Near-Field Birefringence Response of Liquid Crystal Moleculesin Thickness Direction of Liquid Crystal Thin Film Orientated by ShearForce

Abstract

Information of molecular orientation in nematic liquid crystal (LC) isattractive and important for applications in the field of displaydevices. We demonstrate a novel method using a birefringence scanningnear-field optical microscope (Bi-SNOM) with a probe which is insertedinto the LC thin film to detect the molecular orientation from itsbirefringence responses in the thickness direction of the LC thin film.The probe is laterally vibrated when going forward into the LC thinfilm, and the retardation and azimuth angle are recorded as the probegoing down. Firstly, the thickness of the LC thin film is measured bythe shear force detection. Since the shear force acts as a stimulationto reorientate the LC molecules above the substrate surface, we candetect the molecular orientation caused by a polyimide alignmentsubstrate and the effect to molecular orientation caused by vibrationof fibre probe. As a result, the orientation profiling ofthe LC film in depth direction is obtained in both the casesthat the direction of probe vibrating is vertical/parallelto the rubbing direction of the alignment film. Furthermore, the thickness ofcompletely orientated layers just above the substrate surface can alsobe obtained by either vibrating probe or no-vibrating probe. Ultimately,the LC thin film can be modelled in thickness direction from all theresults using this method.