Il y a un besoin de nouvelles technologies photovoltaïques avec une efficacité de conversion lumière-électricité augmentée, qui puissent être des alternatives aux dispositifs plus traditionnels d’efficacité limitée et couteux à base de jonctions p-n. Dans ce contexte, la recherche sur les pérovskites ferroélectriques inorganiques ouvre des possibilités pour le développement de nouvelles approches pour augmenter l’efficacité, par exemple grâce à leur aptitude à séparer les charges électriques photoexcitées par le champ électrique intrinsèque (associé à leur polarisation) qui existe dans chaque maille élémentaire de ces matériaux. Pour profiter de cet avantage, un matériau doit posséder plusieurs propriétés comme la ferroélectricité, une bande interdite d’énergie relativement petite pour pouvoir absorber la lumière et une mobilité des porteurs de charges élevée. Ici, on a synthétisé et étudié des solutions solides Ba(Sn,Ti)O3, qui ont comme composants parents un ferroélectrique BaTiO3 et un paraélectrique BaSnO3. Les transitions de phases cristallographiques et la modification des états des dipôles sont caractérisées par les méthodes de diffraction et la spectroscopie diélectrique. La spectrométrie des photoélectrons X montre une corrélation entre l’évolution non-linéaire de la bande interdite pour les différentes compositions et entre l’évolution des charges locales dynamiques. Les propriétés optiques en température sont dominées par l’arrangement des dipôles dans les compositions ferroélectriques. Pour les autres compositions les propriétés sont plutôt guidées par les défauts. Il a été possible de déterminer les températures critiques des différents mécanismes à partir des caractérisations optiques. Dans ce système Ba(Sn,Ti)O3, les propriétés optiques et le photocourant sont fortement reliés à la structure locale particulière et la nature de la liaison chimique, comme nous avons mis en évidence par la spectroscopie Raman et la spectrophotométrie photoélectronique X. / There is an active search for new photovoltaic technologies with improved efficiency, since the traditional p-n junctions have either the limited efficiency or the increased cost. The research on inorganic ferroelectric perovskites offers opportunities to develop new approaches and increase photovoltaic efficiency, for instance due to capability of these materials to more efficiently separate the photoexcited charges due to the existence of an internal electric field within their unit cell. To profit from this advantage, the material must combine properties like ferroelectricity, relatively small band gap and high charge mobility. In this work, we have synthesized and studied compounds from Ba(Sn,Ti)O3 solid solution, having as end members ferroelectric BaTiO3 and paraelectric BaSnO3. Crystallographic phase transitions and changes of the polar states were characterized by diffraction techniques and dielectric spectroscopy. The non-linear evolution of the band gap for different compounds has been correlated to arise from evolution of the local dynamic charge existing in these compounds, as deduced from X-ray photoelectron spectroscopy. The temperature-dependent optical properties are dominated by polar order in ferroelectric compositions, while for the other compositions the defect-related mechanisms prevail. The critical temperatures for different mechanisms can be determined from optical characterization. In these compounds, the optical properties and photocurrent are strongly related to particularities of the local structure and chemical bonding deduced from Raman and X-ray photoelectron spectroscopies.

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Cette thèse présente l'étude de la dynamique d'un atome ou d'une molécule en interaction avec un agrégat en vue d'étudier comment un petit système (l'atome, la molécule) échange de l'énergie électronique, cinétique et vibrationnelle avec un système possédant de très nombreux degrés de liberté (l'agrégat).Le premier système est l'étude, expérimentale et théorique, de la dynamique en temps réel d'un atome de baryum déposé sur agrégat d'argon (BaArn). L'atome de baryum est excité dans des niveaux de Rydberg, il en résulte une dynamique extrêmement riche entre le chromophore et l'agrégat. L'interprétation théorique a nécessité la conception d'une méthode de dynamique originale, permettant de traiter à la fois le grand nombre d'états excités mis en jeu, couplés à de nombreux degrés de libertés atomiques. La mise en commun des informations théoriques et expérimentales a permis d'établir l'ensemble du chemin réactionnel ayant lieu au cours de cette dynamique.Le deuxième système concerne l'étude par fluorescence de la photo-dissociation de Ca2 déposé sur agrégat d'hélium ou sur agrégat mixte hélium-argon (Ca2Hen ou Ca2ArmHen). Ces résultats sont comparés à ceux obtenu sur agrégat d'argon pur (Ca2Hen). Les différences entre ces trois types de solvant montrent que les interactions sont différentes suivant que le solvant est ''quantique'' (l'hélium) ou ''classique'' (l'argon). Plusieurs canaux réactionnels ont été mis en évidence selon que l'atome de calcium excité qui résulte de la photo-dissociation est libre ou reste solvaté par de l'hélium et/ou de l'argon. Les rapports de branchement entre ces différents canaux ont également été mesurés.

L’étude des matériaux à transition de spin constitue un important challenge du fait de leurspotentialités dans le traitement de l’information, notamment par voie optique. En effet, inscrire uneinformation par la lumière permet d’accéder à des vitesses de traitement extrêmement rapides. Leszones de stabilité de cette information photo-inscrite varient beaucoup avec la température. Cetravail de thèse a consisté à faire converger ces zones vers un même point via la rencontre entre lestransitions de spin thermique et photo-induite. Pour cela, nous avons utilisé deux approcheschimiques : la réalisation de solutions solides sur des systèmes très coopératifs et l’obtention denanoparticules photomagnétiques. Ce manuscrit détaille les résultats obtenus durant ce travail. / The study of spin crossover materials is an important challenge regarding their potentiality ininformation process, especially by optical way. Indeed, writing information with light can allow tospeedup the treatment. The stability areas of this photo-induced information is sensitive to thetemperature. The aim of this work consisted of realise the convergence of this areas toward thesame point through the meeting of the thermal and photo-induced spin transitions. For this purpose,we used two chemical approaches: achievement of metal dilution on very cooperative systems andsynthesis of photo-magnetic nanoparticles. This manuscript describes the results obtained during thiswork.

La propriété d’être réversiblement commutable de certaines protéines fluorescenteshomologues à la GFP ouvre un vaste champ d’applications possibles: notamment le biostockagede données à haute densité et la microscopie à super résolution. Parmi ces protéines,on trouve plusieurs variantes de la GFP, notamment la protéine jaune YFP, et des protéinesfluorescentes issues d'espèces marines Anthozoaires, comme Dronpa ou Padron. Plusieursétudes structurales indiquent que ces protéines fluorescentes photochromiques commutent parisomérisation et protonation couplées du chromophore. Cependant, la synchronisation entreces deux événements, le détail des mécanismes de photo-commutation, et le rôle de ladynamique conformationelle restent incomplètement compris. Par l'utilisation combinée de lacristallographie cinétique et de la spectroscopie optique in cristallo à basse température, nousavons comparé le comportement des protéines YFP, Dronpa et IrisFP, et nous avons étudié endétail le mécanisme photo-physique de commutation chez la protéine Padron. Contrairement àDronpa et IrisFP, la photo-commutation d’YFP est plus efficace à basse température qu’àtempérature ambiante. Nos résultats suggèrent que le mécanisme de commutation d’YFPn'implique pas de changement conformationel majeur, mais plutôt une protonation photoinduitedu chromophore ne nécessitant pas d'isomérisation. Au contraire, les études réaliséessur la protéine Padron nous ont permis de montrer que, dans ce cas, l’isomérisation duchromophore peut se produire indépendamment de sa protonation, et, étonnamment, àtempérature cryogénique. De plus, deux états intermédiaires ont pu être caractérisés au coursdu processus de photo-commutation. La protéine Padron a permis de mettre à jour le premiermarqueur codable génétiquement qui soit efficacement photo-commutable à températurecryogénique. / The property to be reversible switchable of some homologues fluorescents protein ofGFP open a large field for possible applications: such as, high-density data bio-storage andsuper-resolution microscopy. Between these proteins, we find several variants of GFP, such asyellow fluorescent protein, YFP, and fluorescents protein from marine Anthozoary species, asDronpa or Padron. Several structural studies suggest that these fluorescent proteins switch viaisomerization coupled with the protonation of the chromophore. However, thesynchronization between these processes, the detail about the photo-switching mechanism,and the role of conformational dynamics remains unclear. In combination of the kineticcrystallography and the optic spectroscopy in cristallo at low temperature, we have comparedthe YFP behavior, Dronpa and IrisFP, and we have studied in detail the photo-physicmechanism of Padron switching. In contrast to Dronpa and IrisFP, the YFP photoswitching ismore efficient at low temperature than at room temperature. Our results suggest that theYFPswitching is not associated to large structural rearrangements, but mostly a photo-inducedprotonation of the chromophore without isomerization. On the contrary, the studies done withPadron allowed us to show, in this case, the chromophore isomerization can be producedindependently of the protonation, at cryo-temperatures. Moreover, two intermediate stateswere revealed in the photo-pathway. Padron fluorescent protein allows to advance the firstgenetically inserted dye, being photo-switchable at cryogenic temperature

Women in South Africa are discriminated against in various areas of their lives, specifically in the workplace where the power dynamics between men and women are not equally distributed. This qualitative research study in a critical phenomenological research paradigm has allowed me to explore, describe, explain and gain an understanding of the nature of female teachers‟ lived experiences of senior male colleagues‟ exercising of power. It has also allowed me to critically challenge and question female teachers‟ lived experiences by interpreting and making meaning or the power conundrum within a school context. Using a qualitative research design and methodology, I interrogated the power hierarchy in schools by initiating critical dialogue with the participants. This study serves as a voice for female teachers‟ lived experiences regarding the power conundrum. Data was generated by 16 purposefully selected female teachers from various primary and secondary schools in the Dr Kenneth Kaunda district in the North-West Province, more specifically the Matlosana area. The data generation phases consist of two consecutive phases each with different stages. The first phase concerns the photo-elicitation-narratives (written). This is followed by individual photo-elicitation-interviews during the second phase. The data is analysed by means of interpretive phenomenology analysis (IPA). Thereafter themes and categories are identified, and verified during a consensus meeting with independent coders. Two main themes are identified: Theme one is that female teachers experience power as a behaviour that has the potential to evoke feelings that are (im)balanced, thus power evokes feelings of either being nurtured or feelings that are seen as degrading or destructive in nature. Theme two reflects female teachers‟ suggestions of promoting their own well-being. As wellbeing evokes a sense of meaningfulness and belonging in the workplace, it can lead to positive work relationships. When power is misused or abused in the workplace, it results in workplace bullying and abusive behaviour, which has a negative effect not only on employees‟ work performance, but also on their personal life and own health. If the detrimental effects of this phenomenon of power in a school context are ignored, female teachers will continue to experience loss of self-esteem and work withdrawal, and show signs of increased depression as well as high stress levels. / MEd (Learner Support), North-West University, Potchefstroom Campus, 2015

Women in South Africa are discriminated against in various areas of their lives, specifically in the workplace where the power dynamics between men and women are not equally distributed. This qualitative research study in a critical phenomenological research paradigm has allowed me to explore, describe, explain and gain an understanding of the nature of female teachers‟ lived experiences of senior male colleagues‟ exercising of power. It has also allowed me to critically challenge and question female teachers‟ lived experiences by interpreting and making meaning or the power conundrum within a school context. Using a qualitative research design and methodology, I interrogated the power hierarchy in schools by initiating critical dialogue with the participants. This study serves as a voice for female teachers‟ lived experiences regarding the power conundrum. Data was generated by 16 purposefully selected female teachers from various primary and secondary schools in the Dr Kenneth Kaunda district in the North-West Province, more specifically the Matlosana area. The data generation phases consist of two consecutive phases each with different stages. The first phase concerns the photo-elicitation-narratives (written). This is followed by individual photo-elicitation-interviews during the second phase. The data is analysed by means of interpretive phenomenology analysis (IPA). Thereafter themes and categories are identified, and verified during a consensus meeting with independent coders. Two main themes are identified: Theme one is that female teachers experience power as a behaviour that has the potential to evoke feelings that are (im)balanced, thus power evokes feelings of either being nurtured or feelings that are seen as degrading or destructive in nature. Theme two reflects female teachers‟ suggestions of promoting their own well-being. As wellbeing evokes a sense of meaningfulness and belonging in the workplace, it can lead to positive work relationships. When power is misused or abused in the workplace, it results in workplace bullying and abusive behaviour, which has a negative effect not only on employees‟ work performance, but also on their personal life and own health. If the detrimental effects of this phenomenon of power in a school context are ignored, female teachers will continue to experience loss of self-esteem and work withdrawal, and show signs of increased depression as well as high stress levels. / MEd (Learner Support), North-West University, Potchefstroom Campus, 2015

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The aim of this project was to improve the imaging performance of planar superlenses for evanescent near-field lithography. An experimental investigation of the performance of superlenses with reduced surface roughness was proposed. Such an investigation poses significant requirements in regards to process control in thin film deposition of silver onto dielectric substrates. Thin film deposition of silver films, onto silicon dioxide substrates, achieved films with root mean square surface roughness as low as 0.8 nm. While these experiments provided good understanding of the deposition process, significant variability of the surface roughness parameter remained an issue. The diffculty of achieving consistent control of surface roughness led to a finite element method simulation study where this parameter could be readily controlled. An improved understanding of how surface roughness affects superlens imaging performance was obtained from the results of this investigation. Furthermore, it was shown that in order to conduct an experimental investigation to verify the simulation results, it would be necessary to improve the imaging capability of super-resolution lithography protocols to achieve 3σ line edge roughness (LER) of <20 nm. Resist-scheme optimisation was identied as an important factor in this regard. Thus, a novel calixarene-based photoresist was formulated and characterised. The resist demonstrated superior imaging capabilities through interference lithography and evanescent near-field optical lithography, capable of resolving 250-nm period half-pitch line gratings with 3σ LER below 10 nm. The development of this novel photoresist will enable future lithographical investigations to be conducted with improved resolution and imaging fidelity.

Photography today is based more in editing and manipulation than in the physical capturing of the photo. The pervasiveness of photo editing is only going to increase; however, whether an edited photo remains true to the original photo, let alone the original scene, is left for the photographer to determine. Photographers attempt to create the "perfect" image and are willing to sacrifice the original photo in the process. The finished product becomes in many cases an entirely different photo from the original, to the extent that it is more a product of the editing software than the actual camera. My project takes the form of a photo-editing manual, viewable in both physical and digital format, and an exhibition of the final images. None of the images are so extreme that it is immediately clear that they have been manipulated; however, as they are all images of Scripps College, people who are familiar with the campus will be able to recognize that something is off. I see these images as products of editing software more than products of a camera. I have exaggerated commonly used editing techniques to draw attention to their excessive use in photography today. In the manual, the manipulation and changes suggested become gradually more extreme, so that if the reader does not a first question the instructions, he or she will be sure to by the end.