Fabrication and characterization of hybrid liquid crystal devices

Abstract

This thesis describes new characterization techniques that can be used to investigate nematic liquid crystal (LC) materials and systems, and experimental studies of new hybrid LC devices.

The characterization techniques include an all-optical method for determining nematic viscosities, a multi-spectrum analysis (VTF) of the electro-optic response of an LC device subject to an AC field, and a measurement of two-beam coupling (TBC) in photorefractive LC systems subject to an AC field. The time response measurement is the first experimental study of fast director oscillations seen when a modulated field is applied to a cell, and it has been shown that Erickson-Leslie theory can be used to determine the rotational viscosity by fitting to these oscillations. The VTF has been used to show that the conductivity of the LC E7 is 2 x that of TL205, and can explain the origin of higher beam coupling in E7 photorefractive devices. The AC driven TBC and its analysis has proved that a non-ohmic photoconductor will lead to two distinct beam coupling regimes in frequency space, and has shown that optimum beam coupling efficiency can be obtained by tuning the AC frequency.

The range of new hybrid LC devices investigated here include cells using an LC doped with multiferroic nanoparticles, and photorefractive cells that use a new electrode material (PEDOT) to reduce injection barriers in standard photorefractive devices, a photorefractive polymer (JTDA16) as an aligning layer, and a photoaligning layer (PAAD) to enhance the modulation depth of induced photorefractive gratings. The multiferroic nanoparticle study showed that a magneto-optic response could be observed at low fields (< 500 Gauss), and that the sol-gel process for growing nanoparticles is not appropriate for creating ferroelectric layers with thicknesses below ~ 15 nm. The new materials for photorefractive cells have shown promising results, with observed diffraction efficiencies up to 13 x higher than a benchmark cell using polyvinyl carbazole as a photoconductor.

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