Optical behaviour of hybrid LC/inorganic nanostructures

Abstract

Porous thin films of dielectric materials have been deposited using e-beam evaporation onto substrates held at highly oblique angles (> 80o), coupled with simultaneous computer controlled substrate motion about two independent axes. This technique, known as glancing angle deposition (GLAD), enables the formation of shaped, isolated nanostructures, including vertical posts, zig-zags, and both helical and polygonal spirals, which exhibit chiral optical properties. GLAD films form the backbone of liquid crystal (LC) hybrid optical materials and devices, and afford key advantages. The porous nature of the GLAD structures allows LCs to uniformly penetrate the film and modify its optical properties. Addition of LCs to GLAD films improves the properties of the films by reducing optical scattering, enhancing transmission, and accentuating existing chiral and linear optical anisotropies. Further, by mixing a dichroic dye with the LCs, polarization selective optical properties can be introduced into the film which can be used to augment the functionality of GLAD films. It has been found that addressing hybrid GLAD films with an electric field reorients the LCs, allowing one to switch the optical properties of the composite film. This behaviour extends to LCs mixed with dichroic dye, allowing one to switch the selective polarization properties with an applied voltage. Using results based on spectroscopic ellipsometry, we will examine the optical properties and switching behaviour of LC/dichroic dye hybrid GLAD films and discuss how the results allow one to infer the alignment of LCs in GLAD films, as well how the addition of dichroism to the film affects the selective transmission of both linearly and circularly polarized light.