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

Abstract

It is well known that today two main and well studied methods for alignment of liquid crystals has been used, namely: rubbing and photoalignment technologies, that lead to the change of anisotropic properties of aligning layers and long-range interaction of the liquid crystal molecules in a mesophase. In this manuscript, we use the nonlinear laser lithography technique, which was recently presented as a fast, relatively low-cost method for a large area micro and nanogrooves fabrication based on laser-induced periodic surface structuring, as a new perspective method of the alignment of nematic liquid crystals. 920 nm periodic grooves were formed on a Ti layer processed by means of the nonlinear laser lithography and studied as an aligning layer. Aligning properties of the periodic structures of Ti layers were examined by using a combined twist LC cell. In addition, the layer of the nanostructured Ti was coated with an oxidianiline-polyimide film with annealing of the polymer film followed without any further processing. The dependence of the twist angle of LC cells on a scanning speed and power of laser beam during processing of the Ti layer was studied. The azimuthal anchoring energy of Ti layers with a periodic nanostructure was calculated. The maximum azimuthal anchoring energy for the nanostructured Ti layer was about 4.6 × 10 −6 J/m 2 , which is comparable to the photoalignment technology. It was found that after the deposition of a polyimide film on the periodic nanostructured Ti layer, the gain effect of the azimuthal anchoring energy to~1 × 10 −4 J/m 2 is observed. Also, AFM study of aligning surfaces was carried out.

Femtosecond laser-induced damage threshold of nematic liquid crystals at 1030 nm

“…Thus, PVA is not a critical issue for most of LCbased laser shapers. However, for mixtures with higher LIDT (saturated compounds or glassy LC mixtures [19]), alternative anchoring techniques [34] might be preferred . LIDT results with single-shot exposure are shown in Fig.…”

Influence of Periodic Non-Uniformities of Well-Structured Sapphire Surface by LIPSS on the Alignment of Nematic Liquid Crystal

“…The formation of LIPSS is a simple and high-speed technique for structuring surfaces which has already previously been demonstrated for LC alignment [ 35 , 36 , 37 , 38 , 39 ]. For the first time, the alignment of the nematic liquid crystal 5CB on a pre-rubbed polyimide layer structured with LSFL was studied in [ 35 ], employing a UV Nd:YAG laser with nanosecond pulses.…”

“…Furthermore, the usage of HSFL generated on a conductive indium-tin oxide (ITO) layer as an aligning layer was studied in [ 38 ]. In addition, structuring titanium (Ti) layers with LSFL and the usage as an aligning layer for the orientation of LCs was investigated in [ 36 , 37 ]. Depending on the processing parameters, namely the laser pulse fluence, Φ, and scanning speed, υ , the properties of LSFL on titanium aligning layers were studied in [ 37 , 39 ].…”

“…In addition, structuring titanium (Ti) layers with LSFL and the usage as an aligning layer for the orientation of LCs was investigated in [ 36 , 37 ]. Depending on the processing parameters, namely the laser pulse fluence, Φ, and scanning speed, υ , the properties of LSFL on titanium aligning layers were studied in [ 37 , 39 ]. It has been shown that the structured Ti-layers additionally modified by polyimide layers can essentially increase the azimuthal anchoring energy (AAE), W φ , which is one of the main characteristics of the aligning layer [ 36 , 37 ].…”

“…Depending on the processing parameters, namely the laser pulse fluence, Φ, and scanning speed, υ , the properties of LSFL on titanium aligning layers were studied in [ 37 , 39 ]. It has been shown that the structured Ti-layers additionally modified by polyimide layers can essentially increase the azimuthal anchoring energy (AAE), W φ , which is one of the main characteristics of the aligning layer [ 36 , 37 ]. Unfortunately, the structured Ti-layers possess a low transparency [ 39 ].…”