Ce projet de thèse porte sur le traitement de films de graphène dans la post-décharge en flux de plasmas micro-ondes d’azote à pression réduite. Différentes considérations de contamination de surface des échantillons se sont avérées cruciales pour ce travail. Par exemple, en présence d’hydrocarbures, les traitements dans les différentes régions de la post-décharge montrent des profils de production de dommages, d’incorporation d’azote et de fonctionnalisation de contaminants distincts. Le traitement agressif qu’offre la post-décharge proche résulte en la formation de complexes amorphes graphène-hydrocarbures responsables d’une forte hausse de la teneur en azote (jusqu’à 49%) pour des désordres modérés (D:G = 1.3). Pour les traitements dans la post-décharge lointaine, les hydrocarbures jouent un rôle de couche protectrice permettant une incorporation monotone (jusqu’à 18%) à très faible dommage (D:G < 0.3). Les espèces azotées sont néanmoins faiblement liées de sorte que le transfert vers un substrat de SiO2 engendre une perte importante (> 80%) de la teneur en azote. Des considérations d’inhomogénéité de surface des films de graphène ont motivé le développement d’une nouvelle méthode d’analyse des cartographies Raman obtenues par un imageur hyperspectral. L’étude des spectres Raman au niveau des domaines versus aux joints de grains ont permis de mettre en évidence un mécanisme d’auto-réparation des joints de grains relié à l’anisotropie de la migration des adatomes de carbone en surface. L’accumulation de ceux-ci aux joints de grains mène à une émission d’adatomes responsable de l’annihilation de paires de Frenkel. Dans les plasmas azotés, il s’avère que ce mécanisme est également responsable d’une incorporation sélective d’azote aux domaines de croissance du graphène. Lorsque amorphisé, le dopage sélectif s’estompe puisque le transport des adatomes de carbone aux joints de grains, ainsi que l’accumulation essentielle au processus d’auto-réparation, deviennent entravés. Finalement, la recombinaison en surface d’atomes d’azote et la désexcitation de métastables N2(A) sont identifiés comme principaux agents pour la production de dommages dans la post-décharge en flux d’azote. Un modèle d’incorporation impliquant la formation de dommages et l’adsorption d’atomes d’azote est proposé. En présence d’espèces oxydantes dans la post-décharge d’azote, la formation de dommages demeure limitée par les populations de N et de N2(A). / This thesis project deals with the treatment of graphene films in the flowing afterglow of microwave nitrogen plasmas at reduced pressure. Various surface contamination considerations were found to be crucial for this work. For example, in the presence of hydrocarbons, the treatments in the different regions of the afterglow show distinct damage production, nitrogen incorporation and contaminant functionalization profiles. The aggressive treatment offered by the early afterglow results in the formation of amorphous graphene-hydrocarbon complexes responsible for a sharp increase in the nitrogen content (up to 49%) at moderate disorders (D: G = 1.3). For the treatments in the late afterglow, the hydrocarbons act as a protective layer, allowing a monotonic incorporation (up to 18%) with very low damage (D: G < 0.3). Nitrogenous species are found to be weakly bound so that transfer to an SiO2 substrate generates a significant loss (>80%) of the nitrogen content. Considerations of surface inhomogeneity of graphene films have motivated the development of a new analysis method of Raman maps obtained by hyperspectral imager. The study of Raman spectra at growth domain versus grain boundary has revealed a self-healing mechanism of grain boundaries linked to the anisotropy of the migration of carbon adatoms at the surface. The accumulation of these at grain boundaries leads to an emission of atoms responsible for the annihilation of Frenkel pairs. In nitrogenous plasmas, this mechanism is also found to be responsible for the selective incorporation of nitrogen into the growth domains of the graphene. For amorphous graphene, selective doping fades as the transport of carbon adatoms to grain boundaries, and therefore the accumulation essential to the self-healing process, becomes impeded. Finally, the surface recombination of nitrogen atoms and the de-excitation of metastable N2(A) are identified as the main agents defect generation in the nitrogen flowing afterglow. An incorporation model involving the formation of damage and adsorption of nitrogen atoms is proposed. In the presence of oxidizing species in the nitrogen afterglow, damage formation remains limited by populations of N and N2(A).

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.

The electronic and magnetic structure of the colossal magneto resistance material La1-xSrxMnO3, the high-k and strain tailoring compounds REScO3 (Sm, Gd, Dy) and the multiferroic LuFe2O4 was investigated by means of x-ray spectroscopic techniques. SQUID measurements of La1-xSrxMnO3 (x = 0.125, 0.17, 0.36) were compared with XMCD results. The very good agreement between these two experiments proofs the applicability of the correction factor for the spin magnetic moment and the importance of charge transfer. The magnetic moment measured by SQUID and that determined from XMCD proofs that the magnetic moment is completely localized at the Mn ions for different temperatures and magnetic fields. For x = 0.125 the orbital magnetic moment determined from XMCD corresponds to the structural changes in the phase diagram. Additionally the measured orbital moments correspond to anomalies in magnetization versus temperature curves. The magnetic and electronic structure of the rare earth scandates (SmScO3, GdScO3 and DyScO3) were investigated by means of XPS, XES, XAS, SQUID and neutron powder diffraction. The magnetic measurements reveal antiferromagnetic coupling at low temperatures in agreement with neutron diffraction data. With XAS and XES at the O K-edge in comparison with band structure calculations of the unoccupied oxygen states, the band gaps of REScO3 were determined and it was found that these values are corresponding to the Sc-O mean distances. The electronic and magnetic structure of LuFe2O4 was presented. The valence state of Fe ions was determined to 50% divalent and 50% trivalent by XPS of Fe 2p and 3s levels. The big orbital magnetic moment found by XMCD could explain a discrepancy between the magnetic measurements and the spin configuration, which was confirmed by XMCD.

Indiana University-Purdue University Indianapolis (IUPUI) / Osteogenesis imperfecta is a rare congenital disease commonly characterized by brittle bones caused by mutations in the genes encoding Type I collagen, the single most abundant protein produced by the body. The murine model (oim) exists as a natural mutation of this protein, converting its heterotrimeric structure of two Col1a1 molecules and a single Col1a2 molecule into homotrimers composed of only the former. This defect impacts bone mechanical integrity, greatly weakening their structure. Femurs from male wild type (WT), heterozygous (oim/+), and homozygous (oim/oim) mice, all at 12 weeks of age, were assessed using assays at multiple length scales with minimal sample processing to ensure a near-physiological state. Atomic force microscopy (AFM) demonstrated detectable differences in the organization of collagen at the nanometer scale that may partially attribute to alterations in material and structural behavior obtained through mechanical testing and reference point indentation (RPI). Changes in geometric and chemical structure through the use of µ-Computed Tomography and Raman spectroscopy respectively indicate a smaller, brittle phenotype caused by oim. Changes within the periodic D-spacing of collagen point towards a reduced mineral nucleation site, supported by reduced mineral crystallinity, resulting in altered material and structural behavior in oim/oim mice. Multi-scale analyses of this nature offer much in assessing how molecular changes can compound to create a degraded, brittle phenotype.

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.

Galaxy clusters are the largest gravitationally bound structures in the Universe. Their masses are dominated by dark matter ($\sim$85\% of the mass) with stars representing 1-4\% of their masses. A hot, X-ray emitting gas called the intracluster medium makes most of their baryonic mass. The presence of this gas and of numerous neighbouring galaxies prematurely stop the star formation in clusters. In other terms, more galaxies in clusters are passive than in the general population of galaxies. This effect is mass and position-dependant: high-mass galaxies are more likely to be passive than less massive ones; galaxies inhabiting the cluster core are also less likely to form stars than those in the outskirts. The fraction of passive galaxies is greater in local clusters than in high-redshift ones, because they had more time to evolve. Much is unknown about the cessation of star formation, called quenching, in clusters. Thus, although many examples of infalling galaxies being stripped of their gas have been reported for low-mass galaxies, it is unclear if the most massive members became quenched before or after they become cluster members. The relationship between quenching and the cluster mass is also poorly understood. Despite the variety of methods devised to find clusters of galaxies, most of what we know about quenching in $z\gtrsim 1$ clusters was discovered with optically/infrared-selected cluster samples (clusters found as overdensities of galaxies), or samples of mixed origin. Yet, there is tentative evidence that optically/infrared-selected samples are biased toward having more passive galaxies than those that were X-ray selected. In the present dissertation, quenching is explored in X-ray selected cluster samples. A sample of high-redshift, low-mass galaxy clusters is built by finding galaxy overdensities coincident with sources of extended X-ray emission. A photometry-based analysis reveals that the fraction of quenched galaxies in these clusters is very variable. Moreover, the brightest cluster galaxies are also diverse. Yet, for all the information that photometry can provide, this sample candidate clusters need to be confirmed with spectroscopy. Spectroscopic observations obtained for four candidate clusters are reduced and analysed. The results show that three of them are clusters, the fourth candidate being a superposition of structures. Member spectra are examined to infer their star formation history, and the results shows the existence of an intermediary population of galaxies, where an old stellar population coexists with weak star formation. Finally, the galaxies of a $z=1.98$ X-ray selected cluster, XLSSC 122 are investigated in detail. Photometric data in 12 bands are organized to perform spectral energy distribution fittings, a technique that allows a simplified reconstitution of the history of the star formation. Results show that the members were formed at diverse epochs, the oldest being about 2.5 Gyrs old. Simulations drawn from the Multi Dark Planck 2 are used to infer the mass-scale of the cluster when the oldest galaxies were formed, something that has never been done before. The oldest galaxies were probably formed when XLSSC 122 had accreted $<$10\% of its $z=1.98$ mass, i.e. the mass-scale of a galaxy group. / Graduate

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.

<p dir="ltr">Blood hemoglobin (Hgb) testing is a widely used clinical laboratory test for a variety of patient care needs. However, conventional blood Hgb measurements involve invasive blood sampling, exposing patients to potential risks and complications from needle pricks and iatrogenic blood loss. Although noninvasive blood Hgb quantification methods are under development, they still pose challenges in achieving performance comparable to clinical laboratory blood Hgb test results (i.e., gold standard). In particular, optical spectroscopy can provide reliable blood Hgb tests, but its practical utilizations in diagnostics are limited by bulky optical components, high costs, and extended data acquisition time. Mobile health (mHealth) or diagnostic colorimetric applications have a potential for point-of-care blood Hgb testing. However, achieving color accuracy for diagnostic applications is a complex matter, affected by device models, light conditions, and image file formats.</p><p dir="ltr">To address these limitations, we propose biophysics-based machine learning algorithms that combine hyperspectral learning and spectroscopic gamut-informed learning for accurate and precise mHealth blood Hgb assessments in a noninvasive manner. This method utilizes single-shot photographs of peripheral tissue acquired by onboard smartphone cameras. The palpebral conjunctiva (i.e., inner eyelid) serves as an ideal peripheral tissue site, owing to its easy accessibility, relatively uniform microvasculature, and absence of skin pigmentation (i.e., melanocytes). First, hyperspectral learning enables a mapping from red-green-blue (RGB) values of a digital camera into detailed hyperspectral information: an inverse mapping from a sparse space (tristimulus color values) to a dense space (multiple wavelengths). Hyperspectral learning employs a statistical learning framework to reconstruct a high-resolution spectrum from a digital photo of the palpebral conjunctiva, eliminating the need for complex and costly optical instrumentation. Second, comprehensive spectroscopic analyses of peripheral tissue are used to establish a unique blood Hgb gamut and design a diagnostic color reference chart highly sensitive to blood Hgb and peripheral perfusion. Informed by the domain knowledge of tissue optics and machine vision, the Hgb gamut-based learning algorithm offers device/light/format-agnostic color recovery of the palpebral conjunctiva, outperforming the existing color correction methods.</p><p dir="ltr">This mHealth blood Hgb prediction method exhibits comparable accuracy and precision to capillary blood sampling tests (e.g., finger prick) over a wide range of blood Hgb values, ensuring its reliability, consistency, and reproducibility. Importantly, by employing only a digital photograph with the Hgb gamut-learned color recovery, hyperspectral learning-based blood Hgb assessments allow noninvasive, continuous, and real-time reading of blood Hgb levels in resource-limited and at-home settings. Furthermore, our biophysics-based machine learning approaches for digital health applications can lay the foundation for the future of personalized medicine and facilitate the tempo of clinical translation, empowering individuals and frontline healthcare workers.</p>