Antiferroelectric and ferroelectric switching of a liquid crystal in Langmuir-Blodgett films under strong confinement conditions

An antiferroelectric liquid-crystal (LC) material formed of banana-shaped molecules in the sandwich metal-thin Langmuir-Blodgett film-metal geometry, which is typical of solid-state technology, is investigated. Upon heating the thin-film elements, the material passes to the high-temperature (68–127°C) LC B ₂ phase, which, despite severe limitation on the film thickness (∼100 nm or less), exhibits antiferroelectric switching, which was previously observed only in bulk samples (10 μm thick) of the LC studied. At film thicknesses smaller than ∼40 nm, ferroelectric switching is observed, which is caused by the stabilization of the ferroelectric LC phase by the boundary surfaces. The largest values of the switched polarization of films (∼400 nC/cm²) are comparable with the polarization of bulk samples. The coercive field increases with decreasing film thickness and reaches ∼10⁶ V/cm for the thinnest films. This value corresponds to the intrinsic coercive field of the ferroelectric under conditions of a strong surface effect, which suppresses domain processes. Published in Russian in Kristallografiya, 2006, Vol. 51, No. 5, pp. 898–905. Dedicated to the 60th Birthday of M.V. Kovalchuk The text was submitted by the authors in English.