Elastic light scattering from free sub-micron particles in the soft X-ray regime.

We report the first experimental results on angle-resolved elastic light scattering in the soft X-ray regime, where free sub-micron particles in the size regime between 150 and 250 nm are studied in the gas phase by using a continuous particle beam. Two different types of studies are reported: (i) Angle-resolved elastic light scattering experiments provide specific information on the scattering patterns in the regime of element-selective inner-shell excitation near the Si 2p-edge (80-150 eV). In addition to intense forward scattering, we observe distinct features in the angle-resolved scattering patterns. These are modelled by using Mie theory as well as a model that includes contributions from diffuse and specular reflection. The results are primarily attributed to scattering from soft X-rays in the surface layer. (ii) Spectroscopic experiments are reported, where the photon detector is placed at a given scattering angle while scanning the photon energy near the Si 2p-absorption edge. These results are also analyzed by a Mie model, yielding accurate information of the size distribution.