Sang Bok Jang

Homogeneous self-aligned liquid crystals on wrinkled-wall poly(dimethylsiloxane) via localised ion-beam irradiation

We demonstrate self-aligned liquid crystals (LCs) using a wrinkled-wall polydimethylsiloxane (PDMS) wrinkle structure, which is a key factor to obtain a stable homogeneous alignment state with positive LCs. We constructed the wrinkled walls via localised surface exposure to IB radiation, which passed through a long length localised pattern mask. The creation of the wrinkled wall helped to align the LC molecules homogeneously because the wrinkled wall acted as a guide for the arrangement of positive LC molecules. In addition, we confirmed the stability of the alignment state as the width of the wrinkled wall was changed. Although this wrinkled-wall method is a non-contact method, LC alignment is achieved via an anisotropic topographical guide, which provides the LC molecules with stable homogeneous alignment.

Homogeneous Liquid Crystal Alignment on Ion Beam-Induced Y 2 Sn 2 O 7 Layers

Y2Sn2O7 nanoparticle layer fabricated by ion beam (IB) irradiation after annealing is reported here. Spherical particles were induced after IB irradiation as demonstrated by field emission scanning electron microscopy. When this layer was used as an alignment layer, homogeneous alignment of nematic liquid crystals (LCs) was observed with a small pretilt angle due to van der Waals interactions between LCs and the Y2Sn2O7 layer and interactions between benzene rings of the LCs and broken chemical bonds. The resulting electric-controlled twist nematic cell showed excellent electrical-optical properties, indicating that our approach holds great potential for creating commercial LC displays (LCDs).

Homogeneous alignment of liquid crystals on low-temperature solution-derived gallium oxide films via IB irradiation method

ABSTRACT In this paper, solution-derived gallium oxide (GaO) films are fabricated for the homogeneous alignment of liquid crystals (LCs) after an ion-beam (IB) irradiation process. GaO thin films are prepared under a variety of temperatures and different IB irradiation intensities, and the physicochemical performances of the fabricated GaO thin films are analysed using a UV-vis spectrometer, an atomic force microscope, and X-ray photoelectron spectroscopy. A higher transmittance of 85.40% from GaO thin film is obtained compared with that of polyimide (PI) film (83.52%), which indicates the feasibility for a GaO thin layer to substitute for a conventional PI layer as an alignment layer. LCs are found to align on the GaO thin film after pre-baking at 100°C and homogeneous and uniform low-IB intensity irradiation. We also determined the electro-optical (EO) characteristics of the twisted nematic (TN) cells fabricated with GaO thin layers and found them to be similar to those of cells fabricated with PI layers. Overall, GaO films achieved via the IB irradiation method are promising LC alignment layers due to the method’s low-temperature solution-derived process. GRAPHICAL ABSTRACT

Effect of the annealing temperature and ion-beam bombardment on the properties of solution-derived HfYGaO films as liquid crystal alignment layers

Hafnium yttrium gallium oxide (HfYGaO) films were applied to liquid crystal displays (LCDs) as liquid crystal (LC) alignment layers, replacing conventional polyimide (PI) layers. The HfYGaO alignment layers were prepared by fabricating solution-processed HfYGaO films, annealing them, and treating them with ion-beam (IB) irradiation. The authors studied the effects of annealing temperature and IB irradiation of the solution-derived HfYGaO films on the orientation of LC molecules. The LC molecules on the solution-derived HfYGaO films were homogeneously and uniformly aligned by IB irradiation, irrespective of the annealing temperature. Atomic force microscopy analyses revealed that the surface reformation of the HfYGaO films induced by IB irradiation strengthened the van der Waals force between the LC molecules and the HfYGaO films, leading to uniform LC alignment. Enhanced electro-optical characteristics were observed in the twisted-nematic (TN) LCDs based on IB-irradiated HfYGaO films compared with those of TN-LCDs based on PI layers, demonstrating the high application potential of the proposed solution-derived HfYGaO films as LC alignment layers.

Alignment of liquid crystals on solution-processed HfZnO films via ion beam irradiation

Liquid crystal (LC) alignment layers were prepared by fabricating solution-processed HfZnO films, annealing them, and treating them with ion beam (IB) irradiation, and the effect of annealing temperature upon the resulting film properties was studied. Homogeneous LC alignment was achieved on IB-irradiated HfZnO films. Topographical changes were observed from field-emission scanning electron microscopy as annealing temperature increased. X-ray photoelectron spectroscopy analysis showed that IB irradiation resulted in oxidation of HfZnO surfaces, which caused the LCs to be oriented more uniformly. The best electro-optical characteristics observed corresponded to the annealing temperature of 200°C. The low optimal annealing temperature for fabricating the HfZnO films suggested that this material has remarkable potential for LCD applications.

Unidirectional alignment of liquid crystals on solution-derived hafnium tin oxide films via ion-beam irradiation

We demonstrated the performance of solution-derived hafnium doped tin oxide films annealed at various temperatures via ion-beam irradiation. The Hf:SnO2 films were employed as liquid crystal alignment layers, which were deposited from solution to replace sputtering methods. Homogeneous and uniform liquid crystal alignment was achieved at all annealing temperatures, yielding a high-performance liquid crystal system. Field-emission scanning electron microscopy revealed the surface characteristics of the hafnium doped tin oxide films at various annealing temperatures, and various surface phenomena were observed. High-performance electro-optical properties were observed for the twisted nematic LC cells of hafnium doped tin oxide films annealed at various temperatures. The lowest threshold voltage (2.042 V) and fastest response time (8.494 ms) were achieved at an annealing temperature of 200 °C. Our results revealed the potential of solution-derived hafnium doped tin oxide films as liquid crystal alignment layers.Graphical Abstract

Twisted nematic LC mode with high electro-optical performance and high thermal endurance formed using IB-irradiated poly(methyl methacrylate) as an alignment layer

ABSTRACT We obtained homogeneously aligned liquid crystals (LCs) on ion beam (IB) irradiated poly(methyl methacrylate) (PMMA) by controlling the IB energy. We then examined the LC alignment state using polarized optical microscopy and conducted thermal stability testing. We obtained homogeneous LC alignment at IB energies above 1,400 eV, indicating that strong IB energy facilitates the alignment of LCs on the PMMA surface. This surface was analyzed by atomic force microscopy, and the contact angles (CAs) were measured to elucidate the mechanism of LC alignment. The increased surface energy strengthened the van der Waals interaction between the surface and LCs, thereby inducing stable, homogeneous LC alignment. Electro-optical (EO) characteristics were measured using twisted nematic (TN) LC mode. Compared to LC cells with conventionally used rubbed polyimide (PI), the LC cells with IB-irradiated PMMA exhibited higher thermal budgets and good electro-optical characteristics. These new LC cells have promising potential for advanced LC displays.