Orientation of liquid-crystal molecules on substrates exposed to argon-ion bombardment

Abstract

The possibility for homogeneous orientation of liquid-crystal (LC) molecules was studied after argon-ion bombardment of substrates (Si, Ge) transparent in the infrared (IR) spectral region. The orientation of the LC molecules was monitored by IR spectroscopy. Nematic LC 4-methoxybenzylidene-4′-butylaniline (MBBA) was used to study the molecular orientation. Absorption spectra were analyzed near the band with maximum at 1630 cm −1 corresponding to − CH=N-group vibrations along the long axis of the MBBA molecule. The type and degree of initial orientation of the LC molecules were determined from the correlation of the integrated absorptions of this band without and with an applied electric field (above the threshold voltage for the Fredericksz effect). It has been established that an increased ion fluence results in a planar orientation of the LC molecules and in a gradual transformation of the planar orientation of the molecules to a homeotropic one with preliminary argon-ion bombardment of substrates at energies of 250 eV and 1.25 keV, respectively.