74
3 Potential- or Adsorbate-Induced Changes in Surface Stress …
It is known that the surface stress changes with adsorption of electrolyte anions,
which is named “adsorbate-induced surface stress” [21, 22]. The adsorption of electrolyte anions promotes the rifting of reconstruction [1, 2]. The adsorption of ClO 4
−
ions on the Au (100) electrode surfaces proceeds at potentials more positive than E pzc
[1, 2, 10]. The surface coverage of adsorbed ClO 4
− ions increases with increasing
potential, which enhances the repulsive interaction between adsorbed ClO 4
− ions
through their dipole moments formed by the charge and the corresponding images.
In the case where the adsorbate–adsorbate interaction is repulsive, g as well as γ may
decrease with increasing potential, i.e., with increasing surface coverage of adsorbed
ClO 4
− ions. According to the calculation made by Schmickler and Leiva [23], using
jellium model of metal surface and statistical mechanics of two-dimensional lattice
gas, the potential dependence of g is much larger than that of γ . Moreover, their
calculation results [23] indicated that the surface concentration of electrons has a
direct effect on g while the repulsive adsorbate–adsorbate interaction has an indirect
effect on g. The above theoretical results were also supported by Ibach [24].
3.2.2 Au (111) Surface
The rifting of the reconstructed Au (111)3 × 22
surface as well as the reconstructed Au (100)-(hex) surface has been confirmed by anodic polarization at potentials more positive than the critical potential [8, 9]. The critical potential for lifting
of the Au (111)3 × 22
surface in 0.01 M HClO 4 solution is about 0.4 V (SCE),
which is more negative by about 0.15 V than that for lifting of the Au (100)-(hex)
surface in the same solution. The values of E pzc determined from the differential
capacity minima in the c versus E curves measured in 0.01 M HClO 4 solution [18]
are E pzc = 0.33 and 0.23 V (SCE) for the Au (111)3 × 22
and -(1 × 1) surfaces,
respectively, which are consistent with the results obtained by Kolb [1, 2].
Figure 3.5 shows the electrocapillary (γ vs. E) curves of the Au (111)3 × 22
and -(1 × 1) surfaces calculated from the differential capacity data by Santos and
Schmickler [18]. The symbol of Au (111)-(rec) in Fig. 3.5 is an abbreviation of the
Au (111)3 × 22
surface. It is reminded in Fig. 3.5 that the absolute value of
γ pzc = 1.25 J m
−2 obtained by first-principles calculations [13, 14] is employed for
the Au (111)-(1 × 1) surface in place of γ pzc which was referred to zero for the
Au (111)3 × 22
surface in their original figure [18]. Furthermore, the value of
γ pzc = −4.7 × 10
−3 J m
−2 is chosen for the difference in γ pzc between the Au
(111)3 × 22
and -(1 × 1) surfaces, so that the electrocapillary curves of the
Au (111)-(1 × 1) and -
√
3 × 22
surfaces intersect at 0.4 V (SCE) corresponding
to the critical potential for lifting of the reconstruction in 0.01 M HClO 4 solution,
and thereby γ (E) for the Au (111)-(1 × 1) surface becomes less than that for the
3 Potential- or Adsorbate-Induced Changes in Surface Stress …
It is known that the surface stress changes with adsorption of electrolyte anions,
which is named “adsorbate-induced surface stress” [21, 22]. The adsorption of electrolyte anions promotes the rifting of reconstruction [1, 2]. The adsorption of ClO 4
−
ions on the Au (100) electrode surfaces proceeds at potentials more positive than E pzc
[1, 2, 10]. The surface coverage of adsorbed ClO 4
− ions increases with increasing
potential, which enhances the repulsive interaction between adsorbed ClO 4
− ions
through their dipole moments formed by the charge and the corresponding images.
In the case where the adsorbate–adsorbate interaction is repulsive, g as well as γ may
decrease with increasing potential, i.e., with increasing surface coverage of adsorbed
ClO 4
− ions. According to the calculation made by Schmickler and Leiva [23], using
jellium model of metal surface and statistical mechanics of two-dimensional lattice
gas, the potential dependence of g is much larger than that of γ . Moreover, their
calculation results [23] indicated that the surface concentration of electrons has a
direct effect on g while the repulsive adsorbate–adsorbate interaction has an indirect
effect on g. The above theoretical results were also supported by Ibach [24].
3.2.2 Au (111) Surface
The rifting of the reconstructed Au (111)3 × 22
surface as well as the reconstructed Au (100)-(hex) surface has been confirmed by anodic polarization at potentials more positive than the critical potential [8, 9]. The critical potential for lifting
of the Au (111)3 × 22
surface in 0.01 M HClO 4 solution is about 0.4 V (SCE),
which is more negative by about 0.15 V than that for lifting of the Au (100)-(hex)
surface in the same solution. The values of E pzc determined from the differential
capacity minima in the c versus E curves measured in 0.01 M HClO 4 solution [18]
are E pzc = 0.33 and 0.23 V (SCE) for the Au (111)3 × 22
and -(1 × 1) surfaces,
respectively, which are consistent with the results obtained by Kolb [1, 2].
Figure 3.5 shows the electrocapillary (γ vs. E) curves of the Au (111)3 × 22
and -(1 × 1) surfaces calculated from the differential capacity data by Santos and
Schmickler [18]. The symbol of Au (111)-(rec) in Fig. 3.5 is an abbreviation of the
Au (111)3 × 22
surface. It is reminded in Fig. 3.5 that the absolute value of
γ pzc = 1.25 J m
−2 obtained by first-principles calculations [13, 14] is employed for
the Au (111)-(1 × 1) surface in place of γ pzc which was referred to zero for the
Au (111)3 × 22
surface in their original figure [18]. Furthermore, the value of
γ pzc = −4.7 × 10
−3 J m
−2 is chosen for the difference in γ pzc between the Au
(111)3 × 22
and -(1 × 1) surfaces, so that the electrocapillary curves of the
Au (111)-(1 × 1) and -
√
3 × 22
surfaces intersect at 0.4 V (SCE) corresponding
to the critical potential for lifting of the reconstruction in 0.01 M HClO 4 solution,
and thereby γ (E) for the Au (111)-(1 × 1) surface becomes less than that for the