Polar alignment states of a ferroelectric nematic liquid crystal on obliquely evaporated SiO2 surface layers

Spontaneously polar nematic liquid crystals - so-called ferroelectric nematics - add several functionalities to liquid crystal optics and electro-optics, but are also more complex in terms of surface alignment compared to the well-known conventional non-polar nematics. Here we demonstrate that surfaces coated with obliquely evaporated SiO2 layers facilitate two stable polar surface anchoring states of ferroelectric nematics essentially in the plane of the surface, with azimuthal orientations controlled by the evaporation angle. We also find that the studied material RM734 seems to exhibit a twist, with an estimated pitch of about 10 +/- 5 mu m in the ferroelectric nematic phase, despite the absence of molecular chirality in RM734. One might speculate whether this twist is intrinsic or a result of the strongly polar ferroelectric nematic relieving costly splay deformations into less costly twist deformations.