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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/5942

    Title: 掃描式電子穿隧顯微鏡研究一氧化碳、硫、硫醇分子及氯在釕(001)上的吸附結構;In situ STM study of CO, Sulfur, Benzenethiol, Hexanethiol and Chloride on highly ordered Ru(001) electrode
    Authors: 歐陽良岳;Liang-Yueh OuYang
    Contributors: 化學研究所
    Keywords: 釕(001);電子穿隧顯微儀;循環伏安法;STM;Cyclic Voltammetry;Scanning Tunneling Microscopy;Ru(001)
    Date: 2003-06-20
    Issue Date: 2009-09-22 10:10:50 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 摘 要 本實驗主要探討釕(001)單晶電極表面在非超高真空下的電化學行為。將釕(001)置於充滿氫氣的密閉石英管中鍛燒後,利用循環伏安法(CV)觀察電極在0.1 M過氯酸溶液中的氧化還原圖。CV圖中兩對可逆的氧化還原峰分別代表釕電極上氫與氧的吸附脫附,與超高真空下的文獻比較後,我們證明此製備方法可以得到一個良好排列結構的釕(001)電極表面。 利用高解像的掃描式電子穿隧顯微儀(Scanning Tunneling Microscopy, STM)和循環伏安法(Cyclic Voltammetry)研究一氧化碳、硫、硫醇分子和氯離子吸附於釕(001)電極上的結構與變化。一氧化碳在釕(001)電極上形成的吸附結構依覆蓋度的不同可分成三種,低覆蓋度時20 ? 60個一氧化碳分子聚集成規則的島狀結構,並隨著時間的變化而移動,結構為(?7 ? ?7) R19.1?,覆蓋度為0.14。增加一氧化碳的覆蓋度導致兩種不同的結構,(?3 ? ?3)R30?與(2 ? 2),覆蓋度分別為0.33及0.75。 自我組合單層膜(self-assembled monolayers, SAMs)是目前熱門的研究主題之一,最常見的例子是硫醇分子吸附在金載體後,自然形成規則有序的單層分子薄膜。而以高活性的金屬來製備SAMs則是非常少,本實驗室研究硫、苯硫酚和己烷硫醇吸附於釕(001)電極。硫原子吸附於釕(001)會隨著電位由低電位往高電位產生(2 ? ?3) 、Domain wall和(?7 ? ?7) R19.1˚的規則結構,覆蓋度分別為0.5至0.57。苯硫酚與己烷硫醇在釕電極上吸附結構皆為(2 ? ?3),覆蓋度為0.5,由於烷基碳鏈分子間作用力的影響,其結構皆不會因電位改變而改變。但芳基硫醇分子間 ??????堆疊之凡得瓦作用力大於原子之間的凡得瓦爾半徑推斥力導致硫原子與苯硫酚於單位晶格內的吸附位置不同。 氯及溴陰離子吸附於金屬表面上,可影響釕金屬表面上原子的移動性,具有此種效應的金屬大都是原子之間具有較弱的金屬鍵結,如熔點低的金、銀、銅和鎳。本實驗室發現高熔點的釕(001)電極上於含氯及溴兩種陰離子溶液中,將電位定在0.1 V (vs. RHE) 時會發生載體原子的移動,使得電極上的平台產生位移,產生平台重構的現象,細部觀察其小範圍變化時,在0.4 V觀察到氯離子的吸附,其吸附結構為(?3 ? ?3)R30?,覆蓋度為0.33,往負電位位移至0.2 V時,則可發現氯離子開始脫附。 Abstract This study shows that annealing Ru(001) crystal in an airtight quartz cell purged continuously with hydrogen gas effectively order and clean the single crystal surface of Ru(001). Cyclic voltammetry and in situ scanning tunneling microscopy (STM) are used to examine carbon monoxide (CO) chemisorbed at well-defined Ru(001) electrodes. Three distinctly different structures are obtained in CO-containing 0.1 M HClO4 . At a low CO coverage of 0.14, we find that a (?7 ? ?7)R19.1˚ structure, which restructure to (?3 ? ?3)R30˚ as the coverage is increased to 0.33 ML. At a saturated coverage of 0.75, CO molecules are ordered into a c(2 ? 2)-3CO structure . High resolution (STM) imaging is used to unravel the real-space structures of sulfur atoms, 1-hexanethiol and benzenethiol on well-ordered Ru(001) electrodes in 0.1 M HClO4. Electrochemical potential plays a key role in controlling the coverage and structures. 0.6 V vs. RHE, atomic-resolution STM images several a (?7 ? ?7)R19.1˚-4S structure, ? = 0.57 ML. At ca. 0.1 - 0.3 V (vs. RHE), atomic-resolution STM rendered a (2 ? ?3)-2S unit cell, ? = 0.5 ML. Similarly, 1-hexanethiol and benzenethiol, are also adsorbed (2 ? ?3)-2S, ? = 0.5 ML. Specifically adsorbing anions, such as chloride and bromide, acts on surface defects, such as steps, kinks, adatoms, or vacancies, to result in marked changes in surface morphology. Notably, a mechanically polished Ru(001) electrodes, potentiostated at 0.1 V, gradually becomes smooth in 0.1 M HCl solution . Making the potential positive of 0.4 V (vs. RHE) produces a chloride adlattice arranging in (?3 ? ?3)R30˚. These change in the surface morphology of Ru(001) appears to proceed, via a step faceting/defaceting mechanism, assisted by the adsorbing anions of chloride and bromide. The high mobility of Ru atoms under these circumstance is currently an anomalous phenomenon.
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