Sneak path current is a significant remaining obstacle to the utilization of large crossbar arrays for non-volatile memories and other applications of memristors. A two-terminal selector device with an extremely large current-voltage nonlinearity and low leakage current could solve this problem. We present here a Ag/oxide-based threshold switching (TS) device with attractive features such as high current-voltage nonlinearity (~1010), steep turn-on slope (less than 1 mV/dec), low OFF-state leakage current (~10-14 A), fast turn ON/OFF speeds (<75/250 ns), and good endurance (>108 cycles). The feasibility of using this selector with a typical memristor has been demonstrated by physically integrating them into a multilayered 1S1R cell. Structural analysis of the nanoscale crosspoint device suggests that elongation of a Ag nanoparticle under voltage bias followed by spontaneous reformation of a more spherical shape after power off is responsible for the observed threshold switching of the device. Such mechanism has been quantitatively verified by the Ag nanoparticle dynamics simulation based on thermal diffusion assisted by bipolar electrode effect and interfacial energy minimization.

The aim of the first part of this thesis is to explain the theoretical basis of transmission electron microscopy and to mention fundamental parts of transmission electron microscopes. The next part of this work is focused on possible methods of image segmentation, the use of neural networks in the detection of objects in an image and the subsequent clustering of results. The theoretical part of the thesis is concluded with an explanation of some already published methods of automatic detection of biological structures in microscopic images and theoretical design of the algorithm, which will be subsequently developed. The process of training neural networks in order to automatically detect biological structures in an image is described at the beginning of the practical part. This is followed by an evaluation of the results achieved by these networks. Subsequently, cluster analysis methods are applied to these results, the products of which are compared with each other and also with the results obtained by already published methods.

>Magister Scientiae - MSc / Combating antimicrobial resistant infections caused by nosocomial pathogens poses a major public health problem globally. The widespread use of broad-spectrum antibiotics for the treatment of wound infections has led to the appearance of multidrug-resistant (MDR) microbes which further exacerbates the growth of microbes amongst patients. It may result in prolonged debility of the patient and an increase in healthcare costs due to prolonged hospital stays and expensive treatment regimens to avoid patient-patient transmission. Therefore, it is imperative that alternative sources of treatment to antimicrobial use in wound infections needs to be developed in order to inhibit or kill resistant microbes and to provide point of care medical treatment to the less fortunate at an affordable cost. / 2021-08-30

Au cours de cette étude, nous avons montré que dans les oxydes de fer type perovskite, les ions sulfates (SO42-) pouvaient être utilisés à escient pour apporter de l'anisotropie cristalline et électronique ou bien au contraire pour casser les mises en ordre à longue distance et provoquer l'isotropie du matériau. Ainsi, ce travail a permis d'isoler les composés bidimensionnels : Sr4Fe2.5-x□xO7.25-(3x/2)(SO4)0.5 (avec x=0, 0.25 et 0.5). Ils peuvent être décrits comme une intercroissance SrO/SrFeO2,5/SrFe0,5-x□xO1,25-(3x/2)(SO4)0,5/SrFeO2,5 et cristallisent dans une maille moyenne quadratique I4/mmm (a=ap et c≈29 Å). Les tétraèdres de sulfates non-pontés se présentent de façon transversale par rapport à c ⃗ pour x=0,5 et longitudinale pour x=0 et 0,25 parce que pontés aux pyramides de fer de la couche partagée. Les atomes de fer des couches non-mixtes SrFeO2,5 se situent eux en coordinence pyramidale pour x=0 et pyramidale et octaédrique pour x=0.5 et x=0.25 afin de respecter la trivalence du fer. Quel que soit x, les composés sont antiferromagnétiques de type G (les spins se situant dans le plan (a,b)). Cependant, pour x=0,5, deux configurations magnétiques sont observées, tandis que les composés x=0 et x=0.25 n'en montrent qu'une seule. Dans le composé Sr4Fe2.5□xO7.25(SO4)0.25(CO3)0.25, l'influence des carbonates (CO32-) se ressent directement sur le paramètre d'empilement, qui est plus petit. Cela n'entraîne cependant aucun changement sensible dans les propriétés physiques. Les composés sont des semi-conducteurs présentant de fortes valeurs de résistivité électronique (de l'ordre de 106Ω.cm) et ne sont pas conducteurs ioniques.La phase ordonnée "15R" SrFe0.6Cr0.4O2.8 se désordonne lorsque l'on substitue 10% du fer par des sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) et adopte une structure pseudo-cubique. Ses propriétés physiques sont alors bouleversées puisque l'on passe d'un comportement ferromagnétique à antiferromagnétique (TN=800K). Ce composé très lacunaire en oxygène montre des défauts structuraux plus ou moins étendus et un comportement de type semi-conducteur. Aucun phénomène de conduction ionique n'est observé. / In this study, we have shown that in perovskite-type iron oxides, sulfate ions (SO42-) can be used to bring structural and electronic anisotropy, or on the contrary to break long distance ordering and cause the isotropy of the material.Thus, this work made it possible to isolate the two-dimensional compounds: Sr4Fe2.5-x□x07.25-(3x/2)(SO4)0.5 (with x = 0.25 and 0.5). They can be described as an intergrowth SrO/SrFeO2,5/SrFe0,5-x□xO1,25-(3x/2)(SO4)0.5/SrFeO2,5 and crystallize in a quadratic mean cell I4/mmm (a=ap et c≈29 Å). The unbridged sulfates tetrahedra are oriented transversely with respect to c ⃗ for x=0.5 and longitudinal for x=0 and 0.25 because bridged to the iron pyramids of the shared layer. The iron atoms of the non-mixed layers SrFeO2,5 are in pyramidal coordination for x=0 and pyramidal and octahedral coordination for x=0.5 and x=0.25, in order to respect the trivalence of iron. However, for x=0.5, two magnetic configurations are observed whereas the compounds x=0 and x=0.25 show only one. In the compound Sr4Fe2.5□xO7.25(SO4)0.25(CO3)0.25, the influence of the carbonates (CO32-) is directly felt on the stacking parameter, which is smaller. The compounds are semiconductors with high electronic resistivity values (of the order of 106Ω.cm) and are not ionic conductors.The ordered phase "15R" SrFe0.6Cr0.4O2.8 becomes disordered when 10% of the iron is substituted with sulfates (SrFe0.5Cr0.4O2.1(SO4)0.1) and adopts a pseudo-cubic structure. Its physical properties are then modified because we switch from a ferromagnetic to an antiferromagnetic behavior (TN=800K). This oxygen-deficient compound shows more or less large structural defects and a semiconductor behavior. No ionic conduction phenomenon is observed.

Present doctoral thesis is focused on electron microscopy and spectroscopy investigation of novel metal-oxide anode catalyst for fuel cell application. Catalyst based on Pt- doped cerium oxide in form of thin layers prepared by simultaneous magnetron sputtering deposition on intermediate carbonaceous films grown on silicon substrate has been studied. The influence of catalyst support composition (a-C and CNx films), deposition time of CeOx layer and other deposition parameters, as deposition rate, composition of working atmosphere and Pt concentration on the morphology of Pt-CeOx layers has been investigated mainly by Transmission Electron Microscopy (TEM). The obtained results have shown that by suitable preparation conditions combination we are able to tune final morphology and composition of catalyst. Composition of carbonaceous films and Pt-CeOx layers was examined by complementary spectroscopy techniques - Energy Dispersive X-ray Spectroscopy (EDX), Electron Energy Loss Spectroscopy (EELS) and X-ray Photoelectron Spectroscopy (XPS). Such prepared porous structures of Pt-CeOx are of promising as anode catalytic material for real fuel cell application. Keywords: cerium oxide, platinum, fuel cell, magnetron sputtering, Transmission Electron Microscopy

We present a colloidal synthesis of quaternary Cu–Zn–In–S (CZIS) nanoplatelets (NPLs) by means of partial cation exchange. Starting with the synthesis of highly monodisperse binary CuS NPLs with lateral dimensions of ∼64 nm and thickness of ∼5 nm, we further performed a cation exchange reaction in which copper was partly replaced by indium, leading to Cu–In–S NPLs. To enhance the stability of the resulting NPLs and to improve their optical properties, we carried out the ZnS shell growth via both the heterogeneous nucleation of ZnS on the NPLs and via partial cation exchange on the surface of the particles. The latter reaction resulted, however, in rather an alloyed than the core/shell structure, whereas the reaction between zinc and sulfur precursors yielded unusual cookie-like hexagonal shaped structure, in which ZnS trigonal extensions grew only on one of the basal planes of the plates along the thickness direction. Upon ZnS growth, the lateral dimensions of the resulting core/shell CZIS/ZnS and alloyed CZIS NPLs distinctly increased to ∼80 and ∼75 nm, respectively. The analysis of the optical properties of the alloyed CZIS NPLs showed photoluminescence (PL) in the range from 780 to 820 nm depending on the reaction time and temperature. This PL signal originated mainly from small nanoparticles formed as a byproduct in the synthesis. In contrast to the alloyed NPLs, PL measurements of the core/shell CZIS/ZnS platelets showed a weak emission in the near-infrared region (PL maximum at approx. 1110 nm), which so far has rarely been reported for the copper chalcogenide-based two-dimensional structures.

Lithium-ion batteries(LIBs) have dominated the energy storage market in the past two decades. The high specific energy, low self-discharge, relatively high power and low maintenance of LIBs enabled the revolution of electronic devices and electric vehicle industry, changed the communication and transportation styles of the modern world. Although the specific energy of LIBs has increased significantly since first commercialized in 1991, it has reached a bottleneck with current electrode materials. To meet the increasing market demand, it is necessary to develop high capacity electrode materials.<div><br></div><div>Current commercial anode material for LIB is graphite which has a specific capacity of 372 mAh g-1. Other group IV elements (silicon (Si), germanium (Ge), tin (Sn)) have much higher capacities. However, group IV elements have large volume change during lithiation/delithiation, leading to pulverization of active materials and disconnection between electrode particles and current collector, resulting in fast capacity fading. To address this issue, it is essential to understand the microstructural evolution of Si, Ge and Sn during cycling.<br></div><div><br></div><div>This dissertation is mainly focused on the morphological and structural evolution of Sn and Ge based materials. In this dissertation, anin situ focused ion beam-scanning electron microscopy (FIB-SEM) method is developed to investigate the microstructuralevolution of a single electrode particle and correlate with its electrochemical performance. This method is applied toall projects. The first project is to investigate the microstructural evolution of a Sn particle during cycling. Surface structures of Sn particles are monitored and correlated with different states of charge. The second project is to investigate the morphological evolution of Ge particles at different conditions. Different structures (nanopores, cracks, intact surface) appear at different cycling rates. The third project is to study selenium doped Ge (GeSe) anodes. GeSe and Ge particles are tested at the same condition. Se doping forms Li-Ge-Se network, provides fast Li transport and buffers volume change. The fourth project is to study the reaction front of Ge particle during lithiation. Micron-sized Ge particles have two reaction fronts and a wedge shape reaction interface, which is different from the well-known core-shell mode. The fifth project is to investigate antimony (Sb)-coated porous Ge particles. The Sb coating suppresses electrolyte decomposition and porous structure alleviates volume change. The results in this dissertation reveal fundamental information about the reaction mechanism of Sn and Ge anode. The results also show the effects of doping, porous structuring and surface coating of anode materials.</div>

This thesis explores nanostructuring in TiSiCN, ZrAlN, and TiAlN thin films deposited by cathodic arc evaporation onto cemented carbide substrates, with intended applications for cutting tools. The three systems were found to exhibit age hardening upon annealing, by different mechanisms, into the superhard regime (≥30 GPa), as determined by a combination of electron microscopy, X-ray diffraction, atom probe tomography, erda, and nanoindentation tech- niques. TiSiCN forms nanocomposite films during growth by virtue of Si segregation to the surface of TiCN nanocrystallites while simultaneously pro- moting renucleation. Thus, the common columnar microstructure of TiCN and low-Si-content (≤5 at. %) TiSiN-films is replaced by a “feather-like” nanos- tructure in high-Si-content (≥10 at. %) TiSiCN films. The presence of C promotes the formation of this structure, and results in an accelerated age hardening beginning at temperatures as low as 700 °C. The thermal stability of the TiSiCN films is, however, decreased compared to the TiSiN system by the loss of Si and interdiffusion of substrate species; C was found to ex- acerbate these processes, which became active at 900 °C. The ZrAlN system forms a two-phase nanostructure during growth consisting of cubic ZrAlN and wurtzite ZrAlN. Upon annealing to 1100 °C, the c-Zr(Al)N portion of the films recovers and semicoherent brick-like w-(Zr)AlN structures are formed. Age hardening by 36 % was obtained before overageing sets in at 1200 °C. As-deposited and annealed solid solution Ti0.33Al0.67N thin films were characterized for the first time by atom probe tomography. The as-deposited film was found to be at the very initial stage of spinodal decomposition, which continued during annealing of the film at 900 °C for 2 h. N preferentially segregates to Al-rich domains in the annealed sample, causing a compositional variation between Ti-rich and Al-rich domains, to maintain the stoichiometry for the developing AlN phase. That effect also compensates for some of the coherency strain formed between cubic domains of TiN and AlN. Finally, a possible Kirkendall effect caused by an imbalance in the metal interdiffusion during the spinodal decomposition was discovered.

Wir untersuchen die Phasenbildung von Festkörperlösungen von (InxGa1-x)2O3 experimentell mittels Transmissionselektronenmikroskopie und stützen uns bei der Modellierung auf die Clusterexpansion. Epitaktische (InxGa1-x)2O3 Schichten auf kristallinen Substrate sind durch ausgeprägte Ordnung auf den Kationenuntergittern gekennzeichnet, bei welchem In und Ga sich auf Gitterplätze einbauen auf denen sie die energetisch günstigste Koordination zum Sauerstoff einnehmen. Ausgehend von diesem Befund, modifizieren wir das Modells der idealen Mischung so dass wir die Konfigurationsentropie auf den kationischen Untergittern mit spezifischer Koordinations getrennt betrachten um diese realistisch zu berechnen. Das resultierende Phasendiagramm ist durch enge thermodynamisch Stabilitätsbereiche für die jeweiligen Phasen gekennzeichnet, weil sich gleichzeitig große metastabile Zusammensetzungsbereiche ergeben bei Temperaturen die typisch für epitaktisches Wachstum sind: so ist die monokline Phase im Zusammensetzungsbereich x<0.5 metastabil, die hexagonale Phase für 0.55<x<0.7 und die kubische Bixbyit-Phase für x>0.91. Wird amorphes (InxGa1-x)2O3 kristallisiert in-situ im TEM, bildet sich im Zusammensetzungbereich bis x<0.22 die Spinellphase, die als ungeordnete Variante der monoklinen Phase beschrieben wird. Oberhalb dieser Zusammensetzung ist die kubische Phase stabil. Ursache hierfür ist der Einfluss der maximale Menge an Konfiguartionsentropie auf die Bildungsenthalpie in Strukturen mit vielfältigem Koordinationsumgebungen der Kationen. Der letzte Teil der Arbeit befasst sich mit dem Einflusses der Gitterordnung auf den Materialkontrast bei der Abbildung mittels HAADF (High Angle Annular Dark Field) STEM. Hier wird gezeigt, dass die Anregung des 2s-Bloch-Wellen-Zustands zu langperiodsichen Kontrastoszillationen führt, die die quantitaive Bestimmung der Zusammensetzung mittels Z-Kontrast erschwert es aber erlaubt den Ordnungsparameter bei bekaannter Zusammensetzung zu messen. / We investigate the phase formation in (InxGa1-x)2O3 solid solutions experimentally by means of transmission electron microscopy (TEM) and with computational support using cluster expansion. In the case of epitaxial growth on crystalline substrates, we find strong ordering on the cation sublattices of (InxGa1-x)2O3, energetically driven by the tendency of In and Ga to each assume their preferred coordination environment. Based on this experimental finding, we modify the model of the ideal mixture by considering the configurational entropy on the respective cation sublattices with different coordination separately in order to calculate it realistically. The resulting phase diagram is characterized by narrow thermodynamically stable ranges for each phase, while wide composition ranges of metastable compounds are predicted, which can be achieved at temperatures typical for epitaxy: the monoclinic phase is metastable in the composition range x<0.5, the hexagonal phase for 0.55<x<0.7, and the cubic bixbyite phase for x>0.91. If amorphous (InxGa1-x)2O3 is crystallized in-situ in the TEM, the spinel phase, which is described as a disordered variant of the monoclinic phase, is formed in the composition range up to x<0.22, while above this composition, the bixbyite phase is stable. This shift in stability is explained by the maximum amount of configurational entropy present during crystallization, which strongly influences the formation enthalpy in structures with diverse coordination environments of the cations. The last part of the work deals with the influence of the lattice order on the material contrast when imaging by HAADF (High Angle Annular Dark Field) STEM. It is shown that the excitation of the 2s-Bloch wave state leads to long-period contrast oscillations, which complicate the quantitative determination of the composition by Z-contrast but allows to quantify the order parameter for a given composition.

Les études épidémiologiques sur les effets de la fraction ultrafine de la pollution particulaire et les études sur la toxicité in vitro et in vivo des nanoparticules manufacturées témoignent d’un danger potentiel pour l’homme en raison de nouvelles propriétés physico-chimiques de la matière à l’échelle nanométrique. L’évaluation du risque lié à des expositions professionnelles ou environnementales ou le diagnostic d’un lien causal entre ces expositions et d’éventuelles pathologies peuvent être limités par l’absence de méthode de référence pour caractériser et quantifier les particules nanométriques dans les tissus et fluides biologiques. Ce travail a permis de mettre au point une méthode remplissant ces objectifs, basée sur la préparation des échantillons par digestion alcaline et microfiltration et sur l’analyse en microscopie électronique analytique. L’application de cette méthode dans deux études a permis de confirmer qu’une translocation des particules nanométriques était possible d’une part au niveau pleural avec concentration dans les black spots et d’autre part à travers le placenta avec une possible exposition du foetus. Ce travail a également permis de caractériser des sources d’expositions professionnelles ou environnementales aux particules nanométriques. Sous réserve d’optimiser le coût et le temps nécessaire pour ce type d’analyse, cette méthode pourrait permettre de définir des valeurs de référence sur des échantillons plus larges et représentatifs de la population générale ou être utilisée dans le cadre de la surveillance de travailleurs exposés. / Epidemiologic studies on the health effects of ultrafine particles from atmospheric pollution and in vitro or in vivo studies on manufactured nanoparticles toxicity suggest that potential hazards may result from new physico-chemical properties of materials at nanometric scale. To assess human health risk after occupational or environmental exposure or to demonstrate a causal relationship between such exposures and diseases may be hindered by the lack of reference method to characterize and quantify nanometric particles in biological tissues and fluids. This work allowed us to develop such a method based on samples preparation by alkaline digestion and microfiltration followed by analytical electron microscopy analysis. This method applied in two studies allowed us to confirm that pleural translocation of nanometric particles and accumulation in black spots were possible in human and that they also may pass through the placental barrier with potential fetal exposure. This work also allowed us to characterize some sources of occupational and environmental exposures. After time-cost optimization of this method, it could be used to define reference values on larger population-representative samples or used for the medical follow-up of exposed workers.