Vertical alignment of liquid crystal on a-SiOx thin film using the ion beam exposure

Abstract

In this letter we demonstrate the vertical alignment of liquid crystal on inorganic thin film surfaces using the ion beam exposure. Nematic liquid crystal can be aligned vertically by the rotational oblique evaporation of a-SiOx thin films. However, the electro-optic switching behavior of liquid crystal along random directions results in disclination lines. By using the ion beam exposure, we can achieve highly uniform alignment without disclination lines. We found from x-ray diffraction and x-ray photoemission spectroscopy data that the vertical alignment can be achieved when x approaches 1.5 at the a-SiOx film surface. We have shown that the pretilt angle can be controlled by changing ion beam parameters, such as the ion beam energy, the angle of incidence, and the exposure time. We also have shown that a liquid crystal cell aligned vertically by the ion beam exposure exhibits the voltage-transmittance curve similar to that of a rubbed polyimide cell.

Silicon oxides as alignment surfaces for vertically-aligned nematics in photonic devices

“…These interactions determine the liquid crystal pretilt and polar anchoring energy of the cell. This affects crucial electrooptic factors [4,5], such as threshold voltage and response time of the device [6,7], which may be modified by varying different manufacturing process parameters [8][9][10][11].…”

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

“…The rubbing method is conventionally used to induce the alignment of LC molecules on a polyimide layer due to its simplicity [7][8][9]; however, this process degrades the surface quality of the alignment layer because of the direct contact between the rubbing machine fabric and the polyimide layer, which generates electrostatic charge and debris. Alternative methods based on noncontact processes have been studied, such as the ultraviolet (UV) photoalignment technique, [5,6,[10][11][12][13] oblique deposition, [14][15][16] and ion beam (IB) irradiation [17][18][19][20][21][22]; these methods induce few surface defects in the LC alignment layer relative to the rubbing method. Especially, IB irradiation is commonly used for both inorganic and organic materials.…”

“…Especially, IB irradiation is commonly used for both inorganic and organic materials. Previously, many researchers have investigated inorganic materials to replace conventional polyimide layers, including diamond-like carbon, [17] SiC, [18] SiO x , [19] ZnO, [20] Al 2 O 3 , [21] and SnO 2 . [22] In particular, ZnO films have been studied for use in LC alignment layers because of the stable and uniform LC alignment they allow, as well as the wide band gap of ZnO (3.37 eV).…”

Homogeneous liquid crystal alignment on poly(vinylidene fluoride-trifluoroethylene) films subjected to ion-beam irradiation

“…Various methods are used for LC alignment, including rubbed or photoaligned polymer films, [1][2][3][4][5] evaporated oxides, [6][7][8] selfassembled monolayers [9] and ion-beam (IB)-irradiated organic/inorganic films. [10][11][12][13][14][15][16][17] Mechanical rubbing has been widely used to provide topographical microgrooves that enable uniaxial LC alignment. However, the rubbing method has several problems, including electrostatic charges, debris and mechanical stress, which produce local defects and streaks, thereby resulting in degradation of the display resolution.…”