In mammals, DNA methylation (DNAme) erasure and reinstatement during embryo development and germline establishment are sensitive to the intrauterine environment. Maternal intake of a high-fat diet (HFD), associated with excessive gestational weight gain, has transgenerational effects on offspring health, which may be mediated by changes in DNAme in the germline. Here, we tested the impact of a maternal HFD on embryonic germline DNAme erasure using a rat strain that expresses green fluorescent protein specifically in germ cells. DNAme was analysed by methyl-seq capture in germ cells collected from male and female F1 gonads at gestational day 16. Our data show that although HFD induced global hypomethylation in both sexes, DNAme erasure in female germ cells was more advanced compared to male germ cells. The delay in DNAme erasure in males and the greater impact of HFD suggest that male germ cells are more vulnerable to alterations by exogenous factors.

The electron microscopy and microanalysis techniques available at the CP2M Centre have been used to study the complex precipitation phenomena in a titanium-containing dual phase steel. Nitrides, carbides and carbonitrides of titanium have been characterized at microscopic and nanoscopic scales using carbon extraction replicas and thin foils. Precipitation occurred mainly heterogeneously on existing particles (CaS, TiN). Thin foils have also been examined in a new scanning electron microscope with a field emission gun.

The objective of this work is to determine the origin of a decohesion problem that occurs during the fabrication process of certain integrated circuits. This decohesion takes place at the Ti/dielectric interface with the dielectric being either SiO2 or borophosphosilicate glass (BPSG). The frequency of the decohesion increased when the dielectric is BPSG. In order to understand the reason for the difference in decohesion rates for the two dielectrics, a comparative study was performed before and after annealing. X-ray Diffraction was used to determine the microstructure of the different layers and Transmission Electron Microscopy coupled to Electron Energy Loss Spectroscopy and X-ray Energy Dispersive Spectroscopy was mainly used to characterize the interfaces and nanophases that had formed during annealing. A fundamental difference observed was the Ti/dielectric interface reactivity: in the case of BPSG, an amorphous layer rich in P is formed before the Ti5Si3 silicide. Two hypothesis are put forward in order to explain adhesion failures: a decrease in the rate of Ti5Si3 formation kinetics and/or a decrease of the glass transition temperature induced by P enrichment.

The early stages of stress development during epitaxial growth of metal layers with a large misfit in lattice parameters still need in-depth understanding. In this particular study we have focused on Ag-Cu system, which is immiscible and exhibit a large 14% misfit in lattice parameters. Ag/Cu multilayers have been grown by ultrahigh-vacuum evaporation on Si (111) maintained at -20°C, 35°C or 110°C. The thickness of the individual layers is about 100 Å. All the films present the same (111) orientation with a well defined in-plane orientation: <110> Cu or Ag // <110> Si. The stress was monitored during growth with a home-made laser curvature measurement device. The stress vs thickness behaviour is highly asymmetric when comparing Ag/Cu and Cu/Ag. Indeed Ag grown on Cu does not develop any measurable stress at any thickness or temperature, whereas Cu grows on Ag under tensile temperature and thickness-dependent stress. The temperature dependence of this stress relaxation cannot be interpreted with a standard relaxation model including dislocation motion. A possible way to understand the stress temperature dependence is to consider the evolution of microstructure during growth.

Scanning electron microscopy as well as analytical transmission electron microscopy techniques such as high resolution, electron diffraction, energy dispersive X-ray spectrometry (EDX), parallel electron energy loss spectroscopy (PEELS) and elemental mapping via a Gatan Imaging Filter (GIF) have been used to study complex precipitation in commercial dual phase steels microalloyed with titanium. Titanium nitrides, titanium carbosulfides, titanium carbonitrides and titanium carbides were characterized in this study. Both carbon extraction replicas and thin foils were used as sample preparation techniques. On both the microscopic and nanometric scales, it was found that a large amount of precipitation occurred heterogeneously on already existing inclusions/precipitates. CaS inclusions (1 to 2 μm), already present in liquid steel, acted as nucleation sites for TiN precipitating upon the steel's solidification. In addition, TiC nucleated on existing smaller TiN (around 30 to 50 nm). Despite the complexity of such alloys, the statistical analysis conducted on the non-equilibrium samples were found to be in rather good agreement with the theoretical equilibrium calculations. Heterogeneous precipitation must have played a role in bringing these results closer together.

The structure of a [001] tilt grain boundary Σ=25(710) in germanium was investigated by HREM as prepared and after sulfur segregation. The characterisation of Ge(S) system was performed using techniques such as Auger Electron Spectroscopy, Electron Energy Loss Spectroscopy and radioactive tracer analysis. Before the sulfur introduction, this grain boundary is usually sensitive to the preferential etching during the TEM sample preparation which makes the observation difficult. This effect, depending on experimental conditions, can either partially or completely disappear. The interfacial structure as prepared and after annealing under argon or under hydrogen atmosphere can be described as a stacking of several structures with different energies. After sulfur segregation no preferential etching is observed because the lowest energy structure of the as prepared grain boundary is stabilized. The tilt angle and the plane of the grain boundary remain constant.

We demonstrate remarkably rapid oxidation of (100) silicon at room temperature catalyzed by the presence of Cu3Si. Thermal oxidation of Si is normally carried out at temperatures above 700°C. Oxidation of many metal silicides occurs more rapidly than that of Si, but under controlled conditions results in a surface layer of SiO2. In contrast, the oxidation process described here produces a thick layer of SiO2 underneath the copper-rich surface layer. The SiO2 layer grows spontaneously to over one micrometer in thickness in several weeks in air at room temperature. Analysis by Rutherford backscattering, Auger electron spectroscopy, cross-sectional transmission electron microscopy and scanning electron microscopy reveals the presence of Cu3Si at the buried SiO2/Si interface, epitaxially related to the underlying Si substrate. Catalytic action by this silicide phase appears responsible for the unusual oxidation process.