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Dr Quentin Ramasse


Professeur associé à l’Université de Leeds et responsable du groupe SuperSTEM de Daresbury, sera présent au laboratoire CRISMAT du 12-13 octobre 2015.

A cette occasion, il fera un séminaire lundi 12 octobre à 11:00 dans la salle de réunion du CRISMAT :
"Determining the structure and chemistry of engineered defects in materials with single atom sensitivity in the scanning transmission electron microscope"


Composition of Wide Bandgap Semiconductor Materials and Nanostructures Measured by Atom Probe Tomography and Its Dependence on the Surface Electric Field







Atom probe tomography allows for three dimensional reconstruction of the elemental distribution in materials at the nanoscale. However, the measurement of the chemical composition of compound semiconductors may exhibit strong biases depending on the experimental parameters used. This article reports on a systematic analysis of the composition measurement of III-N binary (AlN, GaN) and ternary compounds (InGaN, InAlN), MgO and ZnO by laser-assisted tomographic atom probe as a function of laser power and applied DC bias. We performed separate series of measurements at constant bias, constant laser pulse energy and constant detection rate, and a spatial analysis of the surface field through detector hitmap ratios of elemental charge states. As a result, (i) we can determine the separate roles of laser energy and surface field - the latter being the dominant factor under standard conditions of analysis, (ii) we compare the behavior of different samples, (iii) different materials and (iv) we critically discuss the reliability of the measurement of InxGa1-xN, InxAl1-xN alloy fraction and of the Tb concentration in rare-earth doped ZnO.


J. Phys. Chem. C, 2014,118, 24136-24151
Lorenzo Mancini,Nooshin Amirifar,Deodatta Shinde,Ivan Blum,Matthieu Gilbert,Angela Vella,FrançoisVurpillot,Williams Lefebvre,
Rodrigue,Lardé,EtienneTalbot,Philippe Pareige,Xavier Portier,Ahmed Ziani, Christian Davesnne, Christophe Durand,Joël Eymery,Raphaël Butté, Jean-François Carlin, Nicolas Grandjean, and Lorenzo Rigutti -

Structural transition at 360K in the CaFe5O7 ferrite : toward a new charge ordering distribution






A detailed structural study has been carried out combining transmission electron microscopy (TEM) observations (ED, HREM), scanning transmission electron microscopy (STEM-HAADF) and X-ray diffraction data versus temperature. The first magnetic and electrical transport measurements are reported in this paper and discussed with respect to the structural features deduced from the current atomic scale observations, ab-initio structural determination and Rietveld refinements of actual model. In addition a sharp peak of magnetic susceptibility and a strong localization, associated to a reversible structural change from monoclinic setting to orthorhombic one, are revealed at 360 K.


 Inorg Chem. 2014 Oct 6 ;53(19):10171-7. doi : 10.1021/ic5011456

C. Delacotte1, F. Hüe 2, Y. Bréard1, S. Hébert1, O. Pérez1, V. Caignaert1, J. M. Greneche3 and *D. Pelloquin1.