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研究生:楊柏儒
研究生(外文):Bor-Ru Yang
論文名稱:以掃描探針顯微術研究電致發光高分子在奈米尺度下的光電特性
論文名稱(外文):Nanoscale Optoelectronic Properties of EL Polymer Investigated by SPM
指導教授:林鶴南
指導教授(外文):Heh-Nan Lin
學位類別:碩士
校院名稱:國立清華大學
系所名稱:材料科學工程學系
學門:工程學門
學類:材料工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:英文
論文頁數:55
中文關鍵詞:導電高分子奈米光電掃描探針顯微術原子力顯微術近場光學顯微術
外文關鍵詞:conducting polymernanooptoelectronicSPMAFMSNOM
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本實驗以導電性原子力顯微術與近場光學顯微術研究奈米尺度下電致發光高分子MEH-PPV的表面形貌對光電特性的影響。其中,導電性原子力顯微術藉由施加偏壓於導電探針上來同步取得地表對電流分佈的影像,並進一步對特定區域量測定點的電壓對電流曲線,再藉由空間電荷限制電流傳輸理論與Poole-Frenkel定律將我們得到的電壓對電流的關係轉換成Poole-Frenkel圖形,並算出其零電場之遷移率與電場係數。而近場光學顯微術則用來量測表面形貌對光強度的分布。
在電性分析方面,掃描結果顯示,電流的分佈並不均勻,有些突起的地方電流值比較大。計算結果指出,突起且有大電流的地方之電場係數與其他論文所報導的相符合,而零電場之遷移率則比巨觀量測結果大了三個數量級,推測其可能原因有二:一是因為在微小尺度下的高分子鏈的能量差異較小,故傳輸較為容易;另一個可能性則為突起處的高分子鏈間交互作用程度較高,使得載子在鏈與鏈之間傳遞較為容易。
此外,重複施加偏壓於不同的溶劑製作而成的樣品,我們發現其結果並不相同。對MEH-PPV溶解度較佳的氯仿所製成之試片在重複掃描之後導電度越來越好,而以甲苯為溶劑之試片在重複掃描之後則越來越差。此結果顯示在溶解性較好的溶劑中,重複加偏壓時,會使得高分子鏈伸展,而增加鏈與鏈之間的交互作用,使得載子的傳輸更為容易。
在光性分析方面,我們分別以雲母與氧化銦錫玻璃為透明基板,旋塗上溶於氯仿的MEH-PPV溶液。掃描結果顯示,在以雲母為基板的樣品,其表面形貌突起之處光較不易透過;而以氧化因錫玻璃為基板的樣品,其突起之處有些地方光反而比較容易通過。推測其原因可能是高分子鏈的排列構造不同對光的穿透性造成影響。
本實驗技術可用來分析電致發光高分子表面形貌對電流和光強度的分佈,並可進一步地藉由重複施加偏壓來對微小的特定區域做電性的改變。
We report nanoscale morphological influences on optoelectronic properties investigated by conducting atomic force microscopy (CAFM) and scanning near-field optical microscopy (SNOM). The CAFM is operated with positive tip bias to get synchronously topography and current images. Furthermore, we use CAFM to measure local I-V curve and transform these data into Poole-Frenkel plot by space charge limited current (SCLC) theory and Poole-Frenkel (P-F) law. The SNOM is used to acquire synchronously topography and optical transmission intensity images.
The CAFM scanning results indicate the current distribution is not homogeneous. It should be noted that some bumps with high current comparing to other region. We measure the local I-V curve and figure out the zero-field mobility and electric coefficient by P-F plot. The calculated electric filed coefficient is consistent to many reports of macroscopic measurement. However, the zero-field mobility is 3 orders of magnitude to macroscopic results. It can be attributed to two reasons: one is that the energy deviation is smaller on nanoscale; the other is that the high current bumps have higher extent of inter-chain interaction. These two reasons make carriers conduct more easily from chain to chain which makes mobility enhanced.
Besides, we prepared MEH-PPV in the different solvents and spin coated them on gold films. As repeat scanning on chloroform prepared sample, the current becomes higher with the times of scanning increasing. But the current of toluene prepared sample becomes smaller. These phenomena indicate the good solvent prepared and gold film based samples have higher extent of inter-chain interaction.
The synchronously optical transmission intensity and topography images are obtained by SNOM. We prepare MEH-PPV in chloroform on two kinds of transparent substrate. The one is ITO glass and the other is mica. The results show that the high bumps on mica based sample have low optical transmission rate. But some high region on ITO based sample has high optical transmission rate.
Our experimental results indicate that different solvents and different substrates generate different morphology. And this makes polymer chain conformation altered accompanying conjugation length elongated or shortened. The conjugation length of electroluminescent polymer influences optoelectronic properties very much. Thus, by this technique, we can change local optoelectronic properties on nanoscale.
Chapter 1 Conducting Polymer Nowadays
1. 1 Discovery of conducting polymer
1. 2 Polymer light emitting diode development
1. 3 Polymer transistor research
1. 4 Terminology of conducting polymer technology
1. 5 Basic optoelectronic principles of PLED
1. 6 Motivation: Enhance polymer mobility by nanoscale investigation
Chapter 2 Carrier Conduction and Recombination in Polymer
2. 1 Carrier injection
2. 2 Carrier transport
2. 3 Recombination and radiation
2. 4 Inter-chain transport influences
Chapter 3 Scanning Probe Microscopy on Polymer
3. 1 Overview of scanning probe microscopy technique on polymer research
3. 2 Conducting atomic force microscopy operation principle
3. 3 Near-field scanning optical microscopy operation principle
Chapter 4 Experiment
4. 1 Sample preparation
4. 2 nanoscale electric measurement by CAFM
4. 3 nanoscale optical properties studied by SNOM
Chapter 5 Results and Discussion
5. 1 Conduction behavior of aggregates
5. 2 Electrical annealing
5. 3 Optical behavior of aggregates
Chapter 6 Conclusion
Chapter 7 Future work
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