Topological defects in smectic islands formed in antiferroelectric freestanding nanofilms

In this work, the authors studied the orientational structure of islands formed in freestanding films as disc-like regions whose number of smectic layers is greater than that in the film. Islands were prepared in thin smectic nanofilms in which the long molecular axes tilt with respect to the normal layer. Geometric restrictions and rigid boundary conditions for the molecular orientation on the boundary of the island and the film induce frustration in the field of molecular ordering and lead to formation of topological defects. Depolarized reflected light microscopy allows the determination of the type of topological defects. Defects with topological charges S = +2, +1, −1, −1/2 were located inside the islands and on their boundary with the film. In the islands, the authors observed unusual structures formed by a complex of defects with positive and negative topological charges. The orientational structure of the field of molecular ordering was calculated taking into account the real and virtual topological defects on the island boundary. Islands with topological defects can be considered as a two-dimensional analogue of a mesoscopic atom.