De nombreuses études ont prouvé l’affaiblissement de la résistance de l’alliage 600 lors de l’oxydation en milieu primaire des réacteurs à eau pressurisée. Celle-ci induit la rupture localisée du matériau notamment par fissure intergranulaire. La nature ainsi que la structure de l’oxyde se développant à la surface de l’alliage sont parfaitement connues. Cependant, l’influence mécanique de l’oxyde sur l’alliage n’a pas été explorée. L’objectif de cette étude est d’apporter des connaissances nouvelles sur l’impact de l’oxydation sur la réponse mécanique de l’alliage. Un système d’analyse, basé sur l’utilisation de nanoplots comme marqueurs de position, a été développé et mis en œuvre afin de mesurer des déformations engendrées par l’oxydation puis par une traction. Le traitement statistique de ces données a permis de déterminer des évènements rares de haute déformation. Les échantillons utilisés ont été caractérisés par MEB, TEM, XPS et ellipsométrie spectroscopique afin d’en déduire l’épaisseur de la couche d’oxyde interne contraignant l’alliage. De plus, le couplage de l’EBSD avec les nanoplots a permis de déterminer un ensemble de paramètres pouvant servir de critère d’alerte à l’initiation de la fissuration intergranulaire. / The loss of the corrosion resistance of the alloy 600, a nickel base alloy, during the oxidation in pressurized water reactor (PWR) has been demonstrated by many studies. It induces the intergranular stress corrosion cracking (IGSCC). If the chemical composition and the structure of the growing oxide are well-known, the mechanical influence of the oxide on the alloy has not been fully studied, yet. This study aims at bringing new knowledge of the oxidation impact on the mechanical response of the alloy. A new methodology is introduced for determining the local nanodeformation of the alloy 600 induced either by an oxidation or by a tensile loading. This method is based on nanodots disposed at the alloy surface as local markers of position. The statistical analysis of these data allowed to determine rare events of high deformation The samples were characterized locally by SEM, TEM, XPS and spectroscopic ellipsometry to characterize the internal oxide which constrains the alloy. The coupling of the EBSD with the nanodots had enabled to determine a set of parameters, which was used as an alarm criterion for the IGSCC initiation.

Ph.D. thesis is focused on the study and determination of layer thickness and optical properties, such as the dispersion dependence of the refractive index of various materials prepared in the form of thin layer. In the first part of this work the theoretical findings in the field of spectroscopic ellipsometry are summarised. These findings are followed by the description and characterization of the light polarization, evaluation of experimental data and determination of the physical properties of studied materials. Experimental and result section of this work is devoted to the preparation and characterization of thin films of the studied materials: titanum dioxide (TiO2), new organic materials (MDMO-PPV, PCDTBT, PCBTDPP, PC60BM, PC70BM) and reduced graphene oxide (rGO). These were all selected with respect to their potential use in the organic photovoltaics.

This master´s thesis is focused on measurement of optical properties of thin layer of materials used in organic solar cells (OSC). The usage of graphene oxides and its reduced forms as parts of hole transport layer (HLT) in OSC were studied. At the beginning of the thesis, there is described basic theory necessary to understand the optical properties of thin layers. The thin layer deposition and reduction of GO are discussed too. The experimental part is aimed to the optical characterization of prepared thin films. The results from optical microscopy, UV-VIS spectroscopy, FT-IR spectroscopy and spectroscopic ellipsometry were obtained. At the end of the thesis, the results are concluded and compared with already published literature.

Diese Dissertation befasst sich mit der Untersuchung der maßgeblichen Herausforderungen der heutigen TMR-Präparation (tunneling magnetoresistance) für beispielsweise Magnetfeldsensor- oder auch Speichertechnologie (MRAM – magnetic random access memory). Im ersten Teil der Arbeit werden die elektronischen, strukturellen und magnetischen Eigenschaften der ferromagnetischen Elektrode eines typischen magnetischen Tunnelkontaktes, z.B. CoFeB, erforscht, wobei spektroskopische Ellipsometrie, magnetooptische Spektroskopie, Röntgendiffraktometrie und Messverfahren für den spezifischen elektrischen Widerstand zum Einsatz kommen. Weiterhin wurde der Einfluss der Temperatur einer thermischen Behandlung auf die optischen und magneto-optischen Merkmale untersucht, wobei eine starke Korrelation zwischen den beobachteten spektralen Merkmalen und der Kristallisation von CoFeB nachgewiesen wurde. Die (magneto-) optische Spektroskopie bietet somit eine zerstörungsfreie und besonders sensitive Validierungsmethode für die Dünnschichtkristallisation, die in die moderne CMOS Herstellungstechnologie integriert werden kann. Der zweite Teil der Arbeit befasst sich mit dem lokalen Tempern unter Verwendung eines fokussierten Laserstrahls, mit dem Ziel die Referenzmagnetisierung in einem magnetischen Tunnelkontakt definiert einzustellen und die Wirkung der hierfür notwendigen thermischen Behandlung auf die übrigen Schichten im Schichtstapel zu untersuchen. Hierzu wurden zahlreiche Parameter für das laserbasierte lokale Tempern variiert, um die optimale Austauschfeldstärke im magnetischen Referenzsystem einzustellen, idealerweise ohne den gegebenen Schichtstapel zu schädigen. Schließlich wurde der Einfluss des laserbasierten Temperns (als auch des Ofentemperns) auf die Unversehrtheit der Schichten und Grenzflächen, insbesondere auf die Diffusion verschiedener Elemente, mittels Röntgen-Photoemissionsspektroskopie untersucht.

Surface chemistry plays a key role in science and technology because materials interact with their environments through their surfaces. Understanding surface chemistry can help alter/improve the properties of materials. However, surface characterization and modification often require multiple characterization and synthesis techniques. Silicon/silica-based materials are technologically important, so studying their surface properties can enable future advancements. In this dissertation, I explore surface modification and characterization of different types of Si/SiO2 thin films, including silicon wafers, fused silica capillary columns, and oblique angle sputtered Si/SiO2 thin films. In Chapters 2-5, I first present a method to rapidly silanize silica surfaces using a gas-phase synthesis that employs a small aminosilane that passivates/deactivates silicon wafers and the inner surfaces of capillary columns. This deposition takes place in a flow-through, atmospheric pressure, gas-phase reactor. This surface modification results in a significant decrease in the number of free surface silanols, which was confirmed by high-sensitivity low energy ion scattering (HS-LEIS), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). I then show that this silanization inhibits atomic layer deposition (ALD) of zinc oxide (ZnO), which is an important optical thin film material. Finally, I performed in-depth characterization of thin films of oblique angle deposited porous Si/SiO2. These films have been used as the active coatings in solid phase microextraction (SPME) devices. The characterization and analysis in this study were mainly by scanning transmission electron microscopy (STEM) and various computational microstructural characterization techniques, e.g., two-point statistics. The rest of my dissertation focuses on XPS data analysis and interpretation. I first show box plots as a simple graphical tool for determining overfitting in XPS peak fitting. I next present a series of chemometrics/informatics analyses of an XPS image dataset from a patterned silicon surface with different oxide thicknesses. This dataset was probed via an initial, graphical analysis of the data, summary statistics with a focus on pattern recognition entropy (PRE), principal component analysis (PCA), multivariate curve resolution (MCR), and cluster analysis (CA).

No description available.

Progress in chemomechanical functionalization was made by investigating the binding of molecules and surface coverage on the silicon surface, demonstrating functionalization of silicon with gases by chemomechanical means, analyzing atomic force microscopy probe tip wear in atomic force microscopy (AFM) chemomechanical nanografting, combining chemomechanical functionalization and nanografting to pattern silicon with an atomic force microscope, and extending chemomechanical nanografting to silicon dioxide. Molecular mechanics of alkenes and alkynes bound to Si(001)-2x1 as a model of chemomechanically functionalized surfaces indicated that complete coverage is energetically favorable and becomes more favorable for longer chain species. Scribing a silicon surface in the presence of ethylene and acetylene demonstrated chemomechanical functionalization with gaseous reagents, which simplifies sample cleanup and adds a range of reagents to those possible for chemomechanical functionalization. Thermal desorption spectroscopy was performed on chemomechanically functionalized samples and demonstrated the similarity in binding of molecules to the scribed silicon surface and to the common Si(001)-2x1 and Si(111)-7x7 surfaces. The wearing of atomic force microscope probe tips during chemomechanical functionalization was investigated by correlating change over time and force with widths of created lines to illustrate the detrimental effect of tip wear on mechanically-driven nanopatterning methods. In order to have a starting surface more stable than hydrogen-terminated silicon, silicon reacted with 1-octene was used as a starting surface for AFM chemomechanical functionalization, producing chemomechanical nanografting. Chemomechanical nanografting was then demonstrated on silicon dioxide using silane molecules; the initial passivating layer reduced the tip friction on the surface to allow only partial nanografting of the silane molecules. These studies broadened the scope and understanding of chemomechanical functionalization and nanografting.

Wafer bonding is important in microelectromechanical systems (MEMS) manufacturing, enabling wafer-level encapsulation and packaging. In this project, different pre-treatments of the polycrystalline silicon surface for eutectic gold-silicon (AuSi) bonding were studied with respect to the resulting bond strength. Native oxides or other surface layers can decrease the interaction between Au and Si, leading to weaker bonds. Different etching methods were investigated to remove native oxide. Spectroscopic ellipsometry (SE), water contact angle measurements and Fourier transform infrared spectroscopy (FTIR) were used to analyze the surfaces. SE measurements showed that the oxide layer grew 5 Å the first 4 hours after HF etch, rinse and dry, but then grew less than this during the following 6 weeks. The measured oxide growth was similar for wafers with other pre-treatments. Through contact angle measurements, it was demonstrated that the different etching methods resulted in different outermost surface layers. None of the contact angles were changed much over several weeks, indicating subsequent oxide growth occurred below a stable outermost layer. For wafer bonding, wafers with bond frame structures were used. After wafer bonding, the bond frames were analyzed with infrared (IR) microscopy and the bonds were shear tested for bond strength. The shorter the exposure time to ambient air atmosphere before bond, the stronger the bond in general. Furthermore, the wafers stored in nitrogen atmosphere exhibited higher bond strengths than the wafers stored in air for the same amount of time, confirming that the growing oxide was the reason for the decreased bond quality during wafer storage. HF (wet/vapor) etched wafers in general had slightly stronger bonds than the other wafers and the wafers etched with HF vapor had the highest average bond strength of all. The IR images showed that white areas in the bond frames were related to decreased bond strength, and that wafers that had longer storage time on average had more white in the bond frames. As a conclusion, to achieve as strong bonds as possible, the waiting time between wafer pre-treatments and bonding should be minimized, and in the waiting time it is beneficial to store the wafers in nitrogen atmosphere. In this study most wafers stored 2 weeks in nitrogen had good bond quality and even wafers stored 3 days in air had acceptable bond strengths. However, using HF to etch away the oxide before bond is preferable compared to the other etching methods, not only to have larger average bond strength, but also to have less bond strength decrease during waiting time before bond. / I tillverkning av mikroelektromekaniska system (MEMS) är skivbondning viktigt för inkapsling och förpackning av mikrosystem på skivnivå. I detta projekt studerades olika förbehandlingar av polykristallina kiselytan, inför eutektisk AuSi-bondning, med avseende på resulterande bondstyrka. Nativoxid eller andra ytskikt kan minska interaktionen mellan guld (Au) och kisel (Si), vilket leder till svagare bond. Flera olika etsmetoder undersöktes för att ta bort nativoxid. Spektroskopisk ellipsometri (SE), mätningar av vattenkontaktvinkel och Fouriertransform infraröd spektroskopi (FTIR), användes för att analysera ytorna. Resultaten från SE-mätningarna visade att oxiden växte 5 Å under de 4 första timmarna efter HF-ets, skölj och tork, men växte sedan mindre än detta under de följande 6 veckorna. Den uppmätta oxidtillväxten var liknande för skivorna med andra förbehandlingar. Kontaktvinklarna var olika för olika förbehandlingsmetoder, vilket visar att de hade olika yttersta ytskikt. Ingen av kontaktvinklarna ändrades mycket under flera veckor, vilket indikerar att den följande oxidtillväxten skedde under ett stabilt yttersta lager. För skivbondning andvändes skivor med bondramar längs chip-kanterna. Dessa bondramar var gjorda av polykristallint Si respektive Au på skivorna som skulle bondas. Efter bondning analyserades bondramarna med infraröd (IR) mikroskopi och skjuvtester gjordes för att bestämma bondstyrkan. Ju kortare tid skivorna exponerades till omgivande luft, desto starkare bond i allmänhet. Dessutom uppvisade skivorna som lagrats i kväveatmosfär högre bondstyrkor än de skivor som lagrats i luft, vilket bekräftar att den växande oxiden var orsaken till den minskade bondkvaliteten under skivlagring. HF-etsade skivor (HF- dipp och HF-ånga) hade något starkare bond än de andra skivorna och de skivor som etsats med HF-ånga hade allra högst genomsnittlig bondstyrka. IR-bilderna visade att vita områden i bondramarna var relaterat till minskad bondstyrka och att skivor som hade längre lagringstid i genomsnitt hade mer vitt i bondramarna. Slutsatsen är att för att uppnå så hög bondstyrka som möjligt ska tiden mellan förbehandlingar och bond minmeras, och under väntetiden är det till fördel att skivorna förvaras i kväveatmosfär. I den här studien hade skivor som förvarats 2 veckor i kväve bra bondkvalitet och även skivor som stått 3 dagar i luft hade godtagbara bondstyrkor. Att använda HF för att etsa bort oxid är dock bättre än att använda någon av de andra etsmetoderna, inte bara för att få högre genomsnittliga bondstyrkor, utan också för att få mindre minskning av bondstyrkan under väntetiden inför bondning.

No description available.

Solar absorber coatings are one of the key components in concentrated solar power (CSP) plants. Currently operating at temperatures up to 565°C and suffering from emissive losses, their energy conversion efficiency could be improved by applying high-temperature stable materials with solar selective properties, i.e. high absorptivity and low emissivity. In this work, the transparent conductive oxide (TCO) SnO2:Ta is developed as a solar selective coating (SSC) for CSP absorbers. Starting with simulations covering basic requirements for SSCs, the deposition process of SnO2:Ta is optimized and extensive optical characterization and modelling are performed. It is shown that upon covering with a SiO2 antireflective layer, a calculated absorptivity of 95% and an emissivity of 30% are achieved for the model configuration of SnO2:Ta on top of a perfect black body (BB). High-temperature stability of the developed TCO up to 800 °C is shown in situ by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The universality of the concept is then demonstrated by transforming silicon and glassy carbon from non-selective into solar selective absorbers by depositing the TCO on top of them. Finally, the energy conversion efficiencies ηCSP of SnO2:Ta on top of a BB and an ideal non-selective BB absorber are compared as a function of solar concentration factor C and absorber temperature TH.