液晶複合材料之特殊性質研究

在本論文中，我們研究液晶與CdSe半導體混合後的光電特性變化，以及利用液晶來操控金奈米柱的表面電漿共振頻率。從我們的研究中獲得了特別有趣的結果，而這些研究結果對於此類材料的應用將非常有用。這些研究成果主要包含： I. 利用CdSe半導體來驅動液晶在沒有外加電壓的情況下，我們提出一種利用雷射光來控制液晶的方法。在設計的裝置中，包含有特殊形狀的半導體以及液晶在其中。我們發現液晶的平均預傾角在改變雷射光強度後，受到相當的變化；而且其變化關係與預期的光伏效應相當符合。此外，產生的電場有垂直與水平分量，使我們能夠進一步控制液晶往任意方向變化。利用這個的方法，將可以設計光開關裝置。 II. 利用電場來操控金奈米柱的表面電漿共振頻率我們報導一種利用電壓來改變金奈米柱混合液晶後的電漿響應吸收光譜方法。在沒有施加電壓之前，觀察到金奈米柱沿著某個摩擦好的配向膜方向排好。而當我們轉動偏振片平行和垂直該方向時，金奈米柱的橫向共振模式分別顯示藍移與紅移；然而金奈米柱的縱向共振模式卻都顯示紅移。利用這個的方法，我們可以同時調控金奈米柱的橫向共振模式與縱向共振模式，而且可以設計顏色調控裝置。

關鍵字

液晶；半導體；硒化鎘；表面電漿子；金奈米柱

並列摘要

In this thesis we report the studies of optical and electrical properties on the composites based on liquid crystals, which include CdSe semiconductors and gold nanorods. Quite interesting results have been obtained from our studies, which are very useful for the understanding as well as application of these materials. They are presented as follows. I. Liquid crystals driven by CdSe semiconductor Schottky diode We report an approach of controlling liquid crystals using a laser beam without external bias. In our design, in addition to liquid crystals, a patterned semiconductor was also included. We discovered that the average pretilt angle of liquid crystals can be controlled by adjusting excitation power, and the relationship was found to follow the possible predicted photovoltaic effect. Besides, the photogenerated field was found to have both perpendicular and horizontal components, which is very useful to control the orientation of liquid crystals to an arbitrary direction. Optical switch devices can be possible to design using our method. II. Electrically controlled surface plasmon resonance frequency of gold nanorods We have presented the voltage-controlled tuning of plasmonic response of absorption spectra of gold nanorods in liquid crystals. We observe that gold nanorods can be aligned along the rubbed polyimide substrate before applying external voltage. It is found that the transverse mode of gold nanorods shows a blue shift and red shift when rotating the analyzer parallel or perpendicular to the rubbing direction, respectively, while all longitudinal modes display a red shift behavior. This work offers an easy way to tune the transverse and longitudinal modes of gold nanorods simultaneously, which makes it feasible to establish the color tunable devices.

並列關鍵字

liquid crystal ； semiconductor ； CdSe ； surface plasmon ； gold nanorod

參考文獻

References of Chapter 1

1. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, Oxford, 1993).

2. P. C. Yeh, and C. Gu, Optics of Liquid Crystal Displays (Wiley, New York, 1999).

5. G. H. Heilmeier and L. A. Zanoni, Appl. Phys. Lett. 13, 91 (1968).

6. G. H. Heilmeier and J. E. Goldmacher, Appl. Phys. Lett. 13, 132 (1968).

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液晶複合材料之特殊性質研究

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