Nathalie Herlin-Boime: "Versatility of laser pyrolysis applied to the synthesis of Silicon and Titanium Oxide Nanoparticles: examples of applications"
von 14:15 bis 15:00
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Dr. Nathalie Herlin-Boime
CEA Paris, France
Versatility of laser pyrolysis applied to the synthesis of Silicon and Titanium Oxide Nanoparticles: examples of applications
In a bottom up approach of nanoscience and nanotechnology, nanoparticles are the first step towards nanostructured materials. The laser pyrolysis (LP) method appears as a versatile method for the synthesis of various oxide and non-oxide nanoparticles. The method is based on the interaction of a powerful IR laser beam with a mixture of gaseous or liquid precursors. Synthesis and examples of application based on silicon nanocrystals and titanium oxide nanoparticles are presented here. Silicon based materials are already widely used in industry for example in electronics. Since the discovery of luminescence of porous silicon, much work has been devoted to "nano-silicon". Using silane as a precursor, it was possible to produce by laser pyrolysis large quantities of free standing single crystalline silicon nanocrystals (nc-Si) with a mean crystallite size as low as 3 nm and a narrow size distribution. As a proof of the efficient quantum confinement effect, the obtained nc-Si exhibit strong photoluminescense (PL) in the visible range with a position of the PL peak depending on their size. These nc-Si can be elements of nanostructured Si-based tandem solar cells where transport properties could be improved while keeping the bandgap close to 1.7 eV (efficient solar light absorption). After P or N doping and deposition by spin coating in a silica layer, a resistivity of the layer was measured as a function of the concentration of doping element. Over the past decades, Titanium dioxide has attracted great interest thanks to its potential applications in various fields such as catalysis, photovoltaic and photoabsoption. For such applications, TiO2 is appreciated due to its wide band gap in the UV region and its high photocatalytic activity towards harmful organic compounds. In order to improve the performances of devices using TiO2, the optical activity of TiO2 can be improved by shifting its gap to the visible region. This shift can be achieved by doping TiO2 with heteroatoms, and by synthesizing original substoichiometric crystalline phases of titania. In this context, using TTIP (titanium tetraisopropoxide) as a precursor, laser pyrolysis could produce a large variety of titanium oxide based nanopowders. The formation of anatase and rutile phases can be chosen through the synthesis conditions, with ratio varying from less than 10 % to 100%. Titanium oxide substoichiometric phases, and in particular an original TiO phase, were also obtained. Structural and electronic characteristics of these materials were investigated by XPS and are reported here in correlation with optical properties. Moreover, first results presented here indicate a very efficient photocatalytic activity when irradiated by visible light.