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Title: Device oriented experimental investigation of the alignment of liquid crystals
Author: Bodammer, Georg
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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Good understanding of the alignment mechanisms of liquid crystals on solid surfaces is a pre-requisite for the successful design and manufacture of high performance liquid crystal-based optoelectronic devices. Apart from selecting certain types of alignment (homogeneous or homeotropic alignment, with a specified liquid crystal pretilt) it is important to ensure liquid crystal alignment uniformity across areas of several square centimeters. Even though uniform alignment of nematic liquid crystals over large areas can be achieved relatively straightforwardly the task of aligning ferroelectric liquid crystals in their SmC* phase is formidable. Liquid crystals can be aligned by a multiplicity of methods. These include the evaporation of thin inorganic solid films, grating structures and Langmuir-Blodgett films, all of which are studied in this work with an emphasis on thin silicon monoxide (SiO) films evaporated at an oblique angle. The study concentrates at first on the analysis of the bounding surfaces found in a typical device environment: namely the transparent conductive indium-tin-oxide (ITO) electrode with a thin film of SiO which has been evaporated over it at an oblique angle. By use of a scanning electron microscope it is shown that the ITO layer exhibits roughness comparable to the usually in device configuration encountered thickness of the subsequently evaporated SiO film. Atomic force microscopy reveals columnar growth of the SiO film while the underlying morphology of the ITO layer still determines the large scale structure of the resulting surface with which the liquid crystal is in contact. Secondary ion mass spectroscopy reveals that the SiO films are oxygen rich and contain molybdenum as a contaminant. Following the appropriate preparation of the bounding surfaces and their assembly into a sandwich structure liquid crystal material is injected. If SiO alignment promoting films are used the final alignment of ferroelectric liquid crystals in their SmC* phase is found to be strongly and irreversibly dependent on the conditions during injection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available