76
3 Potential- or Adsorbate-Induced Changes in Surface Stress …
3.0
2.5
2.0
1.5
/ J m
-2
0.8
0.4
0.0
-0.4
E / V (SCE)
1
3,4
Au (111)-(rec)
Au (111)-(1 x1)
Au (111)-(1 x1)
g
Fig. 3.6 Surface stress versus potential (g vs. E) curves of the Au (111) surfaces in 0.1 M HClO 4
solution measured by a cantilever bending method during continuous anodic polarization from
−0.14 to 0.96 V (SCE) at a potential scan rate of 40 mV s −1 [8, 9]. The numeral in Fig. 3.6
represents the cycle number. The symbol of Au (111)-(rec) in Fig. 3.6 is an abbreviation of the Au
(111)3 × 22
surface. Reprinted from [8], Copyright 1997, with permission from Elsevier
represented by the dotted curve after 3 or 4 cycles. After 3 or 4 cycles, the surface
displayed the unreconstructed Au (111)-(1 × 1) structure even at −0.14 V (SCE).
As shown in Fig. 3.6, both solid and dotted curves coincide at about 0.9 V (SCE)
where the reconstruction is completely rifted. In Fig. 3.6, the absolute value of g
= 2.77 J m
−2 obtained by first-principles calculations [13, 14] is employed for the
Au (111)-(1 × 1) surface at −0.14 V (SCE). The difference in g between the Au
(111)3 × 22
and -(1 × 1) surfaces at −0.14 V (SCE) in Fig. 3.6 is = −
0.42 J m
−2 , which is corrected to = −0.60 J m
−2 for the fully reconstructed Au
(111)3 × 22
. Consequently, the absolute value of g = 2.17 J m
−2 is obtained
for the Au (111)3 × 22
surface. The absolute value of g = 4.32 J m
−2 obtained
for the Au (100)-(hex) surface at −0.14 V (SCE) is significantly larger than g =
2.77 J m
−2 for the Au (111)-(1 × 1) surface at −0.14 V (SCE) in spite of the similar
hexagonal structure. Moreover, the difference of = 1.55 Jm
−2 between the Au
(100)-(hex) and Au (111)-(1 × 1) surfaces at −0.14 V (SCE) is larger by one order
of magnitude than the difference of γ pzc = 0.16 J m
−2 between the Au (100)-(hex)
and Au (111)-(1 × 1) surfaces at E pzc .
The increase in electronic charge density at the metal surface provides the increase
in tensile stress due to the enhancement of attractive force between surface atoms
[7, 20]. The corrugated quasi-hexagonal close-packed structure with parallel stripes
of Au atoms for the Au (100)-(hex) surface [17, 19] may have the high electronic
charge density as compared to the planar hexagonal close-packed structure of the
3 Potential- or Adsorbate-Induced Changes in Surface Stress …
3.0
2.5
2.0
1.5
/ J m
-2
0.8
0.4
0.0
-0.4
E / V (SCE)
1
3,4
Au (111)-(rec)
Au (111)-(1 x1)
Au (111)-(1 x1)
g
Fig. 3.6 Surface stress versus potential (g vs. E) curves of the Au (111) surfaces in 0.1 M HClO 4
solution measured by a cantilever bending method during continuous anodic polarization from
−0.14 to 0.96 V (SCE) at a potential scan rate of 40 mV s −1 [8, 9]. The numeral in Fig. 3.6
represents the cycle number. The symbol of Au (111)-(rec) in Fig. 3.6 is an abbreviation of the Au
(111)3 × 22
surface. Reprinted from [8], Copyright 1997, with permission from Elsevier
represented by the dotted curve after 3 or 4 cycles. After 3 or 4 cycles, the surface
displayed the unreconstructed Au (111)-(1 × 1) structure even at −0.14 V (SCE).
As shown in Fig. 3.6, both solid and dotted curves coincide at about 0.9 V (SCE)
where the reconstruction is completely rifted. In Fig. 3.6, the absolute value of g
= 2.77 J m
−2 obtained by first-principles calculations [13, 14] is employed for the
Au (111)-(1 × 1) surface at −0.14 V (SCE). The difference in g between the Au
(111)3 × 22
and -(1 × 1) surfaces at −0.14 V (SCE) in Fig. 3.6 is = −
0.42 J m
−2 , which is corrected to = −0.60 J m
−2 for the fully reconstructed Au
(111)3 × 22
. Consequently, the absolute value of g = 2.17 J m
−2 is obtained
for the Au (111)3 × 22
surface. The absolute value of g = 4.32 J m
−2 obtained
for the Au (100)-(hex) surface at −0.14 V (SCE) is significantly larger than g =
2.77 J m
−2 for the Au (111)-(1 × 1) surface at −0.14 V (SCE) in spite of the similar
hexagonal structure. Moreover, the difference of = 1.55 Jm
−2 between the Au
(100)-(hex) and Au (111)-(1 × 1) surfaces at −0.14 V (SCE) is larger by one order
of magnitude than the difference of γ pzc = 0.16 J m
−2 between the Au (100)-(hex)
and Au (111)-(1 × 1) surfaces at E pzc .
The increase in electronic charge density at the metal surface provides the increase
in tensile stress due to the enhancement of attractive force between surface atoms
[7, 20]. The corrugated quasi-hexagonal close-packed structure with parallel stripes
of Au atoms for the Au (100)-(hex) surface [17, 19] may have the high electronic
charge density as compared to the planar hexagonal close-packed structure of the