Effects of plasma treatments on correlation between chemical structures of DLC films and liquid crystal alignment

In an effort to obtain an improved liquid crystal (LC) alignment layer for liquid crystal display device applications, amorphous diamond-like carbon thin films were deposited on ITO-coated glass substrates by an rf magnetron sputtering technique at room temperature and then treated with plasma in various atmospheres. The polarized images and pretilt angles of the LC cells showed that LC alignment was enhanced by post-plasma treatments of the films. In Raman and X-ray photoelectron spectroscopy spectra of the films, an increase in the fraction of sp²-bonding was observed after post-plasma treatments of the films. In particular, H₂ plasma-treated film had the largest fraction of sp²-bonding at the film surface and showed much improved alignment capabilities. These results suggest that π-bondings of the sp ²-structure at the surface rather than the bulk play an important role in LC alignment.