Dae Shik Seo

Control of the wrinkle structure on surface-reformed poly(dimethylsiloxane) via ion-beam bombardment

We investigated the surface reformation of poly(dimethylsiloxane) (PDMS) elastomers by means of ion beam bombardment for fabricating wrinkle structures. Oxidation on the PDMS surface formed a silica-like outer layer that interacted with the inner PDMS layer, leading to the formation of wrinkle structures that minimized the combined bending energy of the outer layer and stretching energy of the inner layer. In addition, we controlled the amplitude and period of the wrinkle structures by adjusting the PDMS annealing temperature. As the PDMS annealing temperature was increased, the amplitude and period of the wrinkles formed by IB irradiation changed from 604.35 to 69.01u2009nm and from 3.07 to 0.80u2009μm, respectively.

Localized Ion-Beam Irradiation-Induced Wrinkle Patterns

We observe a localized irradiation-induced wrinkle pattern on poly(dimethylsiloxane) (PDMS) via a long pattern mask. Localized ion-beam irradiation induces an inhomogeneous wrinkle pattern on the treated region. To confirm the inhomogeneity of the entire wrinkle pattern, its morphology was investigated using optical microscopy, which revealed separated regions in the wrinkle pattern. We used atomic force microscopy for quantitative analysis of the wrinkle pattern morphology and analyzed the angular distribution and the direction of compressive stress of the irradiated area. We confirmed the direction of stress release along the distance from the edges, and we achieved control of the orientation of the wrinkle pattern by altering the width of the irradiated area. Investigation of the inhomogeneities in a localized wrinkle formation provides an understanding of the formation mechanism to enhance its performance and application in various fields.

Ion-beam-irradiated solution-derived tin oxide films for liquid crystal orientation

We present the alignment characteristics of liquid crystal (LC) molecules on solution-derived tin(IV) oxide (SnO2) films. Solution processing was used in place of the sputtering method to deposit SnO2 films as LC alignment layers. The LC molecules on the SnO2 surfaces could be homogeneously and uniformly aligned by ion-beam (IB) irradiation. X-ray photoelectron spectroscopy (XPS) analysis indicated surface reformation of the SnO2 films resulting from annealing and that IB irradiation affects the uniform LC orientation. Fast response times of twisted nematic cells constructed with IB-irradiated SnO2 films were observed, which indicates that the proposed IB-irradiated solution-derived SnO2 films have considerable potential for use in the production of advanced LC displays.

Homogeneous liquid crystal alignment characteristics on solution-derived HfYGaO films treated with IB irradiation

Solution-derived HfYGaO films have been treated by ion beam (IB) irradiation and used as liquid crystal (LC) alignment layers. Solution processing was adopted due to its simplicity, high throughput, and facile composition modification. Homogeneous and uniform LC alignment was achieved on the IB-irradiated HfYGaO films, and when these films were adopted in twisted nematic (TN) cells, electro-optical performance comparable to that of TN cells with conventional polyimide layers was achieved, with almost no capacitance-voltage hysteresis. Moreover, LC cells based on IB-irradiated HfYGaO films had a high thermal budget. The proposed IB-irradiated solution-derived HfYGaO films have considerable potential for use in advanced LC applications.

High Performance of the Electrically Controlled Birefringence Mode in Solution-Derived La2O3 Film Using Low Temperature

We demonstrated the electro-optical characteristics of multi-stacked solution-derived La2O3 films in low temperature. Uniform and homogeneous liquid crystal (LC) alignment was achieved, and the films showed high performance. The electro-optic characteristics of the electrically controlled birefringence (ECB) mode with La2O3 layers were comparable to layers derived from polyimide, which indicated that La2O3 film had potential as an alignment layer due to its low threshold voltage (1.70 V) and fast response time (3.17 ms). The LC alignment on the solution-derived La2O3 surfaces was attributed to Van der Waals forces between LC molecules and La2O3 films. X-ray photoelectron spectroscopy demonstrated that the number of layers of coating changed the chemical structure, thereby shifting the binding energy and altering the bonding intensity.

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.

Conductive Polyaniline for Potential Application in Anisotropic Conductive Films

Polyaniline (PANI) was investigated for use in bonding packages of flexible printed circuit boards (FPCB). The contact resistance of the anisotropic conductive film used in the current study was significantly lower than that of the PANI powder, with an average contact resistance of 0.47xa0Ω, as compared to 7.1xa0Ω for the PANI powder. Nevertheless, the suitability of PANI for conductive ball bonding was investigated via bonding of a FPCB, and the possibility for the use of PANI as the core polymer in conductive balls was determined by simulating the ohmic loss and signal distortion.

Vertically aligned liquid crystal mode on UV-cured reactive mesogen using imprinting method

We report a novel imprinting method employing an ultraviolet (UV) cured reactive mesogen (RM) hardened in a homeotropic orientation. During UV curing, selectively photopolymerized bonds were created and RM molecules were aligned vertically. Based on X-ray photoelectron spectroscopy (XPS) results, we confirmed than an increased atomic percentage of the alignment layer was made from the RM, which was UV cured using the imprinting method. The measurement of retardation showed the anisotropic nature of the imprinted substrates. Also, vertically aligned (VA) liquid crystal (LC) cells created by this imprinting method showed superior electro-optic (EO) properties as compared with the rubbing method.