Cette étude concerne la caractérisation optique non linéaire (NL) principalement d’ordre 3 dans le visible, l’UV et l’IR en régime picoseconde de différents matériaux tels que certains solvants, le niobate de lithium et les nano-feuilles de graphène. Nous présentons d’abord les expressions des susceptibilités NL. Nous décrivons ensuite la technique de caractérisation Z-scan et ses variantes. Nous présentons une nouvelle méthode qui combine les avantages de Z-scan avec ceux de la microscopie en champ sombre. Nous montrons que cette technique d’imagerie, nommée DFZscan (Dark Field Z-scan), peut mesurer les coefficients de réfraction NL en présence d'une forte absorption NL. Les résultats expérimentaux montrent une importante amélioration de la sensibilité. Finalement, nous comparons les réponses NL des solvants les plus utilisés, dont l’eau qui possède la réfraction NL la plus faible. Ce liquide est utilisé pour caractériser la réponse NL d’une suspension de points quantiques de graphène. Grâce à un modèle simple, nous estimons l'indice de réfraction et d’absorption NL d'une nanofeuille de graphène monocouche. Nous étudions également les non linéarités d’ordres supérieurs dans les matériaux liquides (toluène) et solides (LiNbO3) en vue d’applications potentielles pour la génération de la deuxième harmonique et des modulateurs de guides d'ondes. Ces coefficients peuvent intéresser une grande communauté de chercheurs dans des domaines aussi variés que la filamentation, les solitons, le traitement tout optique du signal et les réseaux de télécommunications. / This study concerns the nonlinear (NL) optical characterization mainly of order 3 in the visible, UV and IR in the picosecond regime of different materials such as solvents, lithium niobate and graphene nanosheets. We first present the expressions of NL susceptibilities. We then describe the Z-scan characterization technique and its variants. We present a new method that combines the advantages of Z-scan with those of dark field microscopy. We show that this imaging technique, called DFZ-scan (Dark Field Z-scan), can measure NL refractive coefficients in the presence of high NL absorption. The experimental results show a significant improvement in the sensitivity. Finally, we compare the NL responses of the most commonly used solvents, including water with the lowest NL refraction. This liquid is used to characterize the NL response of a suspension of graphene quantum dots. Using a simple model, we estimate the refractive index and absorption index NL of a single-layer graphene nanosheet. We also studied higher order non-linearities in liquid (toluene) and solid (LiNbO3) materials for potential applications in second harmonic generation and waveguide modulators. These coefficients can be of interest to a large community of researchers in fields as diverse as filamentation, soliton, all-optical signal processing and telecommunications networks.

<p>U okviru doktorske disertacije predstavljene su elektronska i fononska struktura odabranih organometalnih materijala koji u svom sastavu imaju metale cink, kobalt ili bakar i organsko jedinjenje piridoksalaminogvanidin (PLAG). Predstavljene su realizacija i karakteristike organske svetleće diode zasnovane na najboljem od ispitivanih materijala. Urađena je detaljna analiza fotoluminescentnih spektara i njihovo razlaganje na proste komponente koristeći Lorencov model. Izvršeno je poređenje sa od ranije poznatim materijalom koji pokazuje visok stepen luminescencije. S obzirom da istraživanja vezana za organske svetleće diode uzimaju sve veći zamah i da ove diode postaju sve prisutnije u industrijskoj serijskoj proizvodnji, napravljena je detaljna analiza ove tehnologije i mehanizama koji se kriju iza nje. Urađeno je podrobno istraživanje kako na nivou elektrona u datim supstancama, tako i na nivou sloja organske svetleće diode. Na kraju je izvršena analiza rada diode sa integrisanim slojem sa materijalom koji u sebi sadrži cink i PLAG.</p> / <p>In this thesis electronic and phonon structure of specific organometallic<br />materials which have zinc, cobalt, copper metals and organic compound<br />pyridoxalaminoguanidin are presented. Implementation and characteristics of<br />organic light emitting diode based on the best material among examined<br />ones are also showed up. Detailed analysis of photoluminescence spectra<br />was done and its decomposition to its elementar components using<br />Lorentzian multipeak method. Comparison to well-known material that shows<br />high level of luminescence was implemented. In accordance to the fact that<br />research of organic light emitting diodes expands and that these diodes start<br />to be more present in industrial serial production, detailed analysis of this<br />technology and mechanisms behind it are made. Thorough research was<br />done both on electron level in these substances and organic light emitting<br />diode layer level. Finally, analysis of diode operation with integrated layer<br />made of material which includes zinc and pyridoxalaminoguanidin compound<br />is implemented.</p>

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The selective laser melting (SLM) process allows for the control of unique part form and function characteristics not achievable with conventional manufacturing methods and has thus gained interest in several industries such as the aerospace and biomedical fields. The fabrication processing parameters selected to manufacture a given part influence the created material microstructure and the final mechanical performance of the part. Understanding the process-structure and structure-performance relationships is very important for the design and quality assurance of SLM parts. Image based analysis methods are commonly used to characterize material microstructures, but are very time consuming, traditionally requiring manual segmentation of imaged features. Two Python-based image analysis tools are developed here to automate the instance segmentation of manufacturing defects and subgranular cell features commonly found in SLM 316L stainless steel (SS) for quantitative analysis. A custom trained mask region-based convolution neural network (Mask R-CNN) model is used to segment cell features from scanning electron microscopy (SEM) images with an instance segmentation accuracy nearly identical to that of a human researcher, but about four orders of magnitude faster. The defect segmentation tool uses techniques from the OpenCV Python library to identify and segment defect instances from optical images. A melt pool structure generation tool is also developed to create custom melt-pool geometries based on a few user inputs with the ability to create functionally graded structures for use in a virtual testing framework. This tool allows for the study of complex melt-pool geometries and graded structures commonly seen in SLM parts and is applied to three finite element analyses to investigate the effects of different melt-pool geometries on part stress concentrations. / Master of Science / Recent advancements in additive manufacturing (AM) processes like the selective laser melting (SLM) process are revolutionizing the way many products are manufactured. The geometric form and material microstructure of SLM parts can be controlled by manufacturing settings, referred to as fabrication processing parameters, in ways not previously possible via conventional manufacturing techniques such as machining and casting. The improved geometric control of SLM parts has enabled more complex part geometries as well as significant manufacturing cost savings for some parts. With improved control over the material microstructure, the mechanical performance of SLM parts can be finely tailored and optimized for a particular application. Complex functionally graded materials (FGM) can also easily be created with the SLM process by varying the fabrication processing parameters spatially within the manufactured part to improve mechanical performance for a desired application. The added control offered by the SLM process has created a need for understanding how changes in the fabrication processing parameters affect the material structure, and in turn, how the produced structure affects the mechanical properties of the part. This study presents three different tools developed for the automated characterization of SLM 316L stainless steel (SS) material structures and the generation of realistic material structures for numerical simulation of mechanical performance. A defect content tool is presented to automatically identify and create binary segmentations of defects in SLM parts, consisting of small air pockets within the volume of the parts, from digital optical images. A machine learning based instance segmentation tool is also trained on a custom data set and used to measure the size of nanoscale cell features unique to 316L (SS) and some other metal alloys processed with SLM from scanning electron microscopy (SEM) images. Both these tools automate the laborious process of segmenting individual objects of interest from hundreds or thousands of images and are shown to have an accuracy very close to that of manually produced results from a human. The results are also used to analyze three different samples produced with different fabrication processing parameters which showed similar process-structure relationships with other studies. The SLM structure generation tool is developed to create melt pool structures similar to those seen in SLM parts from the successive melting and solidification of material from the laser scanning path. This structural feature is unique to AM processes such as SLM, and the example test cases investigated in this study shows that changes in the melt pool structure geometry have a measurable effect, slightly above 10% difference, on the stress and strain response of the material when a tensile load is applied. The melt pool structure generation tool can create complex geometries capable of varying spatially to create FGMs from a few user inputs, and when applied to existing simulation methods for SLM parts, offers improved estimates for the mechanical response of SLM parts.

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[pt] Neste trabalho é apresentado o estudo dos dispositivos orgânicos emissores de luz fosforescentes (PHOLED) baseados em compostos de baixo peso molecular. O estudo foi fundamentado nas análises dos complexos baseados no íon de Ir3+: [Ir(t-pzp)2pic] [fac-Ir(t-bupzp)3] e outros complexos já estudados anteriormente a base de Eu3+: [Eu(DBM)3PHEN] e [Eu(DBM)3DMSO2]. No desenvolvimento dos PHOLEDs, a dopagem de uma matriz orgânica com estes complexos reveste uma importância fundamental. Por tanto, como o intuito de estudar e analisar estes sistemas os complexos foram dopados com diversas concentrações em diferentes matrizes orgânicas. Os resultados obtidos revelaram que no caso dos complexos de Ir3+ os melhores valores da concentração do complexo encontram-se na faixa 13-15 porcento em peso. Já no caso dos complexos de íons de terra rara (Eu3+) as melhores concentrações devem ser superiores a 15 porcento em massa, para que ocorra uma transferência de energia eficiente e mantendo o espectro de emissão dos complexos resultando em um aumento da eficiência externa dos dispositivos. Neste trabalho foi desenvolvida também, uma metodologia que, combinando as técnicas de XRF e RBS, permite elaborar um gráfico de calibração para a determinação da concentração efetiva do dopante nos diferentes filmes co-depositados. Finalmente, para aumentar a eficiência dos PHOLEDs foi investigado o efeito da vibração do substrato durante a deposição térmica dos filmes. Os resultados indicam uma redução na densidade de aglomerados e na rugosidade, além de uma melhoria na homogeneidade dos filmes depositados. O aumento de 40 porcento na eficiência do dispositivo fabricados indica que a técnica de vibração é promissora para o desenvolvimento de dispositivos eficientes. / [en] This thesis reports the investigation of the phosphorescent organic light emitting devices (PHOLED) based on low molecular compounds. The study was carried out by analyzes the optical and electrical characteristics of thin films of Ir3+: [Ir(t-pzp)2pic] and [fac-Ir(t-bupzp)3] and other complexes based on Eu3+: [Eu(DBM)3PHEN] and [Eu(DBM)3(DMSO)2]. In developing of PHOLEDs, technology, the doping of an organic matrix with these complexes has a fundamental importance. Therefore, in order to investigate these systems Ir3+ and Eu3+ organic complexes were used as doping with a variety of concentrations in different organic matrix. The results revealed that in the case of Iridium complexes the best values are in the range 13-15 percent. On the other hand, for the rare earth complexes the best concentrations should be greater than 15 percent in order to obtain a efficient energy transfer preserving the emission spectrum of the complexes. Furthermore, the use of the doping results in an increased of the external efficiency of the device. In this work, a methodology combining the XRF and RBS techniques was also developed which allows the direct determination of the effective dopant concentration in co-deposited films through a calibration curve. Finally, to increase the efficiency of the PHOLEDs, the effect of mechanical vibration of the substrate on the thin films characteristics during the thermal deposition was investigated. The results indicate a reduction in the clusters density and film roughness, and an improved homogeneity of the deposited films. The 40 percent increase in efficiency of the devices fabricated under these conditions is a clear indication that the technology holds promise for the development of efficient devices.

This thesis presents a study on two types of X-ray diffraction methodologies applied to the characterization of amorphous materials. The purpose of this study was to assess the feasibility of measuring the diffractive spectrum of amorphous materials by Energy-Dispersive X-ray Diffraction (EDXRD) utilizing Cadmium Zinc Telluride detectors. The total scattering intensity (coherent plus incoherent scatter) spectra precisely measured by high-energy Wide-Angle X-ray Scattering (WAXS) were compared to the EDXRD spectra to determine the level of agreement between the two techniques. The EDXRD spectra were constructed by applying a spectra fusing technique which combined the EDXRD spectra collected at different scattering angles rendering a continuous total scattering spectrum. The spectra fusing technique extended the momentum transfer range of the observed scattered spectrum beyond the limitations of the X-ray source and CZT detection efficiencies. Agreement between the WAXS and fused EDXRD spectra was achieved. In addition, this thesis presents the atomic pair correlation functions and coordination numbers of the first coordination shell for four hydrogen peroxide solutions of varying mass concentrations using Empirical Potential Structural Refinement (EPSR). The results are compared to the state-of-the art ad initio quantum mechanical charge field molecular dynamics (QMCF MD) model of the hydrogen peroxide in solution to support the model's predictions on why hydrogen peroxide is stable in water. The EPSR results using the coherent scattering intensity calculated from the WAXS data set predicts a hydration shell of 6.4 molecules of water surrounding hydrogen peroxide. The results also indicate that hydrogen peroxide is more likely to behave as a proton donor than acceptor. These findings are in agreement with QMCF MD model of aqueous hydrogen peroxide. / Physics