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ABSTRACT: The vertical alignment of liquid crystals having negative dielectric anisotropy on an amorphous silicon oxide (a-SiO(x)) thin film is the consequence of the anisotropic interaction between liquid crystals and a-SiO(x) thin films. To investigate the mechanism of the vertical alignment, we changed the physicochemical characteristics of alignment layers by controlling the composition, since the anisotropic interaction depends on the nature of both liquid crystals and an alignment layer. The variation of composition gives rise to a change in the polarizability, which is a simple measure of induced-dipole strength at the surface of the alignment layer. There is a critical transition point from planar to vertical alignment of liquid crystals, and it is the long-range van der Waals interaction that is responsible for the vertical alignment. The competition between long-range van der Waals interaction and short-range dipolar interaction were investigated and analyzed in terms of the interfacial energy between liquid crystals and an alignment layer.
Langmuir 06/2009; 25(14):8306-12. · 4.19 Impact Factor
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Jong Bok Kim,
Ju Ri Lim,
Jin Seol Park, Han Jin Ahn,
Min Jung Lee,
Sung Jin Jo,
Mihee Kim,
Daeseung Kang,
Se Jong Lee,
Youn Sang Kim,
Hong Koo Baik
Advanced Functional Materials 04/2008; 18(8):1340 - 1347. · 10.18 Impact Factor
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Jong Bok Kim,
Kyung Chan Kim, Han Jin Ahn,
Byoung Har Hwang,
Jong Tae Kim,
Sung Jin Jo,
Chang Su Kim,
Hong Koo Baik,
Chu Ji Choi,
Min Kyoung Jo,
Youn Sang Kim,
Jin Seol Park,
Daeseung Kang
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ABSTRACT: The authors fabricated a no-bias pi cell using a dual alignment layer with an intermediate pretilt angle via a rubbing. In the dual alignment layer system, the competition between crest region favoring the vertical alignment and trough region favoring planar alignment made it possible to achieve various pretilt angles, and adjusted pretilt angle from 90° to 20° with rubbing. In addition, as the intermediate pretilt angle plays a role in eliminating the activation energy and thus allowing formation of the initial bend state in pi cell fabrication, this approach achieved a no-bias pi cell for a liquid crystal display with both low power consumption and fast response.
Applied Physics Letters 07/2007; 91(2):023507-023507-3. · 3.84 Impact Factor
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ABSTRACT: The authors demonstrate the production of amorphous fluorinated carbon (a-C:F) thin film with adjustable wetting properties, inducing variable liquid crystal (LC) pretilt angles. To control the surface wetting properties, they apply a dual radio frequency magnetron system with a controlled power ratio of targets. In this manner we obtain various compositional surfaces with fluorine and carbon components and adjust the surface energy with regard to the various compositions. Whereas the fluorine-rich a-C:F layer shows a preference for homeotropic (vertical) LC alignment, the carbon-rich a-C:F layer shows a planar LC alignment. To achieve uniform LC alignment with a proper pretilt angle, an accelerated Ar+ ion beam irradiates the films after the deposition process. The ion beam selectively destroys the surface bonding of the a-C:F films, yielding an intermediate pretilt angle.
Applied Physics Letters 06/2007; 90(25):253505-253505-3. · 3.84 Impact Factor
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ABSTRACT: The authors introduce variable liquid crystal (LC) pretilt angles via ion beam (IB) irradiation of silicon carbide (SiC) layers of various compositions. To control the composition of the SiC layer, the authors altered the rf power ratio between the graphite target and silicon target. The pretilt angle of the silicon-rich SiC layer was constant regardless of IB irradiation angle; however, the carbon-rich SiC layer showed variable pretilt angles, depending on IB irradiation angle. The authors attribute variable pretilt angle to the competition between van der Waals interactions, favoring the vertical alignment, and pi-pi interactions, favoring the LC alignment parallel to IB direction.
Applied Physics Letters 02/2007; · 3.84 Impact Factor
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ABSTRACT: The mechanism of liquid crystal (LC) alignment has been investigated during the last few decades for inorganic materials as well as for organic materials; however, it has not been clearly confirmed for some alignment materials. Inorganic alignment materials such as amorphous silicon oxide (a-SiOx) and hydrogenated amorphous silicon oxide (a-SiOx:H) are deposited on indium tin oxide (ITO) films on glass by reactive sputtering deposition. After deposition, the inorganic alignment materials are irradiated using an Ar+ ion beam (IB) for LC alignment. On the basis of the experimental results, a-SiOx films deposited by the sputtering do not align the LC, but a-SiOx:H films treated with varying IB energies, IB incident angles, IB doses, and IB irradiation times have excellent alignment properties and electrooptical properties, identical to those of polyimide (PI). These results imply that inorganic alignment layers irradiated by IB can be adopted as an LC alignment layer instead of rubbed PI. Additionally, hydrogen plays an important role in LC alignment because of the difference in alignment properties between a-SiOx films and a-SiOx:H films. We investigate the mechanism of IB-treated inorganic alignment layers and suggest that LCs are aligned by chemical effects, such as van der Waals interaction, more than by physical effects, such as morphology effects, in the inorganic alignment layer irradiated by IB.
Langmuir 12/2005; 21(24):11079-84. · 4.19 Impact Factor
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ABSTRACT: Homogeneous and homeotropic orientations of nematic liquid crystal (NLC)
are investigated on various inorganic thin films which are exposed to Ar
ion-beam. It is the novel investigations which results in a completely
dry processing technique for both the thin film deposition and alignment
steps. In the case of homogenous alignment on diamond-like carbon (DLC)
layer, optical band gap and the polar surface energy are investigated in
order to elucidate the alignment mechanism by ion beam (IB) irradiation.
We elucidate the role of surface polarity in DLC films with respect to
the LC orientation. On the other hand, FDLC thin films are selected by
homeotropic alignment layer with regard to the relationship between
surface tension and LC orientation. Selected pretilt angles in the range
of 71.1-89.8° can be easily obtained with ion beam
irradiation. It is sensitively changed by thin films composition and the
angle of ion beam irradiation.
Japanese Journal of Applied Physics 05/2005; 44:4092. · 1.06 Impact Factor
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ABSTRACT: a-C:F thin films with varying fluorine content were prepared by plasma CVD and the sputtering method as inorganic alignment layers for overcoming the disadvantages of conventional liquid crystal (LC) alignment layers. The material and structural properties were investigated by X-ray photoelectron spectroscopy, Fourier transform infrared absorption, and contact angle measurement. For elucidation of the liquid crystal alignment layers, LC cells with a-C:F films were fabricated, followed by examination of the textures of the LC and electro-optical characteristics. The fluorine concentrations of a-C:F films were controlled by changing the mixture gas ratio (RG) in CVD and applied power ratio (RP) in the sputter system. An increase in RG and RP led to increase fluorine incorporation, and the film microstructure changed from a diamond-like to a polymer-like structure. In addition, the sputtered a-C:F films showed a higher fluorination than the CVD sample since the PTFE target was only composed of CF2 functional groups. Surface composition influenced the surface energy of thin films and an extremely hydrophobic property was obtained in the case of fluorine-rich a-C:F films. LC orientations were observed in various compositions of a-C:F films, and the vertically self-aligned LC textures confirmed that a sputtered a-C:F film is a good candidate for an alignment layer without any post-treatment.
Diamond and Related Materials.
