Liquid crystal alignment on the a-C:H films by Ar plasma ion immersion

A plasma ion immersion treatment has been developed to enhance the liquid crystal (LC) alignment on the hydrogenated amorphous carbon (a-C:H) layer in an inductively coupled plasma (ICP) chamber. No LC alignment was observed for the a-C:H layer tilted at an angle of 0° during the bombardment with plasma ions. The LC alignment occurs for the a-C:H layer tilted at an angle of 30° or 60°. Their pretilt angles (∼ 1.4°) are approximately the same. The azimuthal anchoring strength is 1.98 × 10- 6 J/m2 at a tilted angle of 30° and 1.14 × 10− 4 J/m2 at a tilted angle of 60°. The mechanism for the LC alignment is attributed to the oblique incidence of ions within the matrix sheath of non-uniform thickness near the a-C:H surface under a negative pulse bias. The matrix sheath of non-uniform thickness is confirmed by the plasma density distribution in the ICP chamber and the X-ray photoemission spectra across the a-C:H layer.