Enhancement of ferroelectricity in Langmuir-Blodgett multilayer films of weak-polar organic molecules

Ferroelectricity in Langmuir-Blodgett (LB) films (Z-type and alternated Y-type) of nitrogencrown (NC) and arachidic acid (AA) was investigated by electric polarization measurements and small angle X-ray diffraction (SAXD). For Z-type AA LB multilayer and the AA LB films incorporating barium ions, as well as for Z-type NC LB multilayer and the Y-type NC/AA alternating LB films, hysteresis loops of the samples were observed and confirmed existence of the remnant polarizations in the LB films. Their corresponding remnant polarizations were found to be 15, 180, 450 and 9400 μC m^-2, respectively. Therefore, the maximum ratios of remnant polarizations up to 620 (9400/15)-folds were obtained from NC/AA alternating LB films. The enhancement of ferroelectricity in NC/AA alternating LB films was observed for the first time. It was demonstrated that the enhancement of ferroelectricity in the LB films could be created by incorporation of barium ions into the LB film structures and strong interaction due to electron clouds redistribution largely originated from the compact insertion configuration of AA between two chains of NC molecules in interleaving films.