130
4 Changes in Surface Stress Associated with Underpotential …
g
Fig. 4.15 Average surface stress change (in the cathodic and anodic stress response) as a
function of the net cathodic charge density c obtained for a series of potential step from 0.38 V
(SSE) down to various potentials [20]. The data points marked with ● and in Fig. 4.15 correspond
to the results of two separate experiments performed in the narrow (UPD) and wide potential (OPD)
regions, respectively. Reprinted with the permission from [20], Copyright 2009, American Chemical
Society
step from 0.38 V (SSE) down to various potentials for the (111)-textured Au thinfilm (with a thickness of 250 nm) electrode in 0.1 M H 2 SO 4 solution containing 10
−3
M H 2 PdCl 4 [20]. The data points marked with ● and in Fig. 4.15 correspond to
the results of two separate experiments performed in the narrow (UPD) and wide
potential (OPD) regions, respectively. At the potential step to the Pd-UPD region
(more positive than 0.08 V), the surface stress increases toward tensile direction
and subsequently keeps a steady-state value, depending on the step-down potential.
When the potential is reversed back to 0.38 V (SSE), the surface stress returns to
its original value, indicating that the surface stress change due to the Pd-UPD is
reversible.
In contrast, at the potential step to the Pd-OPD region, the surface stress jumps
initially toward tensile direction and increases continuously, depending on the stepdown potential, which reflects the steady-state growth of the bulk-deposited Pd layer
in the Pd-OPD region. In Fig. 4.15, the value of is about 0.4 J m
−2 at c = −
4.5 C m
−2 corresponding to the cathodic charge density required for the formation
of the Pd-UPD monolayer and it increases linearly with a slope of −0.14 V in the
Pd-OPD region ( c < −4.5 C m
−2 ). Since the lattice parameters for bulk Pd and
Au are a = 0.389 and 0.408 nm, respectively, the Pd-UPD layer has +4.9% lattice
mismatch with respect to the Au substrate. The contribution of the lattice mismatch
to the surface stress for the pseudomorphic (1 × 1) Pd-UPD layer on the Au (111)
electrode [20] may be estimated by
=
E Pd(111)
1 − ν Pd(111)
ε mf d Pd(111) n,
(4.24)
4 Changes in Surface Stress Associated with Underpotential …
g
Fig. 4.15 Average surface stress change (in the cathodic and anodic stress response) as a
function of the net cathodic charge density c obtained for a series of potential step from 0.38 V
(SSE) down to various potentials [20]. The data points marked with ● and in Fig. 4.15 correspond
to the results of two separate experiments performed in the narrow (UPD) and wide potential (OPD)
regions, respectively. Reprinted with the permission from [20], Copyright 2009, American Chemical
Society
step from 0.38 V (SSE) down to various potentials for the (111)-textured Au thinfilm (with a thickness of 250 nm) electrode in 0.1 M H 2 SO 4 solution containing 10
−3
M H 2 PdCl 4 [20]. The data points marked with ● and in Fig. 4.15 correspond to
the results of two separate experiments performed in the narrow (UPD) and wide
potential (OPD) regions, respectively. At the potential step to the Pd-UPD region
(more positive than 0.08 V), the surface stress increases toward tensile direction
and subsequently keeps a steady-state value, depending on the step-down potential.
When the potential is reversed back to 0.38 V (SSE), the surface stress returns to
its original value, indicating that the surface stress change due to the Pd-UPD is
reversible.
In contrast, at the potential step to the Pd-OPD region, the surface stress jumps
initially toward tensile direction and increases continuously, depending on the stepdown potential, which reflects the steady-state growth of the bulk-deposited Pd layer
in the Pd-OPD region. In Fig. 4.15, the value of is about 0.4 J m
−2 at c = −
4.5 C m
−2 corresponding to the cathodic charge density required for the formation
of the Pd-UPD monolayer and it increases linearly with a slope of −0.14 V in the
Pd-OPD region ( c < −4.5 C m
−2 ). Since the lattice parameters for bulk Pd and
Au are a = 0.389 and 0.408 nm, respectively, the Pd-UPD layer has +4.9% lattice
mismatch with respect to the Au substrate. The contribution of the lattice mismatch
to the surface stress for the pseudomorphic (1 × 1) Pd-UPD layer on the Au (111)
electrode [20] may be estimated by
=
E Pd(111)
1 − ν Pd(111)
ε mf d Pd(111) n,
(4.24)