Chemical Nanopatterns via Nanoimprint Lithography for Simultaneous Control over Azimuthal and Polar Alignment of Liquid Crystals

Abstract

We report on the use of chemical patterns to align a nematic liquid crystal (LC) in LC cells. Chemical patterns on the micro-and nanoscale, down to 50 nm in feature size, were fabricated by combining nanoimprint lithography (NIL) with subsequent reactive-ion etching (RIE), chemical modification with a fluorinated silane in the gas phase, and lift-off. Simultaneous control over both polar and azimuthal orientation of the LCs is possible by using the chemical nanopatterns as LC alignment layers. The polar orientation depends on the ratio of the homeotropic/planar surface potential areas, while the LC azimuthally orients along the direction of the silane patterns.All LC applications utilize the simple principle that LCs can easily be aligned by proper treatment of the contact surfaces. Consequently, better control over the LC alignment is one of the key aspects for the next generation of LC displays.

Competing alignments of nematic liquid crystals on square-patterned substrates

“…For stripe patterns, they found that the polar orientation depends on the relative areas of the homeotropic and planar regions but that the azimuthal anchoring always runs along the direction of the stripes. Scharf and co-workers [13,14] undertook further investigations of systems with competing alignment regions. Subsequent innovations by the groups of Abbott [15] and Evans [16] centered on the development of patterns of combinations of alkanethiols deposited as self-assembled monolayers (SAMs) on gold.…”

Nematic liquid-crystal alignment on stripe-patterned substrates

“…The concept of simultaneous alignment of azimuthal and * Electronic address: d.j.cleaver@shu.ac.uk polar orientation of LCs by chemical nanopatterns has also been suggested experimentally [5][6][7]. In 2005, Scharf et al [8,9] discussed the alignment properties of nematic LCs on surfaces containing homeotropic and planar alignment areas on the same substrate. They showed that the polar orientation depends on the ratio of the homeotropic/planar surface potential areas, while the LC azimuthally orients along the direction of the stripes [10].…”

Liquid crystal alignment induced by micron-scale patterned surfaces

“…An alternative approach that has received some interest involves patterning the aligning surfaces with either topographic relief features or flat micron-scale regions imposing different LC orientations, e.g., checkerboard or stripe patterns alternating between horizontal and vertical alignment. Techniques used for patterning the surfaces include AFM inscription [5], photolithography [6], nanoimprinting [7], and micro and nanoprinting of chemical alignment patterns [8][9][10][11].…”