Nematic order melting on rough surfaces measured by surface plasmon resonance

Our measurements by a plasmon technique show that the structure of grazing incidence (85 degrees) evaporated SiOx thin films is highly porous. A large fraction of the voids is open and can be penetrated by a nematic liquid crystal put into contact with the SiOx layer. The nematic material in the voids remains disordered (isotropic) in the whole nematic range. This indicates that the director orientation in the volume of the liquid crystal must, at least in this case, be determined by other mechanisms than the ordering of molecules in the grooves of the rough surface. Further, we have found a transition region where the order parameter gradually decreases from the bulk value to zero (disorder) at the surface with a coherence length of approximately 8 nm.