- 學位論文
電漿射束處理含氫非晶質碳膜的液晶配向
Liquid crystal alignment on hydrogenated amorphous carbon films treated by plasma beam scanning
摘要
本篇論文係探討電漿射束處理含氫非晶質碳膜的液晶配向機制。利用電容式電漿系統沈積均勻及高透光度的含氫非晶質碳膜，經電漿射束處理後，含氫非晶質碳膜所組裝的液晶胞具有良好的液晶配向特性。研究主要以偏光顯微鏡及量測預傾角來檢視液晶配向特性，並藉由材料分析檢測含氫非晶質碳膜的特性，探討電漿射束處理與含氫非晶質碳膜的交互作用，以瞭解液晶分子在含氫非晶質碳膜上的配向機制。 由拉曼光譜檢測顯示，電漿射束能破壞含氫非晶質碳膜表面的化學鍵結，光電子能譜分析指出經電漿射束處理後，含氫非晶質碳膜表面的氧含量增加。由於被破壞的化學鍵結容易形成懸鍵，在含氫非晶質碳膜接觸大氣的過程中，大氣中的氧容易與非晶質碳膜表面的碳懸鍵形成碳氧鍵結，導致氧含量增加。經電漿射束處理的非晶質碳膜，再以氫氣電漿束鈍化碳膜的懸鍵，能減少碳氧鍵結，導致液晶的預傾角下降。非晶質碳膜表面的碳氧鍵結含量與液晶分子的預傾角有正相關性。 比較以傳統棉刷刮聚亞醯胺膜與電漿射束處理含氫非晶質碳膜的差別，經棉刷磨擦的聚亞醯胺膜具有均勻的液晶配向，以傳統棉刷刮含氫非晶質碳膜，液晶配向不均勻。由於含氫非晶質碳膜比聚亞醯胺膜更硬，傳統棉刷無法在含氫非晶質碳膜形成微凹溝或分子鏈的異向性。以電漿射束處理聚亞醯胺膜或含氫非晶質碳膜，皆具有均均的液晶配向特性，顯示微凹溝或分子鏈的異向性不是電漿射束的主要配向機制。 研究結果顯示電漿射束處理含氫非晶質碳膜的液晶配向機制主要為偶極力及化學鍵結異向性。電漿射束的掃瞄方向造成含氫非晶質碳膜表面的懸鍵具有異向性，懸鍵所形成的碳氧鍵結提供分子尺度的化學鍵結異向性，碳氧鍵結的偶極力及化學鍵結異向性造成液晶分子能整齊排列在碳膜表面上。
並列摘要
The mechanism of liquid crystal (LC) alignment on hydrogenated amorphous carbon (a-C:H) films pre-treated with plasma beam scanning was proposed in this thesis. The a-C:H films exhibit uniform and high optical transmission, which was prepared in a capacitively-coupled-plasma enhanced chemical vapor deposition chamber. The LC cells made of the plasma-beam-scanned a-C:H films exhibit excellent characteristics of LC alignment. The LC alignment was characterized by a polarizing optical microscope and the pretilt angles were measured using the rotation crystal method. Raman spectra and X-ray photoemission spectroscopy (XPS) were used to analyze the characteristics of plasma-beam-scanned a-C:H films. Raman spectra indicate that the plasma beam scanning process can break chemical bonds on the surface of an a-C:H film. The occurrence of bond-breaking on a-C:H films can generate some dangling bonds for the further formation of C-O bonds during air exposure. XPS data support both the formation of C-O bonds and the increase of oxygen content occured on the surfaces of plasma-beam-scanned a-C:H films. The dangling bonds generated from first plasma beam scanning can be passivated or erased by second hydrogen plasma beam scanning. The second hydrogen plasma beam scanning can reduce the C-O bonds and also the LC pretilt angles on a-C:H films. The C-O bonds on the surfaces of a-C:H films correspond to the pretilt angles of LC cells. The characteristics of LC alignment on Polyimide (PI) films and a-C:H films were compared by using mechanical rubbing and plasma beam scanning. The rubbed PI films exhibit uniform LC alignment. And poor LC alignment occurs on the rubbed a-C:H films. The rubbing process can not generate microgrooves or stretches of carbon chains on a-C:H films due to its high hardness. On the other hand, the PI films and a-C:H films exhibit uniform LC alignment after plasma beam scanning. The phenomenon implies that the mechanism of LC alignment is not microgrooves or stretches of carbon chains. The mechanism of LC alignment on plasma-beam-scanned a-C:H films is the dipole-dipole interaction induced from anisotropic chemical bonds. The scanning direction of plasma beam provides some anisotropic dangling bonds to generate anisotropic C-O bonds on the surfaces of a-C:H films. The dipole moment of C-O bonds and its anisotropy induces LC molecules to align on a-C:H films.