Comparison of Cu Auger electron transitions between the superconductor YBa2Cu3O7-x and the oxides of Cu—O system

Auger electron spectroscopy (A.E.S.) has been employed to investigate the valence of copper in superconducting YBa2Cu3O7-x ceramics. Comparison of A.E.S. spectra of YBa2Cu3O7-x with CuO and Cu2O oxides shows a very specific LM45M45 electronic transition for copper in the superconductor. A very clear doublet splitting of the L 3M45M45 transition is observed in YBa2Cu3O7-x. This result can be attributed approximately to the existence of two valency states Cu+ and Cu2+ for copper. Another interpretation could be to consider the existence of a strong splitting in the 3d orbital level of copper.Nous avons utilisé la spectrométrie d'électrons Auger pour étudier la valence du cuivre dans des matériaux supraconducteurs YBa2Cu3O7-x. La comparaison des spectres Auger de YBa2Cu3O7-x avec ceux des oxydes CuO et Cu 2O montre l'existence d'une transition électronique LM45M 45 pour le cuivre dans le supraconducteur. Un dédoublement très prononcé de la transition L3M45M45 est observé dans le cas de YBa2Cu3O7-x. Ce résultat peut être attribué approximativement à l'existence de deux états de valence Cu + et Cu2+. Une autre interprétation pourrait être de considérer qu'il existe un dédoublement très prononcé dans les niveaux des orbitales 3d du cuivre dans le supraconducteur

Study of the chemical and structural organization of SIPOS films at the nanometer scale by TEM-EELS and XPS

International audienceTwo films of semi-insulating polycrystalline silicon (SIPOS) have been prepared by low pressure chemical vapor deposition (LPCVD). Their physico-chemical properties are studied at the nanometer scale with transmission electron microscopy (TEM)–electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) techniques by taking into account two main input parameters: the oxygen content and the condition of post-deposition anneal. The compositions of the films are SiO0.17 and SiO0.48. They are made of nanocrystalline silicon embedded in a SiOx matrix with different oxidation states of the silicon atoms. The less the films are oxygenated or the more the films are heat-treated, the more the fraction of crystallized silicon. This study provided a strong baseline to set up a process of fabrication for applications such as high voltage transistors

ÉTUDE DE PROCÉDÉS D'EXTRACTION DU SOUFRE DE MINERAIS SULFURÉS À HAUTE TEMPÉRATURE. APPLICATION DES PLASMAS

Des calculs d'équilibres thermodynamiques effectués sur les systèmes Fe-S-Ar, Fe-S-C-Ar, Fe-S-C-H2-N2 à T = 2000K montrent que l'extraction totale et sélective du soufre par vaporisation dans le cas du simple traitement thermique de Fe1-xS n'est pas possible. Inversement, l'extraction de soufre peut être sélective si le sulfure de fer est vaporisé en présence de carbone solide ou de méthane. Des essais de vaporisation d'un minerai de type "pyrotine FeS" dans un four rotatif à torche plasma s'accordent avec les résultats de l'étude thermodynamique. Le traitement thermique à T ≈1600 K du minerai sous azote présente une faible efficacité. Des fontes fer-carbone constituent les résidus des traitements du minerai en présence de carbone. Des traitements de courte durée en présence de méthane permettent l'obtention d'un mélange de sulfure de fer et de fer à faible teneur en carbone.Thermodynamical equilibrium calculations concerning Fe-S-Ar, Fe-S-C-Ar and Fe-S-C- H2-N2 chemical systems at T = 2000K show that all sulfur present in iron sulfides ores cannot be recovered by vaporization process without simultaneous iron vaporization. Sulfur can be extracted without iron vaporization by a carbo reduction process using solid coal or gaseous methane. Vaporization experiments carried out in a plasma reactor are in good agreement with our thermodynamical results. High temperature treatments of a sulfide ore has a low efficiency for sulfur extraction at T = 1600 K. Thermal treatments of the same ore with carbon allows to obtain cast iron. We obtained a mixture of iron sulfide and iron by short thermal treatments under methane

SiCN coatings prepared by PACVD from TMS-NH3-Ar system on steel

SiCN coatings with continuous composition between Si3N4 and Sic (rich in Si) have been prepared by acting on the tetramethylsilane (TMS)/ammonia ratio in the gas phase. The deposit compositions (10 μm thick films) have been investigated by different means which stress the difficulties encountered. Nevertheless the trends are in fair agreement. An increase in ammonia partial pressure favors the incorporation of N in the deposits. XPS studies of the samples lead to the conclusion that the chemical environments of Si, C, N are more complicated than in a mixture situation ; there would be various bonding States. Deposition rates range from 12 μm h-1 up to 30 μm h-1 and are largely increased when dilution is reduced. Hardness and Young's modulus are driven by the C/N ratio : HV lies between 22.6 GPa (Si3N4) to 26.2 GPa (SiC) with respectively apparent Young's modulus from 250-295 up to 357-431. All the films exhibit an adhesion of same order though N tends to increase the critical loads

ADHERENCE AND PROPERTIES OF SILICON CARBIDE BASED FILMS ON STEEL

Coatings of silicon carbide with various compositions have been obtained in a r.f plasma assisted process using tetramethylsilane and argon as input gases. Some properties against mechanical applications of such deposits on steel have been investigated. Residual stresses and hardness are reported and discussed in relation with plasma parameters and deposit composition. By scratch testing, it was shown that the silicon carbide films on steel denote a good adherence when compared with previous data encoutered in the litterature for titanium carbide or nitride deposits though low critical load values. Adherence is discussed in relation to the nature of the interfacial zone examined hy Auger depth profiling. It is conclude that the films have promising variable properties which can be optimized by acting on plasma parameters

Compositional Effects on Morphology, Structure and Superconducting Properties of YxBay CuzO7-δ Thin Films Prepared by Metalorganic Chemical Vapour Deposition

In this paper we report the preparation of quasi-stoichiometric layers (Ba-deficient and Ba-rich) by MOCVD. The compositional effects on the morphology, structure and superconducting properties were studied too

XPS study of CVD silicon thin films deposited on various substrates from SiH4 gaseous precursor

CVD silicon films were deposited from SiH4 pyrolysis on amorphous SiO2 layers heated at various temperatures in the range 560-620°C, and on amorphous SiNx or polycrystalline silicon layers at 580°C. According to the substrate temperature, the silicon films can be completely crystallized for the highest temperature, or amorphous for the lowest temperature, in the case of a-SiO2 substrates. For intermediate temperatures (570 or 580°C), the silicon films are crystallized near the a-SiO2 substrate and then amorphous up to the surface, when they are entirely amorphous on a-SiNx or c-Si substrates as shown elsewhere by TEM and SEM observations. X.P.S. valence band spectra, core levels photoelectrons and SiKL2,3L2,3 Auger transitions examinations, have shown that a lower growth rate of the silicon films on the a-SiO2 substrate at 570 or 580°C leads to the formation of nanocrystallized silicon deposits at the early stage of the deposition. For a-SiNx substrate, a higher growth rate was observed at the first stage of the deposition, at 580°C. These results can contribute to the understanding of the relationship between the structure changes of the deposit and the nature of the substrates