Nanopattern transfer on bismuth gallium oxide surface via sol-gel stamp process applied for uniform liquid crystal alignment

Abstract

A convenient aligning method using nanoimprint lithography is introduced. Sol-gel-processed bismuth gallium oxide (BGO) thin films that are one-dimensionally nanopatterned by polydimethylsiloxane molds are used for the liquid crystal (LC) alignment layer. The one-dimensional nanopatterns are transferred to the films at a curing temperature of 250 °C. Atomic force microscopy data present clear line grooves on the surfaces, which allow the LCs to align parallel to this pattern in one direction. Polarized optical microscopy and pre-tilt angle data support uniformity of the LC alignment, indicating that the surface nanopatterns act as alignment guides for LC molecules. X-ray photoelectron spectroscopy data shows active thermal oxidation at a curing temperature of 250 °C, which contributes to nanopattern transfer on BGO film. Thermal endurance tests of the BGO films show good thermal stability until 180 °C. The twisted nematic cells in the BGO layer also show superior electro-optical performances compared with the conventional rubbed polyimide layer. From these characteristics of the nanopatterned BGO alignment layer and owing to its simple fabrication, we expect that this new alignment technique can be used for producing next-generation LC devices to replace the conventional rubbing process.