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

• Published in: Nanomaterials (Basel, Switzerland) Vol. 12; no. 3; p. 508
• Main Authors: Gvozdovskyy, Igor, Kazantseva, Zoya, Schwarz, Simon, Hellmann, Ralf
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.02.2022; MDPI
• Subjects: aligning layers; Alignment; Anisotropy; azimuthal anchoring energy; Crystal structure; Crystals; Energy; Femtosecond pulses; Homogeneity; Infrared lasers; laser-induced periodic surface structuring; Lasers; Light; Liquid crystals; Microscopy; Nematic crystals; nematic liquid crystals; Periodic structures; Periodicity; Polymers; Sapphire; structured sapphire layers; structured sapphire layers; laser-induced periodic surface structuring; nematic liquid crystals; aligning layers; azimuthal anchoring energy
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano12030508

In this study, we report on the alignment properties of nematic liquid crystals on various transparent structured sapphire layers formed by laser-induced periodic surface structures (LIPSS). One-dimensional LIPSS (1D-LSFL) are generated by infrared femtosecond laser pulses along parallel lines covering an area of 5 × 5 mm , with a line spacing that is varied between 7 and 17 µm. These periodic structures, employed as alignment layers, have a spatial periodicity of about 980 nm, a modulation depth of about 100 nm, and exhibit a high quality due to being characterized by a high degree of homogeneity and parallelism of the structured features. It is found that such alignment layers of the sapphire surface lead to a decreasing azimuthal anchoring energy, when the width of the unstructured gap is increased. Modifying the sapphire surface by an ITO-coating with further deposition of a polyimide film increases the azimuthal anchoring energy by a factor of about four up to ~ 4.25 × 10 J/m , when the minimum width of the unstructured gap is 7 µm. Comprehensive measurements and comparisons of the azimuthal anchoring energy as well as the pretilt angle for the 1D-LSFL, unstructured gaps, and entire areas depending on the width of unstructured gaps are presented and discussed.