Development of a novel microreactor for improved chemical reaction conversion

Microreactors have been widely studied over the past two decades for different chemical reactions, to develop new analytical capabilities, and to obtain high mixing performance in the reactors. The main objectives of this work are to investigate the effect of different microchannel structures on the fluid properties and mixing behavior in microreactors, and to design, fabricate, and test a novel microreactor for higher conversion in a chemical reaction. The development of this novel microreactor is intended to provide a valuable guideline in achieving enhanced chemical mixing and to make available a solid research base for optimization of the yield of chemical reactions in microchannels. Most of the current microreactors are designed with straight or zigzag microchannels [3]. In this research work, we have developed a novel omega-shaped microreactor, which yields higher conversion through mixing enhancement. It offers the advantages of reducing the mixing distance of the reactant species, stretching and folding the flow, generating vorticities which overcome any uneven distribution of the reactant, and consequently improve conversion efficiency in a typical reaction. Fluid properties of the omega channel reactor have been investigated by means of computational fluid dynamic (CFD) simulation to validate the criteria of the omega channel design. A stochastic Markov chain process has been used to study fluid flow, and to describe the residence time distribution functions for the microreactors considered in this work. Based on theoretical predictions, three kinds of microreactors with straight, zigzag, and omega-shaped microchannels, have been designed and fabricated using optical lithography and dry etching methods. To compare the efficacy of the microreactors, Fischer-Tropsch reactions have been carried out using sol-gel encapsulated ion and cobalt catalysts in the microchannels. The experimental results show that the conversion efficiency for an omega-shaped reactor is 17% greater than that for a conventional straight channel microreactor, and is 12% greater than that for the zigzag-shaped channel microreactor. The data is consistent with the CFD simulation and stochastic modeling results. The novel omega-shaped microreactor offers a better alternative to straight and zigzag channel microreactors and provides a better micro-fluidic system for microscale total analysis applications

Additive Manufacturing of Conducting Polymers: Recent Advances, Challenges and Opportunities

Unformatted postprintConducting polymers (CPs) have been attracting great attention in the development of (bio)electronic devices. Most of current devices are rigid 2D systems and possess uncontrollable geometries and architectures that lead to poor mechanical properties presenting ion/electronic diffusion limitations. The goal of the article is to provide an overview about the additive manufacturing (AM) of conducting polymers, which is of paramount importance for the design of future wearable 3D (bio)electronic devices. Among different 3D printing AM techniques, inkjet, extrusion, electrohydrodynamic and light-based printing have been mainly used. This review article collects examples of 3D printing of conducting polymers such as poly(3,4-ethylene-dioxythiophene) (PEDOT), polypyrrole (PPy) and polyaniline (PANi). It also shows examples of AM of these polymers combined with other polymers and/or conducting fillers such as carbon nanotubes, graphene and silver nanowires. Afterwards, the foremost application of CPs processed by 3D printing techniques in the biomedical and energy fields, i.e., wearable electronics, sensors, soft robotics for human motion, or health monitoring devices, among others, will be discussed.This work was supported by Marie Sklodowska-Curie Research and Innovation Staff Exchanges (RISE) under the grant agreement No 823989 “IONBIKE”. N.A. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 753293, acronym NanoBEAT

On the development of slime mould morphological, intracellular and heterotic computing devices

The use of live biological substrates in the fabrication of unconventional computing (UC) devices is steadily transcending the barriers between science fiction and reality, but efforts in this direction are impeded by ethical considerations, the field’s restrictively broad multidisciplinarity and our incomplete knowledge of fundamental biological processes. As such, very few functional prototypes of biological UC devices have been produced to date. This thesis aims to demonstrate the computational polymorphism and polyfunctionality of a chosen biological substrate — slime mould Physarum polycephalum, an arguably ‘simple’ single-celled organism — and how these properties can be harnessed to create laboratory experimental prototypes of functionally-useful biological UC prototypes. Computing devices utilising live slime mould as their key constituent element can be developed into a) heterotic, or hybrid devices, which are based on electrical recognition of slime mould behaviour via machine-organism interfaces, b) whole-organism-scale morphological processors, whose output is the organism’s morphological adaptation to environmental stimuli (input) and c) intracellular processors wherein data are represented by energetic signalling events mediated by the cytoskeleton, a nano-scale protein network. It is demonstrated that each category of device is capable of implementing logic and furthermore, specific applications for each class may be engineered, such as image processing applications for morphological processors and biosensors in the case of heterotic devices. The results presented are supported by a range of computer modelling experiments using cellular automata and multi-agent modelling. We conclude that P. polycephalum is a polymorphic UC substrate insofar as it can process multimodal sensory input and polyfunctional in its demonstrable ability to undertake a variety of computing problems. Furthermore, our results are highly applicable to the study of other living UC substrates and will inform future work in UC, biosensing, and biomedicine

Strategic design of flow structures for single (bio) particle analysis using droplet microfluidic platform

This thesis is designed to meet the need for knowledge of droplet-based encapsulation strategies by carrying out systematic fundamental studies based on a double-cross configuration. This configuration has been commonly used for co-encapsulation of particles or cells with multiple reagents. Particular attention is also paid to the simplicity and robustness of the channel network for real-world applications. Proposed methods of single-particle encapsulation and integration of multiple functional components are validated by the first two projects. The goal of the first project is to co-encapsulate a 1micrometer magnetic bead (MB) with multiple Quantum Dots (QDs) for further bio-decorating the QD surfaces with different molecules (i.e. single-strand DNA). The goal of the second project is to integrate into a single device a two-step reaction assay for functionalizing the surface of QDs with oligonucleotide strands while QDs are immobilized on MBs. The QD-Oligonucleotide conjugate serves as bio-sensing probes for nucleic acid detection. Additionally, to provide the fundamental knowledge for non-microfluidic-researchers to apply this approach in their single-encapsulation applications, a comprehensive experimental study is designed to span a wide range of operating parameters

FABRICATION OF HIGH FIDELITY, HIGH INDEX 3D PHOTONIC CRYSTALS USING A TEMPLATING APPROACH

In this dissertation, we demonstrate the fabrication of high fidelity 3D photonic crystal through polymer template fabrication, backfilling and template removal to obtain high index inversed inorganic photonic crystals (PCs). Along the line, we study the photoresist chemistry to minimize the shrinkage, backfilling strategies for complete infiltration, and template removal at high and low temperatures to minimize crack-formation. Using multibeam interference lithography (MBIL), we fabricate diamond-like photonic structures from commercially available photoresist, SU-8, epoxy functionalized polyhedral oligomeric silsesquioxane (POSS), and narrowly distributed poly(glycidyl methacrylate)s (PGMA). The 3D structure from PGMA shows the lowest shrinkage in the [111] direction, 18%, compared to those fabricated from the SU-8 (41%) and POSS (48%) materials under the same conditions. To fabricate a photonic crystal with large and complete photonic bandgap, it often requires backfilling of high index inorganic materials into a 3D polymer template. We have studied different backfilling methods to create three different types of high index, inorganic 3D photonic crystals. Using SU-8 structures as templates, we systematically study the electrodeposition technique to create inversed 3D titania crystals. We find that 3D SU-8 template is completely infiltrated with titania sol-gel through a two-stage process: a conformal coating of a thin layer of films occurs at the early electrodeposition stage (\u3c 60 min), followed by bottom-up deposition. After calcination at 500 oC to remove the polymer template, inversed 3D titania crystals are obtained. The optical properties of the 3D photonic crystals characterized at various processing steps matches with the simulated photonic bandgaps (PBGs) and the SEM observation, further supporting the complete filling by the wet chemistry. Since both PGMA and SU-8 decompose at a temperature above 400 oC, leading to the formation of defects and cracks, a highly thermal and mechanical stable template is desired for PC fabrication. We fabricate the 3D POSS structures by MBIL, which can be converted to crack-free silica-like templates over the entire sample area (~5 mm in diameter) by either thermal treatment in Ar at 500 oC or O2 plasma, and the porosity can be conveniently controlled by O2 plasma power and time. Since POSS derivatives are soluble in HF aqueous solutions, we successfully replicate the 3D porous structures into polymers, such as PGMA and poly(dimethyl siloxane) (PDMS). We note that all the fabrication processes are conducted at room temperature, including template fabrication, infiltration and removal. Further, using 3D POSS structures as templates, here, we demonstrate the synthesis of 3D photonic crystals from silicon carbide and boron carbide, respectively, which are thermally stable above 1100 oC in Ar. These non-oxide ceramic photonic crystals are potentially useful as ultrahigh temperature thermal barrier coatings that provide thermal protection for metallic components

New Trends and Applications in Femtosecond Laser Micromachining

This book contains the scientific contributions to the Special Issue entitled: "New Trends and Applications in Femtosecond Laser Micromachining". It covers an array of subjects, from the basics of femtosecond laser micromachining to specific applications in a broad spectra of fields such biology, photonics and medicine

Corrosão de silício em solução de NH4OH como forma de afinamento do canal para dispositivos Junctionless-FET

Orientador: José Alexandre DinizDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A indústria da nanoeletrônica é símbolo da inovação tecnológica e está no cerne dos sistemas de informações modernos. Após décadas de inovações em miniaturização e melhoramentos na configuração tradicional dos dispositivos MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor), novos dispositivos precisam ser estudados. Em meio a esses novos dispositivos, o Transistor de Efeito de Campo Sem Junções (Junctionless-Field-Effect-Transistors, ou JL-FET) se destaca devido ao seu menor custo e complexidade de fabricação, ao mesmo tempo que apresenta melhorias em características centrais ao funcionamento do dispositivo, como a corrente quando ligado e quando desligado, menor atraso de chaveamento e menor subthreshold slope. Para obter dispositivos JL-FET compatíveis com aplicações digitais, o canal do dispositivo deve ser fino o suficiente para que todos os portadores de carga estejam depletados para uma tensão de porta nula, isto ocorre quando a espessura é menor do que 100 nm. Neste trabalho, foi estudada a corrosão anisotrópica de silício em solução de NH4OH co-mo forma de afinar estruturas a níveis nanométricos, com foco na fabricação de JL-FETs. Inicial-mente, os dispositivos fabricados com o processo foram simulados numericamente nos ambientes SILVACO Athena e Atlas, para gerar um modelo que auxiliasse no planejamento dos processos propostos. Todos os testes foram feitos em lâminas de silício-sobre-isolante (silicon-on-insulator, ou SOI), inicialmente com 340 nm de silício monocristalino (100) sobre 400 nm de óxido de silí-cio. Primeiro, a corrosão foi caracterizada através de testes já com os padrões necessários para a fabricação dos dispositivos, visto que a taxa de corrosão da solução de NH4OH varia conforme as estruturas expostas. Dispositivos JL-FET foram fabricados utilizando duas maneiras distintas: em uma delas a corrosão de silício em solução de NH4OH ocorre após a definição da região ativa e implantação de dopantes (31P+ ion, dose de 6.1015 atoms.cm-2, e energia de 50 keV), na outra a corrosão de silício em solução de NH4OH ocorre antes de todos os outros processos. Foram obtidos dispositivos com canais com espessuras de 63 nm para o primeiro processo, afinados a partir de estruturas que inicialmente apresentavam 165 nm de espessura. A dopagem do canal nesses dispositivos foi estimada na ordem de 1017atomos/cm3, determinada a partir do método de caracterização Pseudo-MOS, O comportamento observado foi adequado às caracterís-ticas medidas: o dispositivo apresentou contatos Schottky com barreiras de potencial da ordem de 1 V, condizente com a dopagem obtida, e uma tensão de limiar negativa, que também condiz com a dopagem e espessura medidas. Esses resultados foram confirmados pela realimentação dos da-dos obtidos nos modelos de simulação numérica. Foram fabricadas amostras com tempos de corrosão variando entre 50 s e 80 s, utilizando a nova sequência de processos. Sem o efeito da dopagem, este processo apresenta um maior con-trole sobre as taxas de corrosão, permite que sejam fabricados dispositivos pMOS e de maneira geral aumenta a máxima dopagem possível nos dispositivos. Os valores de tensão de corpo que seriam necessários para depletar todos os portadores de carga do canal, V0, foram estimados (en-tre -27 V e -10 V) a partir das medições Pseudo-MOS para todas as amostras fabricadas com o novo processo. Usando estes dados, um fitting foi obtido que representa V0 e sua variação com o tempo de corrosão. Como o V0 indica o quão próximo um dispositivo está de atingir a região de corte, esta curva será usada para guiar os próximos processos de fabricação. Medições ID x VGS mostraram uma melhoria na razão Ion/Ioff conforme o tempo de corrosão aumenta, de 1 nas amostras sem corrosão até aproximadamente 1.13 na amostra corroída por 80 segundos. A transcondutância também apresentou evolução similar, de valores nulos nas amostras sem corrosão a 3.5 µS na amostra corroída por 80 segundos. Concluindo, a corrosão anisotrópica de silicio em solução de hidróxido de amônio (NH4OH) foi desenvolvida para a fabricação de dispositivos JL-FET com espessura de 63 nm na região de canal, esse processo é necessário pois os dispositivos necessitam dimensões menores do que 100 nm. Este tipo de corrosão é acessível e barato, apresenta uma taxa de corrosão desprezível para o óxido de mascaramento e não causa contaminação com íons ou outros materiais no substrato de silícioAbstract: The industry of nanoeletronics is a symbol of technological innovations and one of the cores of modern-day information systems. After decades of innovations in miniaturizing and improving the traditional inversion-type MOSFET device, its once thought to be unbound potential seems to be arriving at its limits. Among the new devices proposed to sustain the historical increase in computing power and efficiency, the Junctionless-Field-Effect-Transistor (JL-FET) stands out as an alternative that can lower the cost and complexity of fabrication, while at the same time improving key figures such as on and off current, switching delay and subthreshold slope. To achieve JL-FET devices that are compatible with state of the art switching applications, the device channel must be thin enough to enable full charge carrier depletion for null gate volt-age, usually a few dozen nanometers. In this work, the silicon anisotropic etching in NH4OH solution was developed as means to thin structures to the required thicknesses for JL-FET fabrication. Initially, the devices were simulated numerically on SILVACO Atlas and Athena environments, so as to generate a numeri-cal model that could help on planning and implementing the proposed processes. Every test was carried out in 340 nm silicon (100) over 400 nm Silicon Dioxide Silicon-On-Insulator (SOI) wa-fers. Building on previous works that measured minimum etch rate at 2.5 nm/s for the specific structures, JL-FET devices were fabricated by two distinct processes. In the original process the silicon etching in NH4OH solution took place after the active region is already defined and etched and after ion implantation (31P+ ion, dose of 6.10^15 atoms.cm-2 , and energy of 50 keV) was carried out to achieve the channel doping. An updated process was proposes, in which the NH4OH solution silicon etching takes place before any other process, among the advantages of this process flow, the structures can be characterized optically midway through the fabrication and the etching rate becomes even for both pMOS and nMOS devices. Devices with channel thickness of 63 nm were fabricated using the original process, thinned from 165-nm-thick SOI layers. The dopant concentration on the channel region was estimated at approximately 1017 atoms/cm3, obtained by the Pseudo-MOS characterization technique. The device presented Schottky electrical contacts with potential barriers of approximately 1 V and also presented a negative threshold voltage, due to the dopant concentration and thickness of the channel. These results were confirmed by feeding the obtained data back in the numeric simu-lation models. Samples with etching times between 50 s to 80 s were fabricated using the updated process, alongside unetched samples. Without the doping effect, this process presents an improved control over the etching rates, enables the fabrication of pMOS devices and an overall larger dopant concentration on the devices. The voltage necessary to deplete every charge carrier in the channel, V0, were estimated (between -27 V and -10 V) using the Pseudo-MOS measurements for all the samples fabricated using the updated process. Using this data, a fitting was performed to obtain a V0 versus etching time plot. As V0 is closely related to the ability of the transistor to achieve cut-off, this figure will be used to guide future fabrication efforts. ID x VGS measurements also showed increased Ion/Ioff ratios as the etching time increases, from 1 in the unetched sample, to approximately 1.13 in the sample etched for 80 seconds. The transconductance also presented similar evolution, ranging from virtually null on the unetched samples, to approximately 3.5 µS on the sample etched for 80 seconds. In conclusion, we developed the anisotropic etching of silicon in an ammonium hydroxide (NH4OH) solution as a way to allow the fabrication of JL-FET devices, with channel thickness up to 63 nm, because these devices require dimensions thinner than 100 nm. This kind of etching is accessible and cheap, presents almost negligible etching rate to the oxide hardmask used to define the etched regions and does not cause the introduction of contaminating ions and materials on silicon substrateMestradoEletrônica, Microeletrônica e OptoeletrônicaMestre em Engenharia Elétrica88882.329374/2019-01  CAPE

3D Printed Microfluidic Devices

3D printing has revolutionized the microfabrication prototyping workflow over the past few years. With the recent improvements in 3D printing technologies, highly complex microfluidic devices can be fabricated via single-step, rapid, and cost-effective protocols as a promising alternative to the time consuming, costly and sophisticated traditional cleanroom fabrication. Microfluidic devices have enabled a wide range of biochemical and clinical applications, such as cancer screening, micro-physiological system engineering, high-throughput drug testing, and point-of-care diagnostics. Using 3D printing fabrication technologies, alteration of the design features is significantly easier than traditional fabrication, enabling agile iterative design and facilitating rapid prototyping. This can make microfluidic technology more accessible to researchers in various fields and accelerates innovation in the field of microfluidics. Accordingly, this Special Issue seeks to showcase research papers, short communications, and review articles that focus on novel methodological developments in 3D printing and its use for various biochemical and biomedical applications

Micro/Nano-Chip Electrokinetics

Micro/nanofluidic chips have found increasing applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics has become the method of choice in these micro/nano-chips for transporting, manipulating and sensing ions, (bio)molecules, fluids and (bio)particles, etc., due to the high maneuverability, scalability, sensitivity, and integrability. The involved phenomena, which cover electroosmosis, electrophoresis, dielectrophoresis, electrohydrodynamics, electrothermal flow, diffusioosmosis, diffusiophoresis, streaming potential, current, etc., arise from either the inherent or the induced surface charge on the solid-liquid interface under DC and/or AC electric fields. To review the state-of-the-art of micro/nanochip electrokinetics, we welcome, in this Special Issue of Micromachines, all original research or review articles on the fundamentals and applications of the variety of electrokinetic phenomena in both microfluidic and nanofluidic devices

INVESTIGATION OF PYROELECTRIC EFFECT GENERATED BY LITHIUM NIOBATE CRYSTALS INDUCED BY INTEGRATED MICROHEATERS

This thesis work focuses on the investigation of the pyroelectric effect from the –Z surface of Lithium (LiNbO3) crystal using different microheater (µH) designs fabricated on the +Z surface of the crystal. Thermal analyses of the microheater designs were performed both theoretically and experimentally using COMSOL™ Multiphysics and FLIR SC7000 thermocamera respectively. The pyroelectric effect was investigated analysing the current impulses detected using a metallic probe detector connected to an oscilloscope. The temperature variation induced by the microheater causes a spontaneous polarization in the crystal resulting in the formation surface bound charges. The electric field generated between the probe and the crystal surface causes the charge emission that appears as a voltage impulse on the oscilloscope. In an ambient condition, the air layer act as a dielectric thin film layer at few hundreds of microns between the detector probe and crystal surface gap spacing. It was demonstrated and validated that the threshold field strength require to generate the PE was near the dielectric breakdown of air. The pyroelectric emission shows a higher dependency on the rate of thermalization of the microheater and also the electric field generated between the probes to surface gap spacing’s of crystal. The deep characterization of µHs is investigated, in order to demonstrate the reliability and the effectiveness of these microdevices for all those applications where compact and low-power consuming electrical field sources are highly desirable