Studying the surface reaction between NiO and Al2O3 via total reflection EXAFS (ReflEXAFS).

The reaction between NiO and (0001)- and (1102)-oriented Al2O3 single crystals has been investigated on model experimental systems by using the ReflEXAFS technique. Depth-sensitive information is obtained by collecting data above and below the critical angle for total reflection. A systematic protocol for data analysis, based on the recently developed CARD code, was implemented, and a detailed description of the reactive systems was obtained.

Micro-XANES mapping of buried interfaces: pushing microbeam techniques to the nanoscale.

A specific preparation procedure makes possible to obtain in one shot structural and compositional characterization of a buried interface at the nanometre scale using a micrometre scale probe. A specific example based on dispersive mu-XAS, micro X-ray absorption spectroscopy, shows that nearly-atomic scale changes in local structure, composition, as well as local disorder are faithfully detected. The approach could in principle be applied to any probe with a micrometric resolution.

Metallic versus covalent bonding: Ga nanoparticles as a case study.

A systematic X-ray absorption spectroscopy investigation of the local coordination in gallium nanostructures has been performed as a function of temperature and particle size. It is shown that the nanostructure strongly affects the polymorphism of solid gallium and the (meta)stability range of the liquid phase (in agreement with previous works) and that the surface tension acts in the same direction as hydrostatic pressure in stabilizing the Ga solid phases. The effect of surface free energy is first to favor the metallic arrangement of the delta phase and then to stabilize a liquid-like phase based on dimeric molecules even at 90 K.

Simulation study of wave propagation instabilities for the combustion synthesis of transition metals aluminides.

Interest in the mode of propagation of self-sustaining reactions has been motivated by the influence of the mode on the microstructure and composition of the final product. However, comprehensive studies relating the onset of the various propagation modes to the chemical and phase transformations taking place in the sample are still lacking. In the present work propagation instabilities in self-propagating high-temperature synthesis (SHS) of transition metal aluminides are studied using a computer simulation approach.