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Sodium migration in glasses during electron probe microanalysis is investigated. We observe the change in x-ray emission as a function of time and for various incident electron doses. A specific protocol is used in this study: independently drawn from a multivariate statistical analysis of the data and from an a priori simple model, an exponential decay of the Na signal is clearly established. This model for Na+ migration is only based on an electric field with a linear decrease behavior as a function of depth and it accounts for the main experimental results with no evidence of an incubation time prior to ion migration. The electron densities and the fraction of incident electrons remaining trapped into the glass are deduced from an estimate of ion mobility. The maximum electric field values at the coating/glass interface are also given.

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2014 Les spectres de pertes d'énergie d'électrons de 75 keV à travers des couches minces évaporées de terres rares lourdes (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) dans trois états chimiques différents (métal, hydrure, oxyde) sont composés essentiellement de deux pics dus aux excitations collectives (plasmons) entre 10 et 17 eV et aux excitations d'électrons 5p entre 30 et 40 eV. Une analyse quantitative de la distribution spectrale des intensités nous permet de calculer la fonction perte d'énergie et, par l'intermédiaire d'une transformation de Kramers-Krönig, la constante diélectrique et la force d'oscillateur dipolaire. Les différents résultats sont interprétés en termes de structure de bandes, ce qui nous conduit à proposer un modèle simple pour les transitions interbandes observées dans les oxydes. Abstract. 2014 The energy loss spectra of 75 keV electrons transmitted through thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective « plasmon » excitations in the 10-17 eV energy range and to inner 5p excitations between 30 and 40 eV. A quantitative analysis of the intensity spectral distribution allows one to calculate the energy loss function and, through a Kramers-Krönig inversion, the dielectric constant and the dipole oscillator strength. Various results are then explained in terms of band structure, so that we are lead to propose a simple model for the interband transitions occuring in oxides.

Recent developments in X-ray projection microscopy and X-ray microtomography applied to materials science