Mitochondrial echoes of first settlement and genetic continuity in El Salvador

Background: From Paleo-Indian times to recent historical episodes, the Mesoamerican isthmus played an important role in the distribution and patterns of variability all around the double American continent. However, the amount of genetic information currently available on Central American continental populations is very scarce. In order to shed light on the role of Mesoamerica in the peopling of the New World, the present study focuses on the analysis of the mtDNA variation in a population sample from El Salvador. Methodology/Principal Findings: We have carried out DNA sequencing of the entire control region of the mitochondrial DNA (mtDNA) genome in 90 individuals from El Salvador. We have also compiled more than 3,985 control region profiles from the public domain and the literature in order to carry out inter-population comparisons. The results reveal a predominant Native American component in this region: by far, the most prevalent mtDNA haplogroup in this country (at ~90%) is A2, in contrast with other North, Meso- and South American populations. Haplogroup A2 shows a star-like phylogeny and is very diverse with a substantial proportion of mtDNAs (45%; sequence range 16090–16365) still unobserved in other American populations. Two different Bayesian approaches used to estimate admixture proportions in El Salvador shows that the majority of the mtDNAs observed come from North America. A preliminary founder analysis indicates that the settlement of El Salvador occurred about 13,400±5,200 Y.B.P.. The founder age of A2 in El Salvador is close to the overall age of A2 in America, which suggests that the colonization of this region occurred within a few thousand years of the initial expansion into the Americas. Conclusions/Significance: As a whole, the results are compatible with the hypothesis that today's A2 variability in El Salvador represents to a large extent the indigenous component of the region. Concordant with this hypothesis is also the observation of a very limited contribution from European and African women (~5%). This implies that the Atlantic slave trade had a very small demographic impact in El Salvador in contrast to its transformation of the gene pool in neighbouring populations from the Caribbean facade

Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography

Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C

[Carta a Ignacio Hernando de Larramendi y Montiano]

Información adicional de autor de la carta: Director Ejecutivo, Inx Reinsurance CorporationFotografía número: 115

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 ribbons

International audienc

Evidence of atomic-scale arsenic clustering in highly doped silicon

International audienceLow temperature (675 °C) epitaxial in situ doped Si layers (As, 1.5 at. %) were analyzed by atom probe tomography (APT) to study clustering in a highly arsenic-doped silicon layer. The spatial distribution of As atoms in this layer was obtained by APT, and the distance distribution between first nearest neighbors between As atoms was studied. The result shows that the distribution of As atoms is nonhomogeneous, indicating clustering. Those clusters, homogeneously distributed in the volume, are found to be very small (a few atoms) with a high number density and contain more than 60% of the total number of As atoms. \textcopyright 2009 American Institute of Physics

Evidence of atomic-scale arsenic clustering in highly doped silicon

International audienceLow temperature (675 °C) epitaxial in situ doped Si layers (As, 1.5 at. %) were analyzed by atom probe tomography (APT) to study clustering in a highly arsenic-doped silicon layer. The spatial distribution of As atoms in this layer was obtained by APT, and the distance distribution between first nearest neighbors between As atoms was studied. The result shows that the distribution of As atoms is nonhomogeneous, indicating clustering. Those clusters, homogeneously distributed in the volume, are found to be very small (a few atoms) with a high number density and contain more than 60% of the total number of As atoms. \textcopyright 2009 American Institute of Physics

Atomic-Scale Investigation of SmCo5/alpha-Fe Nanocomposites: Influence of Fe/Co Interdiffusion on the Magnetic Properties

International audiencehe nanostructure of SmCo5/alpha-Fe nanocomposites elaborated by high-energy ball milling was investigated using atom probe tomography. This high-resolution technique allowed obtaining in the real space a 3D mapping of the chemical species (Sin, Co, and Fe) on the atomic scale. 3D reconstructions of the nanostructure of the analyzed samples were realized from the data and show that the majority of the SmCo5/alpha-Fe nanocomposite is composed of alpha-Fe(Co) soft magnetic nanosized crystallites embedded in a Srn-(Co,Fe) hard magnetic matrix. These results confirm the formation of the alpha-Fe(Co) phase and the contamination of the initial Sin Cos by Fe atoms. The interfaces between the alpha-Fe(Co) soft magnetic phase and the Srn-(Co,Fe) hard magnetic phase were also chemically analyzed on the atomic scale. Large graded interfaces were evidenced. Monte Carlo simulations assuming a linear variation of the anisotropy in the intermixed interface between the interdiffusion can lead to an increase in the coercive field. Sm-(Co,Fe) and the Fe(Co) regions indicate that the Fe/Co interdiffusion can lead to an increase in the coercive field

Atomic-Scale Investigation of SmCo5/alpha-Fe Nanocomposites: Influence of Fe/Co Interdiffusion on the Magnetic Properties

International audiencehe nanostructure of SmCo5/alpha-Fe nanocomposites elaborated by high-energy ball milling was investigated using atom probe tomography. This high-resolution technique allowed obtaining in the real space a 3D mapping of the chemical species (Sin, Co, and Fe) on the atomic scale. 3D reconstructions of the nanostructure of the analyzed samples were realized from the data and show that the majority of the SmCo5/alpha-Fe nanocomposite is composed of alpha-Fe(Co) soft magnetic nanosized crystallites embedded in a Srn-(Co,Fe) hard magnetic matrix. These results confirm the formation of the alpha-Fe(Co) phase and the contamination of the initial Sin Cos by Fe atoms. The interfaces between the alpha-Fe(Co) soft magnetic phase and the Srn-(Co,Fe) hard magnetic phase were also chemically analyzed on the atomic scale. Large graded interfaces were evidenced. Monte Carlo simulations assuming a linear variation of the anisotropy in the intermixed interface between the interdiffusion can lead to an increase in the coercive field. Sm-(Co,Fe) and the Fe(Co) regions indicate that the Fe/Co interdiffusion can lead to an increase in the coercive field

Analytical Three-Dimensional Field Ion Microscopy of an Amorphous Glass FeBSi

Three-dimensional field ion microscopy is a powerful technique to analyze material at a truly atomic scale. Most previous studies have been made on pure, crystalline materials such as tungsten or iron. In this article, we study more complex materials, and we present the first images of an amorphous sample, showing the capability to visualize the compositional fluctuations compatible with theoretical medium order in a metallic glass (FeBSi), which is extremely challenging to observe directly using other microscopy techniques. The intensity of the spots of the atoms at the moment of field evaporation in a field ion micrograph can be used as a proxy for identifying the elemental identity of the imaged atoms. By exploiting the elemental identification and positioning information from field ion images, we show the capability of this technique to provide imaging of recrystallized phases in the annealed sample with a superior spatial resolution compared with atom probe tomography. © 2021 Cambridge University Press. All rights reserved

A structural investigation of SmCo5/Fe nanostructured alloys obtained by high-energy ball milling and subsequent annealing

International audienceSmCo 5 /Fe nanostructured alloys with 20 wt% Fe, obtained by high energy ball milling of SmCo 5 and Fe powders, were investigated by 57 Fe Mössbauer spectrometry, X-ray diffraction and tomographic atom probe. The Mössbauer analysis reveals that during the first stages of milling, an interdiffusion of Co and Fe occurs, leading both to the formation of α-Fe(Co) regions in α-Fe and to the introduction of Fe in SmCo 5 regions. Annealing at temperatures up to 650°C for 0.5h promotes interdiffusion further leading to the formation of an unique α-Fe(Co) phase and a Fe-richer Sm(Co, Fe) 5 phase. The Co/Fe interdiffusion is confirmed by tomographic atom probe analysis. The data are discussed and compared to the results of previous magnetic measurements