G. Henn et al., INFLUENCE OF ORDER IN THIN SMECTIC POLYMER-FILMS ON THE STRUCTURE AT THE SURFACE, Physica. B, Condensed matter, 221(1-4), 1996, pp. 174-184
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.