Reflection Anisotropic Spectroscopy as a Tool in the Fabrication of Liquid Crystal Devices

Abstract

We demonstrate the potential of Reflection Anisotropic Spectroscopy (RAS) as a new tool for predicting optical microelectronic device characteristics prior to assembly. The Reflection Anisotropy (RA) of polymer alignment layers has been studied as a function of rubbing. This data contains information about the suitability of the surface as an alignment layer as well as film thickness.

Reflection anisotropy spectroscopy: A probe of rubbed polyimide liquid crystal alignment layers

“…Further rubbing leads to a small reduction in measured anisotropy, consistent with the onset of surface damage observed by AFM. This is in contrast to our previous studies of rubbed nylon 6-6 14 in which we found the RAS signal to collapse completely after only two rubs, as shown by the triangular data points of Fig. 3͑c͒.…”

Azimuth-dependent reflection anisotropy spectroscopy

“…These examples are drawn from a field to which RAS has only very recently been applied, 9,10 namely the construction of liquid crystal displays. Such devices function by the alignment of liquid crystal molecules at surfaces due to some kind of anisotropic surface modification.…”

“…Here we have studied 1 cm square glass substrates coated with a thin indium tin oxide electrode layer followed by a ϳ0.3-m-thick polyimide layer, as used to produce miniature displays and described elsewhere. 9 An atomic force microscopy ͑AFM͒ image of a typical sample after passing under a rotating velvet drum is shown in Fig. 3͑a͒ and clearly shows rub-induced grooves with a depth of ϳ30 nm.…”

“…RAS is now firmly established in the field of semiconductor epitaxy [2][3][4] and this success has stimulated application of the technique to new areas including the study of molecular adsorption, 5 catalysts, 6 Langmuir-Blodgett films, 7 solid-liquid interfaces 8 and liquid crystal alignment layers. 9,10 In this work we expand on our previous report 11 of a generalization of RAS: since normal incidence must be retained, the only possibility is to rotate the sample in the plane of the surface, i.e., to vary the ''azimuthal'' angle. Thus far the systems studied with RAS have been thin biaxial layers and multilayers with one principal axis aligned with the sample normal ͑and the other two axes known͒ on top of isotropic substrates.…”

The Effect of Rubbing Strength on the Formation of Zigzag Defects in Surface Stabilised Ferroelectric Liquid Crystals

“…Mechanical rubbing of a PI film will also result in changes to the physical properties of the film, especially the surface morphology and it has been reported that anchoring energies change with rubbing strength [7]. The examination of rubbed PI films by means of reflection anisotropy spectroscopy (RAS) [8] and reflection ellipsometry [9,10] reveals that mechanical rubbing generates surface anisotropy. These changes in the molecular alignment and surface topography of the alignment layer affect the molecular alignment of the ferroelectric liquid crystal (FLC) layer as it is in direct contact with the PI film.…”