Homeotropic liquid crystal alignments through periodically unidirectional nano-wedges patterned by nanoimprint lithography

This study demonstrates the fabrication of periodically unidirectional nano-wedges using nanoimprint lithography to achieve homeotropic alignments in sandwiched liquid crystal (LC) cells. When electrically operating LC cells for the purpose of electro-optical performance without the occurrence of disclination lines, the LC pretilt angles play an essential role in achieving uniform LC alignments and well-behaved device functions. The periodical nano-wedges composed of asymmetrically sawtooth-like units were just designed for providing LC pretilt angles. We used grayscale electron beam lithography to fabricate nanoimprint master templates with periodically unidirectional nano-wedges with a 1-μm pitch. The photoresist SU-8 was used as the nanoimprint polymer to form nano-wedge structures. An ultrathin poly(dimethylsiloxane) (PDMS) film was coated on the nano-wedges to assist homeotropic LC alignments. The fabricated nano-wedges were capable of better LC alignments than nano-rectangles in the cells, including fewer disclination lines and better optical performance, as supported by the data obtained.