Le Ta₃N₅ fait partie des matériaux les plus prometteurs pour la photo-électrolyse de l’eau. En effet, la bande de valence et la bande de conduction sont situées autour du potentiel d’évolution de l’hydrogène et de l’oxygène et son petit gap (2.1eV) permet l’absorption d’une grande partie du spectre solaire. Par contre la synthèse de ce matériau est difficile à cause de la structure riche en azote (faible diffusion) et de l’état d’oxydation élevé du Ta (+5) dans le cristal de Ta₃N₅. Sa synthèse par pulvérisation cathodique est peu exploitée à ce jour, malgré que cette technique de dépôt permette d’augmenter le rapport ion-neutre arrivant sur le film en croissance et donc de fournir de l’énergie supplémentaire à la surface du film favorisant ainsi la cristallisation. Lors cette thèse, des couches minces de Ta₃N₅ ont été déposées par pulvérisation cathodique dans une atmosphère réactive. Il y est montré que la pulvérisation d’une cible de Ta produit des Ar rétrodiffusés avec des énergies élevées qui augmentent l’incorporation de défauts dans la couche lorsque la polarisation de la cible est élevée. Des films de Ta₃N₅ ont été déposés en mode continu ce qui a permis de maintenir une polarisation faible. Il a été mis en évidence que l’oxygène incorporé dans le cristal joue un rôle crucial pour la déposition du film de Ta₃N₅. De plus, l’oxygène influence fortement les propriétés des couches minces, notamment les propriétés optiques et électroniques. Un nouveau système, augmentant le flux d’ions vers le substrat, a été installé dans le réacteur de dépôt ce qui a augmenté le degré de cristallisation de la phase Ta₃N₅. Les connaissances acquises lors de cette thèse ont été utilisées pour préparer des photoanodes à partir de Ta₃N₅ et leur aptitude à décomposer l’eau sous l’illumination du soleil a été démontrée. / Ta₃N₅ is one of the most promising candidates for efficient water splitting using sunlight due to its band positions with respect to the oxygen and hydrogen evolution potentials and its small band gap of 2.1eV. Its synthesis, however, is challenging given its high content of nitrogen, with its low diffusivity, and the Ta metal atom in a high oxidation state. Few investigations into its synthesis by magnetron sputtering exist to date although this technique offers the possibility of tuning the ion-to-neutral flux ratio onto the growing film. This can change the supply of energy onto its surface and therefore promote the crystallization. In this thesis, reactive magnetron sputtering is investigated for the preparation of Ta₃N₅ thin films. It is shown that sputtering of a Ta target in an Ar atmosphere produces energetic backscattered Ar neutrals at high target potentials. To keep the potential low, Ta₃N₅ is deposited by sputtering in DC mode. The growth of the Ta₃N₅ phase requires the incorporation of oxygen into the lattice. It is shown that optical and electronic properties of these samples vary strongly with the precise amount of oxygen in the thin film. Samples with a high degree of crystallinity are obtained by increasing the N₂⁺ flux onto the substrate by changing the form of the magnetic field of the magnetron. The highly crystalline samples prepared by this method are proven to work as photoanodes for the splitting of water under illumination.

Ce travail s'inscrit dans le cadre d'une thèse Cifre, en partenariat avec la société VIESSMANN Faulquemont SAS, dont l'objectif est d'aboutir à une couche absorbante de nouvelle génération qui vise à réguler de manière passive et réversible la température d'un capteur solaire. Cette couche absorbante est à base de dioxyde de vanadium (VO2), un matériau thermochrome qui présente une transition de phases de type semi-conducteur/métal en fonction de la température. Dans un premier temps, l'élaboration de films de VO2 à 500°C sera présentée puis nous montrerons un procédé inédit et original permettant d'obtenir une phase pure VO2 à partir d'un dépôt effectué à température ambiante. L'étude en température des propriétés optiques et électriques de ces deux types de revêtements sera discutée ainsi que les effets sur la transition de phases de paramètres tels que, la taille de grains ou encore les contraintes internes. Enfin, nous étudierons les propriétés physiques du système biphasé du type VO2+V4O9 qui sous forme de couche absorbante se trouve, in fine, être très avantageux pour la régulation thermique d'un panneau solaire / This work is incorporated within the framework of a Cifre thesis with the partnership of the VIESSMANN Faulquemont SAS society to end in a new generation of absorbent layer in order to regulate the temperature of a solar cell in a passive and reversible way. This absorbent layer is based on vanadium dioxide (VO2), this thermochromic material exhibits a phase semiconductor to metal transition depending on its temperature. In a first step, the synthesis of VO2 films at 500 °C will be exposed and then we will present a new process to obtain a pure VO2 phase with a film deposited at room temperature. The study in temperature of the optical and electrical properties of these two kinds of coatings will be discussed, same as the effects on the phase transition of parameters such as the grain size or the internal stresses. Eventually, we will study the physical properties of a VO2+V4O9 two-phase system as an absorbent layer which is, in fine, very beneficial for the thermal regulation of a solar panel

abstract: The origins of carrier mobility (μe) were thoroughly investigated in hydrogenated indium oxide (IO:H) and zinc-tin oxide (ZTO) transparent conducting oxide (TCO) thin films. A carrier transport model was developed for IO:H which studied the effects of ionized impurity scattering, polar optical phonon scattering, and grain boundary scattering. Ionized impurity scattering dominated at temperatures below ~240 K. A reduction in scattering charge Z from +2 to +1 as atomic %H increased from ~3 atomic %H to ~5 atomic %H allowed μe to attain >100 cm^2/Vs at ~5 atomic %H. In highly hydrogenated IO:H, ne significantly decreased as temperature increased from 5 K to 140 K. To probe this unusual behavior, samples were illuminated, then ne, surface work function (WF), and spatially resolved microscopic current mapping were measured and tracked. Large increases in ne and corresponding decreases in WF were observed---these both exhibited slow reversions toward pre-illumination values over 6-12 days. A hydrogen-related defect was proposed as source of the photoexcitation, while a lattice defect diffusion mechanism causes the extended decay. Both arise from an under-coordination of the In. An enhancement of μe was observed with increasing amorphous fraction in IO:H. An increase in population of corner- and edge-sharing polyhedra consisting of metal cations and oxygen anions is thought to be the origin. This indicates some measure of medium-range order in the amorphous structure, and gives rise to a general principle dictating μe in TCOs---even amorphous TCOs. Testing this principle resulted in observing an enhancement of μe up to 35 cm^2/Vs in amorphous ZTO (a-ZTO), one of the highest reported a-ZTO μe values (at ne > 10^19 cm^-3) to date. These results highlight the role of local distortions and cation coordination in determining the microscopic origins of carrier generation and transport. In addition, the strong likelihood of under-coordination of one cation species leading to high carrier concentrations is proposed. This diverges from the historical indictment of oxygen vacancies controlling carrier population in crystalline oxides, which by definition cannot occur in amorphous systems, and provides a framework to discuss key structural descriptors in these disordered phase materials. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Mittels reaktivem Magnetron-Sputtern hergestellte Indium-Zinn-Oxid-Dünnschichten wurden mit den Methoden der Röntgendiffraktometrie und Röntgenreflektometrie charakterisiert. Es konnte gezeigt werden, dass die Wahl des Arbeitspunktes bei der Schichtabscheidung erheblichen Einfluss auf Kristallitorientierung, Gitterkonstante und Größe der Schichtspannung hat. Zusätzlich wurden mittels des Langford-Verfahrens Korngröße und Mikrospannungen bestimmt. Im Rahmen der röntgenografischen Spannungsmessung zeigten sich nichtlineare Verläufe der Dehnung über sin²Ψ, die mit dem Kornwechselwirkungsmodell nach Vook und Witt erklärt werden.

In der vorliegenden Arbeit wird der reaktive ITO-Abscheidprozess unter Verwendung metallischer In:Sn-Targets eingehend untersucht. Die Schichtabscheidung erfolgt am symmetrisch bipolar gepulstem Dual-Magnetron sowohl auf ruhende als auch bewegte Substrate. Die Arbeit umfasst zwei Teilgebiete. Einerseits wurde der dynamische ITO-Abscheideprozess an einer industrienahen Versuchsanlage umfassend charakterisiert und anhand seiner physikalischen Parameter erfolgreich an eine industrielle Beschichtungsanlage überführt. Andererseits fanden statische Beschichtungen statt. Diese ermöglichen die Analyse der lateralen Verteilung der funktionellen Schichteigenschaften. Dadurch konnte eine Korrelation zu den lateralen Verteilungen der gemessenen Plasmaparameter herausgearbeitet werden.

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

Title: Controllable synthesis, treatment and characterization of anodes for Direct Formic Acid Fuell Cell Author: Mgr. Igor Bieloshapka Department/Institute: Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Ing. Petr Jiříček, CSc., Institute of Physics of the Czech Academy of Sciences, Division of Solid State Physics, Department of Optical Materials Abstract: At this doctoral thesis, anodes were prepared by novel DC magnetron sputtering technique for direct formic acid fuel cells (DFAFCs). Anode part consisted of support material and catalyst. Carbon cloth and polyaniline were used as a support. Palladium and palladium-copper bimetallic catalysts were deposited on the top of the support. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used for investigation of the morphology of the anodes. Composition and chemical states on the anode part were studied by x-ray photoelectron spectroscopy (XPS). Transmission electron microscope (TEM) together with the XPS technique were used for characterizing graphene oxide (GO) and reduced graphene oxide (RGO) as a promising support for the polymer membrane fuel cells. For decreasing the role of substoichiometric PdCx phase and other contaminations on the surface of...

The L10 FePt phase belongs to the most promising hard ferromagnetic materials for high density recording media. The main challenges for thin FePt films are: (i) to lower the process temperature for the transition from the soft magnetic A1 to the hard magnetic L10 phase, (ii) to realize c-axes preferential oriented layers independently from the substrate nature and (iii) to control layer morphology supporting the formation of FePt - L10 self-organized isolated nanoislands towards an increase of the signal-to-noise ratio. In this study, dc magnetron sputtered FePt thin films on amorphous substrates were inve-stigated. The work is focalized on the correlation between structural and magnetic properties with respect to the influence of deposition parameters like growth mode (co-sputtering vs. layer – by - layer) and the variation of the deposition gas (Ar, Xe) or pressure (0.3 - 3 Pa). In low-pressure Ar discharges, high energetic particle impacts support vacancies formation during layer growth lowering the phase transition temperature to (320 +/- 20)°C. By reducing the particle kinetic energy in Xe discharges, highly (001) preferential oriented L10 - FePt films were obtained on a-SiO2 after vacuum annealing. L10 - FePt nano-island formation was supported by the introduction of an Ag matrix, or by random ballistic aggregation and atomic self shadowing realized by FePt depositions at very high pressure (3 Pa). The high coercivity (1.5 T) of granular, magnetic isotropic FePt layers, deposited in Ar discharges, was measured with SQUID magnetometer hysteresis loops. For non-granular films with (001) preferential orientation the coercivity decreased (0.6 T) together with an enhancement of the out-of- plane anisotropy. Nanoislands show a coercive field close to the values obtained for granular layers but exhibit an in-plane easy axis due to shape anisotropy effects. An extensive study with different synchrotron X-ray scattering techniques, mainly performed at the ESRF, BM-20 (ROBL-Beamline), pointed out the importance of in-situ investigations to clearly understand the kinetic mechanism of the A1 to L10 transition and ordering and to control FePt nanoclusters evolution.

Magister Philosophiae - MPhil / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in V02 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-V02 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of V02 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of V02 thin films. A reversible thermal tunability of the optical/dielectric constants of V02 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host matrix.

Title: Controllable synthesis, treatment, and characterization of anodes for Direct Formic Acid Fuel Cell Author: Igor Bieloshapka Department: Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University Supervisor of the doctoral thesis: Ing. Petr Jiříček, CSc., Institute of Physics of the Czech Academy of Sciences, Division of Solid State Physics, Department of Optical Materials Abstract: This doctoral thesis concerns the preparation of anodes with Pd-based catalysts. Anodes were deposited on a support surface with magnetron sputtering. The prepared samples were tested in a direct formic acid fuel cell (DFAFC) station. Polyaniline, graphene oxide (GO) and reduced graphene oxide (RGO) have been additionally investigated as promising support material for polymer membrane fuel cells (FCs). A scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphological differences between the prepared samples. Elemental composition and chemical states on the anode part were studied through X-ray photoelectron spectroscopy (XPS). The results show that the power density of the prepared anodes with 3 nm of palladium thickness is lower only by 30% in comparison with chemically prepared catalysts. The highest power density results were achieved for the...