Optical activity of chiral thin film and liquid crystal hybrids

Using the glancing angle deposition (GLAD) technique, we have fabricated porous, chiral thin films with optically anisotropic helical microstructures that exhibit optical phenomena such as wavelength specific rotation of linearly polarized light. Initial research has shown that the porosity of the films allows for the addition of nematic liquid crystals (NLCs) to the films for promising applications in dynamically switchable devices, while simultaneously enhancing the optical properties of the film. This study describes the fundamental optical behaviour of LC-filled chiral thin films in relation to material, porosity, structure and thickness. It was found that for SiO₂ films, the addition of NLCs increased the effective rotatory power by two-fold when compared with results from the film without added LCs. The rotatory power of Al₂O₃ and MgF₂ films, while being similarly increased by the addition of LCs, exhibited a reversal in sign, or direction of rotation, for the visible wavelength spectrum investigated. The effects of film porosity and structure were studied by varying the angle of incidence from 83° to 86°; it was found that the greater porosity of the films deposited at larger angles allowed for more filling by the LCs and thus a larger increase in rotatory power. Finally, the addition of LCs was observed to shift the wavelength of peak rotation towards smaller values.