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Preparation and characterization of TiO2 and ZnO nanostructures

Thin films and one dimensional nanostructure arrays (in the form of nanorods, nanowires, and nanotubes) are of great interest because of their unique physical and chemical properties. Nanostructured ZnO has gained added interest because of its wide band gap (Eg ~ 3.37 eV) and large exciton binding energy (60 meV) with good carrier mobility, ease of synthesis and nontoxicity, while TiO2 is known as material with excellent chemical and photochemical stability. TiO2 exists in three different crystalline phases: anatase, rutile and brookite, but it was found that anatase ( Eg ~ 3.2 eV) is photo-catalytically more active than other modifications. Ordered TiO2 nanostructures, including nanoparticles, nanotubes, and nanorods have garnered much research for their use in solar energy applications. Nanotubes, which are aligned perpendicular to the conducting substrate, increase electron mobility within the nanotube by directing electrons along a shorter path than nanoparticles. The high surface area of nanotubes, compared to nanorods or flat surfaces, allows for more adsorption by electron donors such as molecular dyes, methil- amonium-halide perovskites and polymers, thus increasing solar photon absorption and charge collection. The possibility of modification the properties of nanostructured thin films of ZnO and TiO2 for photovoltaic and photo-catalytic applications, by adjusting nano-structure and by activation of surfaces is explored. ZnO is produced as film on glass or quartz, by deposition techniques as magnetron sputtering and pulse laser deposition, or on the other hand by spin coating of chemically prepared precursor using sol-gel method followed by annealing. Porous structure were formed by surface etching using plasma or fast heating. TiO2 nanotubes arrays are formed by anodization of titanium foils or thin films spattered on transparent conductive oxide. For photo- catalytic application the surface was further modified by processing in hydrogen atmosphere and/or modification with Ag nanoparticles. For structure characterization Raman spectroscopy, XRD methods, scanning and transmission electron microscopy methods were used. Optical properties were examined by UV-Vis spectroscopy, while photo-catalytic properties under sun-light and visible light was studied on salicylic acid as model pollutant. The properties and application of different TiO2 and ZnO nanostructures for photovoltaic cells as well as application of modified and decorated TiO2 nanostructures for photo- catalysis will be presented.

TiO2 ; ZnO ; thin films ; nanostructures

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