Surface-freezing transitions and novel tilted hexatic phases in smectic liquid-crystal films

We report the first unambiguous identification in a thermotropic liquid crystal of a hexatic smectic-L, a phase with molecular tilt direction intermediate between those of the smectic-I and smectic-F, using electron diffraction in free-standing films of 5-(4 ''-hexyl,3'-fluoro-p-terphenyl-4-oxy) acid ethyl ester. Our structural data directly support the proposed explanation of the unusual stripe phase observed optically. We also describe multiple surface-freezing transitions which occur at lower temperatures and involve novel tilted crystal phases.