3.3 Adsorption of Electrolyte Anions
83
containing 3 × 10
−3 M NaI is stable in the potential region between −0.06 and
0.42 V (SHE). Small reversible current spikes are usually observed in the cyclic
voltammogram at the potential where the
p ×
√
3
-iodine phase is transformed to
the rotated-hexagonal phase [31, 33]. A small rise of anodic current at 0.42 V (SHE)
in the cyclic voltammogram of Fig. 3.10a may be associated with the transformation
from
p ×
√
3
to rotated-hexagonal phase.
The value of g is referred to zero at −0.80 V (SHE) in the g versus E curve of
Fig. 3.10b. The surface stress keeps almost constant in the potential region between
−0.80 and −0.40 V (SHE) where the reconstructed Au (111)3 × 22
surface
is stable. The value of g decreases rapidly toward compressive direction in the
anodic potential scan from −0.3 to −0.1 V (SHE) where the lifting of the reconstruction followed by the adsorption of iodine takes place. The decrease in g toward
compressive direction continues, keeping an almost linear relationship between g
and E in the anodic potential scan from −0.1 to 0.42 V (SHE) where the
p ×
√
3
-
iodine phase is stable. In the cathodic potential scan from 0.42 to −0.80 V (SHE),
the reversed changes in surface stress with a small hysteresis are observed.
According to the SXS study [31], the nearest-neighbor distance a nn between iodine
atoms in the
p ×
√
3
iodine adlayer on Au (111) electrode in 0.1 M KI solution decreases linearly from 0.462 to 0.432 nm with increasing potential due to the
increase in electro-compression. The elastic strain ε in the iodine adlayer can be
calculated from the changes in a nn :
ε =
a nn − a nn,o
a nn,o
,
(3.4)
where a nn,o is 0.462 nm. The minimum distance of a nn = 0.432 is equal to the van
der Waals diameter of iodine atom in which ε amounts to −0.065. The minus sign of
ε means that the elastic strain is compressive. The changes in surface stress toward
compressive direction should be responsible for the changes in elastic strain toward
compressive direction. From the potential correction by the Nernst equation, the
potential range where a nn changes from 0.462 to 0.432 nm in 0.1 M KI solution
corresponds to the potential range of 0.01 to 0.41 V (SHE) in 0.1 M NaClO 4 solution
containing 3 × 10
−3 M NaI. As shown in the g versus E curve of Fig. 3.10b, the
value of (g) = −0.63 J m
−2 is obtained for the change in potential from 0.01 to
0.41 V (SHE). The
p ×
√
3
iodine adlayer on Au (111) is subjected to a uniaxial
electro-compression along the incommensurate direction.
In the continuum model, if one-dimensionally compressed adlayer is regarded as
a free-standing elastic film, the following linear relationship between (g) and ε
holds:
(g) = Y I εd,
(3.5)
83
containing 3 × 10
−3 M NaI is stable in the potential region between −0.06 and
0.42 V (SHE). Small reversible current spikes are usually observed in the cyclic
voltammogram at the potential where the
p ×
√
3
-iodine phase is transformed to
the rotated-hexagonal phase [31, 33]. A small rise of anodic current at 0.42 V (SHE)
in the cyclic voltammogram of Fig. 3.10a may be associated with the transformation
from
p ×
√
3
to rotated-hexagonal phase.
The value of g is referred to zero at −0.80 V (SHE) in the g versus E curve of
Fig. 3.10b. The surface stress keeps almost constant in the potential region between
−0.80 and −0.40 V (SHE) where the reconstructed Au (111)3 × 22
surface
is stable. The value of g decreases rapidly toward compressive direction in the
anodic potential scan from −0.3 to −0.1 V (SHE) where the lifting of the reconstruction followed by the adsorption of iodine takes place. The decrease in g toward
compressive direction continues, keeping an almost linear relationship between g
and E in the anodic potential scan from −0.1 to 0.42 V (SHE) where the
p ×
√
3
-
iodine phase is stable. In the cathodic potential scan from 0.42 to −0.80 V (SHE),
the reversed changes in surface stress with a small hysteresis are observed.
According to the SXS study [31], the nearest-neighbor distance a nn between iodine
atoms in the
p ×
√
3
iodine adlayer on Au (111) electrode in 0.1 M KI solution decreases linearly from 0.462 to 0.432 nm with increasing potential due to the
increase in electro-compression. The elastic strain ε in the iodine adlayer can be
calculated from the changes in a nn :
ε =
a nn − a nn,o
a nn,o
,
(3.4)
where a nn,o is 0.462 nm. The minimum distance of a nn = 0.432 is equal to the van
der Waals diameter of iodine atom in which ε amounts to −0.065. The minus sign of
ε means that the elastic strain is compressive. The changes in surface stress toward
compressive direction should be responsible for the changes in elastic strain toward
compressive direction. From the potential correction by the Nernst equation, the
potential range where a nn changes from 0.462 to 0.432 nm in 0.1 M KI solution
corresponds to the potential range of 0.01 to 0.41 V (SHE) in 0.1 M NaClO 4 solution
containing 3 × 10
−3 M NaI. As shown in the g versus E curve of Fig. 3.10b, the
value of (g) = −0.63 J m
−2 is obtained for the change in potential from 0.01 to
0.41 V (SHE). The
p ×
√
3
iodine adlayer on Au (111) is subjected to a uniaxial
electro-compression along the incommensurate direction.
In the continuum model, if one-dimensionally compressed adlayer is regarded as
a free-standing elastic film, the following linear relationship between (g) and ε
holds:
(g) = Y I εd,
(3.5)