INFLUENCE OF ORDER IN THIN SMECTIC POLYMER-FILMS ON THE STRUCTURE AT THE SURFACE

Vertical and lateral structures of thin films (6-200 nm thick) of a co mbined liquid crystalline polymer with mesogenic groups in the main an d side chains were investigated by X-ray reflectometry and scanning tu nneling microscopy. The liquid crystalline polymer exhibits a choleste ric, a smectic C and a smectic A mesophase. Films prepared by spin-co ating onto glass substrates were investigated as a function of tempera ture in the different mesophases. The main interest was focussed on th e smectic C phase, in which the polymer chains show different orienta tions depending on the film thickness. In films thicker than about 10 nn, chains are oriented perpendicular to the substrate due to interfac e effects. Film thickness constraints in thinner films force chains to lie predominatly flat on the substrate and films partially show dewet ting. X-ray reflection was used for the determination of structural pa rameters like layer thickness, chain orientation, phase sequence, pert urbations in the layered structure and laterally averaged surface roug hness, which partially depend on film thickness. Direct information ab out lateral surface structures on the nanometer length scale was obtai ned from scanning tunneling microscopy. In films thinner than about 10 nm after annealing holes of height of the initial film thickness are observed. In thicker films extended terraces art observed separated by steps of height of single layers. Defects in the layered structure ar e assumed to be responsible for the formation of such a surface struct ure. The surface profile could quantitatively be analyzed by a recent theoretical treatment of edge dislocation in thin liquid crystalline f ilms.