Liquid Crystal Alignment on Hydrogenated Amorphous Carbon Films Scanned by Divergent Ar Plasma Beams

Abstract

The hydrogenated amorphous carbon (a-C:H) films on indium tin oxides (ITO) glass treated with Argon plasma beam scanning exhibited liquid crystal (LC) alignment. No apparent microgrooves appeared on the as-scanned a-C:H film surface observed by atomic force microscope. The pretilt angle depended on the scan direction, which was about 6–7° for forward scan and about 2–3° for both backward and “forward + backward” scans. The total surface energy of the as-deposited and the as-scanned a-C:H films were measured by contact angle measurements and calculated by the Owens–Wendt (OW) method in order to obtain the corresponding dispersive and polar surface energies. The surface of a-C:H films scanned forwardly is more polar than that for other two scan modes, which also exhibited higher pretilt angle. X-ray photoemission spectroscopy (XPS) spectra were used to characterize the O/C ratio on the a-C:H film surface. The relative amount of C–O bonds for forward scan was higher than those for other two scan modes. The scan-direction dependent property such as pretilt angle was attributed to the divergent character of the Ar plasma beams out of the anode layer source. The correlation of O/C ratio to pretilt angle for the as-scanned a-C:H films for different scan direction is discussed.