Abstract
We have studied the alignment of a nematic liquid crystal (LC) material on aluminum subwavelength nanogratings as a function of the period, p, and the slit width to period ratio, w/p. A method, based on Fourier analysis of the transmittance spectra of the LC grating system, has been applied. We show that the gratings provide stable planar alignment only for shorter periods and narrower slits (p < 400 nm, w/p < 2/3). As these parameters increase, the homogeneous surface alignment changes to domains with different tilt angles or to spatially modulated alignment. We have also obtained a 90° twisted LC director distribution, implying sufficiently strong azimuthal LC anchoring at the grating surface.
Highlights
In the age of nanotechnology, various nanostructured materials are under intensive investigation, being considered as perspective research objects for various applications [1,2]
In some cases, different colors are formed within one grating (Figure 3b), which points out the difference in optical retardation and the liquid crystal (LC) alignment
The appearance of the twist demonstrates that the subwavelength aluminum gratings are capable of aligning liquid crystals along their slits with rather small pretilt angles and that the anchoring energy is high enough to balance the elastic torque at the surface, which is provided by the twisted deformation across the LC layer
Summary
In the age of nanotechnology, various nanostructured materials are under intensive investigation, being considered as perspective research objects for various applications [1,2]. The second section is dedicated to data analysis, where besides polarized microscope observations, we apply the Fourier transform technique to the transmittance spectra in order to extract the effective values of the LC extraordinary refractive index.
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