Les recherches sur les matériaux en couches minces dédiées à l'industrie solaire restent un sujet d'intérêt avec le nombre croissant de types de matériaux incorporés en tant qu'absorbeur dans un dispositif solaire. Le besoin de techniques de caractérisation est donc aigu pour l'optimisation des matériaux et leur incorporation dans des cellules photovoltaïques. Dans cette thèse, une méthode de photo-courant basée sur la spectroscopie de photo-courant à transformée de Fourier (FTPS) est utilisée pour effectuer des mesures sur des matériaux en couches minces et des cellules solaires. Notre FTPS a été développée pour réaliser 3 types de mesures: 1.) mesure de réflexion et de transmission (R/T), 2.) spectroscopie du coefficient d'absorption, et 3.) mesure de réponse spectrale, efficacité quantique externe et densité de photo-courant court-circuit. Cette dernière est spécifiquement utilisée pour les cellules solaires. Nous avons utilisé les résultats de R/T pour effectuer une simulation numérique donnant l'épaisseur, l'indice de réfraction, la rugosité du film et le coefficient d'absorption optique. Une modélisation de la densité d'états (DOS) en utilisant le logiciel DeOSt automatisé avec l'algorithme TLBO (Teacher Learner Based Optimization) a été développée pour trouver les valeurs des paramètres de DOS les mieux adaptées afin de reproduire le ∝ expérimental. Une analyse de sensibilité a été faite pour trouver les paramètres DOS les plus importants parmi 15-17 paramètres. Nous avons mesuré plusieurs échantillons de a-Si: H déposés sous différentes conditions de dépôt, et utilisé nos résultats pour étudier leur DOS. Une comparaison des mesures de α sur a-Si: H déposé sur un substrat de verre et incorporé dans une cellule solaire a également été réalisée. Cette étude a conclu qu'une correction du spectre de coefficient d'absorption doit être effectuée pour les mesures sur les cellules solaires. / Investigations on thin film materials dedicated to the solar industry are still a matter of interest with the growing numbers of material types incorporated as absorbers in a solar cell device. The need of characterization techniques is therefore acute for the optimization of materials and their incorporation in solar devices. In this thesis, a photocurrent method based on Fourier Transform Photocurrent Spectroscopy (FTPS) is used to perform the measurements of thin film materials and solar cells. Our FTPS was further developed to perform 3 types of measurements: 1.) reflection and transmission (R/T) measurement, 2.) absorption coefficient spectroscopy and 3.) spectral response, external quantum efficiency, and short circuit photocurrent density measurements. This latter is specifically used for solar cells. We used the R/T results to perform numerical simulations giving the thickness, refractive index, film roughness, and optical absorption coefficient. A modeling of the density of states (DOS) using the software DeOSt automated with the Teacher Learner Based Optimization (TLBO) algorithm was achieved to find the best suited DOS parameter values to reproduce the experimental spectrum of alpha. A sensitivity analysis was performed to find the most important DOS parameters among 15-17 parameters. For the experimental studies, we have measured several a-Si:H thin film samples prepared under different deposition conditions, and used their absorption coefficient; spectra to study their DOS. A comparison of absorption coefficient; measurements on a-Si:H thin films deposited on a glass substrate and incorporated in a solar cell device stack was also conducted. This study concluded that a correction of the absorption coefficient spectrum measured on solar cells had to be done.

Research in superconductivity is heading towards overcoming the limitations imposed by extreme conditions, and promising candidates in this pursuit are superconductors made from hydrides. Carbonaceous Sulfur Hydride (CSH) was reported in Nature 586, 373-377 (2020) as a room-temperature superconductor in the pressure range of 140-267 GPa; however, there is controversy in the literature regarding these results. Here, we use density functional theory to confirm the hypothesis of Nature 596, E9-E10 (2021) that a metallic path is the reason for the sharp drop in resistance interpreted in Nature 586, 373-377 (2020) as indicative of a weak type 2 superconductor. We find that the metallic behavior of CSH is dominated by sulfur p-orbitals, and not by metallization of hydrogen. If CSH would be a superconductor, the predicted Ginzburg Landau parameter would be 1356.9, reflecting an unusually strong type 2 superconductor and thus contradicting the interpretation of Nature 586, 373-377 (2020). The fact that we find no metallic states below 220 GPa casts doubts on the onset of superconductivity at 140 GPa reported in Nature 586, 373-377 (2020). Additionally, the small fraction of active hydrogen density of states at the Fermi level shows that CSH is not a high-temperature superconductor.

The process of spontaneous emission can be dramatically modified by optical micro- and nanostructures. We studied the modification of fluorescence dynamics using a polymer spacer layer fabricated through layer-by-layer (LbL) self-assembly. The advantages of this method are numerous: The self-assembled spacers can possess exceptional smooth surface morphology; The thickness of the spacer can be controlled with nanometer accuracy; And depending on fabrication conditions, the spacer layer is stimuli responsive and its thickness can be dynamically tuned. This thesis contains three interlinked components. First, we vary LbL spacer layer thickness and explore the change in fluorescence lifetime induced by the modified photonic density of states (PDOS), i.e., Purcell effects. Our experimental results agree well with theoretical predictions based on a classical dipole model, which also yields consistent values for the fluorophores' intrinsic fluorescence lifetime and quantum yield near a dielectric as well as a plasmonic interface. Based on this observation, we further demonstrate that self-assembled fluorophores can be used to probe the modified PDOS near optical micro- and nano-structures. These results naturally lead to the second component of our research. In particularly, based on the PDOS-induced changes in fluorescent lifetime, we develop a non-contact method that can measure morphological changes with nanoscale resolution. Our method relies on quantitatively linking fluorophore position with PDOS, and is validated through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. To demonstrate the potential application of this method, we investigated the swelling/deswelling of LbL films induced by pH changes. Our results indicate significant difference between a LbL film composed of a single polymer monolayer and a LbL film with 3 monolayers. Such stimuli-responsive polymers can be used to construct active and tunable plasmonic nano-devices. As a proof-of-principle demonstration, we experimentally confirm that it is possible to utilize the swelling/deswelling behavior of stimuli-responsive films to dynamically control the separation between Au nanoparticles and Texas Red (TR) dyes. This result is based on the strong correlation of TR fluorescence lifetime and nanoparticles-TR separation. Finally, we investigate the impact of different lithography processes on the fluorescence properties of self-assembled fluorophores. We consider three methods: direct fluorophore patterning through ultraviolet (UV) ablation, focused ion beam (FIB) milling of self-assembled fluorophores, and self-assembly of fluorescent materials over plasmonic nano-patterns. / Ph. D.

No description available.

Die elektronische Zustandsdichte ist die grundlegende Größe zum Verständnis von Ladungstransportprozessen in Materialien. In der vorliegenden Arbeit wird eine Methode zur Bestimmung dieser Dichte, die für organische Feldeffekttransistoren (OFET) vorgeschlagen wurde, für organischen Transistoren mit durchlässiger Basis (OPBT) adaptiert. Dabei wird aus temperaturabhängigen Transferkurven die Aktivierungsenergie für den Emitterstrom bestimmt und aus deren Spannungsabhängigkeit die Zustandsdichte abgeleitet. Es wird gezeigt, dass die Anwendung der Methode bei OPBTs unter bestimmten Voraussetzungen möglich ist. Die Qualität der Resultate hängt vom jeweiligen Transistor ab. Ein homogeneres und dickeres Basisoxid, wie es durch Anodisierung der Basiselektrode entsteht, wirkt sich positiv auf die Qualität aus. Die bestimmten Zustandsdichten liegen abhängig vom konkreten Transistor im Bereich 10^18 eV^−1 cm^−3…10^20 eV^−1 cm^−3 in einem Energiebereich von 200 meV. Die Form der Verteilung ist näherungsweise exponentiell mit einer Breite von etwa 4 meV.:1 Einleitung 2 Grundlagen 2.1 Organische Halbleiter 2.1.1 Organische Moleküle und Festkörper 2.1.2 Ladungstransport 2.1.3 Modelle und Konzepte 2.1.4 C60 2.2 Organische Transistoren 2.3 Organischer Transistor mit durchlässiger Basis 2.3.1 Geometrie 2.3.2 Zustände und Transferkurvenabschnitte 2.3.3 Energiediagramm 2.3.4 Anodisierung 2.3.5 Chemische und elektrische Belastung 2.4 Zustandsdichte 2.4.1 Modelle 2.4.2 Zustandsdichtebestimmung 3 Experiment 3.1 Transistoren 3.1.1 Herstellung 3.1.2 Anodisierung 3.2 Temperaturabhängige Transferkurven 3.2.1 Wahl der Parameter 3.2.2 Auswertung der Daten 3.3 Belastungstests und Parametervariation 3.4 Kapazitätsmessung 4 Auswertung 4.1 Bestimmung der Aktivierungsenergie 4.2 Bestimmung der Zustandsdichte 4.2.1 Anwendbarkeit und Zuverlässigkeit 4.2.2 Wahl der Kanaldicke 4.2.3 Kapazitätsbestimmung 4.3 Auswirkung der Anodisierung 4.4 Auswirkung von elektrischer und chemischer Belastung 4.5 Einfluss der Halbleiterschichtdicke 5 Diskussion 5.1 Schlussfolgerungen 5.2 Ausblick A Messdaten / The electronic density of states (DOS) is a fundamental quantity which allows a deeper understanding of charge transport processes in materials. In this thesis, a method proposed for organic field-effect transistors (OFET) will be adapted to organic permeable-base transistors (OPBT). The DOS is extracted from temperature dependent transfer curves by determining the activation energy and calculating its derivative with respect to the applied voltage. It is shown that the application of this method to OPBTs is possible under certain circumstances. The quality of the results depends on the transistor. A more homogeneous and thicker base oxide created by anodization results in a better quality. The resulting DOS lies in the range of 10^18 eV^−1 cm^−3…10^20 eV^−1 cm^−3 in an energy interval of 200 meV. The shape of the DOS is approximately exponential with a width of 4 meV.:1 Einleitung 2 Grundlagen 2.1 Organische Halbleiter 2.1.1 Organische Moleküle und Festkörper 2.1.2 Ladungstransport 2.1.3 Modelle und Konzepte 2.1.4 C60 2.2 Organische Transistoren 2.3 Organischer Transistor mit durchlässiger Basis 2.3.1 Geometrie 2.3.2 Zustände und Transferkurvenabschnitte 2.3.3 Energiediagramm 2.3.4 Anodisierung 2.3.5 Chemische und elektrische Belastung 2.4 Zustandsdichte 2.4.1 Modelle 2.4.2 Zustandsdichtebestimmung 3 Experiment 3.1 Transistoren 3.1.1 Herstellung 3.1.2 Anodisierung 3.2 Temperaturabhängige Transferkurven 3.2.1 Wahl der Parameter 3.2.2 Auswertung der Daten 3.3 Belastungstests und Parametervariation 3.4 Kapazitätsmessung 4 Auswertung 4.1 Bestimmung der Aktivierungsenergie 4.2 Bestimmung der Zustandsdichte 4.2.1 Anwendbarkeit und Zuverlässigkeit 4.2.2 Wahl der Kanaldicke 4.2.3 Kapazitätsbestimmung 4.3 Auswirkung der Anodisierung 4.4 Auswirkung von elektrischer und chemischer Belastung 4.5 Einfluss der Halbleiterschichtdicke 5 Diskussion 5.1 Schlussfolgerungen 5.2 Ausblick A Messdaten

No description available.

The density of single grain states in static granular packings is derived from first principles for an idealized yet fundamental case. This produces the distribution of contact forces P_f(f) in the packing. Because there has been some controversy in the published literature over the exact form of the distribution, this dissertation begins by reviewing the existing empirical observations to resolve those controversies. A method is then developed to analyze Edwards' granular contact force probability functional from first principles. The derivation assumes Edwards' flat measure -- a density of states (DOS) that is uniform within the metastable regions of phase space. A further assumption, supported by physical arguments and empirical evidence, is that contact force correlations arising through the closure of loops of grains may be neglected. Then, maximizing a state-counting entropy results in a transport equation that can be solved numerically. For the present it has been solved using the "Mean Structure Approximation," projecting the DOS across all angular coordinates to more clearly identify its predominant features in the remaining stress coordinates. These features are: (1) the Grain Factor related to grain stability and strong correlation between the contact forces on the same grain, and (2) the Structure Factor related to Newton's third law and strong correlation between neighboring grains. Numerical simulations were then performed for idealized granular packings to permit a direct comparison with the theory, and the data including P_f(f) were found to be in excellent agreement. Where the simulations and theory disagree, it is primarily due to the coordination number Z because the theory assumes Z to be a constant whereas in disordered packings it is not. The form of the empirical DOS is discovered to have an elegant, underlying pattern related to Z. This pattern consists entirely of the functional forms correctly predicted by the theory, but with only slight parameter changes as a function of Z. This produces significant physical insight and suggests how the theory may be generalized in the future.

Photolumineszenz-Techniken spielen eine wichtige Rolle bei der Charakterisierung verschiedener funktionaler Fluorophore in den Lebens- und Materialwissenschaften, in der Biologie und bis hin zu den Quantentechnologien. Ein entscheidender und wichtiger Parameter für den Vergleich von Fluorophoren ist die Quanteneffizienz, die ein direktes Maß für die Umwandlungseffizienz von absorbierten Photonen in emittierte Photonen darstellt. Diese Größe charakterisiert die Nutzbarkeit von Emittern für Anwendungen in optischen Geräten, Einzelphotonenquellen und im biomedizinischen Bereich. Mehrere Techniken wie optische und photothermische Methoden werden verwendet, um die photolumineszente Quanteneffizienz zu messen, und so die Eignung von Fluorophoren für verschiedene Anwendungen zu bewerten. Quanteneffizienz-Messungen können jedoch eine Herausforderung für hochverdünnte Fluorophore sein, die in dünne Schichten eingebettet sind. Die in dieser Arbeit beschriebene Forschung überwindet die Herausforderungen der Quanteneffizienzmessung durch eine Modifikation der Wechselwirkung zwischen Licht und Umgebung. / Photoluminescence techniques play an important role for characterization of various functional fluorophores in the life and material sciences from biology to quantum technologies. A crucial and key parameter for comparing the performance of fluorophores is the photoluminescence quantum efficiency or quantum yield, which presents a direct measure of conversion efficiency of absorbed photons into emitted photons. This quantity characterizes the performance of emitters for applications in optical devices as single photon sources and in the biomedical sector. Several techniques such as optical and photothermal methods are used to measure the photoluminescence quantum efficiency of emitters in various environments and aggregation states. Quantum efficiency measurements can be challenging for fluorophores in solid matrix, in scattering systems and for highly diluted fluorophores embedded to thin films. The research described in this thesis overcomes these challenges by performing quantum efficiency measurement via modifying the spontaneous emission as a fundamental process of light-matter interaction.

No description available.

No description available.