Long-Range Order in Two- and Three-Dimensional Smectic-$B$ Liquid-Crystal Films

This Letter presents x-ray studies of freely suspended smectic liquid-crystal films from 2 to >100 layers thick. Smectic-$B$ thick films of butyloxybenzylidene octylaniline (40.8) have three-dimensional long-range order while thin films are two-dimensional crystals. Large diffuse scattering is observed from soft shear waves, propagating perpendicular to the layers, and three new low-temperature phases with different interlayer order in thick films are found.