In the pursuit of economical and rapid fabrication solutions on the micro and nano scale, polymer replication has proven itself to be a formidable technique, which despite zealous development by the research community, remains full of promise. This thesis explores the potential of elastomers in what is a distinctly multidisciplinary field. The focus is on developing innovative fabrication solutions for planar photonic devices and for nanoscale devices in general. Innovations are derived from treatments of master structures, imprintable substrates and device applications. Major contributions made by this work include fully replicated planar integrated optical devices, nanoscale applications for photolithographic standing wave corrugations (SWC), and a biologically templated, optical fiber based, surface-enhanced Raman scattering (SERS) sensor. The planar devices take the form of dielectric rib waveguides which for the first time, have been integrated with long-period gratings by replication. The heretofore unemployed SWC is used to demonstrate two innovations. The first is a novel demonstration of elastomeric sidewall photolithographic mask, which exploits the capacity of elastomers to cast undercut structures. The second demonstrates that the corrugations themselves in the absence of elastomers, can be employed as shadow masks in a directional flux to produce vertical stacks of straight lines and circles of nanowires and nanoribbons. The thesis then closes by conceptually combining the preceding demonstrations of waveguides and nanostructures. An optical fiber endface is em ployed for the first time as a substrate for patterning by replication, wherein the pattern is a nanostructure derived from a biological template. This replicated nanostructure is used to impart a SERS capability to the optical fiber, demonstrating an ultra-sensitive, integrated photonic device realized at great economy of both time and money, with very real potential for mass fabrication.

Abstract This thesis describes the design, fabrication and operation of a microfluidic device for the screening of biomolecule mixture surface mediated effects. The characterisation of a surface immobilisation strategy that will allow the robust attachment of candidate biomolecules on a substrate for use in cell culture applications. This is carried out in the form of a modified and optimised layer-by-layer surface immobilisation strategy and its subsequent thorough and robust characterisation. This was achieved by compiling and critically analysing large amounts of quartz crystal microbalance with dissipation (QCM-D) data and the model utilised to provide meaningful, physical data as an output. QCM-D data was combined with surface plasmon resonance (SPR) data to validate the assumptions used within the QCM-D model package. Further evidence demonstrating the presence of the multilayer, as described by QCM-D and SPR, is achieved using x-ray photoelectron spectroscopy (XPS). These results show that the multilayer surface is robustly attached to the substrate and consists of a large amount of water whilst being able to immobilise mixtures of four proteins. A custom protocol for fabricating these two layer devices was devised and is presented. Scale limitations have been overcome to provide mixing capabilities for large extracellular matrix molecules to be immobilised on the previously described, microfluidically generated surface immobilisation strategy. The optimisation and characterisation of the mixing within this microfluidic device, affected by the incorporated staggered herring bone mixer is also shown. Using dynamic force spectroscopy (DFS) along with a custom designed force curve data processing and analysis package, the spatial localisation of a mixture of four immobilised biomolecules was determined. The aim of this study was to compare the spatial localization of a mixture of four biomolecules created by; standard cell culture protocols (adsorbed from bulk onto tissue culture polystyrene) and a surface created via microfluidic deposition on top of a previously described surface immobilisation strategy. The design and robust application of this custom analysis package allows the definition of a “Barricade of Specificity” such that interactions between an antibody functionalised AFM tip and a surface composed of a mixture of proteins, to be categorised as either a “true” specific interaction, or a non-specific interaction. The application of this Barricade of Specificity thus allows the spatial localisation of four immobilized biomolecules to be determined with a large degree of accuracy as a result of the large rage of non-specific interactions surveyed and the strict definition of a valid rupture force. The final chapter details the application of the microfluidic platform to enable high throughput screening of the effects of extracellular matrix (ECM) molecules, singly and in combination, with regards to the effect on the expression of cell surface markers on umbilical cord blood (UCB) derived CD34+ cells. Careful selection of candidate ECM molecules, cytokine and oxygen concentration has resulted in little difference in the effect on UCB derived CD34+ cells differentiation state after seven days in culture. The major effect has been the maturation towards lymphocyte and leukocyte precursors. However, of the four ECM molecules tested individually, in binary and in quaternary combinations, osteopontin (Opn) and laminin (Ln) demonstrated differences compared to other surfaces tested. In order to further assess the effect of these protein surfaces on the cell surface marker expression of UCB derived CD34+ cells, further tests are warranted for increased periods of time to enable greater discrimination in marker expression and thus increase our understanding of the fundamental biology of this rare and clinically useful cell source.

The subject of this thesis is the investigation of organic microcavities with implemented unstructured and laterally structured metal layers. The optical properties are studied by means of various spectroscopic techniques and are compared to conventional metal-free devices. It is shown that the large expected absorption caused by the embedded metal is reduced compared to the case of a free-standing metal layer of the same thickness. As a consequence of the interaction of the photonic cavity mode with the metallic structures, two new coupled modes emerge which are called Tamm plasmons. The strength of this coupling and the resulting spectral difference of these modes are defined by the thickness of both the metal layer and the adjacent dielectric layers. These control parameters enable the optimization of the structural design. Accordingly, coherent emission from Tamm plasmons is realized at room temperature. An analytical approach is developed accounting for the experimentally observed polarization splitting of detuned resonances. Next, laterally structured metal layers embedded into organic microcavities are considered. The structuring leads to a confinement of the photonic density of states evident from a clear discretization in energy of the corresponding modes. Applying a photolithographic technique to structure the metal layer into a pattern of regularly placed stripes leads to additional effects due to the resulting periodicity. By exciting this hybrid structure above a certain threshold, periodic arrays of localized cavity modes and metal-based Tamm plasmons are generated. These Bloch-like excited states are capable of phase coupling across the grating. Additionally, surface plasmon polaritons (SPPs) are excited propagating at the interface of the silver and the adjacent dielectric layers. Thanks to the periodicity of the metallic stripes, SPPs are subject to efficient Bragg scattering into the light cone in air. Modes up to order number 30 are detectable as quasi-linear periodic lines in the dispersion pattern. A Fourier analysis reveals an in- or out-of-phase coupling of the modes and a spread of the coherence over macroscopic distances of more than 40 µm. This strategy of embedding metal patterns into an organic microcavity yields a viable route towards electrically contacted organic solid-state lasers. / In dieser Arbeit werden erstmals dünne, unstrukturierte sowie lateral strukturierte metallische Schichten in organische Mikroresonatoren eingebettet und anschließend die optischen Eigenschaften mittels spektroskopischer Verfahren untersucht. Es zeigt sich, dass die erwarteten hohen optischen Verluste durch die Absorption des elektrischen Feldes im Metall deutlich reduziert sind, verglichen mit dem Fall einer freistehenden, nicht eingebetteten Metallschicht gleicher Dicke. Als Folge der Wechselwirkung der photonischen Kavitätsmode mit dem Metall spaltet diese in zwei miteinander gekoppelte Moden auf. Diese neuartigen Moden werden als Tamm-Plasmonen bezeichnet. Die Kopplung sowie die spektrale Differenz beider Moden ist zum einen durch die optischen Eigenschaften und die Dicke der eingebetteten Metallschicht definiert, zum anderen durch die optische Dicke der angrenzenden dielektrischen Schichten. Dadurch ist eine Optimierung des Systems im Hinblick auf Absorption und Emissionswellenlänge der Bauteile möglich, so dass selbst bei Raumtemperatur kohärente Emission eines Tamm-Zustands erzielt werden kann. Eine erarbeitete analytische Rechnung bestätigt und erklärt die experimentell gemessene, polarisationsabhängige Aufspaltung der auftretenden resonanten Moden. Im zweiten Teil der Arbeit sind organische Mikroresonatoren, deren eingebettete Metallschicht in lateraler Richtung auf verschiedene Weisen strukturiert sind, Gegenstand der Untersuchungen. Als Folge dieser Strukturierung kommt es zur lateralen Beschränkung der photonischen Zustandsdichte, was durch eine Diskretisierung der Energiespektren der resultierenden optischen Moden experimentell nachweisbar ist. Werden periodische Metallstreifen mittels Photolithographie erzeugt, so kommt es neben einer weiteren Beeinflussung der Zustandsdichte auch zu Effekten, die durch diese Periodizität bedingt sind. Entsprechend reproduziert sich die Kavitätsmode mehrfach im Impulsraum. Oberflächenplasmonen, die auf der Grenzfläche zwischen dem Metall und den dielektrischen Schichten propagieren, werden auf Grund der Periodizität bis in den experimentell zugänglichen Lichtkegel gestreut. Dabei werden Plasmonenresonanzen bis hin zur 30. Ordnung gemessen. Im letzten Experiment werden derart periodisch strukturierte Metall-Organik-Mikroresonatoren auf ihre Lasertätigkeit hin untersucht. Eine lokal begrenzte optische Anregung mittels eines gepulsten Lasers führt zur Ausbildung verschiedener Bloch-ähnlicher Moden, deren Kohärenz sich lateral bis zu 40 µm ausbreitet. Eine Fourieranalyse zeigt eindeutige und feste Phasenbeziehungen zwischen angrenzenden Maxima der Moden. Zusammenfassend ergeben sich interessante metall-organische Systeme, die minimale Absorption und niedrige Laserschwellen aufweisen und die prinzipielle Eignung zur elektrischen Kontaktierung besitzen.

The ever-increasing need for higher bandwidth and density is one of the motivations for extensive research on planar optoelectronic structures on printed circuit board (PCB) substrates. Among these applications, optical interconnects have received considerable attention in the last decade. Several optical interconnect techniques, such as free space, guided wave, board level and fiber array interconnects, have been introduced for system level applications. In all planar optoelectronic systems, optical waveguides are crucial elements that facilitate signal routing. Low propagation loss, high reliability and manufacturability are among the requirements of polymer optical waveguides and polymer passive devices on PCB substrates for practical applications. Besides fabrication requirements, reliable characterization tools are needed to accurately and nondestructively measure important guiding properties, such as waveguide propagation loss. In three-dimensional (3D) fully embedded board-level optical interconnects, another key challenge is to realize efficient optical coupling between in-plane waveguides and out-of-plane laser/detector devices. Driven by these motivations, the research presented in this thesis focuses on some fundamental studies of optical interconnects for PCB substrates, e.g., developing low-loss optical polymer waveguides with integrated efficient out-of-plane couplers for optical interconnects on printed circuit board substrates, as well as the demonstration of a novel free-space optical interconnect system by using a volume holographic thin film. Firstly, the theoretical and experimental investigations on the limitations of using mercury i-line ultraviolet (UV) proximity photolithography have been carried out, and the metallization techniques for fine copper line formation are explored. Then, a new type of low-loss polymer waveguides (i.e., capped waveguide) is demonstrated by using contact photolithography with considerable performance improvement over the conventional waveguides. To characterize the propagation properties of planar optical waveguides, a reliable, nondestructive, and real-time technique is presented based on accurately imaging the scattered light from the waveguide using a sensitive charge coupled device (CCD) camera that has a built-in integration functionality. To provide surface normal light coupling between waveguides and optoelectronic devices for optical interconnects, a simple method is presented here to integrate 45° total internal reflection micro-mirrors with polymer optical waveguides by an improved tilted beam photolithography (with the aid of de-ionized water) on PCBs. A new technique is developed for a thin layer of metal coating on the micro-mirrors to achieve higher reflection and coupling efficiency (i.e., above 90%). The combination of the capped waveguide technique and the improved tilted UV exposure technique along with a hard reusable metal mask for metal deposition eliminates the usage of the traditional lift-off process, greatly simplifies the process, and reduces fabrication cost without sacrificing the coating quality. For the study of free-space optical interconnects, a simple system is presented by employing a single thin-film polymeric volume holographic element. One 2-spherical-beam hologram is used to link each point light source with the corresponding photodetector. An 8-channel free-space optical interconnect system with high link efficiency is demonstrated by using a single volume holographic element where 8 holograms are recorded.

No description available.

This work presents a new approach of fabricating arrays of electrodes, separated by sub-micrometer gaps allowing the systematic investigation of electric properties of organic semiconductors. The laterally stacked devices are fabricated by using a trench isolation technique for separating different electrical potentials, as it is known for micromachining technologies like Single Crystal Reactive Ion Etching and Metallization (SCREAM). The essential part of this process is the patterning of sub-micrometer trenches onto the silicon substrate in a single lithographic step. Afterwards, the trenches are refilled by SiO2 to allow the precise tuning of the electrode separation gap. The metal electrodes are formed via magnetron sputtering. This technological approach allows us to fabricate device structures with a transport channel length in the range of 100-250 nm by conventional photolithography. In this experiment, three different metals like Au, Co, and Ni were used as the electrode materials, while copper phthalocyanine, being deposited by thermal evaporation in high vacuum, was employed as the organic semiconductor under evaluation. The final aim has been study of spin transport through the organic channel in varied geometry.

The cohesive fracture of thin films is a concern for the reliability of many devices in microelectronics, MEMS, photovoltaics, and other applications. In microelectronic packaging the cohesive fracture toughness has become a concern with new low-k dielectric materials currently being used. To obtain the low-k values needed to meet electrical performance goals, the mechanical strength of the material has decreased. This has resulted in cohesive cracks occurring in the Back End of Line (BEoL) dielectric layers of the microelectronic packages. These cracks lead to electronic failures and occur after thermal loading (due to CTE mismatch of materials) and mechanical loading. To prevent these cohesive cracks, it is necessary to measure the cohesive fracture resistance of these thin films to implement during the design and analysis process. Many of the current tests to measure the cohesive fracture resistance of thin films are based on methods developed for larger scale specimens. These methods can be difficult to apply to thin films due to their size and require mechanical fixturing, physical contact near the crack tip, and complicated stress fields. Therefore, a fixtureless cohesive fracture resistance measurement technique has been developed that utilizes photolithography fabrication processes. This technique uses a superlayer thin film with a high intrinsic stress deposited on top of the desired test material to drive cohesive fracture through the thickness of test material. In addition to developing a technique to measure the fracture resistance of dielectric thin films, the use of carbon nanotube (CNT) forests as off-chip interconnects is investigated as a potential method to mitigate the fracture of these materials. The compressive and tensile modulus of CNT forests is characterized, and it is seen that the modulus is several orders of magnitude less than that of a single straight CNT. The low-modulus CNT forest will help mechanically decouple the chip from the board and reduce stress occurring in the dielectric layers as compared to the current technology of solder ball interconnects and therefore improve reliability. The mechanical performance of these CNT interconnects is investigated by creating a finite-element model of a flip chip electronic package utilizing CNT interconnects and comparing the chip stresses to a traditional solder ball interconnect scenario. Additionally, flip chips are fabricated with CNT forest interconnects, assembled to an FR4 substrate, and subjected to accelerated thermomechanical testing to experimentally investigate their performance.

Microfluidics has seen an explosion in growth in the past few years, providing researchers with new and exciting lab-on-chip platforms with which to perform a wide variety of biological and biochemical experiments. In this work, a volume quantification tool is developed, demonstrating the ability to measure the volume of individual cells at high resolution and while enabling microfluidic sample manipulations. Care is taken to maximise measurement sensitivity, range and accuracy, though novel use of buoyancy and dynamically tunable microchannels. This first demonstration of a microfluidic tunable volume sensor meant volume sensing over a much wider range, enabling the detection of ̴ 1 µm3 E.coli that would otherwise go undetected. Software was written that enables pressure-driven flow control on the scale of individual cells, which is used to great success in (a) sorting cells based on size measurement and (b) monitoring the growth of cells. While there are a number of macroscopic techniques capable of sorting cells, microscopic lab-on-chip equivalents have only recently started to emerge. In this work, a label-free, volume sensor operating at high resolution is used in conjunction with pressure-driven flow control to actively extract particle/cell subpopulations. Next, a microfluidic growth monitoring device is demonstrated, whereby a cell is flowed back and forth through a volume sensor. The integration of sieve valves allows cell media to be quickly exchanged. The combination of dynamic trapping and rapid media exchange is an important technological contribution to the field, one that opens the door to studies focusing on cell volumetric response to drugs and environmental stimuli. This technology was designed and fabricated in-house using soft lithography techniques readily available in most biotechnology labs. The main thesis body contains four scientific articles that detail this work (Chapters 2-5), all published in peer-reviewed scientific journals. These are preceded by an introductory chapter which provides an overview to the theory underlying this work, in particular the non-intuitive physics at the microscale and the Coulter principle.

In this thesis the lateral resolution limits of the Laser Induced Forward Transfer (LIFT) technique are being investigated. LIFT is a laser direct write process with micron and below resolution and is suitable for modifying, repairing and prototyping micro-devices. Single laser pulses with wavelength of 800 nm and duration of 130 fs from a Ti:Sapphire laser system were focused onto a transparent donor substrate coated with thin film to transfer the thin film material in the form of micro-disks through a small air gap onto an acceptor substrate. In this thesis, donor glass substrate coated with 80nm continuous Cr film and also Cr disks array patterned by photolithography or e-beam lithography were used as targets. The ablation threshold and transfer threshold were determined experimentally and compared to results from two-temperature model (TTM) simulations and reasonably agreement was obtained. For the continuous film target, the size of the LIFT disks depend on the laser fluences and the smallest sizes of around 700 nm were obtained near the transfer threshold. For the pre-patterned disks array targets, initially 1.3m Cr disks were fabricated on the donor substrates by photolithography. Small focused, larger defocused and large top-hat laser beams were used to transfer the pre-patterned Cr disks. The morphology of the transferred material and reliability of transfer were studied. It was found that the large top-hat beam gave the most reliable and high quality transfer results, resulting in mostly intact LIFT disks on the acceptor substrate. To push the resolution limit further, 500nm Cr disks fabricated on the donor substrate by e-beam lithography were used. The successful transfer of these 500 nm Cr disks gives a positive indication that LIFT can potentially be extended further to the nano-scale regime (usually defined as having sub-100 nm resolution).

Microfluidics has seen an explosion in growth in the past few years, providing researchers with new and exciting lab-on-chip platforms with which to perform a wide variety of biological and biochemical experiments. In this work, a volume quantification tool is developed, demonstrating the ability to measure the volume of individual cells at high resolution and while enabling microfluidic sample manipulations. Care is taken to maximise measurement sensitivity, range and accuracy, though novel use of buoyancy and dynamically tunable microchannels. This first demonstration of a microfluidic tunable volume sensor meant volume sensing over a much wider range, enabling the detection of ̴ 1 µm3 E.coli that would otherwise go undetected. Software was written that enables pressure-driven flow control on the scale of individual cells, which is used to great success in (a) sorting cells based on size measurement and (b) monitoring the growth of cells. While there are a number of macroscopic techniques capable of sorting cells, microscopic lab-on-chip equivalents have only recently started to emerge. In this work, a label-free, volume sensor operating at high resolution is used in conjunction with pressure-driven flow control to actively extract particle/cell subpopulations. Next, a microfluidic growth monitoring device is demonstrated, whereby a cell is flowed back and forth through a volume sensor. The integration of sieve valves allows cell media to be quickly exchanged. The combination of dynamic trapping and rapid media exchange is an important technological contribution to the field, one that opens the door to studies focusing on cell volumetric response to drugs and environmental stimuli. This technology was designed and fabricated in-house using soft lithography techniques readily available in most biotechnology labs. The main thesis body contains four scientific articles that detail this work (Chapters 2-5), all published in peer-reviewed scientific journals. These are preceded by an introductory chapter which provides an overview to the theory underlying this work, in particular the non-intuitive physics at the microscale and the Coulter principle.