond à une large gamme de matériaux utilisés en ingénierie des structures. La méthode d’homogénéisation développée montre un effet de taille important pour les modules élastiques homogénéisés d’ordre supérieur. Par conséquent, nous développons une formulation indépendante de la taille qui est basée sur des termes de correction liée aux moment quadratique. Dans ce contexte, on analyse l’influence des termes de correction sur le comportement statique et dynamique de composites à inclusion
A discrete dynamic approach (DDM) is developed in the context of beam mechanics to calculate the dispersion characteristics of periodic structures. Subsequently, based on this dynamical beam formulation, we calculate the dispersion characteristics of one-dimensional and two-dimensional periodic media. A sufficiently high order development of the forces and moments of the structural elements is necessary to accurately describe the propagation modes of higher order. These results show that the calculations of the dispersion characteristics of structural systems can be approached with good accuracy by the dynamics of the discrete elements. Besides, non-classical behaviors can be captured not only by higher order expansion but also by higher gradient formulations. To that scope, we develop a higher gradient dynamic homogenization method with micro-inertia effects. Using this formulation, we compute the macroscopic constitutive parameters up to the second gradient, using two distinct approaches, namely Hamilton’s principle and a total internal energy formulation. We analyze the sensitivity of the second gradient constitutive terms on the inner material and geometric parameters for the case of composite materials made of a periodic, layered microstructure. Moreover, we show that the formulations based on the total internal energy taking into account higher order gradient terms give the best description of wave propagation through the composite. We analyze the higher order and micro-inertia contributions on the mechanical behavior of composite structures by calculating the effective static and dynamic properties of composite beams using a higher order dynamic homogenization method. We compute the effective longitudinal static response with higher order gradient, by quantifying the relative difference compared to the classical formulation of Cauchy type, which is based on the first gradient of displacement. We then analyze the propagation properties of longitudinal waves in terms of the natural frequency of composite structural elements, taking into account the contribution of micro-inertia. The internal length plays a crucial role in the contributions of micro-inertia, which is particularly significant for low internal length values, therefore for a wide range of materials used in structural engineering. The developed method shows an important size effect for the higher gradients, and to remove these effects correction terms have been incorporated which are related to the quadratic moment of inertia. We analyze in this context the influence of the correction terms on the static and dynamic behavior of composites with a central inclusion

Orientador: Luiz Carlos Kretly
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Neste trabalho, as diferentes propriedades de superfícies seletivas em frequência, FSS - Frequency Selective Surfaces, são analisadas. As FSS são estruturas planares com células periódicas e podem ser classificadas como uma classe de metamateriais. Para tanto, o mecanismo de trabalho dessas estruturas foi extensivamente estudado, e um método próprio, baseado no modelo de circuito equivalente em conjunto com simulações de onda completa foi proposto. A ferramenta desenvolvida é útil para uma análise preliminar rápida de FSS, a qual foi utilizada para criar uma base de dados de elementos conhecidos na literatura. Diferente dos modelos de análise clássicos, a modelagem analítica proposta, que é uma das principais contribuições do trabalho, usa um simples algoritmo para aproximar a resposta de superfícies seletivas em frequência com geometrias arbitrárias, para incidências normal e oblíqua e para substratos com quaisquer espessuras. Nesse sentido, após a simulação eletromagnética da estrutura, é possível computar a resposta de uma FSS com diferentes parâmetros sem o consumo de tempo das simulações de onda completa. O modelo usa as características peculiares de superfícies de alta impedância, HIS - High Impedance Surface, que dentro de determina faixa comporta-se como condutor magnético perfeito, PMC - Perfect Magnetic Conductor, enquanto no restante da banda tem comportamento de um condutor elétrico perfeito, PEC - Perfect Electric Conductor, para sintetizar absorvedores finos e planares de micro-ondas. As estruturas, compostas de superfície seletiva em frequência resistivas sobre um substrato dielétrico aterrado, são projetadas visando aplicação em diferentes faixas de frequência de absorção e diferentes larguras de banda. Na faixa de 5,5 GHz, objetivou-se satisfazer as especificações dos sistemas WIMAX, WLAN, com os padrões IEEE 802.11a, bem como sistemas de radar, enquanto sinais de outras faixas podem trafegar com atenuação mínima ou nula. Para a faixa mais elevada, projetou-se uma estrutura que oferece absorção sobre a faixa de frequências de 10 GHz a 18 GHz, que pode ser empregada visando aplicações na banda-X e banda-Ku. O método de modelagem para a FSS e para os absorvedores propostos foi validado fisicamente através de montagens experimentais e instrumentação, especialmente desenvolvidas para estas estruturas. Os protótipos dos absorvedores fabricados são extremamente finos e foram medidos por meio de setups de medida em campo aberto e em câmara anecóica. As estruturas projetadas mostraram excelente desempenho para as faixas medidas, mantendo refletividade tipicamente abaixo de -10 dB ao longo de toda a banda. A metodologia desenvolvida nesta pesquisa pode ser ampliada para diferentes faixas de frequências, larguras de banda e aplicações
Abstract: In this work, the different properties of frequency selective surfaces - FSS are analyzed. Frequency selective surfaces are planar structures with periodic cells and can be classified as a kind of metamaterials. To this end, the working mechanism of these structures has been extensively studied, and a proper method based on the equivalent circuit model in conjunction with full-wave simulations was proposed. The developed tool is useful for a fast preliminary analysis of FSS, which was used to create a database of known elements presented in the literature. Unlike of classical analysis model, the proposed analytical modeling, which is one of the main thesis contributions, uses a simple algorithm for approximate the response of frequency selective surfaces with arbitrary shape, for normal and oblique incidence and for substrates with all thicknesses. In this sense, after the electromagnetic simulation of the structure, it is possible to compute the response of an FSS with different parameters without the time consuming full-wave simulations. The model uses the unique characteristics of High-Impedance Surfaces - HIS, which for certain frequency range, behaves as Perfect Magnetic Conductor - PMC, while outside this band behaves as a Perfect Electric Conductor - PEC, for synthesizing thin planar microwave absorbers. The structures, comprising resistive frequency selective surfaces over a grounded dielectric substrate, are designed aiming different absorption frequency bands and different bandwidths. In the 5.5 GHz frequency range, the aim was to satisfy the specifications of WiMAX, WLAN systems, in view of the IEEE 802.11a standards, as well as radar systems, while signals from other bands can travel across with zero or minimal attenuation. To the highest range, the designed structure provides absorption over 10 GHz to 18 GHz frequency range, and can be applied to the X- and Ku- band. The modeling method for the FSS and the proposed absorbers was physically validated through experimental setups and instrumentation, especially developed for these structures. The prototype of the fabricated absorbers are extremely thin and were characterized by using free space and anechoic chamber measurement setups. The designed structures showed excellent performance for measurements ranges, with reflectivity typically below -10 dB over the entire band. The methodology developed in this research can be extended to different frequency bands, bandwidth and applications
Doutorado
Eletrônica, Microeletrônica e Optoeletrônica
Doutor em Engenharia Elétrica

Disertacijos tikslas buvo sukurti metodą periodinių darinių formavimui interferencinės litografijos būdu, polimerizuojant fotojautrias medžiagas, eksperimentiškai ištirti šio metodo galimybes ir ribojimus bei suformuoti mikrodarinius, tinkamus praktiniams taikymams. Eksperimentų metu buvo pademonstruota, kad interferencinės litografijos metodu formuojamų mikrodarinių forma priklauso nuo: lazerinės apšvitos dozės, bangos ilgio, fazės, kampo tarp interferuojančių pluoštų ir pluoštų skaičiaus, o jų tvirtumas labiausiai priklauso nuo lazerinės apšvitos dozės. Šiame darbe taip pat parodyta, kad naudojant interferencinės litografijos metodą viena lazerine ekspozicija galima formuoti mikrovamzdelių ir mikrolęšių masyvus bei karkasus iš biosuderinamos ir biosuskaidomos PEG-DA-258 medžiagos. Be polimerinių darinių formavimo, šiame darbe pademonstruota ir jų fotomodifikavimo galimybė, naudojant fotoįskiepijimo (angl. photo-grafting) technologiją, o taip pat realizuojant variu katalizuojamos azido alkino ciklizacijos (CuAAC) cheminę reakciją parodyta fotoįskiepijimo technologijos ir „klik“ chemijos apjungimo galimybė. Toks paprastas ir universalus būdas atveria naujas galimybes biojutiklių kūrime ir audinių inžinerijoje, nes molekulių imobilizavimas polimero matricoje vyksta trimatėje erdvėje ir tiksliai norimoje vietoje, o trimatė erdvinė gradientinė kontrolė yra labai svarbi daugybėje biotechnologijos taikymų.
The main aim of this work was to develop the formation technique of periodic micro-structures by interference lithography in photosensitive polymeric materials, experimentally investigate possibilities and limitations of the method, and to create micro-structures suitable for practical applications. The shape of the micro-structures fabricated by interference lithography depends on the used laser irradiation dose, laser wavelength, phase, polarization, the angle between interfering beams and the number of the interfering beams, and their rigidity - mainly on the used laser irradiation dose. In this work also the possibility to form micro-tube and scaffolds arrays by using interference lithography was demonstrated and the control of the geometrical parameters of micro-lenses fabricated by interference lithography and manipulating the laser irradiation dose was investigated in depth. The possibility to immobilize the newly synthesized aromatic azides molecules in PEG matrix by photo-grafting technique was also demonstrated and the copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) chemical reaction by using azide “MegaStokes dye 673” was realized, in order to show the capability to combine the photo-grafting technique with “click” chemistry. The developed 3D site-specific functionalization method is simple and versatile; it has potential applications in micro-array based proteome analysis, studies of cell-surface interactions, sensing applications, and drug screening.

A rapid, mask-less deposition technique for writing metal tracks has been developed. The technique was based on laser-induced chemical vapour deposition. The novelty in the technique was the usage of pulsed ultrafast lasers instead of continuous wave lasers in pyrolytic dissociation of the chemical precursor. The motivation of the study was that (1) ultrafast laser pulses have smaller heat affected zones thus the deposition resolution would be higher, (2) the ultrashort pulses are absorbed in most materials (including those transparent to the continuous wave light at the same wavelength) thus the deposition would be compatible with a large range of materials, and (3) the development of higher frequency repetition rate ultrafast lasers would enable higher deposition rates. A deposition system was set-up for the study to investigate the ultrafast laser deposition of tungsten from tungsten hexacarbonyl chemical vapour precursors. A 405 nm laser diode was used for continuous wave deposition experiments that were optimized to achieve the lowest track resistivity. These results were used for comparison with the ultrafast laser track deposition. The usage of the 405 nm laser diode was itself novel and beneficial due to the low capital and running cost, high wall plug efficiency, high device lifetime, and shallower optical penetration depth in silicon substrates compared to green argon ion lasers which were commonly used by other investigators. The lowest as-deposited track resistivity achieved in the continuous wave laser experiments on silicon dioxide coated silicon was 93±27 µΩ cm (16.6 times bulk tungsten resistivity). This deposition was done with a laser output power of 350 mW, scan speed of 10 µm/s, deposition pressure of 0.5 mBar, substrate temperature of 100 °C and laser spot size of approximately 7 µm. The laser power, scan speed, deposition pressure and substrate temperature were all optimized in this study. By annealing the deposited track with hydrogen at 650 °C for 30 mins, removal of the deposition outside the laser spot was achieved and the overall track resistivity dropped to 66±7 µΩ cm (11.7 times bulk tungsten resistivity). For ultrafast laser deposition of tungsten, spot dwell experiments showed that a thin film of tungsten was first deposited followed by quasi-periodic structures perpendicular to the linear polarization of the laser beam. The wavelength of the periodic structures was approximately half the laser wavelength (λ/2) and was thought to be formed due to interference between the incident laser and scattered surface waves similar to that in laser-induced surface periodic structures. Deposition of the quasi-periodic structures was possible on stainless steel, silicon dioxide coated silicon wafers, borosilicate glass and polyimide films. The thin-films were deposited when the laser was scanned at higher laser speeds such that the number of pulses per spot was lower (η≤11,000) and using a larger focal spot diameter of 33 µm. The lowest track resistivity for the thin-film tracks on silicon dioxide coated silicon wafers was 37±4 µΩ cm (6.7 times bulk tungsten resistivity). This value was achieved without post-deposition annealing and was lower than the annealed track deposited using the continuous wave laser. The ultrafast tungsten thin-film direct write technique was tested for writing metal contacts to single layer graphene on silicon dioxide coated silicon substrates. Without the precursor, the exposure of the graphene to the laser at the deposition parameters damaged the graphene without removing it. This was evidenced by the increase in the Raman D peak of the exposed graphene compared to pristine. The damage threshold was estimated to be 53±7 mJ/cm2 for a scanning speed of 500 µm/s. The deposition threshold of thin-film tungsten on graphene at that speed was lower at 38±8 mJ/cm2. However, no graphene was found when the deposited thin-film tungsten was dissolved in 30 wt% H2O2 that was tested to have no effect on the graphene for the dissolution time of one hour. The graphene likely reacted with the deposited tungsten to form tungsten carbide which was reported to dissolve in H2O2. Tungsten carbide was also found on the tungsten tracks deposited on reduced graphene oxide samples. The contact resistance between tungsten and graphene was measured by both transfer length and four-point probe method with an average value of 4.3±0.4 kΩ µm. This value was higher than reported values using noble metals such as palladium (2.8±0.4 kΩ µm), but lower than reported values using other metals that creates carbides such as nickel (9.3±1.0 kΩ µm). This study opened many potential paths for future work. The main issue to address in the tungsten ultrafast deposition was the deposition outside the laser spot. This prevented uniform deposition in successive tracks close to one another. The ultrafast deposition technique also needs verification using other precursors to understand the precursor requirements for this process. An interesting future study would be a combination with a sulphur source for the direct write of tungsten disulphide, a transition metal dichalcogenide that has a two-dimensional structure similar to graphene. This material has a bandgap and is sought after for applications in high-end electronics, spintronics, optoelectronics, energy harvesting, flexible electronics, DNA sequencing and personalized medicine. Initial tests using sulphur micro-flakes on silicon and stainless-steel substrates exposed to the tungsten precursor and ultrafast laser pulses produced multilayer tungsten disulphide as verified in Raman measurements.

Les structures maçonnées sont largement connues en génie civil comme constituant d’une partie des bâtiments, mais également en tant que garnissages réfractaires dans des structures utilisées à hautes températures, par exemple en sidérurgie. Malheureusement, les outils actuels ne sont pas suffisamment puissants pour prédire le comportement de ces structures avec l’apparition de fissures et pour tenir compte du comportement non linéaire d’un des deux constituants (le mortier par exemple). Ce travail de thèse contribue à la modélisation multi-échelles des maçonneries classiques et des garnissages réfractaires avec un faible coût numérique grâce à la technique d’homogénéisation périodique. Les techniques de modélisation et de simulation du comportement des maçonneries sont présentées et développées. L’influence des lois d’interface entre briques et mortier, des paramètres géométriques et matériels, ainsi que de la densité des fissures sur le comportement effectif des maçonneries est étudié. Trois approches (une extension analytique de Cecchi et Tralli, une approche numérique et un modèle micromécanique) sont proposées pour la détermination du comportement effectif d’une cellule périodique dans le cas de maçonneries avec mortier viscoélastique microfissuré et briques saines élastiques ou rigides. Les résultats des calculs sur deux exemples de maçonneries (1D et 2D) ont confirmé que l’approche multi-échelle est une solution appropriée avec une grande capacité à exprimer le comportement des maçonneries viscoélastiques microfissurées. Ce travail, limité au cas sans propagation de fissures, peut être étendu aux mortiers à comportement viscoplastique
Masonry structures are widely used in civil engineering as part of buildings or in refractory linings of structures working at high temperatures, like in steel industry. Unfortunately, the present tools are not powerful enough to predict the behavior of these structures at their micro-cracked state and/or if one of their constituents behaves nonlinearly (e.g. the mortar). This research contributes to the multi-level modeling of classical masonries and refractory linings with a low numerical cost using basically the periodic homogenization technique. Modeling and simulation techniques of masonry behavior are presented and developped. The influence of interface law between bricks and mortar, of geometrical and material parameters, and of crack density on the effective masonry behavior is studied. Three approaches (analytical extension of Cecchi and Tralli, numerical approach and micromechanical modeling) were proposed to determine the effective behavior of a periodic masonry cell with micro-cracked viscoelastic mortar and safe elastic or rigid bricks. The results obtained on two examples of masonry (1D and 2D) confirmed that the multi-scale approach is a suitable solution with a great ability to model the effective behavior of microcracked viscoelastic masonry. This work, actually limited to the case without crack propagation, could be extended to mortars with viscoplastic behavior

Over the past few decades, the study of field distribution at the geometrical focus of a lens (PSF) has gained a huge research interest in field ranging from Nanolithography to microscopy. The central theme of this thesis is to study the intricate details of the field distribution through theoretical modelling, computational studies and experimentation. Specifically, spatial filtering techniques have been proposed to understand and manipulate the field distribution for demanding applications. Based on the findings during the theoretical modelling and computational studies we have proposed light sheet based optical lithography technique. Optical lithography (Photolithography) has emerged as an efficient tool for the fabrication of micro/Nanostructures. It uses photon energy to create patterns on the substrate coated with a photosensitive material. The photochemical reactions which are necessary for the fabrication are spatially confined by the 3D extent of the field distribution. Hence the knowledge of field distribution plays a very crucial role in photolithography. State of the art techniques in optical lithography such as, two photon direct laser writing lithography, interference-based lithography techniques and STED Nano-lithography have made optical lithography a highly sought-after technique for the fabrication of micro/Nanostructures. Specifically, two photon direct lithography is used for making complex 3D structures. Interference based lithography techniques are used for fabricating 1D, 2D and 3D periodic Nanostructures whereas, STED Nano-lithography is capable of fabricating diffraction unlimited structures. The first chapter provides an overview of all the keywords and concepts used in photolithography. A brief summary of the emergence of the field is provided along with the development of different optical lithography techniques. The discovery of photopolymerization process and invention of various photoresist systems has helped in the development of photolithography. These techniques have made physics, chemistry and biology accessible to Nano-scale level. An introduction to photoresist systems and them brief classification is given in this chapter. In addition, we have also provided a brief description to recent techniques in photolithography that is widely used for micro/nanofabrication. Understanding these techniques helps us in identifying the novelty of the proposed lithography technique. A brief introduction is given to understand the field distribution/ point spread function (PSF) that provides the foundation for the entire thesis. In the second chapter, we describe the vectoral model for theoretically understanding the PSF for a spherical lens geometry. This is predominantly since the existing lithography techniques relay on spherical lens geometry. In view of demanding applications, the illumination PSF is tailored by employing spatial filtering techniques. We intend to employ spatial filter in order to add new features to lithography and expand its reach. For example, introduction of spatial filter at the back aperture of an objective lens produce a Bessel like beam which is generally used for applications that requires greater depth of focus. Bessel beams have self-reconstructing property which helps to achieve a greater depth of focus in scattering mediums. The extent of the PSF along the axial direction (z-direction) is 2-3 times greater when compared to the lateral extent. Hence the resolution along z-direction is 2-3 times worse when compared to its lateral counterpart. 4 geometry is generally employed to improve the axial resolution in spherical lens system. But this technique suffers from side-lobes that can cause artefacts. In order to reduce side lobes, we employed spatial filter in a 4_ geometry. A detailed description of these techniques is given in chapter 2. These techniques may add new features to Nano-lithography techniques and bring new applications in Nano-biology and Nanophysics. Chapters 3, 4 and 5 of the theses are dedicated to light-sheet based lithography for the fabrication of micro/Nanostructures. We begin by studying the field distribution at the geometrical focus of a cylindrical lens system. Unlike a spherical lens system, cylindrical lens system has a one-dimensional focusing property that results in a sheet of light. light-sheets are known for their selective plane illumination capabilities. They are widely used in bioimaging and optical microscopy. The intricate details about the field distribution are studied using the vectoral theory for cylindrical lens system. We have conducted experiments to validate the vectoral theory for cylindrical lens. _2 test revealed a good _t between experiment and theoretically obtained values. Like spatial filtering techniques in spherical lens geometry, we have carried out spatial filtering in cylindrical lens geometry to add new functionalists/ features in lithography. It is shown that the introduction of spatial filter at the back aperture of the cylindrical lens has resulted in the generation of multiple light-sheets. Spatial filter structures the incident wave front that is focused by the cylindrical lens thereby resulting in a distinct field distribution at and near the focal plane. The theory behind the generation of multiple light-sheets is discussed in chapter 3. We have demonstrated the generation of multiple light-sheets through computational simulations and experiment. Multiple light-sheets have the capability of illuminating multiple planes of the specimen simultaneously. The experimental results are discussed in chapter 3. Chapter 4 describes the fabrication of periodic micron structures using multiple light sheets. We have used a photoresist mixture which is sensitive to visible light. UV- Vis absorption spectroscopy was used to determine the sensitivity of the photoresist mixture. The photochemistry was studied using a 532 nm continuous laser. We could control the periodicity and the feature size by changing the spatial filter parameters. This technique is hoped to be a single shot fabrication technique for generating high aspect ratio periodic micron structures over a large area. In chapter 5, we have proposed and experimentally demonstrated the generation of periodic Nanostructures using counter propagating coherent light-sheets. The technique involves two opposing cylindrical lenses. When these lenses illuminate the common geometrical focus with a coherent beam of light a constructive interference takes place between two counter propagating light-sheets. The resulting interference structures can be captured on a substrate coated with the photoresist. Selective plane illumination nature of light-sheets is exploited to carry out patterning in the desired plane of a positive photoresist. A mathematical equation is derived that describes the field distribution at and around the common geometrical focus of two opposing cylindrical lens system. Before carrying out the fabrication, we have studied the field distribution in depth through computational simulations. Th periodicity is found to be half the wavelength of illumination light, whereas feature size is found to be approximately one fourth of the wavelength. This clearly indicates that sub-diffraction limited features can be generated using the proposed technique. The remaining part of this chapter describes the fabrication processes for the commercially available photoresist, S1813. This technique can be used for the fabrication of Nano-channels. Interesting applications are in bio-molecular research and protein analysis. Nano-channels are widely used in the detection and analysis of biomolecules such as DNA, proteins and ions. The ability to carve 2D periodic Nanostructures has a great potential for future technology development. Multiple beam interference lithography is most widely used technique for the fabrication of 2D and 3D periodic Nanostructures. In this technique, parameters (like amplitude and polarization angle) of the individual beam and the angle between the beams control the interference pattern. Choosing the right set of parameters for the individual beam is highly challenging. Phase mask lithography can produce desired beams from a single source. But these experiments are highly complex and requires expertise. Processes involved in the fabrication of phase mask are exigent. Chapter 6 describes the fabrication of 2D periodic Nanostructures. We have integrated spatial filtering technique with 2_ illumination to generate of 2D periodic Nanostructures. Theoretical and computational studies show that multiple light-sheets can be generated using an amplitude binary filter. Interference of counter propagating multiple light sheets result in a 2D periodic intensity distribution at the common geometrical focus which can be used for the fabrication of 2D periodic Nanostructures. This technique can be a stepping stone towards the fabrication of nanoelectromechanical systems (NEMS), fabrication of metamaterials and photonic crystals. Finally, we conclude the thesis with a brief description on the contribution of the thesis and the future scope of the research work.

With the progress of microfabrication and nanofabrication technologies, there has been a reawakened interest in the possibility of controlling the propagation of light in various materials periodically structured at a scale comparable to, or slightly smaller than the wavelength. We can now engineer materials with periodic structures to implement a great variety of optical phenomena. These include well known effects, such as dispersing a variety of wavelength to form a spectrum and diffracting light and controlling its propagation directions, to new ones such as prohibiting the propagation of light in certain directions at certain wavelengths and localizing light with defects in some artificially synthesized dielectric materials. Advances in this field have had tremendous impact on modern optical and photonic technologies. This doctoral research was aimed at investigating some of the physics and applications of periodic structures for building blocks of the optical communication and interconnection system. Particular research emphasis was placed on the exploitation of innovative periodic structure-based optical and photonic devices featuring better functionality, higher performance, more compact size, and easier fabrication. Research topics extended from one-dimensional periodic-structure-based wavelength-division-multiplexing (WDM) optical interconnects (beam wavelength selection devices), and liquid crystal beam steerers (beam steering devices), to two-dimensional periodic-structure-based silicon photonic-crystal thermo-optic and electro-optic modulators (beam switching devices). This research was specifically targeted to seek novel and effective solutions to some long-standing technical problems, such as the limited wavelength coverage of coarse WDM devices, small bandwidth of highly dispersed dense WDM devices, low deflection efficiency of high-resolution liquid crystal beam steerers, slow switching speed, large device size, and high power consumption of silicon optical modulators, among others. For each subtopic, research challenges were presented and followed by the proposed solutions with extensive theoretical analysis. The proposals were then verified by experimental implementations. Experimental results were carefully interpreted and the future improvements were also discussed.

碩士
國立中山大學
光電工程學系研究所
97
With the constantly evolving displayer technology, the liquid crystal displayer (LCD) has become widely utilized on the market. As a result, the demand for high-performance LCDs is on the rise. In addition to the color quality and contrast ratio, the brightness of a LCD is also an important issue in LCD applications. Since light source of the LCD depends on the backlight module, it is important to develop efficient a backlight module to improve the brightness of the LCD. The light guide plate (LGP), which makes use of our previously proposed step micro-structure, has two problems. The first is that the thickness limits the dimension of the LGP. The other is that the complex manufacturing process is not suitable for mass-production. Due to these difficulties, we proposed a new design containing periodic trapezoid micro-structures. The periodic micro-structures can be easily fabricated by the ejection-set process. In addition, the dimension of the LGP will not be limited by this new design. In this thesis, we will analyze the performance of our proposed structure and discuss the factors which might affect the output light intensity of the LGP. We made a few dozen prototyping LGPs and measured the output brightness of produced by these periodic micro-structures. The apparent transparent nature of our proposed LGPs is due to the fact that the dimension of the micro-structure is close to the wavelength. Thus the applications of the new LGPs are no longer limited to the LCD backlight modules. It can be also be used for example, as the reading light plate.

博士
國立中正大學
物理學系暨研究所
100
Periodic linear and nonlinear structures have been demonstrated to have unique physical properties due to their singular interaction with electromagnetic waves. These structures allow to have many potential applications, such as creation of a desired photonic bandgap (PBG) materials, i. e., photonic crystal, low loss waveguide and high quality cavity resonator, ultralow threshold laser, nonlinear effect with perfect phase matching, etc. The challenge for researchers is the fabrication of these structures, in a simple manner and an efficient way. Various techniques have been recently studied and demonstrated for this purpose. Among them, holographic lithography (HL) and direct laser writing (DLW) are demonstrated to be very promising, allowing to obtain linear and nonlinear structures, from small to large area, without and with desired defect. Furthermore, these techniques allow to create periodic and quasi-periodic structures at very small length scale, in two dimensions (2D) or three dimensions (3D), which are origine of different applications that cannot be obtained by other techniques. In the framework of this dissertation, we have studied in detail and explored different aspects related to these two techniques to fabricate different kinds of optical functional micro/nano periodic structures, based on polymer materials. Firstly, we investigated a simple and useful method, based on multiple exposure of the two-beam interference pattern, to fabricate different kinds of 2D and 3D periodic linear structures. The experimental results obtained in a suitable fabrication condition, using either SU-8 (negative) or AZ-4620 (positive) photoresist, are in very good agreement with the theoretical predictions. We demonstrated that these structures can be used as templates for creation of photonic bandgap crystals. Indeed, we have used structures obtained by the two-beam interference technique as moulds to grow large-area and uniform vertically aligned 2D periodic ZnO structures by the use of hydro thermal method. These ZnO structure have been also demonstrated to have good superhydrophobicity property. We then studied different parameters that can influence the final fabricated structures; for example, the absorption of material at the exposure light wavelength, the developing effect, the shrinkage of the photoresist, and the energy diffussion, etc. These effects have been demonstrated to be useful for fabricating very special and useful structures, such as microlenses array, nanovein structures, controllable 3D structures, etc. These fabricated structures have been optically characterized and demonstrated be very useful for different applications such as PBG structures. Finally, we demonstrated the fabrication of a 3D polymer quadratic nonlinear (X(2)) grating structure. We have successfully identified the chemical composition and fabrication procedure, which altogether make it possible to realize 3D gratings of a second order nonlinearity in a commonly used polymer. Indeed, by using the one-photon absorption DLW, desired photo-bleached grating patterns were generated in the guest-host disperse-red-1/poly (methylmethacrylate) (DR1/PMMA) active layer. These DR1/PMMA gratings are alternatively assembled with polyvinyl alcohol (PVA), as passive layers, to form an active-passive multilayer structure by using the layer-by-layer process and spin-coating approaches. The corona electric field poling is then applied to obtain a 3D X(2) grating structure. This technique with corresponding fabricated structures are of interest for nonlinear frequency conversion, such as quasi-phase matching second-harmonic generation or multi-color parametric processes.

碩士
中國文化大學
材料科學與製造研究所
91
The objectives of this research were to explore and discuss the influence of particle interactions to colloidal structure, rheological behavior and the resultant particle arrangement in aqueous powder processing. Specific research contents are summaried as follows: 1. Rheological behavior and suspension structure of anatase titanium dioxide (TiO2) nanoparticles dispersed in pure water have been investigated over a range of volumetric solids concentrations (f = 0.05 — 0.12) and shear rates (γ = 101 — 103 s-1). The nanoparticle suspensions generally exhibited a pseudoplastic flow behavior, indicating an existence of particle aggregates in the carrier medium. The suspensions became apparently thixotropic as f was increased above 0.1. Relative viscosity (ηr) of the suspensions followed an exponential form with f , i.e., ηr = 13.47e35.98f . This indicated a pronounced increase in the degree of particle interactions as f increased. Fractal dimension (Df) was estimated from suspension yield-stress (τy) and f dependence, and was determined as Df ~ 1.46 to 1.78 for the nanoparticle suspensions. This suggested that the suspension structure was probably dominated by the diffusion-limited cluster-cluster aggregation (DLCA), due mostly to the strong attractions involved in the interparticle potentials. Maximum solids loading (fm) of the suspensions was determined as fm = 0.146. This relatively low fm value (compared with the random close packing of monosized particles, fm ~ 0.64) partially vindicated the existence of porous, three-dimensional network of interconnected nanoparticles in the carrier liquid. 2. We examined the self-assembled colloidal crystals by using micrometer and submicrometer latex micro spheres of uniform size. The assembled sphere arrays at different sedimentation temperatures and solids concentrations were observed by FE-SEM. (1) For 3μm particle size latex spheres: The packing structure was examined over a range of different temperatures (30~100oC) and volumetric solids concentrations (f = 0.005~0.03). At temperature 100oC and volumetric solids concentration f = 0.02, the assembled colloidal structures were compared. At temperatures between 30~100oC and volumetric solids concentrations f = 0.005~0.01, the resultant colloidal structure appeared rather irregular. At temperatures 30~100oC, the suspension viscosity became apparently increased as f was increased above 0.03, resulted in colloidal structures apparently irregular agglomerate state with faults concentration also increased. (2) For monodispersed particles of different particle sizes (1.03, 0.482 and 0.304 μm) of latex spheres in solution: We examined the assembled structure over a range of different temperature (30~100oC) and volume quantities (1~5ml). Experimental results indicated that the assembled colloidal structures were not much different at this temperature range. We then used a moderate temperature (50oC) for all the subsequent experiments. Colloidal structure with periodic arrangement in micrometer regions (regular area~100 μm2) was obtained. The latex spheres with reduced particle sizes tended to become better periodicity in colloidal structure.

博士
國立中正大學
物理所
98
In this thesis, we focus on the fabrication and research of periodic nano- and micro- optical application structures by self-assembly process. The scales of self-assembly in this thesis were classified as three parts. First, in sub- micro scale, the capillary fore play an important role in the self-assembly process. For example, the spheres in solutions, called colloids, are easily aggregated by capillary force in drying process at room temperature. The spheres always self-assemble into close-packed structures, e.g. face-centered cubic crystals. In our experiments, the colloid SiO2 particles are self-assembled into f.c.c. crystals by capillary force. Such crystals are called “artificial opal”, similar the “opal” in nature can be applied as photonic crystals (PCs). Furthermore, due to the more wide open photonic band gap, the inverse opal is fabricated based on opal templates for more useful applications. In molecular (nano-) scale, the self-assembly can be classified with two types, intra- and inter- molecular self-assembly. In intra- molecular self-assembly, such as protein folding, the structures become stable and regular architectures from random coil polymers. In inter- molecular, such as block copolymers (BCPs) self-assembled with nano- morphologies by phase-separation effect, form a supramolecular from micelle molecules in solution. In micro- scale, the moistures condense on the solution surface of mixing polystyrene and solvent by evaporation-cooling effect which forms to hexagonal porous, called “Breath Figures” (BFs). The advanced applications in microlens and optical diffuser films from BFs will be discussed