The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

Abstract

It is well known that the alignment of liquid crystals (LCs) can be realised by rubbing or photoalignment technologies. Recently, nonlinear laser lithography (NLL) was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time, the usage of the NLL as a perspective method of the alignment of nematics was presented. By NLL, nanogrooves with about 0.92 μm period were formed on Ti layer. The nanostructured Ti layer (NSTL) was coated with oxidianilinepolyimide film with annealing of the polymer followed without any further processing. Aligning properties of NSTLs were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy (AE) of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal AE, obtained for pure NSTL, is comparable with photoalignment technology. It was found that the deposition of polyimide film on NSTL leads to the gain effect of the azimuthal AE. Also, atomic force microscopy (AFM) study of aligning surfaces was carried out.

High-quality alignment of nematic liquid crystals using periodic nanostructures created by nonlinear laser lithography

“…As can be seen from Fig. 10(a) the increase of the scanning speed at a constant laser power (P = 350 mW) leads to the non-monotonically changes of the twist angle for both types of the tested substrates [51]. The increase of the laser power P leads to the monotonous increase of the twist angle of the LC cell at a constant scanning speed, as is shown in Fig.…”

“…It is obvious that the value of the anchoring energy W B , at constant parameters of the NLL structuring (under the experimental conditions) without the change of the laser wavelength (e.g., the usage of a second harmonic generation), that leads to the decrease of the period of nanogrooves, cannot be changed. However, to increase the anchoring energy the usage of the nanostructured Ti layer additionally coated with an ODAPI film was recently proposed in [51]. Contrary to the tested substrate of the first type, here we obtained the tested substrate of the second type with the average value of the depth of grooves within a range A~150-200 nm (for further estimations A = 175 nm) by a trial-and-error method in the dipping technique, but the average value of the period Λ~920 nm is identical with its in [51].…”

“…However, to increase the anchoring energy the usage of the nanostructured Ti layer additionally coated with an ODAPI film was recently proposed in [51]. Contrary to the tested substrate of the first type, here we obtained the tested substrate of the second type with the average value of the depth of grooves within a range A~150-200 nm (for further estimations A = 175 nm) by a trial-and-error method in the dipping technique, but the average value of the period Λ~920 nm is identical with its in [51]. The AFM image and cross section of the nanostructured Ti layer (after processing by the NLL method with υ = 1500 mm/s and P = 350 mW) coated with the ODAPI film (solid "red" circles) are shown in Fig.…”

“…In this case the homogeneity alignment was achieved by, on the one hand, nanogrooves of both the Ti layers and Ti layers coated with the ODAPI film and, on the other hand, the rubbed surface of PI2555. We have considered the nanostructures obtained by the NLL method, as an analogue to the rubbed (or photoaligning) surface with a difference that the period of nanogrooves for the rubbing (or photoalignment) technique is far less than the usage of the NLL [51] or CIG method in [34]. To check our statement that the homogeneous alignment is observed owing to on the one hand, the availability of nanogrooves and on the other hand, the usage of the ODAPI film deposited on nanogrooves, we made two combined twist LC cell, consisting of the reference substrate (rubbed or non-rubbed PI2555) and tested substrate (non-rubbed ODAPI or ODAPI deposited on the nanostructured Ti layer).…”

Nematic Liquid Crystal Composite Materials for DC and RF Switching

“…Photo-induced alignment is another option for patterned alignments in microscale. Along with these, a few other micro-patterning techniques are also reported [113,114]. (b) CNT has a tendency to aggregate in an LC solution.…”