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|Title: ||掃描式電子穿隧顯微鏡研究硫、錫及己烷基雙硫醇分子在銅(100)電極上的表面結構;The structure of Sulfide, Tin and 1,6-Hexanedithiol Overlayers on Cu(100) Electrode: An In Situ Scanning Tunneling Microscopy Study|
|Authors: ||洪詩惠;Shih-Hui Hung|
|Issue Date: ||2009-09-22 10:11:35 (UTC+8)|
|Abstract: ||摘要 本論文分為三個部分，第一部分研究在鹽酸及硫酸中，硫離子於銅(100)電極上的吸附情形：硫離子在酸性溶液中以HS-形式吸附於銅(100)電極上，由於吸附位向不同使表面原子顯現週期性的波浪起伏(moiré pattern)，結構為p(3?2 × 12?2)R45°，覆蓋度為0.305。在硫酸中隨電位的增加，硫離子的覆蓋度增加而形成硫原子團，然而在鹽酸中並無此結構形成，推測在鹽酸中氯離子可促進銅載體的溶解，使硫離子無法聚集形成硫原子團。硫離子在銅(100)電極上的吸附導致載體的重構，由於載體為紓解因硫離子吸附所產生的應力，將釋出部份銅原子而沉積於電極上形成島狀物，然而這些島狀物上仍然有硫離子的吸附，此重構現象導致銅(100)電極表面的粗糙化。 第二部分觀察在鹽酸及硫酸中，錫於銅(100)電極上的沉積：在鹽酸中，高規則度之氯離子吸附層，在電極上對於錫的沉積具有引導作用，錫沿著氯離子的密排方向沉積於銅(100)電極表面，首先形成Cu2Sn3的合金態，其結構為p(3?2 × ?2)R45°，由於銅錫原子間的立體效應，銅原子持續釋出，形成第二種合金態CuSn2，其結構為p(2?2 × ?2)R45°，當表層銅原子完全釋出，則形成(?2 × ?2)R45°的去合金態，覆蓋度為0.5。合金態轉變為去合金態的過程中，釋出的銅原子將再沉積於電極表面，此時錫的沉積由二維轉三維。硫酸中錫的沉積，由於缺乏氯離子的引導，錫原子間的作用力明顯大於載體與錫原子間的作用力，因此在硫酸中，錫的沉積以三維模式進行。 第三部分觀察1,6-己烷基雙硫醇分子在鹽酸中於銅(100)電極上的吸附情形：此雙硫醇分子在銅(100)電極上的吸附，以一端硫離子與電極鍵結，形成”之字形” 分子鏈狀結構(“zig-zag” chains)，簡單定義其單位晶格結構為c(6 × 2)，覆蓋度約0.33，然而”之字形” 鏈狀結構間的緊密程度卻有差異，隨時間並未觀察到其他規則的吸附結構。我們推測1,6-己烷基雙硫醇分子以一端硫離子與銅(100)電極進行鍵結，與表面傾斜某一角度，”之字形” 分子鏈狀結構可能來自於此一分子形成雙硫分子吸附於銅電極上。1,6-己烷基雙硫醇分子在銅(100)電極表面的吸附並無造成載體腐蝕或重構的現象。 Abstract In-situ electrochemical scanning tunneling microscope (EC-STM) has been used to examine layers of chloride and sulfide adlayers on ordered Cu(100) electrode surfaces. The adsorption of chloride anions from hydrochloric acid solutions, results in the formation of a well ordered c(2 × 2)-Cl adlayer and step faceting in the <100> directions of Cu(100). The adsorption of sulfide has been examined either in 0.1 M HCl or H2SO4, a moiré pattern of p(3?2 × 12?2)R45° with a coverage of 0.305 has been consistently observed between the potential range from -0.15 to 0 V. The atomic row of sulfur along the <100> direction was highly “buckled”. At positive potentials, the sulfide adlayers were gradually oxidized to form S8-like clusters in H2SO4, but such sulfur clusters were not found in HCl solutions. This difference was large associated with the existence of chloride anions. Sweeping potential positively initiated a phase transition of not only the adsorbate layer but also the substrate, thus the entire surface morphology was altered. Square and rectangular ad-islands and vacancy islands were produced, leading to a severe roughing of the copper substrate. In-situ STM was used to study Sn electrodeposition on Cu(100) in sulfuric acid solution. Nucleation of Sn seeds electrodepositon of Sn proceeded in a 3D growth mode (Volmer-Weber growth mode), as the Cu surface appeared to be rough. However, electrodeposition of Sn in hydrochloric acid solutions yielded p(3?2 × ?2)R45° and p(2?2 × ?2)R45° ordered surface structures. These structures are likely due to surface alloy phases, where rows of Cu and Sn adatoms differ by ca. 25%, a strain exists in the alloyed phase, and the strain is released by both lateral relaxation and bucklings within the layers. Finally, continuous deposition of Sn displaced Cu atoms in the uppermost layer, causing de-alloy and transform the ordered structure to (?2 × ?2)R45° with a coverage of 0.5. High resolution STM images were used to unravel the real-space structure of 1,6-Hexanedithiol (HDT) on well-ordered Cu(100) electrode in 0.1 M HCl. HDT seems to be strongly adsorbed on Cu(100), resulting in displacement of chloride with HDT molecules. STM revealed the transition from (?2 × ?2)R45° to local c(6 × 2). The latter likely associated with the adsorption of HDT, exhibiting zig-zag chains aligned along the <110> directions. Two neighboring protrusions within the zig-zag pattern are ca. 3.6 Å apart. This structure is tentatively attributed to the formation of sulfide molecules which are adsorbed vertically through the sulfur head-groups.|
|Appears in Collections:||[化學研究所] 博碩士論文|
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