The thesis deals with the preparation, characterization and, in particular, with the switching properties of phase-change material (PCM) thin films. The films were deposited using the Pulsed Laser Deposition (PLD) technique. Phase transformations in these films were triggered by means of thermal annealing, laser pulses, and electrical pulses. The five major physical aspects structure transformation, crystallization kinetics, topography, optical properties, and electrical properties have been investigated using XRD, TEM, SEM, AFM, DSC, UV-Vis spectroscopy, a custom-made nanosecond UV laser pump-probe system, in situ resistance measurements, and conductive-AFM. The systematic investigation of the ex situ thermally induced crystallization process of pure stoichiometric GeTe films and O-incorporating GeTe films provides detailed information on structure transformation, topography, crystallization kinetics, optical reflectivity and electrical resistivity. The results reveal a significant improvement of the thermal stability in PCM application for data storage. With the aim of reducing the switching energy consumption and to enhance the optical reflectivity contrast by improving the quality of the produced films, the growth of the GeTe films with simultaneous in situ thermal treatment was investigated with respect to optimizing the film growth conditions, e.g. growth temperature, substrate type. For the investigation of the fast phase transformation process, GeTe films were irradiated by ns UV laser pulses, tailoring various parameters such as pulse number, laser fluence, pulse repetition rate, and film thickness. Additionally, the investigation focused on the comparison of crystallization of GST thin films induced by either nano- or femtosecond single laser pulse irradiation, used to attain a high data transfer rate and to improve the understanding of the mechanisms of fast phase transformation. Non-volatile optical multilevel switching in GeTe phase-change films was identified to be feasible and accurately controllable at a timescale of nanoseconds, which is promising for high speed and high storage density of optical memory devices. Moreover, correlating the dynamics of the optical switching process and the structural information demonstrated not only exactly how fast phase change processes take place, but also, importantly, allowed the determination of the rapid kinetics of phase transformation on the microscopic scale. In the next step, a new general concept for the combination of PCRAM and ReRAM was developed. Bipolar electrical switching of PCM memory cells at the nanoscale can be achieved and improvements of the performance in terms of RESET/SET operation voltage, On/Off resistance ratio and cycling endurance are demonstrated. The original underlying mechanism was verified by the Poole-Frenkel conduction model. The polarity-dependent resistance switching processes can be visualized simultaneously by topography and current images. The local microstructure on the nanoscale of such memory cells and the corresponding local chemical composition were correlated. The gained results contribute to meeting the key challenges of the current understanding and of the development of PCMs for data storage applications, covering thin film preparation, thermal stability, signal-to-noise ratio, switching energy, data transfer rate, storage density, and scalability.

Two groups of magnetic oxides were investigated in this thesis. Thin films of La2/3Sr1/3MnO3 (LSMO) deposited by pulsed laser deposition (PLD) on SrTiO3 (STO) substrates were characterized by polar and longitudinal magneto-optical (MO) Kerr spectroscopy. Experimental results were compared to theoretical calculations based on the transfer matrix formalism. A very good agreement between experimental and theoretical data revealed high magnetic ordering down to 5 nm of film thickness as well as a mechanism of suppression of double exchange interaction near the LSMO/STO interface. Magnetically doped Ce1-xCoxO2-δ films deposited by PLD on MgO (x = 0.05 and 0.10) and oxidized Si (x = 0.20) substrates were studied by combination of spectroscopic ellipsometry and MO Faraday and Kerr spectroscopy. Both diagonal and off-diagonal permittivity tensor components were obtained and verified by theoretical calculations confronted with experimental data. Diagonal spectra revealed two optical transitions from oxygen to cerium states. Off-diagonal spectra revealed two paramagnetic transitions involving cobalt ions. An essential influence of cobalt doping on the resulting ferromagnetic properties of CeO2 was observed.

Two important mechanisms in preparation of ultrathin films of magnetic oxides were systematically investigated in this work. First, influence of epitaxial strain on resulting magneto-optical properties of La2/3Sr1/3MnO3 (LSMO) ultrathin films was studied. The investigated films were grown by pulsed laser deposition on four different substrates, providing a broad range of induced epitaxial strains. Magnetic properties were found to deteriorate with increasing value of the epitaxial strain, as expected due to the unit cell distortion increasingly deviating from the bulk and effect of the magnetically inert layer. A combination of spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy was used to determine spectra of the diagonal and off-diagonal elements of permittivity tensor. The off-diagonal elements confirmed presence of two previously reported electronic transitions in spectra of all films. Moreover, they revealed another electronic transition around 4.3 eV only in spectra of films grown under compressive strain. We proposed classification of this transition as crystal field paramagnetic Mn t2g → eg transition, which was further supported by ab initio calculations. A key role of strain in controlling electronic structure of ultrathin perovskite films was demonstrated. Dynamic application of...

Title: Optical and magneto-optical studies of ferrimagnetic garnets for photonic and spintronic applications Author: RNDr. Lukáš Beran Department: Intitute of Physics of Charles University Supervisor: RNDr. Martin Veis, PhD., Institute of Physics of Charles University Abstract: This doctoral thesis is devoted to fabrication and systematic char- acterization of physical properties of thin films of iron garnets with potential applications in photonic and spintronic devices. Investigated samples were pre- pared by metallo-organic decomposition and pulsed laser deposition. The study was focused on structural and magnetic characterizaiton along with optical and magneto-optical properties. Obtained experimental results were further con- fronted with theoretical calculations. The application potencial of garnets for photonic devices was discussed based on determined Figure of Merit (Faraday rotation to optical loss ratio). High values were achieved for single crystal thin film of Ce doped yttrium iron garnet on galium gadolinium garnet substrate as well as for pollycrystalline Bi doped yttrium iron garned on silicon substrate. Furthermore, new rare-earth garnets were prepared with attempt to achieve per- pendicular magnetic anisotropy of these film. This was achieved for three di erent materials, which were not...

NiTi alloys with nearly equiatomic chemical composition are the most studied and the most practically utilized materials from the group of the shape memory alloys (SMA). The NiTi alloy has a thermoelastic martensitic transfor- mation (MT), which its two most important properties are based on: the shape memory and the superelasticity. Thin films of NiTi alloys with thicknesses from hundreds of nm to units of µm have a wide use mainly in microelectromechanical systems (MEMS). The doctoral thesis deals with a fabrication of thin NiTi films using a deposition on silicon substrates with two techniques - the magnetron sputtering and the pulsed-laser deposition (PLD), an investigation of their mi- crostructure using x-ray diffraction, a heat treatment of amorphous NiTi films and with a verification of MT using resistometry. Furthermore, thermomechan- ical properties of a system NiTi-polyimide (NiTi-PI), namely a dependence of a curvature radius of a NiTi-PI bilayer on temperature, are studied. 1

<p> Optical metamaterials have triggered extensive studies driven by their fascinating electromagnetic properties that are not observed in natural materials. Aside from the extraordinary progress, challenges remain in scalable processing and material performance which limit the adoption of metamaterial towards practical applications. The goal of this dissertation is to design and fabricate nanocomposite thin films by combining nitrides with a tunable secondary phase to realize controllable multi-functionalities towards potential device applications. Transition metal nitrides are selected for this study due to the inherit material durability and low-loss plasmonic properties that offer stable two-phase hybridization for potential high temperature optical applications. Using a pulsed laser deposition technique, the nitride-metal nanocomposites are self-assembled into various geometries including pillar-in-matrix, embedded nanoinclusions or complex multilayers, that possess large surface coverage, high epitaxial quality, and sharp phase boundary. The nanostructures can be further engineered upon precise control of growth parameters. </p><p> This dissertation is composed of a general review of related background and experimental approaches, followed by four chapters of detailed research chapters. The first two research chapters involve hybrid metal (Au, Ag) - titanium nitride (TiN) nanocomposite thin films where the metal phase is self-assembled into sub-20 nm nanopillars and further tailored in terms of packing density and tilting angles. The tuning of plasmonic resonance and dielectric constant have been achieved by changing the concentration of Au nanopillars, or the tuning of optical anisotropy and angular selectivity by changing the tilting angle of Ag nanopillars. Towards applications, the protruded Au nanopillars are demonstrated to be highly functional for chemical bonding detection or surface enhanced sensing, whereas the embedded Ag nanopillars exhibit enhanced thermal and mechanical stabilities that are promising for high temperature plasmonic applications. In the last two chapters, dissimilar materials candidates beyond plasmonics have been incorporated to extend the electromagnetic properties, include coupling metal nanoinclusions into a wide bandgap semiconducting aluminum nitride matrix, as well as inserting a dielectric spacer between the hybrid plasmonic claddings for geometrical tuning and electric field enhancement. As a summary, these studies present approaches in addressing material and fabrication challenges in the field of plasmonic metamaterials from fundamental materials perspective. As demonstrated in the following chapters, these hybrid plasmonic nanocomposites provide multiple advantages towards tunable optical or biomedical sensing, high temperature plasmonics, controllable metadevices or nanophotonic chips.</p><div><br></div>

Deux mécanismes importants reliant la préparation des couches ultraminces d’oxydes magnétiques à leurs propriétés physiques ont été étudiés dans ce travail. En premier lieu, l’influence de la contrainte épitaxiale sur les propriétés magnéto-optiques de la manganite La₂/₃Sr₁/₃MnO₃ (LSMO) a été étudiée. Les couches ultraminces ont été déposées par ablation laser pulsé sur quatre substrats différents, ce qui a fourni différentes valeurs statiques de la contrainte épitaxiale. Les propriétés magnétiques ont été révélées comme se détériorant avec l’augmentation de la contrainte, ce qui était prévisible à cause de la distorsion grandissante de la maille unitaire ainsi qu’à cause de l’effet de la couche magnétiquement inerte. La combinaison de l’ellipsométrie spectroscopique et de la spectroscopie Kerr magnéto-optique a été utilisée afin de déterminer les spectres des éléments diagonaux et non diagonaux du tenseur de permittivité. L’étude des éléments non-diagonaux a confirmé la présence déjà rapportée de deux transitions électroniques dans les spectres de toutes les couches. De plus, elle a révélé une autre transition électronique autour de l’énergie de 4.3 eV, mais seulement dans les spectres des couches déposées avec une contrainte compressive. Nous avons proposé la classification de cette transition comme une transition paramagnétique du champ cristallin Mn t2g → eg. Cette classification a été confortée par des calculs ab initio. Nous avons ainsi montré le rôle clé de la contrainte dans le contrôle des propriétés magnéto-optiques des couches pérovskites ultraminces. En revanche, l’application dynamique de la contrainte par l’utilisation d’une sous-couche piézoélectrique est restée peu concluante. Le transfert de la contrainte entre la sous-couche piézoélectrique et la couche LSMO nécessite des améliorations ultérieures. En second lieu, l’influence de la désorientation du substrat a été étudiée par rapport à la dynamique de l’aimantation dans l’oxyde SrRuO₃ (SRO). Comme attendu, nous avons trouvé qu’un grand angle de désorientation mène à la suppression de la croissance de plusieurs variants cristallographiques du SRO. Au moyen de la microscopie à force magnétique, nous avons montré que la présence de plusieurs variants de SRO mène à l’augmentation de la densité de défauts agissant comme points d’ancrage ou de nucléation pour les domaines magnétiques. Nous avons donc montré que l’emploi d’un substrat vicinal est important pour la fabrication des couches ultraminces de SRO de haute qualité, avec une faible densité de défauts cristallographiques et d’excellentes propriétés magnétiques. / Two important mechanisms in preparation of ultrathin films of magnetic oxides were systematically investigated in this work. First, influence of epitaxial strain on resulting magneto-optical properties of La₂/₃Sr₁/₃MnO₃ (LSMO) ultrathin films was studied. The investigated films were grown by pulsed laser deposition on four different substrates, providing a broad range of induced epitaxial strains. Magnetic properties were found to deteriorate with increasing value of the epitaxial strain, as expected due to the unit cell distortion increasingly deviating from the bulk and effect of the magnetically inert layer. A combination of spectroscopic ellipsometry and magneto-optical Kerr effect spectroscopy was used to determine spectra of the diagonal and off-diagonal elements of permittivity tensor. The off-diagonal elements confirmed presence of two previously reported electronic transitions in spectra of all films. Moreover, they revealed another electronic transition around 4.3 eV only in spectra of films grown under compressive strain. We proposed classification of this transition as crystal field paramagnetic Mn t2g → eg transition, which was further supported by ab initio calculations. A key role of strain in controlling electronic structure of ultrathin perovskite films was demonstrated. Dynamic application of strain via use of piezoelectric underlayer remained inconclusive, requiring further improvement of the strain transfer from the piezoelectric layer into the LSMO. Second, influence of substrate miscut on magnetization dynamics in SrRuO₃ (SRO) was studied. As expected we found that high miscut angle leads to suppression of multi-variant growth. By means of magnetic force microscopy we showed that presence of multiple SRO variants leads to higher density of defects acting as pinning or nucleation sites for the magnetic domains, which consequently results in deterioration of magnetic properties. We demonstrated that use of vicinal substrate with high miscut angle is important for fabrication of high quality SRO ultrathin films with low density of crystallographic defects and excellent magnetic properties.

The Pulsed Laser Deposition is an established method for the preparation of thin films and nm layer systems. In this work a cross beam PLD system is used as a special development for reduction of macro particle contamination in the growing layer. Two plasma plumes which overlap under a defined angle are produced on separated targets by two synchronized lasers. In the overlapping zone the direction of plasma expansion is changed by interaction of plasma particles. A diaphragm is used to guaranty that only the part of the plasma is deposited on the substrate that has changed the direction of expansion in the interaction zone. Detailed characterizations of plasma properties, deposition and growth conditions were carried out to demonstrate that cross beam PLD is an effective method to reduce macro particle contamination and allows layer growth under reduced energetic loading of the substrate. In the second part of this work cross beam PLD is used to produce Ni/C multilayers and artificial mixtures. The interest is focused on the mechanisms of layer disintegration and structure formation under thermal loading. Possible processes for layer disintegration are discussed on a theoretical background and verified in TEM examinations. / Die Pulsed Laser Deposition ist ein etabliertes Verfahren zur Herstellung dünner Schichten im nm-Bereich. Das in dieser Arbeit verwandte PLD-Zweistrahlverfahren ist eine besondere Entwicklung zur Verringerung der Makropartikelkontamination der Schichten. Zwei synchronisierte Laser erzeugen auf zwei benachbarten Targets zwei Plasmafackeln, die unter einem bestimmten Winkel überlappen, was zu einer Änderung der Ausbreitungsrichtung des Palmas führt. Ein spezielle Blendenanordnung garantiert, dass nur der abgelenkte Teil des Plasmas auf dem Substrat abgeschieden wird, welches für die anfänglichen Plasmafackeln im Schatten liegt. Anhand einer umfangreichen Charakterisierung der Plasma-, Abscheide- und Schichtwachstumseigenschaften wird gezeigt, dass das PLD-Zweistrahlverfahren eine effektive Verminderung der Makropartikelkontamination der Schichten ermöglicht und dass das Schichtwachstum unter deutlich verringertem Energieeintrag im Vergleich zur konventionellen PLD erfolgt. Das Verfahren wird im zweiten Teil der Arbeit angewandt um Ni/C-Multischichten und künstliche Mischungen herzustellen. Das Interesse liegt hierbei auf den Mechanismen des Schichtzerfalls und auf den entstehenden Strukturen bei thermischer Behandlung metastabiler Schichtsysteme. Anhand theoretischer Betrachtungen werden die möglichen Prozess des Schichtzerfalls eingegrenzt und mittels TEM-Untersuchungen verifiziert.

Physical vapor deposition (PVD) refers to the removal of atoms from a solid or a liquid by physical means, followed by deposition of those atoms on a nearby surface to form a thin film or coating. Various approaches and techniques are applied to release the atoms including thermal evaporation, electron beam evaporation, ion-driven sputtering, laser ablation, and cathodic arc-based emission. Some of the approaches are based on a plasma discharge, while in other cases the atoms composing the vapor are ionized either due to the release of the film-forming species or they are ionized intentionally afterward. Here, a brief overview of the various PVD techniques is given, while the emphasis is on sputtering, which is dominated by magnetron sputtering, the most widely used technique for deposition of both metallic and compound thin films. The advantages and drawbacks of the various techniques are discussed and compared.

The discovery of high temperature superconductors led to a tremendous boom in the development of new applications based on this material. Due to the significant anisotropy and the dependence of the critical current density on the misorientation of grains, the so-called coated conductor technology was developed for these materials to realize long wires. These conductors are applied at liquid nitrogen temperature for cables or motors as well as in liquid helium for high-field applications, such as in magnets for particle accelerators or future fusion reactors. One of the main aspects of using superconducting materials in the above-mentioned areas is their high current-carrying capacity, which decreases for a number of reasons. Therefore, studying the superconducting current flow in such conductors remains a priority to understand the main mechanisms and to increase the critical current density in a wide range of temperatures and magnetic fields. The major goal of this thesis was to study the correlation between the local microstructure and the superconducting properties for Ag-doped YBa2Cu3O7−δ (YBCO), (Nd1/3Eu1/3Gd1/3)Ba2Cu3O7−δ (NEG) and the iron-based superconductor Ba(Fe1−xNix)2As2 (Ba122:Ni). Therefore, epitaxial films were grown of these materials by pulsed laser deposition on single crystals and two different commercial coated conductor templates having a different degree of granularity. Experimental techniques such as electron backscattering diffraction (EBSD) and scanning Hall probe microscopy (SHPM) allow to investigate both the local microstructure and local distribution of superconducting current in these films. Ag-doped YBCO films with different thickness were deposited on single crystalline SrTiO3 substrates as well as on RABiTS and IBAD-MgO-based templates. It is expected, that silver as dopant improves the growth of the films, and has a beneficial influence on the current transport across grain boundaries, which is of considerable interest for metal-based templates due to their granular structure. EBSD studies on the local microstructure revealed only minor changes with silver concentration. Nevertheless, an improvement in transport properties was observed for thicker YBCO:Ag layers on SrTiO3 and thin films on both metal-based templates. SHPM measurements show an improvement of the local current distribution, which is probably due to the improvement of the current transport between the grains. NEG films were grown with different thicknesses on RABiTS and IBAD-MgO-based templates for the first time. Structural studies revealed an epitaxial growth of all samples on both metal-based templates. Whereas NEG layers on SrTiO3 showed broad superconducting transitions due to film inhomogeneities, a narrow transition at about 89 K was measured for films grown on the metal templates. However, the critical current density is still inferior to YBCO films of similar thickness. This might be improved by further optimization of the growth and oxygen loading conditions. Finally, the Ba122:Ni films were studied on single crystalline CaF2 substrates and commercial metal-based templates. This material might be interesting for applications due to a low anisotropy, high upper critical fields and critical currents as well as a reduced sensitivity to grain boundaries. Structural studies showed an epitaxial growth on RABiTS templates, whereas no epitaxy was found on IBAD-MgO based tapes. Simultaneously, a broad superconducting transition was observed on the metallic templates, which requires a further optimization of the growth process. Detailed studies of the superconducting and electronic properties for Ba122:Ni films on CaF2 substrates revealed similar properties as for single crystals, which opens the prospects to use such films for different applied and fundamental tasks.