Dissertations / Theses on the topic 'Conductive ink'

Ce projet vise à développer de nouvelles encres à base de nanofils d’argent et de nanocellulose pour des applications conductrices et transparentes. Les nanocelluloses, nanoparticules issues de la cellulose, sont de deux types : les nanocristaux de cellulose (NCC) et les nanofibrilles de cellulose (NFC) et possèdent des propriétés bien spécifiques. Ce travail a consisté d’une part (i) à utiliser la forme tubulaire et rigide des NCC pour produire des nanotubes d’argents par synthèse chimique, avant leur formulation en encre et d’autre part (ii) à utiliser les propriétés d’enchevêtrement des NFC flexibles pour stabiliser des nanofils d’argent commerciaux, habituellement instables en suspension. Les divers résultats de ce projet ont permis d’aboutir à la formulation brevetée et à la commercialisation d’une encre conductrice à base d’une faible quantité d’argent et de NCC et de deux encres conductrices et transparentes à base de NFC et de nanofils d’argent. Les interactions physico-chimiques et la stabilité colloïdale de ces suspensions hybrides ont été étudiée de manière fondamentale, tout en développant des formulations adaptées à divers procédés d’impression, que ce soit à échelle laboratoire mais aussi industrielle
This project aims at developing new conductive inks based on nanocellulose and silver nanowires for transparent and conductive applications. Nanocellulose are nanoparticles extracted from the cellulose and two kinds currently exist: the cellulose nanocrystals (CNC) and the cellulose nanofibrils (CNF). This project have evaluated on one hand the ability of using tubular rigid CNC as template for producing silver nanorods, prior their formulation into conductive inks. On the other hand, the ability of using flexible and entangled CNF to stabilize commercial silver nanowires, usually unstable in suspension, was investigated. The results of this project lead to the patented formulation and commercialization of one low silver content conductive ink based on silver and CNC and two conductive transparent ink based on CNF and silver nanowires. Physico-chemical interactions and colloidal stability of such hybrid suspension have been scientifically studied meanwhile printing process adapted formulation have been successfully designed and tested at laboratory scale but also industrial scale

Ce travail examine le potentiel du procédé jet d'encre pour fabriquer des composants électroniques à bas coût. Trois axes de recherche sont explorés: (i) supports, (H) encres conductrices, et (iii) procédé. Les propriétés de surface du support comme la rugosité ou l'énergie de surface apparaissent comme des paramètres fondamentaux influençant la conductivité des pistes imprimées. Une pré-couche pour adapter les supports papiers avec l'électronique imprimée a donc été proposée. Des traitements alternatifs de frittage des encres nanométalliques ont été testés et de nouvelles encres conductrices à base de nanotubes de carbone (NTC) et de pOlymères conducteurs ont été formulées. Ces encres à base de NTC ont été étudiées plus en détail par l'analyse de l'influence du procédé d'impression et son impact sur les performances et l'organisation du réseau de NTCs. Cette étude donne de nouvelles possibilités pour l'électronique imprimée et ouvre la route à de nouvelles applications bas coût
This work investigates the inkjet printing process to print conductive patterns for producing low cost electronic components. Three fields were explored: (i) substrates, (ii) conductive inks, and (iii) process. Substrate surface properties su ch as roughness or surface energy have a significant impact on conductivity of printed tracks. An innovative solution to make any paper suitable for printed electronics has then been proposed. Infrared and electrical treatments were tested as potential sintering alternatives of nanometallic inks, and new conductive inks based on carbon nanotubes (CNT) and conductive polymers were formulated. This new CNT-based ink has been studied more in details by analyzing influence of inkjet printing parameters and their impact on the CNT network organization and on the conductivity. This study represents an important step in the field of printing electronics, and also opens windows to new low cost applications such as smart packaging or flexible electronics

Conductive ink from a printer allows for the fabrication of conductive material with tight tolerances without the cost and time of chemical etching. This paper explores the use of AGIC printable conductive ink on a paper substrate as design tool for antennas as well as classroom use in antenna education. The antenna designs satisfy the requirements of a compact Global Navigation Satellite System (GNSS) antenna while showing a competitive performance within the current market. One best design is shown along with three other structures. These antennas consist of a bowtie cross-dipole over a reflective disc with conductive-ink grounded structures. In addition to the GNSS antennas, a linear elliptical dipole over a reflective disc with conductive grounded structures is presented. This elliptical antenna design attempts to find the maximum impedance bandwidth beyond the GNSS band. The inexpensive nature of conductive ink allows for its use in a classroom to demonstrate antenna behavior as part of antenna education. An inexpensive approach to the patch antenna using conductive ink is described and paired with a system made of off-the-shelf parts. The system is capable of measuring the power of the received signal. The received signal measurement is not as accurate as using a anechoic chamber but pattern details are visible. This is used to demonstrate aspects of the Friis transmission equation such as distance, polarization, radiation pattern shape, and loss.

The addition of powered components for active assays into paper-based analytical devices opens new opportunities for medical and environmental analysis in resource-limited applications. Current battery designs within such devices have yet to adopt a ubiquitous circuitry material, necessitating investigation into printed circuitry for scalable platforms. In this study, a microfluidic battery was mated with silver-nanoparticle conductive ink to prototype an all-printed sensing platform. A multi-layer, two-cell device was fabricated, generating 200 μA of direct electrical current at 2.5 V sustained for 16 minutes with a power loss of less than 0.1% through the printed circuitry. Printed circuitry traces exhibited resistivity of 75 to 211 10-5 Ω m. Resistance of the printed traces increased upwards of 200% depending on fold angle and directionality. X-ray diffraction confirmed the presence of face-centered cubic silver after sintering printed traces for 30 minutes at 150°C in air. A conductivity threshold was mapped and an ink concentration of 0.636 μL mm-3 was identified as the lower limit for optimal electrical performance.

A new manufacturing paradigm may lower the cost and environmental impact of existing products, as well as enable completely new products. Large scale, roll-to-roll manufacturing of flexible electronics and other functionality has great potential. However, a commercial breakthrough depends on a lower consumption of materials and energy compared with competing alternatives, and that sufficiently high performance and reliability of the products can be maintained. The substrate constitutes a large part of the product, and therefore its cost and environmental sustainability are important. Electrically conducting thin films are required in many functional devices and applications. In demanding applications, metal films offer the highest conductivity.   In this thesis, paper substrates of various type and construction were characterized, and the characteristics were related to the performance of inkjet-printed metal patterns. Fast absorption of the ink carrier was beneficial for well-defined pattern geometry, as well as high conductivity. Surface roughness with topography variations of sufficiently large amplitude and frequency, was detrimental to the pattern definition and conductivity. Porosity was another important factor, where the characteristic pore size was much more important than the total pore volume. Apparent surface energy was important for non-absorbing substrates, but of limited importance for coatings with a high absorption rate. Applying thin polymer–based coatings on flexible non-porous films to provide a mechanism for ink solvent removal, improved the pattern definition significantly. Inkjet-printing of a ZnO-dispersion on uncoated paper provided a thin spot-coating, allowing conductivity of silver nanoparticle films. Conductive nanoparticle films could not form directly on the uncoated paper.   The resulting performance of printed metal patterns was highly dependent on a well adapted sintering methodology. Several sintering methods were examined in this thesis, including conventional oven sintering, electrical sintering, microwave sintering, chemical sintering and intense pulsed light sintering. Specially designed coated papers with modified chemical and physical properties, were utilized for chemical low-temperature sintering of silver nanoparticle inks. For intense pulsed light sintering and material conversion of patterns, custom equipment was designed and built. Using the equipment, inkjet-printed copper oxide patterns were processed into highly conducting copper patterns. Custom-designed papers with mesoporous coatings and porous precoatings improved the reliablility and performance of the reduction and sintering process.         The thesis aims to clarify how ink-substrate interactions and sintering methodology affect the performance and reliability of inkjet-printed nanoparticle patterns on flexible substrates. This improves the selection, adaptation, design and manufacturing of suitable substrates for inkjet-printed high conductivity patterns, such as circuit boards or RFID antennas.

A stretchable silver ink was screen printed to TPU sheets, then tensile coupons of the TPU, both bare and laminated to cotton, Denim and spandex fabric, were subjected to 1000 cycles of 20% uniaxial strain. In-situ resistance measurements of printed traces were processed to generate datasets of maximum and minimum resistance per cycle. A mechanistic fit model was used to predict the resistance behavior of the ink across TPU/fabric levels. The results show that traces strained on TPU laminated to spandex (polyester) fibers had an average rate of increase in resistance significantly lower than that of traces strained on bare TPU. The variation in predicted resistance was significantly lower in the spandex group than in the TPU group. Trace width was not found to have a significant effect on the resistance behavior across TPU/fabric groups. More testing is required to understand the effect of lamination to high elasticity fabrics on resistance behavior as it relates to the viscoelastic properties of the fibers and weave structure.

The layer-by-layer nature of additive manufacturing (AM) allows for access to the entire build volume of a component during manufacture including the internal structure. Voids are accessible during the build process and allow for components to be embedded and sealed with subsequently printed layers. This process, in conjunction with direct write (DW) of conductive materials, enables the direct manufacture of parts featuring embedded electronics, including interconnects and sensors. The scope of previous works in which DW and AM processes are combined has been limited to single material AM processes. The PolyJet process is assessed for hybridization with DW because of its multi-material capabilities. The PolyJet process is capable of simultaneously depositing different materials, including rigid and elastomeric photopolymers, which enables the design of flexible features such as membranes and joints. In this work, extrusion-based DW is integrated with PolyJet AM technology to explore opportunities for embedding conductive materials on rigid and elastomeric polymer substrates. Experiments are conducted to broaden the understanding of how silver-loaded conductive inks behave on PolyJet material surfaces. Traces of DuPont 5021 conductive ink as small as 750?m wide and 28?m tall are deposited on VeroWhite+ and TangoBlack+ PolyJet material using a Nordson EFD high-precision fluid dispenser. Heated drying at 55°C is found to accelerate material drying with no significant effect on the conductor's geometry or conductivity. Contact angles of the conductive ink on PolyJet substrates are measured and exhibit a hydrophilic interaction, indicating good adhesion. Encapsulation is found to negatively impact conductivity of directly written conductors when compared to traces deposited on the surface. Strain sensing components are designed to demonstrate potential and future applications.
Master of Science

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Dr. Manos Tentzeris; Committee Member: Dr. Gregory Durgin; Committee Member: Dr. Joy Laskar.

Dans ce travail, deux encres fonctionnelles pour l’électronique imprimée ont été étudiées. La première est composée d’un polymère semi-conducteur, le poly(3,4-éthylène dioxythiophène) (PEDOT), qui forme un complexe avec un polyanion isolant, le poly(4-styrène trifluorométhyl (bissulfonylimide)) (PSTFSI). Celui-ci stabilise le PEDOT dans l’eau. La deuxième encre contient un polymère piézoélectrique, le poly(fluorure de vinylidène-co-trifluoroéthylène) (P(VDF­TrFE)), dans des solvants organiques. Les propriétés rhéologiques, capillaires et de mouillage de ces encres doivent être ajustées par formulation pour les rendre imprimables par divers procédés d’impression. Les encres PEDOT ont été formulées pour l’impression jet d’encre, la sérigraphie, le dépôt avec une racle rigide (doctor blade) ou le dépôt de lignes avec une lame souple. Il a été montré qu’aucun additif n’est nécessaire pour modifier les propriétés rhéologiques de ces encres : un simple ajustement de la concentration en polymère leur permet de passer d’un comportement Newtonien à rhéofluidifiant avec des propriétés de gel. En revanche, divers additifs ont été ajoutés pour améliorer les propriétés de mouillage, d’élasticité des encres, et de conductivité des films une fois ceux-ci séchés. Les encres P(VDF­TrFE) ont été formulées pour la sérigraphie. Leur comportement newtonien a été rendu rhéofluidifiant en utilisant soit un agent gélifiant, qui modifie l’agencement du polymère en solution, soit un mélange d’un bon et d’un mauvais solvant du polymère, qui résulte en une micro­émulsion. Une fois les propriétés des films séchés étudiées, les deux types d’encres ont été employées pour créer des capteurs de pression fonctionnels
In this work, two organic functional inks for printed electronic were studied. The first is composed of a semi-conducting polymer, poly(3,4-ethylene dioxythiophene) (PEDOT), in complex with an insulating polyanion, poly(4-styrene trifluoromethyl (bissulfonylimide)) (PSTFSI), which stabilizes PEDOT in water. The second ink contains the piezoelectric polymer poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF­TrFE)) in organic solvents. To be processable using a wide range of deposition processes, the rheological behaviors, wettability and capillary properties of these inks have to be adjusted. For that purpose, both types of inks were formulated. PEDOT inks were formulated for inkjet printing, screen-printing, doctor blading, and for a deposition of lines using a soft blade. No additive is necessary to modify the rheological properties of these inks: by simply tuning the concentration in polymer, their behavior go from Newtonian to shear­thinning with gel properties. Further formulations to improve the wettability, the elasticity of the inks, and the conductivity of dried films were performed. P(VDF­TrFE) inks were formulated for screen-printing using a gelifying agent, which modify the organization of the polymer in solution, or a mixture of a good and a poor solvent, which gives rise to a micro-emulsion. The Newtonian inks thereby become shear-thinning. Once the properties of the dried films were studied, both types of polymeric inks were used to create functional pressure sensors

This thesis presents the implementation of some of the basic concepts of digital logic design in a fun and creative way with the help of paper electronics. This involves circuit building on paper using conductive tape or conductive ink and circuit components as electronics craft materials. Paper electronics toolkit called circuit sticker microcontroller which is deployed by a company named Chibitronics and AT89C51 microcontroller were used for the computational functioning of the circuits built on paper. This can be used to teach the fundamentals of digital logic design to the students in their early stage of studies in an attractive way and can help them them gain a better understanding. This thesis can also be helpful in grabbing the attention of high school students and motivate them towards choosing the engineering discipline for their higher studies.

Dans le cadre de la fabrication de dispositifs pour l’électronique organique à grande échelle, les besoins en matériaux conducteurs stables à l’air libre, de coût réduit et compatibles avec les techniques d’impression sont croissants. Ces matériaux sont destinés à remplacer les couches métalliques déposés par des méthodes telles que la gravure ou l’évaporation sous vide. Les travaux présentés dans cette thèse ont pour objectif la mise au point d’une encre imprimable stable à l’air libre, composée de polyaniline dispersée en phase aqueuse. L’originalité de cette thèse est de décrire l’intégralité de ce processus, depuis la synthèse chimique de la charge, à partir du monomère jusqu’à l’intégration de l’encre conductrice dans une cellule solaire organique sous forme d’électrode imprimée, en passant par la formulation de l’encre. La première partie des travaux consacrés à la synthèse chimique de la charge a permis d’obtenir un matériau nano structuré, de taille et morphologie contrôlée, dispersable en phase aqueuse et conducteur. Cette dispersion a ensuite été formulée pour lui conférer des propriétés compatibles avec l’impression jet d’encre et lever des verrous critiques comme la granulométrie. La phase d’essai d’impression jet d’encre a permis de valider l’étape de formulation et d’optimiser la morphologie des gouttelettes éjectées. Les couches minces imprimées ont permis d’atteindre des résistances surfaciques inférieures à 1000 Ω/□. Finalement l’encre conductrice a pu être imprimée en tant qu’électrode supérieure dans des cellules solaires organiques
Considering large-scale development and fabrication of organic electronic devices, needs for low cost conductive printable materials are growing. These materials are designed to replace thin metallic layers deposited via gravure or thermal evaporation. The objective of the work presented in this report is to obtain a conductive and inkjet printable aqueous stable dispersion of polyaniline. Originality of this PhD work is to describe all the steps from the chemical synthesis of polyaniline starting from the monomer, until the integration of the conductive ink in an organic solar cell as a conductive top electrode, through formulation of the ink to meet inkjet printing requirements. During the first part of work dedicated to chemical synthesis of PANI, we managed to produce a nanostructured and conductive material, with controlled size and morphology, which was dispersed in water. This aqueous dispersion was formulated to meet inkjet printing requirements and break technological locks such as particle size in the PANI dispersion. Formulation step was then validated during printing trials, which allowed optimising shape of ejected droplets. Printed PANI thin layers showed sheet resistance below 1000 Ω/□ after 20 printing passes. Finally, conductive ink was printed as a top electrode in fully solution–processed printed organic solar cell

Identificação de Dispositivos por Radiofrequência, do inglês, Radio Frequency Identification Device (RFID), é uma tecnologia para identificação, rastreamento e gerenciamento de produtos, animais e até mesmo pessoas sem a necessidade de um campo visual. Com o objetivo de alcançar custos menores e a utilização de processos de fabricação menos agressivo ao meio ambiente, tornou-se importante o desenvolvimento de novos tipos de etiquetas (tags). Em vista disso, a fabricação de antenas impressas compactas usando tinta condutiva, representa uma boa opção. O objetivo dessa pesquisa é o projeto e fabricação de antenas impressas sobre substratos flexíveis utilizando tinta condutiva composta de nanopartículas de prata. O desenvolvimento deste tipo de etiquetas é justificado principalmente pelos seguintes motivos. Primeiro, o processo reduz o uso de agentes químicos comumente empregados na fabricação convencional, levando a uma significativa redução no impacto ambiental. Segundo, a fabricação utilizando substratos como, por exemplo, papel ou polímero, reduz substancialmente o custo final da etiqueta. Estudos teóricos e práticos, juntamente com simulações eletromagnéticas foram realizados. Dois processos de prototipagem da etiqueta foram executados: um utilizando uma impressora jato de tinta que funciona propelindo gotas de tinta sobre o substrato e o outro utilizando serigrafia ou silkscreen printing que é muito prático para imprimir formas geométricas através de uma tela de fios trançados. Esses métodos de impressão permitiram a produção rápida da antena sem a necessidade de máscaras de fotolitografia, como é amplamente utilizado na indústria eletrônica. Quatro protótipos foram produzidos e medidas foram realizadas para verificar a viabilidade da utilização dessas etiquetas impressas em relação à sua operação, a confiabilidade das informações armazenadas e a troca de dados com o leitor RFID via interface aérea. Os resultados práticos foram comparados com os obtidos de etiquetas comerciais, onde foi possível verificar que a antena fabricada com tinta condutiva é capaz de capturar e radiar ondas eletromagnéticas de forma eficiente, resultando em uma troca de dados confiáveis através da interface aérea.
Radio Frequency Identification Device (RFID), it is a technology using electromagnetic waves for identifying, tracking and management of products, animals and even people without requiring a visual field. Aiming at achieving low costs and using less aggressive manufacturing processes to the environment, it has become important to develop new types of RFID tags. In view of that, manufacturing compact printed antennas using conductive ink represents a good option. The goal of this research is the design of printed antennas on flexible substrates using silver nanoparticles ink. The developing of this type of tags is justified mainly by the following reasons. First, the process reduces the use of chemical agents commonly employed in conventional manufacturing leading to a significant reduction of the environmental impact. Second, the fabrication using substrates such as paper and polymer foils, substantially reduces the final cost of the tags. Theoretical and practical studies along with electromagnetic simulations were conducted. Two process of RFID prototyping were performed: one using an inkjet printer that operates by propelling particles of conductive ink onto the substrate and another using silkscreen printing that is a very practical method to print geometric forms through a twisted wires screen. These technologies allowed fast production of the antenna without requiring photolithographic masks, as it is widely used in the electronics industry. Four prototypes were produced and measurements were taken to verify the feasibility of using RFID tags printed with conductive ink regarding to its operation, reliability of the stored information and the exchange of data with the RFID reader via air interface. Practical results were compared with those obtained of the commercial tags. It was possible to verify that the antenna manufactured with conductive ink was able to capture and radiate efficiently electromagnetic waves, resulting in reliable exchange of data with the reader through the air interface

Ink-jet printing (IJP) using conductive inks, has gained the attention of scientistsand researchers during the past decades. Solar Cells (SCs), Radio FrequencyIdentication (RFID), E-papers and antennas are only some of the applicationsfor which IJP is being applied. IJP facilitates printing complex antenna structureswith a good resolution. The use of the IJP process is compatible with devicefabrication on unusual substrates such as paper, polymer lms (Polyethylenenaphthalate (PEN), Polyethylene terephthalate (PET), Polyimide (PI)), textiles,etc at low temperature. The aim of this study is to design and fabricate antennason paper substrates capable of operating at 2.4 GHz via printing technique.Simulation and experimental studies have been presented for microstrip patchantenna and dipole antenna using Itoh's balun.

Polymers are thermal insulators by they own nature; therefore they are not generally used in the field of heat management. In this field usually metals have a dominant role due to their outstanding heat conduction. However, it could be very interesting the replacement of the commonly used metals with a polymeric based material due to several advantages polymers can provide (weight reduction, galvanic coupling avoidance, chemical resistance, easier and cheaper forming). Due to their intrinsic low values of thermal conductivity however polymers needs to be modified. The easiest way to improve thermal conductivity of polymers generally involves their mixing with highly thermally conductive fillers. This strategy however results in some issues and difficulties which are not easily overcome. First of all the thermal conduction of the filler used has to be taken into account since it is responsible for the thermal enhancement of the polymer matrix. Recently, a lot of attention has focused on carbon based fillers such as carbon fibers, carbon nanotubes, graphite and graphene due to their tremendous intrinsic specific thermal conductivity. The use of these fillers could in fact highly reduce the amount required to achieve a thermal conduction improvement. The reason of that is mostly related to their high aspect ratio, low density, micro-nanometric dimension and high dispersion and distribution degree achievable while mixed in polymers. All these peculiarities result in a high number of continuous thermally conductive paths inside the polymer insulating matrix and therefore to its better thermal performance. Despite these advantages, some drawbacks are present. Among them the continuity of the structure acts in general as the main driving force to the heat conduction improvement, since if the continuity is not guarantee the phonon damping matrix rules on the overall thermal conductivity. Another important factor is related to contact resistance between the filler particles. In order to reduce the contact resistance some strategies could be developed to limit the number of contacts required to cross the material, and among them the increase of the lateral dimension of the filler is one of the main ones. Also the preferential orientation of the filler has a positive effect relatively to the contacts resistance since it decreases the amount of contacts required to cross the material, improving the overall heat conduction efficiency. Relatively to the contacts in addition some effect is also related to their quality which can be developed and studied to improve the efficiency. During this work it was attempted a progressive improvement of the thermal transport of polymeric graphene/graphite based nanocomposites solving the above mentioned issues. A dispersion and distribution approach was done and the most common techniques investigated and progressively improved for different graphene and graphite fillers. Once the best dispersion technique was identified, a progressive refinement of the filler was done: fillers with high lateral dimensions and small packing densities were chosen and materials with higher filler loading prepared. Additional improvement was obtained after a purification of the fillers at high temperature to anneal defects, remove impurities and promote graphitization. Percolation issues were solved creating 3D structures accordingly to two strategies: wool cotton preform infiltration and in particular graphene aerogel creation. Relatively to the first case wool cotton was infiltrated with graphene oxide and a thermal annealing performed. In the second case both isotropic and anisotropic graphene aerogels were created to obtain a 3D self-standing continuous structure. After the polymeric infiltration it was discovered that the aerogel technique allows high thermal conductivity improvement at small filler loadings, minimizing the amount of filler to be inserted, dispersed, and distributed to achieve the desired result.

In organic Bulk Hetero Junction (BHJ) and hybrid/perovskite solar cells, the most employed material used as transparent electrode for the charges collection is transparent conductive oxide (TCO) such as indium doped tin oxide (ITO) or fluorine doped tin oxide (FTO). Beside the high transparency and conductivity (80% on glass substrates and 15 Ω/□, respectively) of ITO and FTO, there are many critical issues: i) limited indium sources, ii) high cost due to the deposition techniques (sputtering, evaporation, pulsed laser deposition and electroplating etc.), iii) high temperature processing and iv) high mechanical brittleness. For these reasons, it is necessary to investigate new materials. The discovery of graphene, in 2004, that led Novoselov and Geim to win the Nobel Prize has opened up new areas of scientific research. In particular, its surprising physical, optical, mechanical and electrical properties have made the graphene one of the most promising material in the modern electronic applications and in particular in the 3rd generation solar cells technology that can be produced cheaply and very fast from solution with printing processes both on plastic and rigid substrates. This work is mainly focused on the use of graphene as a replacement of the conventional transparent conductive oxides. In particular, most of the problems (wettability, annealing temperature etc.) for fabricate solar cells on graphene electrodes were solved. A simple way to decrease the sheet resistance of graphene electrode, by the addition of a metal grid, is presented as well. With the aim to realize high efficiency solar cells, both BHJ with low band gap polymers as active layer and perovskite-based solar cells have been investigated. Firstly, the effects of two different materials (Ni and MoO3), used as p-dopant on bare graphene, were studied and the thickness was optimized in order to reduce the graphene sheet resistance and increase the solar cells performances. Moreover, was investigated the feasibility to realize graphene-based solar cells starting to optimize the deposition of the organic active layer material (blend of P3HT: PC [60] BM or PTB7: PC [70] BM) in terms of annealing temperature and thickness. iv Furthermore, in order to increase the solar cells efficiency, organic-inorganic perovskite ( CH3NH3PbI3-xClx ) material was studied as active layer. As first step, the growth of perovskite active layer was optimized in terms of annealing temperature, photoluminescence and morphology both for direct and inverted architectures. Then, using a planar direct structure, efforts were made to solve the issues related to the realization of perovskite solar cells on graphene electrode. While, in the direct structure, Titania ordered photonics nanostructures were introduced as electron transporting layer (ETL) to increase the light absorbed by the perovskite active layer and the photo-generated current in the solar cells. With the view to replace the conventional transparent conductive electrode, conductive polymers were also investigated. The most promising organic material is PEDOT: PSS, which is a semitransparent and conductive polymer. However, the pristine PEDOT: PSS film, deposited from aqueous solution, has a lower conductivity than the conventional transparent conductive oxide. For this reason, many strategies have been employed to improve the conductivity of this material to obtain a low cost, low temperature and TCO-free perovskite planar heterojunction solar cells on flexible substrate. In particular, it is demonstrated that the highly conductive polymeric material shows potential as a practical replacement for expensive and brittle ITO/PET. Moreover, in the bending test, the ITO-free perovskite solar cells with PEDOT anodes on flexible substrate manifested superior mechanical robustness compared with ITO-based cells, showing the high flexibility of perovskite layer.

This thesis investigates the nano - electrical properties of a metal oxide semiconductor for photovoltaic applications. Three p-Cu2O/n-TiO2 and one TiO2 (bare) samples were investigated during the thesis. The main difference between the three p-Cu2O/n-TiO2 nanowires samples is the thickness of the absorber layer, the cuprous oxide. Amplitude Modulation Kelvin Probe Force Microscopy (AM-KPFM) and Intermodulation Electrostatic Force microscopy (ImEFM) have been employed to map nanoscale surface potential of Cu2O/TiO2 and TiO2 (bare) under ambient condition and under nitrogen atmosphere. The four samples were tested in dark, light condition and the best results were obtained in the case of ALD208 where the thickness of the absorber layer it was the smallest among the set of the samples. The conductive atomic force microscopy it was employed to obtain the current distribution on the surface of the sample and the best result were obtained in the case of ALD208. The scanning electron microscopy showed a sample with a uniform topography where the average diameter of the nanowires was 84 nm in the case of TiO2 (bare) and 118 nm in the case of Cu2O/TiO2. The Micro Raman spectroscopy confirmed the presence of the dominant peaks of titania (as rutile) at 240, 430 and 630 cm-1 and the presence of cuprous oxide 218 and 148 cm-1. The results demonstrate that the use of p-Cu2O/n-TiO2 could make possible to construct a high performance solar cell, which could revolutionise the field of clean energy.

Nowadays the development of new technologies requires materials with unconventional combination of properties. Polymers are classified as electrical and thermal insulating materials, which limits their use for several important technological applications. However, conductive polymers could be used in order to overcame drawbacks in the use of metals, metal alloys and ceramic materials as conductive media. Thermal conductive polymers could be profitably exploited in heat management applications (e.g. heat sink, heat exchangers), while electrical conductive polymers could be used in different fields depending on their electrical conductive values. To enhance the conductive properties of polymers, several approaches has been reported in literature. However, the most established way to achieve this goal consists in the development of suitable composite materials by means of the incorporation of conductive fillers within the polymeric matrix. The choice of the conductive filler is a crucial point in the development of the final material. Due to their extremely high thermal and electrical conductivity, coupled with the low density, the nano-metric scale and the outstanding mechanical properties, carbon-based nanomaterials are the most promising fillers suitable for processing conductive polymers. Since graphene nanoplatelets (GNPs) are considered young materials with potentials not yet fully exploited, multiwall carbon nanotubes (MWCNTs) are nowadays the most established materials used as conductive filler. In this thesis work thermally and electrically conductive polymer composites, filled with carbon-based nanomaterials were investigated. In the first part of the experimental work, particular attention was devoted to the development of GNPs-based thermally conductive polymers. By properly selecting several polymeric matrices and comparing several available processing techniques it was possible to outline a guideline in the use of GNPs as thermally conductive fillers. A strong filler characterization reveals that, in spite to the amount of defects and to the filler purity, the main GNPs properties able to enhance the thermal conductivity of polymers is the lateral dimension. With the aim of developing metal-free circuits integrated in nanocomposite, a laser printing process was successfully exploited in order to obtain electrical conductive paths on the surface of a polymeric materials containing MWCNTs. Starting from the literature knowhow and new experimental results, a complete comprehension of the parameters that affect the laser printing process was achieved by applying a statistical approach. By analysing the experimental outcomes with a statistical approach, it was possible to focus the attention on the main laser parameters that govern the process, thus obtaining multifunctional and multidirectional conductive materials with surface electrical resistance per unit length (inside the tracks) lower than 1 kΩ/cm at 0.5 wt.% of MWCNTs loading content. Finally, by combining outcomes obtained as described above, hybrid carbon-based nanocomposites were developed, with the purpose of enhancing contemporaneously thermal and electrical conductivity. Hybrid materials, obtained starting from a commercial masterbatch containing MWCNTs, demonstrated the possibility to partially replace the high amounts of carbon nanotubes with low cost carbon based materials without worsening the good conductive properties. Not only conductive properties were investigated, but all the studied materials were also characterized by means of mechanical and thermal stability tests, thus demonstrating the possibility of adopting carbon-based polymer nanocomposites as multifunctional materials.

Volume conduction can be defined as the transmission of electric potential and magnetic field generated by a primary current source of brain activation in the surrounding medium, i.e., the human head. Volume conduction simulations are based on sophisticated models whose construction represents a current challenge within the neuroscientific community. Volume conduction models are used in various applications such as electroencephalography (EEG) or magnetoencephalography (MEG) source reconstruction, or in the optimization of the electrode placement in a transcranial electrical stimulation session. Clinical applications based on volume conduction models are, for example, the localization of the epileptogenic zone, i.e., the brain area responsible for the generation of seizures, in the presurgical assessment of focal drug-resistant epilepsy patients, and the antidepressant effects given by transcranial electrical stimulation. Increasing the accuracy of volume conduction simulations is therefore crucial. To the best of our knowledge, the accuracy of volume conduction models have never been validated directly with actual measurements in human patients. The main goal of this thesis is to describe a first attempt to validate volume conduction modeling using electric stimulation stereo-encephalografic (sEEG) data. This work therefore is focused on the research, investigation and test of tools and methods which can be used to describe the accuracy of volume conduction models used in both clinical and basic research. Given a dataset of one pharmaco-resistant epilepsy patient, composed by the anatomical T1 weighted magnetic resonance image (MRI), the electrophysiological signal recorded during electric brain stimulation sessions with sEEG technique and sEEG contact positions extracted by post-implantation CT image, the analysis conducted in this work can be split into three main steps. First, we built volume conduction head models and we simulated the electric potentials during the electric brain stimulations. In this step, we solved the so-called (s)EEG forward problem by means of the finite element method in its classical formulation, and we considered three different conductivity profile to assign to the computational domain, individually extracted by the T1-w MRI. Moreover we computed the solution in meshes with two different resolution, i.e., 1 mm and 2 mm, with three different ways to model the source term, i.e., the partial integration approach, the subtraction approach and Venant’s approach. Second, we extracted the responses to the electric brain stimulations from the actual sEEG measurements. Particular emphasis in this step was given to the optimal referencing systems of sEEG electrodes. Third, we compared the simulated and measured potentials for each of the three volume conduction head models, both in a single shaft and global comparison. The comparison results in overall high relative differences, with only slight modulations given by the distance from the stimulation site, the underlying volume conduction head model used and the compartment where the dipolar source is located. Simulation results show that the computation of sEEG forward problem solution is feasible with the same scheme adopted for scalp EEG in the duneuro software (http:// duneuro.org/), and it is stable for different mesh resolutions and source models also for intracranial electrodes, i.e., for electrodes close to the source positions. From this first validation attempt, we can conclude that the distance contact-source modulates the relative error between measured and simulated potential; for the contacts in the white matter compartment we observed the most accurate results, and the results relative to the three and four compartment results were more accurate than the ones relative to the five compartment results. While we achieved topographical errors within 10% for most of the shafts, the amplitude of simulated and measured potentials notably differs.

The central topic of this thesis was the design and development of a bi-functional thermoplastic polyurethane (TPU) composite, which is halogen-free bio-based flame retardant (UL94-V0) with an electrical resistivity ≤ 1000 Ω.cm and a filler load that does not exceed 25 wt.%. In order to reach this goal, the experimental activities were divided into the following tasks: (a) materials pre-selection, (b) design of experiment (DOE), (c) materials compounding, (d) specimens preparation (injection moulding), and (e) materials characterization (electrical resistivity tests, flammability tests, and microstructure analysis). In other words, the main tasks were identifying the ingredients (in a first stage) and defining the optimal proportions of additives (in a second stage) capable of simultaneously conferring to the polymer of interest the most desirable values of flame retardancy (as high as possible) and electrical resistivity (as low as possible); followed by the material preparation (third stage) and the material characterization (forth stage). The materials (flame retardants and electrically conductive additives) used in the development of this novel formulation were pre-selected mainly based on bibliographical studies. Then, the experimental activities and the analysis of the test results allowed to identify positive and negative effects among the components of the formulation such as synergistic effects among flame retardants on the improvement of the fire resistant performance. The obtained final formulation accomplished the desired target values of flame retardancy (V0 compliant) and electrical resistivity (≤1000 Ω.cm). It was compared to commercial products from the companies RTP, BASF and LUBRIZOL, which are used in the same field of application. The material developed during this work showed a lower electrical resistivity than these commercially available products while being bio-based and V0 (UL-94 test) at the same time. In addition, an innovative online acquisition apparatus for monitoring the surface growth of flame retardant protective layers was designed and developed during this thesis, which provided a deep insight of the dynamic behaviour of a phosphorous-based flame retarded material. The measurement of the surface protective layer growth rate provided a better understanding of the behaviour of the flame retardant systems, correlating the speed of the chemical reaction with the performances of the material.

Due to the worldwide aging population, methods have been sought to improve the efficiency of health care services. It is envisaged that remote monitoring of patients would form part of the solution. Monitoring of patients would be via the use of functionalised undergarments with the required technology embedded within. There have been significant advances in flexible electronics but metal wires are still required for electrical interconnects which compromise the comfort that the garment offers when in contact with skin. Electrically conductive polymers are considered as viable replacements for these metal wires. Electrically conductive polymers can have high electrical conductivities but they can be brittle due to their inherent stiffness. From studies reported in this thesis, various routes to the synthesis of PEDOT, which would lend itself to function in crease and wash resistant conductive inks, were investigated. The task was highly challenging due to the confliction between high conductivity and structural rigidity of typical conductive molecules. A series of monomers, described within, were designed, synthesised and characterised. These monomers provide a foundation for further syntheses to the subsequent novel electrically conductive polymers. In order to assess potential challenges in the formulation of crease and wash resistant conductive inks based on conductive polymers, systems containing PEDOT:PSS were designed, prepared and characterised. It was found that the use of just PEDOT:PSS as the coating for cotton fabric provided an electrically conductive coating which was susceptible to degradation during creasing and washing. To overcome this challenge, a composite of a synthesised latex and PEDOT:PSS was devised which provided an electrically conductive coated cotton fabric with an electrically insulating surface. The electrical resistance could still be measured by incorporating electrodes prior to the application of the final latex layer. Encouragingly, this composite provided a formulation having very low electrical resistances pre- and post-wash.

A wearable body temperature sensor would allow for early detection of fever or infection, as well as frequent and accurate hassle-free recording. This thesis explores the design of a body-temperature-sensing device inkjet-printed on a flexible substrate. All structures were first modeled by first-principles, theoretical calculations, and then simulated in HFSS. A variety of planar square inductor geometries were studied before selecting an optimal design. The designs were fabricated using multiple techniques and compared to the simulation results. It was determined that inductance must be carefully measured and documented to ensure good functionality. The same is true for parallel-plate and interdigitated capacitors. While inductance remains relatively constant with temperature, the capacitance of the device with a temperature-sensitive dielectric layer will result in a shift in the resonant frequency as environmental or ambient temperature changes. This resonant frequency can be wirelessly detected, with no battery required for the sensing device, from which the temperature can be deduced. From this work, the optimized version of the design comprises of conductive silver in with a temperature-sensitive graphene oxide layer, intended for inkjet-printing on flexible polyimide substrates. Graphene oxide demonstrates a high dielectric permittivity with good sensing capabilities and high accuracy. This work pushes the state-of-the-art in applying these novel materials and techniques to enable flexible body temperature sensors for future biomedical applications.

Cette thèse explore le domaine émergent de la plastronique 3D, qui fusionne l’électronique et la plasturgie pour intégrer des circuits électroniques sur des substrats 3D en polymère. Le travail se concentre sur le développement d’encres conductrices pour le procédé In-Mold Electronics (IME), une technique prometteuse pour la production en grand volume de dispositifs plastroniques, en particulier pour les interfaces homme-machine (IHM). Le processus IME comprend plusieurs étapes : l’impression de pistes conductrices sur un film mince de polycarbonate à l’aide d’encre conductrice, le transfert des composants électroniques sur le film et leur connexion au circuit par collage, le thermoformage du film en 3D et le surmoulage 3D par injection de thermoplastique. Après une revue de la littérature sur la plastronique et l’IME, la thèse propose l’étude de différentes formulations d’encres conductrices, en se concentrant sur celles composées d’une matrice polymérique organique contenant des charges d’argent micrométriques. Une méthodologie a été mise en place pour caractériser les encres à chaque étape du processus, en termes de résistivité électrique, d’adhésion, d’étirement et de cisaillement sous contraintes lors des étapes d’impression, de thermoformage et de surmoulage. Le polycarbonate a été utilisé comme matériau de référence pour le film et la matière de surmoulage. Plusieurs encres conductrices ont été élaborées à partir de matériaux organiques issus de la pétrochimie ou de matériaux biosourcés. À partir de matériaux pétrosourcés, nous avons obtenu des encres peu résistives (26 µΩ.cm) et avec une grande capacité de déformation par thermoformage. À partir de matériaux biosourcés, de nouvelles matrices organiques ont été formulées pour obtenir des encres plus responsables. Les encres -bio- se distinguent par leur respect de l’environnement grâce à un liant biodégradable, un solvant vert biosourcé et l’argent recyclable. Les performances atteignent une faible résistivité de 20 µΩ.cm et avec une grande capacité de déformation par thermoformage. Une encre -bio- a été surmoulée avec du polycarbonate, et un démonstrateur IME a été réalisé. Cependant, certaines difficultés persistent et limitent le potentiel d’application de ces formulations. Parmi elles, des cas critiques de délamination et de rupture des pistes conductrices lors du thermoformage. Également, de possible délavage des encres et le détachement des composants électroniques lors de l’étape d’injection peuvent survenir. Ces limitations sont liées aux contraintes géométriques engendrées par le 3D et ont été étudiées. Cependant, par contrainte de temps, toutes les encres n’ont pas pu être testées jusqu’à la réalisation d’un démonstrateur
This thesis explores the emerging field of 3D plastronics, which merges electronics and plastics engineering to integrate electronic circuits on 3D polymer substrates. The work focuses on the development of conductive inks for the In-Mold Electronics (IME) process, a promising technique for the high-volume production of plastronic devices, particularly for human-machine interfaces (HMIs). The IME process involves several steps: printing conductive tracks on a thin polycarbonate film using conductive ink, transferring the electronic components onto the film and connecting them to the circuit by bonding, thermoforming the film in 3D, and 3D overmolding by injection of thermoplastic. After a literature review on plastronics and IME, the thesis proposes the study of different formulations of conductive inks, focusing on those composed of an organic polymer matrix containing micrometric silver fillers. A methodology was set up to characterize the inks at each stage of the process, in terms of electrical resistivity, adhesion, stretching and shear under stress during the printing, thermoforming and overmolding stages. Polycarbonate was used as a reference material for the film and the overmolding material. Several conductive inks were developed from organic materials derived from petrochemicals or bio-based materials. From petro-based materials, we obtained low-resistivity inks (26 µΩ.cm) and with a high deformation capacity by thermoforming. From bio-based materials, new organic matrices were formulated to obtain more responsible inks. The -bio- inks are distinguished by their respect for the environment thanks to a biodegradable binder, a bio-based green solvent and recyclable silver. The performances reach a low resistivity of 20 µΩ.cm and with a high deformation capacity by thermoforming. A -bio- ink was overmolded with polycarbonate, and an IME demonstrator was produced. However, some difficulties persist and limit the application potential of these formulations. Among them, critical cases of delamination and rupture of the conductive tracks during thermoforming. Also, possible washing out of the inks and the detachment of the electronic components during the injection step can occur. These limitations are linked to the geometric constraints generated by 3D and have been studied. However, due to time constraints, not all the inks could be tested until the production of a demonstrator

In comparison to weaving or other techniques that are employed to embed conductive tracks in textile fabric structure, the obvious advantages of printing the desired conductive pattern are the simplicity of the process and the suitability for low volume production runs as well as high volume production runs. However, the generally inferior durability and poorer electrical performance of conductive inks that have been printed onto a textile fabric give rise to challenges. In this study, electrically conductive grades of carbon black pigment were used to formulate screen printing inks for use on textiles. On an equal weight basis, electrically conductive grades impart higher electrical conductivity compared to the printing ink grades of carbon black pigment. However, the conductive grades of carbon black are difficult to disperse and stabilise in aqueous media. Therefore in this study, a procedure was devised initially to prepare stable, waterborne dispersions of a number of highly conductive grades of carbon black pigment. The stability of pigment dispersions was characterised by conducting rheological, particle size and accelerated gravitational sedimentation analyses on appropriate formulations. In order to formulate finished inks from the optimised, stable pigment dispersions, various binders were incorporated in the formulations followed by characterisation of the stability and the electrical properties of the finished inks. Films of the formulated inks were deposited onto various textile substrates. This was followed by testing of the washing and creasing performance of these ink films. It was found that the formulated inks performed considerably better than the tested commercial inks. It was shown that following the ink preparation procedure devised in this study, electrically conductive grades of carbon black pigment can be used to formulate textile printing inks which not only possess very high electrical conductivity but are also durable to withstand washing and creasing of textiles.

Le supraconducteur ?? base de fer KFe[indice inf??rieur 2]As[indice inf??rieur 2] constitue une ??nigme en raison de la sym??trie inusit??e de son param??tre d'ordre. Contrairement aux autres supraconducteurs ?? base de fer, qui sont de sym??trie s-wave, ce mat??riau semble partager la sym??trie d-wave des cuprates comme YBCO. Le transport thermique est une sonde exp??rimentale tr??s efficace pour d??terminer la structure du param??tre d'ordre en r??v??lant la pr??sence de n??uds sur la surface de Fermi o?? le gap en ??nergie associ?? ?? la supraconductivit?? est nul. Ce m??moire pr??sente des donn??es de conductivit?? thermique obtenues dans KFe[indice inf??rieur 2]As[indice inf??rieur 2] selon les axes cristallins a et c et pour diff??rentes orientations du champ magn??tique. Les mesures couvrent un intervalle en temp??rature de 50 mK ?? 500 mK. La pr??sence d'un terme r??siduel lin??aire k[indice inf??rieur 0] / T en champ nul indique la pr??sence de n??uds. L'anisotropie de ce terme r??siduel selon les directions a et c implique que les n??uds sont dispos??s sur des lignes verticales selon l'axe k[indice inf??rieur z] sur tous les feuillets de la surface de Fermi. Ce r??sultat sugg??re fortement un gap de sym??trie d-wave. De plus, k[indice inf??rieur 0] / T n'est pas affect?? par la variation du taux de diffusion dans des ??chantillons de puret??s diff??rentes. Cette propri??t??, appel??e universalit?? de la conductivit?? thermique, est caract??ristique des supraconducteurs de sym??trie d-wave. Bien qu'une r??cente ??tude men??e ?? l'aide de l'ARPES dans KFe[indice inf??rieur 2]As[indice inf??rieur 2] indique plut??t un gap s-wave, le calcul du comportement en champ magn??tique de ce mat??riau ?? partir des valeurs du gap obtenues par l'ARPES est incompatible avec les donn??es exp??rimentales de conductivit?? thermique. La d??pendance en champ magn??tique de la conductivit?? thermique est par ailleurs reproduite presque parfaitement par un mod??le d-wave. D??terminer la sym??trie du param??tre d'ordre du supraconducteur est crucial afin de comprendre le m??canisme d'appariement. ?? cet ??gard, KFe[indice inf??rieur 2]As[indice inf??rieur 2] offre la possibilit?? de faire le lien entre les deux grandes familles de supraconducteurs: les cuprates et les supraconducteurs ?? base de fer.

My thesis is focused on the synthesis of thin films of transparent conductive oxides (TCOs) by colloidal approach for gas sensing applications, solar control and transparent electrode. The work is mainly divided in three different parts. In the first place on the development of nanoparticles of doped conductive oxides and transparent by colloidal synthesis. In particular nanoparticles were synthesized using heat up synthesis that do not require high temperature injection: doped ZnO with trivalent metals such as aluminum and gallium, or doped with tetravalent elements such as Silicon and Germanium, and Niobium doped TiO2 nanoparticles. Free electrons introduced into the crystal by dopants lead to the development of peculiar optoelectronic properties, in particular the formation of a LSPR in the near infrared. In the first part such nanoparticles are also characterized by different techniques and are faced in particular the variations in their morphology and the optical properties as a result of different concentrations of doping. The second part examination was focused on the deposition of TCOs colloidal suspensions and the characterization of TCOs thin film. One of the primary objectives was to obtain functional thin films (such as transparent electrodes or coatings for solar control) using mild heat treatments and through different approaches, using UV lamps or organic acids attacks in order to eliminate most of the organic residues. In this way, by combining heat-up synthesis easily scalable, depositions via spray coating or spin coating (which does not therefore require the use of vacuum or expensive equipment) and heat treatments that do not require excessive temperatures, it is possible to pave the way to an industrialization of the process. The last part focuses on the use of such films for sensor applications, in particular for the detection of H2 and NO2. LSPR is sensitive to changes of the dielectric constant in the neighborhood of the particles, and to variation of charge density, allowing to monitor the gases that interact with the oxide resulting in a shift in the wavelength of the LSPR peak. Optical gas sensing and electrical gas sensing measurements were performed to evaluate different behavior of different dopant concentrations. Measurements in the presence of blue LEDs were also carried out, investigating the role of this radiation in the desorption kinetics of adsorbed molecules. Finally Platinum nanoparticles influence on the detection of hydrogen was also evaluated in order to improve the sensitivity of the sensor exploiting Pt catalytic activity.
Il mio lavoro di tesi si è focalizzato sulla sintesi di film sottili di ossidi trasparenti e conduttivi (TCOs) per via colloidale per applicazioni di gas sensing, solar control ed elettrodo trasparente. Il lavoro è suddiviso principalmente in tre diverse parti. La prima parte si concentra sullo sviluppo di nanoparticelle di ossidi dopati conduttivi e trasparenti per via colloidale. In particolare sono stati sintetizzate, utilizzando sintesi heat-up che non richiedono iniezione ad alta temperatura, nanoparticelle di ZnO dopato con metalli trivalenti come Alluminio e Gallio, oppure dopato con elementi tetravalenti come Silicio e Germanio, e nanoparticelle di TiO2 dopata con Niobio. Gli elettroni liberi introdotti nel cristallo in seguito al drogaggio portano allo sviluppo di peculiari proprietà optoelettroniche, in particolare alla formazione di una LSPR nel vicino infrarosso. Tali nanoparticelle sono state caratterizzate mediante diverse tecniche che permettono di investigare in particolare le variazioni della loro morfologia e delle proprietà ottiche a seguito di diverse concentrazioni di dopante. Nella seconda parte vengono invece approfonditi gli aspetti legati alla deposizione delle sospensioni colloidali ottenute e alla caratterizzazione dei film sottili prodotti. Uno degli obiettivi primari è ottenere film sottili funzionali (ad esempio come elettrodi trasparenti o per rivestimenti solar control) utilizzando blandi trattamenti termici e attraverso diversi approcci, tra cui irraggiamento UV o attacchi con acidi organici in modo da eliminare gran parte dei residui organici. In questo modo, combinando sintesi heat up “non injection” facilmente scalabili, deposizioni tramite spray coating o spin coating (che non richiedano quindi l’uso di vuoto o apparecchiature costose) e trattamenti termici che non richiedano temperature eccessive, è possibile aprire la strada ad una industrializzazione del processo. L’ultima parte si focalizza sull’utilizzo di tali film per applicazioni sensoristiche, in particolare per la rilevazione di H2 e NO2. La LSPR è sensibile ai cambiamenti della costante dielettrica nell’intorno delle particelle ed alla variazione di densità di carica: ciò permette di monitorare i gas che interagiscono con l’ossido analizzando lo spostamento in lunghezza d’onda del picco plasmonico. Sono stati effettuate misurazioni di gas sensing ottico ed elettrico per valutare le diverse performance dei TCOs a diversa concentrazione di dopante. Misurazioni in presenza di LED blu sono state inoltre eseguite, investigando il ruolo di tale radiazione nella cinetica di desorbimento delle molecole adsorbite. Infine è stata anche valutata l’influenza di nanoparticelle di Platino sulla rilevazione di idrogeno al fine di migliorare la sensibilità del sensore sfruttando l’attività catalitica di tali nanoparticelle.

Esistono attualmente varie ragioni per cui ampio interesse scientifico e tecnologico è rivolto verso sistemi di generazione di energia alternativi rispetto ai metodi convenzionali (quali i sistemi a turbine o i motori a combustione interna). Dal punto di vista ecologico, cresce il bisogno di ridurre la produzione di sostanze inquinanti per far fronte a uno sviluppo sostenibile. Da un punto di vista socio-economico, invece, aumenta il bisogno di far fronte a un continuo aumento della richiesta di energia, mentre nello stesso tempo le principali fonti di energia, quali i combustibili fossili, si stanno esaurendo. E infine, da un punto di vista socio-politico, la scarsità delle attuali fonti di energia sta creando drammatiche tensioni tra le varie aree economiche del mondo. La diminuzione della dipendenza mondiale dai combustibili fossili e l’introduzione di forme di generazione di energia alternative potrebbero sanare tale situazione. Il concetto di energia alternativa è stato introdotto già da vari anni. Ci sono diverse fonti d energia alternativa, come l’energia solare, l’energia eolica o la fusione nucleare. Un diverso approccio consiste nello sviluppo di sistemi di generazione di energia alternativi, che siano in grado di lavorare con alti rendimenti e di limitare al massimo la produzione di inquinanti. Allo stato attuale i motori a combustione interna presentano un’efficienza totale del 20-30%. Questo significa che solo il 20-30% dell’energia termica contenuta nel gasolio viene utilizzata come lavoro meccanico. Alti rendimenti si traducono, invece, in costi ridotti per unità di lavoro prodotto. Le celle a combustibile sono sistemi di conversione di energia alternativi i quali permettono la conversione diretta dell’energia chimica dei reagenti in energia elettrica, producendo al contempo basse emissioni inquinanti. Tra i diversi tipi di celle a combustibile, le celle a ossidi solidi (SOFCs) presentano vari vantaggi; tra i primi, lavorando ad alta temperatura (800-100°C) queste celle raggiungono valori di rendimento molto alti, permettono l’uso di diversi combustibili e l’unica emissione inquinante rilevante è quella di CO2, la quale rimane comunque un terzo di quella emessa da un motore a combustione interna a parità di kW/h prodotti. Tuttavia le alte temperature di lavoro comportano anche degli svantaggi: materiali costosi, elevati stress termici, difficoltà nel sigillare la cella, lunghi tempi di accensione e spegnimento del sistema. Per risolvere questi problemi la ricerca è orientata nell’abbassare la temperatura di funzionamento delle SOFCs nel cosiddetto range di temperature intermedie (400-700°C). Abbassare la temperatura di funzionamento si traduce in un peggioramento delle performance dei vari componenti della cella, e per questo lo studio di nuovi materiali risulta essenziale nella prospettiva di rendere le SOFC commercializzabili. Lo scopo di tale lavoro di tesi è appunto lo studio di materiali elettrolitici ed elettrodici che presentino buone proprietà conduttive a temperature di funzionamento intermedie e che allo stesso tempo siano chimicamente stabili. Nel capitolo 1A della tesi si presentano i principi basilari di funzionamento di una SOFC e una breve illustrazione dei materiali più studiati in letteratura sia per le alte e intermedie temperature di funzionamento. In particolare, tra i materiali ceramici con buone proprietà conduttive a basse temperature si trovano i conduttori protonici. Nel Capitolo 2A vengono illustrate le principali proprietà chimico-fisiche ed elettrochimiche di tali materiali ceramici. Molti ossidi perovskitici presentano conduzione protonica a temperature intermedie quando esposti ad atmosfera di idrogeno e/o vapore acqueo. Tuttavia nessuno di questi ossidi presenta contemporaneamente le due proprietà essenziali richieste ad un buon elettrolita: alta conducibilità ionica e buona stabilità chimica. La seconda parte della tesi presenta i risultati del lavoro sperimentale svolto, il quale è stato rivolto alla preparazione e caratterizzazione di conduttori protonici ceramici elettrolitici con alta conducibilità e buona stabilità chimica e allo sviluppo di elettrodi a - hoc per tali elettroliti. Il Capitolo 1B riporta l’ottimizzazione di una tecnica di sintesi sol gel per produrre i seguenti conduttori protonici: BaZr0.8Y0.2O3-δ (BZY) e BaCe0.8Y0.2O3-δ (BCY). Attraverso il metodo di sintesi ottimizzato si sono sintetizzate fasi singole dei suddetti composti. Le basse temperature di calcinazione richieste dal processo hanno portato a polveri di particelle nanometriche. I due composti sono stati sinterizzati in forma di pasticche circolari e caratterizzati elettricamente mediante spettroscopia di impedenza. Inoltre sono stati svolti test termici in flusso di anidride carbonica per valutare la stabilità chimica dei due composti, osservando una buona stabilità solo nel caso del BZY. Tuttavia le performance in cella di tale elettrolita si sono rilevate insufficienti rispetto ai target richiesti per la commercializzazione. Nel Capitolo 2B si è cercato di implementare le prestazioni del BZY sostituendo nel sito B della struttura perovskitica diverse quantità di Ce. Gli elettroliti cosi prodotti sono stati analizzati ai raggi X, sotto il punto di vista della stabilità chimica e della conducibilità elettrica. Il miglior compromesso tra stabilità chimica e conducibilità elettrica è risultato il composto con stechiometria BaZr0.5Ce0.3Y0.2O3-δ. Un ulteriore miglioramento della conduzione elettrica rispetto al BaZr0.5Ce0.3Y0.2O3-δ, pur mantenendo un’ottima stabilità chimica, è stato ottenuto realizzando un elettrolita “a doppio strato”, il quale è descritto nel Capitolo 3B. Una pasticca spessa 1 mm di BCY è stata protetta con uno strato sottile (circa un micron) di BZY cresciuto tramite la tecnica di deposizione a laser pulsato. Questo nuovo elettrolita ha presentato elevata conducibilità e buone prestazioni in cella in termini di stabilità chimica e densità potenza fornita. Nel Capitolo 4B si sono invece investigati elettrodi funzionali per tali elettroliti a conduzione protonica. Un catodo composito e stato realizzato unendo un conduttore misto ionico/elettronico, La1-xSrxCo1-yFeyO3-δ (LSCF), e un conduttore misto protonico/elettronico BaCe0.9Yb0.1O3-δ (10YbBC). L’uso di catodi compositi aumenta i siti di reazione al catodo, diminuendo quindi le cadute di potenziale dovute alle reazioni catodiche.
There are increasing reasons to explore alternatives to conventional energy generation methods (that is to say coal-fired steam turbine and gasoline internal combustion engine). From an ecological point of view, there is the need to reduce the polluting by-products of conventional energy generation. From a socio-economical standpoint, the worldwide demand for energy continues to rise as more and more nations join the group of the industrialized countries, while hydrocarbon fuels go to exhaustion. Finally, from a socio-political perspective, the situation described above has created several and often dramatic tensions between different world economic areas, as evidenced by frequent wars. Lowering the global dependence on oil might reduce such tensions. However, despite all of this, changes in the energy generation methods are extremely slow, as evidenced by the wide (if we cannot say total) use of the internal combustion engine. The concept of alternative energy has been introduced a long time ago. Several different sources of energy are proposed, which can have the potential to replace conventional generation methods. Popular examples include solar radiation, wind motion, and nuclear fusion. Each of these technologies has its own set of problems that have slowed down its commercialization, but much research is being conducted to overcome these problems. In fact, the research towards the development of alternative, highly efficient, eco-friendly energy production technologies is expanding. There is a general push towards higher efficiencies. At present, automobiles based on internal combustion engines have an overall efficiency of about 20-30%. That is, only 20-30% of the thermal energy content of the gasoline is converted into useful mechanical work and the rest is wasted. Higher efficiencies translate into reduced energy costs per unit of work done. Fuel cells, an alternative energy technology, have received growing interest in recent years since they represent one of the most promising energy production systems to reduce pollutant emissions. They are electrochemical devices that allow the direct conversion of chemical energy into electrical energy. Among the different type of fuel cells, solid oxide fuel cells (SOFCs) offer great promise as a clean and efficient technology for energy generation and provide significant environmental benefits. They produce negligible hydrocarbons, CO or NOx emissions, and, as a result of their high efficiency, about one-third less CO2 per kW/h than internal combustion engines. Unfortunately, the current SOFC technology based on a stabilized zirconia electrolyte requires the cell to operate from 700 to 1000°C to avoid unacceptable ohmic losses. These high operating temperatures demand specialized (expensive) materials for fuel cell interconnectors, long start-up time, and large energy input to heat the cell up to the operating temperature. Therefore, if fuel cells could be designed to give a reasonable power output at intermediate temperatures (IT, 400-700°C), tremendous benefits may result. In particular, in the IT range ferrite steel interconnects can be used instead of expensive and brittle ceramic materials. In addition, sealing becomes easier and more reliable; rapid start-up is possible; thermal stresses (namely, those caused by thermal expansion mismatches) are reduced; electrode sintering becomes negligible. Combined together, all these improvements result in reduced initial and operating costs. Therefore, the major trend in the present research activities on SOFCs is the reduction of the operating temperature. The problem is that lowering the operating temperatures lowers the electrolyte conductivity, whereas the electrode polarization greatly increases, reducing the overall fuel cell performance. Considering the described scenario, it is clear how the study of materials assumes a considerable role in lowering SOFC operating temperature. Making SOFCs commercially competitive with conventional energy generation methods means developing a highly efficient and environmental friendly energy production device to provide for a global sustainable energy system. IT-SOFCs represent not only a laboratory research activity, but a great challenge for the entire society. The purpose of the present dissertation is the development of a stable highly-conductive electrolyte and performing electrodes for lower temperature SOFCs. Chapter 1A presents the physico-chemical principles of SOFCs functioning, the demands imposed on the components materials, together with a literature survey on the state of-the art technology. Starting from more “conventional” oxygen ion conducting electrolytes, the need for reducing the operation temperature leads to a discussion on the properties of proton conducting materials as a feasible alternative to reach the goal of fabricating an IT-SOFCs. Chapter 2A describes the main properties of ceramic proton conductors. Several perovskite-type oxides, such as doped BaCeO3, SrCeO3, BaZrO3, and SrZrO3, show proton conductivity in the IT range when exposed to hydrogen and/or water vapour containing atmospheres. They are generally known as high temperature proton conductors (HTPCs). The main challenge in the field of HTPC is to find a compound that concurrently satisfies two of the essential requirements for fuel cell application, namely high proton conductivity and good chemical stability under fuel cell operating conditions. The second part of this dissertation describes the experimental results achieved during the research carried out. In view of the considerations given in Chapter 2a, Chapter 1B describes the optimization of the sol-gel procedure to prepare BaZr0.8Y0.2O3-δ (BZY) proton conductor electrolyte. Producing BZY powders with controlled compositional homogeneity and microstructure using a proper synthesis method could improve the electrochemical performance of this electrolyte. The optimized sol–gel procedure allowed the reduction of the diffusion path up to a nanometric scale, and thus required lower calcination temperatures. Nanocrystalline single-phase powders of BZY were produced at temperatures as low as 1100 °C. The same sol-gel procedure was also used to synthesize BaCe0.8Y0.2O3-δ (BCY) proton conductor electrolyte achieving also in this case nanometric particles powder at the calcination temperature of 100°C. The performance of the synthesized BZY and BCY proton conductors were examined in terms of chemical stability. After exposure to CO2 at high temperatures, the synthesized BZY powders presented good chemical and microstructural stability, differently from BCY which strongly decomposed after the CO2 treatment. Electrical conductivity and fuel cell performance were investigated only for the stable BZY electrolyte, however without achieving the required performance for practical application. Chapter 2 presents the application of the optimized synthetic procedure to the preparation of different proton conductor electrolytes. To further improve the electrochemical performance of barium zirconate electrolyte, the B-site of the BZY perovskite structure was doped with Ce producing several BaZr0.8-xCexY0.2O3-δ compounds (0.0≤x≤0.8). The prepared samples were analyzed in terms of chemical stability in CO2 environment, electrical conductivity, microstructural characteristics, and finally under fuel cell tests. Among the tested electrolytes, the BaZr0.5Ce0.3Y0.2O3-δ composition represented the best compromise between electrical performance and chemical stability. In fact it was able to maintain almost the same chemical stability of BZY, but with improved, more than twice, fuel cell performance. Chapter 3 describes a further improvement of the HTPC electrolyte performance. To obtain a highly conductive and chemically stable proton conductor electrolyte, a sintered Y-doped barium cerate (BCY) pellet was protected with a thin BZY layer, grown by pulsed laser deposition. The overall performance of the bilayer electrolyte turned out to be of great interest for practical use in IT-SOFCs application. The promising performance of this bilayer electrolyte rose from the very good crystallographic matching at the interface between the two materials, as well as the microstructure properties of the protecting layer in terms of uniformity, density and filling factor. However, while the bilayer conductivity was only slightly smaller than the conductivity of the BCY pellet, the measured fuel cell performances were negatively affected by the interface of the Pt electrodes with the BZY layer. For this reason the development of a superior cathode is crucial to make IT-SOFCs based on proton conductors competitive with the more established SOFCs using oxygen-ion conductor electrolytes. Chapter 4 focuses on the optimization of composite cathodes for application in IT-SOFC based on HTCP electrolytes. To explore different cathode materials with respect to the most commonly used for proton conductor electrolytes, such as platinum or cobalto-ferrites, the area specific resistance (ASR) of composite cathodes was investigated. Firstly, BaCe0.9Yb0.1O3-δ (10YbBC) and SrCe0.9Yb0.1O3-δ (10YbSC) were tested as cathode materials since they show mixed protonic-electronic conductivity. However, the ASR of the interface of these cathode materials with Y-doped barium cerate proton conductor electrolyte was extremely large, probably because of their too low partial electronic conductivity. For this reason, La1-xSrxCo1-yFeyO3-δ (LSCF), which presents high electronic conductivity, was combined with 10YbSC or 10YbBC to form composite cathodes. LSCF was chosen also because it allows faster oxygen surface exchange being a mixed O2-/e- conductor. The lowest ASR values were achieved with the composite cathode made of LSCF and 10YbBC in a1:1 ratio. Single phase Pt and LSCF cathodes were tested and it was found that they showed higher interfacial resistance than LSCF/10YbBC(1:1) composite cathode. This finding clearly suggests the importance of the proton conductor phase within the electrode, which actually should increase the triple phase boundary (TPB) density and so improve the cathode performance. The good performance observed for LSCF/10YbBC(1:1) composite cathode make it a cheaper and more efficient alternative to the Pt cathode that can actually improve the performance of IT-SOFCs based on proton conductor electrolytes.

Hybridizing additive manufacturing (AM) structures and direct write (DW) deposition of conductive traces enables the design and physical creation of integrated, complex, and conformal electronics such as embedded electronics and complex routing on a fully AM structure. Although this hybridization has a promising outlook, there are several key AM substrate-related limitations that limit the final performance of these hybridized AM-DW electronic parts. These limitations include low-temperature processability (leading to high trace resistivity) and poor surface finish (leading to electronic shorts and disconnections). Recently discovered ultraviolet-assisted direct ink write (UV-DIW) all-aromatic polyimide (PI) provides an opportunity to address these previous shortcomings previously due to its high-temperature stability (450C) and superior surface finish (relative to other AM processes). The primary goal of this thesis is to characterize the integration of this UV-DIW PI with DW-printed conductive inks as a means for obtaining high-performance hybrid AM-DW electronics. This goal has been achieved through an investigation into the increased temperature stability of AM PI on the conductivity and adhesion of DW extrusion and aerosol jet (AJ) silver inks, determining the dielectric constant and dissipation factor of processed UV-DIW PI, and determining the achievable microwave application performance of UV-DIW PI. These performance measurements are compared to commercially-available PI film and relative to existing AM substrates, such as ULTEM 1010. The temperature stability of UV-DIW PI enabled higher-temperature post-processing for the printed silver traces, which decreased DIW trace resistivity from 14.94±0.55 times the value of bulk silver at 160 °C to 2.16±0.028 times the resistivity of bulk silver at 375 °C, and AJ silver trace resistivity from 5.27±0.013 times the resistivity of bulk silver at 200 °C to 1.95±0.15 times the resistivity of bulk silver at 350 °C. The adhesion of these traces was not negatively affected by higher processing temperatures, and the traces performed similarly on UV-DIW PI and commercial PI. Furthermore, at similar thicknesses, UV-DIW PI was found to have a similar dielectric constant and dissipation factor to commercial Dupont Kapton PI film from 1 kHz to 1 MHz, indicating its ability to perform highly as a dielectric electronics substrate. Finally, the decrease in resistivity was able to decrease the gap in microwave stripline transmission line performance when compared with ULTEM 1010 processed at 200°C, with peak 10 GHz S21 loss differences decreasing from 2.46 dB to 1.32 dB after increasing the UV-DIW processing temperature from 200 °C to 400°C.
Master of Science
Due to the extensive potential benefits and applications, researchers are looking to hybridize additive manufacturing (AM) processes with direct write (DW) techniques to directly print a 3D part with integrated electronics. Unfortunately, there are several key substrate-related limitations that hinder the overall performance of a part fabricated by hybrid AM-DW processes. Specifically, typical AM materials are not capable of providing an electronics substrate with combined sufficient surface resolution, surface finish, and high-temperature processing stability. However, the recent discovery of a novel AM-processable all-aromatic polyimide (PI) presents an opportunity for addressing these limitations as its printed form offers a high surface resolution, superior surface finish, and mechanical stability up to 400 °C. The primary goal of this thesis is to evaluate the benefits and drawbacks of this PI, processed via ultraviolet-assisted direct ink write (UV-DIW) AM, as an AM-DW electronics substrate. Specifically, the author characterized the effect of the increased temperature stability of the printed PI on the resultant conductivity and adhesion of silver inks printed via direct ink write (DIW) and aerosol jetting (AJ) DW processes. These results were also compared to the performance of the inks on commercial PI. Furthermore, the dielectric performance of printed PI was evaluated and compared to commercial PI. To demonstrate and evaluate the hybridized approach in a potential end-use application, the author also characterized the achievable microwave application performance of UV-DIW polyimide relative to the existing highest performance commercially available printed substrate material. The experiments in this thesis found an 83% and 66% decrease in resistivity from extrusion and AJ printed inks due to the ability of the printed PI to be processed at higher temperatures. Furthermore, UV-DIW PI was found to have similar dielectric properties to commercial PI film, which indicates that it can serve as a high-performance dielectric substrate. Finally, the high-temperature processing stability was able to decrease the performance gap in microwave application performance between the higher performing dielectric substrate, ULTEM 1010. These results show that UV-DIW could serve as a dielectric substrate for hybridized AM-DW electronic parts with higher performance and the ability to be deployed in harsher environments than previous AM-DW electronic parts explored in literature.

Isotropically conductive adhesives (ICAs) and inks are potential candidates for low cost interconnect materials and widely used in electrical/electronic packaging applications. Silver (Ag)filled ICAs and inks are the most popular due to their high conductivity and good reliability. However, the price of Ag is a significant issue for the wider exploitation of these materials in low cost, high volume applications such as printed electronics. In addition, there is a need to develop systems compatible with temperature sensitive substrates through the use of alternative materials and heating methods. Copper (Cu) is considered as a more cost-effective filler for ICAs and in this work, Cu powders were treated to remove the oxide layer and then protected with a self-assembled monolayer (SAM). The coating was found to be able to limit the re-oxidation of the Cumicron particles. The treated Cu powderswerecombined with one of two different adhesive resins to form ICAs that were stencil printed onto glass substrates before curing. The use of conventional and microwave assisted heating methods under an inert atmosphere for the curing of the Cu loaded ICAs was investigated in detail. The samples were characterised for electrical performance, microstructure and shrinkage as a function of curing temperature (80-150°C) and time. Tracks with electrical conductivity comparable to Ag filled adhesives were obtained for both curing methods and with both resins. It was found that curing could be accelerated and/or carried out at lower temperature with the addition of microwave radiation for one adhesive resin, but the other showed almost no absorption indicating a difference in curing mechanism for the two formulations.

Le transistor à effet de champ à grille isolée HFET à canal quaternaire GaAlInAs est Particulièrement adapté à la pré-amplification faible bruit dans la photo-réception intégrée à 1. 3- 1. 55J. 1m. Ce travail a pour objectif essentiel l'étude des défauts électriquement actifs dans les couches AlInAs et GaAlInAs qui constituent les différentes zones du transistor (canal, barrière, couche tampon) et de déterminer leur influence sur les performances du dispositif La compréhension du mécanisme de conduction dans les diodes métal/ AlInAs/GaAlInAs nous a permis d'évaluer avec précision et d'une manière directe la discontinuité de la bande de conduction à l'interface entre ces deux semi-conducteurs. Par une technique de spectroscopie de transitoire de capacité DL TS menée sur des structures de diodes Schottky, nous avons identifié les niveaux profonds dans les couches d’AlInAs (E1, E2, E3, E4) et de GaAlInAs (Q3, Q4) élaborées par épitaxie par jets moléculaires; et montré le rôle de chacun d'eux dans le mécanisme de conduction et leur effet sur les performances du dispositif final. De plus, deux défauts supplémentaires (Tl et T2) sont mis en évidence sur les transistors HFET par spectroscopie de transitoire de courant CTS, ces défauts n'ayant pas été observés sur les diodes ont pu être attribués au procédé technologique de fabrication des transistors. Finalement nous avons établi le rôle de ces deux défauts présents dans le canal du transistor sur les performances en bruit du transistor
Field effect transistors with isolated gate (HFET) including a GaAllnAs channel are particularly adapted to the noise pre-amplification for photo-detection in the 1. 3-1. 55μm range. The principal goal of this study is to characterize electrically active defects present in AlInAs and GaAlInAs; two materials which constitute the barrier and the channel of the transistor. The comprehension of the conduction mechanism in Schottky metal/ AlInAs/GaAlInAs diodes allowed us for the first time to determine the values of the discontinuity bands between these two semiconductors. Using Deep Level Transient Spectroscopy (DLTS), we have detected several levels in thick layers of AlInAs (El, E2, E3, E4) and GaAlInAs (Q3, Q4) which we attributed to growth conditions. We have studied also their effects on HFET transistor. Theo, by Current Transient Spectroscopy (CTS) applied to HFET's with different length gates we detected two deep levels Tl and T2 in addition to those revealed by DLTS. We attribute these levels to the technological processes during the realization of the transistors. Finally, we have established the role of these two defects, present in the channel, on the noise performance of the transistor

This thesis studies networks of silver nanowires as a transparent conducting electrode material and presents an investigation into the relationship between electrical and optical properties in the networks. The work focusses on two main aspects: the production of networks via different deposition methods; and the development of a predictive model based on theory that relates the sheet resistance to the optical transmittance. The deposition methods of drop-casting, bar-coating and spray-coating are used to create networks and the randomness of these networks is compared using image analysis in ImageJ, a public domain image processing program, and Wolfram Mathematica, a computer algebra program. It is determined that spray-coating results in the most random networks, therefore all subsequent experiments are carried out using this as the deposition method. Annealing condition tests are carried out on the nanowire networks to determine the optimal annealing conditions required to burn off poly(vinyl pyrrolidone) (PVP) remaining from the nanowire synthesis process and sinter the nanowire junctions to improve network conductivity. The sheet resistances and optical transmittances of the networks are measured and compared to networks created by other research groups. It is found that the networks created in this study exhibited similar optical and electrical properties to those in the literature, obtaining Rs = 100 Ω/sq for T = 81%.The developed model is based on theory and relates the sheet resistance to the optical transmittance using only the length and width of the nanowires used in the network and the mean network coverage as variables. The model can be used to predict the properties of a network if these factors are known. The model is compared with experimental data both from this study and from the literature, along with simulated data from the literature that was obtained by Monte Carlo methods. It is shown that there is an excellent fit between the model and all data that it is compared with. It is demonstrated that < 1% of the network coverage is greater than 2 for typical nanowire networks, proving that the networks are two-dimensional and therefore do not require a bulk regime to describe the relationship, as has been suggested in prior work.

Le brouillard électromagnétique dans lequel nous vivons en permanence estaujourd’hui montré du doigt car, outre les risques sanitaires qu’il pourrait engendrer, illimite l’usage de certaines technologies. L’importance des interférences entre réseauxsans fil, ou la peur du piratage sur ces mêmes réseaux, en sont deux exemples. Cetravail de thèse vise à développer un nouveau moyen de protection contre certaines deces ondes électromagnétiques. Plus spécifiquement, ce travail se focalise sur unetechnologie capable de filtrer uniquement les ondes WiFi et GSM à travers de grandessurfaces d’une habitation, comme un mur. Pour ce faire, la fonctionnalisation d’uncomposant standard des bâtiments, le papier-peint, a été étudié.L’utilisation de surfaces sélectives en fréquence a été retenue. Ces motifs sontdirectement imprimés sur du papier à l’aide d’encre conductrice et de la techniqued’impression flexographique. L’étude s’est également portée sur la réalisation de motifsde filtrage innovants. Les résultats de simulation montrent qu’ils sont capables de filtrerdeux ou trois bandes, qu’ils sont quasiment insensibles à la polarisation et à l’angled’incidence dans une plage allant de 0° à ± 80°. Le travail a ensuite permis dedémontrer la faisabilité pratique de ce concept aux stades laboratoire et industriel.Ensuite, nous avons démontré expérimentalement l’efficacité de ce concept dans lesbandes WiFi. La transmission atteint alors -30 dB. Enfin, une validation expérimentaledu produit en situation réelle a été menée, à savoir la pose du papier-peint sur du plâtre,du bois, l’influence de la colle ou encore la pose d’une couche de papier-peint décoratifpar-dessus le produit.En conclusion, les résultats pratiques obtenus confirment les résultats théoriquesestimés et, permettent à ce nouveau concept, appelé métapapier, d’être suffisammentefficace pour permettre la réduction des ondes WiFi ou GSM
The electromagnetic smog in which we live today is nowadays a real issue because it limits the use of certain technologies and also because there are some potential health risks associated with it, even if the latter is still a controversial subject. The importance of the interferences between wireless networks or the possibility of data hacking on the same networks are two examples. The aim of this thesis is to develop a new way to protect buildings against some of these electromagnetic waves. More specifically, this work focuses on a technology able to filter only the WiFi and the GSM waves through large areas of a home, like a wall for example. To do this, the functionalization of a standard component of buildings, the wallpaper, was studied. The use of frequency selective surface (FSS) was chosen. These patterns are printed directly on paper with a conductive ink printing technology: the flexography. The study also focuses on the realization of innovative filter designs. Simulation results show that these novel FSS are able to filter two or three bands. They are almost insensitive to the polarization and to the angle of incidence in the range of 0° to ±80°. The realization feasibility of this concept in a laboratory or in industrial conditions was demonstrated. Next, an experimental demonstration of this concept in the WiFi bands was carried out. In this context, the transmission coefficient was reached -30 dB. Finally, an experimental validation of the product in real conditions of use was conducted, namely the wallpaper was put over plasterboards or over wood panels. Also, the influence of the glue on the general performances and the placement of a decorative wallpaper over the FSS wallpaper were studied. In conclusion, the practical results obtained confirm and validate the theoretical predictions of this new concept, called metapaper, and show that the practical realizations are efficient enough to allow the reduction of WiFi or GSM signals

Heat transfer is one of the most salient and fundamental research areas for any engineer, due to its ubiquity. Today the energy efficiency requirements are becoming more and more demanding. This motivates engineers to continuously improve the efficiency of heat transfer processes. For such analysis nowadays, the common and the popular practice to infer the temperature field is now commercially available in computer codes. Analytical solutions for the temperature field are also available under the assigned conditions such as Dirichlet, Neumann or Robin, if the thermal conductivity is constant and isotropic. In the cases where conductivity is anisotropic and strongly dependent by temperature or the material is not homogenous, the exact solution of the energy conservation in the body is not possible due to high non linearity in the equations. Despite the complexity of many engineering structures, the present work is undertaken to demonstrate that the reduction to a simpler version of more complex heat conduction equations is possible and the exact analytical solution is comparable with the approximate finite element solution. The topic of the present research study is the resolution of the problems in various engineering fields through the analysis of conduction heat transfer in rigid bodies, transition bodies, steady and transient bodies and the provision of analytical solutions with graphical representation of the results. Namely; in an electrolytic capacitor, a food container and a gas turbine blade. The modelling of them plays an important role because excessive temperatures drastically reduce the lifetime of capacitors, turbine vanes and blades. In the food sterilization it is necessary to know the thermal wave behaviour in order to reduce its associated costs or to guarantee the sterilization time. The last part of this study is the evaluation of the numerical simulation results in order to make a comparison with the analytical results and, when possible, with experimental data. For such analysis a finite element method has been utilized by both commercial and free software; namely, ANSYS™ and FreeFem++. Very good agreements are obtained between both of them.

This thesis presents a comparative study between two silver nanoparticle inks that were deposited using a Drop-on-Demand (DoD) inkjet printer, aiming at finding a functional ink that can be used to print electrodes in Light-emitting Electrochemical Cells (LECs). To achieve this, a DoD inkjet printer was installed and an acquaintance with the printer was attained. Among the two inks, one was employed as received while the other was reformulated, and successful deposition of both the inks was observed. During the reformulation process, it was seen that the highly volatile tetrahydrofuran (THF) solvent can be used to improve the ink properties, in contrast to what is recommended. After that, the inks were deposited on UV-ozone treated glass substrates, sintered at an elevated temperature under ambient conditions, and their specific resistances and thicknesses were measured. Finally, the inks were used to print the anode in a structured sandwich-cell LEC. The performance comparison was conducted by observing the emitted light of the LECs. The results indicate that the reformulated ink performs better, probably due to the lower silver concentration that results in flatter surface, which in turn effectively alleviates shorts.

Measurements of the longitudinal and transverse direct current (d.c.) magnetoresistance of n-type InP samples (carrier density from and the alternating current (a.c.) conductivity of n-type InSb samples (carrier density from have been made at temperatures T down to 0.04 K and in magnetic fields H up to 70 kG. For H=0, the InP samples were nonmetallic. At low temperatures, the conductivity is due to nearest neighbour hopping (NNH) which is followed by variable range hopping (VRH) at lower T as described by the first, and second terms in the expression. In the NNH regime, it is necessary to plot In (p/T) against T1 and this yields values of the activation energy much larger than the traditional In p versus T-1 plots In the VRH regime, Mott's law (x = 1/4) is obeyed. Values of To obtained by considering the temperature dependence of the pre-exponential factor are found to be much higher than if the temperature dependence of this factor is ignored. Good agreement between the theory and experiment is achieved in both NNH and VRH regions if an enhanced dielectric constant is used. Magnetoresistance measurements in both the NNH and VRH regimes are analysed using the theories of Shklovskii and Efros (1984) and reasonable agreement is obtained. The anisotropy of the magnetoresistance in the NNH agrees closely with the expected H2 dependence. In the VRH, In(p(H)/p(0)) varies as T-3/4 and H2 as expected for hopping with a constant density of states at the Fermi level. The InSb samples are metallic-like in zero magnetic field. High magnetic fields are applied to shrink the donor wavefunctions (to induce the metal-insulator transition) and to locate the samples on the insulator side where the measurements are carried out. The d.c. resistivity was measured and at low temperatures was of a VRH type with 1/4 x 1/2, and T0 being magnetic field dependent. Reasonable agreement with the theory is found at high fields. The real and imaginary parts of the a.c. conductivity were measured in the frequency range of 110-105 Hz. The real part of conductivity was found to vary as where s is approaching 1 at low temperatures and high fields but decreasing as T increases. At the lowest temperatures was independent of T but at higher T the temperature dependence is stronger than the linear dependence predicted by the simple pair approximation theory. Data are interpreted in terms of multiple hopping of electrons which becomes important at high temperatures and/or low frequencies. The scaling formula; has been applied to discuss the results for the real part of the conductivity, where and are normalized values and f is a universal function obtained by Summerfield (1985). The scaling parameter -log10A is found to be 3.0 +/- 0.2.The relative dielectric constant, due to donors, calculated from the capacitive part was found to be a decreasing function as the frequency is increased and/or the temperature is lowered. At very low temperatures, depending on the magnetic field, however, a temperature-independent, but frequency-dependent behaviour is observed. The lowest temperature value of the dielectric constant was found to diverge as the magnetic field is reduced towards the metal-insulator threshold value.

Abstract In gravure offset printing, ink is transferred with the help of an offset material from a patterned gravure plate to a substrate. This thesis is concerned with the study and further development of this printing process for electronics; on alumina, glass and polymers. The work has been divided into five parts. In the first section, the printing process is described. The second section describes the composition of the inks for gravure offset printing and the resulting ink properties. It also presents the ink transfer mechanism; the model that explains how the ink is transferred between an offset material and a substrate. The third chapter details the printing process explained by a solvent absorption mechanism. The forth chapter describes the firing/curing of printed samples and their properties. The last chapter describes applications of the method. The inks used to produce conductors on ceramics (ceramic inks) and conductors on polymers (polymer inks) contain silver particles, and were under development for gravure offset printing. The major achieved properties were the high ink pickup to the offset blanket and high transfer percentage to the substrate. 100% ink transfer from blanket to substrate for ceramic inks and almost 100% ink transfer for polymer inks was obtained. The printing of ceramic inks was able to produce 8 μm of relatively thick, 300 μm wide lines with < 10 mΩ/sq. resistance. The minimum line width for conducting lines was 35 μm, with one printing. Multi printing was applied producing as many as 10 times wet-on-wet multiprinted lines with 100 % ink transfer from blanket to substrate resulting in a square resistance of 1mΩ/sq. Polymer inks were able produce a square resistance of 20 mΩ/sq. for 300 μm wide lines after curing at 140 °C for about 15 min, and the minimum width was down to 70 μm. In the optimised manufacturing process, the delay time on the blanket was reduced to 3 s. In addition to ultra-fine-line manufacturing of conductors, the method enables the manufacture of special structures e.g. laser-solder contact pads with 28/28 μm lines/spaces resolution. With industrial printing equipment it is possible to produce 100 m2/h with the demonstrated printing properties.

The work presented in this thesis focuses on the synthesis of nanomaterials, formulation and printing of Ag nanoparticle and nanowire inks for two distinct applications: a) inkjet printing of Ag nanoparticle films on ceramic substrates with the aim of providing a smaller size of printed feature at lower cost than that can be obtained with the conventionally used screen printing, and b) Ag nanowires films prompted by the wide quest of electronics industry for materials with increased flexibility, lower cost and higher transmittance to replace indium tin oxide. Ag nanoparticles with a size of 50 nm were successfully synthesized and dispersed in aqueous medium. Two preparation routes were compared in order to distinguish the effects of solvents treatment of particles and their influence on the suspension characteristics including Ag loading, rheology, surface tension and later the electrical film properties. The co-polymer Pluronic F127 was found to be an effective as a stabiliser leading to the formulation of high silver loading in inks. The processing and characterization of silver films was performed. The aim was to reduce the number of layers in the silver nanoparticles film by increasing the thickness of a single layer with the goal of obtaining a dense and conductive film. An increase in the Ag loading, from 5 wt % to 45 wt % favoured the achievement of denser and thicker film with one layer printing. Addition of SiO2 to the ink formula resulted in denser structure and better adhesion of the printed track then the one without SiO2. A new method for improving the morphology of inkjet printed tracks has been proposed by printing the ink into the structured channels with predefined topography. Silver nanowires were synthesised and dispersed in methanol with help of copolymer F127. They were subsequently deposited on plastic and glass substrates forming conductive and transparent films.

Lo sviluppo di elettroliti polimerici di nuova generazione è un requisito essenziale per la diffusione su grande scala delle celle a combustibile a membrana polimerica. Tali conduttori protonici devono esibire stabilità morfologica, idrolitica, meccanica ed adeguate proprietà di conducibilità (σ~ 0.01 Scm-1) a temperature superiori a 100 °C per bassi valori d’umidità relativa. Nel presente lavoro sono esplorate diverse strategie per la sintesi di polimeri conduttori ibridi organici-inorganici nanocompositi a partire da polimeri termoplastici aromatici. L'impiego di materiali ibridi permette di sfruttare l'effetto sinergico dovuto alla contemporanea presenza di una componente organica, nel caso specifico polimerica, e di una inorganica, nel caso specifico a base di silicio. Tale effetto sinergico si esplica nella possibilità di modulare e controllare la separazione tra la fase idrolifila ed idrofobica da cui fortemente dipendono le prestazioni dell'elettrolita polimerico. Membrane ibride di classe I a base di polietereterchetone solfonato (S-PEEK) sono così state sintetizzate insieme a numerosi esempi di membrane ibride di classe II a base di S-PEEK e polifenilsolfone solfonato (S-PPSU), contenenti come porzione inorganica atomi di silicio diversamente funzionalizzati. La caratterizzazione dei materiali ha riguardato l’analisi della struttura, le proprietà chimico fisiche ed il comportamento elettrochimico. Risultati molto positivi sono stati ottenuti principalmente con due dei sistemi investigati: una miscela polimerica a base di S-PEEK e S-PPSU sililato ed un polimero interconnesso tramite ponti -SO2- (SOPEEK) e sililato (SOSiPEEK).
The development of new generation polymer electrolytes is an essential prerequisite for grand scale commercialisation on of polymer electrolyte membrane fuel cells. These proton conductors must show good morphological, hydrolytic and mechanical stability and an appropriate conductivity (σ ~ 0.01 Scm-1) at a temperature above 100°C at low relative humidity. In this work, diverse strategies for synthesis of hybrid organic-inorganic proton conducting polymer nanocomposites were explored, based on aromatic thermoplastic polymers. The use of hybrid materials permits exploitation of the synergy between the simultaneously present organic polymeric component and an inorganic silicon-based part. These effects can be explained by the possibility to modulate and to control the separation between hydrophilic and hydrophobic parts, which strongly modify the properties of the electrolytic polymer. Hybrid materials of class I based on sulfonated poly-ether-ether-ketone (S-PEEK) were synthesized as well as several examples of hybrid materials of class II based on SPEEK and poly-phenyl-sulfone sulfonated (S-PPSU) and containing as inorganic part diverse functionalized silicon atoms. These materials were characterized from the point of view of structure, physical and chemical properties and electrochemical behaviour. Very positive results were obtained mainly for two investigated systems: a mixture of S-PEEK and S-PPSU silylated polymer and a cross-linked polymer, through -SO2- bridges (SOPEEK) and silylated (SOSiPEEK).

Today’s state of the art additive manufacturing (AM) systems have the ability to fabricate multi-material devices with novel capabilities that were previously constrained by traditional manufacturing. AM machines fuse or deposit material in an additive fashion only where necessary, thus unlocking advantages of mass customization, no part-specific tooling, near arbitrary geometric complexity, and reduced lead times and cost. The combination of conductive ink micro-dispensing AM process with hybrid manufacturing processes including: laser machining, CNC machining, and pick & place enables the fabrication of printed electronics. Printed electronics exploit the integration of AM with hybrid processes and allow embedded and/or conformal electronics systems to be fabricated, which overcomes previously limited multi-functionality, decreases the form factor, and enhances performance. However, AM processes are still emerging technologies and lack qualification and standardization, which limits widespread application, especially in harsh environments (i.e. defense and industrial sectors). This dissertation explores three topics of electronics integration into AM that address the path toward qualification and standardization to evaluate the performance and repeatable fabrication of printed electronics for resilience when subjected to harsh environments. These topics include: (1) the effect of smoothing processes to improve the as-printed surface finish of AM components with mechanical and electrical characterization—which highlights the lack of qualification and standardization within AM printed electronics and paves the way for the remaining topics of the dissertation, (2) harsh environmental testing (i.e. mechanical shock, thermal cycling, die shear strength) and initiation of a foundation for qualification of printed electronic components to demonstrate survivability in harsh environments, and (3) the development of standardized methods to evaluate the adhesion of conductive inks while also analyzing the effect of surface treatments on the adhesive failure mode of conductive inks. The first topic of this dissertation addresses the as-printed surface roughness from individually fusing lines in AM extrusion processes that create semi-continuous components. In this work, the impact of surface smoothing on mechanical properties and electrical performance was measured. For the mechanical study, surface roughness was decreased with vapor smoothing by 70% while maintaining dimensional accuracy and increasing the hermetic seal to overcome the inherent porosity. However, there was little impact on the mechanical properties. For the electrical study, a vapor smoothing and a thermal smoothing process reduced the surface roughness of the surfaces of extruded substrates by 90% and 80% while also reducing measured dissipative losses up to 24% and 40% at 7 GHz, respectively. The second topic of this dissertation addresses the survivability of printed electronic components under harsh environmental conditions by adapting test methods and conducting preliminary evaluation of multi-material AM components for initializing qualification procedures. A few of the material sets show resilience to high G impacts up to 20,000 G’s and thermal cycling in extreme temperatures (-55 to 125ºC). It was also found that coefficient of thermal expansion matching is an important consideration for multi-material printed electronics and adhesion of the conductive ink is a prerequisite for antenna survivability in harsh environments. The final topic of this dissertation addresses the development of semi-quantitative and quantitative measurements for standardizing adhesion testing of conductive inks while also evaluating the effect of surface treatments. Without standard adhesion measurements of conductive inks, comparisons between materials or references to application requirements cannot be determined and limit the adoption of printed electronics. The semi-quantitative method evolved from manual cross-hatch scratch testing by designing, printing, and testing a semi-automated tool, which was coined scratch adhesion tester (SAT). By cross-hatch scratch testing with a semi-automated device, the SAT bypasses the operator-to-operator variance and allows more repeatable and finer analysis/comparison across labs. Alternatively, single lap shear testing permits quantitative adhesion measurements by providing a numerical value of the nominal interfacial shear strength of a coating upon testing while also showing surface treatments can improve adhesion and alter the adhesive (i.e. the delamination) failure mode of conductive inks.

Heart failure patients have dysfunction of the cardiac conduction system that contributes to a high burden of arrhythmias including atrial fibrillation and sudden cardiac death. Heart failure has been associated with the inflammatory response, but it is unknown if inflammation is playing a role in the remodelling of the cardiac conduction system in heart failure. Inflammation has been shown to be present in the myocardium from failing hearts and it is known to have detrimental effects on cardiac function, inducing fibrosis, remodelling of ion channels and even arrhythmias. However, the effect of inflammation on the cardiac conduction system has not been investigated. The aims of this study were to determine if there is an increase of pro-inflammatory cytokines and inflammatory cells in the cardiac conduction system in heart failure. In addition, to identify if there is possible inflammation-associated fibrosis and apoptosis in the cardiac conduction system in heart failure. To test these aims, three models of heart failure were used: a rat model of pulmonary arterial hypertension, a rabbit model of congestive heart failure and a rat model of myocardial infarction. In the rat model of pulmonary arterial hypertension there was a bradycardia, a prolongation of the QT interval, and an increase in the atrioventricular and ventricular refractory periods, suggesting electrical remodelling in these animals. The rats with pulmonary arterial hypertension displayed an increase in pro-inflammatory cytokines such as interleukins 1β and TGFβ in the right side of the heart, including the sinoatrial node and right Purkinje fibres of the cardiac conduction system. In addition, in these areas, there was an increase in components of the extracellular matrix, including fibronectin, collagen I and vimentin. Histology revealed regions of non-myocyte nuclei, only in the right ventricle of the rats with pulmonary arterial hypertension. Immunohistochemistry demonstrated patches of CD68 and vimentin expression (markers for macrophages and fibroblasts, respectively) in the right side of the heart in these animals. TUNEL staining also revealed an increase in apoptosis in the right side of the heart. In the rabbit model of congestive heart failure, the region most affected by inflammation was the right atrium, while few changes were measured in the ventricles or cardiac conduction system. Although these results are surprising, it is suggested that the atria could be more sensitive to the physical stretch produced in this model. In the rat model of myocardial infarction, there were regions of non-myocyte nuclei in the border zone. This region also had increases in pro-inflammatory and fibrosis markers. In conclusion, this work has presented the novel finding that there can be inflammation in the cardiac conduction system in heart failure. This could be contributing to the arrhythmias seen in heart failure patients. This could possibly lead the way to anti-inflammatories as a possible novel therapeutic for heart failure patients.

La conductivité d'hétérojonctions gaas/gaalas a été étudiée, dans l'état de résistance zéro, en fonction du champ magnétique et de la température. Les résultats montrent que la conductivité est due a un processus de conduction par sauts entre plus proches voisins. Des expériences d'émission landau en infrarouge lointain sur les mêmes échantillons présentent un fort épaulement sur la raie de résonance cyclotron. Il semble donc que les expériences de transport et d'optique révèlent la même bande d'états localisés. Une explication qualitative de ces résultats est obtenue en supposant la présence d'impuretés de type coulombien près de l'interface. Des hétérojonctions gainas/inp sont aussi étudiées sur des quasi-géometries de corbino. La conductivité présente un caractère actif entre niveaux de landau.