Layer-dependent surface-induced tilt, hexatic, and positional orders in free-standing 70.7 films

Electron diffraction in free-standing films of 4-n-heptyloxybenzylidene-4-n -heptylaniline of up to 25 molecular layers has revealed the coexistence, a s a function of distance from the surface, of three distinct phases: an out ermost smectic-l layer, several layers of a middle phase, and a smectic-A i nterior. The middle phase is an unusual highly-correlated tilted liquid, wi th hexatic like positional correlations but no long-range bond-orientationa l order, which transforms to the smectic-l at a lower temperature. The disc overy of this unusual middle phase also represents the possibility of a nov el layer-dependent two-stage tilt-induced surface-freezing transition.