dc.description.abstract | 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 moiré 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 moiré 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. | en_US |