The adsorption of 3-mercaptopropanesulfonate (MPS) molecule on a Pt(111) single-crystal electrode and its effect on the deposition of Cu have been examined using in situ scanning tunneling microscopy (STM). MPS admolecules were irreversibly adsorbed in a largely disordered adlayer on bare Pt(111) in 0.1 M HClO(4), irrespective of the presence of chloride, the concentration of MPS, and the applied potential. In comparison, the MPS admolecules readily formed a highly ordered molecular structure identified as (4x2 root 3)rect on Pt(111) precoated with a monolayer of Cu adatoms. The MPS admolecules were adsorbed upright on Pt(111). The cyclic voltammetric results show that the MPS adlayer on Pt(111) would inhibit Cu deposition because the addition of 10 mu M MPS to the electrolyte of 0.1 M HClO(4)+1 mM KCl+1 mM Cu(ClO(4))(2) reduced the amount of the Cu deposit by half, even in the presence of chloride. The texture of the Cu deposit also varied with the surface state of the Pt(111) electrode as the Cu film grew in three-dimensional islands and smooth flakelike morphology on the MPS-modified and Cu-coated Pt(111) electrodes, respectively. In situ STM results indicated that the MPS admolecules stayed afloat rather than buried by the Cu deposit

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The adsorption of bis-3-sodiumsulfopropyldi-sulfide (SPS) on metal electrodes in chloride-containing media has been intensively studied to unveil its accelerating effect on Cu electrodeposition. Molecular resolution scanning tunneling microscopy (STM) imaging technique was used in this study to explore the adsorption and decomposition of SPS molecules concurring with the electrodeposition of copper on an ordered Pt(111) electrode in 0.1 M HClO(4) + 1 mM Cu(ClO(4))(2) + 1 mM KCl. Depending on the potential of Pt(111), SPS molecules could react, adsorb, and decompose at chloride-capped Cu films. A submonolayer of Cu adatoms classified as the underpotential deposition (UPD) layer at 0.4 V (vs Ag/AgCl) was completely displaced by SPS molecules, possibly occurring via RSSR (SPS) + Cl-Cu-Pt → RS(-)-Pt(+) + RS(-) (MPS) + Cu(2+) + Cl(-), where MPS is 3-mercaptopropanesulfonate. By contrast, at 0.2 V, where a full monolayer of Cu was presumed to be deposited, SPS molecules were adsorbed in local (4 × 4) structures at the lower ends of step ledges. Bulk Cu deposition driven by a small overpotential (η < 50 mV) proceeded slowly to yield an atomically smooth Cu deposit at the very beginning (<5 layers). On a bilayer Cu deposit, the chloride adlayer was still adsorbed to afford SPS admolecules arranged in a unique 1D striped phase. SPS molecules could decompose into MPS upon further Cu deposition, as a (2 × 2)-MPS structure was observed with prolonged in situ STM imaging. It was possible to visualize either SPS admolecules in the upper plane or chloride adlayer sitting underneath upon switching the imaging conditions. Overall, this study established a MPS molecular film adsorbed to the chloride adlayer sitting atop the Cu deposit.

Artificial nickel thin films, potentially useful as magnetic materials and electrocatalysts, have been prepared by electrodeposition on noble transition metal electrodes. This study employed scanning tunneling microscopy (STM) and cyclic voltammetry to study electrodeposition of Ni on Pt(111) from 0.1 M KClO 4 + 1 mM HCl + 0.06 M NiCl 2 . Deposition of Ni was noted at potentials more positive than its Nernst potential, as proton discharge and hydrogen evolution occurred concomitantly. Bulk deposition of Ni commenced at potentials more negative than −0.6 V (vs Ag/AgCl), where reduction of water to hydrogen was imminent. The reduction reaction of Ni 2+ ion to Ni metal was a slow process under the present experimental conditions, and not all Ni deposit was removed from the Pt electrode, as indicated by irreversible changes in the voltammetric profiles. In-situ STM provided direct views of the growth process and the atomic structures of the Ni thin film. The first Ni adlayer deposited at E > −0.525 V or the underpotential deposited (UPD) layer was disordered but was transformed into an ordered structure supporting the subsequently deposited Ni adlayers. From the second all the way up to the tenth Ni adlayers, STM imaging revealed prominent moirépatterns exhibiting long-ranged intensity modulations undulating along the ⟨110⟩ direction of the Pt(111) substrate. These moirépatterns are proposed to arise from a stack of Ni(111)-like planes on the Pt(111) electrode. The periodicities of the moirépatterns decreased from 3.0 to 2.5 nm as the Ni deposit thickened from the second to the fourth layer, suggesting that the spacing between Ni adatoms decreased from 0.254 to 0.25 nm.

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