Evanescent Scattering Methods

Resonance Enhanced Dynamic Light Scattering (REDLS)

Schematic of REDLS experiment. At the base of a prism covered with typically 50nm of gold at a specific angle a surface plasmon polariton is exited. The evanescent part, with a penetration depth ξ of 200nm, of this plasmon is used as the incident field in a dynamic light scattering experiment

The development of evanescent light scattering methods to be able to do experiments in the vicinity of solid or liquid interfaces has led to the new method "Resonance Enhanced Evanescent Light Scattering", short REDLS. We use here a surface plasmon polarition as the incident field. Thus we gain an orders of magnitude higher sensitivity compared to traditional evanescent light scattering methods working at total internal reflection. We were able to follow the diffusional behavior of particles of radius smaller than 20 nm. Furthermore we study the rotational behavior of particles anisotropic in form or electron density close to solid interfaces.

Waveguide Enhanced Dynamic Light Scattering (WEDLS)

The limitation to use a noble metal as the interface in REDLS is relieved in the evanescent scattering method Waveguide Enhanced Dynamic Light Scattering (WEDLS) by using a thick layer of a transparent material as PMMA on top of the typically 50 nm gold layer on the prism. Waveguides are excited at specific angles, having a range of penetration depth between 100 and 1000 nm.

Schematic of WEDLS experiment. The difference to the REDLS experiment above is a layer of a transparent material as PMMA or SiOx with typical thicknesses of 1-2µm. The evanescent part, with a penetration depth ξ of 100-1000 nm, of these guided modes is used as the incident field in a dynamic light scattering experiment

Research with these two methods is performed in the fields of Dynamics in thin polymer films and in Dynamics of particles at interfaces to study the influence of solid interfaces on the dynamics of particle and ultrathin polymer films respectively.

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