Effect of extended defects on AlGaN QDs for electron-pumped UV-emitters

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like defects starting at the first AlN buffer/superlattice interface and propagating vertically. These defects are associated with a dislocation that produces strong shear strain, which favors the formation of 30{\deg} faceted pits. The cone-like structures present Ga enrichment at the boundary facets and larger QDs within the defect. The bimodality is attributed to the differing dot size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schr\"odinger-Poisson calculations

Composition Analysis of III-Nitrides at the Nanometer Scale: Comparison of Energy Dispersive X-ray Spectroscopy and Atom Probe Tomography

International audienc

Etude à l échelle atomique de multicouches magnétostrictives TbFe/Co et TbFeCo/Fe (structure, propriétés et effet de l irradiation aux ions lourds)

Pour la première fois, la sonde atomique a permis l étude chimique à l échelle atomique de multicouches magnétostrictives (TbFe2 5nm/Co3 ou 7 nm)x20 et l étude de leurs modifications induites par irradiation aux ions. Elle a révélé l asymétrie des interfaces. La diffusion, sous irradiation, du cobalt a été interprétée par le modèle de la pointe thermique. Leurs profils d aimantation en profondeur ont été déduits des profils de concentration et ont permis de comprendre l augmentation des propriétés magnétiques sous irradiation. Le renversement d aimantation a été étudié selon différents paramètres par réflectométrie de neutrons polarisés. Cette étude a montré que, lors d une configuration parallèle des aimantations, les parois de domaine sont principalement localisées dans la couche de TbFeCo. Un décalage d échange a été mis en évidence à 100K dont le signe dépend de la valeur du champ de refroidissement et donc de la configuration initiale de la couche dure.For the first time, the tomographic atom probe allowed the chemical study at the atomic scale of magnetostrictives multilayers (TbFe2 5nm/Co3 ou 7 nm)x20 and the study of their modifications induced by swift heavy ion irradiation. It revealed the asymmetry of the interfaces. The cobalt diffusion, under irradiation, was interpreted by the inelastic thermal spike model. Depth magnetization profiles were deducted from the concentration profiles of allowed to understandthe increase of the magnetic properties under irradiation. The reversal of magnetization was studied according to various parameters by polarized neutron reflectometry. Tjis study showed that during a parallel configuration of magnetizations, the domain walls are mainly located in the TbFeCo layer. A exchange bias was put in evidence at 100K whose the sign depends on cooking field and then on the initial configuration of the TbFeCo layer.ROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Population parametrization of costly black box models using iterations between SAEM algorithm and kriging

Accepted March, 24, 2016. Published online April, 16, 2016. Journal issue available Feb 23, 2018.International audienceIn this article we focus on parametrization of black box models from repeated measurements among several individuals (population parametrization). We introduce a variant of the SAEM algorithm, called KSAEM algorithm, which couples the standard SAEM algorithm with the dynamic construction of an approximate meta model. The costly evaluation of the genuine black box is replaced by a kriging step, using a basis of precomputed values, basis which is enlarged during SAEM algorithm to improve the accuracy of the meta model in regions of interest

Preparation and Analysis of Atom Probe Tips by Xenon Focused Ion Beam Milling

International audience\textlessp\textgreaterThe damage and ion distribution induced in Si by an inductively coupled plasma Xe focused ion beam was investigated by atom probe tomography. By using predefined patterns it was possible to prepare the atom probe tips with a sub 50 nm end radius in the ion beam microscope. The atom probe reconstruction shows good agreement with simulated implantation profiles and interplanar distances extracted from spatial distribution maps. The elemental profiles of O and C indicate co-implantation during the milling process. The presence of small disc-shaped Xe clusters are also found in the three-dimensional reconstruction. These are attributed to the presence of Xe nanocrystals or bubbles that open during the evaporation process. The expected accumulated dose points to a loss of >95% of the Xe during analysis, which escapes undetected.\textless/p\textgreate

Comparative study of two methods (hexane extraction and NMR) for the determination of oil content in an individual olive fruit

International audienc

Atomic Scale Investigation of Arsenic Segregation in High-k Metal Gate Stacks

International audienc

Investigation of doping in III-nitrides by combining atom probe tomography and EDX spectroscopy

International audienceAtom Probe Tomography (APT) has emerged as a reliable chemical analysis technique as it provides access to the chemical composition of the analyzed material together with the 3D distribution of the atoms in a tip-shaped specimen with hundred-nanometer diameter. Moreover, combining APT with EDX enables first to overcome some artefacts inherent to APT to get quantitative data but also permits to investigate nanostructures from nano-to micro-scale. We have successfully applied these techniques for studying both n-type (Ge) and p-type (Mg) doping of AlGaN layers

Atomic Scale Structural Characterization of Epitaxial (Cd,Cr)Te Magnetic Semiconductor

International audienc