Investigating the effect of SiO2 thin films with sculptured topographies on the alignment properties of liquid crystals

Abstract

In the present work, sculptured thin films (STF) based on silicon dioxide (SiO2) induced on the indium tin oxide (ITO) coated substrates via glancing angle deposition (GLAD) technique using the physical vapor deposition (PVD) process. Our main motive to perform this work is to address the issues we have faced with the traditional alignment method and give a try to overcome those problems. Keeping these challenges in our mind, we are giving here an alternative to traditional method and explored this different alignment technique with GLAD process. We have fabricated a liquid crystal device (LCD) in a way of electrically-controlled birefringence (ECB) and placed the engineered substrates in anti-parallel alignment. Morphological, optical and electro-optic behaviour of resulting device has been studied in the ∼5 μm thick device. Effect of applied voltage on the morphology and electro-optic behaviour of liquid crystal has been established. Interestingly, LC material demonstrates electrically switchable birefringence colours viz. brown, green, pink, purple and mauve colour, under applied electric field in room temperature at 10X magnification under polarizing optical microscope. A very nice extinction and contrast has been obtained with fabricated ECB device, which elucidate the device quality with impeccable alignment without any disclination defects. Besides, the electro-optic characteristics it also shows a significant impact on the liquid crystal properties. The obtained results demonstrate nice optical retardation, a lower Frederick's threshold voltage i.e. 1.5 V and 19.03 dB higher contrast respectively. An impressive switching response time τon of 5.4 ms and τoff = 600 µs at 20 V has attained with respective device as well. Such change in parameters may correspond to the higher electrical torque experienced by the LC molecules on the application of applied field. Anchoring energy and pretilt angle of respective system has been calculated and correlated with observed behaviour. Thus, engineered device with this superior alignment method show remarkable electro-optic results which can open a new way for the development of fast LCD for advanced optical device applications.