Liquid crystal properties make them useful for the development of security devices in applications of

The response time and contrast of vertically-aligned negative nematics depend critically on the aligning surface and its induced pretilt. Pretilt can be tuned up using obliquely evaporated inorganic oxides as alignment surface.A thorough study of pretilt angles induced by aligning sur faces of thermally evaporated SiO", has been carried out on several commercial and experimental negative nematic mixtures.Morphology of SiO", with different evaporation angles has been studied by Field Emission Scanning Electron Microscopy. Some