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12 September 2007 Three-dimensional alignment of liquid crystals in nanostructured porous thin films
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Oblique evaporation of inorganic materials has long been used to induce alignment in liquid crystals, often for the purpose of controlling the pretilt angle in a liquid crystal cell. These alignment layers are relatively dense, keeping the liquid crystals above the surface of the inorganic layer. By evaporating at increasingly oblique angles (> 80°), the alignment layer can be made porous, allowing liquid crystals to infiltrate the film and to align to individual nanostructures. By coupling simultaneous computer controlled substrate motion during evaporation, a process known as glancing angle deposition (GLAD), the nanostructures can be grown in a variety of useful shapes, including helices, polygonal spirals, zigzags and periodically bent S-shaped columns. Alone, these films exhibit properties such as linear and circular polarization selective Bragg reflection, and full three-dimensional photonic bandgaps. By infiltrating liquid crystals into the voids of the film, one can align liquid crystals in three dimensions, as well as tune and switch the film's optical properties. Additionally, the GLAD film can be used to template polymerizable liquid crystals for subsequent monomer infiltration. In this work, using spectroscopic ellipsometry, we examine the effects of liquid crystal infiltration on various film structures made from a variety of metal oxides, for both varying film thickness and deposition angle. Techniques for filling a porous film with a known volume of liquid crystals are also presented. Additionally, we examine the switching behaviour for these films under applied electric fields. Finally, we compare experimental and simulated results used to predict and optimize the optical properties of these hybrid films.
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Nicholas Wakefield and Jeremy Sit "Three-dimensional alignment of liquid crystals in nanostructured porous thin films", Proc. SPIE 6654, Liquid Crystals XI, 665404 (12 September 2007);

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