非接觸式配向層的製備與表面特性研究 ─離子束轟擊聚醯亞胺法和分子自組裝法

Abstract

液晶配向層（alignment）是LCD中重要的元件之一，隨著顯示器尺寸的上升和品質的要求，非接觸的配向技術逐漸取代傳統的刷膜配向方式。本研究內容主要分為兩個部份，分別是利用氬、氮及氫離子束轟擊（ion beam bombarded）聚醯亞胺薄膜，以及在類鑽碳表面成長矽烷分子自組裝（molecular self-assembled）薄膜，這兩種非接觸的配向方式製備液晶的配向層，並利用同步輻射X光近緣吸收微結構光譜（NEXAFS）及X光電子能譜（XPS）的技術，研究配向處理後薄膜表面的分子排列位向（orientation order）與化學結構組成（chemical composition）所產生影響。 研究結果顯示，PMDA-ODA聚亞醯胺薄膜在較低的離子能量轟擊下，會有較佳的鍵結異向性，以125 eV的氬離子束施予樣品51015 ions/cm2的暴露量後，可以得到最佳的配向效果；雖然氮離子處理之樣品配向效果不如氬離子，但氮離子束可在較寬的能量及暴露量範圍內，得到一定程度的配向效果；而氫離子束則是最不利於PMDA-ODA材料上的配向。在化學結構上，可以觀察到C=C及C=O鍵結有明顯的破壞情形，並且各元素間，是隨著入射的能量及離子數量選擇性的脫離表面。除了鍵結的破壞以外，也有C=N、N-O及-COO-等新的化學結構生成。 另外，我們也成功地在類鑽碳薄膜上成長3-Aminopropyl -triethoxysilane（APS）自組裝分子膜，並在進一步修飾1-Isothiocyanato-naphthalene（NIC）於APS分子末端， 利用NIC分子上naphthalene基團特定的排列位向，放大氫離子束轟擊配向的效果；最佳的處理條件為依序浸泡30分鐘APS溶液及2小時NIC溶液，而其表面上整體芳香環的雙色性比率（dichroic ratio）為氫離子束轟擊樣品的1.5倍。The liquid crystal alignment is an important issue in liquid crystal display (LCD). With the increasing of screen sizes, non-contact alignment techniques are developed to replace the conventional mechanical rubbing of polyimide film. Our research is divided into two main parts. The first part involves using argon, hydrogen, and nitrogen ion beams to bombard polyimde film with different ion energies and dosage to produce different alignment layers; the second part involves using naphthalene functionalized siloxane self-assemb on diamond-like carbon film. Using polarization-dependent near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectra (XPS), the planar and out-of-plane orientation order and chemical composition of the alignment surfaces are investigated. Our results show that the C=C and C=O bonds in PMDA-ODA polyimide films are selectively depredated depending on the energy level and dosage of the ion beam. In addition to bond breaking, new bonds – such as C=N, N-O, and –COO- – are formed after the ion beam treatment. As for the surface anisotropy, low energy treated PMDA-ODA polyimide have more preferential asymmetric alignment, especially in the case of argon ion bombardment with energy 125 eV and dosage 51015 ions/cm2. However, nitrogen ion bombardment shows the surface alignment in a large range of ion energy and dosage because its radius and mass is relatively small. The bombardment of hydrogen ion results in hydrogenation of the aromatic ring to form saturated alkanes and therefore, is not a good ion source for PI alignment. In the second part, we successfully modified diamond-like carbon (DLC) with 3-aminopropyl-triethoxysilane by the self-assembly method and grafted the naphthalene ring onto its terminal group. This procedure can amplify the alignment effect resulting from hydrogen ion beam bombardment (H-DLC). The optimal way of preparing such a surface is to immerse the H-DLC in 3-aminopropyl-triethoxysilane solution for 30 minutes and 1-Isothiocyanato-naphthalene solution for 2 hours in sequence. The dichroic ratio of the aromatic ring on the resulting surface is 1.5 times of that without molecular attachment.