Abstract
The mechanism of liquid crystal (LC) alignment on hydrogenated amorphous carbon (a-C:H) films pre-treated with plasma beam scanning was proposed in this thesis. The a-C:H films exhibit uniform and high optical transmission, which was prepared in a capacitively-coupled-plasma enhanced chemical vapor deposition chamber. The LC cells made of the plasma-beam-scanned a-C:H films exhibit excellent characteristics of LC alignment. The LC alignment was characterized by a polarizing optical microscope and the pretilt angles were measured using the rotation crystal method. Raman spectra and X-ray photoemission spectroscopy (XPS) were used to analyze the characteristics of plasma-beam-scanned a-C:H films.Raman spectra indicate that the plasma beam scanning process can break chemical bonds on the surface of an a-C:H film. The occurrence of bond-breaking on a-C:H films can generate some dangling bonds for the further formation of C-O bonds during air exposure. XPS data support both the formation of C-O bonds and the increase of oxygen content occured on the surfaces of plasma-beam-scanned a-C:H films. The dangling bonds generated from first plasma beam scanning can be passivated or erased by second hydrogen plasma beam scanning. The second hydrogen plasma beam scanning can reduce the C-O bonds and also the LC pretilt angles on a-C:H films. The C-O bonds on the surfaces of a-C:H films correspond to the pretilt angles of LC cells.The characteristics of LC alignment on Polyimide (PI) films and a-C:H films were compared by using mechanical rubbing and plasma beam scanning. The rubbed PI films exhibit uniform LC alignment. And poor LC alignment occurs on the rubbed a-C:H films. The rubbing process can not generate microgrooves or stretches of carbon chains on a-C:H films due to its high hardness. On the other hand, the PI films and a-C:H films exhibit uniform LC alignment after plasma beam scanning. The phenomenon implies that the mechanism of LC alignment is not microgrooves or stretches of carbon chains.The mechanism of LC alignment on plasma-beam-scanned a-C:H films is the dipole-dipole interaction induced from anisotropic chemical bonds. The scanning direction of plasma beam provides some anisotropic dangling bonds to generate anisotropic C-O bonds on the surfaces of a-C:H films. The dipole moment of C-O bonds and its anisotropy induces LC molecules to align on a-C:H films.