利用掃描式電子穿隧顯微鏡研究併環?吩衍生物及紅螢烯於金(111)上之吸附行為

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題名:	利用掃描式電子穿隧顯微鏡研究併環?吩衍生物及紅螢烯於金(111)上之吸附行為
作者:	羅淑容;Luo,Shu Rong
貢獻者:	化學學系
關鍵詞:	掃描式電子穿隧顯微鏡;分子吸附;金(111)電化學界面;併環?吩;紅螢烯;In situ STM;Molecular adsorption;Au(111) electrified interface;Thienothiophene;rubrene
日期:	2013-07-24
上傳時間:	2013-08-22 11:39:57 (UTC+8)
出版者:	國立中央大學
摘要:	有機薄膜上分子的空間結構和排列位向，會影響分子與載體之間的電荷傳導，進而影響到有機薄膜電晶體(OTFTs)的性能。因此我們利用掃描式電子穿隧顯微鏡探討併環?吩衍生物和紅螢烯(rubrene)分子在金(111)電極上的吸附結構。首先，探討DFP-DTT (C6F5-DTT-C6F5) 於金(111)電極上的吸附行為及結構。對於DFP-DTT，在0.05~0.85 V電位區間時，吸附分子形成整齊的（5 × 4√3）結構，其覆蓋度為0.05。推測DFP-DTT分子中心的?吩(電子雲密度低為正端)會與另一列分子的全氟苯(電子雲密度高為負端)形成靜電吸引力，使分子間的極性降低，藉此種方式形成穩定結構。電位對DTT為主架構的分子來說，分子吸附層於金(111)電極上的吸附與脫附皆是可逆的反應。另外，發現藉電位控制FPP-DTT (C6H5-DTT-C6F5)分子，使分子在負電位(-0.2 V，對可逆氫電極)脫附後，再調整至正電位(+0.3 V，對可逆氫電極)，FPP-DTT分子可重新吸附於金表面並重新排列成整齊的二維結構。我們發現可藉此種電位控制使分子重新排列，分子吸附層的排列規則度有大幅度的改善，金電極面上單一分子區塊整齊結構的範圍由15 nm擴大至100 nm以上，且整齊結構可穩定的存在於0.05~0.7 V。有機分子中心以DTT為主體的三個分子(DP-DTT，C6H5-DTT-C6H5；FPP-DTT，C6H5-DTT-C6F5；DFP-DTT，C6F5-DTT-C6F5)，依各種不同比例混合發現，只有DP-DTT與DFP-DTT分子能產生共吸附（6√3 × 6√3）的結構，覆蓋度為0.0556。推測DFP-DTT分子兩端的全氟苯(電子雲密度較高為負端)會和相鄰的DP-DTT分子兩端的苯環(電子雲密度較低為正端)形成靜電吸引力，增加分子間的作用力，因此可更穩定的吸附在金(111)電極上。最後，探討紅螢烯(rubrene)於金(111)電極上的吸附行為及結構。紅螢烯分子會在金(111)表面形成規則度良好的整齊結構，低覆蓋度結構為(√3 × 10)，而高覆蓋度結構則為(√3 × 9)。在高覆蓋度的分子吸附層上，分子列上會有不明亮紋產生，推測這些亮紋是由金原子組成的排列，因為紅螢烯為一立體的分子，平整的金(111)表面可能並非最有利於紅螢烯分子的吸附，表面上突起的金原子列可能和扭曲的分子形成較佳的鍵結環境，導致分子更穩定的吸附在電極上。突起的金原子列可能來自於金表面的結構變化，或來自於台階缺陷。不論低覆蓋度或是高覆蓋度的紅螢烯單層膜，改變電位將造成紅螢烯分子吸附層不可逆的變化。 The orientation and spatial structure at metal electrode can affect the efficiency of charge injection at the molecular/metal interface and thus the performance of OTFTs. In situ scanning tunneling microscopy (STM) was used to reveal the spatial structures of thienothiophene derivatives and rubrene molecules deposited on Au(111) electrode. First of all, the structures of DFP-DTT(C6F5-DTT-C6F5) adsorbed on Au(111) electrode were examined. For DFP-DTT, it was found that these admolecules could form a long range ordered adlattice characterized as (5 × 4√3) with a coverage of 0.05. Presumably, it will form the attraction between the thienothiophene of the molecular center (electronpositive) and the two perfluorophenyl groups at the two ends of the DFP-DTT (electronegative) to compensate molecular dipole moments. However, the adsorption and desorption of the DTT-based molecules were reversible by potential control. In addition, the molecular adlayer of FPP-DTT (C6F5-DTT-C6H5) desorbed at -0.2 V, and then switching the potential to +0.3 V for the FPP-DTT molecules readsorbed on Au(111) electrode. After potential modulation rearranged the molecular adlayer, the order adlayer size and potential window were larger than molecular Self-Assembled Monolayer. The size along x-axis measuring of order structures was larger from 15nm to 100nm and the potential window was expanding from 0.05~0.2 V to 0.05~0.7 V. The molecular center was DTT-based for DP-DTT, FPP-DTT and DFP-DTT, it was mixed with different ratio to form coadsorbed structures. Only DP-DTT and DFP-DTT could coadsorb on Au(111), the structure as (6√3 × 6√3) with a coverage of 0.0556. Presumably, it will form the attraction between the two phenyl groups at the two ends of DP-DTT (electronpositive) and the two perfluorophenyl groups at the two ends of the DFP-DTT (electronegative) to compensate molecular dipole moments. Lastly, the structures of rubrene adsorbed on Au(111) electrode were examined. The rubrene molecules could form a long range ordered adlattice that characterized as (√3 × 10) and (√3 × 9) with low and high coverage, respectively. Noteworthy, we also could find some bright lines sat on those order arrays due to the special three-dimensional geometry of rubrene moleculars. These moleculars would distort themselves to match the size of gold adatoms and further to generate more stable conformation. However, the adsorption and desorption of rubrene molecules were irreversible by the potential control.
顯示於類別:	[化學研究所] 博碩士論文

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