Characterization of Tungsten Trioxide Thin Film Deposited by Spin Coating and the Effect on Their Insertion in Liquid Crystal Cells

ABSTRACT

The asymmetric insertion of oxide layers having mixed conduction properties (ionic and electronic) in liquid crystal cells induce various kinds of electro-optical response of the liquid crystals, and this behaviour has been related to the structural differences of the inserted films. In this work, is reported a structural study of such oxide films deposited on indium tin oxide (ITO) covered glasses. To have further confirmations of the model and a better understanding of the basic mechanism underlying the rectification effect and the connections with the structural and electrical properties of the films, WO₃ layers have been studied before and after thermal. Moreover the gelification via spin-coating, has been implemented and the optimization test of various relevant parameters have been performed. The chemical, structural and optical evolution has been extensively investigated as a function of the thermal annealing treatment, by performing vibrational spectroscopy analysis (micro-Raman and IR) impedance spectroscopy characterization and spectroscopic ellipsometry, before testing the films into the NLC cells.

Keywords:

• electro-optical response
• nematic liquid crystals
• spectroscopic ellipsometry
• tungsten trioxide
• vibrational spectroscopy

Acknowledgments

The authors are indebted to Tiziana Barone and Giuseppe De Santo for their technical assistance to the vibrational spectroscopy measurements. The present investigations have been done in the framework of the Italian MIUR research project “Piani di Potenziamento della Rete Scientifica e Tecnologica” Cluster No. 26-P4.