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Title Interaction of Organic Molecules with Metal Passivated Silicon Surfaces Studied via STM Author Petr Zimmermann Department Department of Plasma and Surface Science Supervisor Doc. RNDr. Pavel Sobotík, CSc. Department of Plasma and Surface Science Abstract Organic molecules offer a wide range of optical, electronic or chemical properties. Coupling them to silicon could pave way to novel applications and devices, however, a controlled molecular functionalization of silicon remains challenging due to the presence of highly reactive dangling bonds on its surfaces. We attempt to decrease the reactivity of low index silicon surfaces with an ultra-thin layer of a metal adsorbates and study their interaction with organic molecules via scanning tunnelling microscopy. In the first part we investigate the interaction of ethylene, a small unsaturated molecule, with tin and indium 1D chains grown on Si(001) - 2 × 1. The chains consist of dimers structurally analogous to the dimers of the underlying Si(001) - 2 × 1 surface. Aided by photoelectron spectroscopy we find that the Sn chains are less reactive than the Si(001) surface and that the absence of a π dimer bond renders indium chains inert. In the second part we study the interaction of copper phthalocyanine, a small macrocyclic heteroaromatic compound, with the...

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A new powder processing approach to produce oxidation resistant molybdenum alloys for high temperature use has been developed. Oxidation protection is provided by fine dispersion of silica glass particles within a molybdenum matrix. As the molybdenum oxidizes, the glass is exposed and melts to form a self-healing protective oxide coating. Additionally, homogeneously dispersed Mo5SiB2 and/or Mo2B provide boria upon oxidation which reduces glass viscosity and allows flowing glass to coat the surface while remaining solid internally. This is similar to the oxidation protection used in Mo-3Si-1B (wt%) systems; however embedding the glass directly into the Mo matrix and eliminating the Mo3Si (A15) phase provides the same volume of glass at lower volume fractions of brittle phases and also without embrittling Si impurities in solution in Mo. Additionally the glass composition can be tailored for different applications and different temperatures beyond that achievable in Mo-Si-B based systems. A variety of microstructures, compositions and additional components for improved oxidation protection are also explored, and mechanisms of the oxidation protection are discussed.

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Discover of new energy sources and solutions are one of the important global issues nowadays, which has a big impact on economy as well as environment. One of the methods to help to mitigate this issue is to recover wasted heat, which is produced in large quantities by the industry, through vehicle exhausts and in many other situations where we consume energy. One way to do this would be using thermoelectric (TE) materials, which enable direct interconversion between heat and electrical energy. This thesis investigates how the novel material combinations and nanotechnology could be used for fabricating more efficient TE materials and devices. The work presents synthesis, processing, and electrical characterization of group IV materials for TE applications. The starting point is epitaxial growth of alloys of group IV elements, silicon (Si), germanium (Ge) and tin (Sn), with a focus on SiGe and GeSn(Si) alloys. The material development is performed using chemical vapor deposition (CVD) technique. Strained and strain-relaxed Ge1-x Snx (0.01≤x≤0.15) has been successfully grown on Ge buffer and Si substrate, respectively. It is demonstrated that a precise control of temperature, growth rate, Sn flow and buffer layer quality is necessary to overcome Sn segregation and achieve a high quality GeSn layer. The incorporation of Si and n- and p-type dopant atoms is also investigated and it was found that the strain can be compensated in the presence of Si and dopant atoms.  Si1-xGexlayers are grown on Si-on-insulator wafers and condensed by oxidation at 1050 ᵒC to manufacture SiGe-on-insulator (SGOI) wafers. Nanowires (NWs) are processed, either by sidewall transfer lithography (STL), or by using conventional lithography, and subsequently manufactured into nanoscale dimensions by focused ion beam (FIB) technique. The NWs are formed in an array, where one side is heated by a resistive heater made of Ti/Pt. The power factor of NWs is measured and the results are compared for NWs manufactured by different methods. It is found that the electrical properties of NWs fabricated with FIB technique can be influenced due to Ga doping during ion milling. Finally, the carrier transport in SiGe NWs formed on SGOI samples is tailored by applying a back-gate voltage on the Si substrate. In this way, the power factor is improved by a factor of 4. This improvement is related to the presence of defects and/or small fluctuation of nanowire shape and Ge content along the NWs, generated during processing and condensation of SiGe layers. The SiGe results open a new window for operation of SiGe NWs-based TE devices in the new temperature range of 250 to 450 K. / <p>QC 20160907</p>

Modern spark ignition engines are downsized and boosted to meet stringent emission standards and growing customer demands on performance and fuel economy. They operate under high intake pressures and close to their limits to engine knock. As the intake pressure is increased knock becomes the major barrier that prevents further improvement on downsized boosted spark ignition engines. It is generally accepted that knock is caused by end gas autoignition ahead of the propagating flame. The propagating flame front has been identified as one of the most influential factors that promote the occurrence of autoignition. Systematic understanding and numerical relation between the propagating flame front and the occurrence of knock are still lacking. Additionally, knock mitigation strategy that minimizes compromise on engine performance needs further researching. Therefore the objectives of the current research consist of two steps: 1). study of turbulent flame propagation in both naturally aspirated SI engine. 2) study of the relationship between flame propagation and the occurrence of engine knock for downsized and boosted SI engine. The aim of the current research is, firstly, to find out how turbulent flames propagate in naturally aspirated and boosted S.I. engines, and their interaction with the occurrence of knock; secondly, to develop a mitigation method that depresses knock intensity at higher intake pressure. Autoignition of hydrocarbon fuels as used in spark ignition engines is a complex chemical process involving large numbers of intermediate species and elementary reactions. Chemical kinetics models have been widely used to study combustion and autoignition of hydrocarbon fuels. Zero-dimensional multi-zone models provide an optimal compromise between computational accuracy and costs for engine simulation. Integration of reduced chemical kinetics model and zero-dimensional three-zone engine model is potentially a effective and efficient method to investigate the physical, chemical, thermodynamic and fluid dynamic processes involved in in-cylinder turbulence flame propagation and knock. The major contributions of the current work are made to new knowledge of quantitative relations between intake pressure, turbulent flame speed, and knock onset timing and intensity. Additionally, contributions have also been made to the development of a knock mitigation strategy that effectively depresses knock intensity under higher intake pressure while minimizes the compromise on cylinder pressure, which can be directive to future engine design.

The subject of the thesis is growth of aluminium structures one-dimensional chains on Si(100) surface. Growth characteristics of Al on Si(100) at room temperature and at higher temperature and various coverages were measured using STM. The results are discussed with respect to previous experiments and a way to find the value of activation energy of surface migration is proposed. An important part of the thesis is preparation and tests of a new low-temperature UHV apparatus for STM experiments. Functions of the apparatus are described. A way to prepare clean Si(100) surface as well as the methods of achieving atomic-scale resolution in STM were found in conditions previously unknown. A test of evaporators for Al and Sn is described. Al deposition has not been successful in the new apparatus yet. Sn deposition has been successful and low-temperature structures of tin on Si(100) were observed. They differ from room-temperature structures and contain kinks which were previously observed only in Al structures.

The present work focuses on two strategies contributing to the development of high efficiency, cost-effective photovoltaic (PV) technology for renewable energy generation: the design of new materials offering enhanced opto-electronic performance and the investigation of material degradation processes and their role in predicting the long-term reliability of PV modules in the field. The first portion of the present work investigates the integration of a novel CdTe-ZnO nanocomposite material as a spectral sensitizer component within a thin-film, hybrid heterojunction (HJ) PV device structure. Quantum-scale semiconductors have the potential to improve PV device performance through enhanced spectral absorption and photocarrier transport. This is realized via appropriate design of the semiconductor nanophase (providing tunable spectral absorption) and its spatial distribution within an electrically active matrix (providing long-range charge transport). Here, CdTe nanocrystals, embedded in an electrically active ZnO matrix, form a nanocomposite (NC) offering control of both spectral absorption and photocarrier transport behavior through the manipulation of nanophase assembly (ensemble effects). A sequential radio- frequency (RF) magnetron sputter deposition technique affords the control of semiconductor nanophase spatial distribution relative to the HJ plane in a hybrid, ZnO-P3HT test structure. Energy conversion performance (current density-voltage (J-V) and external quantum efficiency (EQE) response) was examined as a function of the location of the CdTe nanophase absorber region using both one dimensional solar cell capacitance simulator (SCAPS) and the experimental examination of analogous P3HT-ZnO based hybrid thin films. Enhancement in simulated EQE over a spectral range consistent with the absorption region of the CdTe nanophase (i.e. 400–475 nm) is confirmed in the experimental studies. Moreover, a trend of decreasing quantum efficiency in this spectral range with increasing separation between the CdTe nanophase region and the heterojunction plane is observed. The results are interpreted in terms of carrier scattering/recombination length mitigating the successful transport of carriers across the junction. The second portion of the research addresses the need for robust PV performance in commercial module as a primary contributor to cost-effective operation in both distributed systems and utility scale generation systems. The understanding of physical and chemical mechanisms resulting in the degradation of materials of construction used in PV modules is needed to understand the contribution of these processes to module integrity and performance loss with time under varied application environments. In this context, the second part of present study addresses microcracking in Si–an established degradation process contributing to PV module power loss. The study isolates microcrack propagation in single-crystal Si, and investigates the effect of local environment (temperature, humidity) on microcrack elongation under applied strains. An investigation of microindenter-induced crack evolution with independent variation of both temperature and vapor density was pursued in PV-grade Si wafers. Under static tensile strain conditions, an increase in sub-critical crack elongation with increasing atmospheric water content was observed. To provide further insight into the potential physical and chemical conditions at the microcrack tip, micro-Raman measurements were performed. Preliminary results confirm a spatial variation in the frequency of the primary Si vibrational resonance within the crack-tip region, associated with local stress state, whose magnitude is influenced by environmental conditions during the period of applied static strain. The experimental effort was paired with molecular dynamics (MD) investigations of microcrack evolution in single-crystal Si to furnish additional insight into mechanical contributions to crack elongation. The MD results demonstrate that crack-tip energetics and associated cracking crystal planes and morphology are intimately related to the crack and applied strain orientations with respect to the principal crystallographic axes. The resulting fracture surface energy and the stress-strain response of the Si under these conditions form the basis for preliminary micro-scale peridynamics (PD) simulations of microcrack development under constant applied strain. These efforts were integrated with the experimental results to further inform the mechanisms contributing to this important degradation mode in Si-based photovoltaics.

Cette thèse visait à développer des techniques d'ablation au laser et de fragmentation dans des liquides pour la synthèse de nouveaux NPs ayant des fonctionnalités utiles. L’approche de la thèse est axée sur l’élaboration de la technique ablative au laser pour la synthèse de matériaux conventionnels avec des paramètres pour des applications biomédicales sélectionnées, ainsi que sur le développement de cette technique pour la synthèse de nouveaux nanomatériaux destinés à des applications biomédicales. En particulier, il comprend:1. Nous avons élaboré un régime de fragmentation laser fs à partir de colloïdes de Si pour la synthèse de NPs de Si ayant une taille, une cristallinité et un état d'oxydation contrôlables.Nous avons testé un certain nombre d’applications biomédiales particulières de Si Si préparés de cette manière.2. Nous avons développé une technique d'ablation et de fragmentation au laser fs pour fabriquer des noyaux Au NPs et des carottes en Au-Si nus pour SERSapplications. Une approche est basée sur l'ablation au laser de la cible Au dans une solution colloïdale de NP Si.3. Pour la première fois, nous avons synthétisé de nouveaux NP plasmoniques à base de nitrure de titane. Nous avons également montré qu’une étape supplémentaire de fragmentation du laser fs entraînait une diminution de la taille des NP à 5 nm. En outre, nous avons constaté que ces NP ont un très large pic d'extinction dans le proche IR.4. Pour la première fois, nous avons démontré la synthèse de NPs organiques fluorescentes d'un luminophore à émission induite par agrégation spécialement conçu (AIE LP). La luminosité de ces NP a été jugée comparable à celle des points quantiques. / This thesis as aimed at the development of techniques of fs laser ablation and fragmentation in liquids for the synthesis of novel NPs having useful functionalities. The approach of the thesis is focused on the elaboration of the laser ablative technique for the synthesis of conventional materials with parameters for selected biomedical applications, as well as the development of this technique for the synthesis of novel nanomaterials for biomedical applications. In particular it includes:1. We elaborated a regime of fs laser fragmentation from Si colloids for the synthesis of Si NPs having controllable size, crystallinity and oxidation state. We tested so-prepared Si NPs a number of particular biomedial applications.2. We elaborated a technique of fs laser ablation and fragmentation to fabricate bare Au NPs and Au-Si core-shells for SERSapplications. One approache is based on laser ablation of Au target in colloidal solution of Si NPs. 3. For the first time we synthesized novel plasmonic NPs based on titanium nitride. We also showed that an additional fs laser fragmentation step leads to the decrease of NPs size to 5 nm. Besides, we found that such NPs have a very broad extinction peak in the near IR.4. For the first time we demonstrated the synthesis of fluorescent organic NPs of specially designed aggregation-induced emission luminophore (AIE LP). The brightness of such NPs was determined to be comparable to that of quantum dots.