Synchrotron radiation based soft X-ray spectroscopy as a probe of structural properties and reactivity of isolated nanoparticles

During the past decade, a world-wide industrial expansion of nanoparticles (NPs) has been taking place at the junction between fundamental and applied sciences. "Nanoparticle" is usually defined as a system extanding from several thousands to millions of atoms, and its size is expressed in nanometers. The particular interest for NPs mainly results from their particular physical properties at the nanometer scale, but also from their large « surface to bulk » ratio. Hence, more active sites are available at the surface, enhancing their reactivity. This characteristic is used in numerous fields of applications (heterogeneous catalysis, cleanup, photovoltaics, nanomedicine). This expansion of nanotechnologies involves the development of new methods for the characterization of these new kinds of materials, which takes a considerable part in our daily life. Among the methods of matter characterization, synchrotron radiation based soft X-ray spectroscopy has been shown to be a powerful technique for the study of atoms and molecules as well as materials, and appears today as an efficient technique of characterization in surface science.
The idea is to combine the atomic selectivity of the spectroscopy applied to dilute matter, with the surface sensitivity of soft X-ray spectroscopy, to study isolated nanosystems in the gas phase, by XPS in the energy range of soft X-ray. We will present here the first results obtained by this approach at the PLEIADES beamline of SOLEIL synchrotron radiation facility. The experiments carried out in this work relate to materials often used in the industrial and biomedical fields: TiO2 NPs, Silicon and glycosylated polystyrene NPs. We show how XPS on isolated NPs allows us to answer concrete questions, as the surface reactivity of the NPs, processes and oxidation dynamics, the doping efficiency or the interface ligand/NP.