Photoinduced anchoring on a chalcogenide surface

We present basic characteristics and a model of photoinduced anchoring of liquid crystals (LCs) on a chalcogenide surface. It was found that characteristics of the alignment strongly depend on the LC material for the same chalcogenide glass. The photoalignment is partially reversible and can be controlled by changing the light polarization direction. We propose a model in which the existence of dichroic units on the chalcogenide surface and competition between two mechanisms of the photoalignment is suggested. The first mechanism is related to the light-induced anisotropy on the chalcogenide surface and results in an easy orientation axes of a LC parallel to the polarization of the incident light. The second mechanism is attributed to an energy transfer from the dichroic units after the light absorption to the LC molecules adsorbed on the chalcogenide surface. The transferred energy causes polarization-sensitive desorption of the LC molecules from the chalcogenide surface and the light-induced easy orientation axis of a LC perpendicular to the incident light polarization. The competition between these mechanisms leads to the observed change of the direction of the easy axis with the exposure.