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A simple method for vapour-phase deposition of a silane surfactant is presented, which produces tuneable homeotropic anchoring in liquid crystals. Both the zenithal anchoring energy and surface slip are measured by fitting to the latching threshold versus pulse width characteristic of a zenithal bistable nematic liquid crystal device based on a deep, submicron grating. The method is shown to give microscopic anchoring strength between 5 × 10-5 and 2 × 10-4 J/m2, with a surface slip of about 100 nm. The silanated surfaces are characterized using atomic force microscopy and X-ray photoelectron spectroscopy, which show a direct relationship between the surface coverage of silane groups and the resulting anchoring energy.

The influence of an asymmetric periodic grooved cell surface on the 2D static director configuration of a nematic liquid crystal has been investigated. The minimum in the Frank-Oseen free energy was solved numerically with the Rapini-Papoular form of the surface anchoring energy at the nematic-grating interface. Results are presented for the variation of pretilt angle in the tilted bulk director field as a function of the surface groove depth, pitch and asymmetry and the bulk parameters. The simulations demonstrate the existence of two energetically degenerate high and low pretilted bulk alignment configurations. The pretilt values in these two regimes and also for the low tilt regime with finite surface anchoring are consistent with experimental results. An effective increase in the resolution of the model is obtained by using an irregular grid to describe the surface profile.

Liquid crystal phase effect devices have been an area of interest for some time. Our studies have involved creating phase effect diffractive elements and investigating their physical properties. These devices have been shown to possess high diffraction efficiencies at short wavelengths and to have short switching times. The research has included theoretical work which has shown very good agreement with our observations.

Current nematic liquid-crystal (LC) displays rely on voltage-induced reorientation of the director (the average molecular direction) within the bulk of the LC layer. In these devices, the surface region of the LC is strongly anchored to the cell walls and does not undergo reorientation at normal operating voltages. This situation is not optimal and indeed modelling has shown that weak anchoring of the LC can in principle lead to lower operating voltages and improved steepness in the electro-optic response1. Achieving weak anchoring in practice has proved difficult. Soft rubbing of a polymer2 or photoinduced ordering of a polymer3 coating the cell walls can lead to weak azimuthal (in-plane) anchoring, but a memory effect is still present which prevents high-speed surface reorientation. Some surface treatments, such as obliquely evaporated silicon oxide, can also induce weak anchoring, but only for a restricted range of temperatures4,5. Here we report a different approach to weak anchoring, which relies on the addition of small percentages of oligomeric molecules to the LC. This approach results in very small zenithal (out ofsubstrate plane) and azimuthal (in plane) anchoring energies. When applied to nematic displays, such treatments lead to a halving of the operating voltage.

The switching properties of most liquid-crystal electro-optic devices rely mainly on the reorientation of the average molecular direction (director) within the bulk of the liquid-crystal layer1. Reorientation of the director at or near the surfaces of the layer usually has an insignificant effect on device performance. Here we describe a different configuration in which a nematic liquid crystal is placed between a flat surface treated to induce a parallel anchoring of the director and a grating surface treated to give a perpendicular anchoring. We show that this configuration leads to an effective azimuthal anchoring at the grating surface that depends on the applied voltage when the nematic phase has negative dielectric anisotropy (that is, the director has a tendency to align perpendicular to the applied field). This leads to a voltage-controlled twist effect in the liquid-crystal cell that is highly sensitive to the grating profile. Furthermore, this twist effect possesses an electro-optic response which is far less dependent on viewing angle compared to many other liquid-crystal display configurations. We therefore suggest that this technology might find application in the next generation of liquid-crystal displays.

The preferred method is described for controlled grating replication from carrier film onto LCD motherglass. This method utilises selective adhesion to the motherglass enabled by the patterned deposition of an adhesion promoter onto the glass surface. Other approaches are compared with regard to throughput and yield in manufacture.

Transflective displays are ideal for portable applications used in both bright sunlight and darkened rooms. Display bistability is also advantageous for ensuring low power consumption, but the choice for transflective geometries is then severely limited. Grating-aligned Zenithal Bistable Devices ZBD™ are readily fabricated in either single polariser reflective or transflective modes using a number of different device geometries. Both retardation and polarisation rotation modes are reported.

Zenithal Bistable Devices (ZBD) are grating aligned nematic liquid crystal devices-which retain the written image after removal of the field and despite mechanical stress. This makes them a most suitable candidate for application in high information content, plastic displays. A novel ZBD configuration is reported which offers significantly improved optical performance, particularly whilst the image is being updated.

The ability of surface relief gratings to align liquid crystals has been known for many years. Renewed interest has recently been stimulated through the invention of novel devices in which the grating gives the additional benefit of bistability. This allows complex images to be retained without constant updating, and without the need for Thin Film Transistors at each pixel. Two types of bistable liquid crystal have been demonstrated: azimuthal bistability using bi-gratings, and zenithal bistability using gratings that give surface alignment to the liquid crystal director parallel to the local surface normal. The latter type is called ZBD and gives exceptional performance compared to all other bistable display technologies. This is because the nematic liquid crystal has different tilts in the direction of the applied field, allowing latching times of better than 40 microseconds (at 30 V) and switching thresholds below 10 V. The orientation of the liquid crystal is not required to change at the surface when switching between the two states and so there are no problems with image sticking. Also, the bistability is surface induced, which makes the states exceptionally tolerant to mechanical stress. An 83 by 90 pixel display is demonstrated, illustrating the potential of this exciting new technology.