Argon (Ar) plasma beam scanning treatments were applied to modify the surfaces of polyimide (PI) films deposited on indium tin oxide glasses in favor of liquid crystal (LC) alignment. LC cells were filled with twist nematic LC (ZLI-2293) on the PI films (Chisso 5310) treated with Ar plasma beam scanning. LC alignment occurs for the as-scanned PI films. The modifications of the PI films were characterized by using atomic force microscope and X-ray photoemission spectroscopy. The grooving mechanism is considered not responsible for the LC alignment. The C 1s, N 1s, and O 1s core level spectra support that Ar plasma beam scanning can induce a bond-breaking process of C=O bonds to create available carbon dangling bonds for the re-formation of C–O bonds. A dipole field is generated through the re-formation of C–O bonds, which may favor the LC alignment via the dipole–dipole interaction.
Abstract— Novel anode layer plasma within minimum chamber space was developed for non‐contact alignment process. The plasma‐treated polyimide (PI) surface showed no particle contamination and no micro‐scratches. Surface morphology was investigated by using scanning electron microscope (SEM), an atomic force microscope (AFM), and X‐ray photoemission spectroscopy. The different oxygen‐to‐carbon ratio ([O]/[C] ratio) for XPS spectra indicated a composition change after plasma treatment. Surface pretilt angles were varied from 0 to 2.1° under different plasma exposure times. Finally, a prototype 20.8‐in. QXGA IPS‐mode gray‐scale medical liquid‐crystal display was successfully demonstrated with high contrast ratio, excellent uniformity, and wide viewing angle using this new plasma‐beam‐alignment technique.
The liquid crystal alignment of fluorinated amorphous carbon (a-C:F) films which were deposited on the indium tin oxide (ITO) glass have shown to be improved by plasma beam processing. The experimental results indicated that excellent alignment characteristics regarding the range of pretilt angles and the alignment uniformity in a-C:F alignment films were improved by using the H2/Ar plasma beam processing. In this study, measurements of a-C:F film properties and liquid crystal (LC) cell characteristics were performed to investigate the relationship between the ratio of H2/Ar gaseous mixture and the LC alignment characteristics. The use of different gases allows enhanced control of the final surface chemical and physical properties. It was observed from the atomic force microscopy (AFM) results that the ion bombardment of films has a minimal impact on the alignment properties. Moreover, the X-ray photoemission spectroscopy (XPS) results showed that the H2/Ar plasma beam processing induces bond-breaking and chain scission. The results also indicated that the C–F bonds are broken by Ar+ and H radicals, while the benzene rings have carbon dangling bonds for the formation of C–O bonds in a-C:F films. Finally, the F/C ratio of a-C:F films was observed to be controlled by the H2/Ar ratio and the pretilt angles could be obtained from measurements of LC cells shown on a-C:F films.
The hydrogenated amorphous carbon (a-C:H) films on indium tin oxides (ITO) glass treated with Argon plasma beam scanning exhibited liquid crystal (LC) alignment. No apparent microgrooves appeared on the as-scanned a-C:H film surface observed by atomic force microscope. The pretilt angle depended on the scan direction, which was about 6 -7 for forward scan and about 2 -3 for both backward and ''forward + backward'' scans. The total surface energy of the as-deposited and the as-scanned a-C:H films were measured by contact angle measurements and calculated by the Owens-Wendt (OW) method in order to obtain the corresponding dispersive and polar surface energies. The surface of a-C:H films scanned forwardly is more polar than that for other two scan modes, which also exhibited higher pretilt angle. X-ray photoemission spectroscopy (XPS) spectra were used to characterize the O/C ratio on the a-C:H film surface. The relative amount of C-O bonds for forward scan was higher than those for other two scan modes. The scan-direction dependent property such as pretilt angle was attributed to the divergent character of the Ar plasma beams out of the anode layer source. The correlation of O/C ratio to pretilt angle for the as-scanned a-C:H films for different scan direction is discussed.
The oxygen plasma post‐treatment was adopted for alignment preparation in Ar plasma alignment process. The light leakage at the dark state was suppressed by the new treatment. The NEXAFS data suggested that the out of plane carbonyl groups have been regenerated under oxygen plasma post‐treatment. The polar anchoring energy was two times increased comparing to the Ar treated PI. The cell's EO properties by new plasma treatment were comparable to the rubbed PI surface.
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