Synthesis and characterization of quantum dot coated silicon dioxide surfaces and their application for optical sensing of surface charges in dusty low temperature plasmas

Abstract

In the experimental part of the following thesis to acquire the academical grade Master of Science (M.Sc.), two different procedures were developed which enable to coat pre-functionalized CdSe/ZnS-core/shell quantum dots onto silicon dioxide single crystal wafers as well as onto pre-functionalized silicon dioxide microspheres in a size range of 4 to 11 µm through amide formation between the surfaces of the quantum dots and the corresponding SiO2 surfaces. To enable the coating of the single crystals, they first had to be hydrophilized through peroxymonosulfuric acid (H2SO5) which was formed in-situ through mixing sulfuric acid and hydrogen peroxide in a ratio of 1:2. After hydrophilization, the free hydroxy groups on the surface were used to form a layer of (3-aminopropyl)triethoxysilane (APTES) via organosiloxane formation to generate free primary amino groups, which were then used to form amides between the single crystal surface and the quantum dots. In the case of microparticles, the existing amino groups on the surface reduced the need of further derivatization before the main reaction, but an activation agent for carboxylic groups, namely 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was applied to ensure a fast amide formation through the decomposition of the activated O-isoacylurea intermediate formed between EDC and the carboxylic acid groups of the quantum dot surfaces. The optimized amide formation was observable through e.g. UV-VIS spectroscopy, fluorescence microscopy and other techniques. After the successful development of both procedures, the coatings were tested in a low temperature RF argon discharge plasma at the facilities of TU Eindhoven. After the tests, the data showed that further optimization of the procedures will be needed in terms of degradation protection in plasma environments and coating homogeneity/quantitative coating of both substrates.