Structural and chemical characterization of fluorinated amorphous carbon films (a-C:F) as a liquid crystal alignment layer

摘要

a-C:F thin films with varying fluorine content were prepared by plasma CVD and the sputtering method as inorganic alignment layers for overcoming the disadvantages of conventional liquid crystal (LC) alignment layers. The material and structural properties were investigated by X-ray photoelectron spectroscopy, Fourier transform infrared absorption, and contact angle measurement. For elucidation of the liquid crystal alignment layers, LC cells with a-C:F films were fabricated, followed by examination of the textures of the LC and electro-optical characteristics. The fluorine concentrations of a-C:F films were controlled by changing the mixture gas ratio (R_G) in CVD and applied power ratio (R_P) in the sputter system. An increase in R_G and R_P led to increase fluorine incorporation, and the film microstructure changed from a diamond-like to a polymer-like structure. In addition, the sputtered a-C:F films showed a higher fluorination than the CVD sample since the PTFE target was only composed of CF_2 functional groups. Surface composition influenced the surface energy of thin films and an extremely hydrophobic property was obtained in the case of fluorine-rich a-C:F films. LC orientations were observed in various compositions of a-C:F films, and the vertically self-aligned LC textures confirmed that a sputtered a-C:F film is a good candidate for an alignment layer without any post-treatment.