Nesta dissertação foram investigadas as propriedades ópticas e estruturais em filmes ultrafinos e de um sistema de moléculas isoladas de poli (9,9 dioctilfluoreno) (PFO). As amostras poliméricas foram produzidas sobre substrato de quartzo empregando a técnica de spin-coating a partir de soluções de PFO em clorofórmio. Através desse método foi possível obter filmes extremamente finos e moléculas isoladas, com boas condições para o estudo de processos fotofísicos. Técnicas espectroscópicas, tais como, microscopia confocal de fluorescência (LSMC), espectroscopia de absorção UV/Vis, bem como espectroscopia de fotoluminescência foram utilizadas neste trabalho. Inicialmente, o método de preparação dos filmes através de sucessivas diluições foi avaliado pelos espectros de absorção mostrando que é possível obter informação da absorção molecular por medidas de absorbância em condições extremas de baixa diluição. Medidas de fotoluminescência a baixa temperatura de 5 K mostraram que a fase &#946; pode ser induzida em filmes ultrafinos de PFO em clorofórmio. Através da técnica de microscopia confocal foi realizada a sondagem de um pequeno conjunto molecular considerado neste trabalho como sistema de molécula isolada, no qual permitiu um melhor entendimento sobre os mecanismos associados à tensão e/ou a organização da cadeia polimérica (fase planar &#946; e fase não planar), induzida pelo substrato, que afeta fortemente as propriedades de emissão. Emissões foram resolvidas pela primeira vez em moléculas isoladas entre as energias da fase &#946; e da fase não planar que foram associadas a perturbações da estrutura planar por conformações primárias da cadeia, como dobras e torções distribuídas ao longo da cadeia. Além disso, moléculas isoladas de PFO sobre o substrato de quartzo possuem a estrutura da fase &#946; congelada à temperatura ambiente. Esta estrutura é perturbada pelas vibrações atômicas do substrato que alargam a linhas de emissão, sem quebrar a conformação ordenada rígida imposta pelo substrato. Além disso, foi possível comparar as propriedades como eficiência da emissão e migração do estado excitado entre filmes ultrafinos e em moléculas isoladas. / Optical and structural properties of ultrathin films and isolated molecules of poly (9,9 dioctylfluorene) (PFO) are investigated in this work. The polymeric films were produced on top of quartz substrate by spin-coating technique from PFO chloroform solutions having different dilutions. Through this method it was possible to obtain extremely thin films (<10 nm) and isolated molecules, with suitable quality that allowed the study of photophysical processes at molecular level. We employed three spectroscopic techniques to characterize such ultrathin films, namely, confocal fluorescence microscopy (LSMC), UV/Vis absorption spectroscopy and temperature dependent photoluminescence spectroscopy. The spincoated films were initially prepared though successive dilutions in PFO/CHCl3 solutions. We demonstrate that it is possible to obtain information of the molecular structure by using absorbance measurements under extreme conditions of low molecular dilution. Measurements of photoluminescence at low temperatures (5 K) showed that the phase &#946; may be induced in ultrathin films of PFO in chloroform. Using confocal microscopy we probed a small molecular assembly considered in this work as an isolated molecule system, which allowed to understand of mechanisms associated with stress and/or the organization of the polymer chain (phase planar &#946; and phase non-planar), induced by the substrate, which strongly affects the emission properties. Emissions in isolated molecules have been resolved for the first time between the energies of the &#946; phase and the amorphous phase that were associated to perturbations of the planar structure by primary chain conformations, such as folds and twists distributed along the chain. In addition, PFO isolated molecules have frozen &#946; phase structure at room temperature on the quartz substrate. This structure is disturbed by the atomic vibrations of the substrate that broaden the emission lines without breaking the ordered conformation imposed by the rigid substrate. Moreover, it was possible to compare the properties of the efficiency emission and excited state migration between ultrathin films and isolated molecules.

Nesta dissertação foram investigadas as propriedades ópticas e estruturais em filmes ultrafinos e de um sistema de moléculas isoladas de poli (9,9 dioctilfluoreno) (PFO). As amostras poliméricas foram produzidas sobre substrato de quartzo empregando a técnica de spin-coating a partir de soluções de PFO em clorofórmio. Através desse método foi possível obter filmes extremamente finos e moléculas isoladas, com boas condições para o estudo de processos fotofísicos. Técnicas espectroscópicas, tais como, microscopia confocal de fluorescência (LSMC), espectroscopia de absorção UV/Vis, bem como espectroscopia de fotoluminescência foram utilizadas neste trabalho. Inicialmente, o método de preparação dos filmes através de sucessivas diluições foi avaliado pelos espectros de absorção mostrando que é possível obter informação da absorção molecular por medidas de absorbância em condições extremas de baixa diluição. Medidas de fotoluminescência a baixa temperatura de 5 K mostraram que a fase &#946; pode ser induzida em filmes ultrafinos de PFO em clorofórmio. Através da técnica de microscopia confocal foi realizada a sondagem de um pequeno conjunto molecular considerado neste trabalho como sistema de molécula isolada, no qual permitiu um melhor entendimento sobre os mecanismos associados à tensão e/ou a organização da cadeia polimérica (fase planar &#946; e fase não planar), induzida pelo substrato, que afeta fortemente as propriedades de emissão. Emissões foram resolvidas pela primeira vez em moléculas isoladas entre as energias da fase &#946; e da fase não planar que foram associadas a perturbações da estrutura planar por conformações primárias da cadeia, como dobras e torções distribuídas ao longo da cadeia. Além disso, moléculas isoladas de PFO sobre o substrato de quartzo possuem a estrutura da fase &#946; congelada à temperatura ambiente. Esta estrutura é perturbada pelas vibrações atômicas do substrato que alargam a linhas de emissão, sem quebrar a conformação ordenada rígida imposta pelo substrato. Além disso, foi possível comparar as propriedades como eficiência da emissão e migração do estado excitado entre filmes ultrafinos e em moléculas isoladas. / Optical and structural properties of ultrathin films and isolated molecules of poly (9,9 dioctylfluorene) (PFO) are investigated in this work. The polymeric films were produced on top of quartz substrate by spin-coating technique from PFO chloroform solutions having different dilutions. Through this method it was possible to obtain extremely thin films (<10 nm) and isolated molecules, with suitable quality that allowed the study of photophysical processes at molecular level. We employed three spectroscopic techniques to characterize such ultrathin films, namely, confocal fluorescence microscopy (LSMC), UV/Vis absorption spectroscopy and temperature dependent photoluminescence spectroscopy. The spincoated films were initially prepared though successive dilutions in PFO/CHCl3 solutions. We demonstrate that it is possible to obtain information of the molecular structure by using absorbance measurements under extreme conditions of low molecular dilution. Measurements of photoluminescence at low temperatures (5 K) showed that the phase &#946; may be induced in ultrathin films of PFO in chloroform. Using confocal microscopy we probed a small molecular assembly considered in this work as an isolated molecule system, which allowed to understand of mechanisms associated with stress and/or the organization of the polymer chain (phase planar &#946; and phase non-planar), induced by the substrate, which strongly affects the emission properties. Emissions in isolated molecules have been resolved for the first time between the energies of the &#946; phase and the amorphous phase that were associated to perturbations of the planar structure by primary chain conformations, such as folds and twists distributed along the chain. In addition, PFO isolated molecules have frozen &#946; phase structure at room temperature on the quartz substrate. This structure is disturbed by the atomic vibrations of the substrate that broaden the emission lines without breaking the ordered conformation imposed by the rigid substrate. Moreover, it was possible to compare the properties of the efficiency emission and excited state migration between ultrathin films and isolated molecules.

Die Herstellung von ultradünnen Germaniumdioxidfilmen auf Metallsubstraten ist erstmals erfolgreich gelungen. Die Filmstruktur konnte mittels oberflächensensitiven Techniken mit atomarer Präzision und chemischer Sensitivität aufgelöst werden. Zur Untersuchung werden STM-Bilder analysiert und durch niederenergetische Elektronenbeugung (LEED), eine dynamischen LEED-Studie und extern ausgeführte Dichtefunktionaltheorieberechnungen (DFT) ergänzt. In dieser Arbeit werden atomar aufgelöste Rastertunnelmikroskopiebilder (STM) von ultradünnen Germaniumdioxid- und Siliziumdioxidfilmen direkt verglichen. Ziel der Analyse ist es, den Einfluss des Metallsubstrats auf die Struktur von Oxidfilmen zu untersuchen. Zu diesem Zweck werden ultradünne Germaniumdioxid-Filme auf Ru(0001), Pt(111) und Au(111) abgeschieden und mit Siliziumdioxid-Filmen auf verschiedenen Substraten verglichen, die in früheren Studien untersucht wurden. Germaniumdioxid und Siliziumdioxid sind eng miteinader verknüpft. Hierbei sind Struktur und chemische Eigenschaften als äquivalent anzusehen. Es wurden drei verschiedene Netzwerkstrukturen aufgeklärt: Monolagen-, Zickzack- und Bilagenfilme. Die einzelnen Bausteine in diesen Filmsystemen bestehen aus verzerrten Tetraedern, in denen ein Germaniumatom von vier Sauerstoffatomen umgeben ist. Benachbarte Tetraeder sind durch Ge-O-Ge-Bindungen miteinander verknüpft und binden im Fall der Monolagenfilme an das darunterliegende Metallsubstrat. In Bilagenfilmen hingegen gibt es keine chemischen Bindungen zum Substrat, wodurch die Filmstruktur flexibler wird. Durch Variation der Herstellungsbedingungen kann man rein kristalline, amorphe oder Phasen mittlerer Ordnung erhalten. Es ist wichtig hervorzuheben, dass der amorphe Germaniumdioxid-Bilagenfilm ein neues amorphes zweidimensionales Material darstellt. / The preparation of metal-supported ultrathin films of germanium dioxide, termed also germania, has been successfully achieved for the first time. The structure of the films is elucidated with atomic precision and chemical sensitivity using surface science techniques. The investigation is performed by analyzing STM images and is complemented by low-energy electron diffraction (LEED) patterns, a dynamical LEED study, and external support from density functional theory (DFT) calculations. In this work, we compare side-by-side atomically-resolved scanning tunneling microscopy (STM) images of ultrathin films of germania and silica. The analysis aims to investigate the impact of the metal support on the structure of oxide films. For that purpose, ultrathin germania films are grown on Ru(0001), Pt(111) and Au(111), and compared with previously reported silica ultrathin films supported on different substrates. Germania has been widely associated with silica since they are considered to be structural and chemical equivalent materials. Three main network structures have been characterized: monolayer, zigzag and bilayer films. In all systems, the building block consists of a distorted tetrahedron with a germanium atom surrounded by four oxygen atoms. Adjacent tetrahedra connect to each other through Ge-O-Ge bonds and, in the case of the monolayer films, they also bind to the metal support. Conversely, in bilayer films there are no chemical bonds to the metal substrate, thus providing more flexibility to the film structure. Through a meticulous control of the preparation conditions one can obtain a purely crystalline phase, an amorphous one, or one with intermediate order. It is important to highlight that the amorphous germania bilayer film represents a new 2-dimensional amorphous material.

Concentration of Ce3+ is one of the most important parameters that influence the reactivity of ceria based catalyst. In this work we examine different experimental approaches for controlling Ce3+ concentration in cerium oxide model catalyst systems such as: i) influencing the stoichiometry of ceria, ii) introducing high valence doping agent, and iii) growing ultra thin ceria films with a strong metal substrate interaction. Structure, morphology and chemical state of prepared reduced ceria based systems were examined by means of surface science techniques: scanning tunneling microscopy, low-energy electron diffraction and X-ray photoelectron spectroscopy. In the present work an original method of ceria film reduction was introduced that allows stepwise control on stoichiometry and degree of film reduction (i). Further we introduce preparation procedures for well-ordered tungsten doped ceria model system (ii) and for the high quality 2D ultrathin ceria system on Cu (1 1 1) (iii). Preparation methods and model systems introduced in this work incorporate different physicochemical principles of Ce3+ induction and provide a variety of model systems useful for examining different effects that diversely prepared Ce3+ ions have on the activity of the catalyst.

<p>The study of ultrathin magnetic films offers novel magnetic phenomena due to the reduced symmetry of these 2D systems. The magnetic anisotropy differentiates behaviour in ultrathin films from the bulk environment, as additional anisotropies emerge from the ultrathin film thickness and the inherent strain of ultrathin films. In this work, the in-plane magnetic anisotropy of strained ferromagnetic (FM) ultrathin Co(0001) films grown on a W(110) substrate is measured over a range of temperatures (150-320 K). Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) were used to determine the film structure and thickness. The anisotropy is derived from the quotient of the saturation magnetization and the transverse susceptibility, which are measured using the surface magneto-optic Kerr effect (SMOKE).</p> <p>This work’s second objective is to study the Néel transition in antiferromagnetic (AFM) ultrathin films. The zero net magnetization of AFM materials and the minute sample size of ultrathin films make magnetic measurements impossible with conventional methods. An alternative approach is to study a single AFM ultrathin film that is coupled by the interfacial exchange interaction to a FM ultrathin film. The upper layers of ultrathin Co/W(110) films were oxidized to produce ultrathin CoO/Co/W(110) films, creating an AFM/FM bilayer system. SMOKE measurement of the transverse magnetic susceptibility of the FM Co layer reveal the Néel transition of the AFM layer indirectly through the interfacial exchange interaction.</p> / Master of Science (MSc)

O desenvolvimento da nanociência e nanotecnologia promoveu uma nova fronteira no estudo da matéria, permitindo que materiais já conhecidos tivessem suas propriedades redescobertas ao serem manipulados em nível molecular. Vários materiais vêm apresentando relevância na nanociência e nanotecnologia, como os nanotubos de carbono (CNTs), nanopartículas (NPs) e óxido de grafeno, uma vez que os CNTs e óxido de grafeno são dotados de propriedades mecânicas, térmicas e elétricas que os tornam apropriados para o desenvolvimento e a aplicação em dispositivos, especialmente na área biotecnológica e de sensores. Diversas áreas se beneficiam com o uso da tecnologia em nanopartículas (NPs), por exemplo: alimentícia, médica, agronegócio, cosmética, etc. Uma possível perspectiva na utilização desses nanomateriais em sistemas biológicos torna muito interessante investigar como tais materiais interagem em nível molecular com modelos de membranas celulares e com células. Esta tese tem como objetivos: i) investigar detalhadamente a interação entre nanopartículas (Fe3O4/Dextran; Fe3O4/PDAC; PDAC; Dextran) e nanotubos de carbono com modelos de membranas celulares; e ii) desenvolver nanofibras poliméricas pela técnica de electrospinning para ser utilizada com óxido de grafeno como modelos mimetizados (scaffolds) para a diferenciação de células-tronco neurais. Os filmes ultrafinos foram fabricados utilizando as técnicas de Langmuir e Langmuir-Blodgett. Esses nanomateriais foram avaliados através da técnica de Espectroscopia vibracional por Geração de Soma de Frequências. A espectroscopia SFG é sensível a interfaces. Nanofibras de Poli(&#949;-Caprolactone) foram fabricadas pela técnica de electrospinning. Scaffolds com óxido de grafeno/Nanofibras de Poli(&#949;-Caprolactone) foram desenvolvidos como suportes sólidos para a diferenciação de células-tronco neurais de rato. Óxido de grafeno em diferentes concentrações foi incorporado nas nanofibras poliméricas. Os modelos deste sistema foram investigados por imagens de Microscopia Eletrônica de Varredura. Os resultados mostraram que a carga eletrostática de cada fosfolipídio utilizado pode influenciar nas interações com os nanomateriais (nanopartículas ou nanotubos de carbono), podendo resultar em uma desestruturação no modelo de membrana celular. Scaffolds contendo nanofibras de Poli(&#949;-Caprolactone) com óxido de grafeno representaram um eficiente modelo mimetizado para a interação/diferenciação de células-tronco neurais de rato conforme revelado por imagens de Microscopia Eletrônica de Varredura. Estas imagens mostraram que o sistema de nanofibras de Poli(&#949;-Caprolactone) com 1,0 mg/mL de óxido de grafeno foram ideais para a diferenciação de oligodendrócitos em células-tronco neurais de rato. / The development of nanoscience and nanotechnology promoted a new frontier on the study of matter, allowing conventional materials to exhibit novel or improved properties. Several materials show relevance in nanoscience and nanotechnology, such as carbon nanotubes (CNTs), nanoparticles (NPs) and graphene oxide. CNTs and graphene oxide, for example, exhibit unique mechanical, thermal and electrical properties, which make them appropriate to the development and application in devices, especially in biotechnology and sensors areas. Many areas are benefited from the use of nanoparticles (NPs), such as food, medical, agrobusiness, cosmetic etc. The perspective regarding the use of nanomaterials in biological systems requires the understanding on how these materials interact at the molecular level with cell membrane models and with cells. The objectives of this thesis are: i) to investigate the interaction between nanoparticles (Fe3O4/Dextran; Fe3O4/PDAC; PDAC; Dextran) and carbon nanotubes with cell membrane models; and ii) to develop polymeric nanofibers via electrospinning technique, to be used with graphene oxide as mimic models (scaffolds) in the differentiation of neural stem cells. The cell membrane models were manufactured using Langmuir and Langmuir-Blodgett techniques. These nanomaterials were evaluated through Sum Frequency Vibrational Spectrosocopy (SFG). Poly(&#949;-Caprolactone) nanofibers were manufactured by electrospinning technique. Scaffolds with graphene oxide/Poly(&#949;-Caprolactone) were developed as solid supports for differentiation of rats neural stem cells. This biosystem was investigated via Scanning Electron Microscopy and biochemical essays. The results showed that the charge of each phospholipid influenced the interactions with the nanomaterials (nanoparticles or carbon nanotubes), in some cases, resulting in a disruption of the cell membrane model. Scaffolds with Poly(&#949;-Caprolactone) nanofibers obtained via electrospinning with graphene oxide represented an efficient mimic model for interaction/differentiation of neural stem cells as shown via Scanning Electron Microscopy. The images revealed that the PCL nanofibers system with 1.0 mg/mL of graphene oxide were ideal to the differentiation of oligodendrocytes in neural stem cells.

O desenvolvimento da nanociência e nanotecnologia promoveu uma nova fronteira no estudo da matéria, permitindo que materiais já conhecidos tivessem suas propriedades redescobertas ao serem manipulados em nível molecular. Vários materiais vêm apresentando relevância na nanociência e nanotecnologia, como os nanotubos de carbono (CNTs), nanopartículas (NPs) e óxido de grafeno, uma vez que os CNTs e óxido de grafeno são dotados de propriedades mecânicas, térmicas e elétricas que os tornam apropriados para o desenvolvimento e a aplicação em dispositivos, especialmente na área biotecnológica e de sensores. Diversas áreas se beneficiam com o uso da tecnologia em nanopartículas (NPs), por exemplo: alimentícia, médica, agronegócio, cosmética, etc. Uma possível perspectiva na utilização desses nanomateriais em sistemas biológicos torna muito interessante investigar como tais materiais interagem em nível molecular com modelos de membranas celulares e com células. Esta tese tem como objetivos: i) investigar detalhadamente a interação entre nanopartículas (Fe3O4/Dextran; Fe3O4/PDAC; PDAC; Dextran) e nanotubos de carbono com modelos de membranas celulares; e ii) desenvolver nanofibras poliméricas pela técnica de electrospinning para ser utilizada com óxido de grafeno como modelos mimetizados (scaffolds) para a diferenciação de células-tronco neurais. Os filmes ultrafinos foram fabricados utilizando as técnicas de Langmuir e Langmuir-Blodgett. Esses nanomateriais foram avaliados através da técnica de Espectroscopia vibracional por Geração de Soma de Frequências. A espectroscopia SFG é sensível a interfaces. Nanofibras de Poli(&#949;-Caprolactone) foram fabricadas pela técnica de electrospinning. Scaffolds com óxido de grafeno/Nanofibras de Poli(&#949;-Caprolactone) foram desenvolvidos como suportes sólidos para a diferenciação de células-tronco neurais de rato. Óxido de grafeno em diferentes concentrações foi incorporado nas nanofibras poliméricas. Os modelos deste sistema foram investigados por imagens de Microscopia Eletrônica de Varredura. Os resultados mostraram que a carga eletrostática de cada fosfolipídio utilizado pode influenciar nas interações com os nanomateriais (nanopartículas ou nanotubos de carbono), podendo resultar em uma desestruturação no modelo de membrana celular. Scaffolds contendo nanofibras de Poli(&#949;-Caprolactone) com óxido de grafeno representaram um eficiente modelo mimetizado para a interação/diferenciação de células-tronco neurais de rato conforme revelado por imagens de Microscopia Eletrônica de Varredura. Estas imagens mostraram que o sistema de nanofibras de Poli(&#949;-Caprolactone) com 1,0 mg/mL de óxido de grafeno foram ideais para a diferenciação de oligodendrócitos em células-tronco neurais de rato. / The development of nanoscience and nanotechnology promoted a new frontier on the study of matter, allowing conventional materials to exhibit novel or improved properties. Several materials show relevance in nanoscience and nanotechnology, such as carbon nanotubes (CNTs), nanoparticles (NPs) and graphene oxide. CNTs and graphene oxide, for example, exhibit unique mechanical, thermal and electrical properties, which make them appropriate to the development and application in devices, especially in biotechnology and sensors areas. Many areas are benefited from the use of nanoparticles (NPs), such as food, medical, agrobusiness, cosmetic etc. The perspective regarding the use of nanomaterials in biological systems requires the understanding on how these materials interact at the molecular level with cell membrane models and with cells. The objectives of this thesis are: i) to investigate the interaction between nanoparticles (Fe3O4/Dextran; Fe3O4/PDAC; PDAC; Dextran) and carbon nanotubes with cell membrane models; and ii) to develop polymeric nanofibers via electrospinning technique, to be used with graphene oxide as mimic models (scaffolds) in the differentiation of neural stem cells. The cell membrane models were manufactured using Langmuir and Langmuir-Blodgett techniques. These nanomaterials were evaluated through Sum Frequency Vibrational Spectrosocopy (SFG). Poly(&#949;-Caprolactone) nanofibers were manufactured by electrospinning technique. Scaffolds with graphene oxide/Poly(&#949;-Caprolactone) were developed as solid supports for differentiation of rats neural stem cells. This biosystem was investigated via Scanning Electron Microscopy and biochemical essays. The results showed that the charge of each phospholipid influenced the interactions with the nanomaterials (nanoparticles or carbon nanotubes), in some cases, resulting in a disruption of the cell membrane model. Scaffolds with Poly(&#949;-Caprolactone) nanofibers obtained via electrospinning with graphene oxide represented an efficient mimic model for interaction/differentiation of neural stem cells as shown via Scanning Electron Microscopy. The images revealed that the PCL nanofibers system with 1.0 mg/mL of graphene oxide were ideal to the differentiation of oligodendrocytes in neural stem cells.

La capacité à cartographier le champ magnétique à l'échelle nanométrique serait un atout crucial pour étudier les propriétés magnétiques des solides ainsi que certains phénomènes de transport, mais aussi pour des études fondamentales en biologie. Cette thèse porte sur la réalisation d'un microscope de champ magnétique d'un genre nouveau, qui promet une résolution spatiale de quelques nanomètres, une sensibilité de l'ordre du nanotesla, et fonctionne aux conditions ambiantes. Ce microscope est basé sur le défaut azote-lacune du diamant, dont les propriétés quantiques peuvent être exploitées pour en faire un magnétomètre ultrasensible de taille atomique. Dans un premier temps, nous présenterons le fonctionnement et la réalisation du microscope à défaut azote-lacune, qui consiste essentiellement en un microscope à force atomique sur la pointe duquel un nanocristal de diamant est attaché. Nous testerons le microscope en imageant le champ de fuite généré par un cœur de vortex dans un microdisque ferromagnétique. Dans un second temps, nous appliquerons le microscope à l'étude de couches ferromagnétiques ultraminces. Ces systèmes présentent un intérêt à la fois fondamental, les effets d'interfaces restant encore largement inexplorés à ce jour, et technologique, puisqu'ils sont à la base de propositions pour la réalisation de nouvelles mémoires magnétiques à basse consommation d'énergie. Nous étudierons d'abord la nature des parois de domaines dans ces couches ultraminces, ce qui nous permettra de révéler l'existence d'une interaction Dzyaloshinskii-Moriya d'origine interfaciale dans certains échantillons. Nous étudierons ensuite les sauts nanométriques d'une paroi de domaine induits par l'agitation thermique. Nous démontrerons en particulier le contrôle de ces sauts par un laser, ce qui nous permettra de visualiser et explorer le paysage énergétique de la paroi. / The ability to map the magnetic field at the nanometer scale would be a crucial advance to study the magnetic properties of solids as well as some transport phenomena, but also for fundamental studies in biology. This thesis deals with the realisation of a magnetic field microscope of a new kind, which promises a spatial resolution down to a few nanometres, a sensitivity of the order of a few nanoteslas, and operates under ambient conditions. This microscope is based on the nitrogen-vacancy defect in diamond, whose quantum properties can be harnessed to make an ultrasensitive, atomic-size magnetometre. In the first part, we will present the basic principles and the realisation of the nitrogen-vacancy defect microscope, which consists essentially in an atomic force microscope on the tip of which a diamond nanocrystal is grafted. We will test the microscope by imaging the stray field generated by a vortex core in a ferromagnetic microdisk. In the second part, we will apply the microscope to the study of ultrathin ferromagnets. These systems are interesting both from the physical point of view, as interface effects have been little explored so far, and for technology, as they are the cornerstone of several proposals for realising novel magnetic memory devices with low energy consumption. We will first study the nature of domain walls in these ultrathin ferromagnets, which will enable us to reveal the existence of an interface-related Dzyaloshinskii-Moriya interaction in some samples. Next, we will study the nanometric jumps of a domain wall induced by thermal fluctuations. In particular, we will demonstrate control over these jumps using a laser, which will allow us to visualise and explore the wall's energy landscape.

This diploma thesis studies magneto-optical (MO) response of epitaxial thin films of Co-doped ceria. Thin films were characterized by XPS, LEED, STM, spectroscopic ellipsometry and measurement of MO activity. The work focuses on studying MO response of the films depending on film thickness, cobalt concentration, oxidation state of cerium and chemical state of cobalt. Spectra of MO response consist of low energy region where the MO activity is mediated by transitions from defect induced states to conduction band and high energy region where a peak of MO activity appears which we attribute to transitions from valence band to conduction band. In this work we qualitatively explain the effects of the physico- chemical states of the thin films on the structure of the obtained MO spectra, mainly on the appearance of the MO activity in the low energy region, and on the changes of the position of the MO peak. Compared to other preparation methods the epitaxial thin films allow achieving a shift of the MO peak in the direction of higher photon energy.

This diploma thesis studies magneto-optical (MO) response of epitaxial thin films of Co-doped ceria. Thin films were characterized by XPS, LEED, STM, spectroscopic ellipsometry and measurement of MO activity. The work focuses on studying MO response of the films depending on film thickness, cobalt concentration, oxidation state of cerium and chemical state of cobalt. Spectra of MO response consist of low energy region where the MO activity is mediated by transitions from defect induced states to conduction band and high energy region where a peak of MO activity appears which we attribute to transitions from valence band to conduction band. In this work we qualitatively explain the effects of the physico- chemical states of the thin films on the structure of the obtained MO spectra, mainly on the appearance of the MO activity in the low energy region, and on the changes of the position of the MO peak. Compared to other preparation methods the epitaxial thin films allow achieving a shift of the MO peak in the direction of higher photon energy.