Two direct consolidation methods usually used for advanced ceramics have been combined in this project in order to develop a novel fabrication route for traditional ceramics. Specifically the method used is based on the Additive Manufacturing extrusion process using direct writing of high solid loading ceramic pastes and then freeze-casting to solidify the deposited material. This novel fabrication method, for which a patent has been granted, has been christened “Direct Writing Freeze-Casting” (DWFC). Although the DWFC process is the subject of investigation by other researchers for a range of different applications, including the production of medical implants with alumina, the research presented in this thesis focuses on its use in the manufacture of white wares, giftware, and applied arts and crafts in general. This new system will provide designers, potters, artists, craft makers and manufacturers with a flexible and automated way of manufacturing porcelain objects. One of the major challenges to be overcome to exploit the DWFC process is the development of suitable slurry material formulations. Initial trials demonstrated that it is not possible to use conventional clay based porcelain materials with a platelet shaped microstructure which inhibits freeze casting. In this thesis the development and characterisation of non plastic porcelain slurry, based on substitution of kaolin (clay) with a calcined clay material (molochite), which can be processed using this new method is presented. The new non plastic porcelain formulation, which has a high solid load of 75.47% wt., has been subjected to detailed analysis to assess its suitability at each stage of the process; extrusion, freeze-casting (solidification) and firing.

Over the 1980’s, the introduction of Additive Manufacturing (AM) technologies has provided alternative methods for the fabrication of complex three-dimensional (3D) synthetic bone tissue implant scaffolds. However, implants are still unable to provide post surgery feedback. Implants often loosen due to mismatched mechanical properties of implant material and host bone. The aim of this PhD research is to fabricate an integrated strain gauge that is able to monitor implant strain for diagnosis of the bone healing process. The research work presents a method of fabricating electrical resistance strain gauge sensors using rapid and mask-less process by experimental development (design of experiment) using the nScrypt 3Dn-300 micro dispensing direct write (MDDW) system. Silver and carbon electrical resistance strain gauges were fabricated and characterised. Carbon resistive strain gauges with gauge factor values greater than 16 were measured using a proven cantilever bending arrangement. This represented a seven to eight fold increase in sensitivity over commercial gauges that would be glued to the implant materials. The strain sensor fabrication process was specifically developed for directly fabricating resistive strain sensor structures on synthetic bone implant surface (ceramic and titanium) without the use of glue and to provide feedback for medical diagnosis. The reported novel approach employed a biocompatible parylene C as a dielectric layer between the electric conductive titanium and the strain gauge. Work also showed that parylene C could be used as an encapsulation material over strain gauges fabricated on ceramic without modifying the performance of the strain gauge. It was found that the strain gauges fabricated on titanium had a gauge factor of 10.0±0.7 with a near linear response to a maximum of 200 micro strain applied. In addition, the encapsulated ceramic strain gauge produced a gauge factor of 9.8±0.6. Both reported strain gauges had a much greater sensitivity than that of standard commercially available resistive strain gauges.

Microstructures are usually fabricated on the surface of optical sheets to improve the optical characteristics. In this study, a new fabrication process with UV (ultraviolet) laser direct writing method is developed to embed microstructures inside the glass. Then the optical properties of glass such as reflection and refraction indexes can be modified. Single- and multi-layer microstructures are designed and embedded inside glasses to modify the optical characteristics. Both luminance and uniformity can be controlled with the embedded microstructures. Thus, the glass with inside pattern can be used as a light guide plate to increase optical performance. First, an optical software, FRED, is applied to design the microstructure configuration. Then, UV laser direct writing with output power: 2.5~ 2.6 W, repetition rate: 30 kHz, wave length: 355nm and pulse duration: 15ns is used to fabricate the microstructures inside the glass. The effect of pattern dimension such as the pitch, the layer gap, and the number of layer on the optical performance is discussed. Machining capacity of UV laser is ranging from micron to submicrometer; hence various dimensions of dot, line width, and layers can be easily embedded in the glass by one simple process. In addition, the embedded microstructures can be fabricated less damage and contamination. Finally, the optical performance of the glasses with various configurations is measured by using Spectra Colorometer (Photo Research PR650) and compared with the simulated results.

No description available.

<p>In this research, we have studied the interaction between femtosecond laser and dielectric material, especially borosilicate glass, and its applications. Using laser direct writing (LDW), optical fiber sensors and selective metallization of glass surface were explored. For ultrafine selective metallization, supersonic spray deposition system was introduced combining to femtosecond laser direct writing.</p>

Baigiamojo darbo tikslas – sukurti precizinių kampinių skalių formavimo įrenginį. Darbe yra išanalizuoti kampinių skalių formavimo metodai ir jų realizacijos sistemos, išskirti kampinių skalių formavimo neapibrėžties sandai, suformuoti darbo tikslai, užduotys. Yra išanalizuotos ir ištirtos optimalios įrenginio komponentės. Pasiūlyta įrenginio schema. Nustatyti rastrinių skalių originalų formavimo neapibrėžties atsiradimo dėsningumai. Išskirtos trys pagrindinės paklaidų grupės: judesio, temperatūrinės, kalibravimo. Darbe pateikiama tyrimo metodika – tyrimų eiga, tyriami mazgai ir sistemos, rezultatų apdorojimo metodika. Tyrimo rezultatai pateikti grafiškai, apdoroti statistiniais metodais, apibendrinantys rezultatai apkroksimuoti parametrinėmis funkcijomis. Darbą sudaro 9 dalys: įvadas, problemos analizė ir užduoties formulavimas, precizinių suklių tyrimai, kampo matavimo sistemos kalibravimo tikslumo tyrimas, temperatūrinių gradientų ir jų poveikio tyrimas, linijinių poslinkių matavimų tyrimai, kampinių skalių originalų konstrukcijos parinkimas ir pagrindimas, išvados, literatūros sąrašas. Darbo apimtis – 83 p. teksto be priedų, 55 iliustracijų, 35 bibliografinių šaltinių. Atskirai pridedami priedai. / Final work is dedicated for development of device for precision angular glass scales originals forming. Methods of angular scales forming and their realization have been analyzed. Distinguished angular scales forming elements of uncertainty. Work objectives and tasks have been formed. There are analyzed and researched the optimum device composition. Device scheme is proposed. Angular raster scales forming uncertainty occurrence of patterns determined. Identified three main error groups: motion, temperature and calibration. The work presents research methodology – research process, research components and systems, research data processing techniques. The results are presented graphically and processed by statistical methods, summarized results approximated by parametrical functions. Thesis consists of 9 chapters: introduction, problem analysis and formulation of the task, precision spindle research, angle measuring system accuracy research, temperature gradients and their impact research, linear displacement measurement study, angular scales original forming stand design selection and justification, conclusions, references. Thesis consist of: 83 p. text without appendixes, 55 pictures, 35 bibliographical entries. Appendixes included.

The objective of this research is to investigate the use of laser direct writing to micro-pattern low loss passive optical channel waveguide devices using a new hybrid organic/inorganic polymer. Review of literature shows previous methods of optical waveguide device patterning as well as application of other non-polymer materials. System setup and design of the waveguide components are discussed. Results show that laser direct writing of the hybrid polymer produce single mode interconnects with a loss of less 1dB/cm.

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.

La fabrication de surfaces polymères complexes avec des chimies et des topographies contrôlées à l’échelle micro et nanométrique est en pleine expansion en raison de la large gamme d'applications. Une nouvelle méthode prometteuse consiste à utiliser la photopolymérisation radicalaire contrôlée par les nitroxydes (NMP2) qui exploite une alcoxyamine photosensible (AA).Pour démontrer le potentiel de fabrication de surfaces de polymères complexes, un film de polymère a d'abord été formé en irradiant avec une formulation contenant un mélange de monomère acrylique et l’alcoxyamine. Ensuite, le dépôt d'un second monomère acrylique sur ce film durci peut redémarrer une nouvelle réaction de photopolymérisation du fait de la présence d'alcoxyamines à la surface. Les radicaux peuvent être réactivés par exposition aux lampes UV et permettent de commencer un nouveau procédé de polymérisation. Une autre alternative est d'utiliser l’écriture directe par laser pour produire des structures en 2D ou 2.5D de polymère, en déplaçant le faisceau laser sur la surface de l'échantillon.Un soin particulier a été axé sur l'impact de paramètres photoniques et chimiques sur le processus de repolymérisation. Les mécanismes moléculaires qui régissent la repolymérisation pourraient être déduits de cette étude.Certaines applications montrent le potentiel de l'alcoxyamine pour générer des surfaces hydrophiles / hydrophobes ou fluorescentes pour des applications avancées. / The fabrication of complex polymer surfaces with controled chemistry and topography at the micro and nanoscale has drawn a huge attention during the last years due to the wide range of applications. A promising new method consists in using the nitroxide mediated photopolymerization (NMP2). this method exploits a photosensitive alkoxyamine (AA) that creates latent reactive radical species.To demonstrate the potential for fabrication of complex polymer surfaces, a polymer film was first formed by irradiating with a formulation containing a mixture of acrylic monomer and alkoxyamine. Then, depositing a second acrylic monomer over this cured film can reboot a new photopolymerization reaction due to the presence of alkoxyamines at the surface. The radicals can be reactivated by exposure to UV and start a new polymerization process. Another alternative is to use UV-laser direct writing to produce 2D or 2.5D polymer structure by displacing the laser beam at the surface of the sample.A special care was focused on investigating the impact of photonic and chemical parameters on the extend of the repolymerization process. The molecular mechanisms governing the repolymerization could be deduced from this study.Some applications are provided showing the potential of the alkoxyamine for generating hydrophilic/hydrophobic or fluorescent surfaces for advanced applications.

Sub-surface modification using a frequency doubled Ti: Sapphire femtosecond (fs) laser at 1kHz repetition rate, producing 100-fs pulse duration at 400nm, is studied in order to fabricate optical components within non-photosensitised polymethyl methacrylate (PMMA). This thesis explores the feasibility of producing three-dimensional optical devices in bulk polymers and polymer optical fibre (POF) using fs laser direct-writing techniques. For effective and optimal structuring, the laser writing parameters and focusing conditions, such as focusing depth, translation speed, and accumulated fluence are investigated by means of photo-modification thresholds; structural changes in dimensions and morphologies; and the magnitude of the refractive index modulation. The highest refractive index change is 3.2x10^(-3) achieved by using a dry (non-immersion) 0.45-NA objective for a single laser scan. Variations in damage threshold with focusing depths are attributed to a combination of material absorption or surface scattering of light due to contamination or surface imperfections, as well as oxygen diffusion and spherical aberration. Distortion of the laser-induced feature size and shape due to spherical aberrations is controlled and compensated by adjusting the laser power near the damage threshold. Permanent refractive index structures with cross-sectional dimensions of 2μm by 0.9μm and 3μm by 1.4μm are demonstrated at depths of 300μm and 500μm below the surface, resulting in the axial/ lateral ratio of 2.2 and 2.1, respectively. A novel phenomenon relevant to effects of translation speed on the fs laser modification is observed for the first time. As translation speeds reduce from 1.2 to 0.6mm/s, the optical damage threshold power decreases by 6μW, whilst other writing conditions remain constant. However, the damage threshold increases by 74μW with decreasing speeds from 0.6 to 0.35mm/s. This significant increase in threshold power enables inscription of refractive index gratings <5μm below the surface, because irradiation on the surface or near the surface initiates ablation rather than refractive index changes, and this forms a limit for writing useful structures. Compensating for this limit by using appropriate writing parameters highlights the potential of fabricating three-dimensional integrated optical circuits in thin (100μm) polymer substrates. Finally, highly localised fabrication of long period gratings into step-index single mode polymer fibres is demonstrated by removing distortion effects due to the curved surface. The distortion is compensated by sandwiching the fibre with two flat PMMA sheets, between which index-matching oil (n=1.5) is injected. This arrangement enables precise laser micro-structuring with flat interfaces and continuous inner material. The first demonstration of a 250-μm-period fibre grating, resulting in attenuation bands in the visible spectral region at 613, 633, 728, 816, 853, 877 and 900nm, is presented.