Structural characterization of various chiral smectic-C phases by resonant X-ray scattering

We report the results of resonant x-ray diffraction at the sulfur K-edge performed upon free-standing films of a thiobenzoate liquid-crystal compound. Our data provide the first direct structural evidence of distinct periodicities in several chiral Sm-C phases, including 2-layer, 3-layer, and 4-layer superlattices in Sm-C^*A, Sm-C^*_FI1, and Sm-C^*_FI2, respectively. In Sm-C^*_α, periodicity incommensurate with the layer spacing was detected. The racemic compound version was also studied. The results are consistent with a “clock model” of the Sm-C^* variant structures.