![]() ![]() To show that this deposition technique can also be used to deposit conductive coatings on nanoparticles, SiO2 nanoparticles have been coated with conductive TiN layers. Electron microscope analysis (TEM) tells us that particles have a core-shell structure in which the SiO2 core is coated by a homogenous TiO2 layer. The growth rate is 0.32 Å per ALD cycle and independent of precursor pulse time and exposure. ![]() With this reactor, silica (SiO2) nanoparticles are coated with 1.6 nm TiO2 layers. Furthermore, the possibility of extensive monitoring of the reactor is provided. In the design of the reactor that, is used for loose nanoparticles, care has been taken to make the reactor both safe and versatile in operation. The ALD precursors, tetrakis-dimethylaminotitanium (TDMAT) and water, are added to the carrier gas and hence brought into contact with the nanoparticles and layer-by-layer form a TiO2 shell on the particles. In this reactor, the nanoparticles are agitated by a constant flow of inert carrier gas. The next step in the research was to deposit coatings on individual nanoparticles with a fluidized bed ALD reactor (FB-ALD) that was specially developed for this purpose. Analysis of the experimental results with the model shows that the corrosion starts in small defects in the TiO2 coating and that the corrosion spreads mostly in lateral directions. The photocorrosion mechanism is investigated with electrochemical measurements in which the photocurrent over time can be described with a model that strongly resembles the Johnson-Mehl-Avrami model for phase transitions in solids. The experiments with TiO2-coated CdS films in photoelectrochemical hydrogen production cells show that, even though the samples are coated with protective TiO2 layers, the CdS remains sensitive to photocorrosion. By repeating this cycle coatings can be made atomic layer by atomic layer. After completion of pulse A, precursor B is fed to the reactor and reacts with component A to form component C and prepare the surface of the substrate for a new pulse of component A. ![]() This chemisorption reaction is self-limiting and stops whenever the complete substrate is covered with a monolayer of component A. The first step in this process is chemisorption of precursor A. The TiO2 coating was deposited with Atomic Layer Deposition (ALD), a technique used to deposit extremely thin layers of material by letting two precursors (A and B) react on the surface of a substrate to form product C. #Core shell nanoparticles thesis fullThe goal of this research was to deposit a TiO2 layer that was thick enough to provide full protection against corrosion, yet thin enough to enable electrons to be transferred between the CdS electrode and the electrolyte. The use of thin coatings as protective layers is investigated by coating thin CdS films,which can be used as photo-catalyst in solar hydrogen production cells, with thin, inert titanium dioxide (TiO2) to protect the CdS from corrosion under influence of solar radiation. The experiments show that indeed we can make a Ohmic contact between TiN and CdS, meaning that the contact resistance between the two materials is low and that current is not blocked by the contact. The first chapter describes the electrical contact between titanium nitride (TiN), which is a metallically conductive material that is used as contact material in electronic devices, and cadmium sulfide (CdS), a II-IV semiconductor that is used in (second generation) thin film solar cells and to increase light absorption in Grätzel-type solar cells. This thesis deals with the development of a synthesis process for core-shell nanoparticles, existing of a core that is coated with a thin layer of material that is able to provide protection, or electrical contacts. #Core shell nanoparticles thesis how toThe second challenge is, thus how to make electrical contacts without compromising the material’s nanostructure. Furthermore, when nanoparticles or nanostructures are used in electronic devices, lowresistive electrical contacts should be made between electrodes and nanoparticles. This phenomenon is increased by the large surface area available for corrosion. The first is protection of nanoparticles against corrosion and oxidation. There are, however some challenges that need to be overcome in the development of nanoparticle-based devices. This gives them properties that can make them suitable for the development of highly efficient and improved micro-electronics, sensor,medicine, batteries, catalysts and third generation solar cells. Reducing particle size or material structure size to nanometer scale can make the material properties, such as light absorption and electronic structure, change compared to the same materials at normal scale. Materials for Energy Conversion and Storage Towards the production of core-shell nanoparticles with fluidized bed ALD ![]()
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