Structure of freely suspended chiral smectic films as determined by x-ray reflectivity and optical ellipsometry - art. no. 021702

We report on a combined x-ray reflectivity and optical ellipsometry study o f freely suspended smectic (Sm) films of a chiral liquid crystalline compou nd with the phase sequence Sm-A-Sm-C-alpha*-Sm-C*- Sm-C-gamma*-Sm-C-A*. Usi ng tilt magnitude profiles from x-ray reflectivity as input to model the av erage optical properties obtained by ellipsometry, tilt direction profiles are also obtained. In this way realistic models can be elaborated for the v arious types of chiral Sm-C films. We find that the surface layers are more tilted than the interior layers due to surface interactions and finite siz e effects. For the ferrielectric Sm-C-gamma* phase the tilt direction profi le corresponds to a three-layer helix, in agreement with the clock model of chiral Sm-C phases. In thin films the surface interactions suppress the bu lk helix structure of the Sni-C-alpha* phase and a Sm-C-A*-like structure i s formed with an anticlinic layer-by-layer alternation of the tilt directio ns.