Creation of submicron orientational structures in thin liquid crystal polymer layers

Abstract

Submicron orientational patterns were created in thin liquid crystal polymer films. A rubbed polyimide layer was locally modified by hatching it with the small tip of a simplified atomic force microscope. A nematic liquid crystal mixture, that can be spin-coated and polymerized at room temperature was used to transfer the lithography from the polyimide into the liquid crystal polymer. Gratings as small as 240 nm periods were fabricated. The domain boundaries, which are nothing else than twist disclination lines attached to the substrate surface, influence the topography on a distance much larger than the film thickness. This topographic effect, which consists of a groove and a wall parallel to the boundary, was investigated as a function of the scratching angle, the film thickness and the size of the structure.

Nano-rubbing of a liquid crystal alignment layer by an atomic force microscope: a detailed characterization

“…The load force for the present ANR was limited below ∼30 nN in order to avoid disruption of the tip geometry as much as possible. Note that this load range is considerably low in comparison with those adopted by previous workers [9][10][11][12]15], who used hard (probably highly crystalline) polyimides such as LX-1400 (Hitachi Chemical). For these stiff polyimides, the effects of ANR can barely appear in this low and moderate 3 Manufacturer's specifications.…”

“…Using the stylus of an atomic force microscope (AFM), one can locally conduct the rubbing process in any small region down to the nanometre scale. The structural anisotropy induced by the AFM nano-rubbing (ANR) technique was demonstrated to be sufficiently strong to induce good LC orientation even at a moderate load force [9][10][11][12], and the ANR was recently successfully applied to fabricating novel electrooptical LC devices requiring nano-and micro-scopically textured surface alignment such as the highly efficient switchable diffraction grating and the surface-induced bistable 0957-4484/02/020133+05$30.00 © 2002 IOP Publishing Ltd Printed in the UK nematic devices [13][14][15][16]. Despite its obvious drawbacks such as limited size and long processing time, the ANR technique enables, by its nature, us to precisely control the direction and strength of rubbing, which is hardly possible in the conventional rubbing process.…”

Observation of twist nematic liquid-crystal lines

“…4,6 This alignment method has already been applied to obtain specific configurations of polymer layers, 5 LC gratings, 6 as well as controllable gray scale 7 and bistability 8 properties. Recently, this method was also used for studying the mechanism of LC alignment 9 and was even shown to successful induce alignment on indium-tin oxide substrates.…”