Orientation of Liquid Crystalline Molecules on Mid-IR Transparent Plates Subjected to Ion Bombardment

Abstract

Optical absorption of the nematic liquid crystal 4-methoxybenzilidene-4′-butylaniline (MBBA) was examined to study a possibility of homogenous orientation of liquid crystalline (LC) molecules on the silicon and germanium substrates subjected to argon ion bombardment. The integral absorption near the 1630 cm⁻¹ absorption band maximum, commonly assigned to the group -CH˭N- vibrating along the MBBA long axis was analyzed before and after the application of the electric field above the threshold voltage of the Fredericksz effect. It was shown that upon increasing ion fluences, the preliminary bombardment of the substrates by argon ions with energies of 250 eV lead to the planar molecule orientation. Argon ions of 1.25 keV, however, promote planar orientation only until fluences of the order of 1 · 10¹⁸ ion · cm⁻² and change the orientation for homeotropic at higher fluences.

Keywords:

• Germanium
• infrared absorption
• ion bombardment
• ion fluence
• liquid crystal
• silicon

Acknowledgment

The authors are grateful to Dr. I. S. Hasanov for assistance at argon ion bombardment. This work has been supported by Science and Technology Center in Ukraine (grant No 5352).