Philosophiae Doctor - PhD / The framework agreement in the year 2000 by the international community to launch Generation IV program with 10 nations, to develop safe and reliable nuclear reactors gave rise to the increased interest in the studies of SiC and the effect of different irradiations on solids. Silicon carbide is a preferred candidate used in harsh environments due to its excellent properties such as high chemical stability and strong mechanical strength. The PBMR technology promises to be the safest of all nuclear technology that have been developed before. SiC has been considered one candidate material being used in the fabrication of pebble bed fuel cell. Its outstanding physical and chemical properties even at high temperatures render it a material of choice for the future nuclear industry as whole and PBMR in particular. Due to the hostile environment created during the normal reactor operation, some of these excellent properties are compromised. In order to use this material in such conditions, it should have at least a near perfect crystal lattice to prevent defects that could compromise its strength and performance. A proper knowledge of the behavior of radiation-induced defects in SiC is vital. During irradiation, a disordered crystal lattice occurs, resulting in the production of defects in the lattice. These defects lead to the degradation of these excellent properties of a particular material. This thesis investigates the effects of various radiation effects to 6H-SiC. We have investigated the effects of radiation induced damages to SiC, with a description of the beds and the importance of the stability of the SiC-C interface upon the effects of radiations (y-rays, hot neutrons). The irradiated samples of 6H-SiC have been studied with various spectroscopic and structural characterization methods. The surface sensitive techniques such as Raman spectroscopy, UV-Vis, Photoluminescence and Atomic Force Microscopy will be employed in several complimentary ways to probe the effect of irradiation on SiC. The obtained results are discussed in details.

Ce travail a été réalisé dans l’I. R. P. H. E. (Institut de Recherche sur les Phénomènes Hors Équilibre), unité de recherche de l’Université d’Aix-Marseille en collaboration avec l’Université de la Sarre, la Faculté de Physique Expérimentale. Cette étude est consacrée à une meilleure compréhension de la microcirculation du sang in vitro, ainsi que des phénomènes collectifs qui prennent place dans la microcirculation. Il se concentre principalement sur la margination en fonction du contrast de rigidité dans une suspension de globules rouges. L’expérience modale a été développée pour étudier la margination, causée exclusivement par le contraste de la déformabilité entre les deux sous-populations de globules rouges: les saines et les rigidifiées / This work was carried out in collaboration between I.R.P.H.E. (Institut de Recherche sur les Phénomènes Hors Équilibre), research unit of Aix-Marseille University and University of Saarland, Faculty of Experimental Physics (Naturwissenschaftlich-Technische Fakultät der Universität des Saarlandes) and aims to investigate microcirculatory hydrodynamics of blood in vitro. The study is dedicated to better understanding of complex collective phenomena that take place in microcirculation of blood through microfluidic in vitro experiments. It mainly focuses rigidity based margination in suspension of RBCs. For this purpose, model experiment was developed to examine margination caused exclusively by contrast of deformability between two sub-populations of RBCs

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Structural and morphological characterization of a Si(110) film heteroepitaxied on 3C-SiC(001)/ Si(001) on-axis template by chemical vapor deposition has been performed. An antiphase domain (APD) free 3C-SiC layer was used showing a roughness limited to 1 nm. This leads to a smooth Si film with a roughness of only 3 nm for a film thickness of 400 nm. The number of rotation domains in the Si(110) epilayer was found to be two on this APD-free 3C-SiC surface. This is attributed to the in-plane azimuthal misalignment of the mirror planes between the two involved materials. We prove that fundamentally no further reduction of the number of domains can be expected for the given substrate. We suggest the necessity to use off-axis substrates to eventually favor a single domain growth.

Amorphous and nano- or micro- crystalline silicon thin films are intensively studied materials for photovoltaic applications. The films are used as intrinsic layer (absorber) in p-i-n solar cells. As opposed to crystalline silicon solar cells, the thin films contain about hundred times less silicon and can be deposited at much lower temperatures (typically around 200 0 C) which saves energy needed for production and makes it possible to use various low cost (even flexible) substrates. However, these films have a complex microstructure, which makes it difficult to measure and describe the electronic transport of the photogenerated carriers. Yet, the understanding of the structure and electronic properties of the material at nanoscale is essential on the way to improve the efficiency solar cells. One of the main aims of this work is the study of the structure and mechanical properties of the mixed phase silicon thin films of various thicknesses and structures. The key parameter of microcrystalline silicon is the crystallinity, i.e., the microcrys- talline volume fraction. It determines internal structure of the films which, in turn, decides about many other properties, including charge transport and mechanical sta- bility. Raman microspectroscopy is a fast and non-destructive method for probing the...

>Magister Scientiae - MSc / Insight into the effects of isothermal and non-isothermal annealing on bi-metallic thin film is important for material synthesis and application in everyday use. The effects of isothermal annealing on bi-metallic thin films has long been studied using various heating methods from a resistively heated filaments, by transferring heat via conduction, convection and irradiation. The effect of each method have been widely reported in literature. The diffusion coefficient and activation energies of the constituent atoms can calculated for each annealing method. On the other hand, the effects of non-isothermal annealing on bi-metallic thin films has not been comprehensively studied, and there are areas of this annealing regime that need further investigation. In this study a femtosecond laser with a 1064 nm central wavelength was used to anneal bi-metallic thin films of Zinc-Tin (Zn-Sn) on a substrate.

Cerium oxide has become an outstanding material in catalytic applications over the last decades. In this thesis, the morphology and atomic structure of thick cerium oxide films and ceria single crystals is investigated by non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM). The ceria films are prepared by annealing cycles from room temperature up to 1100K in ultra high vacuum (UHV) and in an oxygen atmosphere. The films exhibit large smooth terraces separated predominantly by O-Ce-O triple layer height step edges but in contrast to the ceria single crystals some inhomogeneities are observed on the terraces. By annealing the film at 1020K to 1070K in UHV several intermediate phases can be stabilized ranging from the fully oxidized phase CeO2 to the fully reduced phase Ce2O3. These phases have a unique stoichiometry with regular arranged vacancies in the surface and subsurface as revealed by density functional theory (DFT) calculations. The film can be reoxidized by annealing in an oxygen atmosphere as shown by X-ray spectroscopy (XPS). The annealing in oxygen atmosphere also results in a surface with less inhomogeneities. This makes the ceria films an excellent model system for catalytic applications. Further in this thesis a measurement series exhibiting absorbed water on the film surface is presented and discussed. Also line defects observed on the film and on the single crystal are analyzed.

Hot Electron Nanoscopy and Spectroscopy (HENs) is a current-sensing AFM technique recently developed in our lab, which have proven a new kind of response on conduction at the nanometer scale, casting a new light for the comprehension of electronic states in nanomaterials. Direct imaging of DNA structure has long been investigated, with the development of HENs technology, more structural information about DNA could be revealed by simultaneous measurements of height, phase, Raman signal, and conductivity. With the aim of applying it for the first time on biological molecules, customized double-stranded DNA sequences, including thiol-modified oligonucleotides are designed to create preferential conductive paths through the basis as a benchmark system for the technique on biomolecules. This work aims to a final goal to characterize hot-electron current between gold tip and thiol modified DNA which ideally is covalently bonded to the gold surface and optimized for the application. In this work, high density of DNA absorbed by SERS active gold surface with atomic flat islands has been prepared for HENs application. The samples have been characterized by AFM, SKPM and Raman Spectroscopy, as non-destructive and controlled interactive image analysis. High-resolution images of DNA have been acquired, S-S and Au-S bonding of DNA anchored on SERS active gold substrate are also visible with Surface-enhanced Raman and Tip-enhanced Raman signals. A submolecular feature has also been found in both topographical and electrical results. Herein, we report the synthesis and characterization steps to obtain the optimized operation standard.

Partitioning of poly(ethyleneglycol) (PEG) molecules in 2-D and 3-D systems is presented as a self-assembly approach for controlling non-specific adsorption of proteins at interfaces. Lateral restructuring of multi-component Langmuir monolayers to accommodate adsorbing proteins was investigated as a model 2-D system. Ferritin adsorption to monolayers containing cationic, nonionic, and PEG bearing phospholipids induced protein sized binding pockets surrounded by PEG rich regions. The number, size, and distribution of protein imprint sites were controlled by the molar ratios, miscibility, and lateral mobility of the lipids. The influence of PEG chain length on the ternary monolayer restructuring and protein distribution was also investigated using DSPE-PEGx (x= 7, 16, 22). Monolayer miscibility analysis demonstrated that longer PEG chains diminished the condensed phase formation for a fixed ratio of lipids. Thus, incorporation of longer PEG chains, intended to diminish protein adsorption outside of the imprint sites of cationic / non-ionic lipids, leads to dramatic changes in monolayer phase behavior and protein distribution in this 2-D system. The assembly of PEG-amphiphiles at elastomer surfaces and subsequent protein adsorption was investigated as a model 3-D system. Polydimethylsiloxane (PDMS) substrates were modified with block copolymers comprised of PEG and PDMS segments by two methods: (1) the block copolymer was mixed with PDMS during polymerization; (2) the block copolymer diffused into solvent swollen PDMS monoliths. Hydrophilic surfaces resulted for both approaches that, for 600 D block copolymer, exhibited up to 85% reduction in fibrinogen adsorption as compared to native PDMS. Higher MW block copolymers (up to 3000 D) resulted in less hydrophilic surfaces and greater protein adsorption, presumably due to diffusion limitations of copolymer in the PDMS monolith. All modified PDMS surfaces were dynamic and restructured when cycled between air and water. PDMS transparency also decreased with increase in block copolymer concentration for both methods, limiting this modification protocol for applications requiring high polymer transparency. The 2-D system presents a bottom-up approach, where adsorbing protein constructs the binding site, while the 3-D system presents a top down approach, where protein-binding elements may be introduced into the PEG-bearing polymer for fabrication of surfaces with controlled protein adsorption.

abstract: Near-field thermal radiation occurs when the distance between two surfaces at different temperatures is less than the characteristic wavelength of thermal radiation. While theoretical studies predict that the near-field radiative heat transfer could exceed Planck’s blackbody limit in the far-field by orders of magnitudes depending on the materials and gap distance, experimental measurement of super-Planckian near-field radiative heat flux is extremely challenging in particular at sub-100-nm vacuum gaps and few has been demonstrated. The objective of this thesis is to develop a novel thermal metrology based on AFM bi-material cantilever and experimentally measure near-field thermal radiation. The experiment setup is completed and validated by measuring the near-field radiative heat transfer between a silica microsphere and a silica substrate and comparing with theoretical calculations. The bi-material AFM cantilever made of SiNi and Au bends with temperature changes, whose deflection is monitored by the position-sensitive diode. After careful calibration, the bi-material cantilever works as a thermal sensor, from which the near-field radiative conductance and tip temperature can be deduced when the silica substrate approaches the silica sphere attached to the cantilever by a piezo stage with a resolution of 1 nm from a few micrometers away till physical contact. The developed novel near-field thermal metrology will be used to measure the near-field radiative heat transfer between the silica microsphere and planar SiC surface as well as nanostructured SiC metasurface. This research aims to enhance the fundamental understandings of radiative heat transfer in the near-field which could lead to advances in microelectronics, optical data storage and thermal systems for energy conversion and thermal management. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019