Interface observation of heat-treated Co/Mo2C multilayers

We study the interface evolution of a series of periodic Co/Mo2C multilayers as a function of the annealing temperature up to 600{\textdegree}C. Different complementary techniques are implemented to get information on the phenomenon taking place at the interfaces of the stack. The periodical structure of Co/Mo2C multilayer is proven by Time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiles which demonstrate the formation of an oxide layer at both air/stack and stack/substrate interfaces. From Nuclear magnetic resonance (NMR) spectra, we observed the intermixing phenomenon of Co and C atoms for the as-deposited sample, and then at annealing temperature above 300{\textdegree}C Co and C atoms separate from their mixed regions. Comparison of NMR results between Co/Mo 2 C and Co/C references confirms this phenomenon. This is in agreement with x-ray emission spectroscopy (XES) measurements. Furthermore the calculation of the Co-C, Co-Mo and Mo-C mixing enthalpy using Miedema's model gives a proof of the demixing of Co and C atoms present within the stacks above 300{\textdegree}C. From the transmission electron microscopy (TEM) analysis, we found the presence of some crystallites within the as-deposited sample as well as the mainly amorphous nature of all layers. This is confirmed using x-ray diffraction (XRD) patterns which also demonstrate the growth of crystallites induced upon annealing.Comment: Published in Applied Surface Science 331, 8-16 (2015). http://dx.doi.org/10.1016/j.apsusc.2014.12.05

Caractérisation par ToF-SIMS des couches de passivation des tubes de générateurs de vapeur en Alliage 690 pour l industrie nucléaire (apport à la compréhension des mécanismes)

Le phénomène de relâchement de nickel en solution est responsable d une partie de la contamination radioactive du circuit primaire des centrales nucléaires à eau pressurisée. Il convient donc, d un point de vue réglementaire, de limiter cette contamination. Le film d oxyde se formant en surface des tubes de générateurs de vapeur (en alliage 690) joue un rôle barrière dans la limitation de ce phénomène. Il apparaît alors primordial de bien maîtriser les phénomènes de formation de cette couche, qui sont eux-mêmes fortement impactés par les paramètres matériaux du tube (taille de grains, écrouissage, etc), ainsi que par les conditions chimiques du milieu primaire (température, pH, etc). L objectif de ces travaux est de caractériser finement les oxydes formés et d établir un lien entre corrosion et relâchement. Cette étude a été réalisée en trois parties. La première partie a consisté à développer une méthodologie de caractérisation poussée des films d oxydes par spectrométrie de masse d ions secondaires à temps de vol (ToF-SIMS). Cette méthodologie est basée sur l étude d oxydes de référence tels que NiO, Cr2O3, NiCr2O4. La seconde partie de ces travaux a été consacrée à l étude de l influence de trois paramètres matériaux sur la composition et la structure du film d oxyde : l orientation cristallographique, la taille de grain, et la teneur en précipité intergranulaire en carbure de chrome. Des effets non négligeables sont observés pour l orientation cristallographique et la teneur en précipité, mais pas pour la taille de grains. Enfin, dans la dernière partie nous avons étudié simultanément l influence des conditions physico-chimiques du milieu primaire sur la cinétique de relâchement et sur la nature du film d oxyde formé. La température et le pH apparaissent comme des paramètres influençant la corrosion et le relâchement.The nickel release in solution is responsible for part of the radioactive contamination of the primary circuit of the Pressurized Water Reactor (PWR) nuclear power plants. For safety issues, it is very important to limit this contamination. The oxide film formed on the steam generators (SG) tubes surface (in Alloy 690) plays an important role as diffusion barrier in the limitation of this phenomenon. It appears paramount to well control the phenomena of oxide film formation, which themselves are strongly impacted by the materials parameters of the tube (size of grains, work hardening, etc), like by the chemical conditions of the primary education medium (temperature, pH, etc). The double objective of this work is to finely characterize oxide film formed on SG tubes and to establish a relation between corrosion and release. This study was carried out in three parts. The first part consisted of the development of a extensive use of the time of flight secondary ion mass spectrometry (ToF-SIMS) to characterize oxide films. This methodology is based on the study of oxide reference sample. The second part of this work was devoted under investigation of the influence of three materials parameters on the composition and the structure of oxide film: crystallographic orientation, grain size, and content of chromium intergranular carbide precipitate. Considerable effects are observed for the crystallographic orientation and the content of precipitate, but not for the grain size. Lastly, the last part studies simultaneously the influence of the physicochemical conditions of the primary education medium on the kinetics of relaxation and the nature of formed oxide film. The temperature and the pH seem parameters influencing corrosion and the relaxation.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Development of intentional contamination in iron by bath for silicon wafers and evaluation of VPD-Bulk and LPD-Bulk for metallic contaminants analyses by ICPMS

International audienceThis paper offers a preliminary study for the analysis of metallic contamination on frontend patterned wafers obtained by two different techniques based on the etching of the whole patterns, LPD-Bulk and VPD-Bulk coupled with an ICPMS. To elaborate the analysis of patterned wafers, methods were first verified and optimised on reference Si wafers. Both techniques are complementary methods for the etching of wafers. LPD-Bulk enables a fast etching of several micrometres of Si but with less precision than VPD-Bulk, which is more adapted for the etching of layers thinner than1 micrometre. The intentional contamination in SC1 and H2O bath of monitoring wafers showed that contamination in H2O is better controlled due to the absence of chemical reactions, competition between oxidation and etching processes occurring during SC1. And diffusion of contaminants at the tested temperatures from 20°C to 80°C, does not occur. Heat treatment should be applied to allow the diffusion of metallic contaminants in the bulk of the wafers

Surface investigation on Ce_xZr_1-xO₂ compounds

Viii, 88 hlm,; 33 c