The effects of high loading rates (HLR), and nano reinforcement on the mechanical response of adhesively-bonded SLJs with composite adherends, subjected to different loading (strain) rates are systematically investigated. The results are then compared to those of neat thermoset resin and thermo-plastic adhesive. More specifically, nano-reinforced and neat resin bonded joints mating carbon/epoxy and glass/epoxy adherends were subjected to tensile loadings under 1.5 and 3 mm/min and tensile impacts at a loading rate of 2.04E+5 mm/min. In some cases, additional tests were conducted under 15, 150, and 1500 mm/min to obtain additional properties gained using the nano-reinforcements for use in the further numerical investigations. The HLR tests were conducted, using a modified instrumented pendulum equipped with a specially designed impact load transfer apparatus. The dispersion of nanoparticles was facilitated using a mechanical stirrer and a three-roll mill machine. The failure mechanisms were studied with a scanning electron microscope.

Mes travaux de thèse portent sur l’interaction de type FRET (tranfert d’énergie résonant de Förster) entre une nanostructure semiconductrice colloïdale individuelle et le graphène. La première partie concerne l’établissement de la théorie du FRET et ce pour plusieurs types de nanostructures. Vient ensuite la partie expérimentale, à commencer par le montage optique ainsi que les méthodes d’analyse, tant pour la spectroscopie que pour la photoluminescence. Par la suite, nous décrivons les résultats obtenus pour divers types de nanocristaux sphériques en interaction directe avec le graphène (incluant des multicouches) : le transfert d’énergie a des effets drastiques sur la photoluminescence mais aussi sur le clignotement des nanocristaux. Puis nous étudions la dépendance du FRET avec la distance ; dans le cas des boîtes quantiques, nous observons une loi en 1/z^4. Par contre, dans le cas de nanoplaquettes, la fonction est plus complexe et dépend de la température. / My PhD subject is the FRET interaction (Förster-like resonant energy transfer) between single colloidal semiconductor nanostructures and graphene. The first part is about the development of the interaction theory with the graphene for several types of nanostructures. Then comes the experimental part, and firstly the optical setup together with the analysis methods, for both spectroscopy and photoluminescence. After that, we describe our results about different types of spherical nanocrystals directly interacting with graphene (which can be multilayer) : the energy transfer has a huge effect on the photoluminescence, as well as the blinking behaviour of the nanocrystals. Then we measure the dependency of the energy transfer as a function the distance ; in the case of quantum dots, we observe a 1/z^4 law. On another hand, in the case of nanoplatelets, the function is more complex and depends on the temperature.

Une approche mixte théorique/expérimentale a été utilisé pour analyser les composants semi-conducteurs des cellules solaires à boites quantiques, ainsi que les interfaces qui se forment entre eux. En ce qui concerne la partie théorique de cette thèse, tout d'abord on a identifié un protocole computationnel pour décrire les propriétés géométriques et électroniques du bulk et les surfaces de CdSe. Après, les nanoplaquettes CdSe de plusieurs épaisseurs et passivé par plusieurs ligands distincts ont été simulés. Ensuite, une hétéro-structure nanocristal - semi-conducteurs à large bande interdite a été modélisée, et ses propriétés structurelles, vibrationnelles et électroniques ont été calculées. Expérimentalement, des semi-conducteurs à large bande interdite sous le forme de nanobatôns, ainsi que des nanocristaux sous forme des nanoplaquettes et des boîtes quantiques CdSe ont été synthétisées. Les nanobatôns ont été sensibilisés avec des nanocristaux CdSe préparés ex situ et in situ. Ces hétérostructures semi-conducteurs ainsi préparées ont été caractérisées par spectroscopie d'absorption UV-VIS et Raman. Enfin, des cellules solaires incorporant ces systèmes ont été fabriquées et testées. L'approche combiné expérimentale/théorique qu'on a utilisée a rendu possible de contre-valider la capacité des méthodes expérimentales et théoriques pour caractériser les systèmes semi-conducteurs étudiées lors de cette thèse. De plus, on a pu établir des indications générales pour la sélection des composants pour ces dispositifs. Cette approche mixte peut être étendu pour étudier des hétérostructures semi-conducteurs dans une vaste gamme des applications optoélectroniques. / A mixed theoretical/experimental approach was used to analyze the semiconductor components of quantum dot sensitized solar cells and the interfaces formed between them. We first identified a computational protocol that accurately and efficiently describes the bulk and surface geometrical and electronic properties of CdSe. Then, we simulated CdSe nanoplatelets of various thicknesses, passivated by different ligands. Next, a model of the sensitizer - wide band gap semiconductor heterostructure was built and its structural, vibrational and electronic properties were calculated. In the meantime, computational results were compared to experimental data. Wide band gap semiconductors (WBSC) in the form of nanorods and sensitizer nanocrystals (CdSe nanoplatelets and quantum dots) were synthesized. The WBSC substrates were sensitized both by ex situ and in situ grown CdSe QDs. The as-prepared semiconductor systems were characterized by UV-VIS absorption and Raman spectroscopy. Finally, solar cells based on these heterostructures were fabricated and tested. The applied combined theoretical/experimental approach made it possible to cross-validate the capacity of computational and experimental methods for the characterization of the semiconductor systems studied in this thesis. Moreover, general guidelines for the screening of QDSC components could be drawn from the obtained results. The here proposed mixed theoretical/experimental approach can be extended to other semiconductor heterostructures in a wide variety of optoelectronic applications, and it could contribute to a better understanding of the working principle of these devices and improve their performance.

Ce travail de thèse porte sur le couplage d’émetteurs fluorescents (en l’occurrence des nanostructures semi-conductrices colloïdales) à leur environnement optique. Il se décompose en deux parties : dans la première, des structures photoniques (modes de Tamm optiques) sont caractérisées par le biais de la fluorescence de nanocristaux insérés dans ces structures. Dans la seconde, des nanoplaquettes individuelles de CdSe/CdS sont caractérisées par des études de microphotoluminescence sur différents types de substrats. Dans ces deux études, la mesure du diagramme de rayonnement par imagerie dans le plan de Fourier joue un rôle important, et son principe sera présenté en détail. Le mode optique de Tamm est un mode électromagnétique confiné entre un miroir de Bragg et une couche métallique. Nous avons couplé une couche de nanocristaux de CdSe/CdS avec des modes de Tamm optiques 2D et 0D. Le confinement latéral dans le cas du mode 0D est mis en évidence. Nous avons étudié la relation de dispersion de l’émission issue de différentes portions du disque et comparé ces résultats avec les simulations numériques. Enfin, en excitant différentes position sur le disque, nous avons montré que la direction d’émission dépend fortement de la position de la source au sein de la structure. D’autre part, nous avons mis en place une méthode fine pour déterminer la nature dipolaire (dipôle 1D ou 2D) et l’orientation d’un nano-émetteur individuel. L’idée principale est de mesurer à la fois, pour un seul émetteur, le diagramme de rayonnement et la polarisation d’émission. En choisissant un substrat adapté (de l’or ou du verre), ces mesures donnent des résultats théoriques très différents selon la nature et l’orientation du dipôle. Nous avons ensuite appliqué cette méthode sur les émetteurs nanoplaquettes de CdSe/CdS (dimensions 20x20x2 nm). Un accord parfait entre les mesures et les calculs analytiques nous confirme que l’émission d’une plaquette carrée peut être décrite par un dipôle 2D orienté dans le plan de la plaquette. Nous avons ensuite étudié l’émission d’une plaquette rectangulaire et montré une asymétrie dans le dipôle émetteur. Cette étude montre le rôle de la forme de la plaquette sur son dipôle d’émission, qui pourrait être expliqué par un effet d’antenne diélectrique. / Technological progress in the recent 30 years for reducing the size of semi-conductor materials offers the possibility to fabricate devices in which the electrons and holes are confined in a very small volume in three dimensions. When the dimension of the material is small (a few nanometers), the charges experience quantum confinement effects. This kind of nanomaterial is called nanocrystal or quantum dot [1]. These structures have the remarkable property that the energy levels are discretized, in a sense making them artificial atoms. At the beginning of 1980s, Efros, Ekimov et al. started the growth of II/VI semi-conductor nanocrystals in a vitreous matrix [2]. A few years later, colloidal synthesis methods were developed and nanocrystals with increasingly good optical properties were obtained [3-5]. These emitters have drawn intense attention because of their versatile manipulation in solution and biochemical functionalization, high quantum effciency, and photostability, tunable emission wavelength and broad absorption spectrum. By fluorescence microscopy, it is possible to study the optical properties of individual nanocrystals ; non classical effects such as single photon emission (even for nanocrystals at room temperature) are evidenced. Studying individual nano-emitters offers new ways to test the concepts of electromagnetics in the visible domain. Other manipulations are possible by nano structuring the environment around an emitter ; for instance, the use of antennas, which is ubiquitous in the radio and microwave domains, can be extended to nano-photonics, provided that sufficiently precise nano-fabrication techniques are available. The group "Nanophotonics and quantum optics" at the Institut de NanoSciences de Paris (INSP) studies how to manipulate light by coupling fluorescent emitters (individually or collectively) with their optical environment. The emission properties of nanoemitters depend strongly on their optical environment. This is expressed, as for the decay time of a radiating dipole, by Fermi's golden rule: where the initial and final state of the nanoemitter transition are taken into consideration; the polarization of these states can infuence highly the emission properties (determined by the symmetries of the transition and its associated orientation). The local state density which is mainly determined by the optical environment around the emitter and depends on the emission angular frequency. The electric field at the emitter position is included in the Hamiltonian (for a dipolar electric transition). Previously, our team has studied the coupling between the nanocrystal and different nanophotonic structures such as photonic crystals, plasmonic structures, plasmonic patch antennas etc...

Over the past years, research efforts have focused on adding highly conductive nanoparticles, such as carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), into polymers to improve their electrical conductivity or to tailor their piezoresistive behavior. Resultant materials are typically described by the weight or volume fractions of their nanoparticles. The weight/volume fraction alone is a very global quantity, making it a poor evaluator of a doping configuration. Knowing which particles actually participate in improving electrical conductivity can optimize the doping strategy. Additionally, conductive particles are only capable of charge transfer over a very short range, thus most of them do not form part of the conduction path. Thus, understanding how these particles are arranged is necessary to increase their efficiency. First, this work focuses on polymers loaded with CNTs. A computational modeling strategy based on a full morphological analysis of the CNT network is presented to systematically analyze conductive networks and show how particles are arranged. A definition of loading efficiency is provided based on the results obtained from this morphology analysis. This study provides useful guidelines for designing these types of materials based on important features, such as representative volume element, nanotube tortuosity and length, tunneling cutoff distance, and efficiency. Second, a computational approach is followed to study the conductive network formed by hybrid particles in polymer nanocomposites. These hybrid particles are synthesized by growing CNTs on the surfaces of GNPs. The objective of this study is to show that the higher electrical conductivity of these composites is due to the hybrids forming a segregated structure. Polymers loaded with hybrid particles have shown a higher electrical conductivity compared with classical carbon fillers: only CNTs, only GNPs or mixed CNTs and GNPs. This is done to understand and compare the doping efficiency of the different types of nanoparticles. Finally, some parameters of the hybrid particle are studied: CNT density on GNPs, and CNT and GNP geometries. Recommendations to further improve the composite’s conductivity based on these parameters are presented. It is noted that this work is the first time the hybrid particle is studied through a computational approach.

The surface and interface of the metal nanoclusters and semiconducting nanomaterials play a key role in determining the electronic structure and overall photophysical properties. A single strand DNA stabilizes the metal nanoclusters, but it also influences the structural change, solvation free energy, and photophysical properties. On the other hand, surface and interface states in Pb and Cd chalcogenide nanomaterials affect the phonon mediated hot carrier relaxation. We applied DFT and DFT based non-adiabatic dynamics methods to study the surface and interface?s effects on the photoexcited processes. In the first part, we have studied the Ag nanoclusters' photophysical properties that are affected by the structural isomers, redox potential, nucleobase passivation, and cluster size. Ag nanoclusters are shown alternative reduction potential, which makes nanoclusters of singlet spin multiplicity thermodynamically favorable. Besides, the optically bright transition in the range of 2.5-3.5 eV is shown metal to ligand charge transfer. It is modulated by the s+p+d orbital mixing in the hole and electron states. We also simulate the charge transfer from the photoexcited PbS QD to organic dye (PDI) attached to the QD surface. Depending on the linker group and the dipole moment of neighboring passivating ligands, the PDI-QD conformations are varies. In response to structural change, the total dipole moment is modulated, changing its electronic structure and hence the photoexcited electron transfer rate from the PbS QD to PDI. We also investigate the inorganic-inorganic interactions in the PbCl2 bridged PbSe NPL and PbSe|CdSe Janus heterostructure. The energy dissipation rate of hot electrons is slower in NPL than the hot hole, while hot e-h relaxed to the band-edge by ?1.0ps in the QD. The slower relaxation rate is rationalized by a large average intraband energy difference and smaller coupling term. Besides, the hot carriers in the NPL are spatially separated by ?1.00 ps, which is a favorable condition for the carrier multiplication process. In Janus QD, (100) interfacial layer creates a structural mismatch in the CdSe part. Besides, the energy offset between the valance localized on PbSe and CdSe part is minimum in the PbSe Janus QD of an interface of (111) facet.

No description available.

Nanomaterialen beginnen sich aus der akademischen Welt heraus langsam in kommerzielle Produkte zu entwickeln. Dabei helfen ihnen einzigartige optoelektronische Eigenschaften. Damit ein solcher Übergang gelingt, ist es notwendig, die Nanoteilchen durch geeignete Analyseverfahren zu verstehen und Wege zur gezielten Manipulation bestimmter Eigenschaften analytisch zu begleiten. Die vorliegende Arbeit hat sich zum Ziel gemacht eine spektroelektrochemische Methode, die Potential-modulierte Absorptionsspektroskopie (EMAS), weiterzuentwickeln. Mit EMAS können die optoelektronischen Eigenschaften von Halbleiternanomaterialen untersucht werden, wobei die Methode durch ihre besondere Empfindlichkeit im Vergleich zu anderen spektroelektrochemischen Methoden beeindruckt. Im Rahmen der Arbeit wurde das Spektrum von EMAS zunächst von sphärischen Nanopartikeln auf anisotrope Nanoplatelets erweitert, wobei sowohl ein als auch mehrphasige Systeme betrachtet wurden. Anschließend konnte der Messbereich vom sichtbaren Bereich bis ins nahe Infrarot erweitert werden, was auch die Untersuchung von Partikeln möglich macht, die eine potentielle Anwendung in der Konversion solarer Energie haben. Weiterhin wurden neue Werkzeuge entwickelt und EMAS Varianten betrachtet. Zusammenfassend präsentiert sich EMAS als leistungsstarke spektroelektrochemische Analysemethode deren Weiterentwicklung positiv auf die voranschreitende Nanopartikelforschung wirken wird.

No description available.

The discovery of carbon nanotubes in 1990s popularized a new area of research in materials science called Nanoscience. In the following decades, several carbon based nanoparticles were discovered or engineered and with the discovery of Graphene nanoplatelets (GNP) in 2010, carbon based nanoparticles were propelled as the most promising class of nanoparticles. High mechanical strength and stiffness, excellent electrical and thermal conductivity, and high strength to weight ratios are some of the unique abilities of CNTs and GNPs which allow their use in a wide array of applications from aerospace materials to electronic devices. In the current work presented herein, CNTs and GNPs are added to polymeric materials to create a nanocomposite material. The effects of this nanoparticle addition (a.k.a reinforcement) on the mechanical properties of the nanocomposite polymer materials are studied. Specifically, efforts are focused on studying fracture toughness, a material property that describes the material's ability to resist crack growth. Relative to the conventional metals used in structures, epoxy-based composites have poor fracture toughness. This has long been a weak link when using epoxy composites for structural applications and therefore several efforts are being made to improve their fracture toughness. In the first, second and third chapters, the enhancement of fracture toughness brought about by the addition of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) was investigated. CNT-Epoxy and GNP-Epoxy Compact Tension (CT) samples were fabricated with 0.1% and 0.5% nanofiller weight concentrations. The potential synergistic effects of dual nanofiller reinforcements were also explored using CNT/GNP-Epoxy CT samples at a 1:3, 3:1 and 1:1 ratio of CNT:GNP. Displacement controlled CT tests were conducted according to ASTM D5045 test procedure and the critical stress intensity factor, $K_{IC}$, and the critical fracture energy, $G_{IC}$, were calculated for all the material systems. Significant enhancements relative to neat epoxy were observed in reinforced epoxies. Fracture surfaces were analyzed via scanning electron microscopy. Instances of CNT pullouts on the fracture surface were observed, indicating the occurrence of crack bridging. Furthermore, increased surface roughness, an indicator of crack deflection, was observed along with some crack bifurcations in the GNP-Epoxy samples. In the fourth chapter of Part I, the influence of pre-crack characteristics on the Mode-I fracture toughness of epoxy is investigated. Pre-crack characteristics such as pre-crack length, crack front shape, crack thickness and crack plane profile are evaluated and their influence on the peak load, fracture displacement, and the critical stress intensity factor, $K_{IC}$ is studied. A new method of razor blade tapping was used, which utilized a guillotine-style razor tapping device to initiate the pre-crack and through-thickness compression to arrest it. A new approach of quantitatively characterizing the crack front shape using a two-parameter function is introduced. Surface features present on the pre-crack surface are classified and their effects on the post crack initiation behavior of the sample are analyzed. This study aims to identify and increase the understanding of the various factors that cause variation in the fracture toughness data of polymeric materials, thus leading to more informed engineering design decisions and evaluations. Chapters six and seven of Part II investigate the SHM capabilities of dispersed MWCNTs in mock, inert, and active energetics. In these experimental investigations, the strain and damage sensing abilities of multi-walled carbon nanotube (MWCNT) networks embedded in the binder phase of polymer bonded energetics (PBEs) are evaluated. PBEs are a special class of particulate composite materials that consist of energetic crystals bound by a polymer matrix, wherein the polymer matrix serves to diminish the sensitivity of the energetic phase to accidental mechanical stimuli. The structural health monitoring (SHM) approach presented in this work exploits the piezoresistive properties of the distributed MWCNT networks. Major challenges faced during such implementation include the low binder concentrations of PBEs, presence of conductive/non-conductive particulate phases, high degree of heterogeneity in the PBE microstructure, and achieving the optimal MWCNT dispersion. In chapter seven, Ammonium Perchlorate (AP) crystals as the oxidizer, Aluminum grains as the metallic fuel, and Polydimethylsiloxane (PDMS) as the binder are used as the constituents for fabricating PBEs. To study the effect of each constituent on the MWCNT network's SHM abilities, various materials systems are comprehensively studied: MWCNT/PDMS (nBinder) materials are first evaluated to study the binder's electromechanical response, followed by AP/MWCNT/PDMS (inert nPBE) to assess the impact of AP addition, and finally, AP/AL/MWCNT/PDMS (active nPBE-AL) to evaluate the impact of adding conductive aluminum grains. Compression samples (ASTM D695) were fabricated and subjected to monotonic compression. Electrical resistance is recorded in conjunction with the mechanical test via an LCR meter. Gauge factors relating the change in normalized resistance to applied strain are calculated to quantify the electromechanical response. MWCNT dispersions, and mechanical failure modes are analyzed via scanning electron microscopy (SEM) imaging of the fracture surfaces. Correlations between the electrical behavior in response to the mechanical behavior are presented, and possible mechanisms that influence the electromechanical behavior are discussed. The results presented herein demonstrate the successful ability of MWCNT networks as structural health monitoring sensors capable of real-time strain and damage assessment of polymer bonded energetics. / Doctor of Philosophy / The discovery of carbon nanotubes in 1990s popularized a new area of research in materials science called Nanoscience. Carbon nanotubes (CNTs) are one of several forms of Carbon, meaning a differently structured carbon molecule in the same physical state similar to diamonds, graphite, and coal. In the following decades, several carbon based nanoparticles were discovered or engineered and with the discovery of Graphene (GNP) in 2010, carbon based nanoparticles were propelled as the most promising class of nanoparticles. High mechanical strength and stiffness, excellent electrical and thermal conductivity, and high strength to weight ratios are some of the unique abilities of CNTs and GNPs which allow their use in a wide array of applications from aerospace materials to electronic devices. In the current work presented herein, CNTs and GNPs are added to polymeric materials to create a nanocomposite material, where the term "composite" refers to a material prepared with two or more constituent materials. The effects of this nanoparticle addition (a.k.a reinforcement) on the mechanical properties of the nanocomposite polymer materials are studied. Specifically, efforts are focused on studying fracture toughness, a material property that describes the material's ability to resist crack growth. Fracture toughness is a critical material property often associated with material and structural failures, and as such it is very important for safe and reliable engineering design of structures, components, and materials. Moving from a single function (i.e. mechanical enhancement) to a more multi-functional role, taking advantage of the excellent electrical and mechanical abilities of CNTs, a structural health monitoring system is developed for use in polymer bonded energetics (eg. solid rocket propellants). When a material undergoes mechanical deformation or damage, the measured electrical properties of the material undergo some change as well. Using sensor networks built with multiple CNTs dispersed within a polymeric material, a whole structure can be made into an effective sensor where by simply monitoring the electrical properties, the extent of material deformation and damage can be known. Such a system is geared towards providing early warning of impending catastrophic material failures thus directly improving the safety during material handling and operations.