掃描式電子穿隧顯微鏡對苯胺、己烷基雙硫醇及苯硫酚分子在金電極上的研究; In Situ Scanning Tunneling Microscopy of Aniline, 1,6-Hexanedithiol and Thiophenol adsorbed on Gold Electrode

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题名:	掃描式電子穿隧顯微鏡對苯胺、己烷基雙硫醇及苯硫酚分子在金電極上的研究;In Situ Scanning Tunneling Microscopy of Aniline, 1,6-Hexanedithiol and Thiophenol adsorbed on Gold Electrode
作者:	方宣尹;Hsuan-Yin Famg
贡献者:	化學研究所
关键词:	金(100);金(111);1，6 -己烷基雙硫醇;苯胺;苯硫酚;Au(111);Thiophenol;Hexanedithiol;Aniline;Au(100)
日期:	2004-06-18
上传时间:	2009-09-22 10:12:19 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文分為三個部份，第一部主要利用掃描式電子穿隧顯微鏡(in situ scanning tunneling microscopy , STM)及循環伏安法(cyclicvoltammetry , CV)探討單結晶金(111)電極，在含苯胺的硫酸溶液中，在未達苯胺氧化聚合的電位前，分子在金(111)電極上，所發生的電化學過程與吸附層的空間結構。電化學電位主導分子吸附層的覆蓋度、吸附位向與空間排列結構，在含低濃度的苯胺溶液中，在0. 7、0.72 及0.95 V 分別形成三吸附層，結構為(?21 × ?43)、(2?13 × ?19)及(4 × 3)，覆蓋度為0.088、0.11 及0.125，當電位愈正分子覆蓋度愈高。三者的排列位向皆以氮原子上的孤對電子鍵結在金(111)面上。受電場作用影響，分子中的苯環與金表面成一傾斜角位向排列，當電位愈正其愈傾向於垂直。 CV圖出現兩對可逆的尖細的相轉變峰，由 STM圖可證實其為在電位誘導下，分子排列轉變為不同結構所形成的相轉變峰，且其形成的分子吸附層具有可逆性。在含10 mM 苯胺溶液中形成覆蓋度更高的分子吸附層，在0.53 V形成(4 × 2?3)結構，θ = 0.25。第二部分利用 in situ STM檢測1,6-己烷基雙硫醇(HDT)吸附在單結晶金(111)電極上的空間結構。在負電位下，在含低濃度的 HDT的過氯酸溶液中，金(111)電極表面分子未達飽和吸附時，形成少部分的(2 × ?7)結構，分子以雙硫彎曲的形式吸附，及主要的(4 × ?3)單硫吸附結構；隨溶液中 HDT濃度增加，電極表面吸附分子達飽和覆蓋度，在0.3~0.5 V分子皆以單硫吸附形成(4 × ?3)結構，θ = 0.25 及排列更緊密的錯排結構，在0.5 V後則形成不規則的吸附結構。第三部分使用 in situ STM研究苯硫酚吸附在單結晶金(100)電極上的空間排列結構及表面重構的現象。經苯硫酚修飾的金(100)電極表面，受自組裝分子頭端硫與金原子形成的化學吸附力，與有機部份苯環側面的 π-stacking作用力，使金(100)表面產生明顯的重構，在0.5~0.7 V表面產生由分子聚集吸附所形成的島狀物，其分子結構為(?2 × ?2)，θ = 0. 5，分子主要以硫端吸附在金表面上，苯環與載體呈一傾斜角排列。 Abstract This thesis is divided into three parts. First, we employed cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) to study the spatial structures of aniline on the reconstructed and unreconstructed Au(111) in 0.1 mM aniline + 0.1 M H2SO4. Depending on the electrode potential, three highly ordered adlattices are identified as the coverage increased with potential. Real-time STM imaging revealed the kinetics of two-dimensional phase transitions in the aniline adlayer. Order structures,(?21 × ?43) and (2?13 × ?19) of aniline are identified for the potential regions between 0.7 and 0.72 V respectively. Another structure of (4 × ?3) was observed between 0.9 and 0.95 V. The surface coverage of aniline increased from 0.088 to 0.11, then to 0.125 near saturation. In situ STM imaging revealed that these phase transitions were reversible with respect to potential. When [aniline] > 10 mM, STM discerned an ordered array, (4 × 2?3). This adlayer has a coverage of 0.25 , much higher than those formed at lower concentration. Second, high-resolution scanning tunneling microscopy (STM) has been used to examine the real-space structures of 1,6-hexanedithiol (HDT) on well-ordered Au(111) electrode in 0.1 M HClO4. The concentrations of HDT in the aqueous dosing solutions, together with electrochemical potential, determine the coverage and spatial arrangements of HDT ad-molecules. Low dosages result in two order structures, (2 × ?7), θ = 0.167 and (4 × ?3), θ = 0.25. The former is assigned as a monolayer of dithiols adsorbed via two sulfur headgroups. The latter is assigned as dithiols adsorbed via only one thiol group. High dosages respectively resulted in (4 × ?3), θ = 0.25 and some more densely packed structures at 0.3 ~ 0.5 V, which suggested a stand-up configuration of the ad-molecules. Third, We have employed in situ STM to study the structures of benzenethiol and the reconstruction of well-ordered Au(100)-(hex) electrodes in 0.1 M HClO4. When dosage is low at 0 V, ordered Au(100)-(hex) surface was transformed into Au(100)-(1 × 1) structure with monoatomic high mesas. STM molecular resolution revealed the formation of a highly ordered adlattice of (?2 × ?2) , θ = 0.5, between 0 ~ 0.5 V on Au(100) - (1 × 1). The adlayer consisted of stand-up benzenethiol molecules bonded to gold surface through the Au-S coordination. Intermolecular interaction of benzenethiol molecules is attributed to π-π stacking of phenyl groups. The interaction of Au-S and lateral π-stacking produced island features on terraces, a phenomenon associated with severe etching of Au(100) surface, and aggregations of more benzenethiol ad-molecules at 0.6 ~ 0.7 V.
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