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Liquid-crystal alignment on a-C:H films by nitrogen plasma beam scanning

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10 Author(s)
Wu, K.Y. ; Department of Materials Science and Engineering, National Tsing Hua University, Hsin-Chu City, Taiwan ; Chen, C.-H. ; Yeh, C.-M. ; Hwang, J.
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A plasma beam scanning treatment has been developed to modify the surface of the hydrogenated amorphous carbon (a-C:H) film on the indium tin oxide glass. The plasma beam scanning treatment makes the a-C:H film an excellent layer for liquid-crystal alignment. The qualities of a-C:H films were characterized by using atomic force microscope, micro-Raman spectroscopy, and field-emission scanning electron microscope. The ultrathin a-C:H films were deposited at 50% CH4/(H2+CH4) gas ratio, 100 W radio-frequency power, and a gas pressure of 10 mtorr for 15 min by capacitive-coupled plasma chemical-vapor deposition method. The twist nematic cells were filled with liquid crystal (ZLI-2293) on the a-C:H film treated with different nitrogen plasma beam scanning time. The grooving mechanism is considered not responsible for the liquid-crystal (LC) alignment. Raman spectra suggest that a bond-breaking process of aromatic rings occurs in the a-C:H film. The O1s, C1s, and N1s core-level spectra support that the nitrogen plasma beam scanning treatment induces a bond-breaking process of aromatic rings to create available carbon dangling bonds for the formation of CO bonds. T- he newly formed CO bonds are “directional,” which favor the LC alignment on the a-C:H film.

Published in:

Journal of Applied Physics  (Volume:98 ,  Issue: 8 )