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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.

In January 2004 the USA space agency NASA landed two rovers on the surface of Mars, both carrying the Mainz Mössbauer spectrometer MIMOS II. The instrument on the Mars-Exploration-Rover (MER) Spirit analyzed soils and rocks on the plains and in the Columbia Hills of Gusev crater landing site on Mars. The surface material in the plains have an olivine basaltic signature suggesting physical rather than chemical weathering processes present in the plains. The Mössbauer signature for the Columbia Hills surface material is very different ranging from nearly unaltered material to highly altered material. Some of the rocks, in particular a rock named Clovis, contain a significant amount of the Fe oxyhydroxide goethite, α-FeOOH, which is mineralogical evidence for aqueous processes because it is formed only under aqueous conditions. In this paper we describe the analysis of these data using hyperfine field distributions (HFD) and discuss the results in comparison to terrestrial analogues

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Majority of the authors report elaboration of iron oxide thin films by reactive magnetron sputtering from an iron target with Ar-O 2 gas mixture. Instead of using the reactive sputtering of a metallic target we report here the preparation of Fe 1-x O thin films, directly sputtered from a magnetite target in a pure argon gas flow with a bias power applied. This oxide is generally obtained at very low partial oxygen pressure and high temperature. We showed that bias sputtering which can be controlled very easily can lead to reducing conditions during deposition of oxide thin film on simple glass substrates. The proportion of wustite was directly adjusted by modifying the power of the substrate polarization. Atomic force microscopy was used to observe these nanostructured layers. Mössbauer measurements and electrical properties versus bias polarization and annealing temperature are also reported.

The surface state of carbon nanotubes-Fe-alumina nanocomposite powders was studied by transmission and integral low-energy electron Mössbauer spectroscopy. Several samples, prepared under reduction of the R-Al 1.8-Fe 0.2 O 3 precursor in a H 2-CH 4 atmosphere applying the same heating and cooling rate and changing only the maximum temperature (800-1070°C) were investigated, demonstrating that integral low-energy electron Mössbauer spectroscopy is a promising tool complementing transmission Mössbauer spectroscopy for the investigation of the location of the metal Fe and iron-carbide particles in the different carbon nanotubenanocomposite systems containing iron. The nature of the iron species (Fe 3+ , Fe 3 C , R-Fe, γ-Fe-C) is correlated to their location in the material. In particular, much information was derived for the powders prepared by using a moderate reduction temperature (800, 850, and 910°C), for which the transmission and integral low-energy electron Mössbauer spectra are markedly different. Indeed, R-Fe and Fe 3 C were not observed as surface species, while γ-Fe-C is present at the surface and in the bulk in the same proportion independent of the temperature of preparation. This could show that most of the nanoparticles (detected as Fe 3 C and/or γ-Fe-C) that contribute to the formation of carbon nanotubes are located in the outer porosity of the material, as opposed to the topmost (ca. 5 nm) surface. For the higher reduction temperatures T r of 990°C and 1070°C, all Fe and Fe-carbide particles formed during the reduction are distributed evenly in the bulk and the surface of the matrix grains. The integral low-energy electron Mössbauer spectroscopic study of a powder oxidized in air at 600°C suggests that all Fe 3 C particles oxidize to R-Fe 2 O 3 , while the R-Fe and/or γ-Fe-C are partly transformed to Fe 1-x O and R-Fe 2 O 3 , the latter phase forming a protecting layer that prevents total oxidation.