Optical behavior of chiral thin film-liquid crystal composite materials

Abstract

The glancing angle deposition (GLAD) technique may be used to fabricate thin films with a very porous chiral or helical microstructure, with geometry of the helices controlled and engineered to have specific porosity, helical pitch, and handedness. Such films with chiral morphology exhibit optical rotation and circular dichroism similar to certain classes of liquid crystals, with the pitch and handedness of the chiral film determining the resultant optical properties. When nematic liquid crystals (LCs) are introduced into the pores of chiral GLAD films, a composite material is formed that shows a significant enhancement of the chiral optic response, suggesting an alignment of LC molecules by the underlying inorganic chiral film 'backbone'. Results are presented from a study of the optical behaviour of chiral films fabricated from materials such as silicon dioxide, alumina, and magnesium fluoride, and from study of the effects of parameters such as helical pitch, film thickness, and film porosity on the optical properties. The enhancement of optical response created by impregnating these films with nematic LC is reported. The construction of electro-optic cells containing the composite GLAD/LC films is described, demonstrating reversible electro-optic switching of the LC component within the film.