Insertion of thin films of WO3 in liquid crystal cells

A new kind of a liquid crystal cell has been made by using a standard sandwich configuration with one of the ITO electrodes, covered by a thin layer of tungsten trioxide deposited by r.f. sputtering in a reactive atmosphere of Ar and O-2 gas. In this kind of cell the optical polarisation switching of the cell (observed under a crossed polarizer microscope) occurs only for one of the two directions of the a.c, applied field, while in the usual liquid crystal cells the electro-optic response does not depend on the sign of field. The inhibiting switching configuration corresponds to the anodic polarisation of tungsten trioxide film in which the de-intercalation of cations occurs. Preliminary impedance measurements reveal an ionic diffusion process in such devices (Warburg impedance behavior). These preliminary results suggest speculations about a reverse internal electric field, which is responsible for the increased threshold of optical switching in one direction only of the applied field. (C) 1999 Elsevier Science Ltd. All rights reserved.