Dynamics and Electrooptics of Vertically Aligned Nematics With Induced Pretilt on ${\hbox {SiO}}_{x}$

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 surfaces 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 morphological variations appear at specific evaporation angles. These are related to the pretilt induced by the surface and to the dynamic response of the device.