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.

In situ scanning tunneling microscopy (STM) was used to study the adsorption and polymerization of aniline on Au(111) single-crystal electrode in 0.1 M perchloric acid and 0.1 M benzenesulfonic acids (BSA) containing 30 mM aniline, respectively. At the onset potential of aniline's oxidation, approximately 0.8 V [vs reversible hydrogen electrode], aniline molecules were adsorbed in highly ordered arrays, designated as (3 x 2 square root(3)) and (4 x 2 square root(3)) in perchloric acid and BSA, respectively. These structures consisted of intermingled aniline molecules and perchlorate or BSA(-) anions zigzagging in the <110> directions in HClO(4) and in the <121> directions in BSA. The coverage of aniline admolecule on Au(111) was lower in BSA than in HClO(4). Raising the potential to 0.9 V or more positive values triggered the oxidation and polymerization of aniline. With aniline molecules arranging in a way similar to the backbone of PAN in HClO(4), they readily coupled with each other to produce linear polymeric chains aligned predominantly in the 110 directions of the Au(111). Compared with the results observed in H(2)SO(4) (Lee et al. J. Am. Chem. Soc. 2009, 131, 6468), the rate of polymerization was slower in HClO(4) and the produced PAN molecules tended to aggregate on the Au(111) electrode. PAN molecules generated in HClO(4) were anomalously shorter than those formed in H(2)SO(4). In 0.1 M BSA, PAN molecules produced by small overpotential (eta < 100 mV) could assume linear chains or 3D aggregates, depending on [aniline]. These results revealed molecular level details in electropolymerization of aniline, highlighting the important role of anion in controlling the conformation of PAN molecules and the texture of PAN film.

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In situ scanning tunneling microscopy (STM) was used to study copper deposition at vacancy defects on a copper thin film under potentiostatic conditions at −0.20 V (vs. Ag/AgCl) in a formula containing sulfuric acid, chloride, polyethylene glycol (PEG), and bis-3-sodiumsulfopropyl-disulfide (SPS) -the widely used mixture to facilitate Cu superfilling at recessed features in semiconductor processing. The vacancy island measuring ∼70 nm wide and 12 nm deep sat in the middle of a facetted surface structure at the beginning. Cu deposit nucleated mainly at the rim of the vacancy and grew into stacked Cu(111) facets. These local pyramidal Cu stacks could restructure into wider Cu(111) terraces by transferring Cu atoms rapidly from higher to lower planes. Voltammetric results showed that Cu deposition was suppressed in a plating bath containing 1 mM KCl + 88 μM PEG8000 + 10 −7 M SPS.Steps with sharp edges bunched in the course of Cu deposition. The vacancy island was filled with Cu deposit assuming smooth terraces with sharp step edges aligned mainly in the 121 directions of the Pt(111) electrode, suggesting crystalline packing in the Cu deposit. Atomic-resolution STM imaging revealed a hexagonal array presumed to be the ( √ 3 × √ 3)R30 • -Cl − adlattice.

The chemical identity of supporting electrolyte can affect the rate of oxidative polymerization of aniline and the structure of the produced polyaniline (PAN). While PAN molecules deposited on ordered gold electrodes are linear in sulfuric and perchloric acids, the situation in hydrochloric acid is yet to be characterized by scanning tunneling microscopy (STM). Although aniline molecules were adsorbed in disarray between 0.1 and 0.8 V (vs. reversible hydrogen electrode) in 0.5 M HCl + 30 mM aniline, they drifted toward nuclei formed preferentially at steps on the Au(111) electrode and self-assembled into highly organized PAN molecules upon anodization at E > 0.9 V. Shifting the potential from 0.9 to 0.6 V converted PAN molecules from the pernigraniline to emeraldine state, and an increase of the film's corrugation height. On Pt(111), aniline molecules were also adsorbed in disarray at E < 0.9 V, but anodization yielded winding PAN molecules in 0.5 M HCl + 3 mM aniline.