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Growth of Co film on SiO2/Si substrates with surface roughness of 0.5 nm and 1.6 nm have been studied in-situ using magneto-optical Kerr effect (MOKE) and transport measurements. In-situ measurements jointly suggest that the films grow via Volmer-Weber growth process and proceed via a nonmagnetic, superparamagnetic and a ferromagnetic phase formation on both the substrates. Islands are found to coalesce at film thicknesses ~ 0.6 nm and at ~ 1.5 nm with continuous film formation around film thickness ~1.5 nm and ~ 3.0 nm for smooth and rough substrates, respectively. Ferromagnetic long-range ordering i.e., appearance of magnetic hysteresis loop in both films is observed just after coalesce stage. Observed azimuthal angular dependence of coercivity confirmed the presence of a weak uniaxial magnetic anisotropy (UMA) in both the films, whereas difference in UMA with substrate roughness is interpreted in terms of combined effect of domain wall pinning and internal stresses in the films. Origin of much higher UMA in case of the Co film deposited on ripple patterned substrate of similar root mean square roughness is attributed to the modified long range dipolar stray fields on the surface.

Noble metal nanoparticles (NPs) are the site of a surface plasmon resonance phenomenon resulting from the collective oscillation of their conduction electrons under the effect of an electromagnetic wave. In the case of gold and silver NPs, the resonant frequency is in the visible range, which gives these plasmonic NPs unique optical properties. In particular, the position and intensity of the plasmon resonance depend on their size, shape (aspect ratio) and the index of the host medium. The possible applications require pure samples and mono-dispersed distribution. The chemical synthesis of NPs allows the shape and size of NPs to be controlled. However, it requires the use of stabilizing agents, which lead to surface contamination by synthetic residues. To limit this disadvantage, the physical technique of laser ablation in a liquid medium is a promising alternative, which, however, suffers from a lack of control over the shape and size of the NPs produced. The shape and size of NPs produced by liquid laser ablation (ALML) are closely related to the three essential steps of the process: Target / laser interaction; Mass transport; Laser / NPs interaction suspended in the liquid. In order to understand the mechanisms governing each of these stages, it is necessary to study them separately. In this work, we focused on the mechanisms of interaction between the laser beam and the NPs suspended in the liquid. Depending on the energy density absorbed by the suspended NPs, they undergo fragmentation or remodeling. We then studied the mechanisms behind the phenomenon of fragmentation. The evolution of the shape distribution of NPs during NP fragmentation was studied by developing an original and quantitative technique of in-situ optical spectroscopy. And, the evolution of the volume fraction of NPs during their preparation by ALML by in-situ optical spectroscopy is obtained and analyzed. In parallel with the experimental work, we have developed theoretical models for understanding the mechanisms of formation of metallic nanoparticles by laser ablation in a liquid medium. A modest study on the modeling of optical and thermal properties of the Laser-Nanoparticle interaction is discussed in this thesis., Spécialité doctorale "Physique de la matière condensée" présentée par MANSOUR Yehia Soutenue le le 16 Décembre 2020 Études théorique et expérimentale de la formation des nanoparticules métalliques par ablation laser en milieu liquide. Modélisations des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules.Les nanoparticules (NPs) de métaux nobles sont le siège d’un phénomène de résonance plasmon de surface résultant de l’oscillation collective de leurs électrons de conduction sous l’effet d’une onde électromagnétique. Dans le cas de NPs d’or et l’argent, la fréquence de résonance est située dans visible ce qui confère à ces NPs plasmoniques des propriétés optiques uniques. En particulier, la position et l’intensité de la bande de résonance plasmon peuvent varier en fonction de leur taille, leur forme (rapport d'aspect) et de l'indice du milieu hôte. Les possibilités d’applications nécessitent des échantillons purs et de distribution mono disperse. La synthèse des NPs par voie chimique permet de contrôler dans une certaine mesure la forme et la taille des NPs. Elle nécessite cependant l’utilisation d’agents stabilisants qui mènent à une contamination de surface par les résidus de synthèse. Pour limiter cet inconvénient, la technique physique d’ablation laser en milieu liquide est une alternative prometteuse qui souffre cependant d’un manque de contrôle de la forme et de la taille des NPs produites. La forme et la taille des NPs élaborées par ablation laser en milieu liquide (ALML) sont étroitement liées aux trois étapes essentielles du processus : Interaction cible/laser ; Transport de masse ; Interaction laser/NPs en suspension dans le liquide. Afin d’appréhender les mécanismes régissant chacune de ces étapes, il est nécessaire de les étudier séparément. Dans ce travail, nous nous sommes focalisés sur les mécanismes d’interaction entre le faisceau laser et les NPs en suspension dans le liquide. Suivant la densité d’énergie absorbée par les NPs en suspension, celles-ci subissent la fragmentation ou le remodelage. Par la suite nous avons étudié les mécanismes à l’origine du phénomène de la fragmentation. L’évolution de la distribution de forme des NPs lors de la fragmentation des NPs a été étudiée en développant une technique originale et quantitative de spectroscopie optique in-situ. De même, l’évolution de la fraction volumique des NPs au cours de leur élaboration par ALML par spectroscopie optique in-situ est obtenue et analysée. En parallèle aux travaux expérimentaux, nous avons développé des modèles théoriques pour la compréhension des mécanismes de formation des nanoparticules métalliques par ablation laser en un milieu liquide. Une autre étude approfondie sur la modélisation des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules est discutée dans cette thèse. Un modèle thermique de Takami modifié nommé MTM (Modified Takami Model) a été également introduit. Son utilité importante a été démontrée pour l’interprétation des mécanismes de l’interaction laser-NPs.

Organic-inorganic hybrid perovskites as promising light-harvesting materials have been the focus of scientific research and development of photovoltaics recently. Especially, metal halide perovskites currently become one of the most competitive candidates for the fabrication of solar cells with record certified efficiency over 25%. Despite the high efficiency, many fundamental questions remain unclear and need to be addressed at both the material and device levels, such as weaker stability, poorer reproducibility, easier degradation influenced by water, oxygen, thermal factors, and so on. Based on recent reports, interfacial engineering plays a crucial role in controlling the behavior of the charge carriers and in growing high quality, defect-free perovskite crystals, therefore helping to enhance device performance and operational stability. However, little attention has been paid to the interface interaction mechanism among carrier transport layers and perovskite active layer. It is extremely urgent to explore the perovskite interfaces in details and to find out how its interface structure is relative to the efficiency and hysteresis in perovskites solar cells. Based on the Shanghai Synchrotron Radiation Facility (SSRF), we have established an advanced perovskite photovoltaic device preparation and in-line test system, developed a series of unique surface diffraction analysis methods based on ex situ and in situ grazing incidence X-ray diffraction (GIXRD), and reported a large number of novel synchrotron radiation results on crystallization of the perovskite photovoltaics films. Our main investigations are aimed to deeply in-situ study the perovskite film growth dynamics using synchrotron radiation GIXRD technology in combination with a customized mini online glove box (c(H2O,O2)

The mechanical behavior of carbon aerogels is not very well understood, presenting a bottle-neck in synthesizing aerogels for specific applications where mechanical loads play a role. Accordingly, in this paper, three different types of carbon aerogels with varying mechanical properties and flexibility are synthesized and analyzed. The morphology is characterized by using a scanning electron microscope (SEM) and nitrogen adsorption-desorption isotherms. The mechanical behavior is investigated under uniaxial quasistatic compression as well as in-situ compression under a SEM. While in-situ tests reveal microstructural evolution under deformation, the macroscopic deformation is described by the digital image correlation. Based on cyclic compression tests with step-wise increasing strain amplitude, novel empirical relations are proposed to describe the damage characteristics such as energy dissipation and residual deformation. Furthermore, while testing carbon aerogels under tension is not very feasible, three-point bending tests are conducted and the resulting flexural properties of carbon aerogels are identified.

Humans usually refer to landmarks when they give route directions to pedestrians. One of the reasons why current mobile pedestrian navigation systems do not yet mimic this mode of communication is the lack of available data sources. The usefulness of a crowd-sourced data acquisition approach to overcome this problem has long been mooted. However, to date no empirically sound way of measuring the salience of objects by means of surveys exists. GOAL Given this background, this doctoral work has three goals: 1. To achieve a sound way of measuring salience and its subdimensions, i.e. visibility in advance, cognitive salience, prototypicality, structural salience, and visual salience based on taking dimensions revealed in earlier studies systematically and simultaneously into account. 2. To find subgroups of visual features among the large number of visual attributes known from the literature. 3. To find the most important subdimensions of salience by means of estimating two different structural equation models. Model I is based on assumptions of independence among subdimensions, whereas model II reflects hypotheses of mediation. Taken as a whole, achieving these goals will foster both, the advancement of theories of salience and landmark acquisition methods. METHODOLOGY A large scale, in-situ experiment was implemented, trying to overcome weaknesses of earlier attempts made to estimate salience. An appropriate sample size of buildings and non-buildings was calculated a priori (nobj = 360). Objects were randomly selected based on their geographical coordinates and randomly grouped into nr = 55 routes. Participants were required to rate objects by means of a survey. The questions were derived from empirical evidence found in earlier studies. Each route was walked by two different participants (n = 112), id est (i.e.) two ratings per object were collected for data analysis. FINDINGS Model I and model II were analyzed using PLS Path Modeling and consistent PLS Path Modeling, respectively. The measurement models proposed showed a good fit, although some weaknesses were identified for prototypicality and cognitive salience. Geometrical aspects as well as features like (visual) age turned out to have a stronger impact on visual salience than color. Model I did not yield reasonable structural model results based on consistent Partial Least Squares Path Modeling. Model II, however, showed that visual salience had a very high impact on visibility in advance which, in turn, heavily influenced structural salience. An analysis of the predictive capabilities of model II revealed important, but rather small effects. VALUE OF WORK This doctoral work adds to salience models as well as to its empirical, survey-based, in-situ measurement. The results of the mediation analysis as well as the predictive capabilities of model II suggest that important subdimensions of salience are missing in current theories. Emotional salience and familiarity are identified as two candidate constructs. The structural relationships found during the analysis of model II provide, in combination with the measurement model results, a sound basis to choose important features for surveys which are usable to gain crowd-sourced salience ratings. Furthermore, several important aspects for future studies are identified. These include heterogeneity analyses for different subgroups of users of pedestrian navigation systems as well as local environments different to the historic one used in this study., Zwischenmenschliche Kommunikation über Routen zeichnet sich im Allgemeinen durch die Bezugnahme auf sog. Landmarken aus. Einer der Gründe, weshalb aktuelle Fußgängernavigationssysteme dies nicht tun, ist, dass keine entsprechenden Datenquellen zur Verfügung stehen. Dementsprechend wird seit langem darauf hingewiesen, dass crowd-basierte Ansätze dazu beitragen können, entsprechende Abhilfe zu schaffen. Allerdings existiert bis heute kein Ansatz, der es ermöglicht, die Salience von Objekten fragebogenbasiert empirisch zu erheben. ZIEL DER ARBEIT Dieser Problematik versucht die vorliegende Arbeit durch die Erreichung dreier Ziele zu begegnen. 1. Soll eine Möglichkeit geschaffen werden, Salience und ihre entsprechenden Subdimensionen empirisch fundiert zu bemessen. Hierfür werden die Subdimensionen Visibility in Advance, Cognitive Salience, Prototypicality, Structural Salience und Visual Salience gleichzeitig betrachtet und bereits bekannten Einflussgrößen wird systematisch Rechnung getragen. 2. Wird untersucht, welche Untergruppen von Variablen sich innerhalb der Visual Salience finden lassen. 3. Geht es darum, die Wichtigkeit der Teildimensionen von Salience auf Grundlage zweier Strukturgleichungsmodelle einzuschätzen. Dabei basiert Modell I auf Unabhängigkeitsannahmen während in Modell II Beziehungen zwischen den einzelnen Teildimensionen postuliert werden. METHODIK Die Forschungsfragen wurden mit Hilfe eines groß angelegten In-Situ-Experiments beantwortet. Die entwickelte methodische Herangehensweise wurde dabei von dem Versuch geprägt, bekannte Nachteile früherer Studien zu überwinden. Entsprechend wurde ein geeigneter Stichprobenumfang a priori bestimmt (nobj=360). Diese Objekte wurden auf Grundlage ihrer geographischen Koordinaten zufällig gewählt und als Tupel in insgesamt nr=55 Routen gruppiert. Die Versuchsteilnehmenden mussten zu jedem Objekt, das ihnen zur Bewertung zugeteilt wurde, einen Fragebogen ausfüllen. Die gestellten Fragen wurden systematisch aus früheren empirischen Ergebnissen abgeleitet. Jede Route wurde zweimal von zwei verschiedenen Versuchspersonen begangen (n=112), sodass zwei Bewertungen je Objekt für die Datenanalyse vorlagen. ERKENNTNISSE Beide Strukturgleichungsmodelle wurden mit Hilfe von PLS Path Modeling analysiert. Die reflexiven Messmodellteile zeigten gute Passung, allerdings ergaben sich für Prototypicality und insbesondere für Cognitive Salience erkennbare Schwächen. Visual Salience, welche formativ modelliert war, wurde stärker durch geometrische Aspekte oder (vermeintliches) Alter beeinflusst als durch Farbe. Basierend auf der Schätzung mit Hilfe von consistent PLS Path Modeling zeigte das Strukturmodell von Modell I nur eine äußerst dürftige Passung. Strukturmodell II hingegen fördert einen sehr starken Einfluss von Visual Salience zu Tage. Vor allem Visibility in Advance ist stark durch visuelle Attribute beeinflusst und wirkt selbst stark auf Structural Salience. Im Rahmen der Analyse der Vorhersagefähigkeit von Modell II zeigten sich wichtige, aber kleine Effekte. INTERPRETATION DER ERKENNTNISSE Die vorliegende Arbeit trägt zur Modellbildung von Salience ebenso bei wie zur fragebogen-basierten Messung von Salience in-situ. Die Ergebnisse der Analyse von Modell II zeigen dabei, dass wichtige Subdimensionen von Salience in der aktuellen Theoriebildung fehlen. Emotional Salience und Familiarity sind hier beides denkbare Konstrukte. Die gefundenen Beziehungen zwischen den latenten Variablen und die Güte von deren Messung bilden eine solide Grundlage für die fragebogen-basierte Erhebung von Salience in alltäglichen Situationen. Schließlich konnten wichtige, zukünftige Forschungsarbeiten identifiziert werden. Hierzu gehört die Heterogenitätsanalyse ebenso wie die Untersuchung der Übertragbarkeit der Ergebnisse auf andere Umgebungen.

OPAC interfaces, still the dominant access point to library catalogs, support systematic search but are problematic for open-ended exploration and generally unpopular with visitors. As a result, libraries start subscribing to simplified search paradigms as exemplified by web-search systems. This is a problem considering that systematic search is a crucial skill in the light of today’s abundance of digital information. Inspired by novel approaches to facilitating search, we designed CollectionDiver, an installation for supporting systematic search in public libraries. The CollectionDiver combines tangible and large display direct-touch interaction with a visual representation of search criteria and filters. We conducted an in-situ qualitative study to compare participants’ search approaches on the CollectionDiver with those on the OPAC interface. Our findings show that while both systems support a similar search process, the CollectionDiver (1) makes systematic search more accessible, (2) motivates proactive search approaches by (3) adding transparency to the search process, and (4) facilitates shared search experiences. We discuss the CollectionDiver’s design concepts to stimulate new ideas toward supporting engaging approaches to systematic search in the library context and beyond. Postprint

通常，アルミニウム合金ダイカスト材料は，表面が鋳肌のまま使用される．鋳肌近傍には，欠陥が不均一に分布していると考えられ，試験前にその領域は除去されるため，従来の評価において鋳肌近傍の欠陥はほとんど無視されていると思われる．本研究では，鋳肌を有する試験片を用いて疲労試験を行い，疲労寿命について統計的に解析した．また，表面欠陥を3Dで可視化するとともに，疲労き裂発生のその場観察を行うため，シンクロトロン放射光を用いたマイクロトモグラフィを適用した．これにより，短寿命を呈した試験片の鋳肌近傍には，直径10μm程度のミクロポアが並んで存在し，これが早期の疲労き裂発生を引き起こしたことが明らかとなった．疲労破壊のその場観察は，凝集したミクロポアから疲労き裂が発生したことを明瞭に示した．, Usually, aluminum die-cast alloys are used with casting surface, therefore it can be assumed that defects exist in the sub-surface regions. These defects are largely neglected in conventional evaluations as these regions are removed before testing. In the present study, fatigue tests were performed using specimens with casting surface. Fatigue life was statistically analyzed, and synchrotron radiation X-ray microtomography was also applied to visualize surface defects in 3D together with the in-situ observation of crack initiation. The results revealed that specimens with shorter fatigue lives exhibit aligned micropores of approximately 10μm in diameter in a sub-surface region, which inevitably cause premature fatigue crack initiation. The in-situ observation clearly revealed fatigue crack initiation at agglomerated micropores.

The temperature stability of cubic TiO1.05 titanium monooxide is investigated. An in situ X-ray structural analysis is performed using synchrotron radiation in a high temperature vacuum chamber. It is found that under poor vacuum and at high heating rates of up to 1250 C, the structural transformations in TiO1.05 occur at 630 C. In particular, there is a phase transition from TiO1.05 (space group Fm-3m) to rhombohedraic Ti2O3 (space group R-3c) via Ti2.5O3 (space group Immm). © 2013 Allerton Press, Inc.

International audience; Silicon clathrates are unusual open-framework solids formed by tetrahedrally bonded silicon that show remarkable electronic and thermal properties. The type I structure has a primitive cubic unit cell containing cages occupied by metal atoms to give compositions such as Na(8)Si(46) and Na(2)Ba(6)Si(46). Although their structure and properties are well described, there is little understanding of the formation mechanism. Na(8)Si(46) is typically produced by metastable thermal decomposition under vacuum conditions from NaSi, itself an unusual structure containing Si(4)(4-) polyanions.,In this study, we used in situ synchrotron X-ray diffraction combined with rapid X-ray detection on samples taken through a controlled temperature ramp (25-500 degrees C at 8 degrees C/min) under vacuum conditions (10(-4) bar) to study the clathrate formation reaction. We also carried out complementary in situ high-temperature solid-state (23)Na NMR experiments using a sealed tube loaded under inert-gas-atmosphere conditions. We find no evidence for an intermediate amorphous phase during clathrate formation. Instead, we observe an unexpectedly high degree of structural coherency between the Na8Si46 clathrate and its NaSi precursor, evidenced by a smooth passage of several X-ray reflections from one structure into the other. The results indicate the possibility of an unusual, epitaxial-like, growth of the dathrate phase as Na atoms are removed from the NaSi precursor into the vacuum.