Multi-Dimensional Data Analysis and Processing in Electron-Induced Microanalysis

The new facilities offered by computer controlled data capturing devices allow one to open the field of data acquisition from one or two-dimensional spaces to multi-dimensional ones. The methods used for analysing and processing such data sets have to move in parallel towards multi-dimensionality. Multivariate Statistical Analysis is one of the tools which appear to be promising in : data analysis, data reduction, data processing (multivariate noise filtering), data interpolation and extrapolation. Illustrations of these different possibilities are given in the fields of spatially resolved spectroscopy, time-dependent spectroscopy and elemental mapping from Electron Energy Loss Spectroscopy

Characterization of Small Metallic Clusters by Electron Energy Loss Spectroscopy

Small spherical tin and gallium clusters (diameters in the range 2 to 80 nm), prepared with a liquid metal ion source, were analysed in a scanning transmission electron microscope (STEM) by electron energy loss spectroscopy (EELS). Both volume and surface plasmon excitations were investigated and their dependence on the cluster size interpreted by classical and quantum mechanical models. A blue shift of the volume plasmon energy with decreasing radius R of the cluster was clearly detected. The full width at half maximum (FWHM) of the peak, related to the damping of the volume plasmon excitation, showed a dependence in 1/R. The reported variation of the surface plasmon energy with R was consistent with earlier predictions or experiments

Single photon emitters based on Ni/Si related defects in single crystalline diamond

We present investigations on single Ni/Si related color centers produced via ion implantation into single crystalline type IIa CVD diamond. Testing different ion dose combinations we show that there is an upper limit for both the Ni and the Si dose 10^12/cm^2 and 10^10/cm^2 resp.) due to creation of excess fluorescent background. We demonstrate creation of Ni/Si related centers showing emission in the spectral range between 767nm and 775nm and narrow line-widths of 2nm FWHM at room temperature. Measurements of the intensity auto-correlation functions prove single-photon emission. The investigated color centers can be coarsely divided into two groups: Drawing from photon statistics and the degree of polarization in excitation and emission we find that some color centers behave as two-level, single-dipole systems whereas other centers exhibit three levels and contributions from two orthogonal dipoles. In addition, some color centers feature stable and bright emission with saturation count rates up to 78kcounts/s whereas others show fluctuating count rates and three-level blinking.Comment: 7 pages, submitted to Applied Physics B, revised versio

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Analysis of the electron excitation spectra in heavy rare earth metals, hydrides and oxides

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.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

Oxygen segregation on a dislocation core in germanium studied by electron energy loss spectroscopy

Nanoanalyses performed on a dislocation core in germanium give evidence of oxygen precipitation : a few hundreds of oxygen atoms at a mean concentration of 5 % were detected. A radiation induced oxygen desorption is also observed under the electron beam for which a mixed knock-on and ionization process is proposed. This phenomenon is the main limiting factor for a more quantitative analysis.Des analyses à l'échelle du nm sur le cœur de dislocation dans le germanium ont mis en évidence la présence de l'oxygène : quelques centaines d'atomes d'oxygène à une concentration moyenne de 5 % sont détectés grâce à un microscope électronique à balayage muni d'un filtre de vitesse. Une désorption d'oxygène induite par les électrons est observée sous le faisceau. Ce phénomène est interprété comme étant la succession d'un processus d'ionisation puis de diffusion assistée par choc à l'interface oxyde-germanium