Die Strukturen der Erdalkalimetall-Subnitride (EA2N) von Calcium, Strontium und Barium ermöglichen mit ihrem schichtartigen Aufbau aus EA6N-Oktaedern Intercalationsreaktionen. Die Redox-Intercalation von Stickstoff in Sr2N wurde an Einkristallen untersucht. Nur durch eine drastische Erhöhung des Reaktionsgasdruckes im Vergleich zu den Reaktionen an mikrokristallinen Proben wurde die Intercalation der Diazenidionen in die Kristalle zu Sr4N3 und SrN möglich. Für eine analoge Intercalation von Wasserstoff in Sr2N konnten die Reaktionsbedingungen dahingehend optimiert werden, dass erstmals phasenreines Strontiumnitridhydrid (Sr2N)H bzw. deuterid (Sr2N)D erhalten wurde. Anhand von Intercalationsreaktionen mit Sr2N Kristallen konnte gezeigt werden, dass der Intercalationsprozess, erkennbar an der deutlichen Farbänderung von schwarz nach bersteinfarben, von außen nach innen fortschreitet. Als Methode zur räumlich aufgelösten Analyse wurde die Laserablation, in Kombination mit einem ICP - Massenspektrometer (LA-ICP-MS) verwendet. In der Literatur beschriebene Quantifizierungsstrategien wurden auf die Anwendbarkeit für die gegebene Fragestellung untersucht. Mit der ortsaufgelösten Analyse von Einkristallen konnte gezeigt werden, dass die Intercalation von Stickstoff in die Kristalle kontinuierlich von den Kanten zur Kristallmitte fortschreitet.

Plasticity in crystalline solids is controlled by the microscopic line defects known as “dislocations”. Decisive role of dislocations in crystal plasticity in addition to fundamentals of plastic deformation are presented in the current thesis work. Moreover, major features of numerical modeling method “Discrete Dislocation Dynamics (DDD)” technique are described to elucidate a powerful computational method used in simulation of crystal plasticity. First part of the work is focused on the investigation of strain rate effect on the dynamic deformation of crystalline solids. Single crystal copper is chosen as a model crystal and discrete dislocation dynamics method is used to perform numerical uniaxial tensile test on the single crystal at various high strain rates. Twenty four straight dislocations of mixed character are randomly distributed inside a model crystal with an edge length of 1 µm subjected to periodic boundary conditions. Loading of the model crystal with the considered initial dislocation microstructure at constant strain rates ranging from 103 to 105s1 leads to a significant strain rate sensitivity of the plastic flow. In addition to the flow stress, microstructure evolution of the sample crystal demonstrates a considerable strain rate dependency. Furthermore, strain rate affects the strain induce microstructure heterogeneity such that more heterogeneous microstructure emerges as strain rate increases. Anisotropic characteristic of plasticity in single crystals is investigated in the second part of the study. Copper single crystal is selected to perform numerical tensile tests on the model crystal along two different loading directions of [001] and [111] at two high strain rates. Effect of loading orientation on the macroscopic behavior along with microstructure evolution of the model crystal is examined using DDD method. Investigation of dynamic response of single crystal to the mechanical loading demonstrates a substantial effect of loading orientation on the flow stress. Furthermore, plastic anisotropy is observed in dislocation density evolution such that more dislocations are generated as straining direction of single crystal is changed from [001] to [111] axis. Likewise, strain induced microstructure heterogeneity displays the effect of loading direction such that more heterogeneous microstructure evolve as single crystal is loaded along [111] direction. Formation of slip bands and consequently localization of plastic deformation are detected as model crystal is loaded along both directions. / <p>QC 20151015</p>

El conocimiento de las características interfaciales es de suma importancia para poder desarrollar materiales que sean capaces de dar lugar a reacciones electrocatalíticas eficientes. Por esta razón, en esta tesis se muestran diferentes estudios interfaciales sobre superficies monocristalinas de platino y cobre en diferentes electrolitos. Además se estudian las características de la interfase electrodoldisolución con superficies de platino modificadas con adátomos de hierro, cobalto y níquel. Para ello, se han empleado las técnicas de voltametría cíclica, espectroscopía infrarroja con transformada de Fourier, desplazamiento de carga con CO y salto de temperatura inducido por láser. Los resultados muestran cómo varía el campo eléctrico interfacial disminuye al aumentar el recubrimiento de hierro y níquel en la superficie de platino. Este efecto tiene un gran impacto en la reacción de evolución de hidrógeno, ya que la mejora electrocatalítica de esta reacción está relacionada con la energía de reorganización de las moléculas de agua, la cual, depende de la fortaleza del campo eléctrico interfacial. Los estudios realizados en medio alcalino para las diferentes superficies de cobre y platino sin modificar muestran una correlación entre el potencial de máxima entropía y las funciones de trabajo para cada una de las diferentes orientaciones atómicas superficiales. Por otro lado, debido a la aplicabilidad de las nanopartículas en los sistemas reales de conversión de energía, se realizaron experimentos de sincrotrón empleando la técnica de Bragg coherent difraction imaging con el objetivo de estudiar el deterioro de las nanopartículas en condiciones operando.

The diethyl ester of o-phenylenebis(oxamic acid) (opbaH2Et2) was treated with an excess of RNH2 in MeOH to cause the exclusive formation of the respective o-phenylenebis(N(R)-oxamides) (opboH4R2, R = Me 1, Et 2, nPr 3) in good yields. Treatment of 1–3 with half an equivalent of [Cu2(AcO)4(H2O)2] or one equivalent of [Ni(AcO)2(H2O)4] followed by the addition of four equivalents of [nBu4N]OH resulted in the formation of mononuclear bis(oxamidato) type complexes [nBu4N]2[M(opboR2)] (M = Ni, R = Me 4, Et 5, nPr 6; M = Cu, R = Me 7, Et 8, nPr 9). By addition of two equivalents of [Cu(pmdta)(NO3)2] to MeCN solutions of 7–9, novel trinuclear complexes [Cu3(opboR2)(L)2](NO3)2 (L = pmdta, R = Me 10, Et 11, nPr 12) could be obtained. Compounds 4–12 have been characterized by elemental analysis and NMR/IR spectroscopy. Furthermore, the solid state structures of 4–10 and 12 have been determined by single-crystal X-ray diffraction studies. By controlled cocrystallization, diamagnetically diluted 8 and 9 (1%) in the host lattice of 5 and 6 (99%) (8@5 and 9@6), respectively, in the form of single crystals have been made available, allowing single crystal ESR studies to extract all components of the g-factor and the tensors of onsite CuA and transferred NA hyperfine (HF) interaction. From these studies, the spin density distribution of the [Cu(opboEt2)]2− and [Cu(opbonPr2)]2− complex fragments of 8 and 9, respectively, could be determined. Additionally, as a single crystal ENDOR measurement of 8@5 revealed the individual HF tensors of the N donor atoms to be unequal, individual estimates of the spin densities on each N donor atom were made. The magnetic properties of 10–12 were studied by susceptibility measurements versus temperature to give J values varying from −96 cm−1 (10) over −104 cm−1 (11) to −132 cm−1 (12). These three trinuclear CuII-containing bis(oxamidato) type complexes exhibit J values which are comparable to and slightly larger in magnitude than those of related bis(oxamato) type complexes. In a summarizing discussion involving experimentally obtained ESR results (spin density distribution) of 8 and 9, the geometries of the terminal [Cu(pmdta)]2+ fragments of 12 determined by crystallographic studies, together with accompanying quantum chemical calculations, an approach is derived to explain these phenomena and to conclude if the spin density distribution of mononuclear bis(oxamato)/bis(oxamidato) type complexes could be a measure of the J couplings of corresponding trinuclear complexes. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Die vorliegende Arbeit fokussiert auf die Synthese von organisch/anorganischen Hybridmaterialien mit multifunktionalen Eigenschaften unter ausschliesslicher Darstellung dieser Materialen mit Hilfe des „wet chemistry“ Zugangs. Ausgehend von der Darstellung und Charakterisierung von isomorphen bzw. isostrukturellen Hybridmaterialien der allgemeinen Zusammensetzung catena-{[Me3NH][MCl3·2H2O]}n (Mtac) (MII = Mn, Co, Ni, Cu, tac = [Me3NH]Cl3·2H2O]) speziell mittels IR und UV/vis Spektroskopie ist beschrieben, wie sich aus diesen entsprechende bi-, tri-, und auch tetra-heterometallische Koordinationspolymere der allgemeinen Zusammenseztung {MxM´ytac}n, {MxM´yM´´ztac}n, {MxM´yM´´zM´´´ttac}n (MII = M ≠ M´≠ M´´≠ M´´´≠ M´´´´ und x, y, z, t als prozentualer Metallgehalt) herstellen lassen und welche limitierende Faktoren zu berücksichtigen sind. Leifähigkeitsmessungen an Einkristallen ausgewählter Koordinationspolymere werden vorgestellt. Zusätzlich werden die durch Rekristallisation von Nitac erhaltenen zwei verschiedenen Koordinationspolymere der Formel {[Me3NH]3{NiCl4}{NiCl3}}n und {[(Me3NH]{NiCl3}}n in Bezug auf ihre ungewöhnlichen strukturellen und magnetischen Eigenschaften vorgestellt und beschrieben. Die durch Austausch von [Me3NH]+ Kationen gegen [Et3NH]+ bzw. protonierten aromatischen N-haltigen Kationen wie [2,2’-bipyH2]2+, [4,4’-bipyH2]2+ and [1,10-phenH2]2+ erhaltenen Reaktionsprodukte aus Umsetzungen mit Hilfe des “wet chemistry” Zugangs werden im Hinblick auf ihre Festkörperstrukturen beschrieben. Die erfolgreiche Darstellung einer neuen Familie von perylentetracarboxylato-basierenden Komplexen, die teilweise hervorragende Löslichkeiten besitzen, wird beschrieben sowie die strukturellen, magnetischen und lumineszierenden Eigenschaften ausgewählter Vetreter. / The thesis presented here is focused on the synthesis of organic/ inorganic hybrid materials with multifunctional properties by means of the “wet chemistry” approach. The synthesis and characterization of hybrid materials with the general composition catena-{[Me3NH][MCl3·2H2O]}n (Mtac) (MII = Mn, Co, Ni, Cu, tac = [Me3NH]Cl3·2H2O]) is described. Due to their isomorphic and/ or isostructural character, bi-, tri-, and even tetra-heterometallic chains of the general formula {MxM´ytac}n, {MxM´yM´´ztac}n, {MxM´yM´´zM´´´ttac}n (MII = M ≠ M´≠ M´´≠ M´´´≠ M´´´´ and x, y, z, t is the percentage of each metal content) were synthesized and characterized. Limitating factors of the synthesis of these types of heterometallic coordination polymers are discussed. Furthermore, the conductive properties of selected representatives were investigated. Additionally, the products obtained from recrystallization of Nitac, two different novel 1D coordination polymers of the formula {[Me3NH]3{NiCl4}{NiCl3}}n and {[(Me3NH]{NiCl3}}n are described with respect to their structural and magnetic properties. Efforts to replace the [Me3NH]+ cations of Mtac compounds by [Et3NH]+ cations as well as by protonated aromatic amines as [2,2’-bipyH2]2+, [4,4’-bipyH2]2+ and [1,10-phenH2]2+ are reported next with respect to the structural exploration of obtained hybrid materials by the “wet chemistry” approach. Finally, the synthesis of a new family of perylene tetracarboxylate (ptc) based soluble complexes is reported. Structural, magnetic and luminescence properties of selected representatives of this new series of soluble ptc derivatives are reported.

<p>Developing the next generation soft optoelectronic materials is of great importance for achieving high-performance, low-cost electronics. These novel material systems bring about new chemistry, physical phenomena, and exciting properties. Organic inorganic hybrid two-dimensional perovskites and organic stable radical molecules are two exciting material systems that bear high expectation and await extensive exploration.</p> <p>Organic inorganic hybrid two-dimensional perovskites are considered one of the solutions to the pressing instability issue of halide perovskites toward commercialization. Moreover, dimension reduction of perovskites creates new opportunities for using two-dimensional perovskites as thermoelectric applications due to the ultralow thermal conductivity. However, two-dimensional perovskite thermoelectric is still at its’ incipient stage of development, therefore a timely proof of potential is required to draw further research interests.</p> <p>In earlier part of this work, the two-dimensional perovskites featuring π-conjugated ligands are synthesized and optimized for high thermoelectric performance. With material design, device engineering, intensive measurements, and careful data analysis, we successfully showed that two-dimensional perovskites are competitive candidate for the emerging thermoelectric materials. Furthermore, temperature and carrier concentration dependencies on thermoelectric properties were also established, giving future researchers a generalized optimization strategy. </p> <p>Organic stable radical molecules are promising for organic electronics as stable radicals don’t require high conjugation for efficient solids-state charge transport. Thanks to their unique redox capability and the unpaired electrons, organic radicals have many unique electronic and magnetic properties that could be useful in spin-related applications. However, the understanding in charge transport mechanisms as well as structure-to-properties correlation remain shallow.</p> <p>In later part of this work, we achieved the highest recorded long channel electrical conductivity of non-conjugated radicals. Meanwhile, the important role of close packing between radical sites was demonstrated by slightly changing chemical design that resulted in drastic change in electrical conductivity. Finally, we concluded that the solid-state charge transport in non-conjugated species is governed by variable range hopping mechanisms. </p>

This project is in collaboration with the Hydro-Quebec Research Institute (IREQ) and the Canadian Centre for Electron Microscopy (CCEM) on the mechanical test performance of miniature-scale micro-tensile specimens. The objective of the thesis project is to create an efficient and reliable fabrication route for producing micro-tensile specimens and to validate the accuracy of a newly custom-built micro-tensile bench at IREQ. The fabrication techniques developed and outlined in this thesis use the underlying fundamental physical mechanisms of secondary electron microscopy (SEM), focused-ion beam (FIB), and the femtosecond (fs)-laser machining for producing optimal quality micro-tensile specimens. The mechanical testing of the specimens is geared towards studying the localized deformation occurring in the microstructure when the size of the specimen only limits a number of grains and grain boundaries in order to target the specific detailed measurement of the mechanical behaviour of individual grains and interfaces. The goal for creating an optimal fabrication route for micro-tensile specimens is to carry out micro-mechanical testing of the primary turbine steels of 415 martensitic stainless steel used in the manufacture of Francis turbine components at Hydro-Quebec. The mechanical testing of single phase and interphase interface 415 steel micro-tensile specimens are considered building blocks to developing digital twin models of the steel microstructure. The experimental data from the mechanical tests would be fed into the crystal plasticity finite element models (CPFEM) that are currently being developed by researchers at IREQ. With the development of digital twin models, engineers at IREQ would be able to predict crack initiation at the microstructure level (prior to crack propagation into macro-scale cracks) by observing the evolution of the grain’s crystallographic orientation and morphology, as well as deformation mechanisms such as martensite formation and twinning produced from localized induced strains in the microstructure. In addition, self-organized dislocation processes such as dislocation nucleation and dislocation escape through the free surface can also be studied using the CPFEM models for size-limited mechanical deformation behaviour of miniature-scale mechanical test specimens. The fabrication routes studied in this thesis project use the combination of the fs-laser and plasma focused ion beam (PFIB) to machine the micro-tensile specimens. (100) single crystal copper was the ideal material chosen to validate the accuracy of the micro-tensile bench and quality of the fs-laser-machined tensile specimens, due to its ductile nature and well-characterized properties studied in literature. A mechanical size effect was studied for single crystal copper specimens with different gauge thicknesses. It was observed from the micro-tension testing that the strength of the specimens increased with decreasing gauge thickness occurring in the size-limited tensile gauges. In addition, it was determined there was negligible differences in the size effect seen between the PFIB-machined copper micro-tensile specimens and the fs-laser-machined micro-tensile specimens, demonstrating that the fs-laser is a reliable machining route for the micro-tensile specimens. X-ray computed tomography was used to validate the correct geometry of the machined gauge section produced from an innovative gauge thinning method adopted from IREQ’s research collaborator, Dr. Robert Wheeler. As well, finite-element analysis (FEA) was performed to determine the deformation behaviour under both linear-elastic and non-linear elastoplastic conditions of (100) copper and 415 steel models simulated in pure tension, prior to the fabrication of the micro-tensile specimens, respectively. Furthermore, significant progress has been made towards targeting martensite grains in the 415-steel microstructure using electron backscattered diffraction (EBSD) analysis to produce single crystal and interphase interface micro-tensile specimens. A workflow towards grain targeting using EBSD analysis has been developed, as well as for the relocation of grains using reference fiducial marks for future fabrication of the single crystal and interphase interface 415 micro-tensile specimens. / Thesis / Master of Applied Science (MASc) / Hydro-Quebec is an energy utilities company that operates the design of Francis hydro-turbines to supply hydroelectric power across the province of Quebec. The hydro-turbines have an expected service life of 70 years. Unfortunately, the turbines can get replaced by new ones prior to reaching half of its service life, due to the development of severe fatigue crack growth in the primary components of the turbines. A solution proposed by the researchers at the Hydro-Quebec Research Institute (IREQ) is to determine a linkage between the turbine’s steel’s microstructure and the mechanical behaviour of the turbine steels. Deformation of the material starts at the microstructure level, where dislocations glide through the material lattice, causing both reversible (elastic) and irreversible (plastic) deformation. Therefore, a solution was proposed by the researchers at IREQ to create computational models of the steel microstructure to predict the deformation of the steel’s microstructure. Being able to predict the deformation mechanisms through the simulation models of the microstructures allows for engineers at Hydro-Quebec to schedule regular maintenance of the turbines more efficiently and provide metallurgists the knowledge on what is occurring at the microstructure level and what can be done to improve the chemical and physical composition of the steel. To develop the digital twin models, experimental data must be collected through mechanical testing of miniature mechanical test specimens of the turbine steels. The mechanical properties of the single phases and interphase interface specimens are fed into the models as building blocks to building a microstructure map of the turbine steels. Micro-tension testing of micro-tensile specimen provides direct information about the material’s mechanical properties. In this work, a reliable and efficient fabrication route for micro-tensile specimens was developed for the purpose of extracting mechanical properties of single phase and interphase interface turbine steel specimens using focused ion beam (FIB) and femtosecond laser machining.

No description available.

Nanomaterials have attracted great interest due to the unique physical properties and great potential in the applications of nanoscale devices. Two dimensional atomic crystals, which are atomic thickness, especially graphene, have triggered the gold rush recently due to the fascinating high mobility at room temperature for future electronics. The crystal structure of nanomaterials will have great influence on their physical properties. Thus, this thesis is focused on developing the methods to control the crystal structure of nanomaterials, namely quantum dots as semiconductor, boron nitride (BN) as insulator, graphene as semimetal, with low cost for their applications in photonics, structural support and electronics. In this thesis, firstly, Mn doped ZnSe quantum dots have been synthesized using colloidal synthesis. The shape control of Mn doped ZnSe quantum dots has been achieved from branched to spherical by switching the injection temperature from kinetics to thermodynamics region. Injection rates have been found to have effect on controlling the crystal phase from zinc blende to wurtzite. The structural-property relationship has been investigated. It is found that the spherical wurtzite Mn doped ZnSe quantum dots have the highest quantum yield comparing with other shape or crystal phase of the dots. Then, the Mn doped ZnSe quantum dots were deposited onto the BN sheets, which were micron-sized and fabricated by chemical exfoliation, for high resolution imaging. It is the first demonstration of utilizing ultrathin carbon free 2D atomic crystal as support for high resolution imaging. Phase contrast images reveal moiré interference patterns between nanocrystals and BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes using a newly developed equation method. Double diffraction is observed and has been analyzed using a vector method. As only a few microns sized 2D atomic crystal, like BN, can be fabricated by the chemical exfoliation. Chemical vapour deposition (CVD) is as used as an alternative to fabricate large area graphene. The mechanism and growth dynamics of graphene domains have been investigated using Cu catalyzed atmospheric pressure CVD. Rectangular few layer graphene domains were synthesized for the first time. It only grows on the Cu grains with (111) orientation due to the interplay between atomic structure of Cu lattice and graphene domains. Hexagonal graphene domains can form on nearly all non-(111) Cu surfaces. The few layer hexagonal single crystal graphene domains were aligned in their crystallographic orientation over millimetre scale. In order to improve the alignment and reduce the layer of graphene domains, a novel method is invented to perform the CVD reaction above the melting point of copper (1090 ºC) and using molybdenum or tungsten to prevent the balling of the copper from dewetting. By controlling the amount of hydrogen during the growth, individual single crystal domains of monolayer over 200 µm are produced determined by electron diffraction mapping. Raman mapping shows the monolayer nature of graphene grown by this method. This graphene exhibits a linear dispersion relationship and no sign of doping. The large scale alignment of monolayer hexagonal graphene domains with epitaxial relationship on Cu is the key to get wafer-sized single crystal monolayer graphene films. This paves the way for industry scale production of 2D single crystal graphene.

This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.