Investigation of the alignment phenomena using a-C:H thin films for liquid crystal alignment materials

A high pretilt angle is generated by hydrogenated amorphous carbon (a-C:H) thin films treated with an ion beam method. a-C:H thin films are deposited by remote plasma enhanced chemical vapor deposition and are modified by an Ar ion beam at an incidence angle of 45° using an Kaufman ion gun. Ion beam irradiation results in the decrease of the thickness of a-C:H thin films and the increase of the sp² fraction. The optical transmittance of the ion beam irradiated a-C:H is more affected by thickness than sp² fraction. An excessive ion beam irradiation, 5 min Ar ion beam, results in the increase of the surface roughness of the a-C:H thin films and the pretilt angle has very low value. The pretilt angle is controlled by the thickness, sp² fraction and the surface roughness.