Neste trabalho, investigou-se capacitores MOS fabricados sobre superfícies irregulares contendo formas retangulares periódicas com 100 nm de altura, obtidas a partir de corrosão por plasma localizadas. Os óxidos de porta com 4,5 nm de espessura foram crescidos em ambientes ultrapuros de O2 ou pirogênico a fim de comparar a uniformidade de cobertura sobre os degraus verticais dos perfis retangulares. Foi mostrado que a oxidação pirogênica ou convencional na temperatura de 850 ºC permite obter óxidos de porta sobre degraus com altura de 100nm com baixa corrente de fuga e alto campo de ruptura. Esse comportamento pode ser interpretado como óxidos de porta perfeitamente amoldados sobre os degraus de 100nm de altura. O impacto deste resultado é agora a possibilidade de implementar óxidos de porta para transistores de porta envolvente e FinFETs. / In this work, it was investigated MOS capacitors fabricated onto periodic rectangular shapes, 100 nm in height, obtained by localized plasma etching onto silicon wafer surfaces. 4.5-nm gate oxide growth was performed in ultrapure dry O2 or pyrogenic environments in order to compare the coverage uniformity at the step edges of rectangular shapes defined onto the silicon surfaces. It was shown that pyrogenic and conventional oxidation at 850 ºC allows one to obtain gate oxides on 100nm-stepped silicon surfaces with low leakage current and high dielectric breakdown field. This behavior can be understood as highly conformal gate oxides over silicon steps with height of 100 nm. The impact of this result is now the feasibility of implementing gate oxides for surrounding gate transistors (SGT\'s) and FinFETs.

Neste trabalho, investigou-se capacitores MOS fabricados sobre superfícies irregulares contendo formas retangulares periódicas com 100 nm de altura, obtidas a partir de corrosão por plasma localizadas. Os óxidos de porta com 4,5 nm de espessura foram crescidos em ambientes ultrapuros de O2 ou pirogênico a fim de comparar a uniformidade de cobertura sobre os degraus verticais dos perfis retangulares. Foi mostrado que a oxidação pirogênica ou convencional na temperatura de 850 ºC permite obter óxidos de porta sobre degraus com altura de 100nm com baixa corrente de fuga e alto campo de ruptura. Esse comportamento pode ser interpretado como óxidos de porta perfeitamente amoldados sobre os degraus de 100nm de altura. O impacto deste resultado é agora a possibilidade de implementar óxidos de porta para transistores de porta envolvente e FinFETs. / In this work, it was investigated MOS capacitors fabricated onto periodic rectangular shapes, 100 nm in height, obtained by localized plasma etching onto silicon wafer surfaces. 4.5-nm gate oxide growth was performed in ultrapure dry O2 or pyrogenic environments in order to compare the coverage uniformity at the step edges of rectangular shapes defined onto the silicon surfaces. It was shown that pyrogenic and conventional oxidation at 850 ºC allows one to obtain gate oxides on 100nm-stepped silicon surfaces with low leakage current and high dielectric breakdown field. This behavior can be understood as highly conformal gate oxides over silicon steps with height of 100 nm. The impact of this result is now the feasibility of implementing gate oxides for surrounding gate transistors (SGT\'s) and FinFETs.

This master’s thesis is focused on preparation and analysis of ultrathin CaF2 (calcium fluoride) films on a graphene substrate. CaF2 was deposited in UHV conditions at substrate temperatures in the range from 20 °C to 400 °C. The material was deposited on Si(111) with a native SiO2 layer and on a substrate with a CVD graphene layer. The deposited films were analyzed by XPS, AFM and SEM. Moreover four different sample holders for deposition purposes were designed in this work.

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.

We report approaches to grow ultrathin Ru films for application as a seed layer and Cu diffusion barrier. For chemical vapor deposition (CVD) with Ru3(CO)12 we show the role surface hydroxyl groups have in nucleating the Ru islands that grow into a continuous film in a Volmer-Weber process, and how the nucleation density can be increased by applying a CO or NH3 overpressure. Thinner continuous films evolve in the presence of a CO overpressure. We report an optimun ammonia overpressure for Ru nucleation and that leads to deposition of smoother Ru thin films. Finally, we report a comparison of amorphous Ru films that are alloyed with P or B and demonstrate 3-nm thick amorphous Ru(B) films function as a Cu diffusion barrier.

<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)

Objetivos: (1) determinar a carga de fratura e o modo de falha de laminados cerâmicos ultrafinos processados via CAD-CAM em função da microestrutura do material (vitrocerâmica à base de dissilicato de lítio ou porcelana à base de leucita); (2) desenvolver metodologia de ciclagem mecânica para determinar o tempo de vida e o modo de falha de laminados cerâmicos ultrafinos processados via CADCAM. Materiais e métodos: dezesseis dentes humanos, incisivos centrais superiores, foram utilizados para confecção dos espécimes. Os dentes sofreram mínimo preparo, em esmalte, para adequada adaptação dos laminados cerâmicos ultrafinos. Os laminados de dissilicato de lítio e de porcelana foram confeccionados via CAD-CAM e cimentados com cimento resinoso sobre os dentes. Quatro espécimes de cada grupo foram levados à máquina de ensaios universal para determinação da carga de fratura dos laminados. Para o desenvolvimento de metodologia para determinação do tempo de vida dos laminados, uma série de testes piloto foi realizada, utilizando-se diferentes parâmetros como: tipo de antagonista (dentes naturais ou roletes metálicos), carga aplicada (20, 30 ou 40 N) e esquema de ciclo mastigatório (incisão ou deslizamento). Os padrões de falha dos laminados foram analisados em um estereomicroscópio, e os resultados obtidos no ensaio de carga de fratura foram analisados por ANOVA e teste de Tukey. Resultados: o valor médio obtido de carga de fratura para o dissilicato de lítio foi de 431,8 ± 217,9 N, enquanto que para a porcelana foi de 454,4 ± 72,1 N. Não houve diferença estatística entre os valores de carga de fratura encontrados, porém, o desvio padrão e o coeficiente de variação da vitrocerâmica foram muito superiores em relação aos da porcelana. Houve diferença no modo de falha dos materiais testados, sendo que a porcelana apresentou um maior número de falha por lascamento e o dissilicato de lítio apresentou maior quantidade de falha da estrutura dental. Na ciclagem mecânica, para cada condição testada, uma resposta diferente foi obtida. No tipo de ciclo incisão, os antagonistas (dente natural) fraturaram quando as cargas de 30 N e 40 N foram aplicadas. No tipo de ciclo deslizamento, o antagonista (dente natural) sofreu desgaste da borda incisal com carga de 30 N. Para o antagonista rolete metálico, quando a carga de 30 N foi aplicada ocorreu fratura do laminado, e quando aplicada a carga de 20 N, houve desgaste excessivo do rolete metálico. Conclusão: (1) o material utilizado não afetou a carga de fratura dos laminados cerâmicos ultrafinos quando o teste estático foi utilizado. Entretanto, o modo de falha foi significativamente diferente, sendo que a porcelana sofreu mais lascamentos do que o dissilicato de lítio; o qual, por sua vez, apresentou a maioria das falhas relacionadas à estrutura dental. (2) Não foi possível determinar uma combinação de parâmetros de ciclagem mecânica que permitisse a determinação dos parâmetros de fadiga para laminados cerâmicos ultrafinos, já que o número máximo de ciclos alcançados foi de 536.818 ciclos. Dessa forma, estudos futuros precisam ser realizados para que uma metodologia apropriada permita determinar parâmetros de fadiga clinicamente relevantes para laminados cerâmicos ultrafinos em dentes anteriores. / Objectives: (1) to determine the fracture load and the failure mode of the ultra-thin ceramic laminates processed via CAD-CAM according to the microstructure of the material (lithium disilicate-based glass-ceramic or leucite-based porcelain); (2) to develop a fatigue methodology capable of determining the lifetime of ultra-thin ceramic laminates processed via CAD-CAM. Materials and methods: sixteen human maxillary central incisors were used to produce the specimens. The teeth required minimal preparation on the enamel for proper adaptation of the ultra-thin ceramic laminates. Ceramic laminates made of lithium disilicate and feldspathic porcelain with thicknesses between 0.3 mm to 0.5 mm were produced via CAD-CAM and cemented with resin cement. Four specimens of each group were taken to a universal testing machine to determine the fracture load of the laminates. For the development of a fatigue methodology, a series of pilot tests was performed using different parameters such as: type of antagonist (natural teeth or metal roller), applied load (20, 30 or 40 N), and type of masticatory cycle (incision or sliding). Failure modes were analysed using a stereomicroscope. Fracture load data were analysed by ANOVA and Tukey\'s test. Results: the mean fracture load obtained for the glass-ceramic was 431.8 ± 217.9 N, while that obtained for the porcelain was 454.4 ± 72.1 N. There was no statistical difference between the mean fracture load values; however, the standard deviation and the coefficient of the variation of the glass-ceramic were both higher than those obtained for the porcelain. There was also a difference in the failure modes for the two materials tested. The porcelain showed a higher number of factures due to chipping and the lithium disilicate showed a higher number of tooth structure failure. The fatigue experiment showed different results depending on the condition analysed. In the incision cycle, the antagonists (natural tooth) fractured when loads of 30 N and 40 N were applied. In the slide type of cycle, the antagonist (natural tooth) suffered wear on the incisal edge after applying 30 N of load. For the metal roller antagonist, when a 30 N load was applied, the ceramic laminate fractured, and when a 20 N load was applied, an excessive wear of the metal roller occurred. Conclusion: (1) The material used did not affect the fracture load of ultra-thin ceramic laminates when the static test was used. However, the failure mode was significantly different, as porcelain suffered more chipping than the lithium disilicate; which, in turn, showed most fails related to the tooth structure. (2) It was not possible to determine the combination of the mechanical cycling parameters that would allow the determination of fatigue parameters for ultra-thin ceramic laminates, since the maximum number of cycles reached was 536,818 cycles. In this way, future studies need to be carried out so that a clinically relevant methodology can be developed to determine the fatigue parameters of ultra-thin ceramic laminates in the anterior teeth.

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.

Die grundlegenden Aspekte chemischer Reaktionen auf Oberflächen können anhand von geeigneten Modelsystemen unter Vakuumbedingungen untersucht werden. Siliciumdioxid (SiO2) als wichtiges Material für hochmoderne Technologieanwendungen in der Mikroelektronik, Photonik und Katalyse, war Gegenstand zahlreicher Studien, um die Beziehungen zwischen der atomaren Struktur und funktionalen Eigenschaften von Silizium-basierten Materialien zu erklären. Diese Arbeit untersucht die Wechselwirkung von Gasen mit epitaktisch gewachsenen Silikat-Dünnschichten auf einem Ru(0001) Einkristall. Unter Verwendung von Infrarot-Reflexions-Absorptions-Spektroskopie (IRAS) und temperaturprogrammierter Desorptionspektroskopie (TPD) konnten die Hydroxy-Spezies auf reinen Silikatfilmen als isolierte Silanole (Si-OH) identifiziert werden. Isotopenexperimente haben gezeigt, dass sich thermisch stabile Oberflächenhydroxylate hauptsächlich aus der Adsorption von Wassermolekülen bilden. Ein Austausch der Silanole mit Sauerstoffatomen im Kristallgitter während des Dehydroxylierungsprozesses wurde nicht beobachtet. Durch die Adsorption von Gasen wie CO, H2 und O2 bei erhöhtem Druck, lässt sich auf komplexere Prozesse schließen. Dies beinhaltet Gastransport durch Poren im Film, was mit strukturellen Defekten in dem Silikatfilm verbunden ist, sowie nachfolgende Adsorption und Diffusion auf dem unterliegenden Ru(0001)-Substrat. Während der Einlagerung der Moleküle in die Silikatschicht bleibt der Oxidfilm auch unter hohem Druck (~ 10 mbar) sowie hoher Temperatur (~900 K) intakt. Solch ein Hybridsystem, welches eine robuste Siliciumdioxidmembran mit einem sich darunter befindlichen, chemisch aktiven Metall kombiniert, könnte ein interessantes Materialsystem für technische Anwendungen darstellen, insbesondere zur Herstellung von Katalysatoren und Sensoren sowie für Korrosionsanwendungen. / The fundamental aspects of the chemical reactions at surfaces can be elucidated by using well-defined model systems under the controlled conditions provided by vacuum-based techniques. Silicon dioxide (SiO2) as one of the crucial materials in modern technological applications, including microelectronics, photonics, and catalysis, has been subjected to numerous studies in order to rationalize relationships between the atomic structure and functional properties of silica-based materials. This work marks the attempt to understand interaction of ambient gases with a well-ordered, ultrathin silicate film grown on a Ru(0001) substrate. Using infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD), hydroxo species, primarily in the form of isolated silanols (Si-OH), were identified on pristine silicate films. Isotopic experiments demonstrated that surface hydroxyls form primarily from the water molecules. Silanols do not undergo scrambling with the lattice oxygen atoms upon dehydroxylation. Steps on a silicate sheet and/or “holes” in these ultrathin films are proposed as active sites for hydroxylation. Adsorption of gases such as CO, H2 and O2 at elevated pressures revealed a more complex behavior. It involves gas transport through the pores, associated with structural defects in the silicate film, subsequent adsorption, and diffusion across the Ru(0001) surface underneath. During this intercalation, the silicate film stays intact even under high pressure (~10 mbar) and high temperature conditions (~900 K). The silicate layer does however strongly passivate the Ru surface towards RuO2(110) formation that readily occurs on bare Ru(0001) under the same conditions. Such a hybrid system, which combines a robust silica “membrane” and a chemically active metal underneath, could become an interesting material for technological applications, in particular in catalysis, sensors and anti-corrosion applications.