J.L. Guille

Structure and magnetic properties of Co+-implanted silica

Abstract Cobalt has been implanted at 30 and 160 keV in three different silica-based substrates. TEM observations and magnetization measurements performed at RT and 5 K show that, after implantation, cobalt is present both as metal particles, few nanometers in size and as smaller oxide particles. Optical absorption measurements show that the presence of oxide particles is linked to the formation of Si–Si bonds during implantation. After thermal treatment under hydrogen, cobalt is entirely in the metallic form and saturation magnetization becomes close to its theoretical value. Last, the initial amount of oxide depends on the OH− content of the substrate.

Reduction of copper in soda-lime-silicate glass by hydrogen

Abstract The reduction of copper in soda-lime-silicate glasses by hydrogen was measured as a function of time and copper content within the temperature range 440 to 650°C. Copper is reduced to the metallic state in a surface layer whose thickness increases with time and temperature and decreases with copper content. A well developed periodical precipitation of copper particles is observed in the reduced layer. The reduction is accompanied by an alteration of the glass composition in which there is an increase of the copper content and a reduction of the calcium content. The growth kinetic of the reduced layer, followed by optical spectroscopy and measurement of the layer thickness, is analyzed with regard to the tarnishing model.

Metal (Fe, Co, Ni) Nanoparticles in Silica Gels: Preparation and Magnetic Properties

Metal containing silica gels with a Me/Si molar ratio between 0.01 and 0.2 are submitted to thermal treatment under hydrogen within the temperature range 600 to 1000°C. The changes occurring during these treatments are followed by X-ray diffraction, transmission electron microscopy, Mössbauer spectrometry and static magnetization measurements.During these treatments, nickel is nearly totally reduced to metal particles, the mean size of which increases from 3 to 10 nm with increasing temperature, but does not vary appreciably with nickel content. These particles exhibit a classical superparamagnetic behavior and are stable towards reoxidation when reexposed to air at room temperature.Iron and cobalt behave in a notably different manner. First, in both cases, silicates may be formed during the thermal treatment and consequently the reduction to the metallic state is not complete unless it occurs at high temperature (1000°C and above). Secondly, the particles formed are much less stable toward reoxidation, especially in the case of iron. Accordingly, the evolution of the magnetic behavior is much more complex than in the case of nickel.

Optical properties of copper-doped silica gels

Abstract Copper-doped silica xerogels, obtained by the sol-gel process, have been submitted to various thermochemical treatments. Depending on copper concentration, treatment time, temperature and atmosphere, different copper species are present in the final product: Cu + ions (isolated or dimers), cuprous oxide nanoparticles and metallic copper. These species have been characterized by their optical properties (absorption and luminescence). Some of the materials obtained could be useful for applications or fundamental studies.