Self-assembling peptides have emerged as new nanobiomaterials and received considerable attention in the areas of nanoscience and biomedical engineering. In this category are ionic-complementary peptides, which contain a repeating charge distribution and alternating hydrophobic and hydrophilic residues in the amino acid sequence, leading to the unusual combination of amphiphilicity and ionic complementarity. Although their self-assembled nanostructures have been successfully applied as scaffoldings for tissue engineering, novel materials for regenerative medicine and nanocarriers for drug and gene/siRNA delivery, aspects of the assembly process remain unclear. Since many of these applications involve peptide-modified interfaces and surfaces, a better understanding and control of the peptide assembly on a surface are very crucial for future development of peptide-based applications in nano-biotechnology. This thesis contains two major parts: (i) fundamental study of the assembly of a model ionic-complementary peptide EAK16-II on surfaces and (ii) potential applications of such a peptide in surface modification and nanofabrication. In the fundamental study, EAK16-II assembly on negatively charged mica was first investigated via in-situ Atomic Force Microscopy (AFM). It was found that EAK16-II nanofiber growth on mica is surface-assisted and follows a nucleation and growth mechanism involving two steps: (i) adsorption of nanofibers and fiber clusters (from the bulk solution) on the surface to serve as the seeds and (ii) fiber elongation from the active ends of the seeds. Such a process can be controlled by adjusting the solution pH since it modulates the adsorption of the seeds and the growth rates. Unlike what is observed on mica, EAK16-II formed well-ordered nanofiber patterns with preferential orientations at angles of 60° or 120° to each other on hydrophobic highly ordered pyrolytic graphite (HOPG) surfaces, resembling the crystallographic structure of the graphite. Nanofiber formation on HOPG is also surface-assisted and adopts a nucleation and growth mechanism that can be affected by solution pH. The pH-dependent adsorption of peptides to HOPG is attributed to the resulting changes in peptide hydrophobicity. It was also found that EAK16-II assembly can be induced by the mechanical force of a tapping AFM tip. It occurs when the tip cuts the adsorbed EAK16-II nanofibers into segments that then serve as seeds for new nanofiber growth. This finding allows one to locally grow nanofibers at specific regions of the surface. The tip cutting has been combined with the effect that solution pH has on peptide assembly to develop a new AFM lithography method to fabricate local patterned peptide nanostructures on HOPG. To study the use of EAK16-II for surface modification applications, the wettability and stability of the peptide-modified surfaces were characterized. EAK16-II-modified mica becomes slightly hydrophobic as the water contact angle increases from <10° to 20.3 ± 2.9°. However, the hydrophobicity of the HOPG surface is significantly reduced, as reflected in a contact angle change from 71.2 ± 11.1° to 39.4 ± 4.3°. The EAK16-II-modified mica surface is stable in acidic solution, while the modified HOPG surface is stable in both acidic and alkaline solutions. The peptide-modified HOPG shows potential as a biocompatible electrode for (bio)molecular sensing. The ability of EAK16-II to form nanofibers on surfaces has also promoted research on peptide-based metallic nanowire fabrication. Our approach is to provide EAK16-II with metal ion binding ability by adding a GGH motif to the C-terminus. This new peptide EAK16(II)GGH has been found to form one-dimensional nanofibers while binding to Cu2+ ions. The dimensions of the nanofibers were significantly affected by the nature of the anions (SO42-, Cl- and NO3-) in the copper salt solution. This work demonstrates the potential usage of EAK16-II for nanowire fabrication.

Flexible electronics attract research and commercial interests in last 2 decades for its flexibility, low cost, light weight and etc. To develop and improve the electro-mechanical properties of flexible electrodes is the most critical and important step. In this work, we have performed nanomechanical and electro-mechanical characterization of materials for flexible electrode applications, including metallic nanowires (NWs), indium tin oxide (ITO)-based and carbon nanotube (CNT)-based electrodes. First, we designed and developed four different testing platforms for nanomechanical and electro-mechanical characterization purpose. For the nano/sub-micro size samples, the micro mechanical devices can be used for uni-axial and bi-axial loading tests. For the macro size samples, the micro tester will be used for in situ monotonic tensile test, while the fatigue tester can be used for in situ cyclic tensile or bending testing purpose. Secondly, we have investigated mechanical behaviors of single crystalline Ni nanowires and single crystalline Cu nanowires under uni-axial tensile loading inside a scanning electron microscope (SEM) chamber. We demonstrated both size and strain-rate dependence on yield stress of single-crystalline Ni NWs with varying diameters (from 100 nm to 300 nm), and themolecular dynamics (MD) simulation helped to confirm and understand the experimental phenomena. Also, two different fracture modes, namely ductile and brittle-like fractures, were found in the same batch of Cu nanowire samples. Finally, we studied the electro-mechanical behaviors of flexible electrodes in macro scale. We reported a coherent study integrating in situ electro-mechanical experiments and mechanics modeling to decipher the failure mechanics of ITO-based and CNT-based electrodes under tension. It is believed that our combined experimental and simulation results provide some further insights into the important yet complicated deformation mechanisms for nanoscale metals and fracture mechanism for flexible electrodes applications.

Self-assembling peptides have emerged as new nanobiomaterials and received considerable attention in the areas of nanoscience and biomedical engineering. In this category are ionic-complementary peptides, which contain a repeating charge distribution and alternating hydrophobic and hydrophilic residues in the amino acid sequence, leading to the unusual combination of amphiphilicity and ionic complementarity. Although their self-assembled nanostructures have been successfully applied as scaffoldings for tissue engineering, novel materials for regenerative medicine and nanocarriers for drug and gene/siRNA delivery, aspects of the assembly process remain unclear. Since many of these applications involve peptide-modified interfaces and surfaces, a better understanding and control of the peptide assembly on a surface are very crucial for future development of peptide-based applications in nano-biotechnology. This thesis contains two major parts: (i) fundamental study of the assembly of a model ionic-complementary peptide EAK16-II on surfaces and (ii) potential applications of such a peptide in surface modification and nanofabrication. In the fundamental study, EAK16-II assembly on negatively charged mica was first investigated via in-situ Atomic Force Microscopy (AFM). It was found that EAK16-II nanofiber growth on mica is surface-assisted and follows a nucleation and growth mechanism involving two steps: (i) adsorption of nanofibers and fiber clusters (from the bulk solution) on the surface to serve as the seeds and (ii) fiber elongation from the active ends of the seeds. Such a process can be controlled by adjusting the solution pH since it modulates the adsorption of the seeds and the growth rates. Unlike what is observed on mica, EAK16-II formed well-ordered nanofiber patterns with preferential orientations at angles of 60° or 120° to each other on hydrophobic highly ordered pyrolytic graphite (HOPG) surfaces, resembling the crystallographic structure of the graphite. Nanofiber formation on HOPG is also surface-assisted and adopts a nucleation and growth mechanism that can be affected by solution pH. The pH-dependent adsorption of peptides to HOPG is attributed to the resulting changes in peptide hydrophobicity. It was also found that EAK16-II assembly can be induced by the mechanical force of a tapping AFM tip. It occurs when the tip cuts the adsorbed EAK16-II nanofibers into segments that then serve as seeds for new nanofiber growth. This finding allows one to locally grow nanofibers at specific regions of the surface. The tip cutting has been combined with the effect that solution pH has on peptide assembly to develop a new AFM lithography method to fabricate local patterned peptide nanostructures on HOPG. To study the use of EAK16-II for surface modification applications, the wettability and stability of the peptide-modified surfaces were characterized. EAK16-II-modified mica becomes slightly hydrophobic as the water contact angle increases from <10° to 20.3 ± 2.9°. However, the hydrophobicity of the HOPG surface is significantly reduced, as reflected in a contact angle change from 71.2 ± 11.1° to 39.4 ± 4.3°. The EAK16-II-modified mica surface is stable in acidic solution, while the modified HOPG surface is stable in both acidic and alkaline solutions. The peptide-modified HOPG shows potential as a biocompatible electrode for (bio)molecular sensing. The ability of EAK16-II to form nanofibers on surfaces has also promoted research on peptide-based metallic nanowire fabrication. Our approach is to provide EAK16-II with metal ion binding ability by adding a GGH motif to the C-terminus. This new peptide EAK16(II)GGH has been found to form one-dimensional nanofibers while binding to Cu2+ ions. The dimensions of the nanofibers were significantly affected by the nature of the anions (SO42-, Cl- and NO3-) in the copper salt solution. This work demonstrates the potential usage of EAK16-II for nanowire fabrication.

Les matériaux conducteurs transparents font partie intégrante de très nombreux dispositifs optoélectroniques (de type cellule solaire, OLED, capteur tactile, etc.). Pour des raisons techniques et économiques (évolution des marchés vers les applications flexibles),d’importantes recherches sont mises en œuvre pour remplacer les couches minces d’oxydes métalliques (principalement en ITO) actuellement utilisées. En effet, de par sa faible résistance mécanique à la flexion et son coût d’élaboration élevé, l’ITO ne répond pas aux besoins de ces marchés émergents. L’utilisation de nanomatériaux en solution, et en particulier de nanofils métalliques, apparaît comme une alternative très prometteuse qui offre la possibilité d’utiliser des méthodes d’impression bas coût et grande surface. Ces travaux de thèse présentent les procédés de synthèse et purification de nanofils d’argent et de cuivre à forme facteur de forme. L’impression par spray de réseaux 2D percolants permet la réalisation d’électrodes flexibles démontrant d’excellentes propriétés optoélectroniques.Les nanofils d’Ag semblent toutefois être de meilleurs candidats que les nanofils de Cu (synthèse multi-grammes, impression grande surface, meilleure stabilité à l’air, etc.). Ainsi,après avoir identifié les principaux verrous technologiques ayant trait à l’utilisation des AgNF (rugosité, adhésion, travail de sortie, stabilités environnementales/électriques), différentes solutions ont été proposées dans le but d’améliorer les performances et de rendre les nanofils d’argent compatibles avec l’intégration en dispositif. Le potentiel des nanofils d’argent en tant que remplaçants de l’ITO a été confirmé grâce à l’intégration d’électrodes dans divers dispositifs fonctionnels (cellule solaire organique, capteur capacitif ou encore film chauffant). / Transparent conductive thin films are widely used in technologies like solar cells, light-emitting diodes, and display technologies. The fabrication of transparent conductive films is currently realized with thin films of transparent conductive oxides (TCOs), and in particular indium tin oxide (ITO). The as-made ITO transparent conductors suffer from limitations like costly fabrication process and brittleness. The use of solution-processable nanomaterials, and especially metallic nanowires, appears as a promising alternative since it affords a large area, low-cost deposition method with high performances.This thesis report that by optimizing synthesis methods and printing methods, flexible electrodes demonstrating excellent opto-electronic properties were performed, either with the use of a percolating network of silver nanowires or copper nanowires. The silver nanowires, however, seem to be better candidates than the copper nanowires (synthesized substantial amount, printing large area, better stability in air, etc.). Thus, having identified the main technological barriers related to the use of Ag NW (roughness, adhesion, work function, electrical/environmental stabilities), different solutions have been proposed in order to make the silver nanowires compatible with as many devices for integration.The potential of silver nanowires as replacements for ITO was confirmed through the integration of electrodes in various functional devices (organic solar cell, capacitive touch sensor or the film heater).

L’objectif de ces travaux est pour d’apporter des solutions innovantes à la réalisation de dispositifs passifs performants et compacts, susceptibles d’intéresser les concepteurs de circuits RF et millimétriques. Ces dispositifs sont basés notamment sur des lignes microrubans à ondes lentes sur substrat structuré, que cela soit sur PCB avec des vias borgnes pour la RF, ou nanostructurés sur membranes à nanofils pour le millimétrique. Les travaux complets comprennent (i) une analyse de la topologie, (ii) un développement du modèle équivalent validée par des simulations électromagnétiques (HFSSTM) et des mesures sur PCB et sur des membranes brésiliennes en millimétrique, (iii) des abaques de conceptions et (iv) des applications à la conception des nouveaux dispositifs passifs miniaturisés. Notre lignes offrent une grande souplesse de conception et peuvent être placées indifféremment sur le substrat structuré sans modification de leurs paramètres électriques. Un nouveau coupleur hybride miniaturisé par l’utilisation de cette ligne est présenté comme une preuve de concept. Pour aller plus loin, une étude comparable des structures de lignes microrubans couplées à ondes lentes est développée. Le principe du couplage sur substrat structuré est d’abord exposé avec une présentation de ses avantages et inconvénients, puis un modèle est également proposé dans le but de réaliser un coupleur co-directif 0-dB miniaturisé par l’utilisation de ces lignes. De plus, un des parties essentielles de ces travaux concerne l’utilisation de la structure microruban à onde lente pour la miniaturisation de dispositifs passifs non-réciproques : un nouvel isolateur microruban compact avec l’introduction de vias dans le ferrite et une nouvelle conception de circulateur miniaturisé sur le substrat ferrite-diélectrique avec un réseau de vias borgnes. / This work focuses on providing innovate solutions into the realization of high-quality and compact passive devices for designer on RF and millimeter-wave bands. These devices are based on slow-wave microstrip lines on structured substrate, either on PCB with blind vias for RF applications, or on metallic nanowire membrane. The complete works include (i) an analysis of topology, (ii) a development of equivalent model validated by the electromagnetic simulations (HFSSTM) and the measurements, (iii) design charts and (iv) applications on design of novel miniaturized passive devices. These transmission lines give the flexibility for designers and capability to be indifferently placed on structured substrate without any impact on their electrical parameters. A novel miniaturized hybrid coupler using this line is proposed, as a proof of concept. In the other hand, a comparable study on the structure of slow-wave coupled microstrip lines is developed. The principal of coupling on structured substrate is shown for their advantages and drawbacks and then an electrical model is also proposed in order to realize a miniaturized 0-dB forward-wave directional coupler using these lines. Moreover, an essential part of this thesis concerns the utilization of the slow-wave microstrip structure to miniaturize the non-reciprocal passive devices: a novel microstrip isolator with the introduction of vias inside the ferrite and a novel design of the miniaturized circulator on a ferrite-dielectric substrate with blind vias.