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.

No description available.

No description available.

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.

Made available in DSpace on 2016-06-02T20:16:51Z (GMT). No. of bitstreams: 1 5339.pdf: 3033412 bytes, checksum: 3e684081236853aacfacccef70bd4635 (MD5) Previous issue date: 2009-10-02 / Financiadora de Estudos e Projetos / Lead titanate zirconate modified with lanthanum, or PLZT, is one the most ferroelectric compounds utilized in electronic devices, due to its versatility and low production costs in comparison with single-crystalline materials. When adequately prepared, this system presents good optical (high optical transmission) properties, in the visible and near infrared range, and can be electro-optically characterized. Recently, in the end of 90 s, it was verified its high potential as host of photoluminescent ions, as the lanthanide (rare-earth) family. The possibility to use its electro-optic properties (due to its ferroelectric characteristics) and its photoluminescent properties (achieved by the doping process) together ,enlarges the range of application of this system. In this way, the electro-optical characterization of doped PLZT ceramics becomes essential, besides the photonic characterization. In this work, the Senarmont compensator method for electro-optical characterization, or dynamic method, was instrumented, and the values of the induced (due to the quadratic electrooptic effect, Kerr) and permanent (due to the linear electro-optic effect, Pockels) birefringence were determined as a function of the temperature, wave-length and electric-field frequency, of the rare-earth (Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3) doped PLZT, with La/Zr/Ti=9/65/35, ceramics. The results shown a relationship between of the electro-optic (electro-optic coefficients, or birefringence values) and the dielectric, ferroelectric and structural properties (studied in others works) of the ceramics, that were related with the site occupancy and the structural defects due to the aliovalent dopant. It also can be identified two distinct birefringence dependence as a function of the electric field, for the same electro-optic effect (Kerr, or Pockels), identified as a function of the doping process. In the case of electro-optical characterizations in function of the variable frequency, was observed an agreement with the characterization ferroelectric results made in other works in GCFerr, being evidenced the reduction of electro-optical properties with increasing frequency, where if it observed the occurrence of anomalies in the Pockels response with direct influence on the response Kerr. The characterization as a function of wavelength showed the occurrence of two types of behavior depending on the dopant ion used, being one of them the reduction of the values of birefringence with increasing wavelength (the samples pure and doped ions neodymium (Nd) and ytterbium (Yb)), with a tendency to expected behavior in the literature, however, in the second was seen irregular increase birefringence with increase wavelength (for samples doped with ions holmio ( Ho), erbium (Er) and thulium (Tm),not existing relation with to the theoretical models adopted. In relation the characterization as a function of temperature, this was carried through in a temperature interval that understood the characteristic temperatures of systems relaxores (freezing temperature (TF), the maximum dielectric permittivity (TM (e)) and Burns (TB)), except for the sample doped with neodymium ions, whose freezing temperature is below interval worked. By the curve of birefringence (Δn) as a function of temperature was possible to determine the temperature of maximum birefringence for each of the samples, correlated them with each other. Through the curve (d Δn / dt) vs. T was possible to identify a relationship between the maximum variations, positive and negative birefringence with the temperature characteristics TF and TB. / Entre os sistemas ferroelétricos, o sistema titanato zirconato de chumbo modificado com lantânio (PLZT) é um dos mais amplamente utilizados em dispositivos eletrônicos, dada sua versatilidade em aplicações e relação de custo quando comparado aos materiais monocristalinos utilizados nessa mesma área. Quando preparado pelo devido método de síntese, apresenta excelentes propriedades óticas (altos valores de transmissão ótica) desde a região do visível ao infravermelho próximo, possibilitando uma adequada caracterização de suas propriedades óticas e eletro-óticas. Recentemente, a partir do final da década de 90, foi verificada sua alta potencialidade como matriz hospedeira para íons fotoluminescentes, como os da família dos lantanídeos (ou terras-raras). A possibilidade do uso conjunto das propriedades eletro-óticas (dado seu caráter ferroelétrico) e de suas propriedades luminescentes (devido à incorporação de dopantes laser-ativos) aumentou ainda mais a possibilidade de aplicação desses materiais. Desse modo, a caracterização eletro-ótica das cerâmicas de PLZT dopado torna-se indispensável, além de sua caracterização fotônica. Sendo assim, neste trabalho foi instrumentado um sistema de caracterização eletro-ótica, utilizando o método do compensador Senarmont, também conhecido como método dinâmico, para determinar os valores da birrefringência induzida (devido ao efeito eletro-ótico quadrático, Kerr) e a permanente (devido ao efeito eletro-ótico linear, Pockels) em função da temperatura, comprimento de onda e frequência do campo elétrico de prova para composições cerâmicas de PLZT na razão La/Zr/Ti=9/65/35, dopadas com os óxidos terras-raras Nd2O3, Ho2O3, Er2O3, Tm2O3 e Yb2O3, na quantidade de 1,0% em peso. Os resultados mostraram que há uma relação entre as propriedades eletro-óticas encontradas (seja na forma de valores dos coeficientes eletro-óticos, ou na variação da birrefringência) com as propriedades dielétricas, ferroelétricas e estruturais (já observadas em outros trabalhos do grupo de pesquisa no qual esta dissertação foi realizada) das cerâmicas que, por sua vez, foram relacionadas com o tipo de ocupação e de defeitos gerados devido à incorporação dos dopantes. Além disso, foi possível observar que para uma mesma composição pode ocorrer a presença dos dois tipos de efeitos eletro-óticos - Kerr e Pockels - com proporções distintas em função do tipo de dopante. Através desse método, para esse conjunto de amostras, também foi possível identificar dois tipos distintos de variações da birrefringência em função do campo elétrico para um mesmo efeito eletro-ótico (Kerr, ou Pockels), que também puderam ser associados com o tipo de ocupação dos dopantes. Em se tratando das caracterizações eletro-óticas em função da variável frequência, foi observada uma concordância com os resultados da caracterização ferroelétrica, realizada em outros trabalhos no GCFErr, sendo evidenciada a redução das propriedades eletro-óticas com o aumento da frequência, em que se observou a ocorrência de anomalias na resposta Pockels com influência direta na resposta Kerr. A caracterização como uma função do comprimento de onda mostrou a ocorrência de dois tipos de comportamentos, dependendo do íon dopante utilizado, sendo um deles a redução dos valores da birrefringência com o aumento do comprimento de onda (caso das amostras pura e dopadas com os íons neodímio (Nd) e itérbio (Yb)), havendo certa tendência ao comportamento previsto em literatura, no entanto, no segundo caso foi constatado o aumento irregular da birrefringência com o aumento do comprimento de onda (caso das amostras dopadas com os íons holmio (Ho), érbio (Er) e túlio (Tm), não havendo relação com os modelos teóricos adotados. Quanto à caracterização em função da temperatura, esta foi realizada em um range de que compreendeu as temperaturas características de sistemas relaxores (de freezing (TF(e)), máxima permissividade dielétrica (TM(e)) e Burns (TB(e))), exceto para a amostra dopada com o íon neodímio, cuja TF(e) estava abaixo do intervalo considerado. Através da curva de birrefringência (Δn) em função da temperatura foi possível determinar a temperatura de máxima birrefringência para cada uma das amostras, correlacionado-as entre si. Através da curva de (dΔn/dt) vs. T, foi possível constatar uma relação entre as máximas variações, positiva e negativa, da birrefringência com as temperaturas características TF e TB.

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.