Chul Gyu Jhun

Alignment of liquid crystal on a polyimide surface exposed to an Ar ion beam

In this paper properties of nematic liquid crystals aligned on polyimide surfaces exposed to a low-energy Ar ion beam are investigated. We studied how the pretilt angle of a liquid crystal cell is affected by ion-beam conditions, such as the energy of the incident ions, the angle of incidence, and the exposure time. X-ray photoelectron spectroscopy data indicate that ion-beam exposure changes the chemical bonding states of the polyimide surface, which may be one of the main causes of anisotropic liquid crystal alignment. We also found that twisted-nematic cells fabricated by the ion-beam alignment method have the voltage holding time enough for application to thin-film-transistor liquid crystal displays.

Tristate liquid crystal display with memory and dynamic operating modes

So far, monostable and bistable liquid crystal display (LCD) modes have independently been researched and developed. The authors propose a tristate LCD that can be operated in memory mode as well as dynamic mode. The proposed device has a unique texture of splay, π twist, and bend states with applied voltages and is operated in memory mode or dynamic mode by selective switching of two states among them. They demonstrate switching characteristics of the tristate LCD. This tristate LCD has a long term memory time for memory mode as well as a fast response time for dynamic mode.

Simple method for measuring the high pretilt angle of nematic liquid crystals

Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°–20° and 70°–90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle.

Disclination velocity in bistable chiral splay nematic liquid crystal device

We investigate how miscellaneous parameters influence the velocity of the disclination line in a bistable chiral splay nematic liquid crystal (BCSN LC) device, using a model derived from the relationship of the free energy loss rate with dissipation energy. The disclination velocity is consistently coupled with the free energy difference between two stable states, rotational viscosity, and damping factor, in which the free energy difference is the most influential. The relationships between the energy difference and the parameters of the BCSN LC device were elucidated by examining the portrait of bistable curves. The calculated velocities of the disclination motion were also confirmed by comparing them with the measured results.

Optical Bouncing in Bistable Chiral Splay Nematic Liquid Crystal Device

We investigated experimentally and theoretically the switching behavior of the bistable chiral splay nematic liquid crystal (BCSN LC) device with a vertical field. We observed optical bouncing during a relaxation process. We found that the origin of this optical bouncing could be distinguished from those of the twisted nematic (TN) and chiral-homeotropic liquid crystal (CHLC) cells by analyzing the director profiles obtained from a numerical simulation. The origin of the optical bouncing was the twist transition from the bend state. The validity of our study was verified by showing that the optical bouncing can be precluded when the twist transition is suppressed and the bend state is maintained by an appropriate vertical field.

Double-Pulse Scan of Field Sequential Color Driving of Optically Compensated Bend Cell

We propose an overdriving method by double-pulse scan (DPS) within each subframe time. We applied this method to a field-sequential color (FSC) driving of a thin-film-transistor liquid crystal display (TFT-LCD) in the optically compensated bend (OCB) mode. We have shown by experiment that DPS shortens gray-to-gray response time remarkably so that FSC driving can be applied to amorphous silicon (a-Si) TFT-LCDs with extended graphics array (XGA) resolution.

Polyimide surface bombarded with Ar atomic beam

The alignment mechanism of a polyimide surface bombarded with an atomic beam is investigated. Atomic beam treatment of polyimide films allows a liquid crystal (LC) to align parallel to the beam direction. This alignment mechanism is demonstrated by the selective destruction of double bonds in polyimide. The optical retardation measurement using a photoelastic modulator (PEM) indicates that the in-plane crystalline order of the polyimide chain that occurred by rubbing is not created by atomic beam exposure. The atomic force microscopy (AFM) image of the polyimide surface modified by atomic beam exposure shows that its directional topography does not appear. The binding energy of core electrons of each element measured by X-ray photoelectron spectroscopy (XPS) describes the variation of the chemical bonding state on the polyimide surface exposed to atomic beam. These experimental results illustrate that LC alignment is achieved from the overlap of the p-orbitals of polyimide and LC.

Multidomain Structure for Infinite Memory Time of Bistable Chiral Splay Nematic Liquid Crystal Device

To embody an infinite memory time for the bistable chiral splay nematic liquid crystal (BCSN LC) device, we propose a multidomain structure in which a π/2 twist domain is formed around the BCSN LC device. We investigate how the multidomain structure of the BCSN LC device affects the propagation of a disclination line using a subpixel model. By analyzing the multidomain structure using the subpixel model, the free energy is minimized when the disclination line is located at the boundary between the two different domains. We also demonstrate experimentally that, by forming a π/2 twist domain around the pixel of the BCSN LC device, the propagation of the disclination line can be prevented and an infinite memory time can be achieved.

Optimal design of omni-directional viewing angle switching panel.

A viewing angle switching (VAS) panel used for the conversion of wide and narrow viewing angle has been demonstrated. Unlike the previous VAS panels, this one features a pair of same-handed circular polarizers and it is capable of switching the viewing angle omni-directionally from wide to narrow or vice versa by electrically controlling the birefringence effect of the LC layer which is sandwiched in between. To explain how it works, the design principle as well as the optimization of both wide and narrow viewing modes will be elaborated hereinafter.

Recent advances in holographic recording media for dynamic holographic display

Abstract An overview of the recent advances in the state-of-the-art holographic recoding media dedicated to the dynamic holography display is presented in this paper. Unlike the traditional holographic media, those materials enable the