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Highlights  In situ calcification (aragonite) of a 3.3 Ga microbial biofilm  Calcification probably due to the activities of a photosynthetic consortium of microorganisms within the biofilm including heterotrophic sulphur reducing bacteria  Preservation of the metastable carbonate phase by the organic matrix and secondary silicification  Oldest known occurrence of aragonite.

Platinum loaded carbon layers were synthesized by a two-step plasma sputtering process. 200 nm thick columnar (columns with an average diameter of 20 nm) carbon films having a large open porosity were formed in the first step. Using the same plasma system, the films were subsequently loaded with platinum. SEM, TEM and Rutherford backscattering spectrometry analysis show that platinum diffuses into the carbon layer and forms nano-sized particles (mean diameter ca. 3 nm) along and around the carbon nanocolumns and down to the film/support interface. Optimized catalytic layers were formed at low plasma pressure operation (<1 Pa) and had an upper platinum loading limit of about 0.1 mg.cm -2 .

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International audienceThe pulsed laser ablation method has been used to form GaAs nanocrystals. A quadrupled frequency Nd:yttrium-aluminum-garnet laser beam is focused onto a GaAs single crystal target, and a nitrogen flowing gas is sent at the neighborhood of the target in order to transfer in an ethanol bath, the nanoparticles grown in gas phase. The composition of the particles is close to stoichiometry and transmission electron microscopy analyses highlight zinc-blende GaAs nanocrystals with a rather well defined size: 5-8 nm diameter. The low temperature photoluminescence and photoluminescence excitation spectra show quantum confinement of about 870 meV via an emission band in the visible range (500-560 nm) for the GaAs nanocrystals produced by laser ablation without any postannealing treatmen

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This paper deals with the synthesis of high-magnetization porous silicon-based nanocomposites. Using well-controlled organometallic synthesis of ferromagnetic FeCo nanoparticles, the impregnation of mesoporous silicon has been performed by immersion of porous silicon in a colloidal solution. The technique was optimized by controlling the temperature, the immersion duration, and the solvent nature. The characterization of the nanocomposites showed a homogeneous filling of the pores and a high magnetization of 135 emu/cm3. Such composites present a great interest for many applications including data storage, medical instrumentations, catalysis, or electronics.