Layer-by-layer crystallization and the role of fluctuations in free standing smectic films

Specular x-ray reflectivity has been used to study the changes in the therm al fluctuation behavior of eight layer freely suspended N-(4-n-butoxybenzil idene) -4-n-octylaniline (4O.8) films during the process of successive laye r-by-layer crystallizations. Each of these steps is preceded by the formati on of an-intermediate layer structure with in-plane hexatic ordering. We fi nd an unusually large reduction of the fluctuations after the emergence of only the first hexatic toplayer. The fluctuation profiles over the film are in all cases quenched at the surfaces though less so after each crystalliz ation step. This behavior supports theoretical arguments that heretic order is reduced by out-of-plane smectic layer fluctuations. [S1063-651X(99)5111 1-2].