In Situ Electrochemical Scanning Tunneling Microscopy of Ni(111), Ni(100), and Sulfur-Modified Ni(100) in Acidic Solution

Abstract

Single-crystal Ni electrodes were investigated by in situ electrochemical scanning tunneling microscopy (STM) under potential control in 0.05 M Na2SO4 at pH 3.0. On Ni(111), a Ni(111)-(1×1) structure was observed in high-resolution STM images acquired at cathodic potentials. Under passivation by forming oxide layers, a hexagonal lattice with an interatomic distance of 0.29 nm was discerned, which was attributed to oxide layers of NiO(111) or Ni(OH)2(0001). On Ni(100), a square lattice with a p(2×2) of oxygen was observed even at cathodic potentials. The p(2×2) structure was converted to a quasi-hexagonal structure in the passive region due to the formation of bulk oxide films. Sulfur adatoms chemically attached on Ni(100) formed a c(2×2) adlattice, which was consistently observed even under the anodic dissolution of the underlying Ni substrate. The dissolution of Ni from the S-modified Ni(100) was found to proceed in the layer-by-layer mode, forming atomically flat terraces extending over large areas.

<I>In-situ</I> Electrochemical Atomic Force Microscopy with Atomic Resolution of Ni(110) in Neutral and Alkaline Aqueous Solution

“…Scanning tunneling microscope (STM) and atomic force microscope (AFM) are one of the most powerful tools to investigate the structure of metal surface not only in vacuum, 1,2) but also in aqueous solution. Various investigations have been carried out on the surface structures of Ni single crystals in aqueous solution by ex situ 3,4) and insitu [5][6][7] STM, and there has been a gradual accumulation of experimental data for the structure of both Ni substrate and the oxide layer, especially in sulfuric acid solution (pH < 3.0). For example, Suzuki et al 6) has succeeded in in-situ observation of bare and oxidized surfaces of Ni(100) and Ni(111) with atomic resolution by means of electrochemical STM (EC-STM).…”

“…Various investigations have been carried out on the surface structures of Ni single crystals in aqueous solution by ex situ 3,4) and insitu [5][6][7] STM, and there has been a gradual accumulation of experimental data for the structure of both Ni substrate and the oxide layer, especially in sulfuric acid solution (pH < 3.0). For example, Suzuki et al 6) has succeeded in in-situ observation of bare and oxidized surfaces of Ni(100) and Ni(111) with atomic resolution by means of electrochemical STM (EC-STM). Ex situ 3,4) and in-situ 7) STM investigations revealed the epitaxial relationship between the Ni substrate and the oxide layer, as well as those structures.…”

In Situ Electrochemical Atomic Force Microscopy with Atomic Resolution of Fe(110) in Sodium Sulfate Aqueous Solution.

“…On the other hand, the charge consumption of peak (A 1 ) estimated from the CV shown in Fig. 2 35,36) and Co(OH) 2 (0001)//Co(0001).…”

“…Especially, the STM and AFM investigation at atomic scale with the electrochemical oxidation processes of a well-defined electrode surface of base metals, such as copper, 32,33) nickel [34][35][36] and cobalt, 37) is intriguing because it gives information about the epitaxial relationship between anodically formed oxide layer and substrate.…”

Phase Transitions Involving Dissociated States of Water at the Electrochemical Ni(111)/H2O Interface

“…We suggest that this is because the present study has only considered phenomena occurring at low coverage. Models that include higher coverages and sufficient lateral interactions will be required to describe the formation of higher coverage overlayers as observed in the studies by Suzuki et al 20 and Nakamura et al 21 .…”