Le microscope à effet tunnel (STM) permet une analyse spatiale et spectroscopique de surfaces à l'échelle atomique. Mise en évidence peu après l'invention du STM, la lumière émise par la jonction tunnel contient des informations pertinentes sur les propriétés électroniques et optiques de surfaces ou de nano-objets.<br /><br />La thématique dans laquelle s'inscrit cette thèse est la luminescence induite par STM sur substrat semiconducteur à large bande interdite. Les travaux ont porté sur la reconstruction de surface SiC(0001)3x3 du carbure de silicium (SiC) et s'articulent autour de trois parties.<br /><br />La première partie est consacrée à l'étude de la luminescence de la jonction tunnel métal/vide/SiC(0001)3x3. Cette étude, en parallèle à des mesures de spectroscopie tunnel, a mis en évidence les mécanismes et propriétés de transport électronique le long des états de surface du SiC.<br /><br />Une deuxième partie est dédiée à l'adsorption de molécules organiques sur la surface SiC(0001)3x3. La fonctionnalisation organique du SiC est une étape indispensable pour l'étude de molécules individuelles mais aussi pour la conception de matériaux hybrides organique/inorganique. La résolution submoléculaire du STM associée à des calculs ab initio en collaboration ont dégagé un modèle de chimisorption détaillé de la phthalocyanine hydrogénée.<br /><br />La dernière partie décrit des simulations numériques, basées sur le formalisme des tenseurs de Green, de la lumière émise par la jonction tunnel. Ces travaux ont permis de modéliser d'une part l'influence de la forme de la pointe du STM sur le spectre de la lumière émise, d'autre part l'inhibition de la fluorescence de molécules individuelles excitées par STM.

Le béton armé (BA) a été largement étudié, surtout à travers son comportement mécanique et ses capacités physico-chimique. Par contre la notion de réparation des ouvrages de génie civil par des solutions composites est plus rarement traitée. Cette recherche porte essentiellement sur : l'analyse de l'influence du degré de fissuration sur la résistance ultime des éprouvettes réparées et l'application des concepts de fiabilité afin d'estimer la probabilité de défaillance. Dans ce but, des poutres en BA ont été pré fissurées par des essais en flexion 3 points jusqu'à 2 niveaux différents d'endommagement puis réparées. L'insertion d'une tige en composite (soit fibre de carbone, soit fibre de verre) et le collage d'une plaque en carbone sur la face tendue de la poutre courte, ont été utilisés comme méthodes de réparation. Lors des essais en flexion de poutres réparées, leur comportement a été évalué à l'aide d'un microscope à longue distance et par la technique d'émission acoustique. A partir des résultats obtenus, nous avons constaté que les deux méthodes de réparation sont très efficaces. En effet, les éprouvettes réparées ont considérablement augmenté leurs résistances ultimes. Une approche probabiliste utilisant les méthodes Monte Carlo et FORM pour déterminer la probabilité de défaillance de l'éprouvette testée en flexion trois points a été utilisée. Ces résultats nous ont permis d'élaborer des abaques qui mettent en relation la force résistante de l'éprouvette, le coefficient de variation et la probabilité de défaillance.

Electron vortex beams (EVBs) are electron beams with a doughnut-like intensity profile, carrying orbital angular momentum due to their helical phase shift distribution. When employed in an electron microscope, they are expected to be efficient for the detection of magnetic signals. In this report I have investigated high angle annular dark field (HAADF) images obtained using EVBs. This was done for 300 K and 5K. For 5 K,  I also compared HAADF images from an ordinary electron beam with HAADF images from an electron vortex beam. What was found was that EVBs produced doughnuts around the atomic columns. However, when taking the size of the electron source into account, this phenomena could no longer  be observed. When comparing images from EVBs with images from ordinary electron beams, I found that the intensity of scattered electrons around atomic columns was broader for EVBs. This was persistent even after taking the source size into account. / Elektronvirvelstrålar (EVS) är elektronstrålar med en munk-liknande intensitetsprofil. Dessa bär på rörelsemängdsmoment på grund av sin fasdistribution. När de används i ett elektronmikroskop förväntas de vara effektiva för detektering av magnetiska signaler. I denna uppsats har jag undersökt high angle annular dark field (HAADF) bilder som erhållits med hjälp av EVS. Detta gjordes för 300 K och 5K. För 5 K, jämförde jag även HAADF bilder från en vanlig elektronstråle med HAADF bilder från en elektronvirvelstråle. Vad jag fann var att EVS producerade en munkformad intensitetsfördelning runt atomerna. Men när hänsyn till storleken på elektronkällan togs i beaktande kunde inte detta fenomen observeras längre. När bilder från EVS jämfördes med bilder från vanliga elektronstrålar, fann jag att intensiteten av spridda elektroner runt atomkolumnerna var bredare för EVS. Detta kunde observeras även efter att jag tagit hänsyn till elektronkällans storlek.

We have advanced the state-of-the-art for nano-fabrication of carbon nanotube (CNT) based field emission devices, and have conducted experimental and theoretical investigations to better understand the reasons for the high reduced brightness achieved. We have demonstrated that once the CNT emitter failure modes are better understood and resolved, such CNT emitters can easily reach reduced brightness on the order of 10⁹ A m⁻² sr⁻¹ V⁻¹ and noise levels of about 1%. These results are about 10% better than the best brightness results from a nanotip emitter archived to date. Our CNT emitters have order of magnitude better reduced brightness than state-of-the-art commercial Schottky emitters. Our analytical models of field emission matched our experimental results well. The CNT emitter was utilized in a modified commercial scanning electron microscope (SEM) and briefly operated to image a sample. We also report a successful emission from a lateral CNT emitter element having a single suspended CNT, where the electron emission is from the CNT sidewall. The lateral CNT emitters have reduced brightness on the order of 10⁸ A m⁻² sr⁻¹ V⁻¹, about 10X less than the vertical CNT emitters we fabricated and analyzed. The characteristics of the lateral field emitter were analyzed for manually fabricated and directly grown CNT emitters. There was no significant difference in performance based on the way the CNT emitter was fabricated. We showed that the fabrication technique for making a single CNT emitter element can be scaled to an array of elements, with potential density of 10⁶-10⁷ CNT emitters per cm². We also report a new localized, site selective technique for editing carbon nanotubes using water vapor and a focused electron beam. We have demonstrated the use of this technique to cut CNTs to length with 10s of nanometers precision and to etch selected areas from CNTs with 10s of nanometers precision. The use of this technique was demonstrated by editing a lateral CNT emitter. We have conducted investigations to demonstrate the effects of higher local water pressure on the CNT etching efficiency. This was achieved by developing a new method of localized gas delivery with a nano-manipulator. / text

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Šiame darbe yra aptariamos elektroninės mikroskopijos technologijos, elektroninių mikroskopų pagrindiniai veikimo principai, jais gaunami vaizdai bei apdorojimo metodai, funkcionalumo praplėtimo galimybės. Ypatingas dėmesys yra skiriamas – Artimo lauko optinio skenavimo mikroskopijai (SNOM – Scanning Near-Field Optical Microscopy). Darbo eigoje suprojektuota ir sukurta programinė įranga, leidžianti prie SNOM tipo mikroskopo prijungti nestandartinį grįžtamojo signalo įrenginį - fotonų skaitiklį. Fotonų skaitiklis yra daug jautresnis už standartiškai naudojamą fotodaugintuvą, tai leidžia SNOM mikroskopu atlikti naujus eksperimentus, kaip fluorescencijos tyrimas, tiriamųjų objektų žymėjimas kvantiniais taškais ir kt. Suprojektuota programa valdo SNOM naudodama sąsajas su mikroskopo programine įranga, sinchronizuoja fotonų skaitikliu gaunamus rezultatus, generuoja vaizdus, pateikia galimybes juos išsaugoti įvairiais formatais. Atlikus programos funkcionalumo tyrimą realiomis sąlygomis, buvo atrasti ir pašalinti programos trūkumai (susiję su sinchronizacija ir SNOM zondo veikimo ypatumais), bei nustatytos fotonų skaitiklio greitaveikos ribos, maksimalios fotonų skaičiaus reikšmės, rekomenduojama matavimo periodo trukmė. Darbe naudojamo fotonų skaitiklio greitaveikos problemoms spręsti pasiūlytas fotonų skaitiklio vienlustės sistemos projektas. Vienlustei sistemai sukurti buvo naudojami duomenys, surinkti programinės įrangos kūrimo ir testavimo metu. Pateikiami vienlustės sistemos... [toliau žr. visą tekstą] / This paper describes technologies used in electronic microscopy, mainly SNOM (Scanning Near-Field Optical Microscopy) and functionality extension possibilities. Software that enables using a photon counting unit as a supplementary input device was designed and presented. The photon counting device is much more sensitive than standard input device, thus new experiments as fluorescence research and Q-dot marking becomes available. The designed software collects data from photon counting unit and utilizes scripts to link with default SNOM software that controls probe movement. While testing the software, issues related to latency and synchronization helped to find out timing limits and optimal probe movement paths. To improve quality and speed of the whole scanning process a system-on-chip (SoC) project is presented. The paper provides details of SoC design, operation and limitations.

In this thesis, we test some interactions involving surfaces processes at the nanometer scale. The experiments are conducted with a highly sensitive interferometric Atomic Force Microscope (AFM), achieving a resolution down to E-28m2/Hz for the measurement of deflection. Combined with original thermal noise analysis, this tool allows quantitative characterization of the mechanical response of micrometer and nanometer sized systems, such as microcantilevers or carbon nanotubes, on a large frequency range.The first part of my work deals with the viscoelasticity of the coating of AFM cantilevers. Evidenced by a 1/f thermal noise at low frequency, this phenomenon is present when a cantilever is coated with a metallic layer (gold, aluminium, platinium, etc...). Using the fluctuation dissipation theorem and Kramers Kronig relations, we extract the frequency dependance of this viscoelastic damping on a wide range of frequency (1Hz to 20kHz). We find a generic power law dependence in frequency for this dissipation process, with a small negative coefficient that depends on materials. The amplitude of this phenomenon is shown to be linear in the coating thickness, demonstrating that the damping mechanism takes its roots in the bulk of the metallic layer.The second part of my work tackles new experiments on the interaction of carbon nanotubes with flat surfaces. Using our AFM, we perform a true mechanical response measurement of the rigidity and dissipation of the contact between the nanotube and the surface, in a peeling configuration (the nanotube is partially absorbed to the substrate). The results of this protocol are in line with the dynamic stiffness deduced from the thermal noise analysis, showing an unexpected power law dependence in frequency for the contact stiffness. We suggest some possible physical origins to explain this behavior, such as an amorphous carbon layer around the nanotube.

The mechanical behavior of a high pressure die cast AM60B Mg alloy is studied. Constant load amplitude fatigue tests were conducted at room, elevated and cold temperatures, with a stress ratio of R=0.1, and frequency of 30 Hz. The objective was to identify the possible effects of temperature on fatigue life cycle. In addition, fatigue crack propagation tests were conducted to ascertain the fatigue response of the alloy and determine its fatigue crack growth rate as a function of the applied stress ratio, experimentally, analytically and computationally, using Walker’s model. The results demonstrated that temperature had a significant influence on the fatigue life, and that the life increased at cold temperature but decreased at elevated temperature as compared to that evaluated at room temperature. In this study, the limit for applicability of LEFM was established for AM60B magnesium alloy. In addition, fatigue crack propagation test results were used to evaluate the coefficients of the Paris model.

The main objective of nanotechnology is to build self-powered nanosystems that are ultrasmall in size, exhibit super sensitivity, extraordinary multi functionality, and extremely low power consumption. As we all know that 21st century has brought two most important challenges for us. One is energy shortage and the other is global warming. Now to overcome these challenges, it is highly desirable to develop nanotechnology that harvests energy from the environment to fabricate self-power and low-carbon nanodevices. Therefore a self-power nanosystem that harvests its operating energy from the environment is an attractive proposition. This is also feasible for nanodevices owing to their extremely low power consumption. One advantageous approach towards harvesting energy from the environment is the utilization of semiconducting piezoelectric materials, which facilitate the conversion of mechanical energy into electrical energy. Among many piezoelectric materials ZnO has the rare attribute of possessing both piezoelectric and semiconducting properties. But most applications of ZnO utilize either the semiconducting or piezoelectric property, and now it’s time to fully employ the coupled semiconducting-piezoelectric properties to form  the basis for electromechanically coupled nanodevices. Since wurtzite zinc oxide (ZnO) is structurally noncentral symmetric and has the highest piezoelectric tensor among tetrahedrally bonded semiconductors, therefore it becomes a promising candidate for energy harvesting applications. ZnO is relatively biosafe and biocompatible as well, so it can be used at large scale without any harm to the living environment. The synthesis of another transition metal oxide known as Co3O4 is also important due to its potential usage in the material science, physics and chemistry fields. Co3O4 has been studied extensively due to low cost, low toxicity, the most naturally abundant, high surface area, good redox, easily tunable surface and structural properties. These significant properties enable Co3O4 fruitful for developing variety of nanodevices. Co3O4 nanostructures have been focused considerably in the past decade due to their high electro-chemical performance, which is essential for developing highly sensitive sensor devices. I started my work with the synthesis of ZnO nanostructures with a focus to improve the amount of harvested energy by utilizing oxygen plasma treatment. Then I grow ZnO nanorods on different flexible substrates, in order to observe the effect of substrate on the amount of harvested energy. After that I worked on understanding the mechanism and causes of variation in the resulting output potential generated from ZnO nanorods. My next target belongs to an innovative approach in which AFM tip decorated with ZnO nanorods was utilized to improve the output energy. Then I investigated Co3O4 nanostructures though the effect of anions and utilized one of the nanostructure to develop a fast and reliable pH sensor. Finally to take the advantage of higher degree of redox chemistry of NiCo0O4 compared to the single phase of nickel oxide and cobalt oxide, a sensitive glucose sensor is developed by immobilizing glucose oxidase. However, there were problems with the mechanical robustness, lifetime, output stability and environmental adaptability of such devices, therefore more work is going on to find out new ways and means in order to improve the performance of fabricated nanogenerators and sensors.