利用掃描式電子穿隧顯微鏡研究 Cysteine betaine 在金(111)上之吸附結構

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题名:	利用掃描式電子穿隧顯微鏡研究 Cysteine betaine 在金(111)上之吸附結構
作者:	吳家樂;Wu,Chia-le
贡献者:	化學學系
关键词:	掃描式電子穿隧顯微鏡;半胱胺酸甜菜鹼;in situ STM;Cysteine betaine
日期:	2015-07-27
上传时间:	2015-09-23 10:47:34 (UTC+8)
出版者:	國立中央大學
摘要:	本篇論文主要分成兩個部分，第一個部分為cysteine betaine 自組裝在金(111)，依不同電位、陰離子、與pH值，觀察其吸附結構。在0.1M過氯酸、0.4~0.7V，cysteine betaine會以平躺的方式吸附，主要結構為(√21×√37)與(8×8)，覆蓋度為0.093。0.75V時，分子會形成如直立蜂窩狀(6×6)之結構，覆蓋度為0.083；0.8V後分子會有氧化的現象。而在0.1M硫酸0.3~0.5V條件下，會出現結構為(4×5)、覆蓋度為0.2的分子結構。由於硫酸氫根在正電位與分子有競爭吸附，導致在瞬間調整至0.7V時，分子會有雜亂的現象。再將電位調整回0.3V時，整齊結構又會出現，但會有不一樣的結構與覆蓋度，主要的結構為(√7×7)，覆蓋度0.19，相較於(4×5)，覆蓋度變低。0.6V時，分子吸附位向會變為直立、區塊小的結構，結構為(4√3×√21)、(√43×√21)，覆蓋度為0.055與0.059。而在電解液中添加0.3μM cysteine betaine分子的條件下，過氯酸與硫酸皆在0.3~0.5V的會有(4×5)與(√7×7)的結構，硫酸在0.3~0.5V另外出現低覆蓋度結構(8×5√3)與(4×3√3)，覆蓋度分別為0.0375與0.167；過氯酸在0.7V會出現直立結構(√21×12)與(4×4√3)，覆蓋度分別為0.133與0.125。在不同的pH的實驗中，分子會因為不同的pH值帶不同的電性，pH<4.36帶正電，pH>4.36帶負電。STM中在pH=3硫酸鉀電解液會在0.1~0.4V出現(4×5)的結構，覆蓋度0.2；在pH=7.7的PBS情況下，0.3~0.9V出現(√19×3√3) ，覆蓋度0.167。pH=10.9的硫酸鉀電解液，0.4~1V有(√7×7)覆蓋度0.19的主要結構。pH=12.67的PBS在0.7~1.2V出現(4×5)，覆蓋度0.2的結構。第二部分為聚苯胺正電位的分解與使用STM測量聚苯胺電導率的研究。在聚苯胺氧化分解方面，由CV圖中不論在厚層、薄層聚苯胺在0.9~1.4V區間，電流皆有遞減現象。在STM圖中，聚苯胺在0.92V會有彎曲分解現象，0.98V幾乎完全分解。在聚苯胺構型變化實驗中，硫酸聚合之聚苯胺要由彎曲變回直鏈構型需在0.88V，比硝酸與過氯酸更不易辦到(0.8V)。電導率方面，量測不同構型鹽式中間態聚苯胺：薄層聚苯胺0.4V > 0.6V > 0.8V；厚層聚苯胺 0.4V > 0.8V≥0.6V，得知此量測方法與薄膜的堆積緊密度有關，當薄膜排列密度越高電導度越差，反之越鬆散電導率越佳。 ;Two separate subjects are addressed in this thesis. Part I describes cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) results obtained with cysteine betaine adsorbed on a Au(111) electrode as a function of potential, anion and pH. In 0.1M perchloric acid, cysteine betaine was adsorbed mainly in stripe structures designated as(√21×√37) and((8×8) with a coverage (Ɵ) of 0.093 between 0.4 to 0.7V (vs. reversible hydrogen electrode). At 0.75V, these stripe structure transformed into a honeycomb-like structure characterized as (6×6), Ɵ = 0.083. Cysteine betaine molecule was oxidized at E > 0.8V. In 0.1M sulfuric acid, a structure(4×5), Ɵ = 0.2 consisted of betaine between 0.3 to 0.5V, but bisulfate anions competed with cysteine for adsorption on the Au(111) electrode, resulting in a pronounced order-to-disorder phase transition at 0.7V. This transition was quasi-reversible, as the stripe structure appeared again, once the potential was made to 0.3V. The main stripe structure became(√7×7) with a coverage of 0.19 at 0.3V, whose coverage is 5% lower than that of (4×5). At 0.6V, the stripe structure turned into two vertical structures(4√3×√21)and(√43×√21)with a coverage of 0.055 and 0.059 among a mainly disordered adlayer. To both perchloric acid and sulfuric acid, adding cysteine betaine 0.3μM resulted in stripe structures, (4×5) and (√7×7), between 0.3 to 0.5V. (8×5√3) and (4×3√3) structures (Ɵ = 0.0375 and 0.167) were found in sulfuric acid, which contrast (√21×12) and (4×4√3), (Ɵ = 0.133 and 0.125) in perchloric acid. Being a zwitterion ion, betaine is either positively charged or neutral when pH is lower or greater than 4.36. In pH3, 7, 10.9, and 12.67 media, in situ STM revealed (4×5),(√19×3√3)and(√7×7) and structures under proper potential control. Part II addresses the decomposition of polyaniline (PANI) at positive potential and the conductivity of PANI using STM. Regardless of monolayer or multilayer PANI, CV results show decomposition between 0.9 to 1.4V by CV. PANI chains shortened at 0.92V and vastly degraded at 0.98V. The reversibility of PANI’s conformation between straight and crooked forms in sulfuric acid were examined in nitric acid, sulfuric acid, and perchloric acid. The conversion from crooked to straight form occurred at 0.88V in sulfuric acid, as opposed to 0.8V seen in nitric acid or perchloric acid. The conductivity of different conformation PANI measured by STM. Results show that poor correlation between conductivity and anions and variation with potential, in particular, conductivity decreased with more positive potential.
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