隨著現今科技的發展，液晶技術日趨成熟，於智慧型窗戶應用的技術中，早有多種液晶散射光閥已成功被開發，最著名的為聚合物分散型液晶(Polymer Dispersed Liquid Crystals, 縮寫為PDLC)，其多數利用照射UV光或加熱使單體聚合而引致液晶與聚合物發生相分離，並藉由外加電壓得到散射態和穿透態的切換。值得一提的是一般散射型液晶光閥須持續外加電壓方能維持其穿透度，換言之即造成能源的浪費，因此雙(多)穩態散射型液晶光閥的研究便受到相當的重視。
本論文提出利用電控動態手紋結構(Dynamic fingerprint chiral textures)製作一雙(多)穩態散射型液晶光閥，根據實驗結果，利用外加不同頻率的電場可在穿透態及散射態之間作切換，且在電場關閉後仍能維持永久穩定的穿透態及散射態，此動態手紋結構為本論文首先提出。本論文將分別討論(1)動態手紋結構的定義及其切換機制、(2)電控動態手紋結構的光電特性及(3)相關材料特性比較及其生成穩態的原因。其主要散射機制為利用外加高低頻交流電場切換動態手紋結構之區塊大小，外加高(低)頻交流電場可得較大(小)區塊之動態手紋結構而得穿透態(散射態)，此外，由穿透態切換至散射態所需的電場振幅隨頻率降低而減小；反之，由散射態切換至穿透態所需的電場振幅隨頻率增加而減小。除關閉電壓後其穿透度可持續穩定外，該散射型光閥之散射能力與入射光偏振無關，且其穿透態無如上述PDLC有視角的限制。因此，本論文所提出之散射型液晶光閥具有可電控、永久穩態、廣視角、高對比及低操作電壓等特性，相信能在實際應用上有相當的潛力，如顯示器、電子書及電子紙等。

Liquid crystal (LC) technology is getting maturer and maturer nowadays due to its technological development. Many scattering mode LC light modulators are adopted to the application of smart windows. Among them, polymer dispersed LCs (PDLCs) is the most famous technique for such applications. Regarding the fabrication processes, phase separation of LCs and polymers by illuminating with UV light or heating is the most important approach. Additionally, the switching of the light modulator between transparent and scattering modes by applying an external electric field is also achieved. However, most of the scattering mode LC light modulators consume too much power to be suitable for practical application due to the continuous application of electric field. Restated, it causes large power consumption. Accordingly, bistable and multi-stable scattering mode LC light modulators have been paid much attention recently.
This study presents an electrically switchable and permanently stable scattering mode LC light modulator by dynamic fingerprint chiral textures (DFCT). According to the experimental results, stable transparent and scattering modes can be switched between each other after an electric field with different frequencies is applied. To the best of our knowledge, electrically switchable DFCT is demonstrated for the first time in this system. In this thesis, the following three parts, including (1) the definition of DFCT and its electric switching mechanism, (2) the electro-optical properties of electrically switchable DFCT, and (3) the comparison of the electro-optical properties between the other chiral materials and the causes for stabilization of DFCT, will be discussed in detail. Briefly, the main mechanism is the switching between large and small domains of DFCT by applying an electric field with different frequencies. With the application of electric field having high (low) frequency, the LC light modulator presents transparent (scattering) state due to the formation of large (small) domains of DFCT. Besides, the required amplitude to switch the light modulator from a scattering (transparent) state to a transparent (scattering) state decreases as the frequency of the applied electric field increases (decreases). In addition to the permanent stabilization after the applied field is switched off, such a LC light modulator has some other advantages, such as polarization-independent scattering, unlimited viewing angle in transparent mode, and others. Consequently, this study presents a scattering mode LC light modulator with the advantages of electrical switching, permanent stabilization, wide viewing angle, high contrast, low driving voltage, and so on. Considering the practical applications of LC devices, it is believed that such novel textures, DFCT, can be adopted to develop displays, e-books, e-papers, etc.

[1] G. H. Heilmeier, L. A. Zanoni, and L. A. Barton, “Dynamic scattering：A new electrooptic effect in certain classes of nematic liquid crystals,” Proc. IEEE 56, 1162 (1968).
[2] B. Bahoadur, Liquid crystals-applications and uses (World Scientific Press, 1990).
[3] F. Reinizer, “Beitrage zur kenntiniss des cholesterins,” Monatsh. Chem. 9, 421 (1888).
[4] O. Lehmam, “On flowing crystals,” Z. Phys. Chem. 4, 462 (1889).
[5] P. J. Collings, and Michael Hird, Introduction to liquid crystals chemistry and physics, (Taylor ＆ Francis Ltd, 1997).
[6] S. Chandrasekhar, “Recent developments in the physics of liquid crystals,” Contemp. Phys. 29, 527 (1988).
[7] E. G. Virga, Variational theories for liquid crystals, (Chapman & Hall London, 1994).
[8] I. C. Khoo, and S. T. Wu, Optics and nonlinear optics of liquid crystals, (World Scientific, 1993).
[9] O. Francescangeli, S. Slussarenko, and F. Simoni, “Light-induced surface sliding of the nematic director in liquid crystals,” Phys. Rev. Lett. 82, 1855 (1999).
[10] M. Marinelli, and F. Mercuri, “Effects of fluctuations in the orientational order parameter in the cyanobiphenyl (nCB) homologous series,” Phys. Rev. E 61, 1616 (2000).
[11] H. Keller, “History of liquid crystals,” Mol. Cryst. Liq. Cryst. 21, 1 (1973).
[12] G. W. Gray, Thermotropic liquid crystals, (the Society of Chemical Industry 1987).
[13] W. H. de Jeu, Physical properties of liquid crystalline materials, (Gordon & Breach, 1980).
[14] 松本正一，角田市良，液晶之基礎與運用 (國立編譯館, 1996).
[15] P. Yeh, and C. Gu, Optics of liquid crystal displays, (John Wiley ＆ Sons, Inc., 2006).
[16] G. R. Fowles, Introduction to modern optics, 2nd ed., (University of Utah, 1975).
[17] P. G. de Gennes, and J. Prost, The physics of liquid crystals, (Oxford University Press, 1993).
[18] L. M. Blinov, and V. G. Chigrinov, Electrooptic effects in liquid crystal materials, (Springer-Verlag Publishing Co., 1994).
[19] M. Hara, H. Takezoe, and A. Fukuda, “Forced Rayleigh scattering in nCB's (n=5-9) with methyl red and binary mass diffusion constants,” Jpn. J. Appl. Phys. 25, 1756 (1986).
[20] V. Fréedericksz and A. Repiewa, “Theoretisches und experimentelles zur frage nach der natur der anisotropen flüssigkeiten,” Zeitschrift fur Physik 42, 532 (1927).
[21] R. B. Meyer, “Effects of electric and magnetic fields on the structure of cholesteric liquid crystals,” Appl. Phys. Lett. 12, 281 (1968).
[22] M. Gu, ““cholesteric” in the world of liquid crystal displays,” retrieved from http://www.personal.kent.edu/~mgu/ (2011).
[23] S. T. Wu, and D. K. Yang, Reflective liquid crystal displays, (John Wiley ＆ Sons Ltd, 2001).
[24] A. Y. G. Fuh, C. H. Lin, and C. Y. Huang, “Dynamic pattern formation and beam-steering characteristics of cholesteric gratings,” J. Appl. Phys. 41, 211 (2002).
[25] 林啟湟，膽固醇手紋結構液晶薄膜及其應用之研究 (國立成功大學物理研究所, 2002).
[26] P. Rudquist, L. Komitov, and S. T. Lagerwall, “Volume-stabilized ULH structure for the flexoelectro-optic effect and the phase-shift effect in cholesterics,” Liq. Cryst. 24, 329 (1998).
[27] 李學文，穩定型橫向螺旋膽固醇液晶光柵之研究，(國立中山大學光電工程學系, 2012).
[28] C. T. Wang and T. H. Lin, “Bistable reflective polarizer-free optical switch based on dye-doped cholesteric liquid crystal,” Opt. Mat. Express 1, 1457 (2011).
[29] W. Helfrich, “Conduction-induced alignment of nematic liquid crystals：basic model and stability considerations,” J. Chem. Phys. 51, 4092 (1969).
[30] E. Dubois-Vilette, P. G. deGennes, and O. Parodi, “Hydrodynamic Instabilities of nematic liquid crystals under AC electric fields,” J. Physique 32, 305 (1971).
[31] Orsay Liquid Crystal Group, “Hydrodynamic instabilities in nematic liquids under AC electric fields,” Phys. Rev. Lett. 25, 1642 (1970).
[32] P. G. deGennes, “Electrohydrodynamic effects in nematics,” Comments Sol. St. Phys. 3, 148 (1971).
[33] G. Mie, “Contributions to the optics of turbid media particularly of colloidal metal solutions,” Ann. Phys. 25, 377 (1908).
[34] G. H. Heilmeier and J. E. Goldmacher, “A new electric field controlled reflective optical storage effect in mixed liquid crystal systems,” Proc. IEEE 57, 34 (1969).
[35] G. Dir, J. Wyscocki, J. Becker, W. Haas, J. E. Adams, L. Leder, B. Mechlowitz, F. Saeva and J. Dailey, “Cholesteric liquid crystal texture change displays,” Proc. SID 13, 105 (1972).
[36] D. Meyerhofer, and E. F. Pasierb, “Light scattering characteristics in liquid crystal storage materials,” Mol. Cryst. Liq. Cryst. 20, 279 (1973).
[37] E. Jakeman, and E. P. Raynes, “Electro-optic response times in liquid crystals,” Phys. Lett. 39A, 69 (1972).
[38] T. V. Galstyan, V. E. Drnoyan, and S. M. Arakelian, “Self-induced oscillations and asymmetry of the light angular spectrum in a dye doped nematic,” Phys. Lett. A 217, 52 (1996)
[39] Y. C. Liu, K. T. Cheng, H. F. Chen and A. Y. G. Fuh, “Photo- and electro-isomerization of azobenzenes based on polymer-dispersed liquid crystals doped with azobenzenes and their applications,” Opt. Express 22, 4404 (2014).
[40] Z. F. Liu, K. Hashimoto, and A. Fujishima, “Photoelectrochemical information storage using an azobenzene derivative,” Nature 347, 658 (1990).
[41] X. Tong, M. Pelletier, A. Lasia, and Y. Zhao, “Fast cis-trans isomerization of an azobenzene derivative in liquids and liquid crystals under a low electric field,” Angew. Chem. Int. Ed. Engl. 47, 3596 (2008).
[42] T. Enomoto, H. Hagiwara, D. A. Tryk, Z. F. Liu, K. Hashimoto, and A. Fujishima, “Electrostatically induced isomerization of azobenzene derivatives in langmuir-blodgett films,” J. Phys. Chem. B 101, 7422 (1997).
[43] 黃琬翎，摻雜偶氮材料在藍相液晶中之光電特性 (國立成功大學物理研究所, 2011).
[44] S. M. Morris, M. Qasim, K. T. Cheng, F. Castles, D. H. Ko, D. J. Gardiner, S. Nosheen, T. D. Wilkinson, H. J. Coles, C. Burgess, and H. Lee, “Optically activated shutter using a photo-tunable short-pitch chiral nematic liquid crystal,” Appl. Phys. Lett. 103, 101105 (2013).
[45] 許維婷，液晶盒厚度量測方法的研究 (國立成功大學光電科學與工程研究所, 2004).
[46] C. T. Wang, W. Y. Wang and T. H. Lin, “A stable and switchable uniform lying helix structure in cholesteric liquid crystals,” Appl. Phys. Lett. 99, 041108 (2011).
[47] J. Geng, D. Chen, L. Zhang, Z. Ma, L. Shi, H. Cao and H. Yang, “Electrically addressed and thermally erased cholesteric cells,” Appl. Phys. Lett. 89, 081130 (2006).
[48] A. Y. G. Fuh, Z. H. Wu, K. T. Cheng, C. K. Liu, and Y. D. Chen, “Direct optical switching of bistable cholesteric textures in chiral azobenzene-doped liquid crystals,” Opt. Express 21, 21840-21846 (2013).
[49] 吳宗翰，摻雜光敏偶氮染料的全光控膽固醇液晶顯示器 (國立成功大學物理研究所, 2012).