Synchrotron Small Angle X-ray Scattering (SAXS) analysis on Nanosystems –Study of Mesostructure in gas phase & Nanoparticles by Laser ablation

SAXS is a fundamental method for structural analysis of condensed matter with applications covering various fields, from metal alloys to synthetic polymers in solution and in bulk, biological macromolecules,nanoparticles, etc. [1]. As the SAXS measurements are done very close to the primary beam ("small-angles"), the technique profits immensely from the brilliance of X-ray photon beams provided by particle accelerators known as synchrotrons. In this talk a detailed overview on the principles and application of synchrotron SAXS for the analysis of Nanosystems will be explained with the help of two relevant examples; “Gas phase analysis of silica mesostructure” and “Nanoparticles formation by laser ablation”.

The in situ synchrotron gas phase analysis on the mesostructured aerosol silica particles unveils the influence of the basic production parameters on the final formed meso-structure. From the SAXS data, using a simple 2 phase model fit the silica wall thickness and surfactant core radius of the hexagonally ordered mesostructure are estimated. The comparison of data from the gas phase and powder deposit shows that, in general, slower drying conditions (heating temperature about 80 °C) and a medium surfactant to Si ratio (about 0.14) lead to nanostructures of the best quality in terms of well-defined long-range organization [2].

As a second system the dynamics of the nanoparticle produced by pulsed laser ablation in liquid investigated by time-resolved SAXS will be presented. Laser ablation of a gold target in water induces a cavitation bubble in which two different particle species could be identified at maximum bubble extension: (i) primary particles of about 8–10 nm diameter, which show a smooth concentration gradient starting from the target and can also be found outside the cavitation bubble in the free liquid and (ii) secondary particles in the range of 45 nm diameter which have highest concentration in the upper part of the cavitation bubble but do not penetrate into the liquid [3].