<p>The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production.</p><p>The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase.</p><p>The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer.</p><p>Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.</p>

The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production. The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase. The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer. Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.

In ungeordneten Fe70Pd30-Strukturen ermöglicht eine martensitische Umwandlung den magnetischen Formgedächtniseffekt, der in Aktoren genutzt werden kann. Der inverse Effekt kann für hochempfindliche Dehnungsmessungen verwendet werden. Eine Miniaturisierung zu Schichten ermöglicht Anwendungen in mikro- und nanoelektromechanischen Systemen. Ziel dieser Arbeit ist es, die magnetischen Eigenschaften in Abhängigkeit von der Struktur zu bestimmen und die gewünschte Kombination aus beiden auf dickere Schichten zu übertragen. In Kapitel 2 werden die strukturellen Aspekte im Fe-Pd-System und die Besonderheiten des Wachstums dünner Schichten betrachtet. In Kapitel 3 werden die Schichtherstellung mittels Kathodenzerstäubung und die verschiedenen Charakterisierungsmethoden kurz vorgestellt. Kapitel 4 zeigt den Einfluss durch verschiedene Zwischenschichten mit unterschiedlichen Gitterparametern auf die Kristall- und Elektronenstruktur sowie auf die magnetischen Eigenschaften von dünnen, epitaktischen Fe-Pd-Cu-Schichten. Untersuchungen zur kritischen Schichtdicke und Relaxationsmechanismen stehen in Kapitel 5 im Vordergrund. In Kapitel 6 wird die kombinatorische Schichtherstellung vorgestellt, die eine systematische Variation von Struktur und Zusammensetzung für eine praxisnahe Anwendung erlaubt. Außerdem werden Ergebnisse zu freien Schichten gezeigt und der Einfluss des Ablösens auf Morphologie und Struktur diskutiert.

Poor indoor air quality is a source of adverse health effects. TiO2 coatings deposited on well-illuminated surfaces, such as window panes, can be used to fully mineralize indoor air pollutants by photocatalysis. In such applications it is important to ensure stable photocatalytic activity for a wide range of operating conditions, such as relative humidity and temperature, and to avoid deactivation of the catalyst. In this thesis photocatalytic removal of the indoor-pollutant acetaldehyde (CH3CHO) on nanostructured TiO2 films is investigated, and in particular it is proposed how such films can be modified and operated for maximum performance. Catalyst deactivation can be reduced by purposefully changing the surface acidity of TiO2 by covalently attaching SO4 to the surface. Moreover, the overall photocatalytic activity on anatase TiO2 films can be improved by increasing the fraction of exposed reactive {001} surfaces, which otherwise are dominated by {101} surfaces. In the first part of the thesis mode-resolved in-situ FTIR is used to elucidate the reaction kinetics of CH3CHO adsorption and photo-oxidation on the TiO2 and SO4 – modified TiO2 surfaces. Surface concentrations of main products and corresponding reaction rates were determined. Formate is the major reaction product, whose further oxidation limits the complete oxidation to gaseous species, and is responsible for photocatalyst deactivation by site inhibition. The oxidation reaction is characterized by two reaction pathways, which are associated with two types of surface reaction sites. On the sulfate modified TiO2 catalyst fewer intermediates are accumulated, and this catalyst resists deactivation much better than pure TiO2. A hitherto unknown intermediate – surface-bound acetaldehyde dimer with an adsorption band at 1643 cm−1 was discovered, using interplay between FTIR spectroscopy and DFT calculations. The second part of the thesis treats the effect of increasing the relative abundance of exposed {001} facets on the photocatalytic activity of anatase TiO2 films prepared by DC magnetron sputtering. A positive effect was observed both for liquid-phase photo-oxidation of methylene blue, and for gas-phase photocatalytic removal of CH3CHO. In both cases it was found that the exposed {001} surfaces were an order of magnitude more reactive, compared to the {101} ones. Furthermore, it was found that the reactive films were more resilient towards deactivation, and exhibited almost unchanged activity under varying reaction conditions. Finally, a synergetic effect of SO4 – modification and high fraction of exposed {001} surfaces was found, yielding photocatalysts with sustained high activity. The results presented here for facet controlled and chemically modified TiO2 films are of interest for applications in the built environment for indoor air purification and as self-cleaning surfaces. / GRINDOOR

Les travaux présentés dans ce manuscrit traitent de l’optimisation du procédé de dépôt de couches minces sur un fil d’acier inoxydable en mouvement. Deux magnétrons cylindriques inversés (ICM) sont utilisés pour étudier différents aspects de la pulvérisation cathodique. Dans un premier temps, un modèle analytique permettant l’évaluation des contributions thermiques à l’échauffement du substrat est confronté à des séries de mesures. Les résultats obtenus sont concluants mais souffrent de l’inhomogénéité du champ magnétique, lequel est à l’origine de pertes localisées d’électrons secondaires de haute énergie. Afin de limiter la contribution thermique des charges sur le substrat, des anodes auxiliaires, destinées à récupérer le flux d’énergie, sont ajoutées à chaque extrémité des magnétrons. Leur influence sur la distribution du plasma, sur la microstructure et sur la composition chimique des dépôts est alors discutée. Dans une seconde partie, l’étude des magnétrons lors de dépôts réactifs met en avant la nécessité d’homogénéiser le champ magnétique dans les cathodes. Une discussion est alors conduite sur l’influence du champ magnétique sur la distribution des vitesses de dépôt au sein des magnétrons et un modèle analytique, ayant pour but de reproduire les profils de dépôt, est développé sur la base des résultats obtenus. Une étude paramétrique (pression, distance cible – substrat, intensité du champ magnétique) est aussi réalisée afin de déterminer les conditions de dépôt optimales dans un ICM. Finalement, de la modélisation par éléments finis à l’aide d’un logiciel commercial vient clore le manuscrit. / The work presented in this manuscript deals with the optimization of the process of deposition of thin films on a moving stainless steel wire. Two inverted cylindrical magnetrons (ICMs) are used to study different aspects of sputtering. At first, an analytical model allowing the evaluation of the thermal contributions to the heating of the substrate is confronted with series of measurements. The results obtained are conclusive but suffer from the inhomogeneity of the magnetic field, which is responsible for the localized loss of high energy secondary electrons. In order to limit the thermal contribution of the charges on the substrate, auxiliary anodes designed to recover the energy flow, are added to each end of the magnetrons. Their influence on the plasma distribution, the microstructure and the chemical composition of the coatings is then discussed. In a second part, the study of reactive sputter deposition with ICMs highlights the need to homogenize the magnetic field in the cathodes. A discussion is then conducted on the influence of the magnetic field on the distribution of deposition rates within the magnetrons and an analytical model, aimed at reproducing the deposition profiles, is developed on the basis of the results obtained. A parametric study (pressure, target – substrate distance, magnetic field strength) is also performed to determine optimal deposition conditions in an ICM. Finally, finite element modeling using commercial software closes the manuscript.

Volatile organic compounds (VOCs) in the indoor air have adverse effects on the dwellers residing in a building or a vehicle. One of these effects is called sick building syndrome (SBS). SBS refers to situations in which the users of a building develop acute health effects and discomfort depending on the time they spend inside some buildings without having any specific illness. Furthermore, monitoring volatile organic compounds could lead to early diagnosis of specific illnesses through breath analysis. Among those VOCs formaldehyde, acetaldehyde can be listed. In this thesis, VOC detecting thin film sensors have been investigated. Such sensors have been manufactured using semiconducting metal oxides, ligand activated gold nanoparticles and Graphene/TiO2 mixtures. Advanced gas deposition unit, have been used to produce NiO thin films and Au nanoparticles. DC magnetron sputtering has been used to produce InSnO and VO2 thin film sensors. Graphene/TiO2 sensors have been manufactured using doctor-blading. While presenting the results, first, material characterization details are presented for each sensor, then, gas sensing results are presented. Morphologies, crystalline structures and chemical properties have been analyzed using scanning electron microscopy, X-ray diffraction and X-ray photo electron spectroscopy. Furthermore, more detailed analyses have been performed on NiO samples using extended X-ray absorption fine structure method and N2 adsorption measurements. Gas sensing measurements were focused on monitoring formaldehyde and acetaldehyde. However, responses ethanol and methane were measured in some cases to monitor selectivity. Graphene/TiO2 samples were used to monitor NO2 and NH3. For NiO thin film sensors and Au nano particles, fluctuation enhanced gas sensing is also presented in addition to conductometric measurements.

In ungeordneten Fe70Pd30-Strukturen ermöglicht eine martensitische Umwandlung den magnetischen Formgedächtniseffekt, der in Aktoren genutzt werden kann. Der inverse Effekt kann für hochempfindliche Dehnungsmessungen verwendet werden. Eine Miniaturisierung zu Schichten ermöglicht Anwendungen in mikro- und nanoelektromechanischen Systemen. Ziel dieser Arbeit ist es, die magnetischen Eigenschaften in Abhängigkeit von der Struktur zu bestimmen und die gewünschte Kombination aus beiden auf dickere Schichten zu übertragen. In Kapitel 2 werden die strukturellen Aspekte im Fe-Pd-System und die Besonderheiten des Wachstums dünner Schichten betrachtet. In Kapitel 3 werden die Schichtherstellung mittels Kathodenzerstäubung und die verschiedenen Charakterisierungsmethoden kurz vorgestellt. Kapitel 4 zeigt den Einfluss durch verschiedene Zwischenschichten mit unterschiedlichen Gitterparametern auf die Kristall- und Elektronenstruktur sowie auf die magnetischen Eigenschaften von dünnen, epitaktischen Fe-Pd-Cu-Schichten. Untersuchungen zur kritischen Schichtdicke und Relaxationsmechanismen stehen in Kapitel 5 im Vordergrund. In Kapitel 6 wird die kombinatorische Schichtherstellung vorgestellt, die eine systematische Variation von Struktur und Zusammensetzung für eine praxisnahe Anwendung erlaubt. Außerdem werden Ergebnisse zu freien Schichten gezeigt und der Einfluss des Ablösens auf Morphologie und Struktur diskutiert.

The magnetic field is a key feature that distinguishes magnetron sputtering from simple diode sputtering. It effectively increases the residence time of electrons close to the cathode surface and by that increases the energy efficiency of the discharge. This becomes apparent in high power impulse magnetron sputtering (HiPIMS) discharges, as small changes in the magnetic field can result in large variations in the discharge characteristics, notably the peak discharge current and/or the discharge voltage during a pulse. Here, we analyze the influence of the magnetic field on the electron density and temperature, how the discharge voltage is split between the cathode sheath and the ionization region, and the electron heating mechanism in a HiPIMS discharge. We relate the results to the energy efficiency of the discharge and discuss them in terms of the probability of target species ionization. The energy efficiency of the discharge is related to the fraction of pulse power absorbed by the electrons. Ohmic heating of electrons in the ionization region leads to higher energy efficiency than electron energization in the sheath. We find that the electron density and ionization probability of the sputtered species depend largely on the discharge current. The results suggest ways to adjust electron density and electron temperature using the discharge current and the magnetic field, respectively, and how they influence the ionization probability.

The electrocatalytic nitrogen reduction reaction (NRR) is of considerable interest due to its potential for less energy intensive and environmentally friendly ammonia production which is critical for agricultural and clean energy applications. However, the selectivity of NRR compared to the hydrogen evolution reaction (HER) often poses challenges for various catalysts, including Earth-abundant transition metal oxynitrides like Ti, V, and Co. In this work, a comparative analysis of the selectivity of these three metal oxynitrides was conducted, each having different metal oxophilicities. A combination of electrochemical, surface characterizations and density functional theory (DFT) calculations were employed to directly assess NRR and HER activities under the same reaction conditions. Results show that cobalt oxynitrides exhibit NRR activity at pH 10, involving the electrochemical reduction of both lattice-bound nitrogen and dissolved N2, although more HER activity was observed. In contrast, vanadium oxynitride films displayed HER inactivity at pH 7 and 10 but demonstrated NRR activity at pH 7, while titanium oxynitrides were active at pH 3.2 but inactive under neutral and basic pH conditions. These comprehensive studies highlight substantial variations in HER and NRR selectivity based on transition metal oxophilicity/azaphilicity, indicating distinct mechanisms governing NRR and HER mechanisms.

In dieser Arbeit sind Dielektrika mit hoher relativer Permittivität untersucht worden, welche eine Anwendung in dynamischen Halbleiter-Speicherzellen (DRAM) zum Ziel haben. Sie unterstützen das Weiterführen der fortschreitenden Miniaturisierung der Speicherzellen bzw. der Erhöhung der Speicherdichten und dienen als Alternative zu den bisherigen Standardmaterialien SiO2 und Si3N4. Als Herstellungsmethoden für mehrkomponentige Oxide wurden zum einen die Molekularstrahl-Deposition und zum anderen die Ko-Sputterdeposition gewählt, da sie eine sehr große Flexibilität bei der Wahl der abscheidbaren Elemente und Oxide bieten sowie eine hohe Ratenstabilität und Reinheit versprechen. Hierfür wurden Prozesse zur simultanen Abscheidung dünner Schichten aus mehreren Quellen entwickelt und optimiert. Als neuartige Dielektrika wurden ZrO2 und SrZrO3 hergestellt und untersucht. Hierbei wurden besonders die dielektrischen und kristallographischen Eigenschaften in Abhängigkeit von der Stöchiometrie umfangreich analysiert. Die maximale erreichte Dielektrizitäszahl des ZrO2 betrug ca. 30 und die des SrZrO3 ca. 31. Es wurde dargelegt, dass die Dielektrizitätszahl des ZrO2 unter bestimmten Umständen von der Schichtdicke im Bereich von 5 bis 50 nm abhängig ist. Dies konnte durch die Beimischung von Sr erfolgreich stabilisiert werden. Die für DRAM-Anwendungen zum Teil zu hohen Leckstromdichten konnten durch die Entwicklung eines neuen Ausheilverfahrens deutlich verbessert werden. Aufgrund der hohen Dielektrizitätszahl in Verbindung mit gesenkten Leckströmen konnte für ZrO2 eine minimale kapazitätsäquivalente Dicke von CET = 1,2 nm und für SrZrO3 eine CET = 1,4 nm erreicht werden, welche der DRAM-Grenze für Leckstromdichten von J = 100 nA/cm² genügen. Diese Werte sind deutlich geringer als die dünnsten, theoretisch möglichen Schichten des klassischen SiO2 und Si3N4, wodurch sowohl ZrO2 als auch SrZrO3 ihr Potential, als Alternative für Speicheranwendungen zu dienen, unterstreichen. / In this work, dielectrics with a high relative permittivity were investigated, which are intended for the application in dynamic random access memory cells (DRAM). Their successful implementation ensures the continuation of the ongoing scaling of memory devices, thus increasing the storage density. They serve as alternative for the standard materials SiO2 and Si3N4. In order to to grow multi-component oxides, molecular beam deposition as well as co-sputter deposition were chosen, given their high flexibility to evaporate various elements and oxides. Additionally, both hold their promise of a good control of the growth rate and high purity. Therefore processes were developed and optimized for growing thin films by using multiple sources simultaneously. The alternative dielectrics ZrO2 and SrZrO3 were fabricated and analysed. Especially, the dependency of the dielectric and crystallographic properties on the stoichiometry were evaluated comprehensively. The highest achieved relative permittivity for ZrO2 and SrZrO3 were approx. 30 and 31, respectively. Under specific and controllable circumstances, the relative permittivity of ZrO2 was found to depend on the film thickness in the range of 5 to 50 nm. However, the admixture of Sr stabilises the relative permittivity. In some cases, the leakage current densities of ZrO2 and SrZrO3 films were too high for DRAM applications. It was possible to decrease those currents drastically by developing a new healing process. The high permittivity in addition with the improved leakage current densities led in the case of ZrO2 to a minimum capacitance equivalent thickness of CET = 1.2 nm and in the case of SrZrO3 to a CET = 1.4 nm, which fulfill the DRAM leakage current density limit of J = 100 nA/cm². Those values are much lower than the thinnest theoretically possible films of the conventional SiO2 or Si3N4. Therefore, ZrO2 and SrZrO3 accentuate their potential for memory applications.