Surface-induced order near the smectic-A - smectic-C transition: Comparison between ferroelectric and antiferroelectric compounds

Ellipsometric measurements on freely suspended liquid-crystal films are conducted in order to compare the formation of the smectic-C phase at the free surface of two liquid-crystal compounds. Whereas both compounds possess the smectic-A and the ferroelectric smectic-C phase, only one of the compounds shows in addition the antiferroelectric smectic-CA phase. Our results reveal that the latter compound shows a considerably reduced coupling of the molecular tilt in neighbouring smectic layers