Die vorliegende Arbeit beschäftigt sich mit dem Wachstum von BaSnO3/LaInO3 (BSO/LIO) Schichten mittels Plasma-unterstützter Molekularstrahlepitaxie (PAMBE). Für die Realisierung der BSO/LIO Heterostruktur müssen zuvor Wege für ein stabiles Herstellungsverfahren sowohl der BSO als auch der LIO Schichten gefunden werden. Aus diesem Grund beschäftigt sich der erste Teil dieser Arbeit mit den Herausforderungen der Suboxidbildung und Suboxidquellen. Das Wissen um Suboxide ist alt, aber es wurde bisher nicht stark in der Anwendung der Oxid-MBE berücksichtig oder benutzt. Engagierte Studien werden in dieser Arbeit durchgeführt, die zeigen, dass bei Suboxidquellen wie z.B. der Mischung aus SnO2 und Sn sich die Einbaukinetik gegenüber einer elementaren Quelle (z.B. Zinn) vereinfacht. Die in dieser Arbeit herausgearbeitete Effizienz der Mischquellen hat bereits dazu geführt, dass weitere Oxide wie Ga2O3 und SnO mit Hilfe von Suboxid-MBE gewachsen wurden. Im zweiten Teil dieser Arbeit werden die entwickelten Quellen genutzt und die BSO und LIO Wachstumsparameter bestimmt, sowie deren Abhängigkeit im Kontext von thermodynamischen Ellinghamdiagrammen diskutiert. Die Besonderheit beim BSO Wachstum liegt dabei auf der Verwendung einer Mischquelle bestehend aus SnO2 + Sn wodurch SnO Suboxid gebildet wird, welches zum Wachstum beiträgt. Ein zwei-dimensionalen Elektronengas an der Grenzfläche der BSO/LIO Heterostruktur wird realisiert durch gezielte Grenzflächenterminierung mit Hilfe einer Zellverschlusssequenz. Durch die Kontrolle der Grenzflächenterminierung im Monolagenbereich können Ladungsträgerkonzentrationen im Bereich um 3 - 5 × 1013 cm−2 und Beweglichkeiten μ > 100 cm2/Vs zuverlässig und reproduzierbar realisiert werden. / The present work investigates the growth of BaSnO3/LaInO3 (BSO/LIO) heterostructures using plasma-assisted molecular beam epitaxy (PA-MBE). Prior to the realization of the BSO/LIO heterostructure, ways for stable and reliable growth of both BSO and LIO layers have to be developed. Therefore, the first part of this thesis addresses the challenges of suboxide formation and suboxide sources. The knowledge about suboxides is rather old, however, so far it is barely considered or used in oxide MBE. Dedicated studies performed in this thesis show that for suboxide sources such as a mixture of SnO2 and Sn the growth kinetics simplify compared to an elemental source (e.g., Sn). The efficiency of mixed sources, that is worked out in this thesis, already led to the growth of other oxides such as Ga2O3 or SnO using suboxide MBE. In the second part of this thesis growth parameters for BSO and LIO, using the developed sources, are determined and their dependence in the context of thermodynamic Ellingham diagrams is discussed. The growth of BSO is realized by the use of a mixed source consisting of SnO2 + Sn, which forms SnO suboxide that is contributed to the growth. A two-dimensional electron gas at the interface of the BSO/LIO heterostructure is realized by engineering the interface termination using a controlled cell shutter sequence. By controlling the interface termination down to mono layer precision, charge carrier densities in the range of 3 - 5 × 1013 cm−2 and mobilities μ > 100 cm2/Vs can be achieved reliably and reproducibly.

CsPbBr₃ is an inorganic perovskite material that is promising for light-emitting applications. Such applications are known to benefit from an island-type active layer structure, which enhances the device’s light emission efficiency. Here, the impact of the environment on the island formation in thermally deposited bilayers of CsPbBr₃/LiBr is investigated. It is demonstrated that the island formation occurs only in humid environments, leading to an enhancement of the photoluminescence quantum yield by a factor of 350. Timeresolved grazing-incidence wide-angle X-ray scattering experiments document the island growth process and reveal that the LiBr has already changed the perovskite crystal orientation prior to the island formation.

Metallhalogenid Perowskite sind eine aufkommende Klasse von Halbleitermaterialien, die einige der besten Eigenschaften von organischen und anorganischen Halbleitern vereinen. Die Materialien kombinieren eine hohe Leitfähigkeit und modulierbare Bandlücke mit hohem Absorptionskoeffizienten und Löslichkeit in organischen Lösungsmitteln. Verarbeitungsmethoden wie Tintenstrahldruck ermöglichen somit die Herstellung von kristallinen Halbleitern mit direkter Bandlücke aus Lösung. Zunächst werden in einem kombinatorischen Druckprozess drei Perowskittinten, aus drei separaten Druckköpfen, während des Druckprozesses gemischt. Es resultiert eine Reihe von Perowskitfilmen mit genau definierten Zusammensetzungen. Die Kontrolle über die resultierenden Materialeigenschaften wird durch die Herstellung einer Reihe wellenlängenselektiver Fotodetektoren und Langpassfiltern demonstriert, die zu einem tintenstrahlgedruckten dispersionselementfreien Spektrometer kombiniert werden. Weiterhin wird mit den Möglichkeiten eines Tintenstrahldruckers für großflächige Bearbeitung ein etabliertes Verfahren für Tintenstrahl-gedruckte Perowskit-LEDs (PeLEDs) hochskaliert. Mit dem gleichen Druckverfahren und der gleichen Tintenzusammensetzung wurde die aktiv emittierende Fläche von 4 mm² auf 1600 mm² erhöht. Es konnte ein homogener Perowskit Dünnfilm für PeLEDs gedruckt werden, ohne einen Anstieg des Leckstroms mit steigender Fläche zu verursachen. Zuletzt werden die Strukturierungsmöglichkeiten des Tintenstrahldrucks genutzt um zweifarbige PeLEDs herzustellen. Auf einer primären Perowskitschicht wird eine zweite Perowskit-Vorläufertinte aufgebracht. Während des Betriebs erfährt der gemischte Halogenid-Perowskit eine Phasenseparierung und zeigt nur tiefrote Emission von iodidreichen Domänen vor einem hellgrünen emittierenden Hintergrund, dessen Helligkeit nicht durch den Strukturierungsprozess vermindert wird. / Metal halide perovskites are an emerging semiconductor material class that combines some of the best properties of inorganic and organic semiconductors. The material pairs high conductivity and composition-based bandgap tunability with solution processability and high absorption coefficients. Deposition methods like inkjet printing thus allow for the fabrication of crystalline, direct bandgap semiconductors from solution for various applications. First, in a combinatorial printing approach, three perovskite precursor inks, from three separate printheads, are mixed during the printing process. By controlling the perovskite composition, material properties such as the bandgap can be tuned. This is demonstrated by fabrication of a range of wavelength-selective photodetectors and longpass filters, which are combined to yield an inkjet-printed, dispersion element-free spectrometer. Furthermore, using the large-scale capabilities of an inkjet printer, a previously established procedure for inkjet-printed perovskite LEDs (PeLEDs) is upscaled. The actively emitting area is increased from 4 mm² to 1600 mm² using the same printing procedure and ink formulation. This achieved a homogeneous perovskite film, that showed no increase in leakage current, independent of size. Finally, using the patterning capabilities of inkjet printing, dual coloured red/green PeLEDs are fabricated in a sequential printing process. On a primary perovskite layer, a second perovskite precursor ink is deposited. Under operation in a PeLED, the mixed halide perovskite experiences phase segregation and only shows deep red emission from iodide-rich domains against a bright green emitting background, which still performs as well as a non-patterned device.

Tesis por compendio / [ES] La conversión de energía solar a productos químicos se considera una de las estrategias más viables para abordar los problemas derivados del uso masivo de combustibles fósiles y la excesiva emisión antropogénica de CO2. En catálisis asistida con luz, incluida la fotocatálisis y la catálisis fototérmica, el punto clave es el desarrollo de fotocatalizadores eficientes y robustos que puedan utilizar al máximo la energía solar y que sean lo suficientemente estables como para su comercialización. Los materiales basados en perovskitas híbridas orgánicas-inorgánicas han revolucionado el campo de la fotovoltaica en la última década, alcanzando una eficiencia de conversión de luz solar del 23%. Dado que los campos de la fotocatálisis y la fotovoltaica comparten procesos comunes, se abre la posibilidad de aplicación de estos materiales en fotocatálisis. Con el objetivo de confirmar esta posible aplicación de las perovskitas híbridas en fotocatálisis, en esta Tesis Doctoral, se han sintetizado nuevos materiales híbridos de perovskita con el objetivo de mejorar su estabilidad frente a la humedad aprovechando la gran variedad de ligandos orgánicos disponibles, que además pueden ser usados para promover modificaciones superficiales capaces de ajustar las propiedades hidrofílicas / hidrofóbicas. La actividad fotocatalítica de estos nuevos materiales de perovskita se ha estudiado en reacciones modelo para confirmar su estabilidad en las condiciones de reacción. Por otro lado, la reacción de fijación de nitrógeno fotoasistida también ha sido estudiada en detalle en esta Tesis Doctoral. Por un lado, se han sintetizado, caracterizado y testado nuevos complejos organometálicos como foto- y electrocatalizadores homogéneos para esta reacción. Estos han demostrado ser capaces de activar la molécula de dinitrógeno bajo un potencial electroquímico de reducción para formar amoníaco. Por otro lado, se han preparado nanopartículas de rutenio depositadas sobre un material de perovskita a base de titanato como fotocatalizador heterogéneo para la producción de amoniaco en flujo continuo. Además, se ha demostrado que la incorporación de metales alcalinos a este fotocatalizador puede potenciar su actividad fotocatalítica en esta reacción. Así, este material compuesto ha demostrado estar entre los fotocatalizadores más eficientes del estado del arte en la actualidad para esta reacción demostrando además una su elevada estabilidad en las condiciones de reacción. / [CA] La conversió d'energia solar en productes químics es considera una de les estratègies més viables per abordar els problemes derivats de l'ús massiu de combustibles fòssils i l'excessiva emissió antropogènica de CO2. En catàlisi assistida amb llum, inclosa la fotocatàlisi i la catàlisi fototèrmica, el punt clau és el desenvolupament de fotocatalitzadors eficients i robustos que puguen utilitzar al màxim l'energia solar i que siguen prou estables com per a la seva comercialització. Els materials basats en perovskites híbrides orgàniques-inorgàniques han revolucionat el camp de la fotovoltaica en l'última dècada, aconseguint una eficiència de conversió de llum solar del 23%. Atès que els camps de la fotocatàlisi i la fotovoltaica comparteixen processos comuns, s'obre la possibilitat d'aplicació d'aquests materials en fotocatàlisi. Amb l'objectiu de confirmar aquesta possible aplicació de les perovskites híbrides en fotocatàlisi, en aquesta tesi doctoral, s'han sintetitzat nous materials híbrids de perovskita amb l'objectiu de millorar la seva estabilitat enfront de la humitat aprofitant la gran varietat de lligands orgànics disponibles, que amés poden ser usats per a promoure modificacions superficials capaços d'ajustar les propietats hidrofíliques / hidrofòbiques. L'activitat fotocatalítica d'aquests nous materials de perovskita s'ha estudiat en reaccions model per confirmar la seva estabilitat en les condicions de reacció. D'altra banda, la reacció de fixació de nitrogen fotoassistida també ha sigut estudiada en detall en aquesta tesi doctoral. D'una banda, s'han sintetitzat, caracteritzat i testat nous complexos organometàl·lics com foto- i electrocatalitzadors homogenis per a aquesta reacció. Aquests han demostrat ser capaços d'activar la molècula de dinitrogen sota un potencial electroquímic de reducció per formar amoníac. D'altra banda, s'han preparat nanopartícules de ruteni depositades sobre un material de perovskita a força de titanat com fotocatalitzador heterogeni per a la producció d'amoníac en flux continu. A més, s'ha demostrat que la incorporació de metalls alcalins a aquest fotocatalitzador pot potenciar la seva activitat fotocatalítica en aquesta reacció. Així, aquest material compost ha demostrat estar entre els fotocatalitzadors més eficients de l'estat de l'art actualment per a aquesta reacció seva demostrant amés una elevada estabilitat en les condicions de reacció. / [EN] Solar energy to chemicals conversion is regarded to be one of the most plausible strategies addressing the issues of fossil fuel crisis and excessive anthropogenic CO2 emission. For photo-assisted catalysis, including photocatalysis and photothermal catalysis, the key point is the development of efficient and robust photocatalysts that can efficiently utilize the solar energy as well as they are stable enough that meets the requirements for commercialization. Hybrid organic-inorganic perovskites have revolutionized the photovoltaic field in the last decade, reaching a certified sunlight conversion efficiency of 20 %. Since photocatalysis and photovoltaics share common processes, the application of these materials in photocatalysis would be possible. In this Doctoral Thesis, novel hybrid perovskite materials have been synthesized with the aim to improve their stability against moisture by taking advantage large variety of the available organic ligand, which can promote surface modifications capable to adjust the hydrophilic/hydrophobic properties. Additionally, the photocatalytic activity of these novel perovskite materials has been studied in model reactions in order to confirm their stability under reaction conditions. On the other hand, the photo-assisted nitrogen fixation reaction has been also studied in detail in this Doctoral Thesis. on one hand, new organometallic complexes have been synthetized, characterized and tested as homogeneous photo and electrocatalysts for this reaction. They have been demonstrated to be able to activate dinitrogen molecule under electrochemical cathodic potentials to form ammonia. On the other hand, ruthenium nanoparticles deposited on a titanate-based perovskite material have been prepared and tested as heterogeneous photocatalyst for ammonia production in continuous flow. Moreover, it has been demonstrated that the addition of alkali metals to this photocatalyst can boost the photocatalytic activity of this reaction. Thus, this composite material has demonstrated to be among the most efficient photocatalysts in the current state-of-the art for this reaction, as well as very stable under reaction conditions. Considering the large industrial importance of N2 fixation and the mild conditions of pressure and temperature used in the present study, the results of the photo-assisted N2 hydrogenation to ammonia can have a large impact in the area. / Peng, Y. (2021). Hybrid Lead Perovskites as Photocatalysts and Materials for Photo- and Electrocatalytic N2 Reduction [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171731 / Compendio

<p dir="ltr">For reliable, facile, and user-friendly, solution-based synthesis of materials, the colloidal nanocrystal route has proven to be the method of choice for so many. The tunability that this process renders its users---from choice of precursors, solvent systems, and reaction conditions including temperature, pressure, and precursor addition order---is truly second to none. In their simplest form, these nanomaterials are usually comprised of an inorganic core of the desired material and an outer layer of surface-stabilizing molecules called ligands. These ligands provide colloidal stability and allow for the solution-processing of these materials for downstream usage in devices such as light-emitting diodes and photovoltaics, for example. In this thesis, the study and use of colloidal nanomaterials of Cu(In,Ga)(S,Se)₂ (CIGSSe), IIA-IVB-S₃ (including BaZrS₃ and SrZrS₃), alkaline earth polysulfides (IIAS_x; IIA = Sr, Ba; x = 2, 3), and other materials like Cu₂GeS₃ and Cu₂BaSnS₄, for studies into the formation, colloidal stability, and fabrication into solar cells was performed.</p><p dir="ltr">More specifically, an experimental protocol was developed to fabricate high-quality CIGSSe nanoparticles with carbonaceous residues that are substantially reduced from traditional pathways. Traditional methods for synthesizing colloidal CIGS NPs often utilize heavy, long-chain organic species to serve as surface ligands which, during annealing in a Se/Ar atmosphere, leave behind an undesirable carbonaceous residue in the film. In an effort to minimize these residues, N-methyl-2-pyrrolidone (NMP) was used as an alternative surface ligand. Through the use of the NMP-based synthesis, a substantial reduction in the number of carbonaceous residues was observed in selenized films. Additionally, the fine-grain layer at the bottom of the film, a common observation of solution-processed films from organic media, was observed to exhibit a larger average grain size and increased chalcopyrite character over those of traditionally prepared films, presumably as a result of the reduced carbon content, allowing for superior growth. As a result, a gallium-free CuIn(S,Se)₂ device was shown to achieve power-conversion efficiencies of over 11% as well as possessing exceptional carrier generation capabilities with a short-circuit current density (J_SC) of 41.6 mA/cm², which is among the highest for the CIGSSe family of devices fabricated from solution-processed methods. It was shown that pre-selenized films of sulfide nanoparticles instead of selenide nanoparticles performed better as solar cells. While the exact mechanism is still under debate, it appears that the growth phase during selenization, which varies depending on the chalcogen present in the starting material plays an important role.</p><p dir="ltr">The IIA-IVB-S₃ system is just beginning to emerge as a material system shown to be capable of solution-based synthesis methods. This is primarily due to the extremely high oxophilicity of the IVB elements, Ti, Zr, and Hf, necessitating that extreme care and judicial use of inert environments be used to synthesize these materials via solution-based methods. In the IIA-IVB-S₃ system exists some of the chalcogenide perovskites, including BaZrS₃, which are expected to have similar electronic properties to the well-known, high-performing halide perovskites, albeit much more stable, making them attractive prospects as novel semiconductor materials for optoelectronic applications. This work builds upon recent studies to show a general synthesis protocol, involving the use of carbon disulfide insertion chemistry to generate highly reactive precursors, that can be used towards the colloidal synthesis of numerous nanomaterials in the IIA-IVB-S₃ system, including BaTiS₃, BaZrS₃, BaHfS₃, α-SrZrS₃ and α-SrHfS₃. Additionally, we establish a method to reliably control the formation of the BaZrS₃ perovskite, a complication seen in previous literature where BaZrS₃ appears to exist as two different phases when synthesized via colloidal methods. The utility of these nanomaterials is also assessed via the measurement of their absorption properties and in the form of highly stable colloidal inks for the fabrication of homogenous, crack-free thin films of BaZrS₃. In addition to the chalcogenide perovskites, the IIA-S system was also explored to better understand the solution-based formation of these materials and how the control of IIA polysulfides can be achieved. We show that the synthesis of these materials is strongly correlated to the reaction temperature and that the length of the S_n^2- oligomer chain is the dependent variable. We also report on the synthesis of a previously unreported polymorph of SrS₂ which appears to take on the <i>C2/c</i> space group, the same as BaS₂.</p><p dir="ltr">Finally, some discussion is also provided on the use of transmission electron microscopy (TEM) to analyze the crystal structure of materials. Some tips and techniques used throughout this thesis are summarized in this section.</p>

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Cette thèse porte sur l’étude du transport de charge et de spin dans les nanostructures 0D, 2D et les hétérostructures 2D-0D de Van der Waals (h-VdW). Les nanocristaux pérovskite de La0.67Sr0.33MnO3 ont révélé des magnétorésistances (MR) exceptionnelles à basse température résultant de l’aimantation de leur coquille indépendamment du coeur ferromagnétique. Les transistors à effet de champ à base de MoSe2 ont permis d’élucider les mécanismes d’injection de charge à l’interface metal/semiconducteur 2D. Une méthode de fabrication des h-VdW adaptés à l’électronique à un électron est rapportée et basée sur la croissance d’amas d’Al auto-organisés à la surface du graphene et du MoS2. La transparence des matériaux 2D au champ électrique permet de moduler efficacement l’état électrique des amas par la tension de grille arrière donnant lieu aux fonctionnalités de logique à un électron. Les dispositifs à base de graphene présentent des MR attribuées aux effets magnéto-Coulomb anisotropiques. / This thesis investigates the charge and spin transport processes in 0D, 2D nanostructures and 2D-0D Van der Waals heterostructures (VdWh). The La0.67Sr0.33MnO3 perovskite nanocrystals reveal exceptional magnetoresistances (MR) at low temperature driven by their paramagnetic shell magnetization independently of their ferromagnetic core. A detailed study of MoSe2 field effect transistors enables to elucidate a complete map of the charge injection mechanisms at the metal/MoSe2 interface. An alternative approach is reported for fabricating 2D-0D VdWh suitable for single electron electronics involving the growth of self-assembled Al nanoclusters over the graphene and MoS2 surfaces. The transparency the 2D materials to the vertical electric field enables efficient modulation of the electric state of the supported Al clusters resulting to single electron logic functionalities. The devices consisting of graphene exhibit MR attributed to the magneto-Coulomb effect.

Mise au point d'un appareillage permettant des études in situ de réactions solide-gaz dans une large gamme de températures; étude de différentes phases du système SrFeO3-y(y = 0,5-1) en fonction de la température et de la pression partielle d' oxygène; étude des composes du système SnF2 - SnF4 et établissement d' une corrélation entre les paramètres Mössbauer et les propriétés structurales.

Owing to their versatile orbital character with both local and highly dispersive degrees of freedom, transition metal oxides span the range of ionic, covalent and metallic bonding. They exhibit a vast diversity of electronic phenomena such as high dielectric, piezoelectric, pyroelectric, ferroelectric, magnetic, multiferroic, catalytic, redox, and superconductive properties. The nature of these properties arises from sensitive details in the electronic structure, e.g. orbital mixing and orbital hybridization, due to non-stoichiometry, atomic displacements, broken symmetries etc., and their coupling with external perturbations. In the work presented here, these variations of the electronic structure of crystals due to structural and electronic defects have been investigated, exemplarily for the quasi-binary system SrO - SrTiO3 - TiO2. A number of binary and ternary structures have been studied, both experimentally as well as by means of electronic modeling. The applied methods comprise Resonant X-ray Scattering techniques like Diffraction Anomalous Fine Structure, Anisotropy of Anomalous Scattering and X-ray Absorption Fine Structure, and simultaneously extensive electronic calculations by means of Density Functional Theory and Finite Difference Method Near-Edge Structure to gain a thorough physical understanding of the underlying processes, interactions and dynamics. It is analyzed in detail how compositional variations, e.g. manifesting as oxygen vacancies or ordered stacking faults, alter the short-range order and affect the electronic structure, and how the severe changes in mechanical, optical, electrical as well as electrochemical properties evolve. Various symmetry-property relations have been concluded and interpreted on the basis of these modifications in electronic structure for the orbital structure in rutile TiO2, for distorted TiO6 octahedra and related switching mechanisms of the Ti valence, for elasticity and resistivity in strontium titanate, and for surface relaxations in Ruddlesden-Popper phases. Highlights of the thesis include in particular the methodical development regarding Resonant X-Ray Diffraction, such as the first use of partially forbidden reflections to get the complete phase information not only of the tensorial structure factor but of each individual atomic scattering tensor for a whole spectrum of energies, as well as the determination of orbital degrees of freedom and details of the partial local density of states from these tensors. On the material side, the most prominent results are the identification of the migration-induced field-stabilized polar phase and the exergonic redox behavior in SrTiO3 caused by defect migration and defect separation.