| 摘要: | 摘要 Ⅰ. 有機硫醇分子修飾於鉑(111)、金(111)電極： 鉑(111)－利用掃描式電子穿隧顯微鏡(STM)檢測烷基硫醇(己烷基硫醇、壬烷基硫醇、十二烷基硫醇、及十八烷基硫醇)、芳基硫醇(苯硫酚、4-羥基苯硫酚)在單結晶鉑(111)電極上的空間結構。電化學電位主導吸附物的覆蓋度及它們在表面上的排列。當電位在0.1 ~ 0.3 V之間，視溶液中芳基硫醇分子的濃度而定，硫醇分子形成(2 × 2)和(?3 × ?3)R30°兩種結構，覆蓋度分別是0.25及0.33。本實驗之烷基硫醇分子均形成(2 × 2)結構，覆蓋度為0.25。在較正電位下，硫醇分子散亂地聚集成島狀結構，同時降低吸附分子之規則度。由於硫原子及有機硫醇分子均形成相同的結構，硫醇分子之末端硫原子和鉑載體之間的作用力主導分子吸附的最重要動力。 這些有機硫分子吸附層阻絕了鉑(111)和電解質的接觸，它們造成對苯二酚(H2Q)/苯醌(BQ)2 e-/2 H+ 的氧化還原反應速率明顯的遲滯，然而單層硫原子對此反應之動力學僅有些微影響。 金(111)－高解像STM結果顯示，在0.1 M HClO4溶液中以定電位方式吸附己烷基硫醇分子於金(111)上，可形成六種結構：(2?7 × ?57)、(7 × ?31)、(4 × 2?3)、(5 × ?19)、(?19 × ?31) 及(?13 × ?31)R85°，其覆蓋度介於0.1與0.19之間。而苯硫酚吸附在金(111)電極上，形成二種結構：(2?7 × ?31)及(?3 × ?21)，覆蓋度介於0.18與0.3之間。由於烷基和芳基之取代基造成完全不同的結構，可見分子間作用力為控制硫醇分子二維吸附結構的最重要因素。 Ⅱ. 芳基硫醇分子對鍍銅在鉑(111)電極上低電位沉積的影響 當鉑(111)電極上吸附單層之硫醇分子時，由於此分子膜具有阻絕的作用，銅的沉積選擇性的優先在分子膜中缺陷開始，這些位置上首先產生晶核。爾後，更多的銅原子加入晶核的周邊，促成晶核的二維成長，直到所有的鉑(111)面被覆蓋單層的銅原子。根據電化學結果，銅原子層在鉑(111)電極上之剝除電荷量並未受到硫醇分子膜的影響，因此銅原子之空間位置極可能是位於鉑和硫醇分子間，這和報導之銅在經硫醇修飾後之金(111)上的沉積過程完全不同，此時銅原子聚集而成三維的島狀特徵，而大部分有機分子被銅原子所掩蓋。因此有機分子之低表面能量並非引導銅原子沉積的最重要因素，至少對低電位電鍍(UPD)而言，金屬銅和載體的作用力可能是另一項同等重要的因素。 Ⅲ.二苯乙烯(stilbene)衍生物在各種過渡金屬上的自組裝單層膜結構 高解析STM結果顯示二苯乙烯衍生物在金(111)、鉑(111)、銠(111)電極上以不同的分子構形及二維結構吸附，不出所料，這些含有未飽和碳氫化合物以其π-電子和鉑及銠電極形成化學鍵結，因而以平躺方式吸附。但在金上，它們主要是以氮端和金載體形成σ-鍵，因此分子幾乎是直立的構形，就二維的空間排列而言，只有順式-4-胺基二苯乙烯在金(111)電極上形成兩種規則結構，分別是(7 × 3?19)、(2?19 × 3?19)R60°， 其覆蓋度為0.076及0.09。 Abstract Ⅰ.Alkanethiol and Arythiol Molecules on Pt(111) and Au(111) Pt(111)－This thesis is divided into three parts. First high-resolution scanning tunneling microscopy (STM) has been used to examine the real-space structures of alkanethiol (1-hexanethiol, 1-nonanethiol, 1-dodecanethiol, and 1-octadecanethiol) and arylthiol (benzenethiol and 4-hydroxybenzenethiol) on well-ordered Pt(111) electrodes in 0.1 M HClO4. The concentrations of organosulfur compounds in the aqueous dosing solutions, together with electrochemical potential, determine the coverage and spatial arrangements of these ad-molecules. For arylthiol, low and high dosages respectively result in (2 × 2), θ = 0.25 and (?3 × ?3)R30°, θ = 0.33 between 0.1 and 0.3 V. In contrast, all alkanethiol molecules examined in this study are adsorbed in (2 × 2) at a coverage of 0.25. The degree of ordering deteriorates substantially for all molecular adlayers at more positive potentials. The real-space structures of sulfur adatoms and organosulfur molecules are identical, suggesting the preponderance of surface bonding via the sulfur-ends of the ad-molecules. These organosulfur ad-molecules Pt(111) dramatically impede electron transfer of the 2e-/2H+ hydroquinone/benzo- quinone redox couple, whereas a monolayer of sulfur adatoms has little effect on the kinetics of this reaction. Au(111)－Hexanethiol molecules are adsorbed in six order structures respectively (2?7 × ?57)、(7 × ?31)、(4 × 2?3)、(5 × ?19)、(?19 × ?31) 及(?13 × ?31)R85°, θ = 0.18 ~ 0.2. Furthermore, benzenethiol molecules result in (2?7 × ?31)、(?3 × ?21) and (2 × ?31), θ = 0.18 ~ 0.33. Ⅱ. Cu electrodeposition on arylthiol-Pt(111) Underpotential deposition of Cu atom results in islands randomly nucleated at thiol modified Pt(111) electrode. Nucleation of Cu adatoms preferential occurs at defects within the arylthiol monolayer, followed by lateral expansion of the nucleation seeds upon addition of more Cu adatoms. A full Cu adlayer covered the whole surface at the end of deposition according to the electrochemical results, the SAM monolayer exerts little effect on Cu deposition , as the charges contained in the stripping peak are insensitive to the prescence of SAM. Copper adatoms are likely to displace hexanethiol molecules and bond to the Pt substrate directly. Ⅲ.Stilbene derivatives SAMs on transition metal We employed in situ STM to study the adsorption of stilbene derivatives onto Au(111), Pt(111), and Rh(111) in 0.1 M HClO4. Expectedly, these organic molecules are adsorbed with their molecular paralled to planes the surface of Pt and Rh, but at Au(111) surface bonding is formed through the N-ends of there molecules and they are mostly vertically oriented. |
