Surface ordering at the air–nematic interface. Part 2. A spectroscopic ellipsometry study of orientational order

Abstract

* order parameter, air-nematic interface, ellipsometrySpectroscopic ellipsometry has been used to measure enhanced orientational ordering at the nematic-air interface of 8CB as the smectic-A phase was approached by cooling from the isotropic phase. The depth profile of the orientational order has been estimated by calculating the ellipsometric parameters for a homeotropic uniaxial surface film on a uniaxial subphase using the Abelès matrix method. This showed that the depth of the enhanced orientationally ordered region was ~ 10nm at 0.5°C above the nematic-smectic-A transition. This is substantially less than the thickness of the region with surface enhanced smectic order as determined by neutron reflection and a model of the surface structure consistent with both sets of results is proposed. AbstractSpectroscopic ellipsometry has been used to measure enhanced orientational ordering at the nematic-air interface of 8CB as the smectic-A phase was approached by cooling from the isotropic phase. The depth profile of the orientational order has been estimated by calculating the ellipsometric parameters for a homeotropic unaxial surface film on a uniaxial subphase using the Abelès matrix method. This showed that the depth of the enhanced orientationally ordered region was ~ 10nm at 0.5°C above the nematic-smectic-A transition. This is substantially less than the thickness of the region with surface enhanced smectic order as determined by neutron Preprint: to be published in Liquid Crystals 2 reflection and a model of the surface structure consistent with both sets of results is proposed.

Modeling the optical properties of self-organized arrays of liquid crystal defects

“…It must be noted that no anisotropic optical response could be detected on this reference sample. For the liquid crystal layer, we have used the ordinary and extraordinary optical constants of 8CB taken from [18]. We point out that the thickness of the thin film was not a free parameter.…”

Optical Constants of Al-Doped Er₂O₃ Films Prepared by Radio Frequency Reactive Magnetron Sputtering

“…The different data of Ψand ∆obtained for incident angles of 70°and 75°show that optical properties can vary as function of depth because the p-and s-components reflect differently from the interface depending on the angle of incidence. As the angle of incidence(to the interface normal) increases, <r s >steadily increases from a small value but <r p >starts out at a small value and then decreases until it reaches zero at the Brewster angle, θ B , before increasing again [7]. We have tested that the as-deposited film contain an interfacial layer of SiO x and ErO x (ErO or any other nonstoichiometric phase).…”

Determination of the translational order parameter for smectic liquid crystals using small-angle neutron scattering

“…In this paper we discuss the difficulties in measuring the translational order parameter and outline a simple method for determining it in smectic liquid crystals. Our motivation was to determine values of the translational order parameter for the bulk smectic A phase that could be compared with the values determined in surface-induced smectic layers in nematic phases that have been reported elsewhere [13][14][15].…”