聚亞醯胺發光二極體及奈米複合材料之合成與特性研究

Abstract

顯示和奈米科技是近年來不管在基礎學科或高科技產業中相當熱門的兩個課題。本論文將分成兩個部分，共七個章節，針對聚亞醯胺之發光二極體及奈米複合材料的特性 （2–5章），和一維奈米材料的製備兩個主題做深入的研究（6,7章）。

首先在第二章為BAO系列聚亞醯胺發光二極體特性研究。所有合成的BAO系列聚亞醯胺玻璃轉化溫度皆大於250℃，5 wt.-% 熱裂解溫度也大於510℃，顯示良好的熱安定性及機械性質。這些聚亞醯胺也均有螢光特性，而且螢光強度跟分子鏈的排列有密切的關係。進一步將合成之聚亞醯胺製作成單層發光二極體元件，只有BAO-ODPA和BAO-6FDA兩種聚亞醯胺觀察到電致發光性質，BAO-PMDA 和BAO-BPADA兩種聚亞醯胺可能因薄膜均勻性太差導致原件短路。另外，BAO-ODPA在雙層發光二極體元件中（ITO/PPV-PVA/PI/Al）也具有良好的電子傳輸及電洞阻障的功能，可將PPV-PVA發光效率提高兩個級數。

第三章為利用真空蒸鍍聚合製備以BAO-6FDA和BAPF-6FDA兩種聚亞醯胺為發光層之單層發光二極體。利用真空蒸鍍聚合，聚亞醯胺薄膜的厚度可降低至150 Å，兩種聚亞醯胺二極體元件也都表現出4.5V 和6.5V相當低的啟動電壓。經由原子力顯微鏡的分析，BAO-6FDA和BAPF-6FDA兩種聚亞醯胺薄膜皆有良好的表面平整度，分別為8.8 Å和4.7 Å。BAO-6FDA發光二極體具有較寬的電致發光頻譜，其範圍從400 nm 到700 nm。而BAO-BAPF發光二極體則表現出較佳的發光效率，這可能是因為較平衡的電子/電洞注入及較強的分子間電荷轉移作用。

第四章敘述聚亞醯胺/ZnO奈米混成膜的製備與特性。PMDA-ODA和BTDA-ODA兩種不同柔軟度的聚亞醯胺作為高分子基材進行研究。經由FTIR和XPS的分析，推斷ZnO表面的OH基和聚亞醯胺的C=O官能基會形成交鏈，進而提升混成膜的熱和機械性質。另外，穿透式電子顯微照片說明，ZnO奈米粒子分散在較剛硬的PMDA-ODA聚亞醯胺，粒子尺寸會大於分散在較柔軟的BTDA-ODA聚亞醯胺中。

第五章為利用蒸鍍/氧化二段法大量製備ZnO奈米單晶粒子於石英及聚亞醯胺基材上。蒸鍍後的Zn金屬在350℃熱風循環機進行氧化2小時，可完全轉變成透明的ZnO。經由高解析度TEM觀察，製備的ZnO奈米粒子為晶格規則排列的單晶結構，並無晶格缺陷，並顯示出一395 nm 的紫外光發光特性。

第六章敘述oleic acid/1-decanol/ammonium hydroxide 三相系統的inverse hexagonal (HII) 液晶相的製備與特性。HII相位於此三相圖的中央，由21/55/24, 28/27/45和62/5/33 (oleic acid/1-decanol/ammonium hydroxide) 三點組成的三角形區域。在此HII相區域中，隨著1-decanol含量的減少液晶消失溫度(isotropic temperature)變化從55℃到142℃。經由XRD分析，推斷製備的HII相的圓柱直徑為4−4.4 nm，內部水相直徑為1−1.4 nm。在此三相系統中，ammonium hydroxide的含量提高至45 wt.-%，及摻入多種金屬離子，如Ag+, Cu2+, Ni2+, Co2+, Zn2+, 和 Cd2+，皆不會破壞原本規則的HII相。

本論文第七章敘述利用先合成的管狀銀離子先驅物，在室溫下即時還原製備銀奈米電纜（nanocable）。經由FTIR分析，推論配位的銀離子錯合物形成交鏈，自身聚集，進而促成管狀先驅物的形成。此銀離子管狀先驅物長度達數微米，外徑為155−200 nm，徑/長比，管壁厚度為60−70 nm。經甲醛還原後，原本管狀先驅物的中空部份，均勻的被直徑30−45 nm的銀奈米線所填充，形成奈米電纜結構。還原條件，如還原劑濃度和還原方法，對於最後產物的型態有很大的影響。

Display and nano technologies are two hottest topics in recent years not only in academic research but in high-tech industry. This thesis is divided into two parts to investigate the characterization of polyimide (PI)-based light emitting diodes (LED) and nanocomposites (chapter 2−5), and the preparation of one-dimensional nanostructures (chapter 6, 7).

Chapter 2 describes the characteristics of a single layer and a double layer 2,5-Bis(4-aminophenyl)-1,3,4-oxadiazole (BAO)-based PI LED. All the resultant PIs possess high glass transition temperatures ( >250℃) and high decomposition temperatures of 5 wt.-% weight loss (Td, >510℃). They also show obviously fluorescent characteristic, and the intensity is related to the arrangement of the molecular chains. Electroluminescent (EL) spectra were detected when BAO-ODPA and BAO-4,4’-(hexafluoroisopropylidene)diphthalic anhydrid (6FDA) acted as an emitting layer in a single LED device. In addition, in the double layer LED device, ITO/PPV-PVA/BAO-ODPA/Al, BAO-ODPA can be used as an excellent electron transport and electron/hole blocking layer, a significant improvement in the EL efficiency by two order of magnitude.

In chapter 3 presents that BAO and 4,4’-(9-Fluorenylidene)dianiline ( BAPF ) reacting with 6FDA were carried out by using vapor deposition polymerization (VDP) for single layer LED devices. The thickness of the PI thin film can be reduced to 150Å, and both PI-LEDs show low threshold voltages, 4.5V and 6.5V for BAO-6FDA and BAPF-6FDA LEDs, respectively. The root mean square of the surface roughnesses of the BAO-6FDA and BAPF-6FDA PI thin films are 8.8Å and 4.7Å, respectively, which are far smaller than that of wet coating process. The BAO-6FDA LED film emits a broader EL band, covering the full range of visible light (400 nm to 700 nm), than the BAPF-6FDA LED. However, the electroluminescent efficiency of BAPF-6FDA LED is higher than BAO-6FDA LED. It may suggest the better balance on holes and electrons injection in the former and better intermolecular charge transfer.

Chapter 4 reports the study of a series of PI/ZnO nanohybrid films with different ZnO content, which prepared from a rigid pyromellitic dianhydride (PMDA)-4,4’-diaminodiphenylether (ODA) and a flexible 3,3’,4,4’-benzophenonetetracarboxylic acid dianhydride (BTDA)-ODA PI matrixes. Analyses of Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy depict that the ZnO nanoparticles function as a physical crosslinking agent with PI through hydrogen bonding between the OH on the ZnO surfaces and the C=O of the imide groups. This crosslink causes the enhancement of thermal and mechanical properties of the hybrid films. Transmission electron microscopy (TEM) images reveal that the rigid matrix induces larger ZnO particle size (30−40 nm) compared the flexible matrix (10−15 nm).

In chapter 5 describes the study of the evaporation/oxidation two-step approach to massive prepare ZnO nanocrystals on a quartz and a PI film by using a thermal coater and an air-circulating. ZnO crystals were formed via low temperature oxidization at 350℃ for 2h. TEM images show the singular ZnO nanocrystals have regular lattice order without stacking faults. Deposited ZnO on PI film substrates can obtain individual and well distribution nanocrystals with average crystal size is 20-30 nm after dispersing by an ultrasonic bath. In photoluminescence, the produced ZnO nanocrystals exhibit strong UV emission at 395 nm, and no visible emission was detected.

Chapter 6 presents the ternary system oleic acid/1-decanol/ammonium hydroxide exhibiting an inverse hexagonal (HII) liquid crystalline phase, which exists between the compositions 21/55/24, 28/27/45, and 62/5/33 (oleic acid/1-decanol/ammonium hydroxide). The isotropic temperature increases from 55 °C to 142 °C with decreasing 1-decanol content. X-ray diffraction reveals interdigitated columns of 4−4.4 nm diameter with an internal water channel of 1−1.4 nm diameter. The system can tolerate up to 45 wt-% of ammonium hydroxide before the hexagonal phase collapses and can be doped with up to 0.1 mM concentrations of metals such as Ag+, Cu2+, Ni2+, Co2+, Zn2+, and Cd2+.

Chapter 7 describes a simple and efficient method to in situ fabricate silver nanocables at room temperature from a self-assembling silver precursor. Properly control of the reaction condition, such as reagent concentration and method of reduction, is important to obtain well-defined nanocables. In addition, FTIR spectroscopy revealed the organic sheath to be crosslinked via bridging-type coordination to the silver ions, which helps in the formation of the tubular aggregation.