Structural Characterization of Various Chiral Smectic- C Phases by Resonant X-Ray Scattering

Abstract

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 $\mathrm{Sm}\ensuremath{-}{C}_{A}^{*}$, $\mathrm{Sm}\ensuremath{-}{C}_{\mathrm{FI}1}^{*}$, and $\mathrm{Sm}\ensuremath{-}{C}_{\mathrm{FI}2}^{*}$, respectively. In $\mathrm{Sm}\ensuremath{-}{C}_{\ensuremath{\alpha}}^{*}$, 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 $\mathrm{Sm}\ensuremath{-}{C}^{*}$ variant structures.