Scanning Tunneling Microscopy of Superfilling in FormulaContaining Chloride, Polyethylene Glycol andBis-3-Sodiumsulfopropyl-Disulfide

In situ scanning tunneling microscopy (STM) was used to study copper deposition at vacancy defects on a copper thin film underpotentiostatic conditions at −0.20 V (vs. Ag/AgCl) in a formula containing sulfuric acid, chloride, polyethylene glycol (PEG), andbis-3-sodiumsulfopropyl-disulfide (SPS) – the widely used mixture to facilitate Cu superfilling at recessed features in semiconductorprocessing. The vacancy island measuring ∼70 nm wide and 12 nm deep sat in the middle of a facetted surface structure at thebeginning. Cu deposit nucleated mainly at the rim of the vacancy and grew into stacked Cu(111) facets. These local pyramidal Custacks could restructure into wider Cu(111) terraces by transferring Cu atoms rapidly from higher to lower planes. Voltammetricresults 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 smoothterraces with sharp step edges aligned mainly in the 121 directions of the Pt(111) electrode, suggesting crystalline packing in theCu deposit. Atomic-resolution STM imaging revealed a hexagonal array presumed to be the (√3 × √3)R30◦ – Cl− adlattice

Epitaxial Electrodeposition of Nickel on Pt(111) Electrode

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 KClO₄ + 1 mM HCl + 0.06 M NiCl₂. 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 Ni²⁺ 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 <i>E</i> > −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 moiré patterns exhibiting long-ranged intensity modulations undulating along the ⟨110⟩ direction of the Pt(111) substrate. These moiré patterns are proposed to arise from a stack of Ni(111)-like planes on the Pt(111) electrode. The periodicities of the moiré patterns 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 STM Imaging of Bis-3-sodiumsulfopropyl-disulfide Molecules Adsorbed on Copper Film Electrodeposited on Pt(111) Single Crystal Electrode

The adsorption of bis-3-sodiumsulfopropyldisulfide (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 HClO4 t 1 mM Cu(ClO4)2 t 1mMKCl. 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) t Cl_Cu_PtfRS__Ptt t RS_ (MPS) t Cu2t t 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 smoothCu 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

In Situ Scanning Tunneling Microscopy Study of 3-Mercaptopropanesulfonate Adsorbed on Pt(111) and Electrodeposition of Copper in 0.1 M KClO4 þ 1 mM HCl (pH 3)

In situ scanning tunneling microscopy (STM) was used to examine the spatial structure of adsorbed 3-mercaptopropanesulfonate (MPS) molecules on a Pt(111) electrode in 0.1 M KClO4 t 1 mM HCl t 10_7 M MPS (pH 3). Two ordered MPS structures, Pt(111)_(2 _2) (θ = 0.25) and ( √ 3 _ √ 3)R30_ (θ = 0.33) structures were observed at _0.25 V (vs Ag/AgCl). The former (latter) was more important at more negative (positive) potentials. These MPS structures became a disordered adlayer at E > 0.1 V. These restructuring events could result from a progressive increase of the surface coverage of MPS with potential. Shifting the potential negatively could restore the ordered structures of ( √ 3_ √ 3)R30_ and (2_2), but the rather strong Pt-MPS made it difficult for MPS admolecules to desorb from the Pt(111) electrode. By contrast, the MPS adlayer seen in 0.1 M HClO4 was always disordered, regardless of the potential of Pt(111) electrode. (Tu et al., J. Electrochem. Soc. 2010, 157, D206.) It is reasonable to state that potential control, pH, and/or countercations to the sulfonate group of the MPS admolecule could be important in guiding the adsorption of MPS molecules on Pt(111) electrode. Strongly adsorbed MPS molecules on the Pt(111) electrode could impede the rate of Cu2t reduction, thereby inhibiting rather than accelerating electrodeposition of copper under the present conditions. Real-time STM imaging revealed random nucleation of copper adatoms on Pt(111), followed by lateral growth of Cu nuclei upon further deposition. Segregated domains of ( √ 3_ √ 3)R30_, ascribable to MPS and chloride adspecies, were observed atop a monolayer of Cu deposit prior to the commencement of bulk Cu deposition. With a small overpotential (η < 20 mV), multilayer copper was electroplated on Pt(111) in a layered manner, producing atomically smooth Cu deposit capped by patches of (3 _ 3) MPS. By contrast, the Cu deposit on MPS-modified Pt(111) in 0.1 M HClO4 was decidedly rough, as reported earlier