利用掃描式電子穿隧顯微鏡探討羧基硫醇分子對於銅沉積在金(111)上的影響

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題名:	利用掃描式電子穿隧顯微鏡探討羧基硫醇分子對於銅沉積在金(111)上的影響
作者:	賴招珊;Lai,Chao-shan
貢獻者:	化學學系
關鍵詞:	掃描式電子穿隧顯微鏡;循環伏安法;銅沉積;有機添加劑;scanning tunneling microscopy,STM;cyclic voltammetry, CV;copper deposition;organic additives
日期:	2014-07-25
上傳時間:	2014-10-15 14:37:34 (UTC+8)
出版者:	國立中央大學
摘要:	本研究利用循環伏安法(CV)和掃描式電子穿隧顯微鏡(STM)探討羧基硫醇分子於金 (111)上的吸附行為及其對銅沉積的影響。首先，分別對MAA (mercaptoacetic acid)吸附和MAA與銅離子共吸附於金(111)進行觀察，在MAA部分，吸附分子進行自組裝形成兩種結構，分別為(3 × √13)和(7 × √3)；在MAA和銅離子共吸附部分，表面一樣形成兩種結構，且MAA的末端官能基(–COO-)和銅離子間產生鍵結，而於分子列之間可以觀察到有亮紋和亮點存在。在銅沉積於經MAA修飾的金(111)上，發現MAA有助於銅的低電位沉積，與大部分硫醇分子對銅沉積是抑制的現象不同。當銅進行低電位沉積會優先從表面缺陷處和台階邊緣發生，過程中伴隨金島狀物產生，隨著時間鋪滿整個平台；在過電位沉積(-0.1V)時，銅島狀物層沿載體方向成長，銅層之間隨著時間會結合在一起，形成平整的表面，MAA分子被轉置於銅層上形成規則結構。此外，進一步探討氯離子對銅沉積的影響，與不含氯離子的硫酸下進行比較，一開始銅膜的成長會傾向2D模式，接著再以3D形式。經由STM觀察銅層剝除的過程，發現銅的剝除會從能量較高的台階邊緣開始，當銅剝除剩下約3~4層銅時，MAA的吸附會轉變成花紋狀結構，此花紋狀結構推測是MAA吸附於銅上，由於分子與銅原子大小不同造成，當銅完全剝除後，MAA會再吸附回金(111)上，由於覆蓋度的差異，形成(4 × 4)及(5 × √3)的結構。從實驗結果得知，不論在有無氯離子存在的情況下，MAA皆會在銅沉積過程，從金上轉置到銅層的表面吸附；當銅剝除後，MAA再回到金上。最後，針對不同碳鏈長度(3-mercaptopropanic acid, MPA和4-mercaptobutanic acid,MBA)及不同末端官能基(mercaptopropanesulfonic acid, MPS)的硫醇分子於金(111)上進行銅沉積實驗，與MAA結果類似，這些分子在銅沉積過程也有從金(111)轉置到銅層上吸附的現象，當銅層剝除後，又會回到金(111)電極上。;In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) have been used to investigate the adsorption of thiol molecules and its effect on the electrodeposition of copper onto Au(111). First of all, the adsorption of MAA and coadsorption of MAA and copper ions on Au(111) were examined. MAA self-assembled into two order structures, characterized as (3 × √13) and (7 × √3). By contrast, MAA and copper ions were co-deposited via –COO- and Cu2+ coordination in ordered structure with Cu2+ residing in trenches of MAA stripes. For copper deposition on MAA-modified Au(111), MAA admolecules facilitated underpotential deposition (UPD) of copper, which contrasts sharply with the blocking effect observed with typical thiol molecules. In situ STM imaging revealed nucleation of Cu deposit preferentially at surface defects including pits and steps, followed by lateral growth to the entire gold electrode. Meanwhile, a small fraction of gold adatoms aggregated into islands on the Au(111) electrode. At -0.1 V (Ag/AgCl), Cu grew in 3D on the surface, and the islands would coalesce with one another. Bulk Cu deposition produced smooth Cu film onto which MAA molecules segregated into ordered structures. Copper deposition in Cl-containing electrolyte yielded different processes and film morphology. In the initial stage of bulk deposition of Cu film grew in 2D mode, but turned 3D afterward. In situ STM imaging also revealed the copper stripping, which occured at steps firstly. When the Cu deposit was stripped to 3~4 layers thick, a moiré pattern due to MAA admolecules residing on the Cu deposit was observed. Finally, MAA readsorbed on Au(111) when the copper deposite was completely removed. MAA molecules appeared to segregate on the Cu deposite and return to the gold substrate once the Cu deposite was removed in both Cl-free and Cl-containing electrolytes. Lastly, other thiol molecules with different chain length (3-mercaptopropanic acid, MPA and 4-mercaptobutanic acid, MBA) and with different end groups (mercaptopropanesulfonic acid, MPS) were examined. In all cases, surfactant molecules were transferred onto the Cu deposite and returned to the gold electrode once the Cu deposite was stripped off.
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