利用掃描式電子穿隧顯微鏡觀察銅薄膜電極上銦的電化學沉積以及銅銦合金的探討

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题名:	利用掃描式電子穿隧顯微鏡觀察銅薄膜電極上銦的電化學沉積以及銅銦合金的探討
作者:	鮑德;Pao,Te
贡献者:	化學學系
关键词:	掃描式電子穿隧顯微鏡;STM;銅;銦;電化學沉積;合金
日期:	2013-07-24
上传时间:	2013-08-22 11:40:03 (UTC+8)
出版者:	國立中央大學
摘要:	利用掃描式電子穿隧顯微鏡 ( in situ scanning tunneling microscopy，STM ) 與循環伏安法 ( cyclic voltammetry，CV ) 觀察銦 ( indium ) 於多層銅/鉑(111)電極與單層銅/鉑(111)電極上的電化學沉積，以及銦沉積後的銅銦合金探討。在pH 3下的0.1 M K2SO4 + 0.1 mM In2(SO4)3的溶液中，多層銅/鉑(111)電極上有由硫酸氫根的(√3 × √7) R19.1°結構所形成之波浪狀結構( moir? pattern )存在；當電位調整至-0.4 V時(對銀/氯化銀電極)，銦會優先於台階位置進行沉積，隨後繼續由外至內向平台延伸，最後形成一平整單層銦膜。單層銦的沉積由CV結果可知分為兩個階段，第一個階段為覆蓋度較低的結構，為(√37 × √37) R25.3°，隨後由於銦的持續沉積，造成覆蓋度上升，而產生第二階段的單層銦沉積；第二階段單層銦結構是由銦原子的三聚體 ( trimer ) 所構成的小白點組成，由覆蓋度的不同可以分為三種，分別為(√43 × √43) R7.6°、(10 × 10)以及(√13 × √13) R13.9°；而當電位到達-0.6 V時，第二層的銦便迅速沉積，且有因為第二層銦原子坐落位置不同而產生亮暗交錯的波浪狀結構。單層銅/鉑(111)電極上，於pH 3下的0.1 M K2SO4 + 0.1 mM In2(SO4)3的溶液中，有由硫酸氫根的(√3 × √7) R19.1°結構，當電位調整至-0.4 V時，銦會優先於台階位置以及硫酸氫根結構的區域邊界進行沉積，且沉積方式傾向一次沉積兩層，最後當電位達到-0.55 V時，銦膜便會完整鋪滿整個表面。銅銦合金的探討方面，由CV的結果得知，沉積多層銦後，不論銅膜的厚度，皆會產生銅銦合金。STM的實驗主要在說明電沉積銦和銅電極形成合金的時機，多層銅/鉑(111)的結果中，在含氯以及不含氯兩種條件下，進行單層銦的剝除，可以觀察到含氯條件下銦膜可以幾乎被完全剝除，不含氯條件下雖有類似未剝除區域存在，但由CV圖單層銦特徵峰尖銳且對稱的結果參照，未剝除區域應是銅尚未形成整齊排列的結果，因此單層銦膜並不會與多層銅/鉑(111)形成合金。單層銅/鉑(111)電極上的結果中，則是進行兩層銦膜的剝除，而可以觀察到當電位調整至-0.1 V剝除後，未剝除區域上出現銅的硫酸氫根結構，因此推論在沉積兩層的銦膜後，一定量的銅原子會進入銦層中而移動至最上層並蓋住銦原子，當最上層銦原子被剝除後，於銅原子下方的銦原子會較晚被剝除，而造成未剝除區域上出現硫酸氫根的現象，因此相對於多層銅/鉑(111)，單層銦膜會與單層銅/鉑(111)形成合金。 In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to examine the electrodeposition of indium on a copper thin film pre-deposited on a Pt(111) electrode in 0.1 M K2SO4 + 1 mM H2SO4 + 0.1 mM In2(SO4)3. A moir? pattern due to highly ordered Pt(111) - (√3 × √7) R19.1° - Cu + HSO4- structure was observed on the copper thin film. According to CV and STM results, Underpotential deposition (UPD) of indium proceeded in two stages, which started at the lower ends of steps and grew onto terraces at -0.4 V (versus Ag/AgCl). A (√37 × √37) R25.3° structure was found at the first stage, but disappeared with more indium deposit. The second stage of UPD indium yielded three structures, (√43 × √43) R7.6°, (10 × 10) and (√13 × √13) R13.9°. At -0.6 V, the second layer of In grew rapidly, forming ripple – like stripes. The different sites which the second layer atoms sit was the reason of the stripes. To study In deposition on monolayer of Cu thin film on Pt(111), in situ STM was used to reveal the ordered (√3 × √7) R19.1° - Cu + HSO4- structure. Indium nucleated mainly at step sites and at domain boundaries of the ordered HSO4- structure at -0.4 V. Indium deposit tended to grow in two layers at the same time. Despite many defects were present in the In deposit, they was eventually annealed at -0.55 V. To study surface alloying of copper and indium, the anodic peak at 0.2 V could reveal the strip of Cu/In alloy after OPD indium deposition with CV diagrams. However, the sharp and symmetric UPD indium peak illustrate that no alloying effect between UPD indium and copper thin film. In STM images, we focused on the result of indium thin film stripping. Not all multilayer In deposit was stripped off from the Cu thin film in pH 3 sulfate media, which contrasts with complete removal of In deposit in chloride – containing solution. We inferred that the residue was aggregate of randomly arranged copper atoms. On monolayer Cu thin film, In deposit could displace Cu atoms and formed surface alloy. In other words, In could disperse in the first and second atomic planes on the Pt(111) support. Indium atoms in these two layers could be stripped off simultaneously. The moir? structure due to HSO4- appeared on the residue after stripping indium layers at -0.1 V. Because the Cu adlayer had rather different morphology before and after the deposition of In bilayer, it is concluded that mixing between In and Cu occurred under the present conditions.
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