Force microscopy of chiral liquid-crystal surfaces

The free surface of chiral liquid crystals has been observed by optical and scanning force microscopy. In a narrow temperature region near the smectic A* to cholesteric (or isotropic) transition, a unique periodic surface undulation is observed. Both the period and depth are seen to be temperature dependent, though their ratio is approximately constant. This structure appears to be related to the chiral nature of the molecules and may be a result of competing alignment forces, analogous to that predicted by de Gennes and Bouligand. © 1992 IOP Publishing Ltd.