Tomographie électronique analytique : développement de la cartographie chimique 3D à l'échelle du nanomètre et applications aux catalyseurs hétérogènes
ROIBAN, Lucian (2010) Tomographie électronique analytique : développement de la cartographie chimique 3D à l'échelle du nanomètre et applications aux catalyseurs hétérogènes. Thèses de doctorat, Université de Strasbourg.
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This work is devoted to the development of analytical electron tomography for the 3D chemical analysis of nanomaterials, a new technique combining the electron tomography and the energy filtered imaging within an electron microscope. By acquiring series of energy filtered images at different angular orientations of the object, their 3D chemical spatial distribution can be achieved by employing a specific reconstruction algorithm. The energy positions used for the filtering correspond to the ionization edges of the elements of interest. Owing to its double selectivity, this technique is particularly powerful when applied to heterogeneous nanomaterials. In this context, the emphasis has been put on defining a precise methodology that would be implemented at the nanometric scale. To do so, an accurate assessment of all steps of analysis as well as a fine adjustment of experimental conditions and parameters of data treatment are imperatively required. Therefore, model objects have been analyzed in a first step in order to validate our protocol. The procedure as defined was then used for the study of two classes of heterogeneous catalysts, with a spatial resolution of several nanometers. The analysis of all elemental volumes within the very same sample allowed us to quantify key-parameters governing the catalytic activity of these specimens, such as the relative proportion of the components at the surface of a grain. The 3D visualization of the chemical composition of heterogeneous nanomaterials has been already implemented for improving the catalysts synthesis methods.
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