Browsing by Author "Hu, Jia-Wei"

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Annealed zinc oxide films for controlling the alignment of liquid crystals
(2017-08-01)
Hu, Jia-Wei
;
Yang, Sheng-Hsiung
;
Jeng, Shie-Chang
;
光電系統研究所
;
照明與能源光電研究所
It is observed that the anchoring of LC molecules aligned on the ZnO film depends on the surface wettability. We demonstrate that the surface wettability of ZnO films fabricated by sol-gel process can be modified by annealing. The observations using the scanning electron microscope, photoluminescence and X-ray photoelectron spectroscopy for ZnO films have shown that the annealing can modify both the morphologies and chemical compositions of ZnO films, which in turn produces influences on the surface wettability. The surface wettability of as-prepared ZnO film can be controlled from 102 degrees to 60 degrees (contact angle (CA) of water) as the annealing temperature increases from 190 to 250 degrees C. Our experimental results show that the pretilt angles of LCs on ZnO films can be modified over a wide range from 89.5 degrees to 0.5 degrees as the CA of water on the ZnO films changes from 102 degrees to 60 degrees.
Broadband cholesteric liquid crystal devices with poly(N-vinyl carbazole) microstructures
(2015-01-02)
Hu, Jia-Wei
;
Chen, Tai-An
;
Jeng, Shie-Chang
;
光電系統研究所
;
影像與生醫光電研究所
The particular thermally induced phase separation (TIPS) method was developed by using poly(N-vinyl carbazole) (PVK) dissolved in liquid crystal (LC) layer recently. Permanent scattering is produced via the particular TIPS due to the formation of poly-domain LCs. In this work, we applied the particular TIPS to a conventional cholesteric LC (CLC) device. A broadband CLC device with a poly-domain structure was demonstrated by using the particular TIPS of CLC and PVK. The CLC device fabricated by two indium tin oxide glass substrates coated with PVK films generated the rough PVK layers and microstructures when the device was cooled from a temperature higher than the clear point of CLCs. The produced poly-domain planar texture of CLCs still preserved the bistability. A high cooling rate and PVK concentration both increased the reflection bandwidth of the CLC devices.
UV-treated ZnO films for liquid crystal alignment
(2016-01-01)
Hu, Jia-Wei
;
Yang, Sheng-Hsiung
;
Jeng, Shie-Chang
;
光電系統研究所
;
照明與能源光電研究所
The surface wettability of ZnO films prepared by a sol-gel process is altered from hydrophobicity to hydrophilicity via ultraviolet (UV) light irradiation. The results indicate that hydrophilicity of the ZnO films is enhanced along with the increase of UV irradiation energy. The measurements of X-ray photoelectron spectroscopy and photoluminescence show that the amount of oxygen vacancies in ZnO films is increased with the UV irradiation. The results of UV-vis absorption spectroscopy and X-ray diffraction also show that the crystalline quality of the ZnO films is slightly changed after UV treatment. The increase in oxygen vacancies means that water molecules can easily coordinate into the oxygen vacancy sites, leading to the increase of surface wettability. It is observed that liquid crystal (LC) molecules can be aligned on the UV-treated ZnO films, and the orientation of LCs on the UV-treated ZnO films can be tuned from homeotropic to homogeneous alignment by controlling the surface wettability of ZnO films. Our results show that the pretilt angle of LCs on ZnO films depends on their surface wettability, and it can be successfully adjusted over a wide range from 89.5 degrees to 0.5 degrees as the contact angle of water on ZnO films changes from 97 degrees to 60 degrees.