Tip-enhanced near-field optical microscopy on the quasi 1D semiconductors carbon nanotubes and CdSe nanowires

Optical microscopy is widely used to visualize small structures that can not be seen by the unaided human eye. On the nanoscale, however, the diffraction limit prevents conventional microscopy from studying materials with the required spatial resolution. This work reports on tip-enhanced near-field optical microscopy (TENOM), a technique that allows for nanoscale optical imaging with high detection sensitivity. It exploits the locally enhanced optical fields at a laser illuminated metal tip that acts as an optical antenna. The main aims of this work are to develop a better understanding of the signal enhancement mechanisms in TENOM and to apply the technique to different 1D semiconducting nanostructures, namely single-walled carbon nanotubes (SWCNTs) and cadmium selenide nanowires (CdSe NWs). In the first part, the angular distribution of photoluminescence (PL) emission from SWCNTs with and without the optical antenna is studied by imaging the back focal plane of the microscope objective. Using model calculations, it is shown that the PL of SWCNTs on a dielectric substrate can be described as emission from a single in-plane point dipole despite the quasi 1D structure of the nanotubes. The signal enhancement due to the antenna is connected to a substantial redistribution of the angular emission. A procedure for the individual quantification of the excitation and radiation rate enhancement factors is developed and applied to the experimental data. In the second part, nanoscale optical imaging of CdSe NWs using TENOM is presented for the first time. Spectrally resolved imaging reveals different band gaps for different NWs and variations of the PL energy and intensity along single NWs with energy gradients up to 1 meV/nm. Even bundled NWs can be spatially resolved by their PL and Raman signals. The third part reports on the angular and spectral emission properties of CdSe NWs and the tip-induced changes in a TENOM measurement. In contrast to SWCNTs, two perpendicularly oriented point dipoles are required to describe the angular intensity distribution of PL emission from CdSe NWs sufficiently. Again, tip-induced signal enhancement is accompanied by a spatial redistribution of the emission. The theoretical description is more complex than in the case of SWCNTs, because different radiating dipole orientations in the NW have to be taken into account that can interact with the tip. Finally, investigations of the tip-sample distance dependence of PL and Raman scattering are presented and discussed

Enhancing and redirecting carbon nanotube photoluminescence by an optical antenna

We observe the angular radiation pattern of single carbon nanotubes' photoluminescence in the back focal plane of a microscope objective and show that the emitting nanotube can be described by a single in-plane point dipole. The near-field interaction between a nanotube and an optical antenna modifies the radiation pattern that is now dominated by the antenna characteristics. We quantify the antenna induced excitation and radiation enhancement and show that the radiative rate enhancement is connected to a directional redistribution of the emission

Selfextensions of modules over group algebras

Let $KG$ be a group algebra with $G$ a finite group and $K$ a field and $M$ an indecomposable $KG$-module. We pose the question, whether $Ext_{KG}^1(M,M) \neq 0$ implies that $Ext_{KG}^i(M,M) \neq 0$ for all $i \geq 1$. We give a positive answer in several important special cases such as for periodic groups and give a positive answer also for all Nakayama algebras, which allows us to improve a classical result of Gustafson. We then specialise the question to the case where the module $M$ is simple, where we obtain a positive answer also for all tame blocks of group algebras. For simple modules $M$, the appendix provides a Magma program that gives strong evidence for a positive answer to this question for groups of small order

Gewinnung haploider Stammzellkulturen der Maus für genetische Screens

Haploid mouse embryonic stem cells are a handy tool to investigate loss of function mutations. Furthermore, these cells can contribute to chimeric embryos and can be used to introduce genetic modifications into mouse germ lines. Nevertheless, haploid cell cultures have to be maintained by flow sorting on a regular basis due to spontaneous diploidization. Here we present physical differences between haploid and diploid cells, which can be used in applied cell sorting of haploid cell cultures

Seroprevalence and Potential Risk Factors for Helicobacter pylori Infection in Brazilian Children

BACKGROUND: Helicobacter pylori infection has been proved to be of great relevance to public health in unindustrialized countries, especially in low socioeconomic groups. Poor hygiene, deficient sanitation, and crowded conditions have been reported as risk factors for this infection. In this work, we investigated whether social and demographic characteristics were associated with anti-H. pylori IgG antibodies in 1104 children aged 4-11 years old from Salvador, a large city located in northeastern Brazil. METHODS: Standardized questionnaires were used to obtain social, demographic, and environmental data for the studied population in two periods of time (from 1997 to 2003 and in 2005). Anti-H. pylori IgG antibodies were assessed by indirect enzyme-linked immunosorbent assay in 2005. RESULTS: Anti-H. pylori IgG antibody was present in 28.7% of the children. Among the studied variables, the following were positively associated with the presence of anti-H. pylori antibodies in multivariable analyses: age above 8 years old (OR = 1.72, 95% CI = 1.23-2.40), a larger sibling number (OR = 1.66, 95% CI = 1.26-2.18), nursery attendance (OR = 1.49, 95% CI = 1.04-2.12), location of the house at an unpaved street (OR = 2.03, 95% CI = 1.44-2.87) and absence of a flush toilet (OR = 1.32, 95% CI = 1.00-1.74). CONCLUSION: Our data show that H. pylori infection in children from a major Brazilian city is associated with variables indicative of a crowded environment and deficient sanitation/habitation conditions, leading to the conclusion that improvements in hygiene and social conditions may protect children against this infection

Tip-enhanced near-field optical microscopy

Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection sensitivity. In this review, we first illustrate the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales. We then discuss the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence. Different experimental realizations are presented and several recent examples that demonstrate the capabilities of the technique are reviewed

Die Anwendbarkeit des Verfahrens Predictive Analytics im Controlling

Die tiefgreifende digitale Transformation von Wirtschaft und Gesellschaft stellt Unternehmen und insbesondere deren Controlling vor Herausforderungen. Als Teillösung für den Umgang mit diesen Veränderungen wird in dieser Bachelorarbeit eine Anwendung von Predictive Analytics im Controlling untersucht. Die Anwendung wird geprüft, um zu bestimmen, in welchen Bereichen und unter welchen Bedingungen es durchführbar ist, um anschließend beurteilen zu können, ob das Verfahren praktisch anwendbar erscheint. Das Vorgehen beruht auf einer deduktiven Methode und soll durch logische Verknüpfung Rückschlüsse auf die gewünschten Elemente ermöglichen. Als Ergebnis dieser Arbeit wurde eindeutig festgestellt, dass das Verfahren im Controlling anwendbar ist und in den unter-suchten Bereichen deutlich effektivere Prozesse ermöglicht

Des plateformes monocouches moléculaires auto-assemblées, contrôlées et décrites de façon approfondie, pour l'étude des interactions matériau-bactérie à l'échelle moléculaire

Bacterial adhesion is the first step of biofilm formation and in the focus of research interest since several decades. Biofilms cause many problems, sometimes dramatic, for example in health, food packing or waste water purification. Despite of high interest, bacterial adhesion process is only poorly understood yet. In this work, bacterial adhesion was investigated on well-organized and structured model surfaces with various chemistries at molecular scale. For that purpose a characterization methodology was developed to sufficiently analyze monolayers on silicon wafers, and controlled mixed monolayers surfaces with different densities of NH 2 backfilled with CH3 were developed and optimized. These controlled surfaces with different densities of 0 % NH2 up to 100% NH2 were eventually used as tool to study bacterial adhesion in batch and real time conditions. The results demonstrate a significant impact on bacterial adhesion of weak difference in the surface chemistry at molecular scale. In the batch experiments, two so-called "plateaus" zones were determined, in which bacterial adhesion is not significantly different despite the change of the amine concentration on the surface. On the contrary, one transition zone exists between the "plateaus" in which a slight chunge.in the amine concentration leads to a significant increase / decrease of the bacterial adhesion. The same trend of bacteria behavior was observed for different bacterial strains.L'adhésion bactérienne est la première étape du processus de formation d'un biofilm et est un enjeu majeur de la recherche depuis plusieurs dizaines d'années. Les biofilms ont des conséquences parfois dramatiques dans des domaines comme la santé, l'agroalimentaire ou la purification des eaux usées. Toutefois, l'adhésion bactérienne reste un phénomène mal compris. Dans cette thèse, l'adhésion bactérienne est étudiée sur des surfaces modèles très bien organisées et structurées, de chimie de surface variable à l'échelle moléculaire. Une méthodologie de caractérisation adaptée aux monocouches déposées sur wafers de silicium est proposée. Des surfaces modèles composées de monocouches mixtes auto-assemblées de densités variables de NH2 dans un continuum de CH, sont développées et optimisées. Ces surfaces contrôlées, de densités de 0% NH2 à 100% NH2 dans CH3, sont utilisées comme outil pour étudier l'adhésion bactérienne en conditions de culture « batch »et « temps réel ». Les résultats montrent un impact significatif sur l'adhésion bactérienne de faibles différences chimiques à l'échelle moléculaire. Les résultats des expériences menées en conditions « batch » permettent de déterminer deux zones « plateau » dans lesquelles l'adhésion bactérienne ne varie pas significativement malgré des variations importantes de la concentration en groupements amine sur la surface. Une zone de transition entre les zones « plateau » est mise en évidence, dans laquelle une faible modification de la concentration en groupement amine mène à l'augmentation / diminution significative du nombre de bactéries adhérées. Cette tendance est montrée pour deux souches différentes de bactérie

Des plateformes monocouches moléculaires auto-assemblées, contrôlées et décrites de façon approfondie, pour l'étude des interactions matériau-bactérie à l'échelle moléculaire

L'adhésion bactérienne est la première étape du processus de formation d'un biofilm et est un enjeu majeur de la recherche depuis plusieurs dizaines d'années. Les biofilms ont des conséquences parfois dramatiques dans des domaines comme la santé, l'agroalimentaire ou la purification des eaux usées. Toutefois, l'adhésion bactérienne reste un phénomène mal compris. Dans cette thèse, l'adhésion bactérienne est étudiée sur des surfaces modèles très bien organisées et structurées, de chimie de surface variable à l'échelle moléculaire. Une méthodologie de caractérisation adaptée aux monocouches déposées sur wafers de silicium est proposée. Des surfaces modèles composées de monocouches mixtes auto-assemblées de densités variables de NH2 dans un continuum de CH, sont développées et optimisées. Ces surfaces contrôlées, de densités de 0% NH2 à 100% NH2 dans CH3, sont utilisées comme outil pour étudier l'adhésion bactérienne en conditions de culture batch et temps réel . Les résultats montrent un impact significatif sur l'adhésion bactérienne de faibles différences chimiques à l'échelle moléculaire. Les résultats des expériences menées en conditions batch permettent de déterminer deux zones plateau dans lesquelles l'adhésion bactérienne ne varie pas significativement malgré des variations importantes de la concentration en groupements amine sur la surface. Une zone de transition entre les zones plateau est mise en évidence, dans laquelle une faible modification de la concentration en groupement amine mène à l'augmentation / diminution significative du nombre de bactéries adhérées. Cette tendance est montrée pour deux souches différentes de bactérie.Bacterial adhesion is the first step of biofilm formation and in the focus of research interest since several decades. Biofilms cause many problems, sometimes dramatic, for example in health, food packing or waste water purification. Despite of high interest, bacterial adhesion process is only poorly understood yet. In this work, bacterial adhesion was investigated on well-organized and structured model surfaces with various chemistries at molecular scale. For that purpose a characterization methodology was developed to sufficiently analyze monolayers on silicon wafers, and controlled mixed monolayers surfaces with different densities of NH 2 backfilled with CH3 were developed and optimized. These controlled surfaces with different densities of 0 % NH2 up to 100% NH2 were eventually used as tool to study bacterial adhesion in batch and real time conditions. The results demonstrate a significant impact on bacterial adhesion of weak difference in the surface chemistry at molecular scale. In the batch experiments, two so-called "plateaus" zones were determined, in which bacterial adhesion is not significantly different despite the change of the amine concentration on the surface. On the contrary, one transition zone exists between the "plateaus" in which a slight chunge.in the amine concentration leads to a significant increase / decrease of the bacterial adhesion. The same trend of bacteria behavior was observed for different bacterial strains.MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF